Power factor correction control circuit

1. A power factor control circuit for an AC to DC power converter, the circuit comprising:

an inductor configured to receive AC rectified power from an AC line input voltage; and

a switching circuit connected to the inductor and including a switch for switching current through the inductor on and off;

the switching circuit controlling the on-time of the switch, and thereby the charging time of the inductor, by comparing a DC bus voltage to a fixed reference voltage,

the switching circuit controlling the off-time of the switch, and thereby the discharging time of the inductor, by turning the switch off until the inductor current discharges to zero, as detected by the switching circuit, such that the off-time of the switch varies as a function of the peak inductor current during each switching cycle,

wherein the on - time of the switch is controlled to be longer at the zero crossings of the AC line input voltage thereby to achieve lower total harmonic distortion .

2. The power factor control circuit of claim 1 , wherein the switch comprises a MOSFET.

3. The power factor control circuit of claim 2 , wherein the MOSFET operates without a current-sensing resistor connected in series with the source of the MOSFET.

4. The power factor control circuit of claim 1 , wherein the on-time of the switch is modulated as a function of the off-time of the switch to achieve lower total harmonic distortion.

5. The power factor control circuit of claim 1 , wherein the current in the inductor follows the sinusoidal voltage of the AC rectified power as the switching circuit is turned on and off at a much higher frequency than the line frequency of the AC rectified power, thereby eliminating the need to sense the rectified AC line input voltage.

6. The power factor control circuit of claim 1 , wherein the inductor includes a secondary winding which is used by the switching circuit to determine the inductor current.

7. A method of power factor control in an AC to DC power converter using a power factor control circuit having an inductor configured to receive AC rectified power from an AC line input voltage; and a switching circuit connected to the inductor and having a switch for switching current through the inductor on and off, the method comprising the steps of:

controlling the on-time of the switch, and thereby the charging time of the inductor, by comparing a DC bus voltage to a fixed reference voltage,

controlling the off-time of the switch, and thereby the discharging time of the inductor, by turning the switch off until the inductor current discharges to zero, as detected by the switching circuit, such that the off-time of the switch varies as a function of the peak inductor current during each switching cycle, further comprising increasing the on- time of the switch at the zero crossings of the AC line input voltage thereby to achieve lower total harmonic distortion .

8. The method of power factor control of claim 7 , wherein the switch comprises a MOSFET.

9. The method of power factor control of claim 8 , wherein the on-time and off-time of the MOSFET are controlled without a current-sensing resistor connected in series with the source of the MOSFET.

10. The method of power factor control of claim 7 , wherein the on-time of the switching circuit is modulated as a function of the off-time to achieve lower total harmonic distortion.

11. The method of power factor control of claim 7 , wherein the current in the inductor follows the sinusoidal voltage of the AC rectified power as the switching circuit is turned on and off at a much higher frequency than the line frequency of the AC rectified power, thereby eliminating the need to sense the rectified AC line input voltage.

12. The method of power factor control of claim 7 , wherein the inductor includes a secondary winding which is used by the switching circuit to determine the inductor current.