Design power supply (ask)

[Zoegabh]

Hi,

I would like ask about designing power supply,
I want to make power supply that will operate devices that need 12 V and 20A.
I am thinking to use fixed voltage regulator LM 7812, but the problem is i saw in the specification of LM7812, the output current is only 1 A.
I have an idea to increase the current to 20A by making 20 LM7812 paralel.
My question is, Is that right or not? And do you have other idea to get 20 A from the regulator?
And also I have question about transformer, if I am going to use the power supply for the load that will operate of 20 A. Is this means the power rating of secondary transformer should be 12 V * 20A = 240VA right?

Thank you,

 

[itsmoked]

Hello Zoegabh.

You should google for power supply designs.

While designing a power supply like you describe is not 'hard' it is not trivial either. There is really too much to describe here.

You would need a transformer much larger than that!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

The sort of car battery replacement power supply (nominal "12" volts, actually 13.8 volts) is "as common as dirt" in the 2-way radio world. They're available for approximately US$100 to 200 from many suppliers.

If you insist on making one, the normal approach for an old fashioned architecture is a single regulator controlling a bank of 2N3055 pass transistors. The Ham Radio reference books will have schematics.

The advantage of buying one is that it will typically be a more modern 'switching' design. And thus cheaper, less heavy, and more efficient. The good ones provide very clean power.

 

[IRstuff]

In any case, you would NOT use 20 7812's in parallel, as each individual regulator would attempt to regulate the output voltage; a potential disaster in the making.

However, there used to be alternate configurations for devices like the 7812 that allow for much higher output currents, and they are usually in the datasheet.

TTFN

FAQ731-376