Inverter Circuit - ViewSonic VX1933W Service Manual

4.2 Inverter Circuit

1. R503, ZD501, R502, Q501 components convert +14V voltage into +5.0V voltage, and the voltage
supply to IC501. The extra PWM pulse signal (BRIGHTNESS signal) input to control IC through R512,
R514, C510, The LCT pin is set to a DC voltage of 0.7V by using a resistor divider(R507, R516), change
the duty of PWM pulse, will regulate the lamp current. The ON/OFF voltage connect to pin10 of IC501
through D501, R501, A voltage of 2V to pin10 of IC501 enables the IC and activates the striking timer.
The SSTCMP pin of IC501 performs the soft function, the C511 set the time of SST. The operation
frequency determined by external capacitor C512, C521 and resistor R508 connected at CT pin of IC501.
C515 connect the TIMER pin of IC501, the capacitor to set striking time and shunt down delay time.
DRV!, DRV2 output for power MOSFET U501, U502.
2. OZ9938 provides two drive signals for U501, U502, and they work in push pull topology driving, two
transformers are connected in parallel with each transformer driving two lamps in series. Turning each
N-Channel MOSFET "on/off" complementarily, produces an alternating current through the transformer
primary and secondary. The "on" duration of the switches determines the amount of energy delivered to
the CCFLs. R504, C504, R505, C505, R532, C529, R530, C522 are snubber networks, they suppress
Voltage transient spike in drain of power MOSFET.
3. R506, R510, C509, C513, C514, R525, R531, C528, C525, and C527 are connected between high
voltage output connector and ground, the divided AC voltage is inverted DC voltage through D502, D503,
D508, and D509. The sense voltage feed back to VSEN (pin 6 of IC501) for an over voltage/over current
condition during normal operation. R528, R533 are current sense resistor, current sense signal feed back
to Isense (pin 5 of IC501) for lamp "ON" detection.
4.3 I/F Board Circuit
4.3.1 Power Input
+5V is from the power board and supply for U101(FSP2160-3.3V) U105(NT68672UMFG) and panel.
+3.3V output is generated from +5V through C102 filtering, and U101 outputs. +3.3V is used for U108 U105
(NT68672UMFG). +1.2V output is generated from +3.3V through U102 outputs. +1.2V is only used for Scaler
NT68672..
4.3.2 Scaler(NT68672UMFG)
1.) NT68672: The NT68673UMFG is a highly integrated flat panel display controller that
interfaces analog and digital inputs. It combines a triple ADC, a HDMI 1.3 receiver, a high
quality zoom and shrink engine, a multi-color on screen display (OSD) controller and many other
functions in a single chip. It provides the user with a simple, flexible and cost-effective solution
for various flat panel display products.
The NT68673UMFG operates at frequencies up to 205MHz, suitable for LCD monitor up to
WUXGA resolution. The NT68673UMFG also has a built-in 2D noise reduction function to
provide more stable video quality, spread spectrum to provide low EMI solution, sRGB for video
color space convert and post pattern for manufacture test.
The display provided single/double pixel clock LVDS interface.
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