An elementary electronics question.

To draw a line under this, the buck converters (£8 for five delivered!) arrived today. I lashed up a chain of 10 'ultra bright' LEDs in wired in parallel. These things are rated 20,000 mcd, 2.5V max voltage, 50mA max current. I put a 2 ohm limiting resistor in series because the converters are rated at maximum 3A output and I didn't want to blow anything up. I assume that the converters are pure voltage sources and it's up to the user to ensure the load doesn't ask for more than 3A at whatever output voltage is dialed in.

It works beautifully - setting 12V on the supply and 3.6V on the output gave an input current of 130mA and output of 310mA. So a loss of about 440mW. That'll go down when I get it properly wired. The LEDs are eye-burningly bright!

Robin.

Phew!!

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So a loss of about 440mW. Plus 200mW for the 2 ohm resistor.

Fro your amusement here is a job I did a few years back. Worklighting on a PCB Drill.

It uses a Texas Instruments LM3404 and all the control is done by the switcher with the green current sense resistor providing the feedback. Volts in preset current out just connect the LEDs. I generally recon to get somewhere north of 85% efficiency.

regards Martin

As a quick postscript to Robin’s thread …

Anyone wishing to ‘play’ with strings of LED lights could do much worse than dash to Poundland.

[assuming that the store in Flint is representative] There are silly-cheap bargains to be had.

MichaelG.

A post postcript - this project rapidly got out of hand. I'd bought some high intensity LED's and after reading replies to my OP got them working with reasonable efficiency. Then I thought it would be nice to have them pulsing on and off in a random sort of way. I remembered that I have an Arduino Uno which I had never used and thought maybe I could do something with that. But maximum current from from the digital pins is a bit limited, so I bought some MOSFETs. No idea what I was doing so tested them:

That gave me some idea of what they do - I'm very much in the shallow end of the pool I know, but I have to reason things out for myself. Slowly these days!

It gave me confidence to to build a circuit which, with C/R timing networks, gives satisfyingly random pulsed lights.

This electronics thing has now become something of an obsession - I can't stick the workshop temperature (at present about 10C), can't afford to heat it at current prices, but I can do this stuff in the house.

My thanks again to those who have patiently given advice - somehow doing this simple thing has opened a floodgate in my mind.

I had to resort to plan B (no pulsed lights) with the stove but I did do a nice toilet throne which released a helium balloon when the chain was pulled. Completely ridiculous, but the audience seemed to like it.

Robin

Edited By Robin Graham on 01/01/2023 00:04:32

If you want to drive direct off an Arduino you'll do better with logic level mosfets. They manage with lower drive voltage

Thanks Duncan - more useful info. I got around it by making a two-stage driver, but shall look at these devices.

Robin.