Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Patent
1988-03-09
1989-08-22
Jennings, Derek S.
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
361 93, 330207P, 330298, H02H 3087
Patent
active
048601543
ABSTRACT:
A device for protecting an integrated circuit against overload and short circuit currents. The integrated circuit functions such that it is alternatingly switched to an ON or an OFF state, and when in the ON state a supply current (I.sub.M) is amplified by a Darlington-connected transistor step (Q.sub.20,Q.sub.21) and is supplied to the output (OUT) of the circuit across a load resistor (R.sub.LOAD). For an OFF state of the integrated circuit no current is led to the output (OUT). A protective circuit (S) comprising a detection resistor (R.sub.SENSE) is connected in series with said load resistance (R.sub.LOAD). The protective circuit also includes a differential step (D) for sensing a voltaqge (V.sub.SENSE) across the detection resistor (R hd SENSE) and a thyristor (T). Short circuit or overload on the output (OUT) causes an overcurrent to pass through said transistor step (Q.sub.20,Q.sub.21) and through the detection resistor. The increasing voltage (V.sub.SENSE) across the detection resistor due to the overcurrent is sensed by the differential step (D) which thus energizes the thyristor (T) so that the supply current (I.sub.M) is taken through the thyristor (T) instead of through the transistor step (Q.sub.20,Q.sub.21). The transitors (Q.sub.20,Q.sub.21) are thus pinched off, resulting in that the overcurrent is very quickly extinguished. The integrated circuit may be a final step in a semi-conductor relay, for example.
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Linear Circuit Techniques-"5A Regulator with Thermal Gradient Controlled Current Limit" by Dobkin, IEEE, ISSCC 2/16/79.
Jennings Derek S.
Telfonaktiebolaget L M Ericsson
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