Variable Voltage Controller (Analogue controlled)

Discussion in 'The Projects Forum' started by ollieking60@hotmail.com, May 27, 2010.

  1. ollieking60@hotmail.com

    Thread Starter New Member

    Feb 17, 2010
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    Hi

    I have a board that I need to supply with a variable supply of 5 - 15V. It needs to be a separate 'bolt on' circuit supplied with 15V, and a 5 - 15V output. However this output voltage needs to be controlled with a 0-10V analogue input. I have found lots of examples of using variable resistors to alter the output voltage, but how can i encorporate using a 0-10V analogue signal into this?

    Regards

    Oliver King
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    If you're only going to supply it with 15v, then you will need a buck-boost DC-DC converter in order to output a range from 5 to 15v. You would not be able to simply use a regulator like an LM317, or even a low-dropout linear regulator.

    You say you need 5v to 15v out, but at what current?
     
  3. ollieking60@hotmail.com

    Thread Starter New Member

    Feb 17, 2010
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    I need a max current of 2Amps. I dont know what a buck boost DC DC Converter is, could you expand on that a bit please.
     
  4. ollieking60@hotmail.com

    Thread Starter New Member

    Feb 17, 2010
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    If i supplied it with 24V, would that make it simpler?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, supplying it from 24v would only require a "buck-type" DC-DC converter.

    You would not want to use a simple linear regulator such as an LM338 due to the very high power dissipation that would result.

    Are you in the USA? If so, you might find that a pre-manufactured DC-DC converter to be an easy option. Otherwise, you will need to build a circuit.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Last edited: Jun 1, 2010
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    If you'd rather build than buy, it should be possible.

    I picked a switching regulator more or less at random from the Linear Tech catalog:

    http://cds.linear.com/docs/Datasheet/1765fd.pdf

    The variable version of this part simply requires that you send 1.2V into a feedback pin when the output voltage is at its nominal level. Normally that's done with a resistive divider, but it should be possible to do it with an op-amp circuit that combines the 0-10V input with the 5-15V output (hedging slightly because it might not be stable). But I expect it would be OK.
     
  8. ollieking60@hotmail.com

    Thread Starter New Member

    Feb 17, 2010
    11
    0
    Thank you for your help guys. Im not in the US, but i can get hold of a DC-DC module.
    I would rather build a circuit than buy pre manufactured, so using the feedback pin on the switching regulator sounds good. However I am new to electronics, so an example circuit using op-amps to make it controllable with 0-10V would be very helpful.
     
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