Choosing an inductor for a flyback converter - Page 1
Forum section: electronics / beginners

author: amaschas
author_rank: Regular Contributor
timestamp: February 13, 2020, 04:00:45 am
content: Hi all, I've been working on a custom RGB led light panel project, and I've been looking into options for powering the panel off of AC mains. I will be powering 9 rows of 8 LEDs in series(3 rows of R, G and B LEDs) at a max voltage of ~3V using 3 x AL8805 constant current drivers. Each row should draw 200mA at 20-23V, so the total draw will be roughly 40W (probably less, since I used the voltage of the blue LEDs to do the math, and they run at the highest voltage). I'll also be powering a micro controller for PWM dimming, so I'll need a regulator to convert 24V to ~5V, but I think the impact on the overall power draw will be negligible. I figure a 24V 45W power supply would do the job, and I was looking at what it would take to build my own AC/DC power source. I came across this reference design which I think would work for my purposes:https://ac-dc.power.com/sites/default/files/product_document/design_example/der-815_45watt_isolated_flyback_power_supply_for_smart_speakers_using_innoswitch3-cp.pdfMy question is whether it's possible to buy a commercial transformer/coupled inductor for the power supply, rather than winding one from scratch as laid out in the document. I can't imagine that a custom winding would be necessary for a single output at a fairly standard power output. I appreciate any feedback!

author: george.b
author_rank: Frequent Contributor
timestamp: February 13, 2020, 05:52:20 am
content: In general, no, you can't find them off the shelf. An SMPS transformer is tightly coupled to the design parameters, which makes it difficult to offer it as an off-the-shelf, "one size fits all" component.

author: amaschas
author_rank: Regular Contributor
timestamp: February 13, 2020, 05:58:04 am
content: Hrm, in that case maybe designing my own flyback converter is the wrong route to take. I was thinking that it would be good to have isolation in my 30V supply, but maybe I can get away with just isolating the power supply for the microcontroller, since the switches and pots to control the LEDs will all route through there.

author: amaschas
author_rank: Regular Contributor
timestamp: February 13, 2020, 06:17:11 am
content: Quote from: blueskull on February 13, 2020, 06:08:48 amThanks, that really clarifies my route! I'm pretty comfortable working with DC voltages but trying to learn about transforming mains current has been giving me a headache.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 13, 2020, 07:22:24 am
content: You may want to look at some of the Power Integrations documentation, wizards etc. It may help you understand something about the 'custom' nature of trafos for flyback designs. As others, I don't recommend rolling your own or dicking around with mains but if you want to learn, their stuff/ref designs etc deserves recommendation.As to your actual question: Wuerth and others have a small collection of 'standard' trafos but a major advantage of rolling your own is that you can make the trafo (and everything else) fit your application better. You'd obviously loose that advantage, so your delta with repurposing something pre-built decreases even further.