Primary side sense output current regulation

1. A switching power converter comprising:

a transformer including a primary winding coupled to an input voltage and a secondary winding coupled to an output of the switching power converter;

a switch coupled to the primary winding of the transformer, current through the primary winding being generated while the switch is turned on and not being generated while the switch is turned off; and

a controller configured to generate a control signal to turn on or turn off the switch at each switching cycle of the switch to regulate a varying output current at the output of the switching power converter while maintaining a substantially constant average output current at the output of the switching power converter;

wherein the controller is configured to generate the control signal by estimating an average output current for each switching cycle of the switch based on a reset time of the transformer calculated from a sensed output voltage from a previous switching cycle and a regulation voltage corresponding to a peak of the current through the primary winding in the previous switching cycle.

2. The switching power converter of claim 1 , wherein the controller is further configured to estimate the average output current for each switching cycle of the switch.

3. The switching power converter of claim 1 , wherein the controller is further configured to generate the regulation voltage based on a comparison between the average output current and a reference output current.

4. The switching power converter of claim 3 , wherein the controller is further configured to generate the regulation voltage by modifying a previously calculated regulation voltage from a prior switching cycle.

5. The switching power converter of claim 1 , wherein the controller is further configured to generate the control signal based on a comparison between a sensed peak primary side voltage signal corresponding to the peak current through the primary winding and the regulation voltage.

6. The switching power converter of claim 1 , wherein the controller is configured to estimate the average output current by removing high frequency noise from a calculated estimated output current.

7. The switching power converter of claim 1 , wherein the controller is further configured to calculate the reset time of the transformer based on the sensed output voltage.

8. In a controller, a method of controlling a switching power converter, the switching power converter including a transformer coupled between an input voltage and an output of the switching power converter, the transformer including a primary winding coupled to the input voltage and a secondary winding coupled to the output of the switching power converter, and a switch coupled to the primary winding of the transformer, current through the primary winding being generated while the switch is turned on and not being generated while the switch is turned off, the method comprising:

estimating an average output current for each switching cycle of the switch based on a reset time of the transformer from a previous switching cycle calculated from a sensed output voltage and a regulation voltage corresponding to a peak of the current through the primary winding in the previous switching cycle; and

generating a control signal to turn on or turn off the switch at each switching cycle of the switch to regulate a varying output current at the output of the switching power converter while maintaining a substantially constant average output current at the output of the switching power converter based on the estimated average output current.

9. The method of claim 8 , wherein the average output current is further estimated for each switching cycle of the switch based on a period of the previous switching cycle, a number of windings of the transformer, and a resistance of a sense resistor coupled to the switch and ground.

10. The method of claim 8 , further comprising:

comparing the average output current and a reference output current; and

generating the regulation voltage based on the comparison.

11. The method of claim 10 , wherein generating the regulation voltage comprises:

modifying a previously calculated regulation voltage from a prior switching cycle to generate the regulation voltage.

12. The method of claim 8 , further comprising:

comparing a sensed primary side voltage signal corresponding to the peak current through the primary winding and the regulation voltage; and

generating the control signal based on the comparison.

13. The method of claim 8 , wherein estimating the average output current comprises:

calculating an estimated output current; and

removing high frequency noise from the estimated output current to generate the average output current.

14. The method of claim 8 , further comprising:

calculating the reset time of the transformer based on the sensed output voltage.