Voltage supply device having self-testing circuit

A voltage supply device, comprising:

• an output circuit connected to a power source having a high voltage and a low voltage, the output circuit including a first switching transistor and a second switching transistor, both connected in series forming a push-pull circuit the output circuit selectively outputting the high voltage and the low voltage according to operation of the push-pull circuit;
• means for selecting either a test mode in which the voltage supply device is tested under a test voltage that is substantially lower than the high voltage of the power source, or an operation mode in which the voltage supply device normally operates under the high voltage and
• a gate voltage switching circuit, connected to a gate of the first switching transistor and the mold selecting means, for supplying a high gate voltage to turn on the first switching transistor under the operation mode and a low gate voltage to turn on the first switching transistor under the test mode, wherein the gate voltage switching circuit includes:
• a third switching transistor connected to the gate of the first switching transistor, the third switching transistor being turned on to supply the high gate voltage under the operation mode;
• and a fourth switching transistor connected to the gate of the first switching transistor, the fourth switching transistor being turned on to supply the low gate voltage under the test mode.