Veey - Lcd Panel Drive Voltage For Vertical Power Supplies - Brightness Reference - Epson S1D13706 Technical Manual

Epson Research and Development
Vancouver Design Center
2.2 VEEY - LCD Panel Drive Voltage for Vertical Power Supplies - Brightness
Reference
DD_P1
Connecting to the Epson D-TFD Panels
Issue Date: 01/02/23
A negative voltage potential (VEEY) must be provided as a brightness reference and a
temperature compensator to the vertical logic and vertical liquid crystal driving power
supplies. The recommended voltage is -32.0V with a minimum allowable value of -37.0V.
Figure 2-2: "VEE Switching Power Supply" shows a standard topology buck-boost
switching power supply controlled by the S1D13706 output signal GPIO5 (DD_P1).
C1
VCC
220p 50V
R1
1K
D1
PTZTE2536A
Figure 2-2: VEE Switching Power Supply
The circuit in Figure 2-2: "VEE Switching Power Supply" uses GPIO5 (DD_P1), a
S1D13706 output that has a 200KHz - 96% duty cycle signal, as the switching control of
the switching power supply. The duty cycle of the input to the gate of Q1 is varied by the
feedback of VEE through D1. This diode feedback causes an overshoot on the rising edge
of GPIO5 (DD_P1) that is proportional to the output level of VEE. This overshoot settles
to a steady level after a variable time depending on how high the overshoot was. This
variable time causes the high speed CMOS inverter (U1) to trigger at different times,
thereby varying the duty cycle of the control input to Q1.
When Q1 turns on, the inductor L1 builds up its magnetic field using current from VDDH,
and D2 is reversed biased. When Q2 turns off, current flows from L1 causing the voltage
across it to reverse polarity and forward bias D2. The output capacitor C3 is charged and
holds the output voltage with an acceptable output ripple when the cycle repeats (Q1 turns
on). The output voltage is regulated by the feedback controlling the on/off times of Q1. The
longer Q1 is turned on, the more current is stored in L1 and the resulting polarity change
when Q1 is turned off is greater.
VDDH
U1A
1 7 1 2
Q1 3
7W14F
2SJ285
R2
150K
L1
560u
C2
4.7u 16V
VEE
D2
1SS388 C3
2.2u 50V
Page 9
S1D13706
X31B-G-012-03