Beginner Transformer Question - Page 1
Forum section: electronics / beginners

author: brooko
author_rank: Contributor
timestamp: March 17, 2024, 09:13:55 am
content: Hi, I have a small PCB from a cycle light. It doesn't work, in that it is showing that it's powered but won't switch the lights on. When removing the PCB the small transformer coil had detached and I'd like to reconnect it.On the attached photo is a picture of the PCB. Can someone let me know.....1. Presumably T+ and T- are the transformer connections? Is that right?2. I believe one end of the coil was attached to A, is that right... if so do I attached the wire from the inside of the coil or the outside?3. Where should I attach the other coil wire? The T- doesn't look right to me?Thanks, in advance.Andy

author: Ian.M
author_rank: Super Contributor
timestamp: March 17, 2024, 09:21:06 am
content: A transformer has more than one winding so at least three connections if one is shared or four if not. A component with a single winding (and two connections) is an inductor.With that bit of pedantry out of the way, in nearly all cases, it doesn't matter which way round you connect an inductor.Before you do *anything* to the board, look closely at all the solder joints with a magnifier to see if you can find any evidence of the broken off wires.For us to help you figure out the connections, we'd need to understand the circuit, which means we need good, large, well lit, in focus photos of *both* sides of the board, clear enough to read the tiny part numbers.

author: brooko
author_rank: Contributor
timestamp: March 17, 2024, 09:37:55 am
content: Fabulous, thanks Ian... attached is a high def pic of both front and back.'A' had a broken connection wire, which I had removed already (hence you can't see the broken end now).Regards, Andy

author: Ian.M
author_rank: Super Contributor
timestamp: March 17, 2024, 09:51:58 am
content: Unfortunately the image resolution isn't high enough to see the numbers on the MOSFET and driver IC. If your camera has a macro mode, use it! Zoom in on the PCB so it fills the frame with minimal borders, use a white sheet of paper as the background, and don't combine the photos in a single JPEG. Also, this forum recompresses images, so check what you've uploaded, and if the quality has degraded significantly, consider using an external photo sharing site.

author: brooko
author_rank: Contributor
timestamp: March 17, 2024, 10:11:01 am
content: Hello Ian, here goes.Lit from the side to improve contrast, shot through magnifying glass, no macro mode on the lenses I have.The numbers are now legible, hope this helps, Andy

author: Ian.M
author_rank: Super Contributor
timestamp: March 17, 2024, 10:28:43 am
content: Great. That's a KIA50N06 60A N-MOSFET, and aQXA9920LED driver.Fig 1 Typical Application Circuit in theQX9920 datasheetshows the inductor in series with the LEDs, between + supply and the MOSFET Drain, with an anti-parallel diode ('DFW') across the series combo, cathode positive. However I dont think this matches your circuit. The QX9920 can also be mis-applied as a boost converter, see:https://hackaday.io/project/162394/log/156123-first-thoughtswhich is how I think your board is configured.If so, the other inductor lead goes to the junction of the diode anode and the tab of the MOSFET.

author: brooko
author_rank: Contributor
timestamp: March 17, 2024, 10:35:20 am
content: Thanks Ian, brilliant.So that would be 'A' and 'T-' from my first pic?Either way around as the inductor has no polarity?Andy

author: Ian.M
author_rank: Super Contributor
timestamp: March 17, 2024, 10:47:05 am
content: It certainly looks like 'A' and 'T-' (either way round) but I'd spend a bit of time tracing the circuit with a DMM on continuity to see if it matches the connections to theleftrightof the Hackaday schematic's QX9920.

author: brooko
author_rank: Contributor
timestamp: March 17, 2024, 10:59:49 am
content: ITS WORKS.... thanks again Ian.Best Regards, Andy

author: Ian.M
author_rank: Super Contributor
timestamp: March 17, 2024, 11:02:46 am
content: Great. As you have seen, this sort of thing is fairly easy to figure out once you know what ICs are being used, and have sample application circuits to look at. It gets a lot harder if the b*****ds have ground off the part numbers or if its a COB black epoxy blob.