Gating circuit having current measuring and regulating elements and a temperature measuring transistor

摘要

PCT No. PCT/DE95/00039 Sec. 371 Date Jul. 1, 1996 Sec. 102(e) Date Jul. 1, 1996 PCT Filed Jan. 14, 1995 PCT Pub. No. WO95/20783 PCT Pub. Date Aug. 3, 1995The gating circuit has a power transistor (T1, T2, T3) and a current measuring resistor (R5) connected with the power transistor so that a voltage drop at the measuring resistor is a measure of a current flow in the power transistor. This voltage drop is used to trigger a current regulating transistor (T5) and a temperature measuring transistor (T9). Below a predetermined temperature, the current flow is limited solely by the current regulating transistor (T5). Above this predetermined temperature the collector current is further reduced via the temperature measuring transistor (T9) and a further transistor (T10) so as to protect the power transistor from thermal overload.