CN113258537B

CN113258537B - Open circuit protection circuit, switching power supply chip and switching power supply system

Info

Publication number: CN113258537B
Application number: CN202110798166.2A
Authority: CN
Inventors: 吕战辉; 李瑞平
Original assignee: Shanghai Xinlong Semiconductor Technology Co ltd
Current assignee: Shanghai Xinlong Semiconductor Technology Co ltd
Priority date: 2021-07-15
Filing date: 2021-07-15
Publication date: 2021-10-08
Anticipated expiration: 2041-07-15
Also published as: CN113258537A

Abstract

The invention provides an open-circuit protection circuit, a switching power supply chip and a switching power supply system, which are applied to the technical field of switching power supplies. In the open-circuit protection circuit provided by the invention, when an output voltage feedback pin FB of a boosting constant current type switching power supply chip is required to be pulled down and the voltage of a voltage output end reaches a set maximum value and is simultaneously satisfied, the open-circuit protection circuit judges that the open-circuit is a load open circuit, then a power tube of the chip is turned off firstly to enable the chip not to work, then the internal circuit is started to discharge to an external output capacitor, and when the voltage of the output capacitor is reduced to a set safety value, a discharge path in the circuit is closed to reduce loss, so that when a load LED is opened, the chip and a newly-connected LED load can be protected from being damaged by the high voltage of the output capacitor, a voltage stabilizing diode added at the output end of the load LED in the traditional scheme is omitted, and the cost and the complexity in production are reduced.

Description

Open circuit protection circuit, switching power supply chip and switching power supply system

Technical Field

The invention relates to the technical field of integrated circuits, in particular to an open-circuit protection circuit, a switching power supply chip and a switching power supply system.

Background

The switching power supply management chip obtains stable output voltage or current by continuously controlling the on and off of the switching tube, and can be divided into two categories, namely AC/DC (alternating current to direct current) and DC/DC (direct current to direct current). Because the AC/DC switching power supply often includes a DC/DC conversion module, the DC/DC is a basic component of the switching power supply, and the DC/DC switching power supply includes three basic topologies, i.e., a step-down type, a step-up type, and a step-up and step-down type.

When the working voltage of the direct current load is higher than the direct current power supply voltage of the input end, a DC/DC boost type power supply management chip can be used for supplying power to the direct current load, and the DC/DC boost type power supply management chip comprises an output constant voltage type and an output constant current type, wherein the output constant current type can be applied to a system scheme of driving an LED (light emitting diode) by boosting constant current. In the scheme of a system for driving an LED by boosting and constant current, if the LED is damaged due to some reason, the system is open-circuited, once the system is open-circuited, the output voltage can be very high in a very short time, theoretically, the output voltage can reach infinity, and a chip or an output capacitor can be damaged, so that an open-circuit protection circuit is arranged in each boosting chip to limit the voltage of the output terminal to the maximum value allowed by the chip, at the moment, if a new LED load is directly replaced, the high voltage on the output terminal capacitor can be directly applied to two ends of the LED load, and a very large current flows through the LED load in a transient state, so that the LED load is damaged.

At present, in a scheme of driving an LED by using a boost constant current type power supply chip, in order to prevent the situation that a newly connected LED load is damaged due to too high voltage of an output end capacitor when the boost constant current type LED driving power supply is connected to the LED load after being connected to the LED load, a conventional scheme is to add a zener diode at the output end of the boost constant current type LED driving power supply chip to detect the voltage at the output end and require that the clamping voltage of the zener diode is about 1.2 times of the normal operating voltage of the LED load, so that when the output end of the power supply chip is connected to the LED load again, the output voltage is clamped at the two ends of the zener diode, and therefore, when the LED load is connected to the LED load again, the LED load is not damaged due to too high voltage at the output end.

However, although the protection scheme with the additional external components can solve the above problems, the cost of the system scheme of the user is undoubtedly increased, and the protection scheme requires that the clamping voltage of the zener diode is close to the voltage of the LED load, which limits the versatility, that is, the LED loads with different operating voltages require zener diodes corresponding to different clamping voltages, and in the process of using the user or mass production of various output voltage schemes, once the wrong zener diode is selected, the stability of the system will be affected, which undoubtedly also increases the labor cost, because it is necessary to detect whether the correct zener diode is used in each system.

Disclosure of Invention

The invention aims to provide an open-circuit protection circuit, a switching power supply chip and a switching power supply system, so that when a load open circuit occurs in a boosting constant-current switching power supply system, the switching power supply chip is protected, and meanwhile, the problem that a newly-connected LED load is damaged due to overhigh voltage of an output capacitor is solved.

In a first aspect, to solve the above technical problem, the present invention provides an open circuit protection circuit, which is disposed inside a boost constant current type switching power supply chip, an output capacitor and a load are connected to an outside of the boost constant current type switching power supply chip, and the boost constant current type switching power supply chip has an output voltage detection end for detecting an output voltage, an output voltage feedback pin for feeding back a change of the output voltage, and a power tube for adjusting the output voltage.

The open circuit protection circuit includes: and the FB pin voltage detection module is connected with the output voltage feedback pin and used for detecting whether the voltage of the output voltage feedback pin is lower than a first voltage threshold value, if so, a high level signal is output, and if not, a low level signal is output.

And the overvoltage protection module is connected with the output voltage detection end and used for detecting whether the voltage of the output voltage detection end is greater than a second voltage threshold value, if so, a high level signal is output, and if not, a low level signal is output.

And the logic control module is connected with the driving end of the power tube, the FB pin voltage detection module and the overvoltage protection module, and is used for controlling the power tube to be switched off and triggering the output capacitor discharge module to work when the FB pin voltage detection module and the overvoltage protection module both output high-level signals, and latching the output voltage of the logic control module to continuously output the high-level signals and controlling the power tube to be switched off when at least one of the FB pin voltage detection module and the overvoltage protection module outputs low-level signals later until the boost constant-current type switching power supply chip is powered on again.

And the output capacitor discharging module is connected with the output capacitor and used for discharging the output capacitor after being triggered by the logic control module so as to reduce the voltage of the output capacitor.

Optionally, the overvoltage protection module may include: the circuit comprises an input end, an output end, fourth to seventh resistors, a first diode, a twelfth triode and a thirteenth triode.

The cathode of the first diode is connected with the output voltage detection end and serves as the input end of the overvoltage protection module, the anode of the first diode is connected with one end of a fourth resistor, and the other end of the fourth resistor is connected with one end of a fifth resistor and the base electrode of the twelfth triode; the other end of the fifth resistor is connected with a reference ground end; one end of a sixth resistor is connected with a chip working voltage, the other end of the sixth resistor is connected with a base electrode of the thirteenth triode and an emitting electrode of the twelfth triode, a collector electrode of the thirteenth triode is connected with the chip working voltage, and a collector electrode of the twelfth triode is connected with the reference ground end; one end of the seventh resistor is connected with the reference ground end, and the other end of the seventh resistor is connected with the emitter of the thirteenth triode and serves as the output end of the overvoltage protection module to be connected with the logic control module.

Optionally, the logic control module includes a first input terminal, a second input terminal, an output terminal, a fifteenth triode, a sixteenth triode, an eighteenth triode to a twentieth triode, a twenty third triode to a twenty seventh triode, and an eighth resistor to a tenth resistor.

The base electrode of the fifteenth triode is connected with the output end of the overvoltage protection module and serves as a second input end of the logic control module; a collector of the fifteenth triode is connected with a base of the eighteenth triode, and an emitter of the fifteenth triode is connected with a collector of the sixteenth triode; an emitting electrode of the sixteenth triode is connected with the reference ground end, and a base electrode of the sixteenth triode is connected with the output end of the FB pin voltage detection module and serves as a first input end of the logic control module; the emitter of the eighteen triode is connected with the reference ground, the collector of the eighteen triode is connected with the base of a nineteenth triode, the emitter of the nineteenth triode is connected with the reference ground, the collector of the nineteenth triode is connected with the collector of the twentieth triode and the base of the twenty-third triode, the emitter of the twentieth triode is connected with the reference ground, the base of the twentieth triode is connected with one end of an eighth resistor, the other end of the eighth resistor is connected with one end of a ninth resistor, the collector of the twenty-third triode and the collector of a twenty-fourth triode, the other end of the ninth resistor is connected with the base of a twenty-fifth triode, and the emitter of the twenty-fifth triode is connected; an emitting electrode of the twenty-third triode and an emitting electrode of the twenty-fourth triode are both connected with the reference ground end, and a base electrode of the twenty-fourth triode is connected with a collector electrode of the twenty-sixth triode and a collector electrode of the twenty-seventh triode; an emitting electrode of the twenty-sixth triode and an emitting electrode of the twenty-seventh triode are both connected with the reference ground end, and a base electrode of the twenty-seventh triode is connected with one end of the tenth resistor and the input end of the output capacitor discharging module.

Optionally, the output capacitor discharging module may include a first input terminal, a second input terminal, a thirty-third triode, a thirty-second triode, a thirty-third triode, a thirty-fourth triode, and an eleventh resistor.

The base electrode of the thirty-third triode is connected with the output end of the logic control module and serves as a first input end of the output capacitor discharging module, the emitting electrode of the thirty-third triode is connected with the reference ground end, and the collecting electrode of the thirty-third triode is connected with the base electrode of the thirty-second triode; an emitter of the thirty-second triode is connected with the reference ground, a collector of the thirty-second triode is connected with a collector of the thirty-third triode and a base of the thirty-fourth triode, an emitter of the thirty-third triode is connected with the reference ground, and the base of the thirty-third triode is used as a second input end of the output capacitor discharging module; and a collector of the thirty-fourth triode is connected with one end of the eleventh resistor, an emitter of the thirty-fourth triode is connected with the reference ground end, and the other end of the eleventh resistor is connected with an output voltage detection end of the boost constant current type switching power supply chip.

Optionally, the FB pin voltage detection module may include a second resistor, a third triode, to a thirteenth polar tube.

One end of the second resistor is connected with a reference voltage, the other end of the second resistor is connected with one end of the third resistor and the base electrode of the third triode, and the other end of the third resistor and the collector electrode of the third triode are both connected with the reference ground end; an emitter of the third triode is connected with a collector of the fourth triode, a base of the fourth triode and a base of the fifth triode, an emitter of the fourth triode is connected with an emitter of the fifth triode, an emitter of the eighth triode and an emitter of the ninth triode, a collector of the fifth triode is connected with a collector of the sixth triode, a base of the sixth triode and a base of the seventh triode, and an emitter of the sixth triode and an emitter of the seventh triode are both connected with the reference ground; a collector of the seventh triode is connected with a collector of the eighth triode and serves as an output end of the FB pin voltage detection module; the base electrode of the eighth triode is connected with the base electrode of the ninth triode and the collector electrode of the ninth triode, the collector electrode of the ninth triode is connected with the emitter electrode of the thirteenth triode, the collector electrode of the thirteenth triode is connected with the reference ground end, and the base electrode of the thirteenth triode is connected with the output voltage feedback pin of the boosting constant current type switching power supply chip.

Optionally, the open-circuit protection circuit may further include: and the output voltage detection module is connected with the output capacitor discharging module and used for detecting the output voltage and closing the output capacitor discharging module to finish the discharging of the output capacitor when the output voltage is detected to be reduced to the corresponding voltage.

Optionally, the output voltage detection module may include twelfth to fifteenth resistors, and thirty-fifth to forty-second transistors.

A base of the thirty-fifth triode is connected with one end of the thirteenth resistor and one end of the twelfth resistor, an emitter of the thirty-fifth triode is connected with a collector of the thirty-sixth triode, a base of the thirty-sixth triode and a base of the thirty-seventh triode, an emitter of the thirty-sixth triode is connected with emitters of the thirty-seventh triode, the forty-fourth triode and the forty-first triode, a collector of the thirty-seventh triode is connected with a collector of the thirty-eighth triode, a base of the thirty-eighth triode and a base of the thirty-ninth triode, a collector of the thirty-ninth triode is connected with a collector of the forty-fourth triode, and the base of the forty-fourth triode is connected with a base of the forty-first triode, a base of the thirty-eighth triode, a base of the thirty-ninth triode, a base of the thirty-seventh triode, and a base of the thirty-seventh triode are connected with an output terminal of the output voltage detection module, The collector of the forty-first triode and the emitter of the forty-second triode are connected, the base of the forty-second triode is connected with one end of a fourteenth resistor and one end of a fifteenth resistor respectively, the other end of the fourteenth resistor is connected with the output voltage detection end, and the collector of the thirty-fifth triode, the emitter of the thirty-eighth triode, the emitter of the thirty-ninth triode, the collector of the forty-second triode and the other end of the fifteenth resistor are connected with the reference ground end.

Optionally, the open-circuit protection circuit may further include: the reference current generating module comprises a first resistor, a first triode, a second triode, an eleventh triode, a fourteenth triode, a seventeenth triode, a twenty first triode, a twenty second triode, a twenty eighth triode, a twenty ninth triode, a thirty first triode and a forty third triode.

Wherein, the one end of first resistance with reference the ground connection, the other end with the projecting pole of first triode is connected, the base of first triode with reference voltage connects, the collecting electrode of first triode with the collecting electrode of second triode is connected, the base of second triode with the base of eleventh triode the base of fourteenth triode the base of seventeenth triode the base of twenty-first triode the base of twenty-second triode the base of twenty-eighth triode the base of twenty-ninth triode the base of thirty-first triode and the base of forty-third triode all are connected.

The emitting electrode of the second triode, the emitting electrode of the eleventh triode, the emitting electrode of the fourteenth triode, the emitting electrode of the seventeenth triode, the emitting electrode of the twenty-first triode, the emitting electrode of the twenty-second triode, the emitting electrode of the twenty-eighth triode, the emitting electrode of the twenty-ninth triode, the emitting electrode of the thirty-first triode and the emitting electrode of the forty-third triode are all connected with the chip working voltage.

A collector of the eleventh triode is connected with an emitter of the fifth triode and an emitter of the eighth triode of the FB pin voltage detection module, the collector of the fourteenth triode is connected with the collector of the fifteenth triode of the logic control module and the base of the eighteenth triode, the collector of the seventeenth triode is connected with the collector of the eighteenth triode of the logic control module, the collector of the twenty-first triode is connected with the collector of the nineteenth triode, the collector of the twentieth triode and the base of the twenty-third triode of the logic control module, a collector electrode of the twenty-eighth triode is connected with a base electrode of the twenty-fourth triode, a collector electrode of the twenty-sixth triode and a collector electrode of the twenty-seventh triode of the logic control module; a collector of the twenty-ninth triode is connected with a collector of the thirty-second triode of the output capacitor discharging module and a base of the thirty-second triode, a collector of the thirty-first triode is connected with a collector of the thirty-second triode of the output capacitor discharging module and a base of the thirty-fourth triode, and a collector of the forty-third triode is connected with an emitter of the thirty-seventh triode of the output voltage detecting module and an emitter of the forty-fourth triode.

In a second aspect, based on the same inventive concept, the invention further provides a switching power supply chip, and specifically, the switching power supply chip may include the open-circuit protection circuit.

In a third aspect, based on the same inventive concept, the present invention further provides a switching power supply system, and specifically, the switching power supply system may include the switching power supply chip as described above, and an input capacitor, an inductor, a second diode, a load, a sampling resistor, and an output capacitor disposed outside the switching power supply chip.

The positive electrode of the input capacitor is connected with the input end of the boosting constant-current type switching power supply chip, and the negative electrode of the input capacitor and the grounding end of the boosting constant-current type switching power supply chip are both connected with the reference grounding end.

One end of the inductor is connected with the anode of the input capacitor and the input end of the boosting constant current type switching power supply chip, and the other end of the inductor is connected with the power output end of the boosting constant current type switching power supply chip.

The anode of the second diode is connected with one end of the inductor and the power output end of the boosting constant current type switching power supply chip, and the cathode of the second diode is connected with the output voltage detection end of the boosting constant current type switching power supply chip.

One end of the load is connected with the cathode of the second diode and the output voltage detection end of the boosting constant current type switching power supply chip, the other end of the load is connected with one end of the sampling resistor and the output voltage feedback pin of the boosting constant current type switching power supply chip, and the other end of the sampling resistor is connected with the reference ground end.

The anode of the output capacitor is connected with one end of the load, the cathode of the second diode is connected with the output voltage detection end of the boosting constant current type switching power supply chip, and the cathode of the output capacitor is connected with the other end of the sampling resistor and the reference ground end.

Optionally, the first diode may be a voltage regulator tube, and the second diode may be a schottky diode.

Compared with the prior art, the invention has the following beneficial effects:

in the open-circuit protection circuit provided by the invention, when an output voltage feedback pin FB of a boosting constant current type switching power supply chip is required to be pulled down and the voltage of a voltage output end reaches a set maximum value and is simultaneously satisfied, the open-circuit protection circuit judges that the open-circuit is a load open circuit, then a power tube of the chip is turned off firstly to enable the chip not to work, then the internal circuit is started to discharge to an external output capacitor, and when the voltage of the output capacitor is reduced to a set safety value, a discharge path in the circuit is closed to reduce loss, so that when a load LED is opened, the chip and a newly-connected LED load can be protected from being damaged by the high voltage of the output capacitor, a voltage stabilizing diode added at the output end of the load LED in the traditional scheme is omitted, and the user cost and the complexity in production are reduced.

In addition, the open-circuit protection circuit is arranged in the power supply chip and is not influenced by the voltage of the output end (because an external device needs to select a corresponding voltage stabilizing diode according to different output voltages, the external device is greatly influenced by human factors, errors can occur, and the protection function fails), so that the stability of the system can be improved.

Drawings

Fig. 1 is a circuit diagram of an open circuit protection circuit according to an embodiment of the present invention.

Fig. 2 is a circuit diagram of a switching power supply system according to an embodiment of the invention.

Fig. 3 is a simulation diagram illustrating detection of voltages of the boost constant current type switching power supply chip when the LED load is open.

Fig. 4 is a simulation diagram of detection of voltages of the open-circuit protection circuit according to an embodiment of the present invention.

Fig. 5 is a simulation diagram of output voltage detection of an output voltage detection module in the open-circuit protection circuit according to an embodiment of the present invention.

Detailed Description

To further clarify the objects, advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is to be noted that the drawings are in greatly simplified form and are not to scale, but are merely intended to facilitate and clarify the explanation of the embodiments of the present invention. Further, the structures illustrated in the drawings are often part of actual structures. In particular, the drawings may have different emphasis points and may sometimes be scaled differently.

As used in this application, the singular forms "a", "an" and "the" include plural referents, the term "or" is generally employed in a sense including "and/or," the terms "a" and "an" are generally employed in a sense including "at least one," the terms "at least two" are generally employed in a sense including "two or more," and the terms "first", "second" and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicit to the number of technical features indicated. Thus, features defined as "first", "second" and "third" may explicitly or implicitly include one or at least two of the features, "one end" and "the other end" and "proximal end" and "distal end" generally refer to the corresponding two parts, which include not only the end points, but also the terms "mounted", "connected" and "connected" should be understood broadly, e.g., as a fixed connection, as a detachable connection, or as an integral part; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. Furthermore, as used in the present invention, the disposition of an element with another element generally only means that there is a connection, coupling, fit or driving relationship between the two elements, and the connection, coupling, fit or driving relationship between the two elements may be direct or indirect through intermediate elements, and cannot be understood as indicating or implying any spatial positional relationship between the two elements, i.e., an element may be in any orientation inside, outside, above, below or to one side of another element, unless the content clearly indicates otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

As described in the background art, in the scheme of driving the LED using the step-up constant current type power supply chip, if the LED load is damaged, the output end of the boosting constant current type power supply system is opened, once the output end of the system is opened, the voltage of the FB pin of the chip is pulled down, the chip works in the state of the maximum duty ratio, so that the output voltage of the chip can be very high in a very short time, theoretically reaching infinity, which can cause damage to the chip or the output capacitor, therefore, an open-circuit protection circuit is built in each boost chip to limit the output voltage to the maximum value allowed by one chip (the maximum value is often much larger than the normal operating voltage of the LED load), and at this time, if the new LED load is directly replaced, the high voltage on the output end capacitor can be directly applied to two ends of the LED load, and a large current can flow through the LED load in a transient state, so that the newly replaced LED load is damaged.

Therefore, in order to prevent the situation that when the boost constant current type LED driving power supply is switched in again after being switched in the LED load, the output capacitor is too high to cause the damage of the newly switched in LED load, the conventional scheme is to add a zener diode at the output end of the boost constant current type LED driving power supply chip to detect the voltage at the output end, and require the clamping voltage of the zener diode to be about 1.2 times of the normal operating voltage of the LED load, so that when the output end of the power supply chip is switched in an open circuit, the output voltage can be clamped at the two ends of the zener diode, and therefore, when the LED load is switched in again, the LED load cannot be damaged due to the overhigh output voltage.

Therefore, in order to solve the above problems, a core idea of the present invention is to provide an open circuit protection circuit, a switching power supply chip, and a switching power supply system, so as to protect the switching power supply chip and avoid the problem of damage to a newly connected LED load due to an excessively high voltage of an output capacitor when a load open circuit occurs in a boost constant current type switching power supply chip.

An open circuit protection circuit, a switching power supply chip and a switching power supply system of the present invention will be described in further detail below. The present invention will now be described in more detail with reference to the accompanying fig. 1 to 5, in which preferred embodiments of the invention are shown, it being understood that a person skilled in the art may modify the invention described herein while still achieving the advantageous effects of the invention. Accordingly, the following description should be construed as broadly as possible to those skilled in the art and not as limiting the invention.

Referring to fig. 1, and referring to fig. 2, fig. 1 is a schematic circuit diagram of an open circuit protection circuit according to an embodiment of the present invention, and fig. 2 is a switching power supply system including the open circuit protection circuit shown in fig. 1 according to the embodiment of the present invention, where the open circuit protection circuit provided in the embodiment of the present invention may be disposed inside a boost constant current type switching power supply chip 100, an output capacitor COUT and a load LED are connected to the outside of the boost constant current type switching power supply chip 100, and the boost constant current type switching power supply chip 100 has an output voltage detection terminal V0 for detecting an output voltage, an output voltage feedback pin FB for feeding back a change of the output voltage, and a power tube (not shown) for adjusting the output voltage. Also, the boost constant current type switching power supply chip 100 may further have an input terminal VIN and a power output terminal SW. As shown in fig. 1, in an embodiment provided by the present invention, the open circuit protection circuit of the boost constant current type switching power supply may include: the device comprises a reference current generation module 10, an FB pin voltage detection module 20, an overvoltage protection module 30, a logic control module 40, an output capacitor discharge module 50 and an output voltage detection module 60.

The reference current generating module 10 is mainly configured to provide a bias current for each functional module in the open circuit protection circuit. As shown in fig. 1, VREF is a reference voltage, the VREF voltage in this circuit can be designed to be 0.22V, and the reference current in the open protection circuit can be determined by the first transistor Q1 and the first resistor R1, specifically, the formula of the current I1 flowing through the collector of the first transistor Q1 is as follows:

wherein, VQ1BE is the emitter junction voltage of the first transistor Q1, and its value is about 0.7V.

As can be seen from the above formula, by adjusting the resistance of the first resistor R1, an appropriate I1 value of the collector of the first transistor Q1 can be obtained.

Specifically, the reference current generating module 10 may include a first resistor R1, a first triode Q1, a second triode Q2, an eleventh triode Q11, a fourteenth triode Q14, a seventeenth triode Q17, a twenty-first triode Q21, a twenty-second triode Q22, a twenty-eighth triode Q28, a twenty-ninth triode Q29, a thirty-first triode Q31, and a forty-third triode Q43.

One end of the first resistor R1 is connected to the reference ground terminal gnd, the other end is connected to the emitter of the first triode Q1, the base of the first triode Q1 is connected to the reference voltage VREF, the collector of the first triode Q1 is connected to the collector of the second triode Q2, the base of the second triode Q2 is connected to the base of the eleventh triode Q11, the base of the fourteenth triode Q14, the base of the seventeenth triode Q17, the base of the twenty-first triode Q21, the base of the twenty-second triode Q22, the base of the twenty-eighth triode Q28, the base of the twenty-ninth triode Q29, the base of the thirty-first triode Q31, and the base of the forty-third triode Q43.

In this embodiment, the eleventh transistor Q11, the fourteenth transistor Q14, the seventeenth transistor Q17, the twenty-first transistor Q21, the twenty-second transistor Q22, the twenty-eighth transistor Q28, the twenty-ninth transistor Q29, the thirty-first transistor Q31, and the forty-third transistor Q43 may constitute a current mirror. And the collector current flowing through the transistors may be I2 to I10, respectively. Therefore, by setting the device size, the current values of the I2 to the current I10 are obtained at appropriate multiples with reference to the collector current I1 of the first transistor Q1. Illustratively, if Q11= N × Q2, then I2= N × I1. Wherein, the I2 is a collector current flowing through the eleventh transistor Q11, the I3 is a collector current flowing through the fourteenth transistor Q14, the I4 is a collector current flowing through the seventeenth transistor Q17, the I5 is a collector current flowing through the twenty-first transistor Q21, the I6 is a collector current flowing through the twenty-second transistor Q22, the I7 is a collector current flowing through the twenty-eighth transistor Q28, the I8 is a collector current flowing through the twenty-ninth transistor Q29, the I9 is a collector current flowing through the thirty-first transistor Q31, and the I10 is a collector current flowing through the forty-third transistor Q43.

Further, an emitter of the second transistor Q2, an emitter of the eleventh transistor Q11, an emitter of the fourteenth transistor Q14, an emitter of the seventeenth transistor Q17, an emitter of the twenty-first transistor Q21, an emitter of the twenty-second transistor Q22, an emitter of the twenty-eighth transistor Q28, an emitter of the twenty-ninth transistor Q29, an emitter of the thirty-first transistor Q31, and an emitter of the forty-third transistor Q43 are all connected to a chip operating voltage VDD.

A collector of the eleventh transistor Q11 is connected to an emitter of the fifth transistor Q5 and an emitter of the eighth transistor Q8 of the FB pin voltage detection module 20, a collector of the fourteenth transistor Q14 is connected to a collector of the fifteenth transistor Q15 and a base of the eighteenth transistor Q18 of the logic control module 40, a collector of the seventeenth transistor Q17 is connected to a collector of the eighteenth transistor Q18 of the logic control module 40, a collector of the twenty-first transistor Q21 is connected to a collector of the nineteenth transistor Q19, a collector of the twenty-third transistor Q20, and a base of the twenty-third transistor Q23 of the logic control module 40, and a collector of the twenty-eighth transistor Q28 is connected to a base of the twenty-fourth transistor Q24 of the logic control module 40, A collector electrode of the twenty-sixth triode Q26 is connected with a collector electrode of the twenty-seventh triode Q27; a collector of the twenty-ninth transistor Q29 is connected to a collector of the thirty-second transistor Q33 of the output capacitor discharging module 50 and a base of the thirty-second transistor Q32, a collector of the thirty-first transistor Q31 is connected to a collector of the thirty-second transistor Q32 of the output capacitor discharging module 50 and a base of the thirty-fourth transistor Q34, and a collector of the forty-third transistor Q43 is connected to an emitter of the thirty-seventh transistor Q37 of the output voltage detecting module 60 and an emitter of the forty-fourth transistor Q43.

The FB pin voltage detection module 20 is connected to the output voltage feedback pin FB, and is configured to detect whether a voltage of the output voltage feedback pin FB is lower than a first voltage threshold, if so, output a high level signal, and if not, output a low level signal. Specifically, the FB pin voltage detection module 20 may include a second resistor R2, a third resistor R3, and the third through thirteenth diodes Q3 through Q10.

One end of the second resistor R2 is connected to a reference voltage VREF, the other end of the second resistor R2 is connected to one end of the third resistor R3 and the base of the third transistor Q3, and the other end of the third resistor R3 and the collector of the third transistor Q3 are both connected to the reference ground terminal gnd; an emitter of the third transistor Q3 is connected to a collector of the fourth transistor Q4, a base of the fourth transistor Q4, and a base of the fifth transistor Q5, an emitter of the fourth transistor Q4 is connected to an emitter of the fifth transistor Q5, an emitter of the eighth transistor Q8, and an emitter of the ninth transistor Q9, a collector of the fifth transistor Q5 is connected to a collector of the sixth transistor Q6, a base of the sixth transistor Q6, and a base of the seventh transistor Q7, and an emitter of the sixth transistor Q6 and an emitter of the seventh transistor Q7 are connected to the reference ground terminal gnd; a collector of the seventh transistor Q7 is connected to a collector of the eighth transistor Q8, and serves as an output terminal OUT1 of the FB pin voltage detection module 20; the base of the eighth triode Q8 is connected with the base of the ninth triode Q9 and the collector of the ninth triode Q9, the collector of the ninth triode Q9 is connected with the emitter of a thirteenth diode Q13, the collector of the thirteenth diode Q13 is connected with the reference ground terminal gnd, and the base of the thirteenth diode Q13 is connected with the output voltage feedback pin FB of the boost constant current type switching power supply chip 100.

In this embodiment, if it is detected that the voltage of the output voltage feedback pin FB is lower than the voltage V1 across the resistor R3, the output terminal OUT1 of the FB pin voltage detecting module 20 is at a high level, and it can be considered that the voltage of the output voltage feedback pin FB is pulled low. Specifically, the voltage V1 may be set according to the following formula, so that after determining that the output voltage of the output voltage feedback pin FB falls to 1/5 of the reference voltage VREF, the output terminal OUT1 of the FB pin voltage detection module 20 outputs a high level, that is, the output terminal OUT1 of the FB pin voltage detection module 20 outputs a low level when the voltage of the output voltage feedback pin FB is greater than the voltage V1.

VREF is a reference voltage, and R2 and R3 are resistance values of the second resistor and the third resistor.

Further, as can be seen from fig. 1, in the embodiment of the present invention, the overvoltage protection module 30 may be configured to detect whether the voltage of the output voltage detection terminal V0 is overvoltage, and determine that the voltage of the output voltage detection terminal V0 is overvoltage, as a second determination condition for determining whether the boost constant current type switching power supply system meets the condition of load open.

Specifically, the overvoltage protection module 30 may include an input terminal, an output terminal OUT2, fourth to seventh resistors, a first diode DZ1, a twelfth transistor Q12, and a thirteenth transistor Q13.

The first diode DZ1 may be a voltage regulator, a cathode of the first diode DZ1 is connected to the output voltage detection terminal V0 and serves as an input terminal of the overvoltage protection module 30, an anode of the first diode DZ1 is connected to one end of a fourth resistor R4, and the other end of the fourth resistor R4 is connected to one end of a fifth resistor R5 and a base of the twelfth triode Q12; the other end of the fifth resistor R5 is connected to a reference ground gnd; one end of a sixth resistor R6 is connected to the chip operating voltage VDD, and the other end is connected to the base of the thirteenth triode Q13 and the emitter of the twelfth triode Q12, the collector of the thirteenth triode Q13 is connected to the chip operating voltage VDD, and the collector of the twelfth triode Q12 is connected to the ground reference terminal gnd; one end of the seventh resistor R7 is connected to the reference ground gnd, and the other end of the seventh resistor R7 is connected to the emitter of the thirteenth transistor Q13 and serves as the output terminal OUT2 of the overvoltage protection module 30, and is connected to the logic control module 40, so that the logic control module 40 determines whether the boost constant current type switching power supply system meets the second determination condition for the occurrence of the load open circuit through the output terminal OUT2 of the overvoltage protection module 30.

In this embodiment, after the LED load in the system scheme of boosting the voltage and driving the LED with constant current is opened, the output voltage (the output voltage detecting terminal V0) of the switching power supply is continuously increased, and when the output voltage exceeds the maximum output value of the chip design, the output terminal voltage OUT2 of the overvoltage protection module 30 is changed from low level to high level, and it is determined that the chip meets the second determination condition for load opening. When the voltage at the output terminal of the chip is in a normal condition, that is, the voltage at the output voltage detection terminal V0 is smaller than the maximum output value of the chip design, the first diode DZ1 is not broken, the voltage V2 is pulled low through the resistor R5 and is close to ground, that is, V2 is at a low level, the twelfth transistor Q12 is turned on (R6 is a current-limiting resistor), the base of the thirteenth transistor Q13 is connected to ground, the thirteenth transistor Q13 is turned off, so the OUT2 is connected to ground through the resistor R7, and the output is at a low level. When the output end load LED of the chip 100 is damaged or opened, that is, the voltage V0 at the output voltage detection end is greater than the designed maximum output value of the chip, the first diode DZ1 is broken down instantaneously, the voltage V2 becomes high level to turn off the twelfth triode Q12, and at this time, the chip operating voltage VDD is connected to the base of the thirteenth triode Q13 through R6, so that the triode Q13 is turned on, and the output of the OUT2 is high level, thereby implementing the second judgment condition that whether the load open circuit occurs in the switching power supply can be judged according to whether the OUT2 is high voltage. The maximum value of the output voltage can be adjusted by adjusting the value of the first diode DZ 1.

The logic control module 40 is connected to the driving end of the power tube, the FB pin voltage detection module 20 and the overvoltage protection module 30, and is configured to control the power tube to turn off and trigger the output capacitor discharge module to operate when both the FB pin voltage detection module 20 and the overvoltage protection module 30 output high level signals, and latch the output voltage QA of the logic control module 40 to continuously output a high level signal and control the power tube to turn off when at least one of the FB pin voltage detection module 20 and the overvoltage protection module 30 outputs a low level signal after the output end load LED is damaged or opened, until the boost constant current type switching power supply system releases the load LED open circuit state, the boost constant current type switching power supply chip is powered on again to recover the output end voltage QA to a low level signal, namely, the output capacitor discharge module 50 is determined to be triggered according to the determination result, and the determination result is used to determine whether the boost constant current type switching power supply system simultaneously satisfies the first determination condition and the second determination condition. Specifically, the logic control module 40 may include a first input terminal, a second input terminal, an output terminal, a fifteenth transistor Q15, a sixteenth transistor Q16, an eighteenth transistor Q18, a nineteenth transistor Q19, a twentieth transistor Q20, a twenty-third transistor Q23 to a twenty-seventh transistor Q27, and an eighth R8 to a tenth resistor R10.

A base electrode of the fifteenth transistor Q15 is connected to the output end OUT2 of the overvoltage protection module 30 and serves as a second input end of the logic control module 40, a collector electrode of the fifteenth transistor Q15 is connected to a base electrode of the eighteenth transistor Q18, and an emitter electrode of the fifteenth transistor Q15 is connected to a collector electrode of the sixteenth transistor Q16; an emitter of the sixteenth triode Q16 is connected to the reference ground terminal gnd, and a base of the sixteenth triode Q16 is connected to the output terminal OUT1 of the FB pin voltage detection module 20 and serves as a first input terminal of the logic control module 40; the emitter of the eighteen triode Q18 is connected to the ground terminal gnd, the collector of the eighteen triode Q18 is connected to the base of the nineteenth triode Q19, an emitter of the nineteenth transistor Q19 is connected to the ground terminal gnd, a collector of the nineteenth transistor Q19 is connected to a collector of the twentieth transistor Q20 and a base of the twenty-third transistor Q23, an emitter of the twentieth transistor Q20 is connected to the ground reference terminal gnd, a base of the twentieth transistor Q20 is connected to one end of the eighth resistor R8, the other end of the eighth resistor R8 is connected to one end of the ninth resistor R9, the collector of the twenty-third transistor Q20 and the collector of the twenty-fourth transistor Q24, the other end of the ninth resistor R9 is connected with the base electrode of a twenty-fifth triode Q25, and the emitter electrode of the twenty-fifth triode Q25 is connected; an emitter of the twenty-third triode Q23 and an emitter of the twenty-fourth triode Q24 are both connected to the reference ground terminal gnd, and a base of the twenty-fourth triode Q24 is connected to a collector of a twenty-sixth triode Q26 and a collector of the twenty-seventh triode Q27; an emitter of the twenty-sixth triode Q26 and an emitter of the twenty-seventh triode Q27 are both connected to the reference ground gnd, and a base of the twenty-seventh triode Q27 is connected to one end of the tenth resistor R10 and the input end of the output capacitor discharging module 50.

In this embodiment, when the output terminal OUT1 of the FB pin voltage detection module 20 and the output terminal OUT2 of the overvoltage protection module 30 are not high at the same time, the base of the transistor Q18 is shorted with the collector of the transistor Q14, the transistor Q18 is turned on due to the current I3, the voltage QB is shorted with ground to be low, the transistor Q19 is not turned on, the transistor Q26 is also not turned on, and the transistors Q20, Q25, Q27, and Q30 are turned on at a higher voltage than the transistors Q23 and Q24 under the same condition due to the presence of R8, R9, and R10, so that when I3= I4= I5= I6= I7= I8, the transistors Q23 and Q24 are turned on first to pull QA to be low in the initial state, so that the transistors Q20, Q25, Q27, and Q30 will not be turned on. When the output terminals OUT1 and OUT2 are both high, the transistors Q15 and Q16 are turned on, the base of the transistor Q18 is shorted to ground, the transistor Q18 is turned off, the QB is set to high, the transistors Q19 and Q26 are turned on, the bases of the transistors Q23 and Q24 are shorted to ground, the transistors Q23 and Q24 are not turned on, the transistor QA is set to high, the transistors Q20, Q25, Q27 and Q30 are turned on, the DRN signal connected to the collectors of the turned on transistors Q25 is pulled low, so the power tube inside the switching power chip 100 is turned off (when the DRN signal is high, the pulse modulation signal of the switching power chip can normally drive the power tube to be turned on and off), once the QA 27 and Q20 are turned on, the transistors Q23 and Q24 are turned off, so that the Q26 and Q19 do not affect the high QA and the OUT1, QB becomes low level again, QA will not be set low, unless the chip is powered on again to restore the initial state after the open circuit state is released, QA will become low level.

The output capacitor discharging module 50 is connected to the output capacitor COUT, and is configured to discharge the output capacitor COUT after being triggered by the logic control module, so as to reduce the voltage of the output voltage detection terminal V0, that is, when the logic control module 40 determines that the boost constant current type switching power supply system is in the load open circuit state, the output capacitor discharging module is configured to discharge the external output capacitor COUT through the boost constant current type switching power supply via the output voltage detection terminal V0, so as to reduce the voltage of the output voltage detection terminal V0. Specifically, the output capacitor discharging module 50 may include an input terminal, a thirty-third transistor Q30, a thirty-second transistor Q32, a thirty-third transistor Q33, a thirty-fourth transistor Q34, and an eleventh resistor R11.

The base of the thirtieth triode Q33 is connected to the output terminal of the logic control module 40 and serves as the input terminal of the output capacitor discharging module 50, the emitter of the thirtieth triode Q33 is connected to the ground GND, and the collector of the thirtieth triode Q33 is connected to the base of the thirty-second triode Q32; an emitter of the thirty-second triode Q32 is connected to the ground reference terminal gnd, a collector of the thirty-second triode Q32 is connected to a collector of the thirty-third triode Q33 and a base of the thirty-fourth triode Q34, an emitter of the thirty-third triode Q33 is connected to the ground reference terminal gnd, and a base of the thirty-third triode Q33 is used as an output terminal OUT3 of the output capacitor discharging module 50; a collector of the thirty-fourth triode Q34 is connected to one end of the eleventh resistor R11, an emitter of the thirty-fourth triode Q34 is connected to the ground reference terminal gnd, and the other end of the eleventh resistor R11 is connected to the output voltage detection terminal V0 of the boost constant current type switching power supply.

In this embodiment, when the output voltage QA is low, the transistor Q30 is not conducting, but the transistor Q32 is conducting, the base of the transistor Q34 is pulled to ground, the transistor Q34 is not conducting, the conduction state of the transistor Q34 is not affected by the conduction of the transistor Q33, and the output capacitor discharging module 50 is not discharged by the present module because the transistor Q34 is not conducting. When the output voltage QA is at a high level, the triode Q30 is turned on, the base of the triode Q32 is pulled to the ground, the triode Q32 is not turned on, at this time, if the triode Q33 is not turned on, the base of the triode Q34 is set high, the triode Q34 is turned on, at this time, the output capacitor discharges to the ground through the R11, and the R11 plays a role in limiting the current; if the transistor Q33 is turned on, the base of the transistor Q34 is pulled low, and the transistor Q34 is turned off, so the module will not discharge the output capacitor COUT.

The output voltage detecting module 60 is configured to detect the output voltage VOUT, and when detecting that the output voltage VOUT drops to a corresponding voltage, turn off the output capacitor discharging module 50 to end the discharging of the output capacitor COUT. Specifically, the output voltage detecting module 60 may include twelfth to fifteenth resistors R12 to R15, and thirty-fifth to forty-second transistors Q35 to Q42.

One end of the twelfth resistor R12 is connected to the input voltage VIN, the other end of the twelfth resistor R12 is connected to the base of the thirty-fifth triode Q35 and one end of the thirteenth resistor R13, and the other end of the thirteenth resistor R13 is connected to the ground reference terminal gnd; an emitter of the thirty-fifth triode Q35 is connected with a collector of a thirty-sixth triode Q36, a base of the thirty-sixth triode Q36 and a base of a thirty-seventh triode Q37, and a collector of the thirty-fifth triode Q35 is connected with the reference ground terminal gnd; an emitter of the thirty-sixth triode Q36 is connected with an emitter of the thirty-seventh triode Q37, an emitter of the forty-fourth triode Q43 and an emitter of the forty-first triode Q41, a collector of the thirty-seventh triode Q37 is connected with a collector of the thirty-eighth triode Q38, a base of the thirty-eighth triode Q38 and a base of the thirty-ninth triode Q39, and an emitter of the thirty-eighth triode Q38 and an emitter of the thirty-ninth triode Q39 are both connected with the reference ground terminal gnd; a collector of the thirty-ninth triode Q39 is connected to a collector of the forty-fourth triode Q40 and serves as an output end of the output voltage detection module 60, a base of the forty-fourth triode Q43 is connected to a base of the forty-first triode Q41, a collector of the forty-first triode Q41 and an emitter of the forty-second triode Q42, a base of the forty-second triode Q42 is connected to one end of a fourteenth resistor R14 and one end of a fifteenth resistor R15, the other end of the fourteenth resistor R14 is connected to the output voltage detection end V0, and both the collector of the forty-second triode Q42 and the other end of the fifteenth resistor R15 are connected to the reference ground end gnd.

In this embodiment, since the voltage V3 is obtained by dividing the input power voltage VIN by resistors, and the voltage V4 is obtained by dividing the output voltage detection terminal V0 by resistors, when V4 is greater than V3, the output terminal voltage OUT3 outputs a low level, and the transistor Q33 is turned off, that is, the QA is allowed to control the transistor Q34 to be turned on, so as to discharge the output capacitor COUT; when V4 is smaller than V3, the voltage OUT3 at the output terminal outputs a high level, the transistor Q33 is turned on, the base of the transistor Q34 is pulled low, and will not be turned on, and at this time QA is shielded and will not discharge to the output capacitor COUT. Specifically, the resistance ratios of R12, R13, R14 and R15 may be set, and when V0=1.2VIN, V3= V4, that is, once V0 is lower than 1.2VIN, V4 is smaller than V3, and at this time, the transistor Q34 is always non-conductive and will not discharge to the output capacitor COUT. When the chip detects that the load LED is open and discharges the output capacitor COUT, the function can be realized that when the voltage V0 at the output voltage detection end drops to about the input voltage VIN, the output capacitor discharge module is turned off (Q34 is turned off), because once the output voltage is lower than the power supply voltage, VIN charges the output capacitor COUT through the inductor L1 and the diode D1, and at this time, current continuously flows to the ground through the output capacitor discharge module 50 through the pin V0, which increases the power supply loss and should be avoided.

Wherein the first triode Q1, the sixth triode Q6, the seventh triode Q7, the thirteenth triode Q13, the fifteenth triode Q15, the sixteenth triode Q16, the eighteenth triode Q18 to the twentieth triode Q20, the twenty-third triode Q23 to the twenty-seventh triode Q27, the thirty triode Q30, the thirty-second triode Q32, the thirty-third triode Q33, the thirty-fourth triode Q34, the thirty-sixth triode Q36, the thirty-eighth triode Q38 and the thirty-ninth triode Q39 may be NPN type triodes.

Also, the second to fifth triodes Q2 to Q5, the eighth to twelfth triodes Q8 to Q12, the fourteenth triode Q14, the seventeenth triode Q17, the twenty first triode Q21, the twenty second triode Q22, the twenty eighth triode Q28, the twenty ninth triode Q29, the thirty-first triode Q31, the thirty-fifth triode Q35, the thirty-seventh triode Q37, and the forty-third triode Q40 to Q43 may be PNP type triodes.

In the open-circuit protection circuit provided by the invention, when an output voltage feedback pin FB of a boosting constant current type switching power supply chip is required to be pulled down and the voltage of a voltage output end reaches a set maximum value and is simultaneously satisfied, the open-circuit protection circuit judges that the open-circuit is a load open circuit, then a power tube of the chip is turned off firstly to enable the chip not to work, then the internal circuit is started to discharge to an external output capacitor, and when the voltage of the output capacitor is reduced to a set safety value, a discharge path in the circuit is closed to reduce loss, so that when a load LED is opened, the chip and a newly-connected LED load can be protected from being damaged by the high voltage of the output capacitor, a voltage stabilizing diode added at the output end of the load LED in the traditional scheme is omitted, and the cost and the complexity in production are reduced.

In addition, based on the same inventive concept, the invention also provides a switching power supply chip comprising the open-circuit protection circuit (as shown in fig. 1).

In addition, referring to fig. 2, based on the same inventive concept, the present invention further provides a switching power supply system, and fig. 2 is a circuit schematic diagram of the switching power supply system provided in an embodiment of the present invention. As shown in fig. 2, the switching power supply system provided by the present invention may include: an input capacitor CIN, an inductor L1, a second diode D1, a load LED, a sampling resistor RCS, an output capacitor COUT, and a boost constant current switching power supply chip 100 including the open circuit protection circuit shown in fig. 1.

The positive electrode of the input capacitor CIN is connected to the input end VIN of the boost constant current type switching power supply chip 100, and the negative electrode of the input capacitor CIN and the ground terminal GND of the boost constant current type switching power supply chip 100 are both connected to the reference ground terminal GND.

One end of the inductor L1 is connected to the positive electrode of the input capacitor CIN and the input end VIN of the boost constant current type switching power supply chip 100, and the other end is connected to the power output end SW of the boost constant current type switching power supply chip 100.

An anode of the second diode D1 is connected to one end of the inductor L1 and the power output terminal SW of the boost constant current type switching power supply chip 100, and a cathode of the second diode D1 is connected to the output voltage detection terminal V0 of the boost constant current type switching power supply chip 100.

One end of the load LED is connected to the cathode of the second diode D1 and the output voltage detection terminal V0 of the boost constant current type switching power supply chip 100, the other end of the load LED is connected to one end of the sampling resistor RCS and the output voltage feedback pin FB of the boost constant current type switching power supply chip 100, and the other end of the sampling resistor RCS is connected to the ground reference terminal GND.

The anode of the output capacitor COUT is connected to one end of the load LED, the cathode of the second diode D1 and the output voltage detection end V0 of the boost constant current type switching power supply chip 100, and the cathode of the output capacitor COUT and the other end of the sampling resistor RCS are both connected to the reference ground end GND.

The first diode DZ1 may be a voltage regulator, and the second diode D1 may be a schottky diode.

Referring to fig. 3 to 5, fig. 3 is a simulation diagram of detection of voltages of the boost constant current type switching power supply when the LED load is open, fig. 4 is a simulation diagram of detection of voltages of the open circuit protection circuit, and fig. 5 is a simulation diagram of detection of an output voltage of the output voltage detection module 60 in the open circuit protection circuit.

Specifically, as shown in fig. 3, when the output voltage feedback pin FB is lower than the voltage V1, the output voltage OUT1 of the FB pin voltage detection module 20 becomes high (condition 1 for determining open circuit), and the voltage of the output voltage detection terminal V0 gradually increases, and when the output voltage detection terminal V0 exceeds the maximum output value of the chip design, the voltage of the output voltage detection terminal V2 changes from low to high, and the voltage of the output voltage detection terminal OUT2 also changes to high (condition 2 for determining open circuit). A load LED open circuit is detected when both OUT1 and OUT2 are high. As can be seen from fig. 4, when OUT1 and OUT2 are both set high, QA is set high, V5 is also set high, at this time, the DRN signal is pulled low all the time (the chip stops operating, the power tube is turned off), the output voltage detection terminal V0 discharges through R11 and Q34, the voltage is rapidly reduced, when the output voltage detection terminal V0 is lower than the maximum output value of the chip design, OUT2 changes from high level to low level, QB also changes from high level to low level, but QA can keep high level all the time, when the output voltage detection terminal V0 drops to a certain value, it will not discharge to the output capacitor COUT, OUT3 is set high, V5 is pulled low, Q34 is not conductive, and the discharge path is closed. As shown in fig. 5, it can be seen that when the voltage of the output voltage detecting terminal V0 drops to 1.2 times the input voltage VIN, OUT3 changes from low to high and V5 is pulled low, i.e. it is considered that the voltage of V0 has dropped to a safe range and is not discharging the output capacitor COUT.

To sum up, in the open circuit protection circuit provided by the present invention, when the output voltage feedback pin FB of the boost constant current type switching power supply chip is pulled low and the voltage at the voltage output terminal reaches the set maximum value and is simultaneously satisfied, the open circuit protection circuit determines that the load is open, then turns off the power tube of the chip first to make the chip not work, then starts to discharge the external output capacitor through the internal circuit, and turns off the discharge path in the circuit when the voltage of the output capacitor drops to the set safety value to reduce the loss, thereby realizing that when the load LED is open, the chip and the LED load newly connected are protected from being damaged by the high voltage of the output capacitor, and the voltage stabilizing diode added at the output terminal of the load LED in the conventional scheme is omitted, thereby reducing the cost and complexity of production.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example" or "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. And the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments. Furthermore, various embodiments or examples described in this specification can be combined and combined by those skilled in the art.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. It will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. An open circuit protection circuit, set up in the inside of a constant current type switching power supply chip that steps up, the external connection of constant current type switching power supply chip that steps up has output capacitance and load, the constant current type switching power supply chip that steps up has the output voltage who is used for detecting output voltage detection end, is used for feeding back output voltage feedback pin that output voltage changes and is used for adjusting output voltage's power tube, open circuit protection circuit includes:

the FB pin voltage detection module is connected with the output voltage feedback pin and used for detecting whether the voltage of the output voltage feedback pin is lower than a first voltage threshold value or not, if so, a high level signal is output, and if not, a low level signal is output;

the overvoltage protection module is connected with the output voltage detection end and used for detecting whether the voltage of the output voltage detection end is larger than a second voltage threshold value or not, if yes, a high level signal is output, and if not, a low level signal is output;

the logic control module is connected with the driving end of the power tube, the FB pin voltage detection module and the overvoltage protection module, and is used for controlling the power tube to be switched off and triggering the output capacitor discharge module to work when the FB pin voltage detection module and the overvoltage protection module both output high-level signals, and then latching the output voltage of the logic control module to continuously output the high-level signals and controlling the power tube to be switched off when at least one of the FB pin voltage detection module and the overvoltage protection module outputs low-level signals until the boost constant-current type switching power supply chip is powered on again;

2. The open-circuit protection circuit of claim 1, wherein the overvoltage protection module comprises an input terminal, an output terminal, fourth to seventh resistors, a first diode, a twelfth transistor, and a thirteenth transistor;

3. The open-circuit protection circuit of claim 1, wherein the logic control module comprises a first input terminal, a second input terminal, an output terminal, a fifteenth transistor, a sixteenth transistor, an eighteenth transistor through a twentieth transistor, a twenty third transistor through a twenty seventh transistor, and an eighth through a tenth resistor, wherein,

the base electrode of the fifteenth triode is connected with the output end of the overvoltage protection module and serves as a second input end of the logic control module; a collector of the fifteenth triode is connected with a base of the eighteenth triode, and an emitter of the fifteenth triode is connected with a collector of the sixteenth triode; a base electrode of the sixteenth triode is connected with an output end of the FB pin voltage detection module and is used as a first input end of the logic control module; the collector of the eighteenth triode is connected with the base of the nineteenth triode, the collector of the nineteenth triode is connected with the collector of the twentieth triode and the base of the twenty-third triode, the base of the twentieth triode is connected with one end of the eighth resistor, the other end of the eighth resistor is connected with one end of the ninth resistor, the collector of the twenty-third triode and the collector of the twenty-fourth triode, the other end of the ninth resistor is connected with the base of the twenty-fifth triode, and the emitter of the twenty-fifth triode is connected; the base electrode of the twenty-fourth triode is connected with the collector electrode of the twenty-sixth triode and the collector electrode of the twenty-seventh triode; and the emitting electrodes of the sixteenth triode, the eighteenth triode to the nineteenth triode and the twenty third triode to the twenty fifth triode are connected with the reference ground end, and the base electrode of the twenty seventh triode is connected with one end of the tenth resistor and the input end of the output capacitor discharging module.

4. The open circuit protection circuit of claim 1, wherein the output capacitance discharging module comprises a first input terminal, a second input terminal, a thirty-third triode, a thirty-second triode, a thirty-third triode, a thirty-fourth triode, and an eleventh resistor, wherein,

a base electrode of the thirty-third triode is connected with an output end of the logic control module and serves as a first input end of the output capacitor discharging module, an emitting electrode of the thirty-third triode is connected with a reference ground end, and a collector electrode of the thirty-third triode is connected with a base electrode of the thirty-second triode; an emitter of the thirty-second triode is connected with the reference ground, a collector of the thirty-second triode is connected with a collector of the thirty-third triode and a base of the thirty-fourth triode, an emitter of the thirty-third triode is connected with the reference ground, and the base of the thirty-third triode is used as a second input end of the output capacitor discharging module; and a collector of the thirty-fourth triode is connected with one end of the eleventh resistor, an emitter of the thirty-fourth triode is connected with the reference ground end, and the other end of the eleventh resistor is connected with an output voltage detection end of the boost constant current type switching power supply chip.

5. The open-circuit protection circuit of claim 1, wherein the FB pin voltage detection module includes a second resistor, a third triode through a thirteenth triode, wherein,

one end of the second resistor is connected with a reference voltage, the other end of the second resistor is connected with one end of the third resistor and the base electrode of the third triode, and the other end of the third resistor and the collector electrode of the third triode are both connected with a reference ground end; an emitter of the third triode is connected with a collector of a fourth triode, a base of the fourth triode and a base of a fifth triode, an emitter of the fourth triode is connected with an emitter of the fifth triode, an emitter of an eighth triode and an emitter of a ninth triode, a collector of the fifth triode is connected with a collector of a sixth triode, a base of the sixth triode and a base of a seventh triode, and the emitter of the sixth triode and the emitter of the seventh triode are both connected with the reference ground; a collector of the seventh triode is connected with a collector of the eighth triode and serves as an output end of the FB pin voltage detection module; the base electrode of the eighth triode is connected with the base electrode of the ninth triode and the collector electrode of the ninth triode, the collector electrode of the ninth triode is connected with the emitter electrode of the thirteenth triode, the collector electrode of the thirteenth triode is connected with the reference ground end, and the base electrode of the thirteenth triode is connected with the output voltage feedback pin of the boosting constant current type switching power supply chip.

6. The open-circuit protection circuit of claim 1, further comprising: and the output voltage detection module is connected with the output capacitor discharging module and used for detecting the output voltage and closing the output capacitor discharging module to finish the discharging of the output capacitor when the output voltage is detected to be reduced to the corresponding voltage.

7. The open-circuit protection circuit of claim 6, wherein the output voltage detection module comprises a twelfth resistor to a fifteenth resistor, a thirty-fifth transistor to a forty-second transistor, wherein,

a base of the thirty-fifth triode is connected with one end of the thirteenth resistor and one end of the twelfth resistor, an emitter of the thirty-fifth triode is connected with a collector of the thirty-sixth triode, a base of the thirty-sixth triode and a base of the thirty-seventh triode, an emitter of the thirty-sixth triode is connected with emitters of the thirty-seventh triode, the forty-fourth triode and the forty-first triode, a collector of the thirty-seventh triode is connected with a collector of the thirty-eighth triode, a base of the thirty-eighth triode and a base of the thirty-ninth triode, a collector of the thirty-ninth triode is connected with a collector of the forty-fourth triode, and the base of the forty-fourth triode is connected with a base of the forty-first triode, a base of the thirty-eighth triode, a base of the thirty-ninth triode, a base of the thirty-seventh triode, and a base of the thirty-seventh triode, The collector of the forty-first triode and the emitter of the forty-second triode are connected, the base of the forty-second triode is connected with one end of a fourteenth resistor and one end of a fifteenth resistor respectively, the other end of the fourteenth resistor is connected with the output voltage detection end, and the collector of the thirty-fifth triode, the emitter of the thirty-eighth triode, the emitter of the thirty-ninth triode, the collector of the forty-second triode and the other end of the fifteenth resistor are connected with a reference ground end.

8. A switching power supply chip characterized by comprising the open-circuit protection circuit according to any one of claims 1 to 7.

9. A switching power supply system, comprising: the switching power supply chip of claim 8, and an input capacitor, an inductor, a second diode, a load, a sampling resistor, and an output capacitor disposed outside the switching power supply chip,

the positive electrode of the input capacitor is connected with the input end of the boosting constant-current type switching power supply chip, and the negative electrode of the input capacitor and the grounding end of the boosting constant-current type switching power supply chip are both connected with the reference ground end;

one end of the inductor is connected with the anode of the input capacitor and the input end of the boosting constant current type switching power supply chip, and the other end of the inductor is connected with the power output end of the boosting constant current type switching power supply chip;

the anode of the second diode is connected with one end of the inductor and the power output end of the boosting constant-current type switching power supply chip, and the cathode of the second diode is connected with the output voltage detection end of the boosting constant-current type switching power supply chip;

one end of the load is connected with the cathode of the second diode and the output voltage detection end of the boosting constant current type switching power supply chip, the other end of the load is connected with one end of the sampling resistor and the output voltage feedback pin of the boosting constant current type switching power supply chip, and the other end of the sampling resistor is connected with the reference ground end;

10. The switching power supply system according to claim 9, wherein the first diode is a voltage regulator and the second diode is a schottky diode.