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9V to 12V, need help

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Courage

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My 12V wall adapter blew up last week in a power surge and have been rather reluctant to buy a new one since they cost a bit of money that I don't have. After digging through my draw of infinite cables, mainly consisting of cheap and partially cracked <200ma 12/6/9V adapters I came across a nice 9V AC adapter that offered 1A... Two problems:

1) Its an AC-AC adapter, but nothing a bridge rectifier can't fix, so not much of a problem.

2) Unfortuantely it doesn't output enough voltage (I need 12), anybody got a circuit to beef up the voltage to 12V?

I want to use this to power a small bench power supply with 5 and 12V and don't want to play around with a 240/12V transformer or extremely weak <200ma 12V wall plugs, the 5Vs is easy to acheive but I'm not sure how to get 12V from 9V.
 
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Even with only half wave rectification, a big capacitor will charge to 12.6 volts on a 9 VAC input. You won't be able to regulate the 12 volts, though, as there is not enough excess for a 7812 regulator. If you don't mind a bit of ripple, it might do.
 
I don't think I could really deal with the ripple... If I had a 5V and a 7V regualted output and I linked them, I would get 12Vs, right? Can someone advise me on this...
 
A 9VAC transformer gives 9VAC only at its rated output current. It could be 15VAC at a lower current.

If it is actually 9VAC then its peak voltage is 12.7V and its recified and filtered voltage is 11.2VDC. The size of the filter capacitor and whether it has a regulator determines its amount of ripple. The rectified and filtered voltage must be at least 15VDC for an ordinary 12V voltage regulator IC.
 
Sounds viable, but I've heard sending 5 or 7V back through the 7 or 5V line could break the regulator?
 
power supply.PNG
this might help you.
 
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Check out Hosfelt Electronics. They have boatloads of surplus adapters at rock bottom prices. Their catalog is organized by voltage and current output.

**broken link removed**
 
Its fine, I've located a 1.25A 12V power supply block, big surge protected one so I won't be having a blowout (handles a couple of kA)... Its AC unfortuantely but a retifier should do the trick. Anybody got any idea what capacitors I should use... On the power connection and after the 5V regulator on the one line.
 
The filter capacitor depends on your load current, I'll use the higher value for this. Not sure what voltage regulator are you using, but as recommended by the datasheet, a 100 nF at the output of the voltage regulator.

You can use 5 V and 7 V regulator to get 12 V, provided that the voltage supplied is around 15 V (with the consideration of the dropout voltage required by the voltage regulator).
 
Now, I want to split the 12V coming out of the bridge rectifier to a 5V regulator (which will be connected to a socket) and to a 12v socket. I know what caps I will need with the 5V regualtor but what Caps can you recommend for the 12v socket...
 
On my homemade PSU I used a 19000uf capacitor :D

Use what ever you got. I would have at least 1000uf on there.
 
Where do you live?

Mains adaptors are cheap where I live, I've got loads lying aroung the house, I'd send you one but the shipping costs are probably more than it's worth.
 
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