Cap size for voltage regulators?

Discussion in 'The Projects Forum' started by Ladvien, Oct 3, 2012.

  1. Ladvien

    Thread Starter New Member

    Sep 29, 2012
    I'm using dual SN754110 H-Bridge ICs to drive a little tank. I have two V Regs on it--one 12v (for motors) and one 5v (for logic). I don't suppose someone can tell me two things:

    1. The cap size and layout.
    2. My V regs heat up after two minutes (with heatsinks), can someone suggest a better layout or V reg chip? I'm using LM7805C (5v) and L7812CV.

    As always, thank you--from a grateful hack.
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    The best thing is to read the data sheets and application notes for the components. Are you using them at or near their amperage limits? That is the common reason for heating of a component. Capacitors won't have an effect on that.

    Why not use the 12V for Vcc1? The SN754110 will work at that voltage. And would eliminate the need for the 7805.

    The motors themselves would also be happier with unregulated voltage. Since they are electrical not electronic they don't need a regulator.
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
    It depends upon Vraw; what voltage is it and how well filtered is it? And on the current draw on each of the LM78xx regulators; how much?

    Here is my standard connection scheme for LM78xx regulators. If the input is already well filtered, I omit the 1000μF filter cap. The .33μF and .1μF ceramics on the input and output are straight from the datasheet. The 10μF provides additional filtering on the output.
    Last edited: Oct 3, 2012
  4. Audioguru


    Dec 20, 2007
    The load current for the 7805 is very low so it should not be warm without a heatsink.
    Some of the capacitors on your schematic have their polarity backwards.