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  1. #1
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    isolated flyback, high voltage output, mA current

    Hello, i have recently designed a 7V to 200V DC-DC SMPS converter, using LT3757. The output current is in the 1-10mA range. I use a DA2032 from coilcraft with a 1:10 ratio. At steady state, i get peak currents of 1.5A at the primary. My controller supports only non-isolated flyback, due to the nature of the resistive divider from the output.

    I am looking to make another version with isolated output, preferably without an optocoupler, by taking the feedback from the primary, since the exact value of the output voltage doesn't matter too much. I have worked on the previous version using an example circuit from LT, i.e. p.30 of LT3757 datasheet. I am looking for the right controller for my isolated version, and hopefully an example circuit that achieves similar specs. i am searching for recommandations to achieve my goal.

    Thanks in advance!

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  2. #2
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    Re: isolated flyback, high voltage output, mA current

    Hi,

    Have you ever tried using "PI Expert"? There are ICs called LinkSwitch-CV and LinkSwitch-PL families where you don't need to use any optocouplers. However these chips are used in AC-DC converters and SMPS circuits are actually used for AC-DC converters. Do you have an AC-DC converter before your DC-DC converter? Is it possible that you mistakenly used the word "SMPS" instead of "boost"?

    Cheers,
    Ogulcan



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  3. #3
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    Re: isolated flyback, high voltage output, mA current

    it is such low power, you do not need to use opto, you do not need a proper feedback loop...just a hysteretic type comparator feedback using say a digital isolator......and any controller that you like more or less.



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  4. #4
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    Re: isolated flyback, high voltage output, mA current

    You can also try the software called LTpowerCAD, which lets you find the right LT power IC according to the input and output voltages and currents. After filtering accordingly, you can check for example circutis and I'm sure you can find a design without optocoupler.

    Here is the download link for the software: http://www.linear.com/solutions/LTpowerCAD

    Ogulcan



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