LED driver

Fairly trivial to make a CR ballast.

NT

would that be non-isolated from mains? if so I wouldn't fancy it for the lamp part itself ...

yes they're not isolated. I take it your LEDs are touchable then.

NT

not touchable, but the LED strip (unusually all in series) is only separated from the aluminium case by a strip of some tape, the LED part is 3m distant from the driver, with just two single insulated cables for

• and - to it, no earth available ...

The other thought is to replace the LED strip with more conventional 12V LED strip that's cuttable every nth-LED and use a more easily obtainable driver.

You can make isolated CR PSUs by starting with 2 mains transformers back to back. But really if it runs on 90v it should use earth & proper insulation.

NT

I hadn't appreciated what voltage it must have been running at until it died and I dismantled it (30 white LEDs in series at ~3V each) no markings on the PSU, but I notice the output smoothing cap is only 50V rated, so probably explains why it only lasted a couple of years.

C plus a FW bridge is all thats really needed.

If your name isn't bodgit & scarper you need a series R to limit inrush current to a value the LEDs will survive, and to act as a fuse when/if the C shorts. You'll also want a discharge R across the C.

NT

What makes you think the LEDs are a single series chain? Often there are two or more series chains on the tape, connected in parallel, so the driving voltage is lower (or variations such as adjacent LEDs paired in parallel).

Well ... I thought I'd looked closely enough to see it zig-zag as a single run (this tape has no cut marks or resistors) but looking more closely they are in series runs of 5 LEDs, with 6 groups in parallel.

Yes, even still constant 60mA @ 15V drivers seem rare ...

Oh silly, of course now I'm looking for 300mA and there seem to be plenty of those ...

I had a GU10 LED explode. It was definitely series wired.

Apart from the zig-zag track, the other thing that fooled me, was that unlike other tapes which have + and - connections at both ends, this one has + at one end, and - at the other ...

I was just thinking the same. 90 v that is a little odd. Are we sure the leds all still work and that a short somewhere in this sticky insulator is not what has done for the psu in the firs place? Lossless droppers using capacitors are generally only used in cases where you cannot actually touch the cable at all, I used to have one in a pifco torch that was rechargeable, eventually the capacitor went leaky and filled the room with orrible smelling smoke. Yuck. Brian

yes, the LEDs give the occasional flash and flicker

It's one of your favourite SMPSUs, and I've ordered a replacement 300mA

If the herring had 90v across it I'm pretty sure it's a dead herring now

NT

Whereas a Torpedo fish would simply have claimed it was recharging its batteries. :-)