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Emitter Coupled Power Latch

IP.com Disclosure Number: IPCOM000096905D
Original Publication Date: 1962-Jan-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

MacKay, JB: AUTHOR

Abstract

The latch drives a relay coil without damage to a transistor from the inductive spikes developed by the coil. The circuit responds to low power input signals and has rapid turnon and turnoff.

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Emitter Coupled Power Latch

The latch drives a relay coil without damage to a transistor from the inductive spikes developed by the coil. The circuit responds to low power input signals and has rapid turnon and turnoff.

The circuit includes input transistor T1 of one conductivity having an emitter 20, base 22 and collector 24. The base 22 receives an input signal 26 through resistor 28. Collector 24 connects through load resistor 30 to voltage supply 32. Emitter 20 directly connects to transistor T2 of opposite conductivity to that of T1. T2 has an emitter 34, base 36 and collector 38. T1 and T2 have their emitters 20 and 34 directly interconnected. The common emitter connection also connects to ground through resistor 40. The base 36 of T2 is biased from supply 42 through resistor 44. The base 36 also connects through diode 46 to collector 24 of T1. Diode 46 is normally forwardly biased with the T2 base voltage positive with respect to ground, keeping T2 cut off. A load circuit 37, e.g., a relay coil, connects between collector 38 and supply 48.

Normally, T1 and T2 are biased to be non conducting. When the input signal 26 is applied, T1 is turned on. Its collector voltage falls towards ground. Diode 46 is reversely biased and T2 turns on. When T2 conducts, the T1 emitter voltage T1 is reduced below the input voltage level applied to the base 22 so that both transistors remain conducting. Thus, the circuit latches, but may be reset by lowering the input voltage b...