CIRCUIT OPERATIONS
- 119 -
KX-FT21LA
A
A
B
C
B
C
159
160
163
166
167
193
207
STB1
STB2
THDAT
THCLK
THLAT
ADSEL1
AIN2 A/D
CPU
IC1
C77
C74R73
R66
R72
C75
TH-
HEAD
3.3V
0V
0V
Effective signal
ref LEVEL CLAMP
1V
IC1 internal bias
CLAMP
Thermistor
L3 L18
Circuit Diagram
Timing Chart
3-4. SUPERVISION CIRCUIT FOR THE THERMAL HEAD TEMPERATURE
(1) Function
The thermistor changes the resistor according to the temperature and uses the thermistor's characteristics.
The output of pin 193 of IC1 becomes a low level.
Then when it becomes a high level, it triggers point A .
In point C ,according to the voltage output time, the thermal head's temperature is detected.
After the thermal head temperature is converted to voltage in B , it is then changed to digital data in the A/D converter
inside IC1. The CPU decides the strobe width of the thermal head according to this value. Therefore, this circuit can
keep the thermal head at an even temperature in order to stabilize the printing density and prevent the head from
being overheated.
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