Sine wave lamp controller with active switch commutation and anti-flicker correction
A pulse width modulated half bridge dimming controller is provided for dimming a lighting ballast is described. The top half of the bridge is comprised of two switches, the top switch set, and the bottom half of the bridge is comprised of two switches, the bottom switch set. Each switch also has a diode in parallel with it. The drivers for the switches are configured so that each of the switches can be turned on and off independently of all of all the other switches. Preferably, the controller is capable of operating in all four quadrants. In one preferred embodiment the switches are IGBTs. The switches are controlled in a manner so that when one of the switches sets changes states, the second switch set has one switch on and one switch off, so that one of the diodes in the second switch set is disposed to block shoot through and provide a path to allow current to continue flowing in the inductive load.
1. A method of switching power in a controller for pulse width modulation of an inductive load comprised of:
providing a power controller with a first switch set and second switch set, each of said switch sets further comprised of two power switches and each of said power switches having a diode associate with it;
first switching one of the switches of the first switch set;
then switching both switches of the second switch set;
then switching the second of the switches of the first switch set;
then waiting for a period of time related to the desired duty cycle of the pulse width modulation;
then switching the second of the switches of the first switch set;
then switching both switches of the second switch set; and
then switching the first of the switches of the first switch set.
2. The method of claim 1 wherein the switches are IGBTs.
3. The method of claim 1 wherein the switches are MOSFETs or bipolar transistors.
4. The method of claim 1 wherein the associated diode for each switch is an intrinsic diode.
5. The method of claim 1 wherein the associate diode for each switch is an extrinsic diode.
6. The method of claim 1 wherein the inductive load is a lighting ballast.
7. The method of claim 1 wherein the inductive load is power converter or motor.
8. The method of claim 1 wherein the pulse width modulation is switched at a rate below approximately 60 khz.
9. The method of claim 1 wherein the first switch set is the bottom switch set when the input voltage and load current are of the same polarity.
10. The method of claim 1 wherein the first switch set is the top switch set when the input voltage and load current are of opposite polarity.
11. The method of claim 1 wherein when switching both switches of the second switch set the two switches that comprise the second switch set are switched simultaneously or switched separately.