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How to get two separate power supplies from one source?(plus what is a back to back diode?)

Benjamin Ko
Prodigy 80 points
Other Parts Discussed in Thread: LM1086

Hello everyone.

In ADC application, I will need two separate supplies: +5VA and a +5VD , I use  two LM1086s to  achieve this, and the source is one same 24V.

I connect 24GND to AGND together(N108),  then I can't connect 24GND to DGND because I need +5VA and +5VD be separate(N109), will N109 work under this situation? What shall I do with this?

Next I want my AGND and DGND connected with a back-to-back, is this the right back-to-back method?

  • 0
    TI__Mastermind 22610 points

    The circuit for N109 will NOT work as the LM1086 GND pin, and the output load, need a current return path back to the +24V input supply.

    " ... is this the right back-to-back method? ..."

    Depends on what you are trying to accomplish. As drawn, if AGND or DGND are more than about +/- 0.5V apart one of the diodes will conduct. So if your intent is to clamp the two pins so that the voltage difference between AGND and DGND does not exceed approx. +/-0.5V, this will work.

    If you need true galvanic isolation for '+5VD' you need to look at isolated ds-to-dc converters, or you will need separate (and isolated) 24V input supplies.

    www.ti.com/.../offline-and-isolated-dc-dc-controllers-and-converters-products.page