Patent attributes
A pressure switch employs a Wheatstone bridge incorporating piezoresistive elements. The output of the bridge is monitored by a control circuit which produces a first control signal when a high pressure is achieved and produces a second control signal when a low pressure is achieved. The output of the control circuit is coupled to the gate electrode of a high current MOSFET device. The drain electrode of the MOSFET is coupled to one terminal of the motor where the other terminal of the motor is coupled to an operating potential. The source electrode of the MOSFET is coupled to ground. When the monitored pressure reaches a high threshold the MOSFET turns off as biased by the control circuit which in turn disables the motor. If the pressure drops, the control circuit detects this and produces the control signal, which activates the motor through the MOSFET. The gate electrode of the high current MOSFET is also connected to a thermal switch, which thermal switch is mounted on the motor housing and closes when the temperature of the motor exceeds a predetermined value. The closure of the thermal switch or the current switch disables the MOSFET and therefore disables the motor avoiding damage to the system.
