| 摘要 |
PROBLEM TO BE SOLVED: To provide an overheat protection circuit capable of simplifying circuit constitution and executing a sufficient overheat protecting function. SOLUTION: The level of threshold voltage between the base and emitter of transistors(TRs) Q3, Q4 is dropped accompanying the rise in the temperature of the regulated power supply circuit. Since the voltage impressed to a resistor R3 is raised and the flowing current is increased, the current flowing into a resistor R4 is increased and the voltage between the base and the emitter of a TR Q6 is raised. Thereby the TR Q6 is turned on, a TR Q7 is turned on and the base current of a TR Q2 is interrupted. At this time, a current of the same amount as that of the current flowing into a TR Q5 is allowed to flow into a TR Q9 and reference voltage impressed to the bases of the TRs Q3, Q5 is raised. When temperature in the regulated power supply circuit is dropped to a certain degree, the TRs Q6, Q7 are turned off for the first time and a current is allowed to flow into the base of the TR Q2. |
