need voltage controlled power source

**turbochris** · 12-11-2008, 08:07 PM

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
about 1.5 amps.

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.

**FPeter** · 12-12-2008, 01:17 AM

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?

**Rob Withey** · 12-12-2008, 03:01 AM

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).

**turbochris** · 12-12-2008, 07:57 PM

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?