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12V AC to 12V DC Regulator

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cne

New Member
Hi,
I need to take the output of a 12V AC 6A power supply and convert it into 12V DC. I was thinking I would have a bridge rectifier and a capacitor, but that steps up the voltage to almost 16V, so I think I need a regulator. What is the simplest way of making a 12V DC regulator for this application? The equipment needs to be supplied with about 12V, not 16V.
 

DJAE

New Member
You cant do this (not simply/well): Your rectified AC voltage will drop under load (down much closer to 12v, depending on load). Most regulator require at least a volt over their regulated output (12v out would be 13v in). I have always been taught to use a 15v transformer for regulated 12v supplies. 6A is quite a bit of power too, how much power can the transformer supply? If it is quite big (120vA+) you might be OK. It depends; how well regulated/smooth does the DC supply need to be? Could it manage with a 11v supply? If it can cope with just smoothed DC and some fluctuations in supply you could just connect DC, but if it needed regulating the easiest way would be a regulated voltage fed into bases of power bipolar devices (NPN power transistors), or a (expensive) power regulator. Both of these would be LOWER than 12v though (say 11v) as discussed above.

Hope that is some help. Give us more info
 
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aljamri

Member
Hi,

use the 16 volt output as input to the 3-terminals voltage regulator such as LM7812. the attached circuit will give you 12V output but with around 1.5 to 2.5A .
 

DJAE

New Member
Hi,

use the 16 volt output as input to the 3-terminals voltage regulator such as LM7812. the attached circuit will give you 12V output but with around 1.5 to 2.5A .
7812 requires at least 1v more than its 12v output, placing it under load will drop the 16v (12v x 1.414) pretty quick. He also needs 6A.

We need to know the transformer specs and the power requirements of whatever you are powering. Also you'd want a bigger electrolytic as well as the ceramic on the output pin in your drawing if you are using the full 1A (standard 7812 is 1A, not 1.5A and definitely NOT 2.5A!!!!), as well as a heatsink.
 
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alec_t

Well-Known Member
Most Helpful Member
What current do you want to draw at 12V DC?
 

4pyros

Well-Known Member
Most Helpful Member
You could use some high power diodes in series to drop the voltage as long as the load does not change and does not require a regulated supply.
 

throbscottle

Well-Known Member
If the amount of current being drawn by the load is fairly constant, the simplest solution is a zener and series resistor. But I can't help with stuff that involves calculating transformer regulation, and it sounds like you need to know that.
 

cne

New Member
The load will be changing- led lights and electronics. The voltage does need to be 12V or within a few at all times. It is possible that the full 6A will be used. If I just have a bridge rectifier and a smoothing capacitor, how much will the output voltage fluctuate over the current range drawn?
 

4pyros

Well-Known Member
Most Helpful Member
how much will the output voltage fluctuate over the current range drawn
That depends on the current draw of the load. Idon'tt think I can guess.
 

ronv

Well-Known Member
Most Helpful Member
It wouldn't be suprising to see 20 volts at no load and 11 volts at full load depending on the capacitor.
 

aljamri

Member
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alec_t

Well-Known Member
Most Helpful Member
It is possible that the full 6A will be used
You can't get 6A 12VDC from a 6A 12V AC supply. Life (and AC/DC conversion in particular) isn't perfect :(
 

DJAE

New Member
You need to read carefully
Alright... Read on


the 6A OP talking about is his AC input to the bridge, he did not mentioned what is his load Current.
So since he does not mention it, we have no more info we ONLY have the 6a figure to go on: Always assume the worst! As it turns out he thinks he MAY use the full 6.



see the attachment
As i said DEFINATELY NOT 2.5A, so who needs to read carefully now? And if you want to buy 'Bay Linear' rather than any one of the other much more established and reliable manufacturers that's up to you, but i STILL wouldn't recommend running that device at more than 1A, and it would STILL require more that 12v input.

I was trying to help, but appropriately, once i had enough information. You should be more methodical and less critical in your approach to problems my friend!
 
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aljamri

Member
I was trying to help, but appropriately, once I had enough information.
As this is not my thread, I'll make this my final post here,
I was trying too to tell him that it is possible to get 12vdc out of his 16vdc, this is my opinion and if he likes, I can do it for him. This was not against your opinion; still you have a chance to prove your opinion.

You should be more methodical and less critical in your approach to problems my friend!

If I'm critical in my approach, I'll start my post with the things you stated about the dropout voltage and many things in post #2.

Instead, I put my practical idea for him, that I’ve did it in the real life more than 20 times ( if I recall ).
My friend, if you fell offended, I’m sorry , I’m almost 5 years in this forum I’ve never been in such situation, and if One lesson I've learned here, is "NOT TO OFFENSE anybody regardless what he wrote".

This is the place where everybody got to help each other to learn as much as possible, with no offense of any kind.

(Sorry for the OP for taking his space)

Thank you
 
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DJAE

New Member
Aljamri: Definately not offended, just cautious with advice: Have been given so much bad advice as a beginner myself so i like to emphasise the importance of getting all information first. Sorry if i seemed off, was merely joking. Thank you for your polite reply.

Also sorry to OP.

Are you able to provide any futrher details of the cicuit you are powering?
 
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DJAE

New Member
You could probably get 12vDC UNREGULATED, but that would depend on you hitting almost perfect current draw. But if you tell us the circuit chances are that it will be FINE on 10-11v which would be MUCH easier to achieve using NPN transistors and an adjustable regulator.
 

KG4MXV

Member
I would use a 10A full wave rectifier and a 10,000uf DC electrolytic capacitor and you should have close to 20Vdc and use this DC to DC switch mode power supply.
http://www.ebay.com/itm/DC-Converte...ultDomain_0&hash=item43b191d1c1#ht_2707wt_966

it is only 7usd and free shipping.
I have gotten other DC switch mode power supplies from this seller with no problems.
it is rated at 8 amps so if your load max is 6A this should fit the bill nicely.
good luck
 
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