Control circuit and control method of switch circuit and switch power supply circuit

Abstract

The present invention proposes a control circuit, a control method and a switching power supply circuit of a switching circuit, wherein the feedback voltage and the reference voltage representing the output voltage are error-amplified to obtain a compensation voltage; when the compensation voltage is greater than a first threshold, the compensation voltage is clamped at the first threshold, and the compensation voltage controls the main power tube of the switching circuit to turn off; the first threshold is set according to the topological structure, input voltage and output voltage of the switching circuit. The present invention can avoid excessive inductor current, ensure sufficient output, and reduce the overcharge voltage during short circuit recovery.

Description

Technical Field

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

[0002] Among the various control methods of switching converter circuits, constant on time (COT) control is widely used due to its advantages such as fast transient response speed and simple structure. The compensation voltage is obtained by amplifying the error between the feedback voltage and the reference voltage that characterize the output voltage of the switching circuit. In constant on time control, the compensation voltage controls the on time. In the traditional scheme, the on time increases with the increase of the compensation voltage. However, if the compensation voltage is too large, the inductor current will be too large and damage the power tube; if the compensation voltage is too small, the output will deviate too much from the expected value and the output will be insufficient. Therefore, when controlling the switching circuit, it is necessary to compromise the size of the compensation voltage. Summary of the invention

[0003] The object of the present invention is to provide a control circuit, a control method and a switching power supply circuit of a switching circuit with a simple circuit, so as to solve the problems of excessive inductor current and insufficient output existing in the prior art.

[0004] To achieve the above object, the present invention provides a control circuit for a switch circuit, comprising:

[0005] The first operational amplifier performs error amplification on the feedback voltage representing the output voltage and the reference voltage to obtain a compensation voltage;

[0006] a first control circuit, when the compensation voltage is greater than a first threshold, clamping the compensation voltage at the first threshold; when the compensation voltage is less than or equal to the first threshold, the first control circuit outputs the compensation voltage; and controls the main power tube of the switch circuit to turn off according to the compensation voltage;

[0007] The first threshold generating circuit sets the first threshold according to the topological structure, input voltage and output voltage of the switch circuit.

[0008] Optionally, by filtering or sampling and holding the switch node signal of the switching circuit, a signal characterizing the input voltage and a signal characterizing the output voltage are obtained, and the first threshold is set according to the topological structure of the switching circuit, the signal characterizing the input voltage and the signal characterizing the output voltage.

[0009] Optionally, when the switching circuit is a step-down circuit, the first threshold is proportional to the ratio of the output voltage to the input voltage.

[0010] Optionally, when the switching circuit is a boost circuit, the first threshold is proportional to the difference between the output voltage and the input voltage, and inversely proportional to the output voltage.

[0011] Optionally, when the switching circuit is a buck-boost circuit, the first threshold is proportional to the output voltage and inversely proportional to the sum of the input voltage and the output voltage.

[0012] Optionally, when the switching circuit is a flyback circuit, the first threshold is negatively correlated with the ratio of the input voltage to the output voltage, and is positively correlated with the turns ratio of the primary side and the secondary side of the flyback circuit.

[0013] Optionally, the first control circuit includes a first adjustment tube, a second adjustment tube, a current source and a second operational amplifier, the first end of the first adjustment tube is connected to a high potential end, the second end of the first adjustment tube is connected to the current source, and the control end of the first adjustment tube is connected to the output end of the first operational amplifier; the first input end of the second operational amplifier is connected to the second end of the first adjustment tube, the second input end of the second operational amplifier receives a first threshold value, the output end of the second operational amplifier is connected to the control end of the second adjustment tube, the first end of the second adjustment tube is connected to the control end of the first adjustment tube, and the second end of the second adjustment tube is grounded; the second end voltage of the first adjustment tube represents the compensation voltage.

[0014] The present invention also provides a control method for a switching circuit, which performs error amplification on a feedback voltage and a reference voltage representing an output voltage to obtain a compensation voltage; when the compensation voltage is greater than a first threshold, the compensation voltage is clamped at the first threshold, and the compensation voltage controls the main power tube of the switching circuit to shut down; and the first threshold is set according to the topological structure, input voltage and output voltage of the switching circuit.

[0015] The present invention also provides a switching power supply circuit, comprising any one of the control circuits described above.

[0016] Compared with the prior art, the present invention has the following advantages: the feedback voltage and the reference voltage representing the output voltage are error-amplified to obtain the compensation voltage; when the compensation voltage is greater than the first threshold, the compensation voltage is clamped at the first threshold, and the compensation voltage controls the main power tube of the switch circuit to turn off; the first threshold is set according to the topological structure, input voltage and output voltage of the switch circuit. The present invention can avoid excessive inductor current and damage to the power tube, and can also ensure that the output voltage has sufficient output, and can also reduce the overcharge voltage during short circuit recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a control circuit schematic diagram of the switch circuit of the present invention;

[0018] Figure 2 is a schematic diagram of a first control circuit of a switch circuit of the present invention;

[0019] Figure 3 It is a waveform diagram of the switch circuit of the present invention. DETAILED DESCRIPTION

[0020] 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.

[0021] 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.

[0022] 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 proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0023] like Figure 1As shown, the control circuit schematic diagram of the switch circuit of the present invention is illustrated, and the switch circuit includes a main power tube and a synchronous rectifier tube, such as a buck circuit, a boost circuit, a flybuck circuit, etc. The control circuit includes a first operational amplifier U01, a clamping circuit U02 and a clamping value generating circuit U03. The first operational amplifier U01 performs error amplification on the feedback voltage FB and the reference voltage VREF that characterize the output voltage of the switch circuit. The input end of the clamping circuit U02 is connected to the output end of the first operational amplifier U01, and outputs a compensation voltage VCOMP. When the compensation voltage VCOMP is greater than the first threshold clamp, the clamping circuit U02 clamps it at the first threshold clamp. The first threshold clamp is obtained according to different switch circuit topologies, the output voltage VOUT of the switch circuit, and the input voltage VIN. The compensation voltage COMP controls the conduction time of the main power tube of the switch circuit. The larger the compensation voltage COMP, the larger the conduction time and the larger the duty cycle. Therefore, according to the relationship between the duty cycle and the input and output of the switch circuit, the clamping value of the compensation voltage, i.e., the first threshold clamp, can be set according to the input and output of the switch circuit. When the switch circuit is a buck circuit, the first threshold clamp is set to be proportional to the ratio of the input voltage to the input voltage. When the switch circuit is a boost circuit, the first threshold clamp is set to be proportional to the output voltage and inversely proportional to the sum of the input voltage and the output voltage. When the switch circuit is a buck-boost circuit, the first threshold clamp is set to be proportional to the output voltage and inversely proportional to the sum of the input voltage and the output voltage. When the switch circuit is a flyback circuit, the first threshold clamp is set to be positively correlated with the ratio of the input voltage to the output voltage and positively correlated with the turns ratio of the primary and secondary sides of the flyback circuit. In addition to being obtained by sampling, the input voltage and output voltage of the switch circuit can also be obtained by filtering or sampling and holding the switch node signal of the switch circuit to obtain a signal representing the input voltage and the output voltage. For example, in the buck circuit, the voltage at the connection end of the main power tube and the synchronous rectifier tube can be filtered to obtain a signal representing the output voltage, or when the main power tube is turned on, the voltage at the connection end can be sampled and held to obtain a signal representing the input voltage.

[0024] Figure 2The schematic diagram of the first control circuit of the present invention is illustrated. The first control circuit includes a first adjustment tube M1, a second adjustment tube M2, a current source I1 and a second operational amplifier U201. The first end of the first adjustment tube M1 is connected to the high potential end, the second end of the first adjustment tube M1 is connected to the current source I1, and the control end of the first adjustment tube M1 is connected to the control end of the first operational amplifier U01; the first end of the second adjustment tube M2 is connected to the control end of the first adjustment tube M1, and the second end of the second adjustment tube M2 is grounded; the first end of the second operational amplifier U201 is connected to the second end of the first adjustment tube M1, the second end of the second operational amplifier U201 receives a first threshold clamp, the output end of the second operational amplifier U201 is connected to the control end of the second adjustment tube M2, and the voltage at the second end of the first operational amplifier U201 is the compensation voltage COMP2.

[0025] like Figure 3 As shown, the waveform diagram of the switch circuit of the present invention is illustrated. The switch circuit takes the step-down circuit as an example, and combines Figure 1 In the figure, ramp is a ramp signal, COMP is a compensation voltage, when the ramp signal ramp rises to the compensation voltage COMP, the main power tube is turned off, when the compensation voltage COMP rises to the first threshold clamp, the compensation voltage COMP is clamped at clamp; when the clock pulse signal clk is detected, the main power tube is turned on.

[0026] 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. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0027] 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 circuit for a switch circuit, characterized in that: include: The first operational amplifier performs error amplification on the feedback voltage representing the output voltage and the reference voltage to obtain a compensation voltage; A first control circuit, when the compensation voltage is greater than a first threshold, clamps the compensation voltage to output at the first threshold; When the compensation voltage is less than or equal to a first threshold, the first control circuit outputs the compensation voltage; and controls the main power tube of the switch circuit to be turned off according to the compensation voltage; A first threshold generating circuit, which sets the first threshold according to the topological structure, input voltage and output voltage of the switch circuit; According to filtering or sampling and holding of the switch node signal of the switch circuit, a characterization signal of the input voltage and a characterization signal of the output voltage are obtained; the first threshold is set according to the topological structure of the switch circuit, the characterization signal of the input voltage and the characterization signal of the output voltage; When the switch circuit is a step-down circuit, the first threshold is proportional to the ratio of the output voltage to the input voltage; When the switch circuit is a boost circuit, the first threshold is proportional to the difference between the output voltage and the input voltage, and inversely proportional to the output voltage; When the switch circuit is a buck-boost circuit, the first threshold is proportional to the output voltage and inversely proportional to the sum of the input voltage and the output voltage; When the switch circuit is a flyback circuit, the first threshold is negatively correlated with the ratio of the input voltage to the output voltage, and is positively correlated with the turns ratio of the primary side and the secondary side of the flyback circuit.

2. The control circuit of the switch circuit according to claim 1, characterized in that: The first control circuit includes a first adjustment tube, a second adjustment tube, a current source and a second operational amplifier, wherein the first end of the first adjustment tube is connected to a high potential end, the second end of the first adjustment tube is connected to the current source, and the control end of the first adjustment tube is connected to the output end of the first operational amplifier; the first input end of the second operational amplifier is connected to the second end of the first adjustment tube, the second input end of the second operational amplifier receives a first threshold value, the output end of the second operational amplifier is connected to the control end of the second adjustment tube, the first end of the second adjustment tube is connected to the control end of the first adjustment tube, and the second end of the second adjustment tube is grounded; the voltage at the second end of the first adjustment tube represents the compensation voltage.

3. A switching power supply circuit, characterized in that: The invention comprises the control circuit described in any one of claims 1 to 2.

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