BUCK step-down circuit control method, control circuit and BUCK step-down circuit

Abstract

The present invention discloses a control method, a control circuit and a BUCK buck circuit. The on-time of a main switch tube of the BUCK buck circuit is detected. When the on-time of the main switch tube is greater than a first time, a reference voltage of the BUCK buck circuit is controlled to decrease as the on-time of the main switch tube increases. The BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode. The present invention can optimize the linear regulation rate of the BUCK buck circuit.

Description

Technical Field

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

[0002] Please refer to Figure 1 The figure shows a traditional BUCK buck circuit. In the BUCK buck circuit with constant current output, for the sake of circuit simplicity, when the circuit works in critical conduction mode or intermittent conduction mode, the output current value is obtained by sampling the inductor peak current or the main switch peak current, and the control circuit controls the output current according to the output current value. This method does not require direct sampling of the output current, but obtains the output current value by sampling the inductor peak current or the main switch peak current. The slope of the inductor current rise is proportional to the difference between the input voltage and the output voltage. When the instantaneous value of the inductor current is large, the input voltage will drop. When the input voltage is much larger than the output voltage, the rise of the inductor current is approximately linear, as shown in Figure 1. Figure 2 However, when the input voltage and output voltage are close, the rise of the inductor current will be nonlinear, as shown in Figure 2 As shown by the solid line in the middle. However, the control circuit obtains the output current value by sampling the inductor peak current or the main switch tube peak current based on the characteristics of the linear rise and linear decline of the inductor current. When the inductor current rises nonlinearly, the output current value obtained by sampling the inductor peak current or the main switch tube peak current will be biased. Therefore, under the condition of low input voltage, the output current of this control method will be too large, resulting in poor linear regulation. Another simpler constant current control method of the BUCK buck circuit is that the circuit works in the critical conduction mode, and by controlling the inductor current peak value or the main switch tube current peak value as a reference value, the output current value is half of the reference value. This output current control method is also based on the characteristics of the linear rise and linear decline of the inductor current. When the inductor current rises nonlinearly, the output current value obtained by sampling the inductor peak current or the main switch tube peak current will be biased. Therefore, under the condition of low input voltage, the output current of this control method will also be too large, resulting in poor linear regulation. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a control method for a BUCK buck circuit, detecting the on-time of a main switch tube of the BUCK buck circuit, and when the on-time of the main switch tube is greater than a first time, controlling a reference voltage of the BUCK buck circuit to decrease as the on-time of the main switch tube increases, and the BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode.

[0004] Optionally, the feedback voltage and the reference voltage are operationally amplified to obtain the compensation voltage, and the feedback voltage is obtained by sampling the peak current of the inductor or the peak current of the main switch tube.

[0005] Optionally, the BUCK step-down circuit adopts peak current control or constant on-time control.

[0006] Optionally, the reference voltage controls the peak current of the inductor or the main switch tube.

[0007] The present invention also provides a control circuit of a BUCK buck circuit, wherein the control circuit detects the on-time of a main switch tube of the BUCK buck circuit. When the on-time of the main switch tube is greater than a first time, the reference voltage of the BUCK buck circuit is controlled to decrease as the on-time of the main switch tube increases. The BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode.

[0008] Optionally, the control circuit performs operational amplification on the feedback voltage and the reference voltage to obtain a compensation voltage, and the feedback voltage is obtained by sampling the peak current of the inductor or the peak current of the main switch tube.

[0009] Optionally, the BUCK step-down circuit adopts peak current control or constant on-time control.

[0010] Optionally, the reference voltage controls the peak current of the inductor or the main switch tube.

[0011] Optionally, the control circuit includes an operational amplifier circuit, a logic control circuit, and a reference voltage generating circuit. The operational amplifier circuit receives a reference voltage and a feedback voltage, and performs operational amplification on the feedback voltage and the reference voltage to obtain a compensation voltage. The logic control circuit receives the compensation voltage and generates a switching signal based on the compensation voltage. The reference voltage generating circuit receives the switching signal and generates a reference voltage based on the switching signal.

[0012] Optionally, the control circuit includes a logic control circuit and a reference voltage generating circuit, wherein the logic control circuit receives a reference voltage and generates a switching signal according to the reference voltage, and the reference voltage generating circuit receives a switching signal and generates a reference voltage according to the switching signal.

[0013] Another technical solution of the present invention is to provide a BUCK step-down circuit.

[0014] Compared with the prior art, the circuit structure and method of the present invention have the following advantages: the linear regulation rate of the BUCK step-down circuit can be optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The schematic diagram of the structure of the BUCK step-down circuit is shown schematically;

[0016] Figure 2 The waveform curve of the inductor current iL is schematically shown;

[0017] Figure 3 Schematically shows a curve of a reference voltage VREF and a turn-on time TON according to an embodiment of the present invention;

[0018] Figure 4 The structure diagram of the control circuit 100 according to the embodiment of the present invention is schematically shown;

[0019] Figure 5 The structure diagram of the logic control circuit 120 according to the embodiment of the present invention is schematically shown;

[0020] Figure 6 Schematically shows a structural diagram of a logic control circuit 120 according to another embodiment of the present invention;

[0021] Figure 7 Schematically shows a structural diagram of a control circuit 100 according to another embodiment of the present invention;

[0022] Figure 8 The structure diagram of the logic control circuit 120 according to another embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The object of the present invention is to provide a control method for a BUCK buck circuit, which detects the on-time of the main switch tube of the BUCK buck circuit. When the on-time of the main switch tube is greater than a first time, the reference voltage of the BUCK buck circuit is controlled to decrease as the on-time of the main switch tube increases. The BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode. Please refer to Figure 1 As shown, M01 is the main switch tube of the BUCK step-down circuit. Figure 3 As shown, a curve of the reference voltage VREF and the on-time TON according to an embodiment of the present invention is schematically shown. The on-time of the main switch tube is longer at low voltage input than at high voltage input. Therefore, when the on-time is large, the linear regulation rate can be optimized by reducing the reference voltage VREF. Among them, the input of the BUCK buck circuit can be a DC input, or it can be an AC voltage that passes through a rectifier bridge to obtain a DC voltage. The output side load of a common BUCK buck circuit is an LED lamp, because the LED lamp requires a constant current drive. It should also be noted that in Figure 3 In the embodiment, when the main switch is turned on for longer than the first time, the reference voltage VREF decreases linearly with the turn-on time TON. The present invention is not limited to the linear decrease, and may be any decrease curve.

[0027] In one embodiment, the feedback voltage and the reference voltage are operationally amplified to obtain a compensation voltage, and the feedback voltage is obtained by sampling the peak current of the inductor or the peak current of the main switch tube. In this embodiment, the output current is stabilized by closed-loop control. In this embodiment, the BUCK buck circuit can adopt peak current control or constant conduction time control. Among them, the peak current control is to compare the inductor current or the main switch tube current with the first current. When the inductor current or the main switch tube current reaches the first current, the control circuit controls the main switch tube to turn off. Among them, the first current is controlled by the compensation voltage, for example, the first current is proportional to the compensation voltage. The constant conduction control method is to start timing from the turn-on of the main switch tube, and when the timing reaches the second time, the control circuit controls the main switch tube to turn off. Among them, the second time is controlled by the compensation voltage COMP, and the second time can be equal to the compensation voltage COMP, or it can be proportional to the compensation voltage COMP, and so on.

[0028] In another embodiment, an open-loop control mode is adopted and the circuit operates in a peak current control mode. The reference voltage controls the peak current of the inductor or the main switch tube. Because when the BUCK circuit operates in the critical conduction mode, the output current is equal to half of the inductor peak current or the main switch tube peak current, therefore, the output current can be stabilized by directly controlling the peak current of the inductor or the main switch tube.

[0029] The present invention also provides a control circuit of a BUCK buck circuit, wherein the control circuit detects the on-time of a main switch tube of the BUCK buck circuit. When the on-time of the main switch tube is greater than a first time, the reference voltage of the BUCK buck circuit is controlled to decrease as the on-time of the main switch tube increases. The BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode.

[0030] In one embodiment, the control circuit performs operational amplification on the feedback voltage and the reference voltage to obtain the compensation voltage, and the feedback voltage is obtained by sampling the inductor peak current or the main switch tube peak current. In this embodiment, the BUCK step-down circuit adopts peak current control or constant on-time control.

[0031] Please refer to Figure 4 As shown, a schematic diagram of the structure of the control circuit 100 according to an embodiment of the present invention is schematically shown. The control circuit 100 includes an operational amplifier circuit 110, a logic control circuit 120, and a reference voltage generating circuit 140. The operational amplifier circuit 110 receives a reference voltage VREF and a feedback voltage FB, and performs operational amplification on the feedback voltage FB and the reference voltage VREF to obtain a compensation voltage COMP. The logic control circuit 120 receives the compensation voltage COMP, and generates a switch signal TON according to the compensation voltage COMP. The reference voltage generating circuit 140 receives the switch signal TON, and generates a reference voltage VREF according to the switch signal. In this embodiment, a driving circuit 130 is also included, which drives the current to receive the switch signal TON, amplifies the switch signal TON, and thus controls the on and off of the main switch tube.

[0032] When using peak current control, please refer to the block diagram of the logic control circuit Figure 5 As shown, the logic control circuit 120 includes a comparison circuit 121 and a logic circuit 122. The comparison circuit receives the compensation voltage COMP and the inductor peak current iL, or the main switch tube current representing the inductor peak current. When the inductor peak current reaches the first current, the output voltage OFF of the comparison circuit 121 is flipped, and when the logic circuit 122 receives the OFF and flips, the switch signal output by it changes from valid to invalid, and the drive circuit controls the main switch tube of the BUCK buck circuit to turn off. In this embodiment, the switch signal is valid to represent the main switch tube is turned on, and the switch signal is invalid to represent the main switch tube is turned off, wherein the first current is controlled by the compensation voltage, for example, it is proportional to the compensation voltage, and so on.

[0033] When constant on-time control is adopted, the block diagram of the logic control circuit 120 is as follows: Figure 6As shown. The logic control circuit 120 includes a conduction time generating circuit 123 and a logic circuit 122. The conduction time generating circuit 123 receives the compensation voltage COMP. The conduction time generating circuit 123 starts timing from the turn-on of the main switch tube, and when the timing reaches the second time, the output voltage OFF of the conduction time generating circuit 123 is reversed. Among them, the second time is controlled by the compensation voltage COMP, and the second time can be equal to the compensation voltage COMP, or can be proportional to the compensation voltage COMP, and so on. When the logic circuit 122 receives OFF and flips, the switch signal output by it changes from valid to invalid, and the driving circuit controls the main switch tube of the BUCK buck circuit to turn off. In this embodiment, the switch signal is valid to represent the turn-on of the main switch tube, and the switch signal is invalid to represent the turn-off of the main switch tube.

[0034] When open loop control is adopted and the peak current control mode is used, the reference voltage VREF controls the peak current of the inductor or the main switch. Figure 7 As shown. The control circuit 100 includes a logic control circuit 120 and a reference voltage generating circuit 140. The logic control circuit 120 receives a reference voltage VREF and generates a switch signal TON according to the reference voltage VREF. The reference voltage generating circuit 140 receives a switch signal TON and generates a reference voltage VREF according to the switch signal TON. In this embodiment, a driving circuit 130 is also included, which receives the switch signal TON and amplifies the switch signal TON to control the on and off of the main switch tube.

[0035] For a block diagram of the logic control circuit in this embodiment, please refer to Figure 8 As shown, the logic control circuit includes a comparison circuit 121 and a logic circuit 122. The comparison circuit 121 receives a reference voltage VREF and an inductor peak current iL, or a main switch tube current representing the inductor peak current. When the inductor peak current reaches the reference voltage VREF, the output voltage OFF of the comparison circuit 121 flips. When the logic circuit 122 receives OFF and flips, the switch signal outputted by the comparison circuit 121 changes from valid to invalid, and the driving circuit controls the main switch tube of the BUCK step-down circuit to turn off. In this embodiment, the switch signal is valid to represent that the main switch tube is turned on, and the switch signal is invalid to represent that the main switch tube is turned off.

[0036] Another technical solution of the present invention is to provide a BUCK step-down circuit.

[0037] 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.

[0038] 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 BUCK step-down circuit, characterized in that: Detecting the on-time of the main switch tube of the BUCK buck circuit, and when the on-time of the main switch tube is greater than the first time, controlling the reference voltage of the BUCK buck circuit to decrease as the on-time of the main switch tube increases, and the BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode; The reference voltage controls the peak current of the inductor or the main switch tube, and when the peak current of the inductor or the main switch tube reaches the reference voltage, the main switch tube is controlled to be turned off.

2. The control method of the BUCK step-down circuit according to claim 1, characterized in that: The feedback voltage and the reference voltage are operationally amplified to obtain a compensation voltage, wherein the feedback voltage is obtained by sampling the peak current of the inductor or the peak current of the main switch tube.

3. The control method of the BUCK step-down circuit according to claim 1, characterized in that: The BUCK step-down circuit adopts peak current control or constant on-time control.

4. A control circuit of a BUCK step-down circuit, characterized in that: The control circuit detects the on-time of the main switch tube of the BUCK buck circuit, and when the on-time of the main switch tube is greater than the first time, controls the reference voltage of the BUCK buck circuit to decrease as the on-time of the main switch tube increases, and the BUCK buck circuit operates in a discontinuous conduction mode or a critical conduction mode; The reference voltage controls the peak current of the inductor or the main switch tube, and when the peak current of the inductor or the main switch tube reaches the reference voltage, the main switch tube is controlled to be turned off.

5. The control circuit of the BUCK step-down circuit according to claim 4, characterized in that: The control circuit performs operational amplification on the feedback voltage and the reference voltage to obtain a compensation voltage, wherein the feedback voltage is obtained by sampling the peak current of the inductor or the peak current of the main switch tube.

6. The control circuit of the BUCK step-down circuit according to claim 4, characterized in that: The BUCK step-down circuit adopts peak current control or constant on-time control.

7. The control circuit of the BUCK step-down circuit according to claim 5, characterized in that: The control circuit includes an operational amplifier circuit, a logic control circuit, and a reference voltage generating circuit. The operational amplifier circuit receives a reference voltage and a feedback voltage, and performs operational amplification on the feedback voltage and the reference voltage to obtain a compensation voltage. The logic control circuit receives the compensation voltage and generates a switching signal according to the compensation voltage. The reference voltage generating circuit receives the switching signal and generates a reference voltage according to the switching signal.

8. The control circuit of the BUCK step-down circuit according to claim 4, characterized in that: The control circuit includes a logic control circuit and a reference voltage generating circuit. The logic control circuit receives a reference voltage and generates a switch signal according to the reference voltage. The reference voltage generating circuit receives a switch signal and generates a reference voltage according to the switch signal.

9. A BUCK step-down circuit, characterized in that: Comprising a control circuit as claimed in any one of claims 4 to 8.

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