Bridge circuit for operation of brushless DC motor - includes potential-shifting capacitor as source of auxiliary voltage for turn-on of each MOSFET connected to positive supply

摘要

The bridge circuit is formed entirely from n-channel MOSFETs (11,11',12,12'). For the switching of the transistors (11,11') connected to the positive DC supply (+Vcc) an auxiliary potential is produced by a shifting capacitor (13,13') of e.g. 2.2 microfarads connected between a +12V DC rail (17) and the emitter of the phototransistor in an opto-coupler (15,15') whose collector is linked to the gate electrode. The circuitry ensures that this auxiliary potential is built up before the rotor of the motor begins to move, and it is available at a definite level throughout longer standstill periods. ADVANTAGE - Reliable switching of power transistors connected to positive supply conductor is possible without any additional DC-DC converter or p-channel MOSFET voltage source.