BATTERY CHARGER WITH POWER FACTOR CORRECTION

摘要

A battery charger with power factor correction is provided. In particular, the battery charger is configured to work in a discontinuous current mode with a power factor that is almost unity but no bulky electrolytic capacitor is needed in the charger. The charger has a rectification circuit producing a rectified voltage to a first controllable switching circuit, whose output is fed to a series resonant tank series-connecting a first winding of a high-frequency transformer. The second winding thereof is connected to a second controllable switching circuit, whose output is a DC voltage for battery charging. The charger includes a control unit for generating a first control signal and a second control signal to control the first and the second controllable switching circuits, respectively, such that the current flowing in the first winding is substantially phase-aligned with the first control signal's waveform, thereby facilitating power factor correction.

主权项

1. A battery charger for converting an AC voltage to a DC output voltage usable for battery charging, the AC voltage having an AC frequency and being obtainable from an AC source, the battery charger comprising:
a control unit configured to generate a first control signal and a second control signal, each of the two control signals being substantially similar to a periodic pulse train, an instantaneous signal value of each of the two control signals indicating either a first required configuration RC1 or a second required configuration RC2, the two control signals being substantially mutually-synchronized with a time delay between the two control signals; a rectification circuit for rectifying the AC voltage to thereby generate a rectified voltage across two output terminals of the rectification circuit; a first controllable switching circuit having P1in1 and P1in2 as two input ports and P1out1 and P1out2 as two output ports, P1in1 and P1in2 being one-by-one coupled to the two output terminals of the rectification circuit for receiving the rectified voltage, the first controllable switching circuit being reconfigurable in response to the first control signal; a high-frequency transformer having a first winding and a second winding, each of the two windings having two terminals; a series resonant tank comprising a resonating inductor and a resonating capacitor connected in series, the series resonant circuit being further series-connected to the first winding to give a resultant cascade, the cascade having two ends connected to P1out1 and P1out2 for allowing an exciting current to flow through the cascade to excite the second winding; and a second controllable switching circuit having P2in1 and P2in2 as two input ports one-by-one connected to the two terminals of the second winding, and having P2out1 and P2out2 as two output ports such that the DC output voltage is obtainable across P2out1 and P2out2, the second controllable switching circuit being reconfigurable in response to the second control signal; wherein: the first control signal having the instantaneous signal value that indicates RC1 configures the first controllable switching circuit to connect P1in1 to P1out1, and P1in2 to P1out2; the first control signal having the instantaneous signal value that indicates RC2 configures the first controllable switching circuit to connect P1in1 to P1out2, and P1in2 to P1out1; when a voltage difference measured from P1out1 to P1out2 is substantially higher than zero, the second control signal having the instantaneous signal value that indicates RC1 configures P2in1 and P2in2 to be shorted together, and P2out1 and P2out2 to be disconnected from any of P2in1 and P2in2; when the voltage difference is substantially higher than zero, the second control signal having the instantaneous signal value that indicates RC2 configures P2in1 to connect to P2out1, and P2in2 to connect to P2out2; when the voltage difference is substantially lower than zero, the second control signal having the instantaneous signal value that indicates RC1 configures P2in1 to connect to P2out1, and P2in2 to connect to P2out2; when the voltage difference is substantially lower than zero, the second control signal having the instantaneous signal value that indicates RC2 configures P2in1 and P2in2 to be shorted together, and P2out1 and P2out2 to be disconnected from any of P2in1 and P2in2; and the control unit is further configured to real-time adjust the time delay such that the exciting current has a waveform substantially phase-aligned with the first control signal's waveform, thereby facilitating power factor correction.