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Time Delay

IP.com Disclosure Number: IPCOM000074637D
Original Publication Date: 1971-May-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Mumaw, AJ: AUTHOR [+2]

Abstract

This circuit provides a time delay whose duration is selected by varying circuit components controlling the conduction of an SCR. As shown at A, upon application of DC voltage the R2 C2 timing network starts and continues until the threshold voltage determined by zener diode Z1, V(BE) of transistor T2 and the V(GT) of the SCR T1 is reached. The zener diode Z1 now starts conducting turning on the SCR. The anode circuit of the SCR includes relay coil 1 provided with normally open contacts 2 and 3. When the relay coil is energized via the SCR, closed contacts 2 complete a circuit around C2 to discharge the capacitor for timing reset. Contact.3 closes to complete the control circuit. The SCR remains on keeping the coil energized until the voltage is removed.

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Time Delay

This circuit provides a time delay whose duration is selected by varying circuit components controlling the conduction of an SCR. As shown at A, upon application of DC voltage the R2 C2 timing network starts and continues until the threshold voltage determined by zener diode Z1, V(BE) of transistor T2 and the V(GT) of the SCR T1 is reached. The zener diode Z1 now starts conducting turning on the SCR. The anode circuit of the SCR includes relay coil 1 provided with normally open contacts 2 and 3. When the relay coil is energized via the SCR, closed contacts 2 complete a circuit around C2 to discharge the capacitor for timing reset. Contact.3 closes to complete the control circuit. The SCR remains on keeping the coil energized until the voltage is removed. Zener diodes Z2 and Z3 serve to stabilize the charge voltage variations caused by changes in the DC supply.

More flexibility in the delay time of the circuit shown at A is achieved with the circuit shown at B. An additional transistor T3 is added in parallel with T2 and a second resistor R5 is added in series with R2. External contact points 4, 5 and 6 permit selective connection of the resistors in either a parallel or series circuit to obtain the proper value of resistance for the required delay.

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