1. Field of the Invention
The present invention relates to a current limiting circuit for controlled semiconductor power components, in particular to a current limiting circuit for power transistors.
Integrated power circuits require effective protection against current overloading at their outputs, in order to prevent thermal destruction in the event of a possible short circuit.
While the invention is applicable in principle to all controlled semiconductor power components, the present invention and the problem area on which it is based are explained with reference to power ICs using hybrid technology which provide not only MOS power transistors but also bipolar components and CMOS components.
The customary basic principle for such a current limiting circuit consists in the total current flowing through the power transistor or, using the sense cell principle, part of this total current generating a voltage drop across a resistor (also referred to as shunt resistor).
If the voltage drop exceeds a predetermined maximum value, the current limiting circuit loads the drive signal of the power transistor to such a great extent that the output current of the power transistor, which can be determined from the drive signal by way of the family of output characteristic curves, remains below a permissible limit value.
There exist a variety of approaches in the prior art for implementing that basic principle in circuitry terms.
In general, a distinction is made between current-regulation limiting circuits and voltage-regulation limiting circuits.
Current-regulation limiting circuits generally require a filter for masking inrush spikes. Voltage-regulation limiting circuits require temperature compensation circuits. Furthermore, the prior art circuits of both circuit types again themselves require complex protective circuitry for the occurrence of a short circuit.
Examples of that prior art are found in "Smart Power ICs: Technologies and Applications," Murari, Bertotti, and Vignola (Eds.), pp. 328, 400, 426, Springer Verlag, Berlin-Heidelberg-New York, 1996.
U.S. Pat. No. 5,519,341 to Corsi et al. discribes a current limiting circuit for a power transistor with a current sense resistor and a comparator comprising four bipolar transistors and two current sources. The current threshold at which the comparator responds can be set by way of the emitter areas of the cross-connected bipolar transistors.
A further current limiter circuit is disclosed in German patent DE 44 29 716. There, a current mirror circuit is connected to the current sense resistor.