Overvoltage protection circuit for protecting overvoltage corresponding to wide range of input voltage

1. An overvoltage protection circuit connected between a rectifier circuit that rectifies an AC voltage to output a rectified voltage and a load including an input capacitor element connected to both ends of the load, the overvoltage protection circuit comprising:

a semiconductor switch connected between the rectifier circuit and the load; and

a control circuit that controls the semiconductor switch to be turned on or off,

wherein, when the rectified voltage exceeds a predetermined value, the control circuit turns off the semiconductor switch, and detects a voltage potential difference between both ends of the semiconductor switch, and then, for an interval when the voltage potential difference is zero or a predetermined minute value, the control circuit generates a control voltage for turning on the semiconductor switch, and outputs the control voltage to a control terminal of the semiconductor switch, and

wherein the overvoltage protection circuit comprises a current change circuit that gradually changes a current flowing through the semiconductor switch such that a conduction disturbing wave voltage in an output voltage output from the overvoltage protection circuit becomes equal to or lower than a predetermined value at least at one of (A) a timing when the semiconductor switch is turned off and (B) a timing when the semiconductor switch is turned on.

2. The overvoltage protection circuit as claimed in claim 1 ,

wherein the current change circuit comprises an inductor inserted between the semiconductor switch and the rectifier circuit.

3. The overvoltage protection circuit as claimed in claim 1 ,

wherein the current change circuit comprises the control circuit including a current control circuit that generates the control voltage for gradually changing a current flowing through the semiconductor switch.

4. The overvoltage protection circuit as claimed in claim 3 ,

wherein the current control circuit further comprises a resistor inserted between the semiconductor switch and the rectifier circuit,

wherein the overvoltage protection circuit further comprises a low-pass filter that low-pass filters for generating a reference voltage generated at a timing which is based on the rectified voltage and a voltage at a connection point between the semiconductor switch and the load, and

wherein the overvoltage protection circuit generates the control voltage such that a voltage across the resistor coincides with the reference voltage.

5. The overvoltage protection circuit as claimed in claim 3 ,

wherein the current control circuit further comprises a resistor inserted between the semiconductor switch and the rectifier circuit,

wherein the overvoltage protection circuit further comprises a constant current source for generating a reference voltage generated at timing which is based on the rectified voltage and a voltage at a connection point between the semiconductor switch and the load, and

wherein the overvoltage protection circuit generates the control voltage such that a voltage across the resistor matches the reference voltage.

6. The overvoltage protection circuit as claimed in claim 3 ,

wherein the current control circuit further comprises a resistor inserted between the semiconductor switch and the rectifier circuit,

wherein the overvoltage protection circuit further comprises a triangular wave current source for generating a reference voltage generated at timing based on the rectified voltage and a voltage at a connection point between the semiconductor switch and the load, and

wherein the overvoltage protection circuit generates the control voltage such that a voltage across the resistor matches the reference voltage.

7. The overvoltage protection circuit as claimed in claim 1 ,

wherein the current change circuit comprises:

a feedback capacitor inserted between a control terminal of the semiconductor switch and a connection point between the load and the semiconductor switch; and

a control resistor inserted between the control circuit and the control terminal of the semiconductor switch.

8. The overvoltage protection circuit as claimed in claim 1 ,

wherein the input capacitor element comprises a plurality of input capacitors connected in parallel with each other, and

wherein the overvoltage protection circuit further comprises a further semiconductor switch that is connected in series with at least one input capacitors, which is a part of the input capacitors selected from the plurality of input capacitors.

9. A power supply apparatus for supplying a power supply voltage, the power supply apparatus comprising an overvoltage protection circuit,

wherein the overvoltage protection circuit is connected between a rectifier circuit that rectifies an AC voltage to output a rectified voltage and a load including an input capacitor element connected to both ends of the load,

wherein the overvoltage protection circuit comprises:

a semiconductor switch connected between the rectifier circuit and the load; and

a control circuit that controls the semiconductor switch to be turned on or off,

wherein, when the rectified voltage exceeds a predetermined value, the control circuit turns off the semiconductor switch, and detects a voltage potential difference between both ends of the semiconductor switch, and then, for an interval when the voltage potential difference is zero or a predetermined minute value, the control circuit generates a control voltage for turning on the semiconductor switch, and outputs the control voltage to a control terminal of the semiconductor switch, and

wherein the overvoltage protection circuit comprises a current change circuit that gradually changes a current flowing through the semiconductor switch such that a conduction disturbing wave voltage in an output voltage output from the overvoltage protection circuit becomes equal to or lower than a predetermined value at least at one of (A) a timing when the semiconductor switch is turned off and (B) a timing when the semiconductor switch is turned on.