Switching circuit control method, control circuit and switching circuit

Abstract

The present invention discloses a control method, a control circuit and a switch circuit of a switch circuit. The switch circuit includes an inductor or a transformer. The output feedback voltage of the switch circuit and a first reference voltage are amplified by operation to obtain a first voltage. The first voltage and the output current sampling voltage are passed through a compensation circuit to obtain a compensation voltage. The compensation voltage controls the on-time of the main switch tube of the switch circuit. When the current of the inductor or the transformer drops to a first threshold value, after a first time, the main switch tube is turned on, and the first voltage controls the first time. The present invention makes the system stable and has a fast response speed.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a control method for a switch circuit, a control circuit and a switch circuit. Background Art

[0002] In switching power supplies, especially those with AC input, the system has secondary power frequency ripples because the input is rectified. Therefore, in the compensation circuit of the switching power supply with AC input, the compensation speed is lower than half of the power frequency cycle. Although the system can be stable, the response is relatively slow. Therefore, how to achieve system stability in the switching power supply with AC input and speed up the response speed to the output voltage is a control problem in the switching power supply with AC input. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a control method of a switch circuit, a control circuit and a switch circuit, so as to solve the problem of slow system response in the prior art.

[0004] The present invention provides a control method for a switching circuit, wherein the switching circuit includes an inductor or a transformer, and an output feedback voltage of the switching circuit and a first reference voltage are operationally amplified to obtain a first voltage. The first voltage and an output current sampling voltage are passed through a compensation circuit to obtain a compensation voltage. The compensation voltage controls the on-time of a main switch tube of the switching circuit. When the current of the inductor or the transformer drops to a first threshold value, the main switch tube is turned on after a first time, and the first voltage controls the first time.

[0005] Optionally, the switching circuit is an AC input, which is powered by rectification, and the load is an LED lamp.

[0006] Optionally, the switch circuit adopts constant on-time control.

[0007] Another embodiment of the present invention is to provide a control circuit of a switching circuit, wherein the switching circuit includes an inductor or a transformer, and the control circuit includes a compensation circuit. The control circuit performs operational amplification on an output feedback voltage of the switching circuit and a first reference voltage to obtain a first voltage. The first voltage and an output current sampling voltage are passed through the compensation circuit to obtain a compensation voltage. The compensation voltage controls the conduction time of a main switch tube of the switching circuit. When the current of the inductor or the transformer drops to a first threshold value, the main switch tube is turned on after a first time, and the first voltage controls the first time.

[0008] Optionally, the switching circuit is an AC input, which is powered by rectification, and the load is an LED lamp.

[0009] Optionally, the control circuit also includes a first operational amplifier and a switch signal generating circuit, wherein the first operational amplifier performs operational amplification on the output feedback voltage and the first reference voltage to output the first voltage; the compensation voltage generates a switch signal through the switch signal generating circuit, and the switch signal controls the on and off of the main switch tube. The switch signal generating circuit also receives the first voltage, and when the current of the inductor or transformer drops to zero, after a first time, the switch signal generating circuit generates a main switch tube on signal.

[0010] Optionally, the control circuit also includes an output voltage sampling and holding circuit and a current sampling circuit. The switching circuit is a primary feedback circuit of the AC-to-DC circuit. The output voltage sampling and holding circuit obtains an output feedback voltage representing the output voltage by sampling the voltage of the auxiliary winding. The current sampling circuit obtains an output current sampling voltage representing the output current by sampling the current of the main switching tube.

[0011] Optionally, the switch circuit adopts constant on-time control, and the switch signal generating circuit includes an on-time generating circuit. The on-time generating circuit receives the compensation voltage and generates the on-time of the switch tube according to the compensation voltage.

[0012] Optionally, the first threshold is zero.

[0013] Another technical solution of the present invention is to provide a switching circuit.

[0014] Compared with the prior art, the circuit structure and method of the present invention have the following advantages: a stable system and a fast response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a block diagram of an implementation of a control circuit according to an embodiment of the present invention;

[0016] Figure 2 is a block diagram of an implementation of a control circuit according to another embodiment of the present invention;

[0017] Figure 3 is a block diagram of a control circuit according to another embodiment of the present invention;

[0018] Figure 4 A block diagram of adding a limiting circuit to a control circuit according to an embodiment of the present invention;

[0019] Figure 5 A block diagram of an implementation of controlling a switch signal generating circuit by a first voltage in a control circuit according to an embodiment of the present invention;

[0020] Figure 6The present invention is a block diagram of an output feedback voltage and an output feedback current of a control circuit in a flyback circuit according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0022] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0023] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportion, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0024] The present invention provides a control circuit for a switch circuit, the control circuit comprising a compensation circuit, the control circuit performs operational amplification on the output feedback voltage of the switch circuit and a first reference voltage to obtain a first voltage, the first voltage and the output current sampling voltage are passed through the compensation circuit to obtain a compensation voltage, and the compensation voltage controls the conduction time of the main switch tube of the switch circuit. Please refer to Figure 1 As shown, it is an implementation method of the control circuit. The output feedback voltage is connected to the negative input terminal of the operational amplifier 101, the first reference voltage is connected to the positive input terminal of the operational amplifier 101, and the operational amplifier 101 performs operational amplification on the output feedback voltage of the switch circuit and the first reference voltage to obtain a first voltage V102. The first voltage is connected to the positive input terminal of the operational amplifier 104, the output feedback current is connected to the negative input terminal of the operational amplifier 104, the compensation capacitor C101 is connected to the negative input terminal and the output terminal of the operational amplifier 104, the operational amplifier 104 and the compensation current C101 constitute a compensation circuit, the output of the operational amplifier 104 is the compensation voltage, the switch signal generating circuit generates a switch signal according to the compensation voltage, and the switch signal controls the conduction and shutdown of the main switch tube.

[0025] Please continue to refer to Figure 1As shown, the switch circuit includes an inductor or a transformer, and the switch signal generating circuit 105 also receives the first voltage V102. When the switch circuit operates in the discontinuous conduction mode DCM, when the current of the inductor or the transformer drops to the first threshold value, after the first time, the switch signal generating circuit generates a main switch tube conduction signal, and the first voltage V102 controls the first time. The control circuit is particularly suitable for a switch circuit with an AC input, that is, the AC input is passed through a rectifier bridge to obtain a rectified voltage to power the switch circuit, which can speed up the system's response speed to output voltage changes, thereby optimizing the system's dynamic performance. Optionally, the first threshold is zero or near zero. In one embodiment, the output feedback voltage is higher than the first reference voltage. For example, the output feedback voltage is connected to the negative input terminal of the operational amplifier and the first reference voltage is connected to the positive input terminal. The first voltage V102 decreases, and the switch signal generating circuit receives the first voltage. As the first voltage V102 decreases, the first time is increased, thereby forming negative feedback, so that the output voltage decreases. In a circuit with AC input and LED load, when the output is open or the output voltage is too high, this control method can make the output constant voltage, so that the light will not flicker. In traditional circuits, when the output is open, since the output voltage cannot be adjusted, it will enter the BUSRT mode, that is, switching occurs for a period of time (such as several ms), the output voltage rises, and when it hits the overvoltage point, the switching stops for a period of time (such as several ms), causing the light to flicker.

[0026] Please refer to Figure 2 As shown, in order to improve the stability of the system, a capacitor C102 may be added between the negative input terminal and the output terminal of the operational amplifier 101. By adjusting the value of C102, the stability and response speed of the system may be optimized.

[0027] Please refer to Figure 3 As shown, it is an implementation of operational amplifiers 101 and 104. In operational amplifier 101, the first reference current I102 and the controlled current source 1101 are connected in series, and the controlled current source I101 is controlled by the output feedback voltage. The common end of the first reference current I102 and the controlled current source I101 is the first voltage V102. In operational amplifier 104, the controlled current source I103 and the controlled current source I104 are connected in series, and the controlled current source I103 is controlled by the output feedback current. The controlled current source I104 is controlled by the first voltage V102, and the common end of the controlled current source I103 and the controlled current source I104 is the compensation voltage, and the compensation voltage to the reference ground is connected to the compensation capacitor C101. The first voltage V102 to the reference ground can also be connected to the capacitor C102, which can optimize the stability and response speed of the system.

[0028] Please refer to Figure 4As shown, the first voltage V102 can be connected to the limiter circuit 106 to limit the maximum voltage of the first voltage.

[0029] Please refer to Figure 5 As shown, in the operational amplifier, the positions of the two series current sources can be interchanged.

[0030] In one embodiment, the control circuit further includes an output voltage sampling and holding circuit and a current sampling circuit. The switch circuit is a primary feedback circuit of an AC-DC converter. The output voltage sampling and holding circuit obtains an output feedback voltage representing the output voltage by sampling the voltage of the auxiliary winding. The current sampling circuit obtains an output current sampling voltage representing the output current by sampling the current of the main switch tube. Please refer to Figure 6 As shown, it is an implementation method in the flyback circuit. The sampling and holding circuit 113 obtains the output feedback voltage representing the output voltage by sampling and holding the voltage on the voltage-dividing resistors R13 and R14 of the auxiliary winding. The sampling and holding circuit 111 obtains the voltage representing the peak value of the transformer current by sampling the voltage on the main switch tube current sampling resistor R11. The calculation circuit 112 receives the output voltage of the sampling and holding circuit 111, and calculates the output feedback current representing the output current according to the duty cycle of the flyback circuit.

[0031] It should be noted that the implementation of the switch circuit is not limited to the flyback circuit, and may also be other forms of switch circuits such as a BUCK step-down circuit, a BOOST step-up circuit, or a BUCK-BOOST step-up / step-down circuit.

[0032] In one embodiment, the switch circuit adopts constant on-time control, the switch signal generating circuit includes an on-time generating circuit, the on-time generating circuit receives the compensation voltage, and generates the on-time of the switch tube according to the compensation voltage.

[0033] Another technical solution of the present invention is to provide a switching circuit, wherein the switching circuit is AC input and is powered by rectification.

[0034] Another technical solution of the present invention is to provide a control method for a switching circuit, wherein the switching circuit includes an inductor or a transformer, and an output feedback voltage of the switching circuit and a first reference voltage are operationally amplified to obtain a first voltage. The first voltage and the output current sampling voltage are passed through a compensation circuit to obtain a compensation voltage. The compensation voltage controls the conduction time of a main switch tube of the switching circuit. When the current of the inductor or the transformer drops to a first threshold value, the main switch tube is turned on after a first time, and the first voltage controls the first time.

[0035] In one embodiment, the first threshold is zero.

[0036] In one embodiment, the switch circuit is an AC input, which is rectified to power the switch circuit, and the load is an LED lamp.

[0037] In one embodiment, the switch circuit adopts constant on-time control.

[0038] In addition, although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated between the embodiments. For content that is not explicitly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0039] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A control method for a switch circuit, wherein the switch circuit comprises an inductor or a transformer, an output feedback voltage of the switch circuit and a first reference voltage are operationally amplified to obtain a first voltage, the first voltage and an output current sampling voltage are passed through a compensation circuit to obtain a compensation voltage, the compensation voltage controls the on-time of a main switch tube of the switch circuit, when the current of the inductor or the transformer drops to a first threshold value, after a first time, the main switch tube is turned on, and the first voltage controls the first time; in, The compensation circuit includes an operational amplifier and a compensation capacitor, the positive input terminal of the operational amplifier receives the first voltage, the negative input terminal of the operational amplifier receives the output current sampling voltage, the compensation capacitor is connected to the output terminal and the negative input terminal of the operational amplifier, and the output of the operational amplifier is the compensation voltage.

2. The control method of the switch circuit according to claim 1, characterized in that: The switch circuit is AC input, which is powered by rectification, and the load is an LED lamp.

3. The control method of the switch circuit according to claim 2, characterized in that: The switch circuit adopts constant on-time control.

4. A control circuit of a switch circuit, the switch circuit comprising an inductor or a transformer, the control circuit comprising a compensation circuit, the control circuit performs operational amplification on an output feedback voltage of the switch circuit and a first reference voltage to obtain a first voltage, the first voltage and an output current sampling voltage are passed through the compensation circuit to obtain a compensation voltage, the compensation voltage controls the on-time of a main switch tube of the switch circuit, when the current of the inductor or the transformer drops to a first threshold value, after a first time, the main switch tube is turned on, and the first voltage controls the first time; in, The compensation circuit includes an operational amplifier and a compensation capacitor, the positive input terminal of the operational amplifier receives the first voltage, the negative input terminal of the operational amplifier receives the output current sampling voltage, the compensation capacitor is connected to the output terminal and the negative input terminal of the operational amplifier, and the output of the operational amplifier is the compensation voltage.

5. The control circuit of the switch circuit according to claim 4, characterized in that: The switch circuit is AC input, which is powered by rectification, and the load is an LED lamp.

6. The control circuit of the switch circuit according to claim 5, characterized in that: The control circuit also includes a first operational amplifier and a switch signal generating circuit. The first operational amplifier performs operational amplification on the output feedback voltage and the first reference voltage to output the first voltage. The compensation voltage generates a switch signal through the switch signal generating circuit. The switch signal controls the on and off of the main switch tube. The switch signal generating circuit also receives the first voltage. When the current of the inductor or transformer drops to zero, after a first time, the switch signal generating circuit generates a main switch tube on signal.

7. The control circuit of the switch circuit according to claim 4, 5 or 6, characterized in that: The control circuit also includes an output voltage sampling and holding circuit and a current sampling circuit. The switching circuit is a primary feedback circuit of the AC-to-DC circuit. The output voltage sampling and holding circuit obtains an output feedback voltage representing the output voltage by sampling the voltage of the auxiliary winding. The current sampling circuit obtains an output current sampling voltage representing the output current by sampling the current of the main switching tube.

8. The control circuit of the switch circuit according to claim 6, characterized in that: The switch circuit adopts constant on-time control, and the switch signal generating circuit includes an on-time generating circuit. The on-time generating circuit receives the compensation voltage and generates the on-time of the switch tube according to the compensation voltage.

9. The control circuit of the switch circuit according to claim 4, characterized in that: The first threshold is zero.

10. A switch circuit, characterized in that: Comprising a control circuit as claimed in any one of claims 4 to 9.

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