convert 0-5v signal to 0-16V power supply

Discussion in 'General Electronics Chat' started by trs300, May 28, 2010.

  1. trs300

    Thread Starter New Member

    May 22, 2010
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    Hi All, Can anyone suggest the best way to convert a 0 to 5V 20ma signal to a 0 to 16V 1.5A power supply? The power supply source is always no more then 16V and can deliver only 1.5 Amps as it is... So on a 5V signal, I want to get as much current as possible from the 16V power supply (meaning minimal resistance)

    I was thinking to us a FET for this? Would that work? And if so, is there a FET already designed to respond to a 0-5V signal on the gate?

    Or is this a job for a op-amp?

    Thank you in advance.


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  2. SgtWookie

    Expert

    Jul 17, 2007
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    Tell us more about the power supply. Is it controlled by a voltage, or how?
     
  3. trs300

    Thread Starter New Member

    May 22, 2010
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    Still trying to introduce the engine load into the shift firmness controller SgtWookie. The more I got into it the simplier the solution is becomming...

    The car's natural power supply to the TCM is 14V at 1.5A Max. This shifting device taps into that power supply and "Does what it does" to firm up the shift pressure. But if you recall, when this device is set a it's maximum firmess setting (when you get nice firm shifts under high engine load) the low engine load shifts are to stiff...

    If you pull the plug to this device the car simply reverts back to normal operation. I suspect this device is amplifying the PWM signal in some way. But that's beside the point...

    So I created a simple variable power regulator from a LM317T that will adjust a 16V power supply down to almost zero volts using a 5K pot. I put this "Power supply Dimmer" on the 14V power supply lead to the shift firmness device. Then I set the firmness device to Max.

    The effect that the shift firmness device makes deminishes as I back down the supply voltage to it. With the voltage pulled all the way back the device is esentially disabled.

    Now what I need is to be able to increase and decrease the voltage to the device based on the 0-5v 20ma signal I get from the MAP sensor. When calling for maxumim power I would want as little resistance as possibe. Same as closing a switch. Then the device wold work in full power mode same as if I did not put the "Dimmer" circuit in at all...

    Hope this makes sense...

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  4. Norfindel

    Active Member

    Mar 6, 2008
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    I'm confused you want to lower a 0-16v voltage to 0-5v range, or the other way around? Also, how many current does the device need to supply?
     
  5. trs300

    Thread Starter New Member

    May 22, 2010
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    No sir, I'm not trying to lower the 16V to 5V...

    What I'm trying to do is use a 0-5v 20ma signal, to control a power supply voltage...

    Think of it this way. 0-5v 20ma signal = 0-100% = 0-16V power supply. The available power supply to be translated is already at 16V and is limited to 1.5 Amps.

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  6. SgtWookie

    Expert

    Jul 17, 2007
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    This is about as simple as you can get with about an 0.7A output max.

    See the attached.

    [eta]
    It won't go all the way to 0v, nor within about a volt of the positive supply.
     
    Last edited: May 28, 2010
  7. trs300

    Thread Starter New Member

    May 22, 2010
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    Not going to zero does not bother me... Shy one volt of the total available power supply is not the best... Nor is the .7A maximum...

    I was hoping to be able to do 1.5A Continuous and have minimal loss at full power. That was why I was thinking FET. If necessary, maybe use an op-amp to boost the signal to the FET?

    Can two L272's be run in parallel?

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    Last edited: May 28, 2010
  8. SgtWookie

    Expert

    Jul 17, 2007
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    L272 power opamps have two amplifiers in a single package. Yes, you could connect both amplifiers to the single pair of resistors.

    This is the cheapest solution that comes close to meeting your specifications as I can give you within 5 minutes. If you want to go all the way to 14v, then you can build a dc-dc boost converter for about 40 times the cost of the circuit I posted.

    If you used an N-ch power MOSFET, you would need to build a DC-DC boost circuit to get the gate voltage several volts above your existing supply voltage, otherwise you would not be able to reach your positive supply voltage.

    If you used a P-channel power MOSFET, you would need a negative DC-DC buck/boost circuit in order to output below about 4v.
     
  9. trs300

    Thread Starter New Member

    May 22, 2010
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    0
    OK. You convinced me... lol.. If I can run them in parallel to handle distribute the amps then I think it will be just fine... Thanks for your help.

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