A PROTECTED SWITCH A PROTECTED SWITCH

摘要

A protected switch has a power semiconductor device (P) having first and second main electrodes (D and S) for coupling a load (L) between first (2) and second (3) voltage supply lines, a control electrode (G) coupled to a control voltage supply line (4) and a sense electrode (S1) for providing in operation of the power semiconductor device a sense current that flows between the first (d) and sense electrodes (S1) and is indicative of the current that flows between the first (D) and second (S) main electrodes. A control arrangement (S) has a sense resistance (R4) coupled to the sense electrode (S1) and across which a sense voltage is developed by the sense current (I3). A control semiconductor device (M3) has its main electrodes coupled between the control electrode (G) and the second (S) main electrode of the power semiconductor device (P). A semiconductor device (M2) has one (d) of its main electrodes coupled to the control electrode (g) of the control semiconductor device (M3) and the other (s) to the sense resistance (R4). A reference arrangement (50) provides a biasing voltage Vb for the control electrode (g) of the semiconductor device (M2) to cause the semiconductor device (M2) to conduct sufficiently to cause the control semiconductor device (M3) to be non-conducting until the sense voltage reaches a reference voltage determined by the biasing voltage when the semiconductor device (M2) becomes less conducting, causing the control semiconductor device (M3) to start to conduct, so reducing the voltage at the control electrode (G) of the power semiconductor device (P) and thus reducing the current through the power semiconductor device (P).