need help with controlled high current load

Discussion in 'General Electronics Chat' started by Michael5139, Mar 9, 2009.

  1. Michael5139

    Thread Starter New Member

    Mar 9, 2009

    I need to make a controlled load, which is supposed to drain specific amount of current (0-30A), according to specific timing (minimum step is 10ms). the power sourse is a chemical battery - 30v DC

    I was thinking to implement some sort of step up circuit, with PWM modulation, controlled by PC or microcontroller (closed loop).

    hower i'm having trouble making the circuit responsive enough (the 10 ms pulse requirement), while keeping the ripples low enough.
    Also I don't know how to get the whole desired range (0 - 20A)

    Anyone can help me with the concept?

    thanks ahead,
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    I think you need an analog circuit. Use an op amp to drive the mofset. You should be able to google to find op amp constant current circuits. Put in enough resistors so they dissapate most of the power. I would move the current sense to the low side. If the battery is a constant 30v the mosfet would operate just as a switch.

    In your current circuit you would have to find an inductor large enough to smooth out the ripple but small enough to keep the circuit fast enough. Then you would have to drive the mosfet at a very high frequency ( the pwm part ) This would take a good - probably high current - driver.
  3. mik3

    Senior Member

    Feb 4, 2008
    You have to calculate the proper value of inductance according to the switching frequency and use a capacitor too to reduce ripple.