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Protective Circuit

IP.com Disclosure Number: IPCOM000078671D
Original Publication Date: 1973-Feb-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Helwig, K: AUTHOR [+3]

Abstract

Current switch T1, T2 with input emitter followers T5, T6 provides phase-opposed signals for controlling push-pull output stage T3, T4. To prevent T3 and T4 from becoming concurrently conductive, generally very stringent requirements have to be met for power sequencing and the tolerances of operating voltages VN, VH. As a result of the additional protective circuit with transistors T7, T8, T9 these requirements are eliminated.

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Protective Circuit

Current switch T1, T2 with input emitter followers T5, T6 provides phase- opposed signals for controlling push-pull output stage T3, T4. To prevent T3 and T4 from becoming concurrently conductive, generally very stringent requirements have to be met for power sequencing and the tolerances of operating voltages VN, VH. As a result of the additional protective circuit with transistors T7, T8, T9 these requirements are eliminated.

During normal operation of the circuit the additional circuit is not effective, being in the following state?

Because of voltage divider R1/R2, T8 of the current switch consisting of T7, T8 is conductive, so that the required reference potential occurs on the base of T2, and the circuit is ready for operation. Additional diode D1 is not effective.

The protective circuit becomes effective as soon as the critical voltage VN exceeds the most positive value admissible. This voltage is adjusted by divider R1, R2 and can be adapted to the power supply tolerances.

Above the critical voltage, current switch T7, T8 is reset, i.e., T8 is subsequently inhibited. This leads to T2 becoming conductive and retaining this state irrespective of VN. This ensures that output stage transistor T4 is inhibited, so that any hazardous switching of the push-pull stage is safely avoided.

ADVANTAGES - Driver circuits with a current switch input can be operated without power sequencing. - The protective circuit operates at very high speed. - The th...