Voltage regulator not working

Discussion in 'The Projects Forum' started by Daemon, Jun 17, 2011.

  1. Daemon

    Thread Starter Active Member

    Jun 20, 2009
    Hi all

    Can you please have a look at these photos of my breadboarded circuit.
    I input 9vdc into it at the right hand side and I measured from the ground line at the bottom to a positive point just after the voltage regulator(7805) and I still measure 9 vdc.

    Have attached the circuit, and 2 photos of it on breadboard.



  2. AlexR

    Well-Known Member

    Jan 16, 2008
    1. You need at least 10nF (preferably 100nF) from the regulator input pin to common.
    2. You also must be drawing more than 5mA from the regulator for it to function so depending on the minimum load that the PIC presents you may need an additional resistor across the 5Volt line.
    3. Your circuit diagram shows a LM78L05 whereas you are using a LM7805, the pinouts on these is different, check the data sheets!
    4. At the moment the different pinout is of minor importance as you have effectively shorted out the regulator by connecting both input and output to the power bus of your breadboard!
  3. Daemon

    Thread Starter Active Member

    Jun 20, 2009
    Of course I have. I just wasn't seeing it.

    The pin out should be correct, I google searched it before connecting it. With the writing facing you it should be input left, common middle, output right which is the way I have connected it.

    Except for connecting them both to the power bus like an idiot!
    Edit. Have sorted it out now. Moved 3 components down and used the top - rail as the input for the positive and the positive rail to carry the 5v output.

    Thanks for that. Much appreciated.
    Last edited: Jun 17, 2011
  4. SgtWookie


    Jul 17, 2007
    If you had your PIC12F683 in the socket when you powered it up, you may have fried it. :( Hope you didn't... but "stuff happens".

    The LM7805 requires a minimum load of 5mA on the output to provide guaranteed voltage regulation. You can connect a 1k resistor from the 7805 output to ground to make certain it has a sufficient load.
  5. Herrydas

    New Member

    Jun 3, 2015
    This problem is occurs cause of power fluctuation. Check the connections, Looking at the regulator from the face, the three terminals are V+ in, Ground (which is V- in and out) and the last one is V+ out. If it's backwards, it can indeed get hot.