# Thread: need voltage controlled power source

1. ## need voltage controlled power source

I need a voltage source controlled by a 0 to 5 volt input.
The source must run on 16.5 volts dc, the minimum and maximum voltage must be
adjustable by 2 potentiometers, for example, one pot would control the
starting voltage, probably somewhere between 3 to 12 volts when the control
input is at 0 volts and the other pot would control the max voltage
somewhere between 10 to 16 volts when the control input is at 5 volts. As
the control voltage varies between 0 and 5 volts the output would vary
between the minimum and maximum set voltages. It needs to be able to handle

it needs to be simple and reliable, efficiency isn't important. Can't I take a power transistor, put it on a heatsink and bias it with the control voltage through the potentiometers and some resistors to get the effect I want? I'm just not sure as to how I would exactly do this. This circuit is needed to drive some LED light bars.

I need this in a bad way, it's for a really cool project that I can't
disclose yet.

2. Originally Posted by turbochris
...
i dont understand, how do you mean the minimum and maximum level... voltage regulators has only one output that is controllable with 1 pot... or do you need two separate line with different voltages? and 1.5Amps on each?

3. Use an op-amp. If I read correctly what you require is an output that is effectively y=mx+c (where y is output to swing between min and max, x is input to swing between 0 and 5, and m and c are gain and offset set by the opamp circuit).

4. This is what I came up with. Could I use a circuit like this?-

I would adjust P1 until the load had it's minimum required power and then apply 5 volts to the 0 to 5 volt input and adjust P2 until the load had it's maximum required power. Then I hope it doesn't catch on fire and when I vary the control from 0 to 5 volts that I would see the power across the load vary from its min setpoint to it's max setpoint. DO I really need op amps and regulators?

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