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Hoffman Amps Forum image Author Topic: 28v ct tap for 5v relays.  (Read 2502 times)

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Offline Captain chunkulus

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28v ct tap for 5v relays.
« on: June 21, 2019, 07:52:06 am »
Have a transformer that has an extra 28v ct tap. Would like to use it for 5v relays. Can I just use anow lm7805 to drop it down or do I need to do something more drastic? Thanks.
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Offline shooter

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Re: 28v ct tap for 5v relays.
« Reply #1 on: June 21, 2019, 08:37:01 am »
IIRC the lm7805 is good to 35vdc IN, double check though
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Offline DummyLoad

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Re: 28v ct tap for 5v relays.
« Reply #2 on: June 21, 2019, 08:58:22 am »
use 14V (CT to end) and LM7805 or use the part in the link below.


http://www.ti.com/product/TL783


--pete
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Offline sluckey

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Re: 28v ct tap for 5v relays.
« Reply #3 on: June 21, 2019, 09:12:05 am »
If you use that 28V w/CT (14-0-14) with a two diode conventional rectifier and a 470µF (or larger) cap you will get about 20VDC. That's fine for a 7805.
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Offline PRR

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Re: 28v ct tap for 5v relays.
« Reply #4 on: June 21, 2019, 12:03:38 pm »
12V relays would be a better fit, but don't run out to buy some.
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Offline kagliostro

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Re: 28v ct tap for 5v relays.
« Reply #5 on: June 21, 2019, 12:10:13 pm »
« Last Edit: June 21, 2019, 04:03:01 pm by kagliostro »
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Offline Captain chunkulus

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Re: 28v ct tap for 5v relays.
« Reply #6 on: July 01, 2019, 08:40:26 am »
Thanks guys for all your help.  :worthy1:
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