Switching from 12v to 9v

@ichigo-k530MY • Oct 26, 2024

Oct 26, 2024

1.5K

How can I switch from a 12v DC source to a 9v DC source? Something like an automatic transfer switch? The main source is the 12v. If the 12v goes off, it should automatically change to the 9v.
Is there any device that does it automatically or do I have to do it using a μcontroller? Where should I look?

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Ichigo

@ichigo-k530MY • Apr 18, 2013

The main source is the 12v. If the 12v goes off, it should automatically change to the 9v. But once 12v comes back it should switch back to 12v.
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Anand Tamariya

@anand-tamariya-DnfjEX • Apr 18, 2013

uC is the way to go.
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arunchary

@arunchary-VtqB3c • Apr 18, 2013

hi, use a 12v relay to operate this concept in simple way.connect main terminals of relay to 12v and also pin(NO) T1 and 9v to T2(NC) then comm is connected to load.as fig's shows the two different mode first is operated with 12v and 12v output and then below one is operated normally at off of 12v it is at 9v.
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arunchary

@arunchary-VtqB3c • Apr 18, 2013

please follow the figs in following link.
<a href="https://www.dropbox.com/s/xwwta3gemqwxijw/Automatic%20voltage%20changer.docx" target="_blank" rel="nofollow noopener noreferrer">Dropbox - Error</a>

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Ramani Aswath

@ramani-VR4O43 • Apr 19, 2013

May be all that you need is a forward biased diode in series with the 9V +ve terminal.
When the 12V is on this diode will be reverse biased and will not conduct. When the 12 V is off the diode is forward biased and conducts. No relays or other circuits.
I have used such a configuration. It works.
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arunchary

@arunchary-VtqB3c • Apr 19, 2013

ya sir it is also works.........thank you for reducing the circuit concept..
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AT-OK

@at-ok-E0bCzz • May 2, 2013

Just a bit of extention to Mr.#-Link-Snipped-#'s Ans.
Diode must be able to switch fast.
Prefer using the schottky diode.
Best of Luck 👍

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Ichigo

@ichigo-k530MY • May 4, 2013

AT-OK
Just a bit of extention to Mr.#-Link-Snipped-#'s Ans.
Diode must be able to switch fast.
Prefer using the schottky diode.
Best of Luck 👍
Thanks to all of you mates

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oprime

@oprime-Myffqx • May 14, 2013

#-Link-Snipped-# Should we not put diodes in series with both 9V & 12V source?
If we put diode in only 9V connection, when 12V source turns off, the current which is flowing from 9V source will enter the 12V source too and try to charge it.

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AT-OK

@at-ok-E0bCzz • May 14, 2013

#-Link-Snipped-# :Yes,you are right,Buddy.

It need 2 Diodes to make the system work.
Try using #-Link-Snipped-# <--Double Schotky Diode.

Nice Observation.😉

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n.rajeev sharma

@nrajeev-sharma-ykmZu4 • May 31, 2013

i think relay will give u the chance and uc can be exact
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Jeffrey Arulraj

@jeffrey-xA7lUP • May 31, 2013

n.rajeev sharma
i think relay will give u the chance and uc can be exact
Uc is the most expensive But the most reliable once we can ever think of in solving this issue

If the tolerance is to be less than 1% go for uC else for such a simple application that is a pricy solution
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Ramani Aswath

@ramani-VR4O43 • May 31, 2013

oprime
#-Link-Snipped-# Should we not put diodes in series with both 9V & 12V source?
If we put diode in only 9V connection, when 12V source turns off, the current which is flowing from 9V source will enter the 12V source too and try to charge it.
Not if it (12 v supply)is a usual transformer- rectifier kind of supply. The diodes of the rectifier themselves will block the reverse current.

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KenJackson

@kenjackson-mBf7HF • Jun 4, 2013

The diodes are the absolute best solution, if you can tolerate the voltage drop and corresponding power loss across them.

I've seen them referenced as "auctioneering diodes", which seems like an apt name. There's an ongoing auction for who supplies the current, and the source with the biggest voltage wins the bid at that instant.
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