Power factor corrected switched mode power supply
A power factor corrected switched mode power supply including a phase shifter that senses the mains frequency and phase shifts it to produce a phase shifted signal which modulates the switching signal supplied to the switches based on the phase shifted signal. The rate of change of the frequency of the switching signal may be controlled to be greatest in regions of greatest power transfer.
1. A power factor corrected switched mode power supply including:
a power rectifier having an input configured to be coupled to an AC power supply mains;
a switch coupled to an output of the power rectifier;
a voltage sensor coupled to the input or the output of the power rectifier and configured to generate a voltage sense signal that indicates a phase of a voltage of the AC power supply mains;
a phase shifting circuit coupled to the voltage sensor and configured to produce a phase shifted signal from the voltage sense signal; and
a modulator configured to modulate the switch at a frequency that varies responsive to the phase shifted signal.
2. A power factor corrected switched mode power supply as claimed in claim 1 wherein the phase shifting circuit is arranged to produce a phase shifted signal that, when input into the modulator, enables the modulator to produce a switching signal with a frequency having a rate of change which is greatest in regions of greatest power transfer.
3. A power factor corrected switched mode power supply as claimed in claim 1 wherein the phase shifting circuit is arranged to produce a phase shifted signal that, when input into the modulator, enables the modulator to produce a switching signal with a frequency having a rate of change which is at a maximum in or near the region of maximum power transfer.
4. A power factor corrected switched mode power supply as claimed in claim 1 wherein the phase shifting circuit is arranged to produce a phase shifted signal that, when input into the modulator, enables the modulator to produce a switching signal with a frequency having a rate of change which is lowest in regions of lowest power transfer.
5. A power factor corrected switched mode power supply as claimed in claim 1 wherein the phase shifting circuit is arranged to produce a phase shifted signal that, when input into the modulator, enables the modulator to produce a switching signal with a frequency having a rate of change which is at a minimum in or near the region of minimum power transfer.
6. A power factor corrected switched mode power supply as claimed in claim 1 further comprising a sensing rectifier supplying a rectified mains signal to the voltage sensor.
7. A power factor corrected switched mode power supply as claimed in claim 1 wherein the voltage sensor is a resistor divider.
8. A power factor corrected switched mode power supply as claimed in claim 1 wherein the phase shifting circuit is a passive circuit.
9. A power factor corrected switched mode power supply as claimed in claim 8 wherein the phase shifting circuit is an RC circuit.
10. A power factor corrected switched mode power supply as claimed in claim 1 wherein the phase shifting circuit includes a digital phase shifting circuit.
11. A power factor corrected switched mode power supply as claimed in claim 10 wherein the phase shifting circuit includes a digital signal processor.
12. A method of controlling the switching frequency of a power factor corrected switched mode power supply comprising:
generating a voltage sense signal that indicates a phase of a voltage of an AC power supply mains coupled to an input of the power supply;
applying the voltage sense signal to a phase shifting circuit to generate a phase shifted signal; and
varying a frequency of a switching signal supplied to a switch of a converter of the power supply according to the phase shifted signal.
13. A method as claimed in claim 12 wherein a frequency of the switching signal has a rate of change which is greatest in regions of greatest power transfer.
14. A method as claimed in claim 12 wherein a frequency of the switching signal has a rate of change which is at a maximum in or near the region of maximum power transfer.
15. A method as claimed in claim 12 wherein a frequency of the switching signal has a rate of change which is lowest in regions of lowest power transfer.
16. A method as claimed in claim 12 wherein a frequency of the switching signal has a rate of change which is at a minimum in or near the region of minimum power transfer.
17. A power supply comprising:
a rectifier having an input configured to be coupled to an AC power source;
a power converter coupled to an output of the rectifier;
a voltage divider circuit coupled to the rectifier and configured to generate a voltage sense signal;
a phase shifting circuit coupled to the voltage divider circuit and configured to generate a phase shifted signal from an output signal produced by the voltage divider circuit; and
a modulator circuit configured to modulate a switch of the power converter responsive to the phase shifted signal.
18. The power supply of claim 17 further comprising a sensing rectifier coupling the voltage divider circuit to an input of the rectifier.
19. The power supply of claim 17 , wherein the voltage divider circuit is connected to an output of the rectifier.
20. The power supply of claim 17 , wherein the phase shifting circuit is a passive circuit.