OUERHEAT PREVENTIVE TRIGGER CIRCUIT HAVING NARROW THRESHOLD FLUCTUATION RANGE

摘要

PURPOSE: To limit a range of fluctuation in a set intervention threshold by switching on a transistor(TR) when currents flowing to two base-emitter connections are equal to each other after a preset threshold temperature is reached. CONSTITUTION: A current 11 is substantially proportional to a VBE/R1 with a high temperature dependency, and a current 13 is proportional to aΔVBE/R2 with a comparatively small temperature dependency, where R1 and R2 are resistance of two resistors whose value is set preliminarily as a function of other parameters to set a desired intervene threshold temperature andΔVBE is a difference between base-emitter voltages of TRs 3, 4 to form an emitter degenerating current mirror. When currents flowing through two branches of current mirrors are equal to each other, a TR Q7 is conductive as a result of reaching the desired intervention threshold temperature. Then all integrated circuits over-heated in the usual intervention mode of an overheat prevention circuit are switched off.