Cheap EL Inverters?   - Page 1
Forum section: electronics / general

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 14, 2010, 08:14:23 pm
content: I ran into theseLCD'swhich don't have any shipping and handling scams attached. The backlight is electroluminescent and I can recall seeing small inverters that would be much smaller than the 100Vac+ inverter I could build up myself, but can't seem to find any now.I would like 5Vdc in at ~40mA and 70 - 130Vac out at ~150Hz - 2 kHzHas anyone come across a small cheap inverter to pair up with this display?

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 14, 2010, 08:31:16 pm
content: Build one.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 14, 2010, 09:26:37 pm
content: Problem building one is the transformer. Have alook at inverters for EL wire.Another approach is a simple flyback boost converter to generate a high DC voltage, with a 4-transistor H-bridge (or possible half-bridge + cap) to turn th eoutput to bipolar AC.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 14, 2010, 09:44:26 pm
content: It's not that difficult to wind a transformer for 100V output. I remember the time 8 years ago when I made a very similar transformer using the core from a PC power supply filter inductor. I then built a simple self-oscillating flyback converter. It developed about 400-500V at a few mA from 3 series AA batteries. I had a lot of fun with it, such as confusing my science teacher by lighting a neon bulb with just one wire.I also once wound something similar but only 90V output to ring a telephone for an intercom project.

author: DavidDLC
author_rank: Frequent Contributor
timestamp: July 14, 2010, 09:58:45 pm
content: Or check this out:http://www.nerdkits.com/videos/backlight/

author: slburris
author_rank: Frequent Contributor
timestamp: July 15, 2010, 03:55:38 am
content: EL backlights fade over time. How about a nice big display with anLED backlight?http://www.primelec.com/Electronic-Components/LCDs-Displays/2-Inch-X-6-inch-LCD-Dispaly-p2580646.html4 X 40 display for $2.99There's a discussion about these on AVR Freaks:http://www.avrfreaks.net/index.php?name=PNphpBB2&file=printview&t=79791&start=0It seems to say there are A and K terminals, which implies an LED backlight....Scott

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 15, 2010, 07:28:18 pm
content: Quote from: DavidDLC on July 14, 2010, 09:58:45 pmI like this and have been considering building up a variant of a 555 based inverter and this design. I believe I already have most of the parts I need too.Quote from: slburris on July 15, 2010, 03:55:38 amOkay, that works too well. I have 2 of the EL backlit units already. However, the inverters, even when building one oneself would be more than the cost of the LED backlit displays are. Conundrum...Quote from: NiHaoMike on July 14, 2010, 09:44:26 pmYeah, but that is more work than I want to do, and I was hoping to find an excuse to buy a couple more of the displays and have a cheap source of inverters. I have a cold cathode flourescent tube inverter that I salvaged from a scanner, but it doesn't do the trick.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 15, 2010, 08:16:11 pm
content: http://members.misty.com/don/oddbulb.html#elIf your device runs from AC power, you could just use some resistors as current limiting. For 120v, a pair of 15k, 2W resistors (one in each line) limit worst-case fault current to 8mA, regardless of whether or not hot and neutral are wired properly.

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 15, 2010, 09:12:21 pm
content: Quote from: NiHaoMike on July 15, 2010, 08:16:11 pmHeck, I'll try it for fun, but I really wanted to get 150 Hz or better... I may build up thenerdkitsto see how it works.

author: Unknown
author_rank: Unknown
timestamp: July 16, 2010, 05:30:11 am
content: Bah, I thought using direct mains connection for things like this was a thing of the past. Make to treat the EL circuit as dangerous voltage, and observe the proper clearance and isolation ratings that you would for mains. I believe mains-rated equipment is tested with 2kV transients, though I'm not sure if that's for 230V or 110V areas. I would be worried about the proximity of the EL backlight to the user (will the display shatter if the EL is overloaded?), and to logic circuits. If they have insufficient clearance, they too should be treated as mains. Using a small mains-rated transformer (even if it's just a 1:1 isolation transformer) makes your life much easier, which is why almost no one makes consumer equipment without isolation from mains anymore. You still have to be careful with the high voltage, but the transformer will limit the current and damp peaks.

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2010, 12:01:28 pm
content: It's possible to make a simple inverter using a single transistor and a transformer in an arrangement known as a blocking oscillator. Here's an example, Google for more information.Unfortunately a blocking oscillator produces an asymmetrical waveform, the negative side has a higher voltage than the positive. I don't know whether this could be a problem for the EL panel?If so you need a push-pull configuration which needs two transistors and a centre tapped primary.Here's an example, used to drive a fluroscent tube, the principle is the same.

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 16, 2010, 02:30:06 pm
content: Quote from: alm on July 16, 2010, 05:30:11 amTaken into account, but I only intended to do it as a trial, not as a permanent solution. I don't really want 110Vac wired directly to my project. I am going to either find a cheap <$5 inverter for EL wire or build up one of the designs that have been posted here or both.DorkBotPDXhas an awesome deal on PCB boards, anybody up for working on a layout for an EL inverter as a group?

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 16, 2010, 02:52:56 pm
content: Quote from: Hero999 on July 16, 2010, 12:01:28 pmYes, this would work. I built a similar circuit that used a pnp and npn triggered by a 555 to excite a resistive humidity sensor. The problem I may run into is cost. I bought the LCD's because they were cheap, if I can't find a cheap EL inverter or build a couple cheaper than it would be to buy an LED backlit display then I am back to where I started anyways. Thenerdkitscircuit only uses an inductor, which I am sure I have a couple in the junk pile or can scrap easily and can measure the value of. Using a step up transformer design will add more bulk than I want and possibly cost since I would either be limited to using a step up I have on hand or buying one. I have a small fluorescent tube inverter with a step up on it out of a flat bed scanner, but it is stepping the voltage up to more than I want and outside of the range of what my DMM will meausure directly. I used a 2:1 voltage divider and read 600V so I believe it is 1200Vac. It arcs nicely across two wires set about 5mm apart on the output of the transformer, fun...

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2010, 09:21:00 pm
content: It's practically the cheapest way of doing it, one transistor, a resistor, capacitor and a transformer, all right maybe the inductor idea might be the same price or a bit cheaper but would it be as bright or efficient?The good thing about the blocking oscillator is that it will adjust itself to the optimum frequency, as it's self-oscillating.The transformer can be wound on a standard ferrite or probably even a bead, like a Joule thief. I was going to suggest using a photoflash transformer but the voltage will probably be too high. If you want pre-made then maybe an audio transformer would be suitable or perhaps a small common mode choke? You might not need a secondary, the kick-back on the primary might be enough.

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 16, 2010, 10:40:56 pm
content: Quote from: Hero999 on July 16, 2010, 09:21:00 pmI can agree with you on that, I'll rummage through my crap and see if I can come up with a xmfr that will work. I was originally basing my opinion on needing to order parts and what I thought I had. I'll give it a try if I don't have to order anything. I am a little hazy on how to set the frequency, any help there? The frequency is of importance since the brightness o the backlight depends upon frequency.

author: Zero999
author_rank: Super Contributor
timestamp: July 16, 2010, 11:23:12 pm
content: TO be honest, I don't know how to calculate the frequency which will depend on the voltage and the load connected to it. I'm not convinced it's as important as some say, most EL panels I've seen aren't fussy and the ones I have use a blocking oscillator inverter so there can't be that much wrong with it.

author: Rhythmtech
author_rank: Regular Contributor
timestamp: July 17, 2010, 01:26:51 pm
content: Quote from: Hero999 on July 16, 2010, 11:23:12 pmSounds good, I am going to try to set some time aside in the near future to do it. I'll post how it goes. Thanks everyone!