| 摘要 |
PURPOSE: A watch-dog circuit is provided to control on/off of a power supplier. CONSTITUTION: A watch-dog circuit includes a first through fourth transistors (Q30,Q40,Q41,Q42), a light emitting diode(LED40), an operational amplifier(OP40), a first resistor(R42) and a capacitor(C40). The watch-dog circuit comprises a load operated by receiving a power supply voltage from the power supplier. The first transistor is coupled with a power supplying circuit included in the power supplier. The light emitting diode and the first transistor consist of a photo-coupler. The second transistor connects with the light emitting diode. The operational amplifier controls on/off of the second transistor. The third transistor connects with the light emitting diode. One end of the resistor connects with the base of the third transistor. The fourth transistor connects with the other end of the first resistor. The capacitor receives a watch-dog pulse and one end of the capacitor connects with the base of the fourth transistor.
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