Device for protecting an integrated circuit against overload and short circuit currents

Claim 1

Device comprising a protective circuit for protecting an integrated circuit against overload and short circuit currents, the integrated circuit containing, apart from the protective circuit, a first transistor step connected to a second transistor step, a control input, an output and a load resistor connected between said output and earth, the control input controlling the integrated circuit so that it is alternatingly switched on or off, in an ON state a supply current in the circuit being amplified by said second transistor step and delivered to the output of the circuit across the load resistor and no current being taken to the output for an OFF state in the circuit, said protective circuit comprising a detection resistor, connected in series with said load resistor; a differential step for sensing a voltage drop across the detection resistor, said differential step having a first input connected to a first side of the detection resistor and a second input connected to an other side of the detection resistor, and an output connected to a thyristor including a pilot transistor and an ignition transistor, said thyristor having a first connection to the collector on said first transistor step and a second connection to earth, the differential step energising the thyristor when the protective circuit is activated, such that for an integrated circuit in the ON state said protective circuit assumes a ready state in which the input voltage to the pilot transistor falls below the voltage level at which the transistor is energised, such that the protective circuit is activated for overload or short circuit on the output of said circuit, the input voltage to the pilot transistor of the thyristor then exceeding the energising voltage level of the transistor so that the transistor is energised, whereby the protective circuit goes into an active state in which said current is taken through the thyristor instead of through said second transistor step, which is thus pinched off, and the overload or short circuit current is extinguished, and such that the protective circuit works in an active state until the integrated circuit is switched off.