Control circuit and control method of switch circuit

Abstract

The present invention discloses a control circuit and control method for a switching circuit. The switching circuit includes a main power transistor and an inductor connected thereto. The control circuit amplifies the error between the output feedback voltage of the switching circuit and a reference voltage to obtain a compensation voltage. The control circuit generates a first ripple voltage in phase with the inductor current. When the load or input voltage of the switching circuit changes, the control circuit detects the change in the peak / valley value of the first ripple voltage. When the change exceeds a first threshold, the control circuit pulls up or down the peak / valley value of the first ripple voltage. This invention improves the dynamic response capability of the switching circuit.

Description

Technical Field

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

[0002] In the existing technology, the constant on and constant off control methods have fast dynamic response characteristics, but the control depends on the output ripple. When the output ripple is too small, the loop cannot work properly. In addition, the average output voltage is also affected by the output ripple. In order to adapt to the application scenario with small output ripple and eliminate the static error of the output voltage, the constant on control method with ripple injection and output feedback has emerged. Figure 1 As shown in the figure, a schematic diagram of a control circuit with ripple injection is shown, taking a buck circuit as an example. The ripple generator is connected in parallel at both ends of the inductor to generate a ripple signal Vripple. The sum of the ripple signal Vripple and the feedback voltage FB is compared with the compensation voltage COMP to control the switching state of the buck circuit.

[0003] Although active ripple injection eliminates the dependence on output ripple, it also leads to poor dynamic response of the circuit, such as Figure 2 As shown in the figure, when the load suddenly increases, the compensation voltage COMP remains basically unchanged, and the feedback voltage FB decreases, which increases the duty cycle. However, the injected ripple signal Vripple increases with the increase of the duty cycle, thereby offsetting part of the decrease in the feedback voltage FB. That is, (FB+Vripple) does not quickly reflect the changing trend of the output voltage, so that the duty cycle does not increase in time, resulting in a larger pit in the output voltage waveform. Summary of the Invention

[0004] The purpose of the present invention is to provide a control circuit and control method for a fast-response switching circuit, so as to solve the problem in the prior art that the sum of the injected ripple signal and the feedback voltage cannot accurately reflect the dynamic change of the output and the dynamic response speed of the output voltage is slow.

[0005] To achieve the above object, the present invention provides a control circuit for a switching circuit, wherein the switching circuit includes a main power tube and an inductor connected thereto, and the control circuit includes:

[0006] an operational amplifier, amplifying an error between an output feedback voltage of the switching circuit and a reference voltage to obtain a compensation voltage;

[0007] a ripple generating circuit connected to the inductor, configured to generate a first ripple voltage in phase with the inductor current, and detect a change in a peak / valley value of the first ripple voltage when a load or input voltage of the switching circuit changes, and pull up or down the peak / valley value of the first ripple voltage when the change exceeds a first threshold;

[0008] The first comparator compares the sum of the first ripple voltage and the feedback voltage with the compensation voltage to generate a trigger signal for controlling the main power tube to be turned on or off.

[0009] Optionally, the ripple generating circuit includes:

[0010] a ripple generator connected in parallel across the inductor to obtain a first ripple voltage in phase with the inductor current;

[0011] The limiting circuit is connected to the ripple generator, and detects the change of the first ripple voltage peak / valley value when the load or input voltage of the switching circuit changes. When the change exceeds a first threshold, the first ripple voltage peak / valley value is pulled up or down.

[0012] Optionally, the limiting circuit includes:

[0013] a sample-and-hold device, sampling and holding the peak value of the first ripple voltage in each switching cycle;

[0014] a difference circuit, subtracting a peak value of the first ripple voltage from a peak value of the first ripple voltage in a previous switching cycle and taking an absolute value to obtain the variation;

[0015] a second comparator, for comparing the variation with a first threshold value to generate a comparison signal;

[0016] The limiting unit receives the comparison signal, and when the comparison signal indicates that the change amount is greater than the first threshold, pulls up or pulls down the peak value of the first ripple voltage.

[0017] Optionally, the limiting circuit includes:

[0018] A sample-and-hold device, which samples and holds the valley value of the first ripple voltage in each switching cycle;

[0019] a difference circuit, subtracting a valley value of the first ripple voltage from a valley value of the first ripple voltage in a previous switching cycle and taking an absolute value to obtain the variation;

[0020] a second comparator, for comparing the variation with a first threshold value to generate a comparison signal;

[0021] The limiting unit receives the comparison signal, and when the comparison signal indicates that the change amount exceeds a first threshold, pulls up or pulls down the valley value of the first ripple voltage.

[0022] Optionally, the ripple generator comprises,

[0023] a first resistor and a first capacitor, wherein a first end of the first resistor is connected to the first end of the inductor, a second end of the first resistor is connected to the first end of the first capacitor, and a second end of the first capacitor is connected to the second end of the inductor;

[0024] A subtractor is configured to subtract the voltage at the common connection terminal of the first resistor and the first capacitor from the output voltage to obtain the first ripple voltage.

[0025] Optionally, an adaptive timer is also included to control the on or off time of the main power tube according to the input voltage and the output voltage.

[0026] The present invention also provides a control method for a switching circuit, wherein the switching circuit includes a power tube and an inductor connected thereto, and comprises the following steps:

[0027] Amplify the error between the output feedback voltage of the switching circuit and the reference voltage to obtain a compensation voltage;

[0028] generating a first ripple voltage in phase with the inductor current, detecting a change in a peak / valley value of the first ripple voltage when a load or input voltage of the switching circuit changes, and pulling up or down the peak / valley value of the first ripple voltage when the change exceeds a first threshold;

[0029] The sum of the first ripple voltage and the feedback voltage is compared with the compensation voltage to generate a trigger signal for controlling the main power tube to be turned on or off.

[0030] Optionally, the method for limiting the variation range of the first ripple voltage further includes the following steps:

[0031] In each switching cycle, sampling and holding the peak value of the first ripple voltage;

[0032] When the change is greater than the first threshold and the peak value of the first ripple voltage is greater than the peak value of the first ripple voltage in the previous switching cycle, pulling down the peak value of the first ripple voltage to a first voltage, where the first voltage is the sum of the peak value of the first ripple voltage in the previous switching cycle and the first threshold;

[0033] When the change is greater than the first threshold and the peak value of the first ripple voltage is greater than the peak value of the first ripple voltage in the previous switching cycle, pulling up the first ripple voltage to a second voltage, where the second voltage is the difference between the peak value of the first ripple voltage in the previous switching cycle and the first threshold;

[0034] When the peak value of the first ripple voltage is pulled to the first voltage or the second voltage, the first voltage or the second voltage is sampled and held as the peak value of the first ripple voltage in the current switching cycle; the trigger signal controls the main power tube to turn on.

[0035] Optionally, the method for limiting the variation range of the first ripple voltage further includes the following steps:

[0036] In each switching cycle, sampling and holding the peak value of the first ripple voltage;

[0037] When the change is greater than the first threshold, and the valley value of the first ripple voltage is greater than the valley value of the first ripple voltage in the previous switching cycle, when the change is greater than the first threshold, the valley value of the first ripple voltage is pulled down to a third voltage, and the third voltage is the sum of the valley value of the first ripple voltage in the previous switching cycle and the first threshold;

[0038] When the change is greater than the first threshold value, and the valley value of the first ripple voltage is less than the valley value of the first ripple voltage in the previous switching cycle, the valley value of the first ripple voltage is pulled up to a fourth voltage, where the fourth voltage is the difference between the valley value of the first ripple voltage in the previous switching cycle and the first threshold value;

[0039] When the valley value of the first ripple voltage is pulled to the third voltage or the fourth voltage, the third voltage or the fourth voltage is sampled and held as the valley value of the first ripple voltage of the current switching cycle; and the trigger signal controls the main power tube to turn off.

[0040] Optionally, the time for the main power tube to be turned on or off is controlled according to the input voltage and the output voltage.

[0041] Compared with the prior art, the technical solution of the present invention has the following advantages: the present invention limits the peak / valley value of the ripple according to the change in the peak / valley value of the ripple, so that the sum of the ripple and the output feedback voltage accurately follows the change trend of the feedback voltage and responds as quickly as possible, thereby improving the dynamic response speed of the output voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of a control circuit for a conventional switching circuit;

[0043] Figure 2 This is a working signal waveform diagram of a switching circuit in the prior art;

[0044] Figure 3 This is a schematic diagram of a control circuit of a switch circuit according to the present invention;

[0045] Figure 4 This is a schematic diagram of a ripple generating circuit in a control circuit of the present invention;

[0046] Figure 5 This is a working signal waveform diagram of a first embodiment of a switch circuit control method of the present invention;

[0047] Figure 6 This is a working signal waveform diagram of the second embodiment of the switch circuit control method of the present invention. DETAILED DESCRIPTION

[0048] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments and covers any substitution, modification, equivalent method and solution made within the spirit and scope of the present invention.

[0049] 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 also fully understand the present invention without description of these details.

[0050] 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 drawings are simplified and not to exact proportions, and are only used for the purpose of conveniently and clearly illustrating the embodiments of the present invention.

[0051] like Figure 3 The figure shows a schematic diagram of the control circuit of a switching circuit according to the present invention. Taking a step-down switching circuit as an example, the control circuit includes a ripple generation circuit, an adder U03, an operational amplifier U04, a comparator U05, an adaptive timer U06, and a drive circuit U07. The ripple generation circuit further includes a ripple generator U01 and a limiting circuit U02. The ripple generator U01 is connected in parallel across the inductor L0 to generate a ripple voltage Vripple in phase with the inductor current. The limiting circuit U02 is connected to the ripple generator U01 to limit the range of variation of the ripple voltage Vripple. The adder U03 adds the output feedback voltage FB of the switching circuit and the ripple voltage Vripple to generate a voltage V1. The operational amplifier U04 performs an error calculation on the output feedback voltage FB of the switching circuit and a reference voltage VREF to output a compensation voltage COMP. The comparator U05 compares the voltage with the compensation voltage to generate a trigger signal for controlling the on / off of the main power transistor M0. The adaptive timer U06 determines the on / off timing of the power transistor M0 based on the input voltage VIN and the output voltage VOUT.

[0052] like Figure 4 The figure shows a schematic diagram of a ripple generating circuit in a control circuit according to the present invention. The ripple generator includes a first resistor R1, a first capacitor C1, and a subtractor U101. The first resistor R1 and the first capacitor C1 are connected in parallel across the inductor L0 of the switching circuit. A ripple signal is output at the connection point between the first resistor R1 and the first capacitor C1. The ripple signal is subtracted from the output voltage to obtain a first ripple voltage Vripple. The limiting circuit includes a sample-and-hold unit U201, a differentiator U202, a comparator U203, and a limiting unit U204.

[0053] In the constant on-time control mode, the sample and hold device U201 samples and holds the peak value of the first ripple voltage Vripple of each switching cycle. The peak value Vpk1 of the first ripple voltage Vripple of the current cycle is subtracted from the peak value Vpk0 of the first ripple voltage Vripple of the previous switching cycle through the differentiator U202, and the absolute value is taken to obtain the voltage |Vpk1-Vpk0|. The voltage |Vpk1-Vpk0| is compared with the threshold voltage ΔV. If |Vpk1-Vpk0|>ΔV, the voltage V1 at the connection terminal of the first resistor R1 and the first capacitor C1 at this moment is pulled up or pulled down so that the absolute value of the difference between the first ripple voltage Vripple and Vpk1 at this moment is equal to the first threshold ΔV, and the first ripple voltage Vripple at this moment is sampled and held by the sample and hold device U201 as the peak voltage of the current cycle. Specifically, if Vpk1-Vpk0>ΔV, when the main power tube is turned off, the peak value of the first ripple voltage Vripple is pulled down to Vpk0+ΔV; if Vpk0-Vpk1>ΔV, when the main power tube is turned off, the peak value of the first ripple voltage Vripple is pulled up to Vpk0+ΔV; a pull-down current can be generated by the limiting unit U204 to discharge the first capacitor C1 to achieve a pull-down action, and a pull-up current can be generated to charge the first capacitor C1 to achieve a pull-up action, and when the first ripple voltage Vripple is pulled down to the corresponding voltage, the limiting unit stops working.

[0054] In the constant off-time control mode, the sample and hold device U201 samples and holds the valley value of the first ripple voltage Vripple of each switching cycle. The valley value Va1 of the first ripple voltage Vripple of the current cycle is subtracted from the valley value Va0 of the first ripple voltage Vripple of the previous switching cycle through the differentiator U202, and the absolute value is taken to obtain the voltage |Va1-Va0|. The voltage |Va1-Va0| is compared with the threshold voltage ΔV. If |Va1-Va0|>ΔV, the voltage V1 at the connection end of the first resistor R1 and the first capacitor C1 at this moment is pulled up or pulled down so that the absolute value of the difference between the first ripple voltage Vripple and Va1 at this moment is equal to the first threshold ΔV, and the first ripple voltage Vripple at this moment is sampled and held by the sample and hold device U201 as the valley voltage of the current cycle. Specifically, if Va1-Va0>ΔV, when the main power tube is turned on, the valley value of the first ripple voltage Vripple is pulled down to Va0+ΔV; if Va0-Va1>ΔV, when the main power tube is turned on, the valley value of the first ripple voltage Vripple is pulled up to Va0-ΔV; for the specific implementation method of pulling up and down the first ripple voltage Vripple, refer to the above description.

[0055] like Figure 5As shown in the waveform in, it illustrates the waveform of the switching circuit under the constant on-time control mode. When the output voltage drops, when the power tube is turned off, when Vpk1-Vpk0>ΔV, the peak value of the first ripple voltage Vripple is pulled down to Vpk0+ΔV. Specifically, a pull-down current can be generated by the limiting unit U204 to discharge the first capacitor C1, thereby pulling down the peak value of the first ripple voltage Vripple, and the pulled-down first ripple voltage Vripple is used as the peak voltage of the current cycle and is sampled and held by the sample-and-hold device.

[0056] like Figure 6 As shown in the waveform in, it illustrates the waveform of the switching circuit under the constant off-time control mode. When the output voltage drops, when the power tube is turned on, when Va1-Va0>ΔV, the first ripple voltage Vripple is pulled down to Va0+ΔV. Specifically, a pull-down current can be generated by the limiting unit U204 to discharge the first capacitor C1, thereby pulling down the first ripple voltage Vripple, and the pulled-down first ripple voltage Vripple is used as the valley voltage of the current cycle and is sampled and held by the sample-and-hold device.

[0057] 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 they can be replaced and integrated between the embodiments. For content that is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0058] The above-described embodiments do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the scope of protection of this technical solution.

Claims

1. A control circuit for a switching circuit, the switching circuit comprising a main power tube and an inductor connected thereto, the control circuit comprising: an operational amplifier, amplifying an error between an output feedback voltage of the switching circuit and a reference voltage to obtain a compensation voltage; a ripple generating circuit connected to the inductor, configured to generate a first ripple voltage in phase with the inductor current, and detect a change in a peak / valley value of the first ripple voltage when a load or input voltage of the switching circuit changes, and pull up or down the peak / valley value of the first ripple voltage when the change exceeds a first threshold; a first comparator, for comparing the sum of the first ripple voltage and the feedback voltage with the compensation voltage, and generating a trigger signal for controlling the main power tube to be turned on or off; The ripple generating circuit includes: a ripple generator connected in parallel across the inductor to obtain a first ripple voltage in phase with the inductor current; The limiting circuit is connected to the ripple generator, and detects the change of the first ripple voltage peak / valley value when the load or input voltage of the switching circuit changes. When the change exceeds a first threshold, the first ripple voltage peak / valley value is pulled up or down.

2. The control circuit of the switch circuit according to claim 1, wherein: The limiting circuit includes, a sample-and-hold device, sampling and holding the peak value of the first ripple voltage in each switching cycle; a difference circuit, subtracting a peak value of the first ripple voltage from a peak value of the first ripple voltage in a previous switching cycle and taking an absolute value to obtain the variation; a second comparator, for comparing the variation with a first threshold value to generate a comparison signal; The limiting unit receives the comparison signal, and when the comparison signal indicates that the change amount is greater than the first threshold, pulls up or pulls down the peak value of the first ripple voltage.

3. The control circuit of the switch circuit according to claim 1, wherein: The limiting circuit includes, A sample-and-hold device, which samples and holds the valley value of the first ripple voltage in each switching cycle; a difference circuit, subtracting a valley value of the first ripple voltage from a valley value of the first ripple voltage in a previous switching cycle and taking an absolute value to obtain the variation; a second comparator, for comparing the variation with a first threshold value to generate a comparison signal; The limiting unit receives the comparison signal, and when the comparison signal indicates that the change amount exceeds a first threshold, pulls up or pulls down the valley value of the first ripple voltage.

4. The control circuit of the switch circuit according to claim 1, wherein: The ripple generator comprises, a first resistor and a first capacitor, wherein a first end of the first resistor is connected to the first end of the inductor, a second end of the first resistor is connected to the first end of the first capacitor, and a second end of the first capacitor is connected to the second end of the inductor; A subtractor is configured to subtract the voltage at the common connection terminal of the first resistor and the first capacitor from the output voltage to obtain the first ripple voltage.

5. The control circuit of the switch circuit according to claim 1, wherein: It also includes an adaptive timer that controls the time when the main power tube is turned on or off according to the input voltage and the output voltage.

6. A method for controlling a switching circuit, applied to the control circuit of the switching circuit according to any one of claims 1 to 5, wherein the switching circuit comprises a main power transistor and an inductor connected thereto, comprising the following steps: Amplify the error between the output feedback voltage of the switching circuit and the reference voltage to obtain a compensation voltage; generating a first ripple voltage in phase with the inductor current, detecting a change in a peak / valley value of the first ripple voltage when a load or input voltage of the switching circuit changes, and pulling up or down the peak / valley value of the first ripple voltage when the change exceeds a first threshold; The sum of the first ripple voltage and the feedback voltage is compared with the compensation voltage to generate a trigger signal for controlling the main power tube to be turned on or off.

7. The method for controlling a switch circuit according to claim 6, wherein: The method for limiting the variation range of the first ripple voltage further includes the following steps: In each switching cycle, sampling and holding the peak value of the first ripple voltage; When the change is greater than the first threshold and the peak value of the first ripple voltage is less than the peak value of the first ripple voltage in the previous switching cycle, pulling down the peak value of the first ripple voltage to a first voltage, where the first voltage is the sum of the peak value of the first ripple voltage in the previous switching cycle and the first threshold; When the change is greater than the first threshold and the peak value of the first ripple voltage is greater than the peak value of the first ripple voltage in the previous switching cycle, pulling up the first ripple voltage to a second voltage, where the second voltage is the difference between the peak value of the first ripple voltage in the previous switching cycle and the first threshold; When the peak value of the first ripple voltage is pulled to the first voltage or the second voltage, the first voltage or the second voltage is sampled and held as the peak value of the first ripple voltage in the current switching cycle; the trigger signal controls the main power tube to turn on.

8. The method for controlling a switch circuit according to claim 6, wherein: The method for limiting the variation range of the first ripple voltage further includes the following steps: In each switching cycle, sampling and holding the peak value of the first ripple voltage; When the change is greater than the first threshold, and the valley value of the first ripple voltage is greater than the valley value of the first ripple voltage in the previous switching cycle, when the change is greater than the first threshold, the valley value of the first ripple voltage is pulled down to a third voltage, and the third voltage is the sum of the valley value of the first ripple voltage in the previous switching cycle and the first threshold; When the change is greater than the first threshold value, and the valley value of the first ripple voltage is less than the valley value of the first ripple voltage in the previous switching cycle, the valley value of the first ripple voltage is pulled up to a fourth voltage, where the fourth voltage is the difference between the valley value of the first ripple voltage in the previous switching cycle and the first threshold value; When the valley value of the first ripple voltage is pulled to the third voltage or the fourth voltage, the third voltage or the fourth voltage is sampled and held as the valley value of the first ripple voltage of the current switching cycle; and the trigger signal controls the main power tube to turn off.

9. The method for controlling a switch circuit according to claim 6, wherein: The time for the main power tube to be turned on or off is controlled according to the input voltage and the output voltage.

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