Secondary-side controller applied to a flyback power converter and operational method

1 . A secondary-side controller applied to a flyback power converter, wherein the secondary-side controller prevents a secondary side of the flyback power converter from conducting incorrectly, the secondary-side controller comprising:

a first comparison circuit for generating a first comparison signal according to a drain voltage of a synchronous switch of the secondary side of the flyback power converter and a first parameter, wherein the first comparison circuit comprises:

a sample-and-hold circuit for generating a sampled voltage according to the drain voltage;

a first adjustment circuit coupled to the sample-and-hold circuit, wherein the first adjustment circuit updates a reference voltage according to the sampled voltage and the first parameter, and the first parameter is generated from an internal circuit element of the secondary-side controller; and

a first comparator coupled to the synchronous switch and the first adjustment circuit, wherein the first comparator generates the first comparison signal when the drain voltage is greater than the reference voltage;

a second comparison circuit coupled to the first comparison circuit for generating a ready signal according to the first comparison signal and a resistance of an external resistor; and

a gate control signal generating circuit coupled to the second comparison circuit, wherein the gate control signal generating circuit generates a gate control signal to the synchronous switch according to the ready signal and the drain voltage, and the synchronous switch is turned on according to the gate control signal.

2 . A secondary-side controller applied to a flyback power converter, wherein the secondary-side controller prevents a secondary side of the flyback power converter from conducting incorrectly, the secondary-side controller comprising:

a first comparison circuit for generating a first comparison signal according to a drain voltage of a synchronous switch of 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 of an external resistor, wherein the second comparison circuit comprises:

a counter coupled to the first comparison circuit, wherein the counter generates a counting signal according to the first comparison signal;

a second adjustment circuit coupled to the first comparison circuit and the external resistor, wherein the second adjustment circuit updates a reference count according to the first comparison signal and the resistance of the external resistor; and

a second comparator coupled to the counter and the second adjustment circuit, wherein the second comparator generates the ready signal when the count signal is greater than the reference count and after the drain voltage is less than a reference voltage, and the counter resets the count signal when the count signal is greater than the reference count and after the drain voltage is less than the reference voltage; and

a gate control signal generating circuit coupled to the second comparison circuit, wherein the gate control signal generating circuit generates a gate control signal to the synchronous switch according to the ready signal and the drain voltage, and the synchronous switch is turned on according to the gate control signal.

3 . The secondary-side controller of claim 2 , wherein when the count signal is less than the reference count and after the drain voltage is less than the reference voltage, the counter resets the count signal and the second adjustment circuit does not update the reference count.

4 . The secondary-side controller of claim 3 , wherein after the reference count is not updated for more than two consecutive times, the second adjustment circuit updates the reference count.

5 . The secondary-side controller of claim 2 , wherein when the gate control signal generating circuit receives the ready signal and the drain voltage is less than a judgement voltage, the gate control signal generating circuit generates the gate control signal to the synchronous switch.

6 . The secondary-side controller of claim 2 , wherein the flyback power converter operates in a quasi-resonance mode.

7 . An operational method of 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 operational method comprises:

a sample-and-hold circuit of the first comparison circuit generating a sampled voltage according to a drain voltage;

a first adjustment circuit of the first comparison circuit updating a reference voltage according to the sampled voltage and a first parameter, wherein the first parameter is generated from an internal circuit element of the secondary-side controller; and

a first comparator of the first comparison circuit generating a first comparison signal when the drain voltage is greater than the reference voltage;

the second comparison circuit generating a ready signal according to the first comparison signal and a resistance of an external resistor; and

the gate control signal generating circuit generating a gate control signal to a synchronous switch on a secondary side of the flyback power converter according to the ready signal and the drain voltage, wherein the synchronous switch is turned on according to the gate control signal.

8 . An operational method of 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 operational method comprises:

the first comparison circuit generating 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;

a counter of the second comparison circuit generating a counting signal according to the first comparison signal;

a second adjustment circuit of the second comparison circuit updating a reference count according to the first comparison signal and the resistance of the external resistor;

after the drain voltage is less than a reference voltage and when the count signal is greater than the reference count, a second comparator of the second comparison circuit generating the ready signal and the counter resetting the count signal; 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.

9 . The operational method of claim 8 , wherein after the drain voltage is less than the reference voltage and when the count signal is less than the reference count, the count signal is reset and the reference count is not updated.

10 . The operation method of claim 9 , wherein after the reference count is not updated for more than two consecutive times, the second adjustment circuit updates the reference count.

11 . The operational method of claim 8 , wherein when the gate control signal generating circuit receives the ready signal and the drain voltage is less than a judgement voltage, the gate control signal generating circuit generates the gate control signal to the synchronous switch.

12 . The operational method of claim 8 , wherein the flyback power converter operates in a quasi-resonant mode.