+ Post New Thread
Results 1 to 5 of 5
  1. #1
    Junior Member level 1
    Points: 335, Level: 3

    Join Date
    May 2018
    Posts
    17
    Helped
    0 / 0
    Points
    335
    Level
    3

    DC-DC converter to -3.3v

    Hi,

    I need a DC-DC converter with a positive voltage input (+5V) and a negative voltage output (-3.3v) with a current minimum of 2A.

    Can suggest me a circuit or a low cost Converter on a supplier or on ebay?

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 260,279, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,454
    Helped
    13829 / 13829
    Points
    260,279
    Level
    100

    Re: DC-DC converter to -3.3v

    One possible solution is buck converter in inverting configuration, see e.g. http://www.ti.com/lit/an/snva022e/snva022e.pdf



    •   AltAdvertisement

        
       

  3. #3
    Advanced Member level 2
    Points: 2,928, Level: 12

    Join Date
    Aug 2016
    Posts
    511
    Helped
    87 / 87
    Points
    2,928
    Level
    12

    Re: DC-DC converter to -3.3v

    Quote Originally Posted by clros View Post
    Hi,

    I need a DC-DC converter with a positive voltage input (+5V) and a negative voltage output (-3.3v) with a current minimum of 2A.

    Can suggest me a circuit or a low cost Converter on a supplier or on ebay?
    You need an inverting buck-boost. You could design it for 2.5V to 5V input range or so and -3.3V output.

    That's all.
    -------------
    --Akanimo.



    •   AltAdvertisement

        
       

  4. #4
    Super Moderator
    Points: 77,854, Level: 68
    Achievements:
    7 years registered
    Awards:
    Most Frequent Poster 3rd Helpful Member

    Join Date
    Apr 2014
    Posts
    15,787
    Helped
    3592 / 3592
    Points
    77,854
    Level
    68

    Re: DC-DC converter to -3.3v

    Hi,

    Or use a ready to buy isolating one. 5V to 3.3V.

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



  5. #5
    Super Moderator
    Points: 52,947, Level: 56

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    12,950
    Helped
    2580 / 2580
    Points
    52,947
    Level
    56

    Re: DC-DC converter to -3.3v

    Charge pump configured to invert polarity. Notice your 5V supply must provide several Amperes, if you wish to attach a 2A load.

    Click image for larger version. 

Name:	negative supply -3_5V fm 5V via charge pump 4 transistors load 2A.png 
Views:	3 
Size:	37.5 KB 
ID:	155257

    Although diodes make for easier construction, they subtract from the output voltage. Instead transistors are suitable. Bias signals can be obtained from strategic points in the circuit.

    The transistor marked '?' carries 90mA in an upward direction when it's supposed to be off. I tried to shut it off by taking bias voltage from various points. I tried a PNP type. It appears the only way to shut it off is by building a second clock signal.



--[[ ]]--