Method and system of a switching power converter

1. A method of operating a flyback converter, comprising:

switching a primary switch of the flyback converter at a switching frequency, the flyback converter having a feedback circuit acting as a low pass filter with a cutoff frequency, and each cycle of the switching frequency comprising a charge mode that ends at a peak current through a primary winding of a transformer and a discharge mode;

generating, during the switching, a jitter signal having a shape and a jitter frequency; and

ending a plurality of consecutive charge modes at a respective plurality of peak current values of current through the primary winding, the plurality of peak current values define an average value, and wherein peak current values higher than the average value define an envelope in the shape of the jitter signal, and peak current values lower than the average value define an envelope in the shape of the jitter signal that is inverted.

2. The method of claim 1 wherein ending the plurality of consecutive charge modes further comprises:

sensing current through the primary winding to create a sensed current signal;

generating a pulse signal having a pulse frequency above the cutoff frequency;

adding the jitter signal to the sensed current signal when the pulse signal is asserted to create a dithered current signal;

when the pulse signal is asserted, ending at least some charge modes when the dithered current signal meets the current setpoint signal;

adding the jitter signal to a current setpoint signal when the pulse signal is de-asserted to create a dithered setpoint signal; and

when the pulse signal is de-asserted, ending at least some charge modes when the sensed current signal meets the dithered setpoint signal.

3. The method of claim 2 wherein the pulse frequency is half the switching frequency.

4. The method of claim 1 wherein ending each charge mode further comprises:

sensing current through the primary winding to create a sensed current signal;

generating a pulse signal having positive peaks and negative peaks, the pulse signal having a pulse frequency above the cutoff frequency of the feedback circuit;

amplitude modulating the pulse signal with the jitter signal to create a modified jitter signal;

adding the modified jitter signal to the sensed current signal to create a dithered current signal; and

ending each charge mode when the dithered current signal meets a current setpoint signal.

5. The method of claim 4 wherein the pulse frequency is half the switching frequency.

6. The method of claim 1 wherein ending each charge mode further comprises:

sensing current through the primary winding to create a sensed current signal;

generating a pulse signal having positive peaks and negative peaks, the pulse signal having a pulse frequency above the cutoff frequency of the feedback circuit;

amplitude modulating the pulse signal with the jitter signal to create a modified jitter signal,

adding the modified jitter signal to a current setpoint signal to create a dithered setpoint signal; and

ending each charge mode when the sensed current signal meets the dithered setpoint signal.

7. The method of claim 6 wherein the pulse frequency is half the switching frequency.

8. The method of claim 1 wherein ending each charge mode further comprises:

sensing current through the primary winding to create a sensed current signal;

generating a pulse signal having a pulse frequency above the cutoff frequency of the feedback circuit;

creating a dithered current signal by adding the jitter signal to the sensed current signal when the pulse signal is asserted, and subtracting the jitter signal from the sensed current signal when the pulse signal is de-asserted; and

ending each charge mode when the dithered current signal meets a current setpoint signal.

9. The method of claim 8 wherein the pulse frequency is half the switching frequency.

10. A packaged integrated circuit (IC) for controlling a primary side of a flyback converter, the packaged IC comprising:

a gate terminal, a current sense terminal, a voltage sense terminal, and a feedback terminal;

a start controller defining a sense input coupled to the voltage sense terminal, and a start output;

a latch circuit defining a latch input coupled to the start output, a reset input, and a drive output coupled to the gate terminal;

an end controller defining a feedback input coupled to the feedback terminal, a current sense input coupled to the current sense terminal, a gate input coupled to the drive output, and a reset output coupled to the reset input of the latch circuit;

the start controller configured to assert the gate terminal at a switching frequency to create a plurality of consecutive charge modes;

the end controller configured to generate a jitter signal having a shape and a jitter frequency;

the end controller further configured to end the plurality of consecutive charge modes by de-assertion of the gate terminal at a respective plurality of sensed current signals, the plurality of sensed current signals sensed by way of the current sense terminal, and wherein the plurality of sensed current signals define an average value with sensed current signals higher than the average value defining an envelope in the shape of the jitter signal, and sensed current signals lower than the average value defining an envelope in the shape of the jitter signal that is inverted.

11. The packaged IC of claim 10 wherein the end controller further comprises:

a jitter signal circuit defining a jitter output, the jitter signal circuit configured to drive the jitter signal with the shape and the jitter frequency onto the jitter output;

a jitter controller defining the gate input, a current setpoint input coupled to the feedback terminal, a jitter input coupled to the jitter output, a current sense input coupled to the current sense terminal, a dithered setpoint output, and a dithered sense output;

a comparator defining a first input coupled to the dithered setpoint output, a second input coupled to the dithered sense output, and a compare output coupled to the reset output;

wherein the jitter controller is configured to at least one selected from the group comprising: modify the plurality of sensed current values with the jitter signal; modify a current setpoint signal on the current setpoint input with the jitter signal; and modify the plurality of sensed current values with the jitter signal in a first charge mode, and modify the current setpoint signal in a second, consecutive charge mode.

12. The packaged IC of claim 10 wherein the end controller further comprises:

a jitter signal circuit defining a jitter output, the jitter signal circuit configured to drive the jitter signal with the shape and the jitter frequency onto the jitter output;

a jitter controller defining the gate input, a current setpoint input coupled to the feedback terminal, a jitter input coupled to the jitter output, a current sense input coupled to the current sense terminal, a dithered setpoint output, and a dithered sense output;

a comparator defining a first input coupled to the dithered setpoint output, a second input coupled to the dithered sense output, and a compare output coupled to the reset output;

the jitter controller is configured to:

generate a pulse signal having a pulse frequency lower than the switching frequency, the generation based on a gate signal on the gate input;

add the jitter signal to a sensed current signal on the current sense input when the pulse signal is asserted to create a dithered current signal; and

add the jitter signal to a current setpoint signal on the feedback input when the pulse signal is de-asserted to create a dithered setpoint signal.

13. The packaged IC of claim 12 wherein the jitter signal is a triangle wave.

14. The packaged IC of claim 10 wherein the end controller further comprises:

a jitter signal circuit defining a jitter output, the jitter signal circuit configured to drive the jitter signal with the shape and the jitter frequency onto the jitter output;

a jitter controller defining the gate input, a current setpoint input coupled to the feedback terminal, a jitter input coupled to the jitter output, a current sense input coupled to the current sense terminal, a dithered setpoint output, and a dithered sense output;

a comparator defining a first input coupled to the dithered setpoint output, a second input coupled to the dithered sense output, and a compare output coupled to the reset output;

the jitter controller is configured to:

generate a pulse signal having a pulse frequency lower than the switching frequency, the generation based on a gate signal on the gate input;

amplitude modulate the pulse signal with the jitter signal to create a modified jitter signal; and

add the modified jitter signal to a sensed current signal on the current sense input to create a dithered current signal.

15. The packaged IC of claim 10 wherein the end controller further comprises:

a jitter signal circuit defining a jitter output, the jitter signal circuit configured to drive the jitter signal with the shape and the jitter frequency onto the jitter output;

a jitter controller defining the gate input, a current setpoint input coupled to the feedback terminal, a jitter input coupled to the jitter output, a current sense input coupled to the current sense terminal, a dithered setpoint output, and a dithered sense output;

a comparator defining a first input coupled to the dithered setpoint output, a second input coupled to the dithered sense output, and a compare output coupled to the reset output;

the jitter controller is configured to:

generate a pulse signal having a pulse frequency lower than the switching frequency, the generation based on a gate signal on the gate input;

amplitude modulate the pulse signal with the jitter signal to create a modified jitter signal; and

add the modified jitter signal to a current setpoint signal on the feedback input to create a dithered setpoint signal.

16. The packaged IC of claim 10 wherein the end controller further comprises:

a jitter signal circuit defining a jitter output, the jitter signal circuit configured to drive the jitter signal with the shape and the jitter frequency onto the jitter output;

a jitter controller defining the gate input, a current setpoint input coupled to the feedback terminal, a jitter input coupled to the jitter output, a current sense input coupled to the current sense terminal, a dithered setpoint output, and a dithered sense output;

a comparator defining a first input coupled to the dithered setpoint output, a second input coupled to the dithered sense output, and a compare output coupled to the reset output;

the jitter controller is configured to:

generate a pulse signal having a pulse frequency lower than the switching frequency, the generation based on a gate signal on the gate input;

create a dithered current signal on the dithered sense output by adding the jitter signal to a sensed current signal on the current sense input when the pulse signal is asserted, and subtracting the jitter signal from the sensed current signal when the pulse signal is de-asserted.

17. A flyback converter comprising:

a primary-side comprising:

a primary winding of a transformer;

an auxiliary winding of the transformer;

a primary field effect transistor (FET) coupled to the primary winding, the primary FET having a gate;

a sense resistor coupled between the primary FET and ground;

a primary-side controller defining a gate terminal, a current sense terminal, a voltage sense terminal, and a feedback terminal, the gate terminal coupled to the gate, the current sense terminal coupled to a sense node defined between the primary FET and the sense resistor, and the voltage sense terminal coupled to the auxiliary winding;

a secondary-side comprising:

a secondary-side rectifier;

a secondary winding of the transformer coupled to the secondary-side rectifier, the secondary winding arranged for flyback operation;

a feedback circuit coupled to an output node of the flyback converter, and also coupled to the feedback terminal of the primary-side controller, the feedback circuit implements a low pass filter with a cutoff frequency;

wherein the primary-side controller is configured to:

switch the primary FET at a switching frequency, with each cycle of the switching frequency comprising a discharge mode and a charge mode that ends at a peak current through the primary winding;

generate a jitter signal having a shape and a jitter frequency; and

end a plurality of consecutive charge modes at a plurality of respective peak current values, the plurality of peak current values define an average value, and wherein peak current values higher than the average value define an envelope in the shape of the jitter signal, and peak current values lower than the average value define an envelope in the shape of the jitter signal that is inverted.

18. The flyback converter of claim 17 wherein when the primary-side controller ends the plurality of consecutive charge modes, the primary-side controller is configured to:

sense current through the primary winding to create a sensed current signal;

generate a pulse signal having a pulse frequency greater than the cutoff frequency of the feedback circuit;

add the jitter signal to the sensed current signal when the pulse signal is asserted to create a dithered current signal;

add the jitter signal to a current setpoint signal when the pulse signal is de-asserted to create a dithered setpoint signal;

when the pulse signal is asserted, end at least some charge modes when the dithered current signal meets the current setpoint signal; and

when the pulse signal is de-asserted, end at least some charged modes when the sensed current signal meets the dithered setpoint signal.

19. The flyback converter of claim 17 wherein the primary-side controller further comprises:

a start controller defining a sense input coupled to the voltage sense terminal, and a start output;

a latch circuit defining a latch input coupled to the start output, a reset input, and a drive output coupled to the gate terminal;

an end controller defining a feedback input coupled to the feedback terminal, a current sense input coupled to the current sense terminal, a gate input coupled to the drive output, and a reset output coupled to the reset input of the latch circuit;

the start controller configured to assert the gate terminal at the switching frequency to create a plurality of consecutive charge modes;

the end controller configured to generate the jitter signal;

the end controller further configured to end the plurality of consecutive charge modes by assertion of the reset output at a respective plurality of sensed current signals, the plurality of sensed current signals sensed by way of the current sense terminal, and wherein the plurality of sensed current signals define an average value with sensed current signals higher than the average value defining an envelope in the shape of the jitter signal, and sensed current signals lower than the average value defining an envelope in the shape of the jitter signal that is inverted.

20. The flyback converter of claim 17 , wherein when the primary-side controller ends the plurality of consecutive charge modes, the primary-side controller is further configured to:

sense current through the primary winding to create a sensed current signal;

generate a pulse signal having a pulse frequency greater than the cutoff frequency of the feedback circuit; and

create a dithered current signal by adding the jitter signal to the sensed current signal when the pulse signal is asserted, and subtract the jitter signal from the sensed current signal when the pulse signal is de-asserted.