| abstract |
A electrical energizable brake control circuit comprisES an electrically-activatednbrake having a brake coil winding selectively energizable forncorresponding braking action, and a brake drive circuit for energizing thenbrake coil winding, including circuit means for providing a constant current fornbraking action, and for rapidly increasing the brake current through the brakencoil for rapid engagement of the brake without substantial delay. The brakendrive circuit comprises a pulse width modulated switching power supplyncontrolled by voltage feedback from a current loop including the brake coilnwinding, a sensing resistor in the loop providing pulse width modulationnfeedback control signal to the power supply to control current in the loop, anfurther resistor in the loop and solid state switching means such as a FET fornrapidly increasing loop current for brake actuation by bypassing the furthernresistor. The FET may have main terminals connected across the furthernresistor, and be selectively driven into conductive state to bypass the furthernresistor for causing rapid brake action by rapidly increasing energization of thenbrake coil winding. The FET may be selectively returned to a nonconductivenstate to shunt loop current through the further resistor for causing rapid brakenrelease. |