Help please - constant current load

Discussion in 'General Electronics Chat' started by dmanoukis, Jul 10, 2014.

  1. dmanoukis

    Thread Starter New Member

    May 29, 2009
    Hi all,

    I have read more info than I care to admit on constant loads - and am just as lost as I was at the start. my question is:

    I need to create a 400V DC or less constant current load capable of loads up to 2A. Is there a MOSFET that anyone can recommend and are there any reference designs I could use to help plan this out and allow me to rate the components properly.

    Thanks for any suggestions,
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    How do you propose to get rid of 800W of heating?
  3. dmanoukis

    Thread Starter New Member

    May 29, 2009
    Thanks for the quick reply :)

    I was thinking / testing using ceramic based resistors in a TO-220 style package attached to a copper water cooled heat sink.... overkill or do you think it would be sufficient?
  4. crutschow


    Mar 14, 2008
    I think Mike was referring to the maximum heat dissipated in the constant-current control element.

    What are the power resistors for? :confused:
  5. dmanoukis

    Thread Starter New Member

    May 29, 2009
    sorry. I misunderstood the question. would still planning on using the water cooled heat sink with FET's in parallel connected to a Arduino driven PWM output.... But to be honest I am fishing here. I am not sure if this is realistic or the best way to do this...
  6. Sensacell

    Senior Member

    Jun 19, 2012
    Seems reasonable, but I don't see where the PWM fits in? Why not just go linear, the whole point is to waste power, a simple brute-force linear design is all you need.

    If you need digital control, add a DAC to command the current level.
    (or you could just filter a PWM signal to get a DC command voltage... )

    The starting point should be a specification for the range of voltages and current levels you see this device handling, as well as accuracy and load step response time. If the I/V range is narrow, it will simplify the design a bit: you can have fixed resistors dissipating most of the power, rather than big expensive FETs.
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    800v 5A and 7A N-channel FETs (TO-220 pack) are very common and cheap now and are used in SMPS's everywhere.

    Just check the suppliers for FETs that roughly match those specs and have good stock quantities and low prices. They will be the common ones the manufacturers are using.
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
    Your problem is you need to dissipate 800 watts (400v @ 2 amps) someplace. It can be in resistors or FETs - probably about the same cost. Your in to a couple hundred dollars. Is this a price your interested in? I've helped people with a couple of these using copper pipe with water running thru it. Would that work for you?