In the link below, the backlight, 5v at 120 ma, do the pot and resistor take down the voltage and ampage or has he done something to the power supply before it get here and what would i have to change if i wanted 4.1volts at 900ma, takeing said power from my 5volt rail from psu. cheers minging link http://www.turbokeu.com/mycomputer/glcd/glcd.pdf
He's based on the backlight being 3.6V forward voltage, so a 12R resistor gives (5-3.6)/12=117mA max.
complete newb here EH? so the pot reduces the voltage yes? and the resistor is limiting the ampage ? so how do i go about getting 4.2 volts at 900ma from my 5v rail ? thanks again...
bump..sorry to be impatient but i am chomping on the bit to get the backlight fired up, lcd running like a dream in lcd info, studio and powerlcd but i need my backlight, lcd is this one if you were wondering. link.. http://www.powertip.com.tw/product/PG SERIES/PG 240128-A.pdf thanks again
You've got the formula, what more do you need? (5-4.2)/0.9=0.89 ohms, use three 2.7 ohm 0.6W (Maplin M2R7) in parallel. The resistor sets the maximum current, the pot will turn it down. At 900mA an ordinary pot won't do, it needs a wirewound rheostat about 50 ohm 25W. For such high currents the proper solution is a PWM controller.
'someone to hold my hand' Sorry to be a pain mate, thanks for your help, not the answer i was hoping for but, better than frying my backlight, guess i need a few more bits. cheers minging
