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LEDs on SMPS puzzled!

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bigal_scorpio

Active Member
Hi Guys,

Just wondered if anyone has come across this problem before and can explain it to me?

I recently changed some halogen 10w 12v bulbs in some lighting units for white LEDs (3 per unit + 100r resistor), to keep the running costs down as the lights are used for most of the day and night.

The halogens had the regualar 12v ac SMPS unit so I just fed the output through a bridge rectifier and then put a 3300u cap across the output.

The LEDs worked ok but had an annoying slight flicker (the kind you see out of the corner of your eye with flourescents) so I added another cap in parallel with the 3300, another 2500u and guess what, no flicker now, but a weird throbbing dim to bright effect about 5 seconds peak to peak!

Whats happening, I'm baffled, any suggestions please.

BTW I solved the problem by making up a real transformer supply an now all ok as expected, but I would love to know why I got the effects!

Thanks for looking..............Al :confused:
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Because the switchmode power supply was designed to run those specific lights, with that specific load - running a SMPSU on zero load (or near to it) often stops it working properly, and can make it 'blow up'.
 

Hero999

Banned
The smaller load on the output has probably reduced the dampening and throwing it in to oscillation.

If you used one of those old torroidal transformers it wouldn't have been a problem
 
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