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Old 04-15-2010, 04:52 PM
jrekha jrekha is offline
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Default 7905 voltage regulator

Using 7905 voltage regultor can i produe +5V and -5V.
my Vin is 7V
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Old 04-15-2010, 05:28 PM
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beenthere beenthere is offline
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No. If you had a source of -7 volts, you could produce a regulated -5 volts.
First comes the hardware, then the software.
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Old 04-15-2010, 05:39 PM
shivashankari.c14 shivashankari.c14 is offline
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u can produce -5v by using 7905...if u use 7805 u can produce +5v..
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Old 04-18-2010, 05:59 PM
jrekha jrekha is offline
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so i need +5v and -5V, suplly is +7vand -7V.
how to do it using both 7805 and 7905?can i simply connect both together to respective supply, and ground together, to get the outputs??
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Old 04-18-2010, 06:56 PM
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Bill_Marsden Bill_Marsden is offline
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2 volts difference is pushing it a bit, but that is the idea.

You will need 0.1F caps on the output of each regulator, as well as caps on the input (say 3.3F) to keep the regulators from oscillating.

The 7805 and 7905 are pretty close to mirror images of each other. They both have overcurrent and thermal protections. If you push much current through them at all a heatsink is strongly encouraged. With a heatsink they are basically indestructible.

You also need a minimum load. If they will be disconnected from the circuit you might think about adding a 10ma LED circuit on them.
"Good enough is enemy of the best." An old engineering saying, Author unknown.

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Old 04-18-2010, 07:54 PM
Audioguru Audioguru is offline
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7805 and 7905 regulators do not need a minimum load current. Their voltage regulation is spec'd with a load starting with 5mA but without a load the regulation is fine.

The LM317 adjustable regulator needs a minimum load current that is usually set with its veltage setting resistors.
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