DE1788034

1,243,581. Transistor time delay switching circuits. KRAUSS-MAFFEI A.G. 15 Aug., 1969 [20 Sept., 19671, No. 40946/69. Heading H3T. A time delay circuit comprises a potentiometer 5 connected in series with a switching device, shown as transistor, 1 across a supply, a capacitor connected between the tap on 5 and the input of an amplifier, shown as a Schmitt trigger 10, 14, and a constant current device, shown as transistor 20, connected to the amplifier side of the capacitor. When the switch transistor 1 is rendered conducting the voltage at the input of the trigger is reduced by an amount determined by the setting of the potentiometer and the trigger is switched. The capacitor is charged through the constant current transistor until its voltage is sufficient to restore the trigger. A resistor or diode OR gate 2-4 controls the switching transistor 1 and the latter transistor when off allows potentiometer 5 to supply an "on" bias for transistor 14 of the trigger. Further amplifier transistors may succeed the trigger to provide additional and serene sense outputs. The input switch circuit may include a bi-stable circuit which is set to start timing and reset by the output at the end of the timing period. The delay is controlled by the potentiometer and adjustment of the constant current circuit. A lamp 8 connected to the input switch or the output amplifier indicates operation of the circuit. A meter V is switchable into circuit to indicate the potentiometer and thus the time delay, the switch including a back-contact which switches in a resistor equivalent to the voltmeter. A further contact 32 holds the circuit inoperative while the meter is in circuit. The transistors may be formed in an integrated circuit mounted on a printed circuit load. Resistor 24 and diode 25 provide temperature compensation.