Torben said:Sounds like you need an inverter to get the high AC you need. I would suggest just buying one, but you don't say what the make and model or specs of the LCD display are so it's hard to say any more than that.
Try Googling for "electroluminescent backlight inverter schematic"--I found **broken link removed** quickly, but I'm not sure it is suitable for your backlight for two reasons: 1) I don't know what your module is; and 2) I am no inverter expert.
Good luck!
Torben
Torben said:Hi Al,
Check this thread for some more information and a link to an appnote which might help.
Personally I don't see why you couldn't use a 555 at 400Hz to do this, except you'd need to use it to drive a transistor which can handle the high voltage. The circuit given in Figure 2 at **broken link removed** uses a Zetex FMMt458 as the final drive transistor. Are you cool with SMD devices?
I could just be making this more complicated than it needs to be.
Torben
bigal_scorpio said:Hi again Torben,
I like the look of that circuit, and I don't mind using the odd SMD component, but alas I dont have any of the ones in the circuit.
I do however have what I hope would be an equivalent for both the FMMT458 and the FZT857, its the JE340p, sheet attached!
I also have a good few ICM7555 ICs, sheet attached,was thinking would be a possible substitute for both SCT1555 ICs, what do you think?
Anyway thanks for the help so far, its much appreciated........Al
bigal_scorpio said:Hi Torben,
Built the inverter circuit this afternoon! Then spent 4 hours trying to get it to work!
Could be I got something wrong in my translation to Vero board, or maybe the circuit isn't as tolerant of the parts that I had to substitute?
Anyway I am going to have a go at breadboarding it instead I think or do you think it would be worth a try on Proteus or Multisim, just to check the original circuit's operation?
BTW when I did measure the output with my DMM there is about 9v on AC, but is there any possibility that my DMM is not measuring its output correctly?
I was wondering if the frequency was way out would it give a false reading on the meter?
Any thoughts welcome.............Al
Some good quality (Fluke) DMMs are good up to 10-100Khz. A cheap meter may not go as high. Look at the spec sheet for your meter if you have one. If there is no spec sheet, assume it is only accurate up to 500Hz or so.bigal_scorpio said:I was wondering if the frequency was way out would it give a false reading on the meter?
Hai, Unless you are specific of using this only for reasons known to you, Perhaps you may avoid further investing on this and rather go for conventional LED type backlit and with display pin-out to suite your project. I feel it may not cost that much as a ready made inverter.bigal_scorpio said:Hi again,
Just had one question answered and now found another!
Just realised that my LCD display I was planning on using has not got the standard LED backlight, but instead has an Electro Luminescent pad.
I know that they require an AC voltage to drive them but can't find anywhere that has info on building a simple circuit to drive it! One that wouldn't kill it anyway!
So if anyone has a simple way of doing this I would be very grateful, I thought about a 555 timer circuit but it seems to be the only 555 circuit that I CAN'T find on google
Thanks again for looking...........Al
mvs sarma said:Hai, Unless you are specific of using this only for reasons known to you, Perhaps you may avoid further investing on this and rather go for conventional LED type backlit and with display pin-out to suite your project. I feel it may not cost that much as a ready made inverter.
As reg using the present one, what voltage level you need for the back lit to work? Perhaps you can use an clock available on your microchip and using a transistor and inductor, you can make a charge pump and i wonder whether such arrangement would power it. You need not rectify the output.
I feel that when a new LCD display with LED back-lit is cheap enough- no point in designing a aux psu for old version LCD. Perhaps if one has an LCD panel without back lit and pin compatible, better substitute and use ad Normal LCD for day light.Torben said:That's what I was getting at with the "easier to do" idea. I'm thinking maybe the circuit from the ED site is overkill for a LCD backlight. This backlight only wants ~100V at ~400Hz, according to the datasheet.
Torben
bigal_scorpio said:Hi to everyone,
Thanks for simming the circuit Torben, the infor about the peaks and such is nice to know.
Further to Torbens suggestion that the circuit is overkill, I was wondering if simply putting the output of a 555 astable circuit running at the required frequency through a small audio output type transformer could be possible, again I am thinking this simply because I have some of them to hand, and from the specs on the backlight it seems that very little actual current would be drawn.
Which brings me to one final question - would I need to limit the current to the EL as is required when using LEDs or is the EL somehow self regulating?
Thanks for all the suggestions and help guys, keep it coming please.
Al
bigal_scorpio said:Hi Torben,
Just about to start building your circuit when I noticed something iffy. Are C3 and L2 doing anything? There is a link that bypasses them, is this intentional?
I must admit to being a bit lacking in knowledge about inductors so if the bypass is intentional please let me know.
Thanks again.....Al
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