CN106787621B

CN106787621B - Compensation circuit and the control circuit for applying it

Info

Publication number: CN106787621B
Application number: CN201611040473.XA
Authority: CN
Inventors: 陈伟; 王龙奇
Original assignee: Hangzhou Silergy Semiconductor Technology Ltd
Current assignee: Hangzhou Silergy Semiconductor Technology Ltd
Priority date: 2016-11-11
Filing date: 2016-11-11
Publication date: 2019-07-30
Anticipated expiration: 2036-11-11
Also published as: CN106787621A

Abstract

Disclose a kind of compensation circuit and the control circuit using it, by feeding back input voltage to the compensation network to improve the compensation circuit for the response speed of input voltage, thus, it can be superimposed the variation of input voltage on the larger thermal compensation signal for postponing and input current being made preferably to follow input voltage, stablize to keep exporting for input voltage variation quick response while improving the power factor and total harmonic distortion factor of power inverter.

Description

Compensation circuit and control circuit applying same

Technical Field

The invention relates to the power electronic technology, in particular to a compensation circuit and a control circuit applying the same.

Background

In the prior art, in a control loop of a power converter, a compensation circuit is usually used to adjust the speed of the control loop in response to a feedback parameter, and a fast loop is adopted to enable the system to respond to the jitter of an input voltage quickly, so as to eliminate the output current/voltage change caused by the jitter of the input voltage. Fig. 1 is a schematic diagram of a conventional compensation circuit, which generally includes a transconductance amplifier GM and a compensation network CP formed by a compensation capacitor C1 and a compensation resistor R1. Fig. 2 is a circuit diagram of a primary side controlled flyback converter to which the compensation circuit shown in fig. 1 is applied, wherein the control circuit includes a peripheral circuit formed by a resistor, a capacitor, a diode, and the like, and an integrated circuit chip IC. The COMP pin of the integrated circuit corresponds to the output end of the transconductance amplifier GM.

In order to obtain a faster response speed, the compensation capacitor C1 and the compensation resistor R1 are usually set to small values. Therefore, the response speed of the control loop is high, when the input voltage suddenly increases, the loop can be quickly adjusted, and the phenomenon that the output voltage or current is unstable due to the fact that redundant energy is transferred to the output end due to the sudden increase of the input voltage is avoided. When the input suddenly becomes small, the loop can control the power level circuit to increase the energy output and maintain the output voltage or current stable.

However, the change of the compensation signal affects the on-time of the power switch of the switch-type converter, and if the response speed of the control loop is high, the change of the compensation signal in a power frequency period is large, so that the on-time of the power switch is also greatly changed correspondingly, which can cause that the input current cannot follow the input voltage, the waveform distortion of the input current is serious, and the fundamental component is small. Power converters have poor Power Factor (PF) and Total Harmonic Distortion (THD). This is undesirable for the designer.

Disclosure of Invention

In view of the above, the present invention provides a compensation circuit and a control circuit using the same, which can improve the power factor and the total harmonic distortion rate of a power converter while maintaining a stable output with a fast response to the input voltage variation.

In a first aspect, a compensation circuit is provided for a control loop of a power converter, the compensation circuit comprising:

a compensation network for generating a compensation signal;

and the input feedback circuit is used for feeding back the input voltage to the compensation network so as to improve the response speed of the compensation circuit to the input voltage.

Preferably, the compensation network is arranged such that the power converter has a desired power factor and/or harmonic distortion rate.

Preferably, the input feedback circuit is for negatively feeding back the input voltage to the compensation network such that the compensation signal fluctuates in an opposite manner with the input voltage.

Preferably, the compensation network comprises a compensation capacitor and a compensation resistor connected in series between the compensation signal output terminal and the reference terminal.

Preferably, the input feedback circuit includes:

the sampling capacitor is arranged between the sampling end and the reference end;

the divider resistor is connected between the sampling end and the middle end;

the voltage of the sampling end is reversely and synchronously changed along with the input voltage, and the middle end is a common end of the compensation capacitor and the compensation resistor.

Preferably, the input feedback circuit further comprises:

the switching element is connected between an input voltage synchronous end and the sampling end and is synchronously switched on and switched off along with a power switch of the power converter;

the voltage of the input voltage synchronization terminal is synchronized with the input voltage during the conduction period of the power switch.

Preferably, the power converter is a source side control flyback converter, and the voltage synchronization end is a dotted end of the auxiliary winding.

Preferably, the switching element is a diode, a cathode of the switching element is connected with the input voltage synchronization end, and an anode of the switching element is connected with the sampling end; or,

the switching element is a controlled switching element which is synchronously switched on and off along with a power switch of the power converter according to a switch control signal.

In a second aspect, a control circuit is provided for controlling a power stage circuit of a power converter, the control circuit comprising a compensation circuit as described above.

The response speed of the compensation circuit to the input voltage is improved by feeding the input voltage back to the compensation network, so that the change of the input voltage can be superposed on a compensation signal which has larger delay and can make the input current better follow the input voltage, thereby keeping the output stable for the quick response of the input voltage change while improving the power factor and the total harmonic distortion rate of the power converter.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a prior art compensation circuit;

fig. 2 is a schematic diagram of a prior art primary side controlled flyback converter;

FIG. 3 is a schematic diagram of a compensation circuit of an embodiment of the present invention;

fig. 4 is a schematic diagram of a primary side controlled flyback converter of an embodiment of the present invention;

FIG. 5a is a waveform diagram illustrating operation of a power converter without an input feedback circuit;

fig. 5b is a waveform diagram illustrating the operation of a power converter according to an embodiment of the present invention.

Detailed Description

The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.

Meanwhile, it should be understood that, in the following description, a "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".

In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

FIG. 3 is a schematic diagram of a compensation circuit according to an embodiment of the invention. As shown in fig. 3, the compensation circuit includes an amplification circuit AP, a compensation network CP, and an input feedback circuit FB. The amplifying circuit AP is used to amplify the error signal Verr. The amplifying circuit AP may be a transconductance amplifier or an operational amplifier. The compensation network CP is arranged in a manner adapted to the amplification circuit AP. When the amplifying circuit AP is a transconductance amplifier, the compensation network CP may include a compensation capacitor C1 and a compensation resistor R1 connected between the output terminal of the transconductance amplifier and a reference terminal (ground terminal). The compensation capacitor C1 is connected with the output end of the transconductance amplifier, and the compensation resistor R1 is connected with the reference end. When the amplifying circuit is an operational amplifier, the compensation network CP may be a resistor-capacitor network connected across the input and output terminals of the operational amplifier and the input terminal of the error signal. The compensation network CP may be any type of compensation network known in the art for generating the compensation signal Vcomp from the amplified error signal. The compensation signal Vcomp is used to represent the degree to which the average value of the circuit parameter (output voltage or output current or other parameter) deviates from the desired value over a period of time, so that the control loop generates a control signal to adjust the operation of the power stage circuit to keep the output satisfactory. The input feedback circuit FB is used for feeding back the input voltage Vin or a voltage proportional to the input voltage Vin to the compensation network CP to improve the response speed of the compensation circuit to the input voltage. That is, the input feedback circuit FB inputs p Vin and outputs q Vin to the compensation network CP. The input feedback circuit FB, unlike the feedback circuit for obtaining the current circuit state, directly applies the feedback parameter to the compensation network CP, thereby superimposing a component representing the change of the input voltage on the compensation signal Vcomp. Thereby, the control loop may have a faster response speed to a change in the input voltage. Preferably, when it is desired to keep the output stable, the input voltage is negatively fed back to the compensation network so that the compensation signal fluctuates in an opposite manner with the input voltage, whereby a fast adjustment to the input fluctuations is nevertheless achieved.

Thus, the response speed of the compensation circuit to the input voltage is improved by feeding back the input voltage to the compensation network, so that the change of the input voltage can be superposed on the compensation signal which has larger delay and can make the input current better follow the input voltage, thereby keeping the output stable for the quick response of the input voltage change while improving the power factor and the total harmonic distortion rate of the power converter.

It should be understood that the compensation circuit of embodiments of the present invention can be applied to control loops of various different kinds of power converters. The compensation circuit of the embodiment of the present invention is further described below by taking the primary side flyback converter as an example. Fig. 4 is a schematic diagram of a primary side controlled flyback converter according to an embodiment of the invention. As shown in fig. 4, the primary side controlled flyback converter includes a transformer, a power switch Q, a secondary side rectifying and filtering circuit 41, and a control circuit. The transformer comprises a primary winding L1 and a secondary winding L2. The control circuit includes an integrated circuit IC, a compensation network CP, an auxiliary winding L3, an input voltage feedback circuit FB, and other circuits. The power switch Q is connected between the primary winding L1 and the ground terminal, and controls the power output to the secondary side by controlling the time for which the current flows through the primary winding L1. The integrated circuit IC has integrated therein the necessary components of the control loop, such as an error amplification circuit, a zero-crossing detection circuit, and the like. The integrated circuit IC further integrates an amplifying circuit of the compensation circuit, and an external pin of the amplifying circuit is COMP (in this embodiment, a transconductance amplifier is used as an example for the amplifying circuit). On an Integrated Circuit (IC), a pin ZCS is a zero-cross detection pin, ISEN is a primary current detection pin, GND is a reference terminal pin, VIN is a power supply pin, and DRV is a control signal output pin. The compensation network CP is connected to pin COMP to generate a compensation signal at pin COMP. The integrated circuit IC may generate a control signal according to the compensation signal at the pin COMP via the internal circuit and output the control signal to the control terminal of the power switch Q. The auxiliary winding L3 is used to couple with the primary winding and the secondary winding, so as to acquire and obtain the voltage across the secondary winding, and the voltage can be used for zero-crossing detection and can also be used for supplying power to the integrated circuit IC after the circuit is started. In the embodiment of the present invention, since the voltage of the auxiliary winding L3 can represent the input voltage, it can be used as the input voltage synchronization terminal. In the present embodiment, the compensation network CP includes a compensation capacitor C1 and a compensation resistor R1. At this point, by setting the compensation capacitor C1 to have a larger capacitance value while keeping the compensation resistor R1 to have a smaller resistance value, the response speed of the control loop can be slowed down, which can make the input current follow the input voltage better, the input current waveform is closer to sinusoidal, i.e., the fundamental component is larger. Meanwhile, the compensation signal can change less in a power frequency period, so that the conduction time of the power switch Q is basically constant in the power frequency period, and a higher power factor and a better total harmonic distortion rate are obtained. However, if the input feedback circuit is not provided, the output is liable to suddenly change with the input due to slow loop response, resulting in unstable output.

In fig. 4, the input feedback circuit FB includes a switching element D1, a voltage-dividing resistor R2, and a sampling capacitor C2. The switching element D1 is a diode, which is connected between the input voltage synchronization terminal i and the sampling terminal s, and is turned on and off synchronously with the power switch of the power converter. The voltage dividing resistor R2 is connected between the sampling terminal s and the middle terminal m. The middle terminal m is a common terminal of the compensation capacitor C1 and the compensation resistor R1 in the compensation network CP. A sampling capacitor C2 is disposed between the sampling terminal s and the reference terminal. Wherein, the input voltage synchronizing terminal i can be applied with a synchronizing voltage which is inversely and synchronously changed with the input voltage in a predetermined time period in the switching period, and the synchronizing voltage can be obtained in various ways. In fig. 4, the ungrounded end of the auxiliary winding L3 is used as the input voltage synchronizing terminal. When the power switch Q is on, the voltage applied to the primary winding L1 is approximately equal to the input voltage. At this time, the voltage across the secondary winding L2 is proportional to the voltage across the primary winding L1, and its voltage across the same name is lower than that of the ground terminal, so that the voltage across the same name is negative. The voltage at the dotted terminal of the auxiliary winding L3 is proportional to the voltage of the secondary winding L2, the voltage at the dotted terminal is also negative, and its magnitude is proportional to the input voltage Vin. That is, Vi is-kVin, and k is positive. Thus, the voltage at the dotted end of the auxiliary winding L3 varies inversely synchronously with the input voltage. Since the cathode of the diode D1 is connected to the dotted terminal of the auxiliary winding L3, the anode is connected to the sampling terminal s. Therefore, during the time that the power switch Q is conducting, the diode D1 is also conducting. During the turn-off period of the power switch Q, the secondary winding L2 outputs current to the output terminal by using the original stored energy, and the voltage at the end with the same name is positive. The same name terminal voltage of the auxiliary winding L3, which is identical to the secondary winding L2, is also positive. Therefore, during the off period of the power switch Q, the diode D1 is also turned off. Thus, the diode D1 may be turned on or off substantially synchronously with the power switch Q. This causes the sampling terminal to always apply a voltage that varies inversely and synchronously with the input voltage. The sampling capacitor C2 is used for holding the voltage Vs, and meanwhile, the voltage dividing resistor R2 is used for forming a voltage dividing network with the compensation resistor R1 to divide the voltage Vs, and a negative voltage with the amplitude being proportional to the input voltage is applied to the compensation capacitor C1, so that the compensation signal Vcomp changes with the input voltage in a substantially synchronous manner.

Fig. 5a is a waveform diagram illustrating the operation of a power converter without an input feedback circuit. Fig. 5b is a waveform diagram illustrating the operation of a power converter according to an embodiment of the present invention. In fig. 5a, the compensation signal Vcomp remains substantially constant over two power frequency periods, while the intermediate voltage Vm also remains constant, so that, when the input voltage Vin suddenly rises, the circuit cannot respond to this, and the output current rises correspondingly, resulting in an unstable output current Iout. In fig. 5b, after the input feedback circuit is provided, the middle terminal voltage Vm fluctuates in opposite phase with the fluctuation of the input voltage, and since the capacitance value of the compensation capacitor C1 is large, the voltage at both ends thereof remains substantially stable, the compensation signal Vcomp is equal to Vm plus Vc1, which is equivalent to superimposing a constant voltage on Vm, and therefore the compensation signal Vcomp also fluctuates in opposite directions with the fluctuation of the input voltage. When the input voltage suddenly rises, the compensation signal Vcomp is correspondingly reduced, and the control loop adjusts the on-time of the power switch Q accordingly, so that the output current Iout is kept stable. Meanwhile, the circuit can still keep the power factor and the total harmonic distortion rate at expected values due to the large setting of the compensation capacitor C1.

Alternatively, the switching elements in the input feedback circuit FB may be replaced by controlled switching elements, such as metal oxide field effect transistors (MOSFETs), controlled by control signals that control the power switches to turn on and off in synchronization therewith.

Furthermore, the manner of performing negative feedback of the input voltage as shown in fig. 4 is also only an example, and those skilled in the art may select other manners to obtain a parameter that changes inversely synchronously with the input voltage to exert influence on the compensation signal.

If a variable is available which varies inversely synchronously with the input voltage over the entire switching period, the switching element can be omitted.

Meanwhile, the compensation circuit of the embodiment of the invention is not limited to be used in power converters having other topologies, for example, it can be applied in a BUCK (BUCK) converter having an auxiliary winding.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A compensation circuit for a control loop of a power converter, the compensation circuit comprising:

a compensation network for generating a compensation signal;

an input feedback circuit for feeding back an input voltage to the compensation network such that the compensation signal fluctuates with the input voltage in an opposite manner to increase a response speed of the compensation circuit to the input voltage.

2. The compensation circuit of claim 1, wherein the compensation network is configured such that the power converter has a desired power factor and/or harmonic distortion rate.

3. The compensation circuit of claim 1 or 2, wherein the compensation network comprises a compensation capacitor and a compensation resistor connected in series between the compensation signal output terminal and the reference terminal.

4. The compensation circuit of claim 3, wherein the input feedback circuit comprises:

the divider resistor is connected between the sampling end and the middle end;

5. The compensation circuit of claim 4, wherein the input feedback circuit further comprises:

6. The compensation circuit of claim 5, wherein the power converter is a source-side controlled flyback converter, and the voltage synchronization terminal is a dotted terminal of the auxiliary winding.

7. The compensation circuit of claim 5 or 6, wherein the switching element is a diode, a cathode is connected to the input voltage synchronization terminal, and an anode is connected to the sampling terminal; or,

8. A control circuit for controlling a power stage circuit of a power converter, the control circuit comprising a compensation circuit as claimed in any one of claims 1 to 7.