Bridge circuit

Discussion in 'General Electronics Chat' started by egr101, Apr 26, 2010.

  1. egr101

    Thread Starter New Member

    Apr 26, 2010
    i have a circuit being run by a 9V battery into 2 7805's to give 5V. i also have an 18V source coming into the circuit to run a motor through an H-bridge. do i need to keep the grounds separate or create one common ground for all? i ask because currently each 7805 is putting out only 4V. thanks for any help.
    Last edited: Apr 26, 2010
  2. SgtWookie


    Jul 17, 2007
    Post a schematic of your circuit. .png format images are preferred, as they are very compact, not "lossy" like .jpg images, and no extra software is necessary to view them.

    Click the "Go Advanced" and "Manage Attachments" to upload your image from your computer.
  3. kkazem

    Active Member

    Jul 23, 2009
    I would be glad to help you with your problem, but I need to see a schematic with all component values on it. For example, you say you're using 2 each, 7805 regulators. but you don't say how they are used. For example, separately, in parallel, in series? I can't help you and neither can any of our associates without knowing exactly how you have these hooked-up. Also, a picture (photo) of your breadboard would be helpful as well so I can get an idea of how your hookup techniques might be influencing the circuit and its problems.

    In general, you can use a single ground, but the control circuitry should have it's own ground as should the power section, and only have the two connected at one-point in the circuit. This way, you will avoid ground loops that can easily mess-up your control and power circuits. The layout techniques are critical, especially at high frequencies that you would likely be using with your H-bridge.

    I'll wait to hear back if you post a reply with the schematic and photo (if possible) of your circuit.

    Kamran Kazem
  4. Audioguru


    Dec 20, 2007
    The 7805 regulator needs a minimum input of 7V and I betcha your 9V battery is too old to give 7V when it is loaded. Therefore the output of the regulator drops.