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7805 won't power device?

Discussion in 'General Electronics Discussion' started by chuckfoy, Jun 18, 2013.

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  1. chuckfoy

    chuckfoy

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    Jun 18, 2013
    Hi Folks,

    I wonder if I could trouble you for some help. I recently purchased a vehicle with a 6-CD changer in the trunk. My goal is to substitute this device with bluetooth capability. I purchased an interface that converts the CD changer 12-pin plug to an auxillary input. Into this input I've plugged a Belkin F8Z492TTP Bluetooth Music Receiver. I tapped the 12-pin plug to get +12V, which I connected to the input of a 7805 regulator. I've connected 1uf caps to between both the input and output of the 7805 and ground. I'd like to use the output of the 7805 to power the bluetooth receiver, but it will NOT power-on. There is shiny-clean +5V coming out of the 7805 (just like the Belkin's power supply provides), but it doesn't like the 7805. What the heck am I doing wrong??

    Thanks so much...

    Chuck
     
  2. shrtrnd

    shrtrnd

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    493
    Jan 15, 2010
    My first question is, what's the current handling capacity of your 7805?
    Are you using the TO-92 (small transistor-type package), the medium-sized TO-220
    type package, or a big TO-3 Power Transistor type package for your 7805?
     
  3. davenn

    davenn Moderator

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    1,892
    Sep 5, 2009
    And the second question is .... what current does the Belkin F8Z492TTP Bluetooth Music Receiver require .... look at the label on its case

    chances are its much more than one amp

    Dave
     
  4. chuckfoy

    chuckfoy

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    Jun 18, 2013
    Hi,

    Thanks for the reply. This is really driving me nuts. The 7805 I'm using is this one:

    http://www.radioshack.com/product/index.jsp?productId=2062599

    and the Belkin device requires 180mA. I think I'm good. Even when the circuit is loaded with the device the +5V is still there, and the device works fine from the factory AC adapter.

    Mubalabubalah blah! This is a simple thing and I'm so frustrated! Thanks again for your help.

    Chuck
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    To quote Holmes: "When you have eliminated the impossible, whatever remains, however improbable, must be the truth".

    I'd be double checking the connections to the device to insure that they're solid and connected where they should be.

    Chris
     
  6. chuckfoy

    chuckfoy

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    Jun 18, 2013
    Thanks to everyone. I'm going to take Chris' advice. I just wanted to make sure that I wasn't doing anything obviously wrong. Thanks again.
     
  7. chuckfoy

    chuckfoy

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    Jun 18, 2013
    Okay, more info after another attempt. Without the Belkin plugged in, Vin is at +17V and Vout is at +5.4. With the Belkin plugged in, Vin drops to +9V and Vout drops to +4.75, which I'm assuming is below the unit's threshold. What's happening here? Is the capacity of the source insufficient? Can you suggest another approach to get +5V from the source?

    Thanks...

    Chuck
     
  8. shrtrnd

    shrtrnd

    3,774
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    Jan 15, 2010
    What's the output current from your AC adapter?
    (It should be on the unit somewhere)
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    I'm confused! None of this .....

    computes with any of this.....

    What am I missing here? :confused:

    Are you saying that you decided to test the 7805 by powering it and its load from a wall wart? If so the wallwart is being severely loaded. I'd bet if you scoped the output the wallwart it would have ripple up the kazoo!!

    Chris
     
  10. chuckfoy

    chuckfoy

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    Jun 18, 2013
    Gentlemen,

    Solved.

    The feed I tapped for Vin was not a supply line but a signal. Now that I'm using the correct supply line, life is good.

    Thanks again for all your terrific attempts to help the hapless!

    Chuck
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    See, Holmes was smart! ;)

    Chris
     
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