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A LOW-SENSING PROTECTION CIRCUIT FOR BATTERY-POWERED DEVICES

IP.com Disclosure Number: IPCOM000005424D
Original Publication Date: 1980-Aug-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 84K

Publishing Venue

Motorola

Related People

Richard Barnett: AUTHOR

Abstract

This circuit senses load current and thereby provides for three modes of operation: "stand- by/receive", " transmit" and "overload". In "overload", false tripping by transients is prevented by a se- quenced delay which causes the load to remain disconnected until the overload condition is corrected, with automatic reset at that time. During the "standby/receive" mode of operation, very low current drain is present, and a single load current path is available. In "transmit" mode, the load current is increased and an additional current path is also used. If an overload condition occurs, the current in both paths is interrupted for a short time, then the first path is again available for a very brief period. If the overload condition still exists, the delay sequence repeats until a safe level of current is reached, then the circuit again operates normally.

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MOTOROLA Technical Disclosure Bulletin Vol. 1 No. 1 August 1980

A LOW-SENSING PROTECTION CIRCUIT FOR BATTERY-POWERED DEVICES

By Richard Barnett

  This circuit senses load current and thereby provides for three modes of operation: "stand- by/receive", " transmit" and "overload". In "overload", false tripping by transients is prevented by a se- quenced delay which causes the load to remain disconnected until the overload condition is corrected, with automatic reset at that time. During the "standby/receive" mode of operation, very low current drain is present, and a single load current path is available. In "transmit" mode, the load current is increased and an additional current path is also used. If an overload condition occurs, the current in both paths is interrupted for a short time, then the first path is again available for a very brief period. If the overload condition still exists, the delay sequence repeats until a safe level of current is reached, then the circuit again operates normally.

   Referring to the logic/schematic diagram, in the normal conditions of "standby/receive" mode, the load draws a relatively small current. The load current sensor applies a voltage to each of the overload and transmit detectors. Each detector compares that voltage with its own reference voltage from the DC reference source. The overload detector puts a zero on the reset of the control latch. The transmit detec- tor puts a zero on the reset of switch #2. Thus, transistors Ql and Q2 are biased on to supply current for this mode. The diode junction of transistor Q3 is forward biased, holding the voltage on Cl low. As cur- rent in the lo_ad increases for transmission, the output...