Patent ID: 7394668

Claim:
A frequency converter comprising: a rectifier for receiving an AC voltage; a first smoothing capacitance having a first terminal connected with a first output terminal of the rectifier, wherein V i is a voltage at the first terminal of the first smoothing capacitance; a second smoothing capacitance having a first terminal connected with a second output terminal of the rectifier, wherein a second terminal of the first smoothing capacitance is connected with a second terminal of the second smoothing capacitance, wherein V A is a voltage at the second terminals of the first smoothing capacitance and the second smoothing capacitance, and wherein V A is a lower voltage than V i ; a first resistance R 1 connected in parallel with the first smoothing capacitance; a second resistance R 2 connected in parallel with the second smoothing capacitance; a transformer having a first terminal of a primary winding connected with the first terminal of the first smoothing capacitance; a PWM control circuit having a DC power supply input, wherein the PWM control circuit performs switching control of a switch connected with a second terminal of the primary winding of the transformer; a third resistance R 3 having a first terminal connected with the second terminals of the first smoothing capacitance and the second smoothing capacitance and having a second terminal connected with the DC power supply input of the PWM control circuit; an inverter switching device comprising a power transistor and connected with the first terminals of the first smoothing capacitance and the second smoothing capacitance; and an inverter control circuit which controls the inverter switching device.