Search

CN-116365477-B - Switch protection method and circuit for flyback converter and flyback switching power supply

CN116365477BCN 116365477 BCN116365477 BCN 116365477BCN-116365477-B

Abstract

A switching protection method for flyback converter includes sampling preset parameters of flyback converter at same sampling interval time in on period of the first switching tube, taking average value of m times of sampled values as first sampling signal, taking m+i times of sampled values as second sampling signal, increasing i from 1, comparing each second sampling signal with the first sampling signal in turn, outputting protection signal when value of the second sampling signal is smaller than product of comparison coefficient and the first sampling signal, turning off the first switching tube, representing that the first switching tube reaches saturated state, comparing coefficient is larger than 0 and smaller than 1, enabling the protection signal to represent that the first switching tube reaches saturated state, enabling the switching tube to be turned off in time when the switching tube reaches saturated state without sampling source-drain voltage of the first switching tube, and avoiding damage to the switching tube caused by overlarge loss due to saturation of the switching tube.

Inventors

  • XU XIANGYONG

Assignees

  • 杰华特微电子股份有限公司

Dates

Publication Date
20260512
Application Date
20221128

Claims (13)

  1. 1. The switching protection method of the flyback converter is used for carrying out saturation protection on a first switching tube of a primary side in the flyback converter, wherein the flyback converter comprises a primary side winding and a secondary side winding, the first switching tube is grounded through a sampling resistor, and the switching protection method comprises the following steps: Sampling the preset parameters of the flyback converter at the same sampling interval time in the on period of the first switching tube; Setting an initial opening interval, finishing m times of sampling before finishing in the initial opening interval, and performing m+i times of sampling outside the initial opening interval, wherein the initial opening interval is a preset time period after the first switching tube is conducted for a period of time; Taking the average value of the values of the previous m times of sampling as a first sampling signal, taking the value of the (m+i) th time of sampling as a second sampling signal, and increasing i from 1; comparing each of the second sampled signals with the first sampled signal in turn; when the value of the second sampling signal is smaller than the product of the comparison coefficient and the first sampling signal, outputting a protection signal to control the first switching tube to be turned off, The flyback converter further comprises an auxiliary winding, wherein the comparison coefficient is larger than 0 and smaller than 1, the preset parameter is current flowing through the auxiliary winding, and the current flowing through the auxiliary winding represents the source-drain voltage at two ends of the first switching tube.
  2. 2. The switch protection method of claim 1, wherein the protection signal characterizes an increase in source-drain voltage of the first switching tube during conduction, the first switching tube being saturated.
  3. 3. The switch protection method according to claim 1, wherein when the predetermined parameter is a current flowing through the auxiliary winding, a sampling point is at a connection point of a first resistor and a second resistor connected in series to the auxiliary winding, and a voltage at the sampling point is clamped at a low voltage.
  4. 4. The switching protection method of the flyback converter is used for carrying out saturation protection on a first switching tube of a primary side in the flyback converter, wherein the flyback converter comprises a primary side winding and a secondary side winding, the first switching tube is grounded through a sampling resistor, and the switching protection method comprises the following steps: Sampling the preset parameters of the flyback converter at the same sampling interval time in the on period of the first switching tube; Setting an initial opening interval, finishing m times of sampling before finishing in the initial opening interval, and performing m+i times of sampling outside the initial opening interval, wherein the initial opening interval is a preset time period after the first switching tube is conducted for a period of time; Taking the average value of the values of the previous m times of sampling as a first sampling signal, taking the value of the (m+i) th time of sampling as a second sampling signal, and increasing i from 1; comparing each of the second sampled signals with the first sampled signal in turn; when the value of the second sampling signal is smaller than the product of the comparison coefficient and the first sampling signal, outputting a protection signal to control the first switching tube to be turned off, The comparison coefficient is greater than 0 and less than 1, the preset parameter is the slope of the sampling voltage on the sampling resistor, and the slope of the sampling voltage represents the change rate of the primary inductor current.
  5. 5. The switch protection method of claim 4, wherein the protection signal characterizes an increase in source-drain voltage of the first switching tube during conduction, the first switching tube saturating.
  6. 6. The switch protection method according to claim 4, wherein when the predetermined parameter is a slope of a sampling voltage on the sampling resistor, a sampling point is a connection point between the sampling resistor and the first switching tube, and the sampling voltage is a voltage value of a voltage across the sampling resistor after filtering.
  7. 7. A switch protection circuit of flyback converter for saturation protection is carried out to the first switching tube of primary side in flyback converter, wherein, flyback converter includes primary side winding and vice side winding, first switching tube passes through sampling resistor ground connection, switch protection circuit connects sampling resistor with between the first switching tube, switch protection circuit includes: the sampling module samples the preset parameters of the flyback converter at the same sampling interval time in the conduction period of the first switching tube, finishes the previous m times of sampling in an initial opening interval, and performs the (m+i) th time of sampling outside the initial opening interval, wherein the initial opening interval is a preset time period after the first switching tube is conducted for a period of time; The comparison module is connected with the sampling module and is used for sequentially comparing each second sampling signal with the first sampling signal, and outputting a protection signal when the value of the second sampling signal is smaller than the product of the comparison coefficient and the first sampling signal; The driving module is connected with the comparison module and the control end of the first switching tube, receives the protection signal and outputs a driving signal to control the first switching tube to be turned off, Wherein the comparison coefficient is larger than 0 and smaller than 1, the flyback converter further comprises an auxiliary winding, The predetermined parameter sampled by the sampling module from the first sampling point is the current flowing through the auxiliary winding, and the magnitude of the current flowing through the auxiliary winding represents the magnitude of the source-drain voltage at two ends of the first switch tube.
  8. 8. The switch protection circuit of claim 7, further comprising: And the source electrode of the second switching tube is connected at the connection point of the first resistor and the second resistor which are connected in series and are connected with the auxiliary winding, the drain electrode of the second switching tube is grounded, and the control electrode of the second switching tube receives the same driving signal as the first switching tube.
  9. 9. The switch protection circuit of claim 8, wherein the second switch tube is turned on during the first switch tube conduction period clamping the voltage at the first resistor and the second resistor connection point at a low voltage, and the first resistor and the second resistor connection point is the first sampling point.
  10. 10. A switch protection circuit of flyback converter for saturation protection is carried out to the first switching tube of primary side in flyback converter, wherein, flyback converter includes primary side winding and vice side winding, first switching tube passes through sampling resistor ground connection, switch protection circuit connects sampling resistor with between the first switching tube, switch protection circuit includes: the sampling module samples the preset parameters of the flyback converter at the same sampling interval time in the conduction period of the first switching tube, finishes the previous m times of sampling in an initial opening interval, and performs the (m+i) th time of sampling outside the initial opening interval, wherein the initial opening interval is a preset time period after the first switching tube is conducted for a period of time; The comparison module is connected with the sampling module and is used for sequentially comparing each second sampling signal with the first sampling signal, and outputting a protection signal when the value of the second sampling signal is smaller than the product of the comparison coefficient and the first sampling signal; The driving module is connected with the comparison module and the control end of the first switching tube, receives the protection signal and outputs a driving signal to control the first switching tube to be turned off, The comparison coefficient is larger than 0 and smaller than 1, the predetermined parameter sampled by the sampling module from the second sampling point is the slope of the sampling voltage on the sampling resistor, and the slope of the sampling voltage represents the change rate of the primary side inductance current.
  11. 11. The switch protection circuit of claim 10, wherein a filter is connected at a connection point of the sampling resistor and the first switching tube, and the connection point of the filter and the sampling module is the second sampling point.
  12. 12. A flyback switching power supply comprises a transformer, a primary winding, a secondary winding and an auxiliary winding, wherein the auxiliary winding is coupled with the secondary winding or the primary winding, a first switching tube is connected to the primary winding and is grounded through a sampling resistor, and the flyback switching power supply further comprises a switching protection circuit of a flyback converter according to any one of claims 7-9, wherein the switching protection circuit of the flyback converter is used for controlling the conduction state of the first switching tube and performing saturation protection on the first switching tube.
  13. 13. A flyback switching power supply comprises a transformer, a primary winding and a secondary winding, wherein the secondary winding is coupled with the primary winding, a first switching tube is connected to the primary winding and is grounded through a sampling resistor, and the flyback switching power supply further comprises a switching protection circuit of a flyback converter according to any one of claims 10-11, wherein the switching protection circuit of the flyback converter is used for controlling the conduction state of the first switching tube and conducting saturation protection on the first switching tube.

Description

Switch protection method and circuit for flyback converter and flyback switching power supply Technical Field The application relates to the technical field of power electronics, in particular to a switch protection method of a flyback converter, a protection circuit and a flyback switching power supply. Background With the high-speed development of electronic systems, demands of high-power-density and high-efficiency switching power supply converters are increasing, and flyback switching power supplies, forward switching power supplies, double-clamp ZVS converters and the like are widely researched and applied due to excellent characteristics of high efficiency, full-range soft switching, adaptation to high switching frequency and the like. The common flyback switching power supply topological structure comprises a transformer, a primary winding and a secondary winding, wherein a main power switching tube is connected with the primary winding, a secondary rectifying tube is connected with the secondary winding, and the primary side and the secondary side control the switching tube to be turned on and off through respective control circuits. In a current-mode controlled power supply, a peak current is usually set to limit the peak current of a primary winding and a switching transistor of a transformer, and a GaN transistor is often used as a primary or secondary switching transistor at present, but the saturation current of the GaN transistor is smaller than that of the Si transistor. When the saturation current specification of the GaN transistor is smaller, the saturation current of some switching transistors may be even smaller than the set peak current, so that the GaN transistor may reach saturation quickly under the transient or dynamic working condition of the power supply, resulting in the increase of the drain-source voltage of the transistor, the rapid increase of the loss of the switching transistors, and the overheat damage. In order to avoid the damage caused by transistor saturation, a high-voltage device is generally added in a primary side control chip, and the on or off of the switching tube is controlled by detecting the source-drain voltages at two ends of the switching tube, so that the device cost is too high, and the high-voltage device is wasted. Disclosure of Invention In order to solve the technical problems, the application provides a switch protection method, a switch protection circuit and a flyback switching power supply of a flyback converter, which can timely detect that a power tube is saturated and turn off so as to solve the problems in the prior art. According to a first aspect of the present invention, there is provided a switching protection method for a flyback converter for saturation protection of a primary side first switching tube in the flyback converter, wherein the flyback converter includes a primary side winding and a secondary side winding, the first switching tube is grounded through a sampling resistor, the switching protection method includes: Sampling the preset parameters of the flyback converter at the same sampling interval time in the on period of the first switching tube; Taking the average value of the values of the previous m times of sampling as a first sampling signal, taking the value of the (m+i) th time of sampling as a second sampling signal, and increasing i from 1; comparing each of the second sampled signals with the first sampled signal in turn; when the value of the second sampling signal is smaller than the product of the comparison coefficient and the first sampling signal, outputting a protection signal to control the first switching tube to be turned off, Wherein the comparison coefficient is greater than 0 and less than 1. Optionally, the switch protection method further includes: Setting an initial opening interval, finishing m times of sampling before finishing in the initial opening interval, and performing m+i times of sampling outside the initial opening interval, wherein the initial opening interval is a preset time period after the first switching tube is conducted for a period of time. Optionally, the flyback converter includes an auxiliary winding, the predetermined parameter is a current flowing through the auxiliary winding, and a magnitude of the current flowing through the auxiliary winding is indicative of a magnitude of a source-drain voltage across the first switching tube. Optionally, the predetermined parameter is a slope of a sampled voltage across the sampling resistor, and the slope of the sampled voltage is indicative of a rate of change of the primary inductor current. Optionally, the protection signal characterizes an increase in source-drain voltage of the first switching tube during conduction, and the first switching tube is saturated. Optionally, when the predetermined parameter is a current flowing through the auxiliary winding, the sampling point is a connection point of a first resistor and a second re