Trigger circuit

A monostable trigger circuit comprises transistors (TR2 and TR3) arranged with their collectors and bases interconnected. The collector of the transistor TR2 is connected to the base of transistor TR3 via a capacitor (C2), the main current path of a grounded base transistor (TR1) and resistive means (R2, R3). The collector of transistor TR3 is connected to the base of transistor TR2 via resistive means R6, R7). In the stable state all the transistors are OFF, the capacitor C2 is charged, and the output (13) is LOW. A positive pulse input to the base of TR2 switches it ON, which in turn lowers the voltage at points A and B and so switches TR1 ON so that C2 can discharge via R2 R3, which in turn switches TR3 ON making the output (13) high. Thus all three transistors are latched ON. When C2 has discharged sufficiently TR1 switches OFF, followed by TR3 (making the output 13 low again) and TR2. The components C1 C3 and R4 serve to reduce noise, and the diode D1 is optional.