Thermal Head Drive Circuit - Brother PT-1800 Service Manual

3.2.6

Thermal Head Drive Circuit

Figure 3.2-10 shows the thermal head drive circuit.
The print head used in the PT-1800/1810 integrates a heat generator (consisting of 128
heating elements vertically aligned at 180 dpi) and a built-in driver IC.
Synchronizing with the clock on P02, the CPU outputs print data on P00 in the serial
form. Upon receipt of the P01 signal issued by the CPU, the thermal head drive circuit
latches the print data and drives the heating elements of the thermal head according to
the signal issued from P03. Figure 3.2-11 shows the timing scheme of the thermal head
drive.
Capacitor C12 works as a thermal head overheat protector. It cuts off the P03 signal to
shut down invalid drive current if the signal sticks to the Low level due to any
malfunctions of the programs or the CPU.
Since thermal print heads are very sensitive to heat and the head drive source is not
stabilized, the CPU determines the ON-time length of the P03 signal while monitoring the
head drive source voltage and the ambient temperature (refer to Subsection 3.2.7).
Figure 3.2-10 Thermal Head Drive Circuit
Figure 3.2-11 Timing Chart of Thermal Head Drive
III - 10