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Thread: Need help changing voltage settings

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    Senior Member Min's Avatar
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    Question Need help changing voltage settings

    Hi all, in a project im doing I need to change a voltage setting via diode or some other way. I have to get a 5 volt source down to 4.5 volts. I have tried a 1N4148 diode and it dropped it down to 4.66 volts. Thats all that I have on hand to try. Any 1 know what diode should drop it to 4.5v???

    Any help or ideas will be greatly appreciated.
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.



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    Junior Member DMME's Avatar
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    If you have a constant load current use a resistor of suitable value, or even a pair as avoltage divider (wasteful). Given more info on the cct you may get a better answer. A "universal" answer is an LM317 and resistors to set the output voltage
    There are only 10 kinds of people in this world.
    Those that undersatand BINARY and those that don't

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    Senior Member Min's Avatar
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    I`m quite new to this electronic scene. I`ve got a board from a sat receiver and I would like to change the voltage to the card reader. All I know it is putting out 5 volts and I would like to get it down to 4.5 volts. Any suggestions as to where I should start. I`ve got a digital multimeter and if you tell me what settings to put it on and what to test. Like I said, i`m new to this sort of stuff. You mentiond current load, how do I test that for starters???
    If I put a 1N4148 diode and 3 10k resistors inline with it, its gets the 4.5 volts. But I would like to try and do it with just the 1 small component if possible.

    Cheers
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    Junior Member DMME's Avatar
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    OK then just use a 1n4001, 1n4004 or 1n4007. The 4148 is small signal and low forward voltage drop. 4001/7 are "normal' and will give about .5/.6V drop.
    If you ended up with 30k inseries as well there must be SFA current draw, about 5 microamps actually.
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    Those that undersatand BINARY and those that don't

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    30k inline.. sounds like you are measuring the voltage with just the multimeter connected. Try with the load connected and the diode DMME suggested, ie any power type diode. The difference between 5 and 4.5v is not much and most circuits would not be affected by running at either.

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    Senior Member Min's Avatar
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    DMME, I will hopfully get some of those diode today and give it a go. If I dont end up getting any today i`ll definetly get some during the week sometime. I`ll post here how it went.

    Thanks for your help, much appreciated.

    Cheers
    Min.
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    Senior Member Min's Avatar
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    Quote Originally Posted by ssrattus View Post
    30k inline.. sounds like you are measuring the voltage with just the multimeter connected. Try with the load connected and the diode DMME suggested, ie any power type diode. The difference between 5 and 4.5v is not much and most circuits would not be affected by running at either.

    I just wanted to drop it by .5 to see if it will help a heating issue.
    Will try today or during the week. Will post what happens.
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    is this for a voltage drop on a jaycar MKII
    dont say linux if i wanted it id install it

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    no its not
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    Could you just throw another voltage regulator in there??
    When you do things right, people won't be sure that you have done anything at all

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    Quote Originally Posted by best4less View Post
    Could you just throw another voltage regulator in there??
    Not to sure on that, I think the reg is suppling power to other things aswell. Not to sure though. Will look into it when I get time during the week.
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    Quote Originally Posted by best4less View Post
    Could you just throw another voltage regulator in there??
    Not for 5v to 4.5v, voltage regulators need more voltage differential to work.

    A IN4004 (or any power diode) should do the trick.

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    From memory there are also low drop regulators, but my memory is fuzzy on the details.

    Depnding on the application, using a small switching circuit might do the trick.
    A simple Op Amp voltage comparitor and a pull down resistor.

    If it's something a little more technical, then a switchmode circuit will the way to get precission. There's more combinations than I can poke a stick at.

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    Does it have to be precisely 4.5V?

    If not, then one option is a 4.3V zener being fed by a resistor..

    Ok, that's two components but it will work and will provide you a stable voltage reference.

    Cheap and easy.

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    Junior Member ishkhan's Avatar
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    Min, are you trying to reduce the heat on your Gamma card?

    ishkhan

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    So what your trying to do is lower the 5v on the humax internal card reader to try and run the white card cooler?
    I too would like to know of a possible fix.

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    Quote Originally Posted by ishkhan View Post
    Min, are you trying to reduce the heat on your Gamma card?

    ishkhan
    I dont have a gamma card yet, but i`m getting the unit ready for when I do.
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    Quote Originally Posted by ssrattus View Post
    Not for 5v to 4.5v, voltage regulators need more voltage differential to work.

    A IN4004 (or any power diode) should do the trick.
    Just tried a 1N4004 and it drop from 5.00 to 4.66. Any other ideas as to how to get it down to 4.50???

    Cheers
    Blown Humax 5400Z, Strong SRT 4658X, Strong 4663X and DM 518.

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    Senior Member z80's Avatar
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    Some say it is due to the overclocking of the card.

    there are articles on the web about changing the crystal in the embedded humax cam....some say 5 megahertz instead of 6 will do it nicely.

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    Quote Originally Posted by Min View Post
    Just tried a 1N4004 and it drop from 5.00 to 4.66. Any other ideas as to how to get it down to 4.50???

    Cheers
    As the diode is only dropping 0.34 volts the circuit can't be drawing much current.

    Put a 470 Ohm resistor to ground after the diode drop, this will pull about 10mA and force the diode to drop about 0.6 volts

    If the circuit draws such little current there can't be much dissipation - how hot do things get ?

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