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Subject: Help with Lighting control

Date: 09/05/00 at 6:10 AM
Posted by: Dev
E-mail: stephen.j.devlin@ac.com
Message Posted:

I am trying to design a decorative lamp for my house which slowly varies the brightness of 12V coloured halogen bulbs.
I am a total novice to electronics but thought it would be fun to try and make this. I have succeeded in building a variable oscillator around a 555 chip and am using it to control one lamp (for now) through a high power transistor.
Its just about working but I don't think I'll get a finished version with 4 lamps working at around 30W without buying a humungous power DC supply (and for some reason high power low voltage DC supplies seem really expensive). I bought a 120W 12V AC power supply (which was really cheap) for halogen lights and was wondering if there is some way of gradually controlling the amount of AC current going to the lights (i.e. not just a relay or Triac). I thought I could put two transistors facing opposite ways but am a bit wary of the high currents the lights can draw (3A). Any ideas? I'm guessing that it will be hard to rectify this power supply. Maybe I could build a low current rectifier for the IC part of the cicuit and not bother with the lamp part - just use the two tranistors? Thanks for any help.

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