+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Junior Member level 1
    Points: 1,950, Level: 10
    Achievements:
    7 years registered

    Join Date
    Jan 2010
    Posts
    17
    Helped
    0 / 0
    Points
    1,950
    Level
    10

    Enable circuit for backup battery boost converter

    Hi!

    I need to realize backup battery with boost converter in my design.
    To minimize battery current I need to keep boost converter disabled until main power is lost.
    Switching to backup battery should be uninterrupted.

    Main power: 8V
    Battery: 3V
    Boost coverter: 7V

    Click image for larger version. 

Name:	Untitled.png 
Views:	5 
Size:	64.9 KB 
ID:	158529

    Could you recommend any cheap and effective way of doing this?

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 2
    Points: 3,332, Level: 13

    Join Date
    Jan 2019
    Posts
    613
    Helped
    157 / 157
    Points
    3,332
    Level
    13

    Re: Enable circuit for backup battery boost converter

    is the enable high or low?

    assuming enable is high, connect two resistors in series from 8V source to ground
    connect the collector of an NPN transistor to enable
    connect base of said transistor to junction of two resistors
    connect emitter to ground.

    when 8 V is present, the transistor will be ON, pulling enable low, boost OFF
    when 8 V is not present, transistor will be OFF, letting enable go high, boost ON

    add a capacitor at SYS to smooth transition

    resistor values not critical
    from 8V to base, about 10k
    from base to ground, about 1K
    transistor - any small signal device useful as a switch, like 2N2222A or 2N3019


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  3. #3
    Super Moderator
    Points: 83,837, Level: 70
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    17,049
    Helped
    3852 / 3852
    Points
    83,837
    Level
    70

    Re: Enable circuit for backup battery boost converter

    Hi,

    Add two resistors an NPN BJT.
    Two resistors as voltage divider from 8V
    Center of divider to bjt_base
    Bjt emitter to GND
    Bjt collector to Boost_EN

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


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  4. #4
    Junior Member level 1
    Points: 1,950, Level: 10
    Achievements:
    7 years registered

    Join Date
    Jan 2010
    Posts
    17
    Helped
    0 / 0
    Points
    1,950
    Level
    10

    Re: Enable circuit for backup battery boost converter

    Thanks for replies.
    Yes enable is active high.



--[[ ]]--