Current source project

Discussion in 'The Projects Forum' started by MisterNo, Apr 8, 2011.

  1. MisterNo

    Thread Starter Member

    Jun 28, 2010
    I'm trying to build voltage to current converter. Trouble is that voltage should be arbitrary waveform (1kHz bandwidth) so that the current source output is not a DC.
    The op-amp I'm using has 8Mhz bandwidth and that is way to fast and creates oscillations in the output waveform. I had no luck with slower op-amps I had to use 3R6 that is about 25k to slow it down, but then I can't have half sinusoid grater than 100Hz and goal is 1kHz. Solution was to add cap 3C10 of 1nF, but whenever current has to rise from 0 to specific value overshoot occurs and I don't know how to solve that problem. Any hints?

  2. SgtWookie


    Jul 17, 2007
    You don't show what opamp nor MOSFET you're using, and some components have missing or invalid values; for example "Zero" for 3R3 is not valid, and 3C10, 3R6 don't have values.

    You do not state the input voltage range, nor the desired output current range, nor what voltage will be available for the current source, nor what the resistance range is for the load.

    There are really too many unknowns at the moment to make any recommendations.
  3. MisterNo

    Thread Starter Member

    Jun 28, 2010
    3R3 is 100 Ohm
    3R6 and 3C10 are as said in the post 25K and 1nF resperctivelly.
    There are two 3R6 (my copy paste mistake) so one in the MOSFEt source is 1 ohm, other in the gate is 25K
    Op-amp is AD847
    Input voltages are 0-2V
    load resistances are up to 50 Ohm
    mosfet is IXFX64N60P
    Voltage for the current source is 100V

    Thanks for reply. The problem is down to overshooting when current rises from 0 to some value