| 摘要 |
PURPOSE:To suppress a defective mode to the best and to prevent an IC from being damaged due to heat, by protecting the operation of a chip at an abnormal high temperature by cutting off a common bias source when a high temperature is applied on the chip. CONSTITUTION:A Zener diode Q12(Vz) biased by a constant current 10 and a diode Q13(Vd) for temperature compensation generate a reference voltage for setting a chip detecting temperature. The reference voltage (Vz+Vd), after being resistor-divided by resistors R5 and R6, is applied on between the base and the emitter of a transistor Q11. Generally, the voltage is set at an operating threshold value at the high temperature between the base and the emitter of the transistor Q11. And when abnormality is generated and a temperature reaches a detecting chip temperature, the transistor Q11 is energized, and the bias current of a start up resistor R1 is bypassed by the transistor Q11, and all of the constant current sources of transistors Q1-Q9 and a constant current sync source are cut off, and the operation of an FD (floppy disk drive) control circuit stops. In such a way, it is possible to prevent the IC from being damaged due to thermal runaway by the abnormal rise of the temperature of the chip.
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