| 摘要 |
PURPOSE:To obtain printing density always equal even when kinds of external power sources different in output voltage are used, by constituting a printing density control circuit of a pulse width control circuit, a voltage detection circuit and a voltage/time converter circuit. CONSTITUTION:Reference voltage Vs is applied to the comparator A in a voltage detection circuit 51 and, when the voltage Vn obtained by dividing the voltage Vin of an external power source by a variable resistor RV1 becomes higher than the reference voltage Vs, the output of the comparator A is set to a higher level and, when the voltage Vn is lower than the reference voltage Vs, the output of the comparator A is set to a lower level. When the output of the comparator A comes to a higher level, the time constant of a one-shot multivibrator M becomes smaller in a voltage/time converter circuit 25 and a pulse width control circuit 12 and, accordingly, the pulse width of voltage applied to a heat generating resistor 4 also becomes shorter. Contrarily, when the output of the comparator A comes to a lower level, the pulse width of voltage supplied to the heat generating resistor 4 also becomes longer accordingly and printing density can be controlled. |
