LCD Drive Voltage (VEE) Generation Circuit
The polarity of the LCD drive voltage (VEE) differs according to the LCD module.
Fig. 2.23 shows the circuit for the LCD module driven by the minus VEE voltage. The
+5 VDC source voltage is switched continuously by the 20 kHz pulses from CBIC (#8) to
energize L5. The reverse voltage generated by L5 is rectified by D6 and regulated by
ZD5. The ZD5 determines the VEE voltage (about -16 V).
The LCD module driven by the plus VEE voltage uses the circuit shown in Fig. 2.24.
The +24 VDC source voltage is switched continuously by the 90 kHz pulses from CBIC
(#8) to energize L2. The voltage generated by L2 is rectified by D5 and regulated by
ZD4 and ZD6. The ZD4 and ZD6 determine the VEE voltage.
VEE voltage is adjusted by turning VR1.
Fig. 2.23 LCD Drive Voltage Generation Circuit (Minus Voltage VEE)
Fig. 2.24 LCD Drive Voltage Generation Circuit (Plus Voltage VEE)