| 摘要 |
<p>PURPOSE:To enable a thermal resistor to be protected against heat damage by providing a protection circuit to latch a drive circuit in 'OFF' position at a time when voltages have exceeded an off-condition transient voltage set higher than a threshold voltage. CONSTITUTION:A thermal head drive circuit 5 is latched in 'OFF' condition until logic power supply voltage Vg exceeds an off-condition cancellation voltage Von set adequately higher than the threshold voltage Vth of a logic circuit which is operated by a logic power supply at the rise time of a logic power supply voltage Vg. In addition, at the time when the logic power supply voltage Vg has exceeded the off-condition transient voltage Voff which is set lower than the voltage Von and higher than the voltage Vth, the drive circuit 5 is latched in 'OFF' condition by a protection circuit 11 composed of a latching signal generation circuit 9 and a latching circuit 10. Thus the sequential operation of a power supply becomes unnecessary and at the same time a thermal resistor 2 can be protected against heat damage caused by logic power supply failure.</p> |
