Dual power supply with Buck converter.

Discussion in 'The Projects Forum' started by computerman2013, Jan 7, 2013.

  1. computerman2013

    Thread Starter New Member

    Jan 7, 2013
    3
    0
    I searched around but was not able to find what i was looking for. Maybe that is because what i want to do is not the right method?

    I am open to suggestions as well. I am just stuck.

    This is what i have so far but i cannot control the negative side correctly. The top (positive) works but the negative side seems to need negative voltage.

    I am trying to have a lower chip count so i don't want to use an op amp if possible.

    Thank you for any insight you could lend me.

    The bottom is not completed and i left off the buck to the right of the circuit because i cannot even get the correct voltage to it.

    I was attempting something similar to the top on the bottom without luck.
    Thanks =)
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,053
    3,244
    The bottom should give you a half-wave negative rectified voltage. Don't know why it doesn't. :confused:

    Note that you need resistors in the collector and base of Q2 or you will zap Q2 and/or Q1.
     
  3. computerman2013

    Thread Starter New Member

    Jan 7, 2013
    3
    0
    Yes there are current limiting resistors up top now =) I poped one by accident the first time through.

    The bottom works and gives me -20V but the problem is i cannot control any transistors as all the base voltages are negative and i need to be able to control with 0-5V not negative voltage.

    Thanks
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,053
    3,244
    You can control a negative voltage with a positive voltage by using a grounded base PNP transistor. The control voltage goes through a resistor to the emitter and the collector goes to the negative voltage load. Note that the control voltage emitter current approximately equals the collector current for a grounded base configuration.
     
    Last edited: Jan 8, 2013
    computerman2013 likes this.
  5. computerman2013

    Thread Starter New Member

    Jan 7, 2013
    3
    0
    I totally forgot about that!

    I learned about it but never applied it before thanks for the help i spiced it and it worked so i will try it a little later today.

    Thank you for the help.
     
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