alphanumeric lcd display powering

jmurba

Hi all,

mabye someone could help me.
well, on my oxymeter circuit I use a standard alphanumeric lcd, the data sheet gives an absolute rating voltage supply of 5.5 volts, the rest of my circuit works with any voltage from 3v to 18v
I use 4 alcaline AA batteries,
when the batteries are new they deliver me a 6,4 voltage, minus the non return diode voltage drop I have with new baterries 5.8 volts...so 0.3 v volt more then the absolute ratings of my display data sheet....
I can't find standard displays that would tolerate a high supply voltage... and I would not like to use a regulator....

any idea on what I could do ?????

regards

jean mi

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paulraymaekers

.... use 2 diodes .... :-)

simple and effective!

paul

(ps: you also have diodes with 0.4V drop!)

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PeteS

A five volt zener and a resistor.

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jmurba

Hi paul,

Of course I thought of this solution, but the new baterry tension varies a lot, I had some starting at 7 v (4 AA 1,5 nominal), ans some other 6,4...grr

so it is difficult to find the good configuration....

but for the average baterries (with a max of 6.5 volt new) a one volt drop diode seems something intesseting.

regards

jean mi

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KevJ

Will the display run at 5.0 Volts ?

Why don't you want to use a regulator ?
78L05 is small and wouldn't be any less reliable than any of the other suggestions.

Kevin

divetheworld

I would agree.

Brent

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jmurba

Hi Kevin

of course I thought of using a regulator, but precisely I was trying to avoid this solution
the linear ones have a big consumption, and the others , regulateurs a découpag (don't know their name in English) are really noisy...

In addition even for the low drop regulators the tension must use a supply tention of 0.87 volt above their nominal tension, and for a 5 volt circuit and a 6 volt nominal battery tension the gap is really narrow... grrr

if you had a non reverse polarity diode the window will be totaly closed

if I use a tension regulator I will be forced to use a 9 volt batterry .

I don't want to use a special lithium battery, cause I want to be able to drop in any supermaket on the planet buy a common baterry and go diving in case the one in the gauge is flat.

4 AA were a good solution for me...

to be honest the gauge works well now even if the display supply exceeds it's absolute tension rating.....

but it is not really resonnable not to follow the component data sheet recommendations...

any way I am gonna have a look to the regulator you mentionned .

thanks a lot

jean mi

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jmurba

yes it is a simple linear regulation system, but it consumes power...as far as I know...
and it is also noisy
but anyway...

I really wonder what solution is in use in diving computers, cause they have the same problem, the batterry tension varies a lot...

regards

jean mi

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PeteS

It's as simple as it gets, and it requires no "headroom" whatsoever, unlike a regulator.

As for noise, sling a small cappy on the output to snub any HF noise. But I wouldn't mind betting that your display is fairly noise tolerant anyway. But a zener isn't that noisy anyway. After all, you are supplying it from a DC source, not a rectified AC source. No hum, or diode switching to suppress.

Consumes power? Only if you get the resistor too low in value causing a high current to flow through the zener diode. Resistor current should be full load current of the display plus a bit, under worst case battery conditions which is lowest voltage.

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Pete S.

http://www.steggle.co.nz

Every silver lining has a cloud

jmurba

Hi pete,

your solution seems the most reasonnable in fact....
I have a 6mv comsumption, and when buzzer ring and hud alarm is on the consumption climb up to 20mv,
so as a matter of fact it is not really high
I am gonna test it and see if it increases the consumption, anyway I have 3000 mA to 4000 mA baterries... and for the moment 400 hour duration....so a littlebit more won't kill me...
thanks for your help , I will keep you aware of the results.
regards
jean mi

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