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Time Delay Circuit

IP.com Disclosure Number: IPCOM000076504D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Nunnery, WB: AUTHOR

Abstract

The time-delay circuit shown can provide a time delay using relatively small values for the storage capacitor, and since the capacitor is substantially fully discharged at each cycle, the circuit can be recycled immediately after its operation without appreciable change in the time-delay period. The circuit uses a transistor switch 1 in series with a load circuit 2 across a power source. A series circuit of a resistor 3 and capacitor 4 are connected across a power supply by a switch 6, to start charging the junction point 7 at an exponential rate. The junction 7 is connected to the base of transistor 1 by an SUS (silicon unilateral switch) 5, which has the characteristics of starting conduction at a fixed voltage across it, but maintaining conduction through it until the voltage drops to a much lower level.

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Time Delay Circuit

The time-delay circuit shown can provide a time delay using relatively small values for the storage capacitor, and since the capacitor is substantially fully discharged at each cycle, the circuit can be recycled immediately after its operation without appreciable change in the time-delay period. The circuit uses a transistor switch 1 in series with a load circuit 2 across a power source. A series circuit of a resistor 3 and capacitor 4 are connected across a power supply by a switch 6, to start charging the junction point 7 at an exponential rate. The junction 7 is connected to the base of transistor 1 by an SUS (silicon unilateral switch) 5, which has the characteristics of starting conduction at a fixed voltage across it, but maintaining conduction through it until the voltage drops to a much lower level.

When switch 6 is closed, the current through resistor 3 starts to charge capacitor 4 but transistor 1 during this time has no base current and no current passes through the load 2. When capacitor 4 has charged to the firing voltage of the SUS 5 plus the Vbe voltage of transistor 1, the SUS 5 starts conducting to discharge capacitor 4 through the base of transistor 1 to start current flow through load 2. Transistor 1 will be turned on for the time needed to discharge capacitor 4 to the turn-off voltage of SUS 5 plus the Vbe of transistor 1. If the switch 6 remains closed, capacitor 4 will start to recharge when SUS 5 turns off and will start...