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irishron40
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Joined: 22/09/2014
Location: Ireland
Posts: 251

Posted: 03:00pm 30 Nov 2015

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hi i want to supply a constant stable 2volt dc to a little dc motor.

my power supply is 11 to 13 volt from car battery.

what would be the best way

i was thinking to use a lm7805 and then reducing it back using a 4 diodes.
I think the n4001 had a 0.7 forward voltage drop

4 diodes would drop about 2,8 volts leaving me with 2.2volt output

would this be an acceptical way of doing this?

thx

ronEdited by irishron40 2015-12-02

powerednut

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Joined: 09/12/2009
Location: Australia
Posts: 221

Posted: 05:56pm 30 Nov 2015

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its not a great option, but depending on what your doing with your small motor you might be okay.

The best (least energy lost) way would be to use a switching regulator in a buck, or other step-down, configuration. The LM2596 is pretty easy to work with. You'll need a number of external components which you may not have - a schottky diode, an inductor and a couple of low ESR electrolytic capacitors. details in the datasheet on how to calculate what component values you want. Or you can get a pre-made board from china for about $1.10.

Next best option would be to use either a fixed or adjustable voltage regulator to give you the right voltage. The LM317 is a cheap, readily available choice.

Pete Locke
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Joined: 26/06/2013
Location: New Zealand
Posts: 181

Posted: 06:47pm 30 Nov 2015

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powerednut said
The best (least energy lost) way would be to use a switching regulator in a buck, or other step-down, configuration. The LM2596 is pretty easy to work with. You'll need a number of external components which you may not have - a schottky diode, an inductor and a couple of low ESR electrolytic capacitors.

Bang on. Buck regulators work very well for high input/output voltage difference. All the bits (except for the regulator chip) can be ratted from dead computer or other switch mode power supplies. Also, google buck regulator circuit, and there are quite a few discrete component variations not needing a chip. Buck regulation can also be added to a standard 3 terminal regulator to increase the efficiency.

irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251

Posted: 09:25am 03 Dec 2015

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the lm7805 and 4 diodes did the trick thx

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