Secondary side controller applied to flyback power converter and operation method thereof

Abstract

The invention discloses a secondary side controller applied to a flyback power converter. The secondary side controller comprises a first comparison circuit, a second comparison circuit and a grid control signal generation circuit. The first comparison circuit generates a first comparison signal according to a drain voltage of a synchronous switch on a secondary side of the flyback power converter and a first parameter. The second comparison circuit generates a ready signal according to the first comparison signal and the resistance value of the external resistor. The gate control signal generating circuit generates a gate control signal to the synchronous switch according to the ready signal and the drain voltage. Therefore, the resonance shielding time can be maximized according to the starting time of the power switch in the previous period, the resonance interval of the drain voltage can be judged more accurately, and the secondary side of the flyback power converter can be prevented from being mistakenly conducted so as to improve the stability of the flyback power converter.

Description

Technical Field

[0001] The present invention relates to a secondary side controller applied to a flyback power converter and an operating method thereof, and more particularly to a secondary side controller for preventing the secondary side of the flyback power converter from being mis-conducted and an operating method thereof. Background Art

[0002] After the synchronous switch on the secondary side of the flyback power converter is turned off, the drain voltage of the synchronous switch will begin to resonate. If the resonance convergence speed or amplitude of the drain voltage is too large, the secondary side controller set on the secondary side of the flyback power converter may misjudge and cause the synchronous switch to be turned on by mistake. If the primary side of the flyback power converter also meets the conduction condition at this time, it will cause the primary side of the flyback power converter and the secondary side of the flyback power converter to be short-circuited (Short-Through).

[0003] The prior art provides a fixed blanking time during the resonance period of the drain voltage so that the secondary side controller will not turn on the synchronous switch during the resonance period of the drain voltage, resulting in a short circuit between the primary side of the flyback power converter and the secondary side of the flyback power converter. However, during the resonance period of the drain voltage, the resonance convergence speed or amplitude of the drain voltage will be affected by the load of the flyback power converter, so the fixed blanking time may not be able to respond to the change of the load, resulting in the possibility that the synchronous switch may still be turned on by mistake. Therefore, how to improve the shortcomings of the above-mentioned prior art has become an important issue for the designers of the secondary side controller. Summary of the invention

[0004] An embodiment of the present invention discloses a secondary side controller applied to a flyback power converter, wherein the secondary side controller prevents the secondary side of the flyback power converter from being mis-turned on. The secondary side controller includes a first comparison circuit, a second comparison circuit, and a gate control signal generating circuit. The first comparison circuit is used to generate a first comparison signal according to a drain voltage of a synchronous switch on the secondary side of the flyback power converter and a first parameter. The second comparison circuit is coupled to the first comparison circuit and is used to generate a ready signal according to the first comparison signal and the resistance value of an external resistor. The gate control signal generating circuit is coupled to the second comparison circuit and is used to generate a gate control signal to the synchronous switch according to the ready signal and the drain voltage, wherein the synchronous switch is turned on according to the gate control signal.

[0005] Another embodiment of the present invention discloses an operating method for a secondary side controller applied to a flyback power converter, wherein the secondary side controller comprises a first comparison circuit, a second comparison circuit and a gate control signal generating circuit. The operating method comprises the first comparison circuit generating a first comparison signal according to a drain voltage of a synchronous switch on the secondary side of the flyback power converter and a first parameter; the second comparison circuit generating a ready signal according to the first comparison signal and a resistance value of an external resistor; and the gate control signal generating circuit generating a gate control signal to the synchronous switch according to the ready signal and the drain voltage, wherein the synchronous switch is turned on according to the gate control signal.

[0006] The present invention discloses a secondary side controller and an operating method thereof applied to a flyback power converter. The secondary side controller and the operating method can adjust the length of the resonance shielding time of the drain voltage of a synchronous switch corresponding to the secondary side of the flyback power converter along with the opening time of the power switch on the secondary side of the flyback power converter in the previous cycle, so after the drain voltage starts to resonate, the synchronous switch will not be turned on due to the resonance of the drain voltage to ensure that the primary side of the flyback power converter and the secondary side of the flyback power converter will not be turned on at the same time. Therefore, compared with the prior art, the present invention can maximize the resonance shielding time through the opening time of the power switch in the previous cycle, more accurately judge the resonance interval of the drain voltage, and avoid the secondary side of the flyback power converter from being mis-conducted to improve the stability of the flyback power converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic diagram of a secondary side controller applied to a flyback power converter disclosed in the first embodiment of the present invention.

[0008] Figure 2 It is a flow chart of an operation method of a secondary side controller applied to a flyback power converter disclosed in the second embodiment of the present invention.

[0009] Figure 3 is a schematic diagram illustrating a drain voltage of a synchronous switch, a reference voltage, a count signal, a reference count, a ready signal, a gate control signal of the synchronous switch, and a sampled voltage.

[0010] The reference numerals are described as follows:

[0011] 100 Flyback Power Converter

[0012] 102 Primary winding

[0013] 104 Power switch

[0014] 106 Resistors

[0015] 108 Secondary winding

[0016] 200 Secondary side controller

[0017] 202 First comparison circuit

[0018] 204 Second comparison circuit

[0019] 206 Gate control signal generating circuit

[0020] 208 Synchronous switch

[0021] 210 External resistor

[0022] 212, 214, 216, 218, 220 pins

[0023] 222 Optocoupler

[0024] 2022 Sample and hold circuit

[0025] 2024 First adjustment circuit

[0026] 2026 First Comparator

[0027] 2042 Counter

[0028] 2044 Second adjustment circuit

[0029] 2046 Second Comparator

[0030] DRV, GCS gate control signal

[0031] FCS first comparison signal

[0032] GND1, GND2 Ground level

[0033] PRI Primary Side

[0034] POS ready signal

[0035] SEC Secondary Side

[0036] TPLAT counting signal

[0037] TQR Reference Count

[0038] T1-T5 time

[0039] VDET Drain voltage

[0040] VOUT Output voltage

[0041] VCC Operating Voltage

[0042] VDSPLAT sampling voltage

[0043] VPLAT reference voltage

[0044] Steps 300-314 DETAILED DESCRIPTION

[0045] Please refer to Figure 1 , Figure 1 1 is a schematic diagram of a secondary side controller 200 applied to a flyback power converter 100 disclosed in the first embodiment of the present invention, wherein the secondary side controller 200 is used to prevent the secondary side SEC of the flyback power converter 100 from being mis-conducted, and the flyback power converter 100 operates in a quasi-resonance mode. In addition, because the present invention is about the secondary side controller 200 set on the secondary side SEC of the flyback power converter 100, rather than the primary side controller set on the primary side PRI of the flyback power converter 100, for the sake of simplicity Figure 1 ,exist Figure 1 The primary side PRI of the flyback power converter 100 only shows the primary side winding 102, a power switch 104 and a resistor 106. Figure 1 As shown, the secondary side controller 200 at least includes a first comparison circuit 202, a second comparison circuit 204 and a gate control signal generating circuit 206, wherein the first comparison circuit 202 includes a sample-and-hold circuit 2022, a first adjustment circuit 2024 and a first comparator 2026, and the second comparison circuit 204 includes a counter 2042, a second adjustment circuit 2044 and a second comparator 2046. In addition, the coupling relationship between the primary side winding 102, a power switch 104 and the resistor 106, and the coupling relationship between the first comparison circuit 202, the second comparison circuit 204, the gate control signal generating circuit 206, the sample-and-hold circuit 2022, the first adjustment circuit 2024, the first comparator 2026, the counter 2042, the second adjustment circuit 2044 and the second comparator 2046 can be referred to. Figure 1 In addition, the ground level GND1 of the primary side PRI of the flyback power converter 100 is different from the ground level GND2 of the secondary side SEC of the flyback power converter 100 .

[0046] In addition, please refer to Figure 1 , Figure 2 and Figure 3 , Figure 2is a flow chart of an operation method of a secondary-side controller 200 applied to a flyback power converter 100 disclosed in a second embodiment of the present invention.

[0047] Figure 2 The method of operation is to use Figure 1 The flyback power converter 100 and the secondary side controller 200 are described in detail as follows:

[0048] Step 300: A synchronous switch 208 disposed on the secondary side SEC of the flyback power converter 100 is turned off;

[0049] Step 302: Whether the drain voltage VDET of the synchronous switch 208 is greater than a reference voltage VPLAT;

[0050] If yes, proceed to step 304; if no, proceed to step 302 again;

[0051] Step 304: The counter 2042 generates a counting signal TPLAT according to a first comparison signal FCS generated by the first comparator 2026;

[0052] Step 306: After the drain voltage VDET is less than the reference voltage VPLAT, is the counting signal TPLAT greater than a reference count TQR? If yes, proceed to step 308; if no, proceed to step 312;

[0053] Step 308: The second comparator 2046 generates a ready signal POS and the counter 2042 is reset.

[0054] The counting signal TPLAT, and the second adjustment circuit 2044 updates the reference count TQR;

[0055] Step 310: The gate control signal generating circuit 206 generates a gate control signal according to the ready signal POS and the drain voltage VDET.

[0056] Generate a gate control signal DRV to the synchronous switch 208, and jump back to step 300;

[0057] Step 312: The second comparator 2046 does not generate the ready signal POS, the counter 2042 resets the counting signal TPLAT, and the second adjustment circuit 2044 does not update the reference count TQR, and the process returns to step 300;

[0058] Step 314 : After the second adjustment circuit 2044 does not update the reference count TQR again, the second adjustment circuit 2044 forces the reference count TQR to be updated and jumps back to step 300 .

[0059] In step 300, please also refer to Figure 1 and Figure 3 ,like Figure 3 At time T1 shown, the gate control signal GCS for controlling the power switch 104 of the primary side PRI of the flyback power converter 100 to turn on is enabled, so the power switch 104 is turned on, wherein the drain voltage VDET changes with the gate control signal GCS due to the coupling effect between the primary winding 102 and the secondary winding 108 .

[0060] In step 302, please also refer to Figure 1 and Figure 3 Before time T1, if the count signal TPLAT generated by the counter 2042 is greater than the reference count TQR generated by the second adjustment circuit 2044, the second adjustment circuit 2044 can update the reference count TQR according to the turn-on time of the power switch 104 before time T1 (corresponding to the count signal TPLAT before time T1) through the resistance value of an external resistor 210 outside the secondary side controller 200, wherein the reference count TQR=count signal TPLAT*K2, and K2 is controlled by the resistance value of the external resistor 210, and the adjustment circuit 2044 is coupled to the external resistor 210 through the pin 216 of the secondary side controller 200. That is to say, the reference count TQR is related to the turn-on time of the power switch 104 in the previous cycle. In addition, before time T1, if the count signal TPLAT generated by the counter 2042 is greater than the reference count TQR generated by the second adjustment circuit 2044, the first adjustment circuit 2044 can update the reference voltage VPLAT according to the current sample voltage VDSPLAT generated by the sample-and-hold circuit 2022 and a first parameter K1, wherein the first parameter K1 is generated from inside the secondary-side controller 200, and the sample-and-hold circuit 2022 receives the drain voltage VDET through the pin 212 of the secondary-side controller 200.

[0061] Therefore, please also refer to Figure 1 and Figure 3 In step 304, at time T1, the first comparator 2026 compares the current drain voltage VDET with the reference voltage VPLAT generated before time T1, and generates a first comparison signal FCS when the current drain voltage VDET is greater than the reference voltage VPLAT generated before time T1, wherein the first comparator 2026 receives the drain voltage VDET through the pin 212 of the secondary side controller 200. The counter 2042 can start to generate the counting signal TPLAT according to the first comparison signal FCS.

[0062] Please also refer to Figure 1 and Figure 3In step 308, at time T2, because the current count signal TPLAT is greater than the reference count TQR (at this time, the reference count TQR is related to the turn-on time of the power switch 104 in the previous cycle (before time T1)), the second comparator 2046 generates a ready signal POS, the counter 2042 resets the count signal TPLAT, and the second adjustment circuit 2044 updates the reference count TQR (at this time, the reference count TQR is related to the turn-on time of the power switch 104 between time T1 and time T2).

[0063] Please also refer to Figure 1 and Figure 3 In step 310, at time T2, after the gate control signal generating circuit 206 receives the ready signal POS and when the drain voltage VDET is less than a determination voltage (e.g., -0.1V), the gate control signal generating circuit 206 generates a gate control signal DRV to the synchronous switch 208, wherein the gate control signal generating circuit 206 receives the drain voltage VDET through the pin 212 of the secondary side controller 200 and transmits the gate control signal DRV to the synchronous switch 208 through the pin 214 of the secondary side controller 200, and the synchronous switch 208 can be turned on according to the gate control signal DRV.

[0064] In addition, in step 300, if Figure 3 As shown, at time T3, the synchronous switch 208 is turned off, wherein after the synchronous switch 208 is turned off, the drain voltage VDET begins to resonate. Figure 3 As shown, at time T4, the first comparator 2026 compares the current drain voltage VDET with the reference voltage VPLAT generated before time T3, and generates a first comparison signal FCS when the current drain voltage VDET is greater than the reference voltage VPLAT generated before time T3, wherein the first comparator 2026 receives the drain voltage VDET through the pin 212 of the secondary side controller 200. The counter 2042 can generate a counting signal TPLAT according to the first comparison signal FCS.

[0065] In step 312, at time T5, because the current count signal TPLAT is less than the reference count TQR (the reference count TQR is related to the turn-on time of the power switch 104 between time T1 and time T2), the second comparator 2046 does not generate the ready signal POS, the counter 2042 resets the count signal TPLAT, and the second adjustment circuit 2044 does not update the reference count TQR. Because the second comparator 2046 does not generate the ready signal POS, the gate control signal generating circuit 206 does not generate the gate control signal DRV to the synchronous switch 208. In other words, because the reference count TQR (corresponding to the length of the resonance shielding time of the drain voltage VDET) can be adjusted with the turn-on time of the power switch 104 in the previous cycle, after the drain voltage VDET starts to resonate, the synchronous switch 208 will not be turned on due to the resonance of the drain voltage VDET to ensure that the primary side PRI of the flyback power converter 100 and the secondary side SEC of the flyback power converter 100 will not be turned on at the same time.

[0066] In step 314, if the load (not shown) of the secondary side SEC of the flyback power converter 100 is Figure 1 ) is a light load or the voltage of the load changes too much instantaneously, so that the second adjustment circuit 2044 does not update the reference count TQR again, step 302 is re-executed. In addition, in another embodiment of the present invention, when the second adjustment circuit 2044 does not update the reference count TQR for more than two times (for example, three times, four times, five times, etc.) in a row, step 302 is re-executed. That is, when the load is a light load or the voltage of the load changes too much instantaneously, step 314 can ensure that the flyback power converter 100 operates normally.

[0067] In addition, please refer to Figure 1 , the secondary side controller 200 can receive the ground level GND2 and an operating voltage VCC through the pin 218 and the pin 220 respectively. In addition, in one embodiment of the present invention, a primary side controller (not shown) Figure 1 ) can know the state of the output voltage VOUT of the secondary side SEC of the flyback power converter 100 through an optical coupler 222, and decide whether to generate a gate control signal GCS to the power switch 104 to turn on the primary side PRI of the flyback power converter 100 according to the state of the output voltage VOUT.

[0068] In summary, because the secondary side controller and its operation method disclosed in the present invention can adjust the reference count (corresponding to the length of the resonance shielding time of the drain voltage) along with the opening time of the power switch in the previous cycle, after the drain voltage starts to resonate, the synchronous switch will not be turned on due to the resonance of the drain voltage to ensure that the primary side of the flyback power converter and the secondary side of the flyback power converter will not be turned on at the same time. Therefore, compared with the prior art, the present invention can maximize the resonance shielding time through the opening time of the power switch in the previous cycle, more accurately determine the resonance interval of the drain voltage, and avoid the secondary side of the flyback power converter from being mis-conducted to improve the stability of the flyback power converter.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A secondary side controller for a flyback power converter, wherein the secondary side controller prevents the secondary side of the flyback power converter from being mis-conducted, characterized in that Include: a first comparison circuit for generating a first comparison signal according to a drain voltage of a synchronous switch on the secondary side of the flyback power converter and a first parameter; a second comparison circuit, coupled to the first comparison circuit, for generating a ready signal according to the first comparison signal and a resistance value of an external resistor; and A gate control signal generating circuit is coupled to the second comparison circuit, and is used to generate a gate control signal to the synchronous switch according to the ready signal and the drain voltage, wherein the synchronous switch is turned on according to the gate control signal.

2. The secondary side controller according to claim 1, characterized in that The first comparison circuit includes: a sample-and-hold circuit for generating a sample voltage according to the drain voltage; a first adjustment circuit, coupled to the sample-and-hold circuit, for updating a reference voltage according to the sampled voltage and the first parameter, wherein the first parameter is generated from within the secondary-side controller; and A first comparator is coupled to the synchronous switch and the first adjustment circuit, and is used for generating the first comparison signal when the drain voltage is greater than the reference voltage.

3. The secondary side controller according to claim 1, characterized in that The second comparison circuit includes: a counter coupled to the first comparison circuit, for generating a counting signal according to the first comparison signal; a second adjustment circuit, coupled to the first comparison circuit and the external resistor, for updating a reference count according to the first comparison signal and the resistance value of the external resistor; and A second comparator is coupled to the counter and the second adjustment circuit, and is used to generate the ready signal when the drain voltage is less than a reference voltage and the counting signal is greater than the reference count, wherein the counter resets the counting signal when the drain voltage is less than the reference voltage and the counting signal is greater than the reference count.

4. The secondary side controller according to claim 3, characterized in that After the drain voltage is less than the reference voltage and the counting signal is less than the reference count, the counter resets the counting signal and the second adjustment circuit does not update the reference count.

5. The secondary side controller according to claim 4, characterized in that After the reference count is not updated for more than two consecutive times, the second adjustment circuit updates the reference count.

6. The secondary side controller according to claim 1, characterized in that When the gate control signal generating circuit receives the ready signal and the drain voltage is less than a determination voltage, the gate control signal generating circuit generates the gate control signal to the synchronous switch.

7. The secondary side controller according to claim 1, characterized in that The flyback power converter operates in a quasi-resonant mode.

8. An operating method of a secondary side controller for a flyback power converter, wherein the secondary side controller comprises a first comparison circuit, a second comparison circuit and a gate control signal generating circuit, characterized in that Include: The first comparison circuit generates a first comparison signal according to a drain voltage of a synchronous switch on the secondary side of the flyback power converter and a first parameter; The second comparison circuit generates a ready signal according to the first comparison signal and a resistance value of an external resistor; and The gate control signal generating circuit generates a gate control signal to the synchronous switch according to the ready signal and the drain voltage, wherein the synchronous switch is turned on according to the gate control signal.

9. The operating method according to claim 8, characterized in that The first comparison circuit generates the first comparison signal according to the drain voltage of the synchronous switch and the first parameter, comprising: A sampling and holding circuit of the first comparison circuit generates a sampling voltage according to the drain voltage; A first adjustment circuit of the first comparison circuit updates a reference voltage according to the sampled voltage and the first parameter, wherein the first parameter is generated from inside the secondary-side controller; and When the drain voltage is greater than the reference voltage, a first comparator of the first comparison circuit generates the first comparison signal.

10. The operating method according to claim 8, characterized in that The second comparison circuit generates the ready signal according to the first comparison signal and the resistance value of the external resistor, comprising: A counter of the second comparison circuit generates a counting signal according to the first comparison signal; a second adjustment circuit of the second comparison circuit updates a reference count according to the first comparison signal and the resistance value of the external resistor; and After the drain voltage is less than a reference voltage and the counting signal is greater than the reference count, a second comparator of the second comparison circuit generates the ready signal and the counter resets the counting signal.

11. The operating method according to claim 10, characterized in that After the drain voltage is less than the reference voltage and the counting signal is less than the reference count, the counting signal is reset and the reference count is not updated.

12. The operating method according to claim 11, characterized in that After the reference count is not updated for more than two consecutive times, the second adjustment circuit updates the reference count.

13. The operating method according to claim 8, characterized in that When the gate control signal generating circuit receives the ready signal and the drain voltage is less than a determination voltage, the gate control signal generating circuit generates the gate control signal to the synchronous switch.

14. The operating method according to claim 8, characterized in that The flyback power converter operates in a quasi-resonant mode.

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