Frequency to current conversion circuit - provides current amplitude indication as function of pulse repetition frequency for tachometer

摘要

Periodic pulses are converted into a current whose amplitude is a function of pulse repetition frequency. The converter is used in a vehicle tachometer to provide indication of pulse repetition frequency. A capacitor (8) is charged via resistor (7) and zener diode circuit (9). A transistor (12) connected from resistor and capacitor junction to negative supply rail (11) switches for duration of pulse on its base. A Darlington connected emitter follower stage (13) with temperature stabilisation with stabilisation against power supply variations provides current for indicator (19). A filter capacitor (20) ensures current indication is average value.