Quasi-resonant flyback converter controller

1. A flyback converter comprising:

a primary-side circuit configured to receive an input voltage;

a secondary-side circuit configured to generate an output voltage using the input voltage;

a transformer coupling the primary-side circuit to the secondary-side circuit;

a main switch coupled to a primary winding of the transformer and configured to control a current through the primary winding; and

a converter controller comprising:

a primary-side controller in signal communication with the main switch, the primary-side controller being configured to control an on time and an off time of the main switch and to detect one or more valleys of a resonant waveform developed at a node of the main switch during the off time of the main switch;

wherein:

the primary-side controller is configured to operate in a valley reduction mode of operation upon determining that the output voltage is less than a reference voltage of the flyback converter minus a predetermined threshold value; and

the valley reduction mode of operation comprises decrementing, by the primary-side controller, for each switching cycle of the main switch, a number of valleys occurring during that switching cycle of the main switch.

2. The flyback converter of claim 1 , wherein:

the primary-side controller is configured to stop the valley reduction mode of operation upon determining that the output voltage is not less than the reference voltage of the flyback converter minus the predetermined threshold value.

3. The flyback converter of claim 1 , wherein:

during the valley reduction mode of operation, the primary-side controller decrements the number of valleys by one or more for each of the switching cycles of the main switch.

4. The flyback converter of claim 3 , wherein:

during the valley reduction mode of operation, the primary-side controller decrements the number of valleys occurring during each of the switching cycles of the main switch by adjusting the off time of the main switch for each of the switching cycles.

5. The flyback converter of claim 1 , wherein:

the primary-side controller is configured to receive an auxiliary voltage from an auxiliary-winding circuit coupled to the transformer; and

the primary-side controller is configured to detect the number of valleys of the resonant waveform using the auxiliary voltage.

6. The flyback converter of claim 1 , further comprising:

a secondary-side controller, in signal communication with the secondary-side circuit; and

a digital link in signal communication with the primary-side controller and the secondary-side controller;

wherein:

the secondary-side controller is configured to receive the output voltage from the secondary-side circuit and the reference voltage, convert the output voltage into a digital output voltage signal and the reference voltage into a digital reference voltage signal, and transmit the digital output voltage signal and the digital reference voltage signal to the digital link;

the digital link is configured to transmit the digital output voltage signal and the digital reference voltage signal to the primary-side controller; and

the primary-side controller is configured to receive the digital output voltage signal and the digital reference voltage signal and determine if the output voltage is less than the reference voltage minus the predetermined threshold value.

7. The flyback converter of claim 6 , the secondary-side controller comprising:

an analog-to-digital converter (“ADC”) configured to receive the output voltage from the secondary-side circuit and the reference voltage, wherein the ADC is configured to convert the output voltage into the digital output voltage signal and the reference voltage into the digital reference voltage signal; and

an encoder in signal communication with the ADC, wherein the encoder is configured to receive and encode the digital output voltage signal and the digital reference voltage signal into a combined encoded data stream having digital representations of the output voltage and the reference voltage.

8. The flyback converter of claim 7 , wherein the encoder is a finite-state machine.

9. The flyback converter of claim 7 , the primary-side controller comprising:

a decoder configured to receive and decode the combined encoded data stream into a received digital output voltage signal and received digital reference voltage signal; and

a controller in signal communication with the decoder, wherein the controller is configured to receive the received digital output voltage signal and the received digital reference voltage signal and to control the on time and the off time of the main switch based on the received digital output voltage signal and the received digital reference voltage signal.

10. The flyback converter of claim 6 , wherein the digital link is a unidirectional high-speed digital link.

11. A method comprising:

receiving, at a primary-side circuit of a flyback converter, an input voltage;

generating, at a secondary-side circuit of the flyback converter, an output voltage using the input voltage, a transformer coupling the primary-side circuit to the secondary-side circuit;

controlling, using a main switch coupled to a primary winding of the transformer, a current through the primary winding;

controlling, by a primary-side controller of the flyback converter, an on time and an off time of the main switch;

detecting, by the primary-side controller, one or more valleys of a resonant waveform developed at a node of the main switch during the off time of the main switch;

determining, by the primary-side controller, that the output voltage is less than a reference voltage of the flyback converter minus a predetermined threshold value;

beginning, by the primary-side controller, a valley reduction mode of operation based on the determination; and

reducing, by the primary-side controller during the valley reduction mode of operation, a number of valleys occurring at the node of the main switch during one or more switching cycles of a plurality of switching cycles of the main switch.

12. The method of claim 11 , further comprising:

stopping, by the primary-side controller, the valley reduction mode of operation upon determining that the output voltage is not less than the reference voltage of the flyback converter minus the predetermined threshold value.

13. The method of claim 11 , further comprising:

decrementing, by the primary-side controller during the valley reduction mode of operation, the number of valleys occurring during each switching cycle of the plurality of switching cycles of the main switch.

14. The method of claim 13 , further comprising:

adjusting, by the primary-side controller during the valley reduction mode of operation, the off time of the main switch by an amount of time corresponding to an integer number of valleys to decrement the number of valleys occurring during each switching cycle of the plurality of switching cycles of the main switch.

15. The method of claim 11 , further comprising:

receiving, by the primary-side controller, an auxiliary voltage from an auxiliary-winding circuit coupled to the transformer; and

detecting, by the primary-side controller, the number of valleys of the resonant waveform using the auxiliary voltage.

16. The method of claim 11 , wherein:

the flyback converter further comprises a secondary-side controller, in signal communication with the secondary-side circuit;

the flyback converter further comprises a digital link in signal communication with the primary-side controller and the secondary-side controller; and

the method further comprises:

receiving, by the secondary-side controller, the output voltage from the secondary-side circuit and the reference voltage;

converting, by the secondary-side controller, the output voltage into a digital output voltage signal and the reference voltage into a digital reference voltage signal;

transmitting, by the secondary-side controller, the digital output voltage signal and the digital reference voltage signal to the digital link;

transmitting, by the digital link, the digital output voltage signal and the digital reference voltage signal to the primary-side controller; and

receiving, by the primary-side controller, the digital output voltage signal and the digital reference voltage signal, the digital output voltage signal and the digital reference voltage signal being used to determine, by the primary-side controller, that the output voltage is less than the reference voltage of the flyback converter minus the predetermined threshold value.

17. The method of claim 16 , wherein:

the secondary-side controller further comprises an analog-to-digital converter (“ADC”) and an encoder in signal communication with the ADC; and

the method further comprises:

receiving, by the ADC, the output voltage from the secondary-side circuit and the reference voltage;

converting, by the ADC, the output voltage into the digital output voltage signal and the reference voltage into the digital reference voltage signal;

receiving, by the encoder, the digital output voltage signal and the digital reference voltage signal; and

encoding, by the encoder, the digital output voltage signal and the digital reference voltage signal into a combined encoded data stream having digital representations of the output voltage and the reference voltage.

18. The method of claim 17 , wherein the encoder is a finite-state machine.

19. The method of claim 17 , wherein:

the primary-side controller further comprises a decoder and a controller in signal communication with the decoder; and

the method further comprises:

receiving, by the decoder, the combined encoded data stream;

decoding, by the decoder, the combined encoded data stream into a received digital output voltage signal and received digital reference voltage signal;

receiving, by the controller, the received digital output voltage signal and the received digital reference voltage signal; and

controlling, by the controller, the on time and the off time of the main switch based on the received digital output voltage signal and the received digital reference voltage signal.

20. The method of claim 16 , wherein the digital link is a unidirectional high-speed digital link.