Overvoltage protection circuit and overvoltage protection method for switch circuit

Abstract

The present invention provides an overvoltage protection circuit and an overvoltage protection method for a switch circuit, wherein the overvoltage protection circuit comprises a charging circuit, a discharging circuit and a first capacitor, wherein the discharging circuit and the first capacitor form a parallel circuit, wherein the output end of the charging circuit is connected to the high potential end of the parallel circuit; the charging circuit and the discharging circuit are controlled to be turned on and off according to the topological structure and the switch state of the switch circuit; when the voltage of the first capacitor rises to a first threshold value, the overvoltage protection is triggered. The overvoltage protection circuit of the present invention has a fast response speed and is convenient for realizing different overvoltage settings.

Description

Technical Field

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

[0002] The schematic diagram of the overvoltage protection circuit of the switch circuit in the prior art is as follows: Figure 1 As shown, the switch circuit takes the Buck circuit as an example, and the overvoltage protection circuit includes a resistor R1 and a capacitor C1. When the main switch tube M01 of the Buck circuit is turned on, the supply voltage kVin representing the input voltage charges the first capacitor C1 through the first resistor R1; when the main switch tube M01 is turned off, the first capacitor C1 is discharged through the resistor R1. When the voltage V1 on the first capacitor C1 reaches the reference voltage VREF1, it represents the overvoltage of the load, and the main switch tube M01 is controlled to be turned off, triggering the overvoltage protection.

[0003] like Figure 2 Indicated with Figure 1 Corresponding to the working waveform of the overvoltage protection circuit, the energy charged by the first capacitor C1 when the main switch tube M01 is turned on is greater than the energy discharged when the main switch tube M01 is turned off, and the voltage V1 on the first capacitor C1 will gradually increase until it reaches the set value, and overvoltage protection is performed. The overvoltage protection response speed of the prior art is slow. Improving the overvoltage protection response speed will increase the power frequency ripple in the output signal of the switch circuit, and a larger filter circuit is required to suppress a larger power frequency ripple. Summary of the invention

[0004] An object of the present invention is to provide an overvoltage protection circuit and an overvoltage protection method for a switch circuit, so as to solve the problem of slow overvoltage protection response speed in the prior art.

[0005] To achieve the above-mentioned purpose, the present invention provides an overvoltage protection circuit for a switching circuit: comprising a charging circuit, a discharging circuit and a first capacitor, wherein the discharging circuit and the first capacitor form a parallel circuit, and the output end of the charging circuit is connected to the high potential end of the parallel circuit; the on and off of the charging circuit and the discharging circuit are controlled according to the topological structure and the switching state of the switching circuit; when the voltage of the first capacitor rises to a first threshold value, the overvoltage protection is triggered.

[0006] Optionally, the charging circuit and the discharging circuit output a charging current and a discharging current respectively, the charging current is proportional to the output voltage of the switching circuit, and the ratio is a first coefficient; the discharging current is proportional to a set overvoltage protection value, and the ratio is a second coefficient; the proportional relationship between the first coefficient and the second coefficient is set according to the topological structure of the switching circuit.

[0007] Optionally, if the switching circuit is a buck circuit, the first coefficient is equal to the second coefficient; the main switching tubes of the charging circuit and the buck circuit are turned on and off synchronously, and the discharging circuit is always on.

[0008] Optionally, if the switching circuit is a boost circuit, the first coefficient is equal to the second coefficient; the charging circuit is always on, and the on-off timing of the discharging circuit is opposite to the on-off timing of the main switch tube of the boost circuit.

[0009] Optionally, if the switching circuit is a buck-boost circuit or a Cook circuit, the first coefficient and the second coefficient are equal; when the main switch tube of the switching circuit is turned on, the charging circuit is turned on and the discharging circuit is turned off; when the main switch tube of the switching circuit is turned off, the charging circuit is turned off and the discharging circuit is turned on.

[0010] Optionally, if the switching circuit is a flyback conversion circuit, the ratio of the second coefficient to the first coefficient is equal to the primary-to-secondary turns ratio of the transformer in the flyback conversion circuit; when the main switch tube of the flyback conversion circuit is turned on, the charging circuit is turned on and the discharge circuit is turned off; when the main switch tube of the flyback conversion circuit is turned off, the charging circuit is turned off and the discharge circuit is turned on.

[0011] Optionally, the charging circuit includes a first current source and a first switch, the first current source and the first switch are connected in series, and the first current source outputs the charging current.

[0012] Optionally, the discharge circuit includes a second current source and a second switch, the second current source and the second switch are connected in series, and the second current source outputs the discharge current.

[0013] Optionally, the discharge circuit also includes a first resistor, the discharge current is a mirror current of the first resistor current, and the overvoltage protection value is adjusted by adjusting the resistance value of the first resistor.

[0014] The present invention also provides an overvoltage protection method for a switching circuit, wherein a discharge circuit and a first capacitor form a parallel circuit, and an output end of the charging circuit is connected to a high potential end of the parallel circuit; the on and off of the charging circuit and the discharge circuit are controlled according to the topological structure and the switching state of the switching circuit; when the voltage of the first capacitor rises to a first threshold value, overvoltage protection is triggered.

[0015] Optionally, the charging circuit and the discharging circuit output a charging current and a discharging current respectively, the charging current is proportional to the output voltage of the switching circuit, and the ratio is a first coefficient; the discharging current is proportional to the overvoltage protection value, and the ratio is a second coefficient; the proportional relationship between the first coefficient and the second coefficient is set according to the topological structure of the switching circuit.

[0016] Compared with the prior art, the present invention has the following advantages: the discharge circuit and the first capacitor form a parallel circuit, and the output end of the charging circuit is connected to the high potential end of the parallel circuit; the charging circuit and the discharge circuit are controlled to be on and off according to the topological structure and the switch state of the switch circuit; when the voltage of the first capacitor rises to the first threshold, the overvoltage protection is triggered; the charging circuit and the discharge circuit output charging current and discharging current respectively, and the charging current is proportional to the output voltage of the switch circuit, and the ratio is the first coefficient; the discharge current is proportional to the overvoltage protection value, and the ratio is the second coefficient; according to the topological structure of the switch circuit, the proportional relationship between the first coefficient and the second coefficient is set. The overvoltage protection circuit of the present invention has a wide range of applications, a fast response speed, and is convenient for setting different overvoltage protection values. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The schematic diagram of the overvoltage protection circuit of the prior art switch circuit is as follows;

[0018] Figure 2 The working waveform diagram of the overvoltage protection circuit in the prior art;

[0019] Figure 3 The schematic diagram of the overvoltage protection circuit of the switch circuit of the present invention;

[0020] FIG4( a ) is a schematic diagram of an embodiment of the present invention in which the switch circuit is a step-down circuit;

[0021] FIG4( b ) is a schematic diagram of an embodiment of the switch circuit of the present invention being a boost circuit;

[0022] FIG4( c ) is a schematic diagram of an embodiment of the switch circuit of the present invention being a buck-boost circuit;

[0023] FIG4( d ) is a schematic diagram of an embodiment of the present invention in which the switch circuit is a Cook circuit;

[0024] FIG4( e ) is a schematic diagram of an embodiment of the switch circuit of the present invention being a flyback circuit;

[0025] Figure 5 This is a working waveform diagram of the overvoltage protection circuit of the present invention; DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] 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.

[0029] like Figure 3 As shown, the schematic diagram of the overvoltage protection circuit of the switch circuit of the present invention is illustrated, and the overvoltage protection circuit includes a charging circuit, a discharging circuit, a first capacitor C1, a first comparator U1 and a driving circuit U2. The charging circuit includes a series circuit composed of a first current source I1 and a switch k1, wherein the discharging circuit includes a series circuit composed of a second current source I2 and a second switch k2, the output voltage of the second current source I2 is the mirror current of the current on the first resistor R1, and the output voltage of the second current source I1 is the output voltage of the discharge circuit. The preset overvoltage protection value can be flexibly set by adjusting the resistance value of the first resistor R1. The discharge circuit and the first capacitor C1 form a parallel circuit, the high potential output end of the parallel circuit is connected to the output end of the charging circuit, and the other end of the parallel circuit is grounded. The first comparator U1 receives the first capacitor voltage V1 at the same phase input end, receives the first threshold VREF1 at the inverting input end, and its output end is connected to the input end of the driving circuit U2, and the output end of the driving circuit U2 is connected to the control end of the main switch tube M01 in the switch circuit.

[0030] The output voltage of the first current source I1 is the charging current k1*Vin, k1 is the first coefficient, and Vin is the input voltage of the switching circuit; the output voltage of the second current source is the discharging current k2*Vovp, k2 is the second coefficient, and Vovp is the set overvoltage protection value; according to the topological structure and switching state of the switching circuit, the on and off of the charging circuit and the discharging circuit are controlled, that is, the on and off of the switch k1 and the switch k2 are controlled.

[0031] As shown in FIG4(a), a schematic diagram of an embodiment of the switch circuit of the present invention is a step-down circuit. When the switch circuit is a step-down circuit, the current coefficient k1=k2 in the overvoltage protection circuit, the charging circuit is turned on at the same time as the main switch M1 of the step-down circuit, and the discharge circuit is always on. When the charging circuit is turned on, part of the charging current k1*Vin charges the first capacitor C1, and part of it discharges the discharge circuit; when the charging circuit is turned off, the first capacitor C1 discharges to the discharge circuit. According to the working principle of the buck circuit, the output voltage satisfies VOUT=VIN*D>Vovp (D is the duty cycle of the main switch tube M1, and Vovp is the overvoltage protection value), then k1*VIN*ton>k2*Vovp*(ton+toff), then (k1*VIN-k2*Vovp)*ton>k2*Vovp*toff, which indicates that in one switching cycle, the charge amount of the first capacitor C1 is greater than the discharge amount of the first capacitor C1, and the voltage on the first capacitor C1 continues to rise. When the voltage V1 on the first capacitor reaches the first threshold VREF1, overvoltage protection is activated and the main switch M1 is turned off.

[0032] As shown in FIG4(b), the schematic diagram of the embodiment of the switch circuit of the present invention is a boost circuit. When the switch circuit is a boost circuit, the current coefficient k1=k2 in the overvoltage protection circuit, the charging circuit is always on, and the discharge circuit is turned on at the same time as the main switch M1 of the buck circuit. When the discharge circuit is turned on, part of the charging current k1*Vin charges the first capacitor C1, and part of it discharges the discharge circuit; when the discharge circuit is turned off, the charging current k1*Vin charges the first capacitor. According to the working principle of the boost circuit, the output voltage satisfies VOUT=VIN / (1-D)>Vovp (D is the duty cycle of the main switch tube M1, and Vovp is the overvoltage protection value), then k1*VIN*(ton+toff)>k2*Vovp*toff, which indicates that in a switching cycle, the charge amount of the first capacitor C1 is greater than the discharge amount of the first capacitor C1, and the voltage on the first capacitor C1 continues to rise. When the voltage V1 on the first capacitor reaches the first threshold VREF1, overvoltage protection is performed.

[0033] As shown in Figure 4 (c) and Figure 4 (d), the switching circuit of the present invention is a buck-boost circuit and a Cook circuit, respectively. The current coefficient k1=k2 in the corresponding overvoltage protection circuit. When the main switch tube of the switching circuit is turned on, the charging circuit is turned on and the discharging circuit is turned off; when the main switch tube of the switching circuit is turned off, the charging circuit is turned off and the discharging circuit is turned on. According to the working principle of the buck-boost circuit and the Cook circuit, the output voltage satisfies VOUT=VIN*D / (1-D)>Vovp (D is the duty cycle of the main switch tube M1, and Vovp is the overvoltage protection value), then k1*VIN*ton>k2*Vovp*toff, which indicates that in a switching cycle, the charge amount of the first capacitor C1 is greater than the discharge amount of the first capacitor C1, and the voltage on the first capacitor C1 continues to rise. When the voltage V1 on the first capacitor reaches the first threshold VREF1, overvoltage protection is performed.

[0034] As shown in FIG4(e), a schematic diagram of an embodiment of the switch circuit of the present invention is shown, and the current coefficient in the corresponding overvoltage protection circuit satisfies k1=k2*(N2 / N1), where N2 / N1 is the turns ratio between the secondary side and the primary side of the transformer in the flyback circuit. When the main switch tube of the flyback circuit is turned on, the charging circuit is turned on and the discharging circuit is turned off; when the main switch tube of the flyback circuit is turned off, the charging circuit is turned off and the discharging circuit is turned on. According to the working principle of the flyback circuit, the output voltage satisfies VOUT=VIN*(N2 / N1)*D / (1-D)>Vovp, then (N2 / N1)*VIN*ton>Vovp*toff, then k2*(N2 / N1)*VIN*ton>k2*Vovp*toff, that is, k1*VIN*ton>k2*Vovp*toff, which indicates that in one switching cycle, the charge amount of the first capacitor C1 is greater than the discharge amount of the first capacitor C1, and the voltage on the first capacitor C1 continues to rise. When the voltage V1 on the first capacitor reaches the first threshold VREF1, overvoltage protection is activated.

[0035] like Figure 5 As shown, the working waveform diagram of the overvoltage protection circuit of the present invention is illustrated. The upper waveform in the figure is the working waveform of the inductor current iL in the switch circuit, and the lower waveform in the figure is the waveform of the first capacitor voltage V1. In the initial charging process of the first capacitor C1, the charge of the first capacitor C1 is discharged without the end of a switching cycle. When the output voltage Vout is greater than the overvoltage protection value Vovp, according to the above analysis, the charge amount on the first capacitor is greater than its discharge amount, and the voltage V1 of the first capacitor C1 will be gradually raised. When the voltage V1 of the first capacitor C1 rises to the first threshold VREF1, overvoltage protection is performed.

[0036] 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.

[0037] 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. An overvoltage protection circuit for a switch circuit, characterized in that: It comprises a charging circuit for outputting a charging current, a discharging circuit for outputting a discharging current and a first capacitor, wherein the charging current is proportional to the input voltage of the switching circuit and the ratio is a first coefficient, the discharging current is proportional to the set overvoltage protection value and the ratio is a second coefficient, the discharging circuit and the first capacitor form a parallel circuit, and the output end of the charging circuit is connected to the high potential end of the parallel circuit; the on-off of the charging circuit and the discharging circuit are controlled according to the topological structure and the switching state of the switching circuit, and the proportional relationship between the first coefficient and the second coefficient is set according to the topological structure of the switching circuit; when the voltage of the first capacitor rises to a first threshold value, the overvoltage protection is triggered.

2. The overvoltage protection circuit of the switch circuit according to claim 1, characterized in that: If the switch circuit is a buck circuit, the first coefficient is equal to the second coefficient, the charging circuit and the main switch tube of the buck circuit are switched on and off synchronously, and the discharge circuit is always on.

3. The overvoltage protection circuit of the switch circuit according to claim 1, characterized in that: If the switch circuit is a boost circuit, the first coefficient is equal to the second coefficient; the charging circuit is always on, and the on-off timing of the discharge circuit is opposite to the on-off timing of the main switch tube of the boost circuit.

4. The overvoltage protection circuit of the switch circuit according to claim 1, characterized in that: If the switching circuit is a buck-boost circuit or a Cook circuit, the first coefficient is equal to the second coefficient; when the main switch tube of the switching circuit is turned on, the charging circuit is turned on and the discharging circuit is turned off; when the main switch tube of the switching circuit is turned off, the charging circuit is turned off and the discharging circuit is turned on.

5. The overvoltage protection circuit of the switch circuit according to claim 1, characterized in that: If the switching circuit is a flyback conversion circuit, the ratio of the second coefficient to the first coefficient is equal to the primary-to-secondary turns ratio of the transformer in the flyback conversion circuit; when the main switch tube of the flyback conversion circuit is turned on, the charging circuit is turned on and the discharging circuit is turned off; when the main switch tube of the flyback conversion circuit is turned off, the charging circuit is turned off and the discharging circuit is turned on.

6. The overvoltage protection circuit of the switch circuit according to any one of claims 1 to 5, characterized in that: The charging circuit includes a first current source and a first switch, wherein the first current source and the first switch are connected in series, and the first current source outputs the charging current.

7. The overvoltage protection circuit of the switch circuit according to claim 6, characterized in that: The discharge circuit includes a second current source and a second switch, the second current source and the second switch are connected in series, and the second current source outputs the discharge current.

8. The overvoltage protection circuit of the switch circuit according to claim 7, characterized in that: The discharge circuit further includes a first resistor, the discharge current is a mirror current of the first resistor current, and the overvoltage protection value is adjusted by adjusting the resistance value of the first resistor.

9. A method for overvoltage protection of a switching circuit, characterized in that: The discharge circuit and the first capacitor form a parallel circuit, the output end of the charging circuit is connected to the high potential end of the parallel circuit, the charging circuit and the discharge circuit output a charging current and a discharging current respectively, the charging current is proportional to the input voltage of the switching circuit and the ratio is a first coefficient, the discharging current is proportional to the set overvoltage protection value and the ratio is a second coefficient; the on and off of the charging circuit and the discharging circuit are controlled according to the topological structure and the switching state of the switching circuit, and the proportional relationship between the first coefficient and the second coefficient is set according to the topological structure of the switching circuit; when the voltage of the first capacitor rises to a first threshold, the overvoltage protection is triggered.

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