Highly efficient isolated AC/DC power conversion technique
An AC-to-DC power converter that is capable of generating a regulated, isolated DC voltage output from a power factor corrected AC voltage input with improved efficiency. The AC-to-DC power converter is a two-stage power converter including a PFC stage connected in series to a power conversion stage. The PFC stage performs power factor correction using a zero current switching technique, and the power conversion stage includes a zero voltage switched half-bridge converter. The power conversion stage includes a transformer for providing the isolated DC voltage output. The AC-to-DC power converter includes a single feedback control loop for transferring error information from the DC voltage output to the PFC stage, thereby obtaining regulation of the DC voltage output.
1. An AC-to-DC converter, comprising:
an AC power input;
a full bridge rectifier operative to receive AC voltage and current from the AC power input, and to convert the AC voltage and current to rectified voltage and current;
a power factor correction (PFC) stage operative to receive the rectified voltage and current, and to provide power factor corrected voltage and current, wherein the PFC stage includes at least one first switching device operative to switch the rectified current in accordance with a zero current switching technique;
a power conversion stage operative to receive the power factor corrected voltage and current, and to provide an isolated DC voltage output; the power conversion stage includes an isolation transformer having primary and secondary windings, and a plurality of second switching devices operatively coupled to the primary winding of the transformer, the plurality of second switching devices being operative to switch the power factor corrected current in accordance with a zero voltage switching technique; and
a feedback control loop operative to provide error information from the DC voltage output to the PFC stage for controlling a duty cycle of the first switching device, thereby obtaining regulation of the isolated DC voltage output.
2. The AC-to-DC converter of claim 1 , wherein the feedback control loop includes an opto-coupler disposed between the isolated DC voltage output and the PFC stage.
3. The AC-to-DC converter of claim 1 , further including a low pass filter disposed between the transformer and the isolated DC voltage output.
4. The AC-to-DC converter of claim 1 ,wherein the power conversion stage comprises a zero voltage switched half-bridge converter.
5. The AC-to-DC converter of claim 4 , wherein the zero voltage switched half-bridge converter operates at a predetermined duty cycle.
6. The AC-to-DC converter of claim 5 , wherein the predetermined duty cycle is fixed.
7. A method of performing an AC-to-DC power conversion, comprising the steps of:
receiving AC voltage and current from an AC power input;
converting the AC voltage and current to rectified voltage and current;
converting the rectified voltage and current to power factor corrected voltage and current, the converting step including switching the rectified current by at least one first switching device in accordance with a zero current switching technique; and
converting the power factor corrected voltage to an isolated DC voltage outputs;
wherein the second converting step further includes switching the rectified current by the switching device based on error information from the DC voltage output, thereby obtaining regulation of the DC voltage output; and
wherein the third converting step includes switching the power factor corrected current by a plurality of second switching devices in accordance with a zero voltage switching technique.
8. The method of claim 7 , wherein the power factor corrected current is switched by the plurality of second switching devices operating at a predetermined duty cycle.
9. The method of claim 8 , wherein the predetermined duty cycle is fixed.
10. The method of claim 7 , further including the step of low pass filtering the DC voltage output.