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crutschow

Simple & Inexpensive Ideal-Diode MOSFET Circuit

Good for low-drop diode applications, such as blocking battery back-charging or brownout protection

  1. crutschow

    crutschow Well-Known Member Most Helpful Member

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    crutschow submitted a new article:

    Ideal MOSFET Diode Circuit - Ideal diode circuit prevents reverse charging of batteries, etc.

    Read more about this article...
     
    Last edited: Sep 21, 2017
  2. Eric K.

    Eric K. New Member

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    Hi Crutschow, I saw your article posted on the power electronic tips site. Thank you for the circuit diagram, it is just what I'm looking for to make a simple DC UPS for a computer, monitor, and router. I like that your circuit would provide immediate backup power with negligible delay and no reverse current into either the switch-mode supply or the boost converter . You said "Note that there is a reverse voltage limit of the circuit due to the 5V maximum reverse Vbe that can be applied to the BJTs." If my AC power goes down or the AC/DC power supply fails, there will be a reverse voltage of 19V on the top diode as the battery takes over. Will your suggestion of an additional D1 diode and R4 10k resistor be appropriate to protect transistor Q1a from a 19 Vbe reverse bias?

    Thank you for your help 20180418_112435a.jpg
     
  3. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Yes, the resistor and diode will prevent more than a 0.7V reverse bias on the transistor.
    It will have a couple mA reverse current when the input is 0V, but hopefully that's not a problem.

    Regarding your question on the PET website about the minimum voltage for changeover from off-to-on or on-to-off, the simulation shows less than 20mV so I would think it should be not more than 50mV in the actual circuit.
     
  4. dave miyares

    Dave New Member

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  5. Eric K.

    Eric K. New Member

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    Crutschow thank you for your time on this, I'm looking forward to ordering some parts and making it.
     
  6. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Okay let me know the results, if you can.
     
  7. Eric K.

    Eric K. New Member

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    Regarding the matched-pair DMMT3906W, I was looking for an equivalent part in DIP package to use in a breadboard, but I'm seeing "Obsolete". I guess the next best thing is to use a 33006 SMD-to-SIP "proto board adapter".
     

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