Reduction of supply current variations using compensation current control
A power distribution system and method includes a controller that is configured to control a switching power converter. In at least one embodiment, the controller includes a compensation current control circuit to control a compensation current that reduces and, in at least one embodiment, approximately eliminates variations in current drawn by the controller during a particular operational time period. In at least one embodiment, the power distribution system is a lamp that includes the controller, a switching power converter, and one or more light sources, such as light emitting diodes.
1. An apparatus comprising:
a controller to control a switching power converter, wherein the controller includes:
first circuitry that, during at least one operational time period of the controller, is configured to draw a time varying operational current from an external power source; and
a compensation current control circuit to generate a compensation current control signal to control a draw of a compensation current from the external power source by second circuitry so that an average sum of the time varying operational current and the compensation current is approximately constant as the operational current varies in time during the operational time period.
2. The apparatus of claim 1 wherein:
the controller further includes the second circuitry, the secondary circuitry is coupled to the external power source, the second circuitry includes a switch having a control terminal to receive the compensation current control signal, and the compensation current control signal control conductivity of the switch.
3. The apparatus of claim 1 wherein:
the secondary circuit is coupled to the external power source and includes a resistor coupled in series with a switch, and the resistor is external to the controller and the switch is included in the controller.
4. The apparatus of claim 1 wherein the external power source comprises an auxiliary-winding of a transformer in a flyback switching power converter.
5. The apparatus of claim 1 wherein during each voltage cycle of the external power supply, the first circuit draws current for a first period of time and the compensation current control circuit is configured to generate the compensation current control signal to control current draw from the external power source by the second circuitry for a second period of time, the second period of time immediately follows the first period of time, and the compensation current control circuit is configured to control the current draw from the external power source by the second circuitry so that the first period of time plus the second period of time is approximately constant.
6. The apparatus of claim 1 wherein the sum of the time varying operational current and the compensation current represents a total amount of current drawn by the controller.
7. The apparatus of claim 1 wherein the time varying operational current comprises a probe current controlled by the controller.
8. The apparatus of claim 1 wherein the controller is configured to control the switching power converter to provide power to a load.
9. The apparatus of claim 1 wherein the load comprises one or more light emitting diodes.
10. The apparatus of claim 1 wherein the operational period is a time period equal to a half line cycle of a rectified supply voltage to the switching power converter.
11. The apparatus of claim 1 wherein the compensation current control circuit is configured to generate the compensation current control signal to control the draw of the compensation current from the external power source by second circuitry so that the time varying operational current and the compensation current is approximately constant as the operational current varies in time.
12. The apparatus of claim 1 wherein the compensation current control circuit is further configured to disable the compensation current control signal when the controller controls the switching power converter to provide a full output power.
13. A method comprising:
drawing a time varying operational current in a first circuit of a controller from an external power source during at least one operational time period of the controller, wherein the controller is configured to control a switching power converter; and
generating a compensation current control signal to control a draw of a compensation current from the external power source by second circuitry so that an average sum of the time varying operational current and the compensation current is approximately constant as the operational current varies in time during the operational time period.
14. The method of claim 13 further comprising:
applying the compensation current control signal to a switch having a control terminal to receive the compensation current control signal to control the compensation current.
15. The method of claim 13 further comprising:
conducting the compensation current through a dissipating circuit that is external to the controller.
16. The method of claim 13 wherein the external power source comprises an auxiliary-winding of a transformer in a flyback switching power converter.
17. The method of claim 13 further comprising:
during each voltage cycle of the external power supply, drawing current in the first circuit for a first period of time;
generating the compensation current control signal to control current draw from the external power source by the second circuitry for a second period of time, the second period of time immediately follows the first period of time; and
controlling the current draw from the external power source by the second circuitry so that the first period of time plus the second period of time is approximately constant.
18. The method of claim 13 wherein the sum of the time varying operational current and the compensation current represents a total amount of current drawn by the controller.
19. The method of claim 13 wherein the time varying operational current comprises a probe current controlled by the controller.
20. The method of claim 13 further comprising:
controlling the switching power converter to provide power to a load.
21. The method of claim 13 wherein the load comprises one or more light emitting diodes.
22. The method of claim 13 wherein the operational period is a time period equal to a half line cycle of a rectified supply voltage to the switching power converter.
23. The method of claim 13 wherein generating the compensation current signal further comprises:
generating the compensation current control signal to control the draw of the compensation current from the external power source by second circuitry so that the time varying operational current and the compensation current is approximately constant as the operational current varies in time.
24. The method of claim 13 further comprising:
disabling the compensation current control signal when the controller controls the switching power converter to provide a full output power.
25. A lamp comprising:
a light source;
a switching power converter coupled to the light source; and
a controller, coupled to the switching power converter, to control a switching power converter, wherein the controller includes:
first circuitry that, during at least one operational time period of the controller, is configured to draw a time varying operational current from an external power source; and
a compensation current control circuit to generate a compensation current control signal to control a draw of a compensation current from the external power source by second circuitry so that a sum of the time varying operational current and the compensation current is approximately constant as the operational current varies in time.
26. The lamp of claim 25 the light source comprises one or more light emitting diodes.