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    DC-to-DC Converter question

    Hi all. I am designing a circuit and am using an INA105 op amp to generate an adjustable +12 to -12 VDC output. My input will be from a VAWQ6-Q24-D12H DC/DC converter. I will also be needing +15 and -15 VDC to bias the op amp. I'm wondering if I can tap off the output of the first DC/DC converter to provide input power to a VAWQ6-Q24-D15H converter or will that create problems with it drawing down the input to the op amp and not giving me a proper output. I'm going to try to attach my sketch for your consideration. If it's just not really feasible, I have another power supply at my disposal but I'm really trying to conserve space because I don't have a lot of real estate in the cabinet I have to put this in.

    Regards,

    Mike

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  2. #2
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    Re: DC-to-DC Converter question

    The circuit is rather unclear because you are showing less than half of the DC/DC pins. Each converter has two input and three output pins.



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    Re: DC-to-DC Converter question

    Using a DC-DC converter output as your reference is probably a poor choice because its noisy and poorly regulated. It's also wasteful to cascade DC-DC converters (especially isolated ones) unless there is no other choice.

    To me it seems you only need the single +/-15V isolated supply. Then there are a million reference choices. You get what you pay for in terms of accuracy. Look at TL431 on the low end of cost.


    For your problem I think about this topology first. It replaces the relatively costly INA105 with any regular opamp (INA192 is easy to use). Though it works best if you can actually get away with passive zeners or cheaper shunt references otherwise the dual reference becomes a cost penalty. R3/R4 is the pot.

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    Last edited by asdf44; 20th November 2019 at 03:14.



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    Re: DC-to-DC Converter question

    Hi,

    There are really many DC/DC converters directly outputing +15V and -15V.

    Farnell lists more than 800 devices with dual output +/-15V.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: DC-to-DC Converter question

    Quote Originally Posted by FvM View Post
    The circuit is rather unclear because you are showing less than half of the DC/DC pins. Each converter has two input and three output pins.
    I do apologize for that. This was just a quick mock-up that I drew up over a cup of coffee and I was more concerned about it's feasibility than it's total accuracy in representation of all pins concerned. Based upon the other trenchant replies, I'm going to scrap the idea of trying to piggy-back the converters and do something less "lazy."

    @asdf44, I do like the TL431 idea but I already have all the parts required for the circuit so it's a no-cost project at this point. I just need to decide on the final design. That being said, I'm not opposed to revamping in order to make it more stable. It doesn't require tremendous precision (5% is surely sufficient) as I just need to be able to swing a full 20 volts (-10 to +10). I would like to hear your thoughts on using one +/-15V supply and creating reference choices from there.

    Thank you, everyone! I appreciate your thoughts and ideas!!

    Mike



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