| 摘要 |
<p>PURPOSE:To prevent the breaking of heat sensitive heads by a method wherein a circuit is mounted which detects the output of ''H'' level signals from a heat sensitive element drive transistor during time not less than a fixed time. CONSTITUTION:Signals in a ''H'' level are not continuously formed at a portion of resistance 11 normally during time not less than time intervals that transistors 51-54 are each in ON. However, when any of the transistors 51-54 is broken due to some cause and the signals in the ''H'' level continuously flow, a re-trigger mono-stable multivibrator 14 returns to a stable condition after a single, stable time elapses, the signals in the ''H'' level are produced, ''H'' signals are applied to a NAND gate, and the output becomes to signals in a ''L'' level. The ''L'' signals are detected by means of a detecting circuit 16, clear a bit select circuit 8 and turn all of drive elements 91-94 OFF. Thus, currents do not flow through heat sensitive elements 2, and breaking is prevented.</p> |
