Switching circuit

1. A switching circuit, comprising:

input drain, source and gate nodes;

a depletion mode transistor comprising a current path coupled in series with a current path of an enhancement mode transistor, the depletion mode transistor having a higher blocking voltage capability than the enhancement mode transistor; and

an overheating detection circuit for detecting overheating of the switching circuit,

wherein the enhancement mode transistor is an IGFET,

wherein the depletion mode transistor is a Group III-Nitride-based transistor,

wherein the enhancement mode transistor comprises a plurality of transistor cells connected in parallel with each other and integrated in a semiconductor substrate and a biased pn junction integrated in the same semiconductor substrate having a predetermined temperature dependent voltage characteristic.

2. The switching circuit according to claim 1 , wherein the IGFET is a p-channel MOSFET.

3. The switching circuit according to claim 1 , wherein the overheating detection circuit is at least partially integrated in the enhancement mode transistor.

4. The switching circuit according to claim 1 , wherein the enhancement mode transistor comprises a plurality of transistor cells connected in parallel with each other and integrated in a semiconductor substrate and a forward biased pn junction integrated in the same semiconductor substrate having a voltage drop which is inversely proportional to the junction temperature.

5. The switching circuit according to claim 4 , further comprising voltage means coupled to said forward biased pn junction for producing a voltage proportional to said voltage drop.

6. The switching circuit according to claim 5 , wherein the overheating detection circuit comprises threshold means for receiving the voltage and producing a signal when the voltage exceeds a threshold voltage to indicate that said enhancement mode transistor is overheated.

7. The switching circuit according to claim 1 , wherein the enhancement mode transistor comprises a plurality of transistor cells connected in parallel with each other and integrated in a semiconductor substrate and a reverse biased pn junction integrated in the same semiconductor substrate having a reverse leakage current flow which is temperature dependent.

8. The switching circuit according to claim 7 , further comprising voltage means coupled to said reverse biased pn junction for producing a voltage proportional to said reverse leakage current flow.

9. The switching circuit according to claim 8 , wherein the overheating detection circuit comprises threshold means for receiving the voltage and producing a signal when the voltage exceeds a threshold voltage to indicate that said enhancement mode transistor is overheated.

10. The switching circuit according to claim 1 , wherein the overheating detection circuit further comprises a first overheating detection pad and a second overheating detection pad on said semiconductor substrate and coupled to said biased pn junction.

11. The switching circuit according to claim 1 , further comprising at least one overheating detection node.

12. The switching circuit according to claim 1 , wherein the depletion mode transistor is operatively connected in a cascode arrangement to said enhancement mode transistor.

13. The switching circuit according to claim 1 , wherein the depletion mode transistor is directly driven.

14. The switching circuit according to claim 1 , wherein the depletion mode transistor is provided as a discrete component and the enhancement mode transistor is provided as a discrete component.

15. The switching circuit according to claim 1 , wherein the depletion mode transistor and the enhancement mode transistor are mounted adjacent one another in a composite package.

16. The switching circuit according to claim 1 , wherein the depletion mode transistor and the enhancement mode transistor are monolithically integrated.

17. The switching circuit according to claim 16 , further comprising logic for detecting if the temperature has exceeded a predetermined threshold, the logic being integrated in a semiconductor body of the enhancement mode transistor.

18. The switching circuit according to claim 17 , wherein the logic is configured to switch off the switching circuit if the detected temperature exceeds a predetermined threshold value.

19. The switching circuit according to claim 16 , wherein the enhancement mode transistor is silicon-based and an electrical connection between a drain of the enhancement mode transistor and a source of the depletion mode transistor is provided at an interface between the enhancement mode transistor and the depletion mode transistor.

20. The switching circuit according to claim 1 , wherein the depletion mode transistor is a Group III-Nitride-based high electron mobility transistor (HEMT).