CN112994430B - Multi-mode combined short-circuit protection circuit and working method and application thereof - Google Patents

Multi-mode combined short-circuit protection circuit and working method and application thereof Download PDF

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Publication number
CN112994430B
CN112994430B CN202110217339.7A CN202110217339A CN112994430B CN 112994430 B CN112994430 B CN 112994430B CN 202110217339 A CN202110217339 A CN 202110217339A CN 112994430 B CN112994430 B CN 112994430B
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resistor
circuit
voltage
operational amplifier
protection
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CN112994430A (en
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王鲁
曹鹏辉
张小峰
罗伟
付翀丽
王俊峰
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Xian Microelectronics Technology Institute
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Xian Microelectronics Technology Institute
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Priority to PCT/CN2022/077963 priority patent/WO2022179612A1/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/1203—Circuits independent of the type of conversion
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/1213—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for DC-DC converters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention belongs to the technical field of short-circuit protection circuits, and discloses a multi-mode combined short-circuit protection circuit and a working method thereof, wherein the multi-mode combined short-circuit protection circuit specifically comprises a sampling circuit, a constant current protection circuit, a hiccup protection circuit, a reference voltage circuit and a voltage division circuit; the constant-current protection circuit comprises an operational amplifier U1A, the hiccup protection circuit comprises an operational amplifier U1B, when the output of the switching power supply is short-circuited, constant-current protection is firstly carried out, then hiccup protection is carried out, the hiccup protection mode can be started when the set constant-current protection time is reached, the short-circuit fault continuously exists, and the working mode of 'constant-current protection-hiccup protection' is repeated on a protection circuit; and the short-circuit fault of the switching power supply is eliminated, and the normal function is recovered. The short-circuit protection circuit has the advantages of being high in capacity of capacitive load of constant-current protection and low in power consumption of hiccup protection short circuit, meanwhile, the fact that the hiccup protection can be achieved within the designed time of constant-current protection is guaranteed, the problem that the short-circuit power consumption of a high-power switching power supply is large is solved, and the short-circuit protection circuit has the advantage of being high in capacity of capacitive load.

Description

Multi-mode combined short-circuit protection circuit and working method and application thereof
Technical Field
The invention belongs to the technical field of short-circuit protection circuits, and particularly relates to a multi-mode combined short-circuit protection circuit and a working method and application thereof.
Background
The switch power supply is continuously developed towards the characteristics of high power, small volume, high efficiency, high reliability and the like. With the improvement of high efficiency technology, the dissipation power of the switching power supply is effectively controlled, the size is continuously reduced, the power density is higher and higher, but the design difficulty of a short-circuit protection circuit is continuously increased, and the improvement of the reliability of the switching power supply is restricted. At present, two common short-circuit protection circuits are provided, one is a constant-current protection circuit, and the other is a hiccup protection circuit.
(1) Constant current protection circuit
Constant current protection is a precise power control mode, and a protection circuit is shown in figure 1. A sampling resistor or a current transformer is generally used to detect a change in current, convert the current sampling signal into a voltage sampling signal, and perform a differential comparison with a reference level. The differential signal controls the output level through the proportional integral of the operational amplifier, and further controls the level of the feedback signal. The feedback signal controls the output duty ratio by isolated transmission or directly triggering the COM end level of the pulse width controller, and finally, the accurate control of the output power is realized.
When the output end of the switching power supply is in short circuit, the current is rapidly increased to trigger constant current protection, the output duty ratio of the pulse width controller is limited, the output power is greatly reduced, and the purpose of reducing the short-circuit power consumption is achieved. In addition, when the output end of the switching power supply is connected with a large capacitive load to be electrified, the constant current protection can limit the sudden change of the pulse width control duty ratio and continuously change from small to large until the output voltage is established, so that the capacitive load has the advantage of strong capacitive load capacity. However, as the output power of the switching power supply is increased, the current during short-circuit protection is also increased, which leads to continuous increase of short-circuit power consumption and limits the application range of constant-current protection.
(2) Hiccup protection circuit
Hiccup protection is a pulse power control method, and the protection circuit is shown in figure 2. Generally, a sampling resistor or a current transformer is used for detecting input current change, a current sampling signal is converted into a voltage sampling signal, the voltage sampling signal is compared with a reference level, the output level of a comparator is controlled, and then the level of a feedback signal is controlled. The feedback signal directly triggers the COM end level of the pulse width controller, so that the change of the output duty ratio is controlled, the duty ratio is changed from 0, and finally the pulse control of the output power is realized.
When the output end of the switching power supply is short-circuited, the input current is rapidly increased to trigger the output of the comparator to turn over, the output duty ratio of the pulse width controller is increased from 0, and no energy is output; and the hiccup protection time is prolonged, so that the power consumption of short-circuit protection can be greatly reduced. However, when the switching power supply is short-circuited and in the period of collecting pulse power signals, the pulse width control outputs the maximum duty ratio, the transformer is difficult to reset, the saturation problem exists, and the voltage stress and the current stress of power devices such as the transformer, a main power MOS tube and the like are large, the heating is serious, the burning risk exists, and therefore the pulse power time must be set to be short. When the output end of the switching power supply is connected with a large capacitive load to be electrified, the input current is rapidly increased, short pulse power time often cannot provide enough energy for the output load, and hiccup protection is triggered, so that the output voltage of the switching power supply cannot be established, and certain limitation is realized.
Disclosure of Invention
The invention aims to provide a multimode combined short-circuit protection circuit, a working method and application thereof, solves the problem of high short-circuit power consumption of a high-power switching power supply, and has the advantage of strong capacitive load capacity.
The invention is realized by the following technical scheme:
a multimode combined short-circuit protection circuit comprises a sampling circuit, a constant-current protection circuit, a hiccup protection circuit, a reference voltage circuit and a voltage division circuit; the constant current protection circuit comprises an operational amplifier U1A, the hiccup protection circuit comprises an operational amplifier U1B, and the reverse input end of the operational amplifier U1A is connected with the sampling circuit;
the reference voltage reference circuit comprises a resistor R6, a resistor R7, a resistor R8 and a voltage regulator tube Z1; one end of the resistor R8 is connected with the power supply end, the other end of the resistor R6 is connected with the cathode of the voltage regulator tube Z1, and the other end of the resistor R6 is connected with the forward input end of the operational amplifier U1A, the reverse input end of the operational amplifier U1B and one end of the resistor R7; the anode of the voltage regulator tube Z1 and the other end of the resistor R7 are grounded;
the voltage division circuit comprises a resistor R10, a resistor R11, a resistor R12, a voltage regulator tube Z2, a capacitor C4 and a triode Q1; one end of a resistor R10 is connected with the output end of the U1A, the cathode of the diode D3 and one end of a capacitor C2, and the other end of the resistor R10 is connected with the cathode of a voltage regulator tube Z2; the anode of the voltage regulator tube Z2 is connected with one end of a resistor R11 and the base b of a triode Q1; the collector C of the triode Q1 is connected with one end of a resistor R12, one end of a capacitor C4 and the positive input end of an operational amplifier U1B; the other end of the resistor R12 is connected with the power supply end; the other end of the resistor R11 and the emitter e of the transistor Q1 are grounded.
Further, the constant current protection circuit further comprises a resistor R15, a diode D3, a capacitor C2 and a resistor R9; one end of the resistor R9 is connected with the reverse input end of the operational amplifier U1A, and the other end of the resistor R9 is connected with the other end of the capacitor C2; the anode of the diode D3 is connected with one end of the resistor R15 and the feedback signal end; the other end of the resistor R15 is connected with the power supply end.
Further, the hiccup protection circuit further comprises a MOS transistor M1, a resistor R13, a resistor R14, a capacitor C3 and a diode D4; a drain D of the MOS tube M1 is connected with an anode of the diode D3, one end of the resistor R15 and a feedback signal end, and a gate G of the MOS tube M1 is connected with one end of the resistor R14, one end of the capacitor C3 and one end of the resistor R13; the other end of the resistor R13 is connected with the cathode of the diode D4; the anode of the diode D4 is connected with the output port of the operational amplifier U1B; the source of the MOS transistor M1, the other end of the resistor R14 and the other end of the capacitor C3 are grounded.
Further, the sampling circuit comprises a current transformer L1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a diode D1, a diode D2 and a capacitor C1; one end of a current transformer L1 is grounded, the other end of the current transformer L1 is connected with one end of a resistor R1, the anode of a diode D1 and the anode of a diode D2, and the other end of a resistor R1 is grounded; the cathode of the diode D1 is connected with one end of the resistor R2, and the other end of the resistor R2 is grounded; the cathode of the diode D2 is connected with one end of the resistor R3, the other end of the resistor R3 is connected with one end of the capacitor C1, one end of the resistor R4 and one end of the resistor R5, the other end of the capacitor C1 and the other end of the resistor R4 are both grounded, and the other end of the resistor R5 is connected with the reverse input end of the operational amplifier U1A.
Further, the resistance R13 is 10 to 20 Ω, and the resistance R14 is 1 to 2M Ω.
Further, the resistance R3 is 90 Ω to 110 Ω.
Further, the resistance R4 is 9k Ω to 11k Ω.
The invention also discloses a working method of the multimode combined short-circuit protection circuit when the switching power supply normally works, which comprises the following steps:
the voltage of the inverting input end of the operational amplifier U1A is lower than the reference voltage of the non-inverting input end, the output end is at high level, the diode D3 is cut off in the reverse direction, and the feedback signal at the feedback signal end is not influenced;
the high level of the output end supplies power to a voltage regulator tube Z2 through a be junction of a current limiting resistor R10, a resistor R11 and a triode Q1, and the normal work of the voltage regulator tube Z2 is ensured; a collector of the triode Q1 is powered by a power supply end through a pull-up resistor R12, the triode Q1 is in a saturated conduction state, and a collector of the triode Q1 is at a low level; the level of the positive phase input end of the operational amplifier U1B is lower than the reference voltage of the negative phase input end, the output end of the operational amplifier U1B is at low level, the MOS transistor M1 cannot be started, and the feedback signal at the feedback signal port is not influenced.
The invention also discloses a working method of the multimode combined short-circuit protection circuit when the output of the switching power supply is short-circuited, which comprises the following steps:
the sampling voltage of the inverting input end of the operational amplifier U1A rises, and compared with the reference voltage of the non-inverting input end, the generated differential voltage regulates the output end of the operational amplifier U1A to fall to a low level through a proportional resistor R9 and an integrating capacitor C2; the diode D3 is conducted in the forward direction, the feedback signal at the feedback signal end is pulled down, the feedback signal is positively correlated with the pulse width control output duty ratio, and the pulse width control output duty ratio is limited; the output end of the operational amplifier U1A is at low level, and the voltage regulator tube Z2 is in a cut-off state; the triode Q1 does not work, the voltage of the power supply terminal passes through the resistor R12 to charge the capacitor C4, the charging time of the capacitor C4 is constant current protection time, and the switching power supply is in a constant current protection mode;
the voltage of a positive phase input end of the operational amplifier U1B is higher than the reference voltage of a negative phase input end, the output end of the operational amplifier U1B is inverted to a high level, the voltage is dropped in a positive direction through a diode D4, a current limiting resistor R13 charges a capacitor C3, after the voltage is increased to the threshold voltage of a grid electrode of an MOS tube M1, the MOS tube is started, a drain electrode and a source electrode are conducted, a feedback signal at a feedback signal end is pulled down to 0 from a low level, the pulse width control output is turned off, and the switching power supply has no energy output; at the moment, the sampling voltage of the inverting input end of the operational amplifier U1A rapidly drops, the voltage regulator tube Z2 is started to work, the output end of the operational amplifier U1B is inverted to be at a low level, the capacitor C3 starts to discharge through the resistor R14, the voltage drops to the position before the grid threshold voltage of the MOS tube M1, the MOS tube M1 is in a conducting state, and the switching power supply is in a hiccup protection mode;
if the short-circuit fault exists continuously, the sampling voltage of the inverting input end of the operational amplifier U1A rises again, and the working process is repeated.
The invention also discloses a high-power switching power supply which comprises the multi-mode combined short-circuit protection circuit.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention designs a short-circuit protection circuit for a high-power switching power supply, which comprises a sampling circuit, a constant-current protection circuit, a hiccup protection circuit, a reference voltage circuit and a voltage division circuit, wherein the sampling circuit is connected with the sampling circuit; the constant current protection circuit comprises an operational amplifier U1A, and the hiccup protection circuit comprises an operational amplifier U1B, so that the constant current protection circuit has the characteristics of strong capacitive load capacity of constant current protection and low power consumption of hiccup protection short circuit. The sampling line uses the current transformer to sample the input current, the loss is low, the current signal is converted into a relatively stable direct current level, the influence of the input voltage is small, the temperature drift is mainly related to the output load current, and the protection design is facilitated; the circuit uses a current transformer to collect input current and convert a current signal into a voltage signal; the double operational amplifiers are adopted for signal processing, one operational amplifier is used for proportional integral, constant current protection control is carried out, constant current time is adjusted, and the larger capacitive load capacity of the switching power supply is ensured; and the other operational amplifier is used as a comparator to perform hiccup protection control, adjust hiccup time and greatly reduce short-circuit power consumption.
Furthermore, the sampling circuit of the invention uses two diodes, the sampling signal is processed into a direct current level which is mainly related to the output load current, the constant current protection point is stable, and the sampling circuit is suitable for the switch power supply with wide range of input voltage.
Further, the resistance of the resistor R3 is small, the charging time of the capacitor C1 is generally shorter than 1 switching power supply period, the resistance of the resistor R4 is large, and the discharging time of the capacitor C1 is generally longer than 100 switching power supply periods, so that the stability of the sampling voltage is ensured.
The invention also discloses a working method of the multimode combined short-circuit protection circuit when the output of the switching power supply is short-circuited, wherein the working time sequence of the short-circuit protection is determined, and the constant-current protection is firstly carried out, and then the hiccup protection is carried out; and the hiccup protection mode can be started when the set time of the constant current protection is reached; the short-circuit fault continuously exists, and the protection circuit repeats a working mode of constant-current protection-hiccup protection; and the short-circuit fault of the switching power supply is eliminated, and the normal function is recovered. Through bleeder circuit design, guaranteed to carry out the constant current protection earlier, belch the protection again, also guaranteed simultaneously that the time that the constant current protection arrived the design just can get into the protection of belch, both solved the big problem of high-power switching power supply short-circuit consumption, had the advantage that capacitive load ability is strong again.
The multimode combined short-circuit protection circuit is applied to a high-power switching power supply, not only solves the problem of high constant-current protection power consumption, but also solves the problem of weak capacitive load protection capacity caused by hiccup, and simultaneously avoids the risk of internal device over-current stress.
Drawings
Fig. 1 is a schematic diagram of a conventional constant current protection circuit connection;
FIG. 2 is a schematic diagram of a conventional hiccup protection circuit connection;
FIG. 3 is a schematic diagram of the multi-mode combined short-circuit protection circuit connection of the present invention;
FIG. 4 is a graph of the critical node voltage waveforms for the multi-mode combined short protection circuit of the present invention;
FIG. 5 is a schematic diagram of a line connection of a constant current protection line applied to a switching power supply;
FIG. 6 is a schematic diagram of the hiccup protection circuit applied to the circuit connection of the switching power supply;
FIG. 7 is a schematic diagram of the multi-mode combined short-circuit protection circuit applied to the circuit connection of the switching power supply of the present invention;
FIG. 8 is a waveform diagram of the voltage measured at the key node of the short-circuit protection circuit according to the present invention;
FIG. 9 is a waveform diagram of the measured output current of the multi-mode combined short-circuit protection circuit according to the present invention;
FIG. 10 is a waveform diagram of the multi-mode combined short-circuit protection circuit with 2000 μ F full load and output voltage start-up according to the present invention.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
As shown in fig. 3, the invention discloses a multimode combined short-circuit protection circuit, which comprises a sampling circuit, a constant current protection circuit, a hiccup protection circuit, a reference voltage circuit and a voltage division circuit; the sampling circuit comprises a current transformer L1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a diode D1, a diode D2 and a capacitor C1; the reference voltage reference circuit comprises a resistor R6, a resistor R7, a resistor R8 and a voltage regulator tube Z1; the voltage division circuit comprises a resistor R10, a resistor R11, a resistor R12, a voltage regulator tube Z2, a capacitor C4 and a triode Q1; the constant-current protection circuit comprises an operational amplifier U1A, a resistor R15, a diode D3, a capacitor C2 and a resistor R9; the hiccup protection circuit comprises an operational amplifier U1B, a MOS transistor M1, a resistor R13, a resistor R14, a capacitor C3 and a diode D4.
One end of the current transformer L1 is grounded, and the other end is connected with one end of a resistor R1, the anode of the diode D1 and the anode of the diode D2. The other end of the resistor R1 is grounded. The cathode of the diode D1 is connected with one end of the resistor R2, and the other end of the resistor R2 is grounded. The cathode of the diode D2 is connected with one end of the resistor R2. The other end of the resistor R2 is connected with one end of the capacitor C1, one end of the resistor R4 and one end of the resistor R5. The other end of the capacitor C1 is grounded, and the other end of the resistor R4 is grounded. The other end of the resistor R5 is connected with one end of the resistor R9 and the inverting input end of the operational amplifier U1A.
The other end of the resistor R9 is connected with one end of a capacitor C2, the other end of the capacitor C2 is connected with the output end of the operational amplifier U1A, the cathode of the diode D3 and one end of the resistor R10, and the other end of the resistor R10 is connected with the cathode of the voltage regulator tube Z2. The port 01 is connected with one end of a resistor R8, one end of a resistor R12, one end of a resistor R15 and the positive power supply port 8 end of an operational amplifier U1A. The other end of the resistor R8 is connected with one end of the resistor R6 and the cathode of the voltage regulator tube Z1. The anode of the zener tube Z1 is grounded. The other end of the resistor R6 is connected with one end of the resistor R7, the positive phase input port 3 end of the operational amplifier U1A and the negative phase input port 6 end of the U1B, and the other end of the resistor R7 is grounded. The anode of the voltage regulator tube Z2 is connected with one end of a resistor R11 and the base b of a triode Q1. The other end of the resistor R11 is connected to ground. The emitter e of transistor Q1 is connected to ground. The collector C of the transistor Q1 is connected with the other end of the resistor R12, one end of the capacitor C4 and the non-inverting input port 5 of the U1B. The other terminal of the capacitor C4 is connected to ground. The negative power supply port of the operational amplifier U1B is grounded. An output port 7 of the operational amplifier U1B is connected with an anode of a diode D4, a cathode of a diode D4 is connected with one end of a resistor R13, and the other end of the resistor R13 is connected with one end of a capacitor C3, one end of a resistor R14 and a gate G of a MOS transistor M1. The other terminal of the capacitor C3 is connected to ground. The other end of the resistor R14 is connected to ground. The source S of the MOS transistor M1 is grounded. The drain D of the MOS transistor M1 is connected with the anode of the diode D13, the other end of the resistor R15 and the port 02. The port 01 is connected to the supply voltage, and the port 02 is connected to the feedback signal.
The current transformer L1 detects the input current IINSampling current is IINAfter being rectified by a diode D1, the 1/N voltage flows through a sampling resistor R2 to form a sampling voltage R2IINand/N. Resistor R1 provides a reset loop for the current transformer. The cathode of the diode D2 is equipotential with the cathode of the diode D1, and the sampling voltage R2 is IINthe/N charges a capacitor C1 through a resistor R3, and discharges a capacitor C1 through a resistor R4 to form stable direct-current voltage which is transmitted to the 2 end of the inverting input port of the operational amplifier U1A through a resistor R5. The port 01 is a power supply end, supplies power to a voltage regulator tube Z1 through a current limiting resistor R8, and provides reference voltage through voltage division of a resistor R6 and a resistor R7.
The working waveform of the voltage of the key node in the short-circuit protection circuit is shown in figure 4. The output load of the switching power supply t1 is short-circuited at the moment, and the protection circuit enters into work. Firstly, entering a constant-current short-circuit protection mode for t 2-t 3; after the constant current protection time is over, entering a hiccup protection mode for t 3-t 4; the short-circuit fault continuously exists, and the protection circuit repeats a working mode of constant-current protection-hiccup protection; at time t5, the short-circuit fault of the switching power supply is eliminated, and the normal function is recovered.
The operation of the short-circuit protection circuit components is described in detail below.
When the switching power supply normally works, the voltage at the 2 end of the inverting input port of the operational amplifier U1A is lower than the reference voltage at the 3 end of the non-inverting input port, the 1 end of the output port of the operational amplifier is at high level, and the diode D3 is cut off in the reverse direction, so that the feedback signal at the 02 position cannot be influenced. The high level at the output port 1 end of the operational amplifier supplies power to a voltage regulator tube Z2 through a junction of a current limiting resistor R10, a resistor R11 and a triode Q1 to ensure the normal work of the voltage regulator tube Z2; a voltage regulator tube Z2, a resistor R10 and a resistor R11 divide voltage to ensure that the base level of the triode Q1 is higher than 0.7V; the collector c of the triode Q1 is powered by the port 01 through the pull-up resistor R12, the resistance value of the resistor R12 is large, the triode Q1 is guaranteed to be in a saturated conduction state, and the collector c of the triode Q1 is at a low level. The operational amplifier U1B is used as a comparator, the voltage at the terminal of the positive phase input port 5 of the operational amplifier U1B is lower than the reference voltage at the terminal of the negative phase input port 6, the voltage at the terminal of the output port 7 of the operational amplifier U1B is at low level, the MOS transistor M1 cannot be turned on, and the feedback signal at the port 02 cannot be influenced.
The resistor R12 is 100k omega-200 k omega, the charging time of the resistor R12 to the capacitor C4 is constant current protection time which is about 5 times of the starting delay of the switching power supply generally, and the larger capacitive load capacity of the switching power supply is ensured; the resistor R14 is 1M omega-2M omega, the discharge time of the resistor R14 to the capacitor C3 is hiccup protection time which is about 10 times of the constant current protection of the switching power supply, and the small short-circuit power consumption of the switching power supply is ensured; the resistor R13 is a current-limiting resistor, generally 10-20 omega, and avoids damage of surge current to components.
When the output of the switching power supply is short-circuited, the sampling voltage at the 2 end of the inverting input port of the operational amplifier U1A is quickly increased and compared with the reference voltage at the 3 end of the non-inverting input port, and the generated differential voltage is subjected to proportional amplification by a resistor R9 of the operational amplifier U1A and integral action by a capacitor C2 to adjust the level of the 1 end of the output port of the operational amplifier U1A to be reduced to be low level; the diode D3 is conducted in the forward direction, the feedback signal at the port 2 is pulled down, and the feedback signal is positively correlated with the pulse width control output duty ratio, so that the pulse width control output duty ratio is limited; the output port 1 end of the operational amplifier U1A is at low level, and cannot reach the voltage stabilizing value of a voltage stabilizing tube Z2, and the voltage stabilizing tube Z2 is in a cut-off state; the triode Q1 does not work, the voltage of the port 01 passes through the resistor R12 to charge the capacitor C4, the charging time of the capacitor C4 is the constant current protection time, and the switching power supply is in the constant current protection mode. The voltage of the end 5 of the normal-phase input port of the operational amplifier U1B is higher than the reference voltage of the end 6 of the reverse-phase input port, the end 7 of the output port of the operational amplifier U1B is turned to be at a high level, the forward voltage drop is realized through a diode D4, a current-limiting small resistor R13 charges a capacitor C3, the threshold voltage of the grid electrode of an MOS tube M1 is reached, the MOS tube is started, a drain-source electrode is conducted, a feedback signal at the port 02 is pulled down to 0 from a low level, the pulse width control output is turned off, the energy output of a switching power supply is avoided, and the power consumption is very small; at the moment, the sampling voltage drops rapidly, the voltage regulator tube Z2 is started to work, the output end of the operational amplifier U1B is inverted to be at a low level, the capacitor C3 starts to discharge slowly through the resistor R14, and the resistor R14 is set to be a large resistor, so that the MOS tube M1 is in a conducting state for a long time, the short-circuit power consumption is greatly reduced, and the switching power supply is in a hiccup protection mode. And if the short-circuit fault exists continuously, the sampling voltage at the end 2 of the inverting input port of the operational amplifier U1A rises rapidly again, and the working process is repeated.
As shown in fig. 5, the circuit for applying the constant current protection mode to the switching power supply is generally used for adjusting a post-stage feedback signal of the switching power supply, controlling an output duty ratio of the pulse width controller through isolation feedback, and is often applied to switching power supplies with output power of 50W or less.
The circuit applying the hiccup protection mode to the switching power supply is shown in fig. 6, and is generally used for adjusting a preceding-stage feedback signal of the switching power supply, directly controlling the output duty ratio of the pulse width controller, and is widely applied.
The circuit applied to the switching power supply in the multi-mode combined short-circuit protection mode of the invention is shown in fig. 7. The current transformer is adopted for signal sampling, and the diode D1 and the diode D2 have the effects of inhibiting temperature drift, preventing current from flowing backwards and the like; the resistor R3 is designed to be 90-110 omega, the resistance of the resistor R3 is small, the charging time of the capacitor C1 is generally shorter than 1 switching power supply period, the resistor R4 is designed to be 9-11 k omega, the resistance of the resistor R4 is large, and the discharging time of the capacitor C1 is generally longer than 100 switching power supply periods, so that the stability of sampling voltage is ensured; the output of the operational amplifier U1A is delayed from high level to low level, the use of the voltage regulator tube Z2 ensures that the base b of the triode Q1 obtains a determined level (high level or low level), and the triode Q1 works in a determined mode (cut-off state or saturated conduction state); the VCC2 charges a capacitor C4 through a resistor R12, and the voltage on the capacitor C4, namely the time when the voltage at the positive phase input port 5 of the operational amplifier U1B reaches the reference voltage at the negative phase input port 6 is the time of constant current protection; the voltage of VCC2 is higher than the reference voltage, the designed constant current time is reached, the level of the output port 7 of the operational amplifier U1B is normally turned over, the capacitor C3 obtains a sufficiently high voltage which is higher than the threshold voltage of the MOS transistor M1, and the MOS transistor is turned on and conducted; the diode D4 plays a role in forward charging and reverse current cutoff, the charge of the capacitor C3 is slowly discharged through the resistor R14, and the hiccup time is the time when the voltage on the capacitor C3 is reduced to the threshold voltage of the MOS transistor.
The short-circuit protection circuit has stable sampling signals and is mainly related to output load current; determining the working time sequence of short-circuit protection, firstly performing constant-current protection, and then performing hiccup protection; and the hiccup protection mode can be started when the set constant current protection time is reached. The high-power switching power supply has the advantages that the problem of high constant-current protection power consumption is solved, the problem of weak capacitive load capacity of hiccup protection is solved, and the risk of internal device over-current stress is avoided.
The circuit is applied to a DC/DC converter, the working frequency is 500kHz, the input voltage is 28V, the output voltage is 5V, the output current is 20A, and the output power is 100W, and the circuit is shown in figure 7. The current transformer samples input current, a port 01 is connected with a rear-stage power supply VCC2, and a port 02 is connected with a feedback signal. When the output load of the DC/DC converter is short-circuited, the actual measurement waveform of the voltage of the key node of the short-circuit protection line is shown in fig. 8, the waveform of the current of the output load is shown in fig. 9, and the starting waveform of the output voltage of the capacitive load with 2000 muF is shown in fig. 10.
As shown in fig. 8, the channel 1 is a voltage waveform at the inverting input port 2 of the operational amplifier U1A, the channel 2 is a voltage waveform at the non-inverting input port 5 of the operational amplifier U1B, the channel 3 is a gate voltage waveform of the MOS transistor M1, and the channel 4 is a drain voltage waveform of the MOS transistor M1.
As shown in fig. 9, the channel 1 is a voltage waveform at the inverting input port 2 of the operational amplifier U1A, and the channel 4 is an output current waveform when the output load is short-circuited.
As shown in fig. 10, the channel 1 is a DC/DC converter, and outputs a voltage start waveform when the input voltage is 28V, the output current is 20A, and the capacitive load is 2000 μ F.
As shown in fig. 8 and 9, the actual test waveform substantially coincides with the theoretical analysis waveform in fig. 4. The constant current protection time is about 15ms, the hiccup protection time is about 150ms, and the average value of short-circuit power consumption is about 5W; as shown in fig. 10, with a capacitive load start waveform of 2000 muf, there is no start overshoot and the start delay is about 2.5 ms. The novel short-circuit protection circuit is applied to military DC/DC series converter design with bus input of 20V-50V and output power of 100W.
The invention is tested and verified. The voltage-variable DC/DC converter is applied to a DC/DC converter, the working frequency is 500kHz, the input voltage is 28V, the output voltage is 5V, and the output current is 20A. When a constant-current protection circuit is adopted, as shown in fig. 5, the short-circuit power consumption is about 30W, and the capacitive load capacity is 2000 muf; with the hiccup protection circuit, the short circuit power dissipation is about 5W and the capacitive load capability is 300 muf, as shown in fig. 6. By adopting the short-circuit protection scheme of the invention, as shown in fig. 7, the short-circuit power consumption is about 5W, the capacitive load capacity is 2000 muF, the capacitive load capacity is stronger, and the short-circuit power consumption is obviously reduced.

Claims (8)

1. A multimode combined short-circuit protection circuit is characterized by comprising a sampling circuit, a constant-current protection circuit, a hiccup protection circuit, a reference voltage circuit and a voltage division circuit; the constant current protection circuit comprises an operational amplifier U1A, the hiccup protection circuit comprises an operational amplifier U1B, and the reverse input end of the operational amplifier U1A is connected with the sampling circuit;
the reference voltage reference circuit comprises a resistor R6, a resistor R7, a resistor R8 and a voltage regulator tube Z1; one end of the resistor R8 is connected with the power supply end, the other end of the resistor R6 is connected with the cathode of the voltage regulator tube Z1, and the other end of the resistor R6 is connected with the forward input end of the operational amplifier U1A, the reverse input end of the operational amplifier U1B and one end of the resistor R7; the anode of the voltage regulator tube Z1 and the other end of the resistor R7 are grounded;
the voltage division circuit comprises a resistor R10, a resistor R11, a resistor R12, a voltage regulator tube Z2, a capacitor C4 and a triode Q1; one end of a resistor R10 is connected with the output end of the U1A, the cathode of the diode D3 and one end of a capacitor C2, and the other end of the resistor R10 is connected with the cathode of a voltage regulator tube Z2; the anode of the voltage regulator tube Z2 is connected with one end of a resistor R11 and the base b of a triode Q1; the collector C of the triode Q1 is connected with one end of a resistor R12, one end of a capacitor C4 and the positive input end of an operational amplifier U1B; the other end of the resistor R12 is connected with the power supply end; the other end of the resistor R11 is grounded with an emitter e of the triode Q1;
the constant current protection circuit further comprises a resistor R15, a diode D3, a capacitor C2 and a resistor R9; one end of the resistor R9 is connected with the reverse input end of the operational amplifier U1A, and the other end of the resistor R9 is connected with the other end of the capacitor C2; the anode of the diode D3 is connected with one end of the resistor R15 and the feedback signal end; the other end of the resistor R15 is connected with a power supply end;
the hiccup protection circuit further comprises a MOS transistor M1, a resistor R13, a resistor R14, a capacitor C3 and a diode D4; a drain D of the MOS tube M1 is connected with an anode of the diode D3, one end of the resistor R15 and a feedback signal end, and a gate G of the MOS tube M1 is connected with one end of the resistor R14, one end of the capacitor C3 and one end of the resistor R13; the other end of the resistor R13 is connected with the cathode of the diode D4; the anode of the diode D4 is connected with the output port of the operational amplifier U1B; the source electrode of the MOS transistor M1, the other end of the resistor R14 and the other end of the capacitor C3 are grounded;
and when the output of the switching power supply is short-circuited and reaches the set constant current protection time, starting the hiccup protection mode.
2. A multimode combined short-circuit protection circuit as claimed in claim 1, characterized in that the sampling circuit comprises a current transformer L1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a diode D1, a diode D2 and a capacitor C1; one end of a current transformer L1 is grounded, the other end of the current transformer L1 is connected with one end of a resistor R1, the anode of a diode D1 and the anode of a diode D2, and the other end of a resistor R1 is grounded; the cathode of the diode D1 is connected with one end of the resistor R2, and the other end of the resistor R2 is grounded; the cathode of the diode D2 is connected with one end of the resistor R3, the other end of the resistor R3 is connected with one end of the capacitor C1, one end of the resistor R4 and one end of the resistor R5, the other end of the capacitor C1 and the other end of the resistor R4 are both grounded, and the other end of the resistor R5 is connected with the reverse input end of the operational amplifier U1A.
3. A multimode combined short-circuit protection circuit as claimed in claim 1, characterized in that the resistor R13 is 10 Ω -20 Ω and the resistor R14 is 1M Ω -2M Ω.
4. A multimode combined short-circuit protection circuit as claimed in claim 2, characterized in that the resistance R3 is between 90 Ω and 110 Ω.
5. A multimode combined short-circuit protection circuit as claimed in claim 2, characterized in that the resistance R4 is between 9k Ω and 11k Ω.
6. The working method of the multimode combined short-circuit protection circuit in the normal operation of the switching power supply as claimed in any one of claims 1 to 5, characterized by comprising the following steps:
the voltage of the inverting input end of the operational amplifier U1A is lower than the reference voltage of the non-inverting input end, the output end is at high level, the diode D3 is cut off in the reverse direction, and the feedback signal at the feedback signal end is not influenced;
the high level of the output end supplies power to a voltage regulator tube Z2 through a be junction of a current limiting resistor R10, a resistor R11 and a triode Q1, and the normal work of the voltage regulator tube Z2 is ensured; a collector of the triode Q1 is powered by a power supply end through a pull-up resistor R12, the triode Q1 is in a saturated conduction state, and a collector of the triode Q1 is at a low level; the level of the positive phase input end of the operational amplifier U1B is lower than the reference voltage of the negative phase input end, the output end of the operational amplifier U1B is at low level, the MOS transistor M1 cannot be started, and the feedback signal at the feedback signal port is not influenced.
7. The working method of the multimode combined short-circuit protection circuit in the short-circuit of the switching power supply output according to any one of claims 1 to 5, characterized by comprising the following steps:
the sampling voltage of the inverting input end of the operational amplifier U1A rises, and compared with the reference voltage of the non-inverting input end, the generated differential voltage regulates the output end of the operational amplifier U1A to fall to a low level through a proportional resistor R9 and an integrating capacitor C2; the diode D3 is conducted in the forward direction, the feedback signal at the feedback signal end is pulled down, the feedback signal is positively correlated with the pulse width control output duty ratio, and the pulse width control output duty ratio is limited; the output end of the operational amplifier U1A is at low level, and the voltage regulator tube Z2 is in a cut-off state; the triode Q1 does not work, the voltage of the power supply terminal passes through the resistor R12 to charge the capacitor C4, the charging time of the capacitor C4 is constant current protection time, and the switching power supply is in a constant current protection mode;
the voltage of a positive phase input end of the operational amplifier U1B is higher than the reference voltage of a negative phase input end, the output end of the operational amplifier U1B is inverted to a high level, the voltage is dropped in a positive direction through a diode D4, a current limiting resistor R13 charges a capacitor C3, after the voltage is increased to the threshold voltage of a grid electrode of an MOS tube M1, the MOS tube is started, a drain electrode and a source electrode are conducted, a feedback signal at a feedback signal end is pulled down to 0 from a low level, the pulse width control output is turned off, and the switching power supply has no energy output; at the moment, the sampling voltage of the inverting input end of the operational amplifier U1A rapidly drops, the voltage regulator tube Z2 is started to work, the output end of the operational amplifier U1B is inverted to be at a low level, the capacitor C3 starts to discharge through the resistor R14, the voltage drops to the position before the grid threshold voltage of the MOS tube M1, the MOS tube M1 is in a conducting state, and the switching power supply is in a hiccup protection mode;
if the short-circuit fault exists continuously, the sampling voltage of the inverting input end of the operational amplifier U1A rises again, and the working process is repeated.
8. A high power switching power supply comprising a multimode combined short circuit protection circuit according to claims 1 to 5.
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