Push-pull IC with adjustable PWM control

Discussion in 'The Projects Forum' started by DedeHai, Mar 19, 2009.

  1. DedeHai

    Thread Starter Active Member

    Jan 22, 2009
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    Hi there

    I'm stuck on a fairly simple task. I want to make a DC/DC converter using a driver IC that is able to perform push-pull operation (applying Vcc or GND alternatingly to the inductor). I experimented with the TL494 but the problem with that one is, that the max. duty cycle ist about 45%, limiting the available output power.
    If i operate it in parallel output mode, the duty cycle can go up to over 90%, but I loos the push-pull ability (which I need for the converter to be bi-directional). I was looking at some datasheets from standert TI dc-dc controllers which would fulfill all specs BUT: they provide a fixed reference voltage to the positive input of the error amplifier, meaning the output voltage of the converter is fixed, but i want to control the output voltage with a control voltage (which is easyly possible with the TL494).
    So what I need is a simple DC-DC controller IC, that proviedes up to 200mA output current with push-pull operation and having both (positive and negative) error amplifier inputs available on a pin.
    Thanks in advance
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Does it need to be in a single IC, or can you use a PWM generator/control feeding an H-Bridge driver?
     
  3. DedeHai

    Thread Starter Active Member

    Jan 22, 2009
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    Using two chips would also be possible, but not as elegant. What would you suppose I use as the controller IC to drive the bridge?
    I thought with so many different DC/DC controllers out there it should be possible to find one that does exactly what the TL494 does but with a max. duty-cycle of 90% instead of 45%...
     
  4. AchMED

    Active Member

    Aug 5, 2008
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  5. DedeHai

    Thread Starter Active Member

    Jan 22, 2009
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    Thanks a lot for the input, but none of the ICs you suggested have both error-amplifier inputs available on pins, giving me only a fixed voltage at the output (except adjustable with a potentiometer). I need to have access to both, postive and negative error amplifier inputs.
    I just thought I could use the TL494 as a half-bridge driver to generate the PWM signal. But what I would need in addition is a half-bridge driver like the fairchild FAN73832N, taking a PWM as an input and handling the dead time but having the FETs integrated into the IC. The ones I found having integrated high and low side switches did not take a PWM as an input.
     
  6. AchMED

    Active Member

    Aug 5, 2008
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    Are you trying to build a high power variable output SMPS?
     
  7. DedeHai

    Thread Starter Active Member

    Jan 22, 2009
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    Not at all. I'm just building a bi-directional current source, 10V, 200mA that can be controlled by a computer to control the force of an electromagnet.

    I think I found a possible solution:

    Hook one of the outputs of the TL494 (in parallel mode) to a IRS2004 which then provides the voltages for two mosfets (in half-bridge configuration).
    So I can do it with 2 ICs, one half bridge and some extra components (plus the inductor, capacitor and diode(s) for the dc/dc converter)
     
  8. lmartinez

    Active Member

    Mar 8, 2009
    224
    6
    The High Speed PWM Controller UC3825B is a very good chip. I hope you find it useful
     
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