PURPOSE: To prevent a heat generating element from being broken, even if any abnormality should be produced in the energization time control thereof, by arranging the first and second timers adapted to output respective signals with input from the first and second triggers and a control circuit for the energization to the element.
CONSTITUTION: A signal which gives a fall edge at a fixd cycle is applied to an input A as input to a retriggerable mono-stable multivibrator 1 serving as a timer. A signal D obtained is connected to a clear terminal of another mono- stable multivibrator 2 while maintained at a triggerable level. Under such a condition, when the vibrator 2 receives an input B, it generates a signal E having a fixed pulse width t1 (not shown) to be determined by the constants of a capacitor C1 and a resistor R1. Therefore, the heat generating element is controlled by an input C while it won't be energized beyond the time equivalent to the pulse width t1 of a signal E unless a fall edge is applied to the input B again. When any abnormality occurs, the signal E won't give any level enough to energize the heat generating element thereby protecting the element.
NAKAMURA NORIKAZU
ISHIHARA TAMIO
