PWM external frequency singal

Discussion in 'Analog & Mixed-Signal Design' started by stobby, Jan 20, 2019.

  1. stobby

    Thread Starter New Member

    Jun 20, 2018
    19
    0
    Hi, I have previously tried asking this question to no avail, However this time i have simplified my question and come at it from another angle.

    Most cheap PWM circuits for controlling heavy dc loads (10amps plus) Have only duty cycle control with a fixed frequency. I want to add an external signal generator to supply frequency control to the PWM. So to summarize im just trying to largely amplify a signal generator's signal.

    I may be using multiple PWM's in parallel to reach my target amperage of 250amps.

    Here's an idea of the PWM and signal generator

    Kind regards
    pwm.JPG
    siggen.jpg
     
  2. TANDBERGEREN

    Active Member

    Jan 20, 2014
    90
    5
    No problem at all.
    It is actually quite easy to use several powertransistors in paralel to obtain the current You need to drive Your eqiupment.

    Do you have any experience in building power electronics at all?
    Key here is to use the most suitable transistors, and drive them properly.
    Lowside regulation by MOS-FETs is the safest way.
    Actually You may drive several transistors directly from the generator at the bottom of Your text.
    Just attach the output of the generator via a resistor to each gate of the MOS-FETs, and You probably could drive houndred of Ampere with ease.
    Beware of the power You may release. Proper fuses should be included in Your build.
     
  3. dendad

    Well-Known Member

    Feb 20, 2016
    2,278
    598
    Be prepared to release a lot of the Magic Smoke!
    You cannot just run multiple PWMs in parallel, but you can add more FETs off the one PWM.
    As for changing the frequency, it does depend on how your board generates the signal.
    If it is a processor, you will have to alter the code.
    But if it is a 555, you can change the component values.
    I don't think you can just feed a variable frequency in as the on/off time control needs to be a adjusted to track the frequency.
    It may be easier to start with an Arduino and play with that at low power first to get your PWM signal working first, then feed that output into the FET drive circuit.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    9,207
    2,176
    It looks as though the PWM generator module in your pic has + and - inputs for adjusting the frequency. My guess is a variable resistor would connect there, but the datasheet should tell you if that's the case, or whether a variable voltage or some other control is required.. What 'signal generator' do you have in mind?
     
  5. stobby

    Thread Starter New Member

    Jun 20, 2018
    19
    0
    Thanks for all the input everyone, I think i will purchase the two devices as pictured in my post and just have a fiddle at lower power levels and see if i can control the frequency.

    however i also wonder if a couple of these big infineon IGBT's could be utilized instead, with the output from the signal generator directly on the gates.
    Infineon_62_mm_power_module.png
     
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