Can you guess how this works??

Discussion in 'General Electronics Chat' started by jimmiegin, Apr 26, 2014.

  1. jimmiegin

    Thread Starter Member

    Apr 4, 2014
    Hi all, I put the title as this is a quick post before the morning commute but will update with better info....unless you can guess what or rather how this works.It was built to vary the power to a bog standard soldering iron to give some level of heat control. It is a variable power supply that is clearly home build. It is made up of... (240v in) two caps with two parallel resistors, A couple of other resistors, large and heat sink mounted transistor and a pot with an ldr I think in parallel. An red led that is not anywhere close to the ldr and the pot is turned for voltage vary. I will soon upload some pics when I get back with a friends cam. But can anyone think of a circuit with this combo to give a varied output?
  2. Wendy


    Mar 24, 2008
    A standard light dimmer might do it.
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Agreed! I use a similar one for controlling the temperature of a solder pot in a production process.

    You can get a TRIAC based motor speed controller module cheap from ebay. Or a complete drill speed controller from HarbourFreight in a safe box with mains plugs for about $40.
  4. jimmiegin

    Thread Starter Member

    Apr 4, 2014
    Ok so now my question is....... Dose this circuit sound like a dimmer that chopping the waveform? I ask as I was thinking of using it as another variable supply for audio application so the question of possible crap on the supply was the main reason I started this thread. Also I am wondering what on earth the light dependant resistor is doing in this circuit?? If it is possible tell me without you actually seeing it! If it is not viable to use this supply I will just gave to build a mosfet variable supply. Again I will actually post a pic when I actually get my hands on the cam I was promised. Thank you guys for your replies.
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    So where are these pictures.....
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    It does to me. Pot varies LED current varies LDR resistance varies turn-on point of triac/scr/whatever. It apparently doesn't provide mains isolation so would not be suitable as a supply for audio gear. Can you post a pic or schematic?