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3408 Views 3 Replies Latest reply: Oct 29, 2011 5:41 PM by RWM RSS
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Dec 16, 2009 2:36 PM

How to design high votage amplifier?

Hi,


I need to design an amplifier for 100KHz, 5Vp-p square wave amplifed to 50Vp-p signal with zero crossing (i.e. +25v to -25V)

I am thinking to use OPA2544 Op-amp from TI/Burr-brown with +/-27V supplies. I have attached the circuit here, I do not simulation tools to simulate it.

could any body verify the circuit and post the suggestions?

schm.JPG

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  • Currently Being Moderated
    1. Dec 17, 2009 4:05 AM (in response to vips)
    Re: How to design high votage amplifier?

    This part will not do what you want.

     

    Check the data sheet carefully:

     

    The gain bandwidth product is only 1.4MHz - this means that the open loop gain will be only 14 at 100kHz and 1.4 at 1MHz - you are trying to amplify a square wave at 100kHz which means that if you want it to look halfway reasonable on a scope you need a closed loop bandwidth of 1Mhz. You should be looking for an amplifier with a gain bandwidh product more like 1MHz * (10 for the open loop gain) * 10 (for some feedback) - ie a gain bandwidth product of 100MHz !

     

    Your output should be a sqare wave wih 50V pp amplitude at 100kHz - if you allow the rise and fall times to be 10% of the period that means that your output must slew 50V in 1uS - so the slew rate of your chosen chip must be at least 50V/uS but the OPA2544 only offers 8V/us.

     

    The data sheet also shows that the output can only get within 4.2V of the supply rails (at 0.5A output current) so a sensible design margin would be 5V which means you should use +/-30V supply rails.

     

    You don't need simulation tools to choose a part - just check the basics.

     

    When you are ready to simulate you can get a free (and good) simulator from Linear Technology (LT Spice IV on www.linear.com).

     

    If you explained what you need the output to do it might be possible to advise you better.

  • Currently Being Moderated
    2. Oct 29, 2011 2:35 PM (in response to michaelkellett)
    Re: How to design high votage amplifier?

    Vipul,

     

    Did you find an amplifier that fit your application?  I have a similar requirement and would like to know if you found a solution before posting a fresh post.   In my case, I want to find a test board with the chip and use it for testing.  Thanks. J.

  • Currently Being Moderated
    3. Oct 29, 2011 5:41 PM (in response to vips)
    Re: How to design high votage amplifier?

    If you need only square wave, you can try circuit similar to stated below:

     

    HVamp.png

     

    C1 and C2 should improve speed, similarly D1 and D2 (optional - Schottky diodes have high reverse current, in this case about 100uA and it must be considered when designing circuit). BD139/140 have fT about 160MHz so I think should be fast enough.

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