Can anyone tell me how can I get 1.2V at 15A output?

I want to make a circuit which receives 12V or 9V input (from a computer charger e.g.) and give 1.2 V (like a Nihm battery) at 15A. I was told I could use LM317 to regulate voltage but i need more information. Any help? thanks.

My first question is where are you going to get a source to deliver that kind of current at that low of a voltage.

Regulating the voltage is not that easy either as something has to absorb the voltage loss at that current. The LM 317 can act as the driver for the voltage regulator but it cannot be the voltage regulator delivering 15 amps as they are only rated for 1 to 1.5 amps.

Suppose you had a 12 volt source that can give you 15 amps - then the regulator brings it down to 1.2 volts - so the regulator has to absorb 10.8 volts at 15 amps which gives you a power level of 162 watts that has to be dissipated as heat. By the way this is a classical design and not that of a switching power supply.

Maybe Colin can come up with the switching power supply version.

Assuming I have a charger with 12V @ 1A, is it possible to raise A to 15A?

Analogy- Your trying to fill a garden hose from a squirt gun!

NO......12v@1amp=12 watts
12v@15 amps=180 watts

Where are the additional 168 watts coming from?

A common and efficient way to convert 12 volts to 1.2 volts at 15 amps is using a "buck" converter.

An example of this is the Linear Technology LTM4627 uModule. Given an efficiency of 85% the 12 volt supply will need to supply 1.5 amps.

http://www.linear.com/product/LTM4627

So if I have an AC 230V current how can get 1.2V and 15A ?

That's even harder ... first you need to reduce the voltage. This is commonly done with a transformer, which can be expensive. The good news is that transformers are pretty efficient. AC can be converted to DC with a bridge rectifier - though at 15A it would be really big and expensive, lots of capacitors to filter or average the output, and then a good switching regulator design that can output 15A - most switching regulator designs output 1 to 3A - you'd need lots of external parts. If it was easy everybody'd do it.

Sry, I missed the decimal point! Still not possible just less impossible. 1.2 vault x 15 amps is 18 watts so still 6 watts short. and that's assuming 100% efficiency which doesn't happen.

Anyone else curious to know what in the world would require 1.2 volts DC at 15 amps? I suspect there are simpler ways to do the job!

I have a feeling that you have been given a bum steer here. An efficient switch mode power supply can easily give a much highrer output current ( at a lower voltage of course) than the input current. May I suggest you look at switch mode power supplies on the web as a first step. I have built a low voltae AC supply capable of tens of amps from a 12 volt DC source with an oscillator and IRF50 MOS FETS. If you need to use a linear regulator as the discussion sems to indicate, then a low voltage square wave generated from the 12 volts as mentioned above has almost no lo loss. This could act as a pre regulated input for your linear regulator.. Hope this helps.

Of course it can increase the current at a lower voltage, but you can't make watts out of thin air. 1.2v @ 15 A is 18 W. No linear regulator that I know can handle anywhere near 15A and switching power supply that supplies 15A is no piece of cake either. I'm also not sure why you would need a linear regulator with a 15A switching regulator as a pre-stage.

The LM317 is adjustable voltage regulator that can handled a maximum current of 1 ampere. In order to handled a 15 amperes current you need a current boost transistor. The 2N3055 transistor is commonly used as current boost. For 15 ampere you need at least 4 pcs 2N3055. Provided that the circuit receives a 12V or 9V at 20 amperes. The output of LM317 is directly coupled to the base of the 4 pcs 2N3055. The collectors is directly connected to the input which is 12V or 9V. The emitters are connected to 0.15 ohms 10 watts wirewound resistors before goes to output. Good luck