Building an AC/DC power board - Page 1
Forum section: electronics / general

author: samfisher92
author_rank: Contributor
timestamp: January 08, 2023, 04:54:16 pm
content: Long story short.I salvaged this LCD screen from this really old laptop i had (motherboard had fried a decade ago, no chance in hell i can get it starting) so to put it together with a Raspberry Pi 3 I have on hand (I know I know it is freaking old but I can't care less about the age) I went to buy this LCD controller from Digitalview (not sure if anyone knows of them but their catalog seems pretty solid on their page)Counter lady shipped the package and then I realised that I didn't ask her for the power adapter for the board. I asked her and she told me that the power adapter for the board is 50 USD and shipping charge would be 35 USD so total would be 85 USD which translates to SGD$115 in my place. No chance in hell I am getting it. I ain't that dumb to blow such money away.So I thought, since it requires a 12V / 4A(min) power source and uses a 2-pin molex cable input according to the user manual, why don't I challenge myself to build my own power board for this board?I draw inspiration from standard laptop chargers as they definitely provide enough juice for this controller board and they use these relatively small-sized transformers inside it to step down the mains voltage. What kind of transformers are these? Are they technically off-the-shelf kind? what kind of power rating (in VA of course) am I supposed to look at like for instance my office laptop uses a power brick that steps down 100-240V, 1.7A AC input to 19.5V, 3.33A DC output?I am totally open to any opinion here.P.S. salvaged LCD screen runs on LVDS ancient technology

author: mariush
author_rank: Super Contributor
timestamp: January 08, 2023, 05:26:14 pm
content: You can buy 12v 4-6A adapters of all kinds for as low as 10-15$.It costs more to ship a classic transformer due to weight.examples :amazonhttps://www.amazon.com/s?k=12v+laptop+adapter(though careful as lots of no-name adapters from third party sellers or from eBay are often old laptop adapter power supplies recycled and put in new plastic boxes)digikey :12v 20w-300w wallwarts :https://www.digikey.com/short/bdpwn9w312v 20w-200w power supply style :https://www.digikey.com/short/n9bzprvpeven if the barrel connector is different you could just cut the connector ... or you could solder a couple wires on the PCB inside the monitor and install the right female jack to the cables on the monitor.The display's main power consumption will be the backlight ... probably up to 20-25w at maximum brightness. I don't know, depends on panel I guess.

author: samfisher92
author_rank: Contributor
timestamp: January 09, 2023, 03:00:54 pm
content: ooh i didn't think of just cutting off the connector. basically the molex cable is 2-pin to a SMA-looking connector. weird choice of a pair of connectors on each end.also if i get a power adapter i don't have to worry about the mains wiringwell about LCD screens, i have been reading application notes from Linear Technology. It is said that LCD backlight driver design is an interdisciplinary subject that is not for the faint-hearted. Alot of engineering effort is put into designing the inverter needed to drive the LCD backlight and the lamp is very power-hungry. Based on the datasheet i have for the screen, it takes in 685Vac at 6.5mA, 4.45W.hmm good idea, thanks, imma just get the ac adapter on digikey

author: mariush
author_rank: Super Contributor
timestamp: January 10, 2023, 05:35:10 pm
content: A backlight "inverter" is used to convert 110v ac or 220v ac or low voltage to that high voltage required for backlights to start.They make "universal" CCFL inverters and they're available on eBay and other places - typically they are powered from 8v..20v (recommended 12v or more) and have some extra wires like adjust brightness, enable (on/off ) etcexample of such univeral ccfl driver for panels with 2 tube connectors :https://www.ebay.com/itm/255661645079example for monitors with 4 connectors (minimum 10v required for this model) :https://www.ebay.com/itm/255661952278That being an old laptop panel, it may not have the standard high voltage connectors commonly used in backlights for regular lcd monitors so you have to look at the pictures.Alternatively, you can try opening up the panel and replacing the CCFL tubes with led strips, and then use a universal led backlight driver to adjust brightness.example of 2 output "universal" led backlight driver :https://www.ebay.com/itm/175219384723it takes 10v ..36v in, and boosts it up to 35v... 180v (the voltage depends on how many leds you have on led strip, ex 30 leds x 3v = 90v)leds are current controlled, so you can adjust the current from 50mA to 1000mA by adding or removing resistors (as seen in pictures)example of ccfl replacement led strips (even comes with led driver) :https://www.ebay.com/itm/364096008554you can cut the strips to shorter lengths to match your lcd panel size.