On Wednesday, November 4, 2015 at 11:21:25 AM UTC-8, Ian Field wrote:
"N_Cook" wrote in message
...
On 04/11/2015 18:36, Ian Field wrote:
Its a long shot, as its probably a house coded part.

Its a Crivit Sport LED bicycle lamp from the Lidl discount store.
....
Suitable LED parts are on order from Ebay, but I thought I'd have a go
at upgrading it with a switch mode current control.

Replacing the LED chip fixed the intermittent fault, so that pretty much
eliminates the circuit on the PCB.

I'd worry about the light distribution from a replacement LED; an eBay
item usually doesn't have a good angular distribution specification...

But While I'm working on it - I'd like to upgrade it with SMPSU technology.

There are some chips that do this; generally, though, it's going to be a small-outline
surface mount part, and will only work from a limited voltage input range.
This is a typical such part:
http://www.micrel.com/_PDF/mic3289.pdf
which, as I read it, is suitable for three alkaline cells in series (4.5V nominal).

If you are going to have a switchmode supply, it's most efficient to boost voltage
(the switches and diode have lower losses at lower current) and use multiple LEDs
in series.