High current regulator - Which transistors/regs?

Discussion in 'The Projects Forum' started by Flamin_D, May 6, 2010.

  1. Flamin_D

    Thread Starter New Member

    May 3, 2010
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    Im looking to build a regulator for a power supply currently kicking out around 20v DC with no load. Im aiming for between 12 - 14.5v. This design caught my eye:

    [​IMG]
    (Apologies for size the resize doesnt seem to be working)

    The application is for running car amplifiers through UK wall power. A 450Wrms 12-14v amplifier technically shouldnt draw more than 40A, but it would be good to have room to expand, say for example 70 - 100A using low gauge wire.

    Without a regulator the supply sits on 15.2V with the amp powered on for the first 10 mins and creeps up to 16.1V which causes the amp to shut off. When i have the amp playing at good volumes ive seen drops down to 11.3V (due to insufficient transformer which is getting upgraded).

    My question is: Would the above design (perhaps with a few more 2N3055s) work well to regulate the 16/20V down to 12/14V for currents above 40A?

    Thanks for any advice.

    Sam
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Linear regulators are terribly inefficient. You will dissipate a LOT of power in the transistors. They will make good room heaters.

    You really need a switching power supply, as they are much more efficient.
     
    kingdano likes this.
  3. Flamin_D

    Thread Starter New Member

    May 3, 2010
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    For example in computer power supplies?
    I may just stick with my original idea of buying one with 45A on the 12v rail for £40 then. Or maybe there are ways to use the efficient parts of a PC PSU and combine them with other parts to increase the current rating?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    An ATX supply is easy and cheap to convert to a bench supply. However, you need much more power than that, so it's not really viable.

    Automotive circuits really need 13.8v-14.2v anyway. If you're running on 12v, you'll only get about 86% power out of your amp.
     
  5. Flamin_D

    Thread Starter New Member

    May 3, 2010
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    Yeah, at the moment im running at 15v idle and dropping to 11v on a heavy load. I am capible of idling at 20v so could do with turning those extra volts into power by regulating at 13 / 14v.
    Ill soon be using a reversed microwave transformer instead of my current one, so it should most definately be powerful enough to afford loosing some power through the transistors to obtain high current capibilities. Might see if that turns out good... its like £10 compared to £40, and the heat may come in handy in the winter ;)
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    If you are going to re-wind a microwave transformer, you need to use magnet wire of a suitable gauge to carry the current. Don't use ordinary wire like Romex, speaker wire, or typical hook-up wire. You'll need to use AWG9 or larger.
     
  7. Flamin_D

    Thread Starter New Member

    May 3, 2010
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    0
    Yeah ive got some AWG7 laying around. Just out of interest - i think i read somewhere that reversing a microwave transformer (putting the 240v into the secondary) will give you around 14v on what was originally the primary?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    I haven't read that.

    Don't rely on the "I read somewhere that..." kind of thing.

    I don't know where you live, so I don't know what your mains voltage is.
     
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