| 摘要 |
<p>Regulation of the supply voltage to the printing heads of a thermal printer improves uniformity of print density by regulating the temp. of the head during differing time intervals between printing of lines. The interval between printing of successive lines is measured by a counter (5) having a clock input (H), a reset input and an input (1) fed by pulses generated at the ends of each print line. The four outputs of the counter are passed to a latch (6) when the counter resets. The memory has four outputs, each connected to the base of an npn transmiter (T1-T4). The collectors of the transistors drive input resistors (R1-R4) are connected in summing mode to the input of an integrator circuit comprising an operational amplifier (7) and a capacitor (C). A reference voltage connected to the non-inverting input of the operational amplifier is obtd. from a voltage divider including a variable resistor (P1) and a thermistor (TH)which compensates for ambient temp. variation.</p> |
