# Digitally Controlled Current Source for signals - Need help

Discussion in 'LEDs and Optoelectronics' started by efelnavarro09, Jan 18, 2011.

1. ### efelnavarro09

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Jan 18, 2011
I started working on a function generator that gives ouput of different waveforms, such as: sine, sine half wave, sine full rectified, square, triangle, saw tooth, biphasic square, etc. with a constant output of 30Vpp. My question is about how dow I need to handle this signal in order to vary its ouput current in a range of 1mA up to 150mA with a variable Rload in a range of 500Ω up to 10KΩ so the output current must stay "constant" within this range. I need to be able of change the output current digitally, maybe using a DAC, Variable gain opamp...

I have been looking and some theory and circuits about Voltage to Current Converter with grounded and floated load, Current Mirror. But I still don't fully understand how do I need to "connect" the constructed signal into the current block prior to connect it to the RLoad. Since all the examples I found in books, google, connect the respective outputs to a fixed source such as V+ instead of a variable one (maybe AC).

So any idea, further information, example is highly appreciated. Thanks in advance.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
if the current through a load resistance remains constant, the voltage across it is likewise constant.

You can have a voltage source, or a current source. It can't be both.

3. ### efelnavarro09

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Jan 18, 2011
Hello, thanks for your reply. Finally if figure it out how to solve it, may be is no the best way but at the moment it works for my application. Y decided to make a "digital" selector using transistors with different resistance values, i take as an example an application of the L200 voltage regulator. I don't have a very smooth lineal control but for the momment its ok. Thanks.