7-22
2.10 Over voltage protection
Over voltage protection is needed on any power system. If some failure occurs and the voltage of +5Vx is too
high, the power system has over voltage protection circuit. +5Vx system has a comparator (IC20-LM339), if
the voltage of IC20 Pin 9 is higher than ZD03, IC20 Pin 14 will generate a High level output and MOSFET will
turned OFF. And the +5Vx will not support of all system.
The same principle of VLCD. And protection voltage is about (Zener voltage 5V/22K)*(22K+4.7K)= 6.1V.
When voltage is over 6.1V, IC20 Pin 13 will output a High level output and VLCD will not support IC22
(MOSFET) .
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