US Patent 7692475 Switch circuit

A switch circuit is disclosed. The switch circuit comprises: a hysteresis buffer, an electric switch, a first discharge resistor, a second discharge resistor, a capacitor, a feedback resistor, a first reciprocal switch, and a second reciprocal switch. When the second reciprocal switch is turned on, a power supply voltage charges the capacitor, and thus the voltage on the signal input terminal of the hysteresis buffer is decreased. Accordingly, the voltage on the signal output terminal of the hysteresis buffer is decreased, so as to turn on the electric switch. When the first reciprocal switch is turned on, the capacitor is discharged, and thus the voltage on the signal input terminal of the hysteresis buffer is increased. Accordingly, the voltage applied to the signal output terminal of the hysteresis buffer is increased, so as to turn off the electric switch.