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Old 14th Apr 2021, 12:15 am   #2
beery
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Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
Default Re: LightCraft Magnifier Lamp LED upgrade

Hi all,
Here is the final part to the story...

Having tested the PCB layout in cardboard, I now wanted a proper PCB. I also wanted an inbuilt 24V PSU so that the mains switch on the top of the lamp would actually disconnect the input of the PSU from the mains. This was less to do with saving energy, but more to do with having fewer devices permanently switched on that might be a source of modulation hum...

To make the PCB I used a prototyping PCB routed to make the board out of copper clad SRPB. I realise that if anyone wants to get a PCB manufacturer to make it, then it would be cheaper to make 8 identical curved sections and then link them together to make the whole circle.
Next the PSU. I had a look through the box of things I had rescued from the WEE bin at work and I found one suitable PSU. This turned out to be a 6W constant voltage/constant voltage LED driver. By this I mean that it can deliver 24V at up to 350mA, beyond this point is will deliver a voltage of up to 24V at a constant current of 350mA. Typically these drivers have lots of 100Hz ripple in the output. This is intentionally not smoothed out at the primary side of the PSU in order to keep the power factor close to 1 and in any case, hum on LED lamps is fine for most applications. I don't know the exact pedigree of this LED driver, it would have been purchased for evaluation and then the casing discarded when it was put in the scarp PCB pile. Clearly it hadn't really been used though.
The PSU/driver board is smaller than the original fluorescent ballast and simply sits in the casing in the same way that the original ballast did.
So there we have it, quite a fun little project.

Cheers
Andy
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