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LCD contrast programmable negative power supply

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bobytronic

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digital potentiometer lcd negative

Hi,

I'm looking for a solution to design a programmable negative power supply for LCD contrast with a DC/DC converter

-18V<Vout<0V

Somebody has an idee or an Application note (DC/DC converter)???


Regards
 

sadat007

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pwm to dc for lcd contrast

HI,
why not use Digital Potentiometer from Maxim etc.
For -Ve supply for LCD also Maxim good.
OR Opamp with inverting mode, dual supply and input with PWM (from uC) and resistor-capacitor filter to generate -Ve at output.
 

ash

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lcd contrast boost

you can use 7924 for -24v power supply and interface it DAC or digital potentiometer to microcontroller
 

bobytronic

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negative voltage controller 7662

Hi,


The problem is that i have only +- 15 V power supply !! and i want up to -18V !! ==> BucK Boost converter!!
 

ash

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there was a application note on microchip.com that demonstrates +12v to +170v. If you put inductor in (-) line you would get -170v. I didn't read the article but i think switching time of fet specifies outpul voltage.
 

sadat007

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you can also try Doubler (Capacitor+Diode) on -15 if you have +15V,GND,-15V :wink:
 

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hi .. i am using and pwm from avr and some op amps to control contrast
of my lcd via software. If you need higher voltage try icl or maxim 7662 .. it is voltage inverter/doubler in small size and low cost

regards

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robotman

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If I remember correctly, Maxim makes a power supply chip that is a boost/invertor with an external digital up/down control. I have used it, but many years ago.

robotman
 

atomic_ant

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cap charge pump with the PWM coming from your uC, ripple can be reduced by putting a regulator at the output.
 

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