Hi everyone
I want to make a 12v-to-9v regulator. I use LM317 as my regulator and I use the schematic below:
I set R2 to 744Ohm to get 9v.
but this not the case...
my biggest concern is that does this circuit provide 4Amp at the output? can anyone help me?
Look for a "buck converter" on eBay.
Like this one:
eBay link!
US $1.38
OK, that circuit probably would work and if the TIP73 is rated for over 5 A (it is just not worth me looking), it would survive with a substantial heatsink.
But that way of doing it is basically obsolete. 
ALAA72:
the link is great, but I need to design my own board and not to use pre-assembled board available.
Nonsense! 
Paul__B:
But that way of doing it is basically obsolete.
Not the case. There are times when nice, quiet linear regulators are essential. It's horses for courses.
Have a look through RS's catalogue of Buck converters and find some that have the input / output characteristics you need. Download the data sheets for the ones that interest you. Read the data sheets, they usually include example circuits you can copy, some also include examples of recommended board layouts for PCBs. From that you can design your own.
I agree with Paul B though, I'd just buy a ready made one, I'd have to have a very particular reason to make one.
ALAA72:
Hi everyoneI want to make a 12v-to-9v regulator. I use LM317 as my regulator and I use the schematic below:
I set R2 to 744Ohm to get 9v.
but this not the case...
my biggest concern is that does this circuit provide 4Amp at the output? can anyone help me?
What do you mean by "this is not the case"?
What voltage do you get with no load?
What voltage do you get with a load?
What are you using as a 12V supply.
The diagram that @Paul__B has posted with the LM317 works well, in your original circuit did you include the bypass capacitors at the input and output pins?
Tom.... 
Hi,
If you use this LM317 calculator;
R1 = 240R R2 = 744R Vout = 5.125V
but
R1 = 240R R2 = 1500R Vout = 9.062V
Tom...
I think I would have built a simplified version if I needed the linear regulator, starting with something like a 7810 into a decently heatsinked pass transistor. Final Voltage of 9.4V would be perfectly acceptable and would probably load down a bit anyway.
Hi,
Why R1 = 120R, when 240R is suggested in data sheets?
Use two 120R in series for R1 and use 1K5 or 1500R resistor for R2.
"regular power supply" does not cut it, what is its output current rating?
What is the load?
lm317 high current circuit
Tom....
ALAA72:
I ALSO want the output current to be above 4Amp! does that circuit included by Paul__B supports 4Amp?
Did you by any chance look at the image?
I've designed lots of PCBs but so far have not designed any high current power supply.
Low current (up to 200 mA or so), low voltage drop: linear regulator.
Higher current or higher voltage drop: ready-made buck converter mounted onto the PCB.
Why do you think you "need" (as per #2 - weakened to "want" in #12) to design the power supply itself?
I guess the circuit in #1 will do the job, just be aware that you need a pretty big heat sink to get rid of the 12W of heat dissipated in that transistor, and your enclosure needs to have sufficient ventilation to allow the heat sink in turn to get rid of all that heat. The heat sink alone is going to cost you as much as, and takes more space than, the suggested buck converter.
That circuit diagram comes straight from the LM317 datasheet, page7, with a TIP37 modification.
Why don't you just build it, learn from it, and throw it away.
Would be easier to replace the darlington configuration with a single PNP power transistor.
Leo..
ALAA72:
I can just ask you guys, what do you think?
I think you're trying to build a Model-T Ford.
This is the 21st century. Nobody uses linear regulators any more.
Just the occasional one for low currents and/or low noise pre-amps, where dissipation (heat) is not an issue.
Leo..
ALAA72:
actually I do not have enough time to test the whole circuit! I can just ask you guys, what do you think?
Get a buck converter module and be done with it.
You should have a fair shot at getting it to work by very carefully studying the datasheet of that IC, and following the manufacturer's guidelines and suggested parts. Running it at 4A you really want it get it to work as close as maximum efficiency as possible, and that's going to take some thorough testing, measuring, redesigning, and testing some more.
I hope you have the time to test and redo the PCB layout a few times to get the circuit layout right... though:
ALAA72:
actually I do not have enough time to test the whole circuit! I can just ask you guys, what do you think?
It sounds to me like you're still way better off just getting a ready-made module.
What should work as well is carefully copying such a module onto your own PCB.
I do not have enough time to test the whole circuit! I can just ask you guys, what do you think?
I think you are asking for problems. If you are lucky it will work just fine, but I think it is far more likely you will discover some little problem that would have been easy to fix sooner if you'd done the testing you didn't have time for. What we think is beside the point, none of us is perfect either, and even if we were there is no guarantee of how you implement what we suggest.
Better start with something simple, like an LM2596 (3Amp).
Buy an LM2596 buck converter module from ebay for US$1.00 shipped to your door.
Remove all the parts.
Design/make your own circuit board that looks exactly the same as the board you removed the parts from.
Solder all the salvaged parts on.
There you have it.
Leo..
ALAA72:
what do you think about this guys?(attached image)
it's a Buck converter as you said and seems to be just what I wanted...
Yes, now go buy the module and mount it as a daughterboard to your own PCB.
Faster, cheaper, neater, more reliable.
