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Amplifier and Load Protection and Failure Detection via Current Sensing

IP.com Disclosure Number: IPCOM000084577D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR

Abstract

The drawings, as shown in Figs. 1 and 2, depict circuitry which senses and isolates faults in power amplifier 10 or motor 12. The drive signal to control motor 12 is supplied via positive pass transistor element 14 and negative pass transistor element 16. Positive amplifier current overload sense circuit 18 is positioned within the collector circuit of positive pass element 14. Likewise, negative amplifier current overload sense circuit 20 is positioned within the collector circuit of negative pass element 16.

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Amplifier and Load Protection and Failure Detection via Current Sensing

The drawings, as shown in Figs. 1 and 2, depict circuitry which senses and isolates faults in power amplifier 10 or motor 12. The drive signal to control motor 12 is supplied via positive pass transistor element 14 and negative pass transistor element 16. Positive amplifier current overload sense circuit 18 is positioned within the collector circuit of positive pass element 14. Likewise, negative amplifier current overload sense circuit 20 is positioned within the collector circuit of negative pass element 16.

When the IR drop across resistor RS exceeds VBE of transistor OS an overload signal is produced on terminals 22 and/or 24, respectively. The signal on terminals 24 and 22 are fed to exclusive OR circuit 26 and AND circuit 28. If the positive amplifier current overload sense circuit 18 and negative amplifier current overload sense circuit 20 produce an overload signal simultaneously, this indicates a shorted pass element. The output from AND circuit 28 can be used to power down the overall system. The output from exclusive OR circuit 26 will indicate excessive current in only one pass element, and thus be indicative of excessive load current rather than a defective amplifier 10.

Fig. 2 shows a scheme which improves fault detection at a slight additional cost. The load current overload sense circuit 30 has its threshold set slightly lower than the amplifier current overload sense. Amplifi...