Long duration is achieved by separating peak current of timer from charging cuffent. Q1 and R1-R2-R3 form constant-current source whose charging current can be ad justed to as low as several nanoamperes. Q2 acts as source follower to supply current flowing in emitter lead priorto firing of UJT Q3. Diode-con-nected transistor Q1 provides low-impedance discharge path for timing capacitor CE. Delay time varies linearly with setting of R3.- Uni-junction Transistor Timers and Oscillators, Motorola, Phoenix, AZ, 1974, AN-294, p 5.
