Switching circuit for proximity detector - compares collector-emitter voltage of principal transistor with reference and conducts when this is exceeded

摘要

The transistionised switching circuit has a principal switching transistor. This transistor feeds into a load. The transistor is made to conduct by injecting a constant current into the base of the transistor. The circuit has means for comparing the collector-emitter voltage of the principal transistor with a reference voltage. The principal (T5) transistor becomes conducting as soon as its collector-emitter voltage exceeds the reference voltage. The additional circuit has a first auxiliary transistor (T3). The emitter of this auxiliary transistor is connected to the emitter of the principal transistor. The collector of the principal transistor (T5) and the base of the auxiliary transistor (T3) are connected respectively to a common point. The connected to the common point being via two opposed diodes (D1,D2). A second auxiliary transistor (T2) forms with the first auxiliary transistor (T3) two capacitors (2 and C3) resistances (R3-R7) and a diode (D1) an artable multivibrator.