This is a design circuit to generate the -9V supply that is used by the row drivers as the off voltage for the TFT gate. This circuit is very simple design using LM2622. The LM2622 can be used in conjunction with a diode inverter circuit. This is the figure of the circuit;
The diode inverter works in the following manner. When the switch of the LM2622 is open, D4 conducts and the voltage across C7 charges to approximately +9.0V. When the switch closes, the voltage on the SW pin is suddenly dropped to GND. Because the voltage across C7 cannot change instantaneously, the voltage between D4 and D5 is −9.0V when referenced to GND. In general, this configuration will generate an unregulated voltage that is equal in magnitude but opposite in sign to the regulated supply.
[Circuit source: National Semiconductor Notes]
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