GB1028124A - Electrical drive circuit - Google Patents

Abstract

1,028,124. Transistor switching circuits. NATIONAL CASH REGISTER CO. Jan. 9, 1964 [Feb. 13, 1963], No. 1035/64. Heading H3T. [Also in Division F2] A solenoid, particularly for controlling a brake or clutch, is connected in series with a transistor having a load in the emitter circuit and means for turning off the transistor when the voltage across the emitter load has reached a predetermined level, an alternative path being provided for feeding a relatively low-holding current to the solenoid. Fig. 1 shows a system for controlling a brake and a pinch roller in a tape recorder. When positive and negative voltages are respectively fed to terminals 16, 17 a bi-stable circuit 13 is set to such a condition as to turn on a transistor 43 (Fig. 2) in the switching circuit 15 (Fig. 1) and energize the brake solenoid 12. When the voltage across the emitter resistor 44 has risen to a predetermined level, it is passed by a Zener diode 45 and an OR circuit 14 to reset the bi-stable circuit 13, which turns on transistor 30 and turns off transistor 43. The brake solenoid 12, however, is held energized by a current of lower level from a switching circuit 11 (Fig. 1), comprising transistor 66 (Fig. 3), which is turned on by the voltages fed to terminals 16, 17 (Fig. 1) via an amplifier 18 and inverters 19, 60. The holding current is only fed to the solenoid 12 when the initial energizing current has become reduced sufficiently to allow diode 69 (Fig. 3) to become conductive. The brake solenoid 12 is deenergized and the pinch roller clutch solenoid 22 is energized by reversing the polarity of voltages fed to terminal 16, 17 which turn off the switching circuits 11, 15 and turn on similar circuits 20, 21. Differentiating circuits (not shown) are included in the inputs to 13 and 23.