Ripple reduction in light emitting diode (LED)-based light bulb through increased ripple on an energy storage capacitor
A buck stage configured as a second stage of a lamp circuit for a light-emitting diode-based (LED-based) light bulb may reduce manufacturing costs associated with the bulb by reducing a size of a capacitor in the lamp circuit. A controller of the buck stage may adjust a duty cycle of a switch to increase a ripple, such as a voltage ripple, across the capacitor to increase accessibility of energy stored in the capacitor and decrease a ripple, such as in output current, to the LEDs.
1. An apparatus, comprising:
a line voltage input node configured to receive a line voltage input;
a rectifier coupled to the line voltage input node;
a first switching stage coupled to the rectifier and configured to regulate an approximately average current to an intermediate node;
a capacitor coupled to the intermediate node;
a second switching stage coupled to the intermediate node and configured to provide an approximately constant ratio of input to output current, wherein the second switching stage comprises a switch in series with a lighting load;
a first controller coupled to the first switching stage and configured to regulate the first switching stage to maintain an approximately average current out of the first switching stage and into the intermediate node, the average current being averaged over each half line cycle of the input line voltage; and
a second controller coupled to the switch, wherein the second controller is configured to operate the switch to control a ripple on the capacitor to reduce a ripple through the lighting load.
2. The apparatus of claim 1 , wherein the first switching stage is galvanically isolated from the second switching stage.
3. The apparatus of claim 2 , wherein the second switching stage operates at a higher operating frequency than the first switching stage.
4. The apparatus of claim 1 , wherein the lighting load comprises one or more light emitting diodes (LEDs).
5. The apparatus of claim 4 , wherein the first controller is configured to regulate a current through the one or more light emitting diodes (LEDs) as a value approximately equal to the product of the average current from the first switching stage and the ratio of the second switching stage.
6. The apparatus of claim 1 , wherein the controller is integrated into a printed circuit board (PCB) and wherein the first switching stage is integrated into a second printed circuit board (PCB).
7. The apparatus of claim 1 , wherein the second controller is configured to operate the second switching stage at approximately a constant average duty cycle over a period of at least one half of a cycle of the line voltage input.
8. The apparatus of claim 7 , wherein the second controller is configured to:
monitor a voltage across the capacitor; and
reduce a power usage of the lighting load during a peak of the monitored voltage to allow the capacitor to charge.
9. The apparatus of claim 8 , wherein the second controller is configured to reduce a duty cycle of the switch to reduce the power usage of the lighting load.
10. The apparatus of claim 7 , wherein the second controller is configured to:
monitor a current through the lighting load; and
charge the capacitor when the current through the lighting load is below a threshold.
11. The apparatus of claim 1 , wherein the second controller is configured to operate the switch to control a voltage ripple on the capacitor to reduce a current ripple through the lighting load.
12. The apparatus of claim 1 , wherein the first controller is configured to maintain an approximately average current based, at least in part, on a dimmer setting for the lighting load.
13. A method, comprising:
regulating a current to an intermediate node in a first switching stage of a lamp to maintain an approximately average current for each half line cycle of an input line voltage;
delivering current from the intermediate node to a second switching stage of the lamp; and
regulating a ripple in an energy storage capacitor of the second switching stage of the lamp to provide an approximately constant ratio of input to output current.
14. The method of claim 13 , wherein the step of regulating comprises regulating a voltage ripple in the energy storage capacitor.
15. The method of claim 13 , wherein the approximately constant ratio is greater than one.
16. The method of claim 13 , further comprising monitoring a voltage across the energy storage capacitor.
17. The method of claim 16 , further comprising reducing an output current during a peak of the monitored voltage to allow the energy storage capacitor to charge.
18. The method of claim 17 , wherein the step of delivering current from the intermediate node to the second switching stage comprises galvanically isolating the second switching stage from the first switching stage.
19. The method of claim 13 , wherein the step of regulating a voltage ripple comprises regulating an output current to have a current ripple less than approximately 20% of an average voltage on the energy storage capacitor.
20. The method of claim 13 , wherein the step of regulating the current to the intermediate node comprises maintaining an approximately average current based, at least in part, on a dimmer setting for the lamp.
21. The method of claim 13 , further comprising regulating a current through one or more light emitting diodes (LEDs) as a value approximately equal to the product of the average current from the first switching stage and the ratio of the second switching stage.
22. An apparatus, comprising:
a first printed circuit board (PCB):
a line voltage input node configured to receive a line voltage input;
a rectifier coupled to the line voltage input node;
a first switching stage coupled to the rectifier and configured to maintain an approximately average current for each one half of a cycle of the input live voltage;
a transformer coupled to the first switching stage; and
a second printed circuit board (PCB) galvanically isolated from the first printed circuit board (PCB), the second printed circuit board (PCB) comprising:
a lighting output node configured to provide an output current;
a second switching stage coupled to the transformer to receive an input current from the first printed circuit board (PCB) and configured to provide an approximately constant ratio of input current to output current; and
a controller coupled to the second switching stage and configured to operate the second switching stage at approximately a constant average duty cycle over a period of at least one half of a cycle of the line voltage input,
wherein the second switching stage of the second printed circuit board (PCB) is coupled to the first switching stage of the first printed circuit board (PCB) by two wires.
23. The apparatus of claim 22 , further comprising one or more light emitting diodes (LEDs) coupled to the lighting output node.
24. The apparatus of claim 23 , wherein the second switching stage of the second printed circuit board (PCB) comprises an energy storage capacitor, and wherein the controller of the second switching stage is configured to control a ripple on the energy storage capacitor to reduce a ripple at the lighting output node.
25. The apparatus of claim 24 , wherein the controller of the second switching stage is configured to control a voltage ripple on the energy storage capacitor to reduce a current ripple at the lighting output node.