Switching between different supplies

Discussion in 'The Projects Forum' started by alihashemi2002, Aug 28, 2015.

  1. alihashemi2002

    Thread Starter New Member

    Aug 28, 2015
    Hi All:

    I have a PSU that I am designing that has 4 DCDC converters supplying 3.3V,5V,9V, and 12V. There are 8 outputs that can be switched on or off by the uC. I also want to incorporate supply switching for each of the 8 outputs. I'm assuming I'll need a high-side switch. I am very short on I/O pins on the uC. My plan was to use two I/O expanders to gain 16 pins. Then I want to use a 2-4 decoder to drive the gates of the switches. This way I'll only need 16 pins instead of 32. Anyone have any design recommendations on this? Also, does anyone have any recommendations on high-side switches that can work at logic levels? This is my first time doing this, and honestly it isn't really necessary, but, I figured it would be a good idea to use it as a learning opportunity.

    Thanks in advance,
    Ali Hashemi
  2. #12


    Nov 30, 2010
    Four DC to DC converters create 8 outputs, and the 8 outputs can be switched with a uC. The converters also have inputs. You assume you can only switch the high side of the inputs and you want these high side switches to work with logic level voltage...right?

    A drawing would be ever so helpful.
    Things like, "If you have 12 volts, why not use it to switch mosfets on?"
    There are even some good mosfets that work with 5 volts as a switching voltage.
    Why you believe you can only switch the high side is why I need some more information.
  3. alihashemi2002

    Thread Starter New Member

    Aug 28, 2015
    Sorry for the confusion. I'll provide a drawing in a couple minutes as well, but, in the mean time here is what is going on:

    1. 4 DCDC converters create 4 outputs

    2. There are 8 output connectors that will either be connected to one of the supplies or turned off.

    3. I would put more than 8 connectors but due to size, thats the maximum I can provide.

    The idea is that each output connector can either be turned off or switched to any of the 4 output connectors.
  4. alihashemi2002

    Thread Starter New Member

    Aug 28, 2015
    Attached is a very basic block diagram. Hope that helps. The main reason behind my thinking that high side switching is needed is to maintain the selected voltage level on the output. If I use low side, I don't see how I could select between the 4 different voltage level.