Overvoltage protection circuit, power supply device, liquid crystal display device, electronic device and television set

摘要

An overvoltage protection portion (14) includes a transistor (P1) that achieves continuity with an input voltage (VIN) used as an output voltage (VOUT) to an internal circuit when the input voltage (VIN) applied to an external terminal (T1) is not in an overvoltage state. The overvoltage protection portion (14) also includes: a transistor (P2) operating as a short circuit that short-circuits the source and the gate of the transistor (P1) and that interrupts the input voltage (VIN) when the input voltage (VIN) is in the overvoltage state; a resistor (R2); and a Zener diode (ZD1). The overvoltage protection portion (14) also includes: a transistor (NTr1) operating as a bypass circuit that supplies a constant output voltage (VOUT) from the external terminal (T1) to the internal circuit when the input voltage (VIN) is brought into the overvoltage state; a resistor (R3); and a Zener diode (ZD2).

主权项

1. An overvoltage protection circuit comprising:
a first P-channel field-effect transistor including a source connected to an input terminal and including a drain connected to an internal circuit; a first resistor connected between a gate of the first P-channel field-effect transistor and a ground end; a short circuit operable to short-circuit the source and the gate of the first transistor while an application voltage of the input terminal exceeds a predetermined threshold value; and a bypass circuit operable to supply a constant voltage from the input terminal to the internal circuit while the voltage of the input terminal exceeds the threshold value, wherein the short circuit includes: a second P-channel field-effect transistor including a source connected to the input terminal and including a drain is connected to the gate of the first P-channel field-effect transistor; a second resistor connected between a gate of the second P-channel field-effect transistor and the input terminal; and a first Zener diode connected between the gate of the second P-channel field-effect transistor and the ground end, wherein the bypass circuit includes: an NPN transistor whose collector is connected to the input terminal and whose emitter is connected to the internal circuit; a second Zener diode which is connected between a base of the NPN transistor and the ground end; and a third resistor which is connected between the base of the NPN transistor and the input terminal, and wherein each of the first P-channel field-effect transistor, the second P-channel field-effect transistor and the NPN transistor is high-voltage resistant as compared with an element of the internal circuit.