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Thread: How is this for a Supply....

  1. #1
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    Post How is this for a Supply....

    This is out of a electronics catalogue which has the following points...

    "By adding a PNP power transistor to a positive regulator, the output current can be increased above the normal rating of the regulator itself. The circuit shown (I have re-drawn it) can be expected to to deliver in excess of 4A with the PNP heatsinked."

    So, will this really work using 3x 1 Amp Reg and 3 Power Transistors, which should beable to deliver around 12 Amps?

    System: P133, 64MB Ram, 2x 1.05GB HD, 16x2 LCD, 12 Key Keypad, 300W Inverter, FM Modulator, 45x4 CD.

  2. #2
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    I beleive you can just use the one regulator, and a whole lot of transistors. i.e. you need one regulator to keep the circuit "regulated"/stable, and then the transistors just sense the regulator output. You could also get a transistor handling more amps.

  3. #3
    Raw Wave Rob Withey's Avatar
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    Post

    And if you supply 12A at 5V with this (assuming a running battery voltage of 14.4V), your power dissipation will be 12*(14.4-5) = 112.8 Watts. You better have one mother of a heatsink...!


    Rob
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  4. #4
    Dustin Haug
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    I don't see offhand why that wouldn't work. Although I wouldn't try it for 5V because of what Rob said. But for 12V it should work and you'll be dissipation will be around 29 Watts with the car running. Which isn't to bad.

  5. #5
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    Nope, for 12volts it won't work, to run a circuit like that the input voltage has to be higher than that which the regulator would normally use, eg. for a regulatored 12volt output, you would need at least a 15volt input, which, in a car, you can't get, unless you drive a truck or something with a 24volt battery....


  6. #6
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    But, this circuit would work for your 5volt power, this is what I am using.....

  7. #7
    Retired Admin Aaron Cake's Avatar
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    Originally posted by THE_SKINNY_MP3_KID:
    <STRONG>But, this circuit would work for your 5volt power, this is what I am using.....
    </STRONG>
    Technically, yes, it will work. But you will need a massive heatsink and fan to keep those transistors cool at 5V.
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  8. #8
    Dustin Haug
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    It will work for 12V as well, but it may cut out if you listen much with the car off. Maybe this is just me, but I've had a large stereo in my car for almost 7 years now and I've probably listened to it with the engine off for a total of about an hour. With the car running my alternator puts out almost 14 and a half volts so something like this should work fine for 12V. Although maybe some of you do listen with engines off a lot , then you wouldn't want this.

  9. #9
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    Won't work for 12...
    Will work for 5...
    You can try it if you want, but, all that will happen is that your computer will crash because the input voltage is too low for the regulator to regulate properly...
    It won't generate too much heat with 5volts, if you use a 10amp transistor, then only draw 4-5amps the heatsink will get warm, but not hot....

  10. #10
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    Actually, I will change what I said, the regulator on its own needs atleast 14.5volts to regulate properly, add a transistor and it would be more like 16volts....
    IT WON"T WORK!!!!!!!!!!!!!!!!!!

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