# ATX PSU Sleeping mode on 12V. Possible?



## vapago (Jan 24, 2011)

Hello everybody!

I am trying to do such a mode... In few words i will try to explain properly what i want to do. 
I am powering an old car stereo on pc power supply. Everything is ok, i am starting the Power Supplye by shorting 14 and 13 pins on the big plug. The stereo is working properly.
But when i turn off the Power Supply and then start it again, the car stereo do not remeber its unlock code and i used to eneter it again and again at every start.

Is there any way to keep the PSU in sleeping mode, so it powers the memory of the stereo when it is turned off?
Thank you!


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## leroys1000 (Aug 16, 2007)

I don't think so.
ATX power supplies have 5 volt stand by but not 12 volt.
The power supply has to be full on to produce 12 volt output.


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## vapago (Jan 24, 2011)

Ok, thanks for the reply!

If somebody could give me an advice how to keep the memory of the stereo please share it here. Thank you!


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## Frank4d (Sep 10, 2006)

You may be in luck if your car stereo has a wire for constant 12V power, in addition to a wire for switched 12V power.


You would need to wire a 12V output DC-DC converter with 5V input, to the 5V standby output of the power supply, and then connect the constat 12V wire of the car stereo to it. Due to the typical low current rating for the 5V standby output, this may not work; or it might.

Do you have a way to measure the current on the car stereo constant 12V wire? And what is the 5V standby rating on the power supply?


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## cwwozniak (Nov 29, 2005)

If your radio has the separate high current switched 12 volt input and a separate always on low current input for the memory and clock timekeeping as mentioned by *Frank4d*, you could use some suitably rated 12 VDC wall wart power adapter to always power the low current input.

If the low current input is really low, you might be able to get away with using a few AA or C batteries in series to get about 12 volts or a bit more. You could get fancy and use rechargeable batteries and a suitable charging circuit that would run off the main supply when it was on.

EDIT: FWiW, I just looked over the Intel specs (PDF file) for ATX powers supplies. The +5 VDC Standby supply (that is active whenever AC power is connected to the supply) needs to be able to output a minimum of 2.5 Amps and handle surges of 3.5 Amps for up to 3 seconds.


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## vapago (Jan 24, 2011)

Thank you guys for the cool replys!!!

First of all, i must say the truth- my multimeter is gone, i will try to buy a new one soon. Also i am not so in touch with the electronics, units, etc. Sorry, if i say something stupid.
I like the idea with the 5-12V converter. Not sure, but i have 220V-420V converters from a luminiscent lamps. Will it work for a smaller voltage? It is not a problem for me to find such of these converters, even in cheaper way. 
cwwozniak, thank you for the crazy idea of rechargable batteries!!! I will think about it and decide what to do with it. 

Again, thank you for your helpful posts!


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## cwwozniak (Nov 29, 2005)

A high voltage DC-AC Inverter used for EL lamps will not work as a low voltage DC-DC converter. You would need a low wattage DC-DC boost converter that would step up a 5 VDC input to about 12.5 VDC (within typical range of a car battery). 

A few Google searches did not find a ready made device that you could just purchase and connect to a 5 volt power source. You would probably need to design it, buy all the parts and build your own.


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## vapago (Jan 24, 2011)

Ok, thank you very much again for the helpful answers. I will work on it soon and i will post the result as soon as i finish the project.  
Regards!


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