LM317 Variable power supply

[audioguru]

They use 0.1 ohm equalizing resistors with them in the circuit you posted to cancel differences in the gain of the transistors and in the slightly different regulators' voltages. Then the excellent voltage regulation is ruined by the resistors and made good again by the gain of the opamp.

[Staigen]

Also look at my reply's, they are simpler, uses only one IC. For 10 Amps use several transistors, and reduce the current thru LM317 to somewhere around 100 mA before the transistors start to conduct. Restrict the current thru the transistors to 2-3 Amps or so.

//Staigen

[Staigen]

Hi

Which replies??

Replies #124 and #126 in this topic!

//Staigen

[Staigen]

Not exactly, but it is similar, well, maybe not, after a closer look, mine is much simpler, and its safe, and have a good regulation. Audioguru know what i mean, only by the description i gave. I will upload a schematic, as soon i have done one! I will do that at once, but it will take a few minutes or maybee a little moore. See ya!

//Staigen

[Staigen]

Here is the sematic.

//Staigen

[Staigen]

Sorry, forgot values! ???

R1= 6.8 ohms
R2=R3= 0.47 to 1 ohms(depends on current throu transistors)
R4= 120 ohms(acording to datasheet, some LM317 can use 240 ohms, acording to Audioguru)
C1=C2= 0.22 uF
C3=C4= 10 uF
Transistors can be TIP36 or similar

//Staigen

[audioguru]

audioguru, how do you compare the quality of regulation in the circuit I posted with the 0-30V stabilized power supply project?

http://www.electronics-lab.com/projects/power/003/index.html

Hi Zeppelin,
Our project uses an unspec'd zener diode voltage reference operating at a current that is too low for good regulation. If a low-current zener diode is used and the resistor that feeds current to it is changed to give it its required current, and the other modifications to the project that I recommend are done, and its wiring is correct, then it is an excellent regulator.

An LM317 has a 4:1 range of regulation. An LM317A has a much better minimum amount of regulation, about the same as our modified project, if it is wired correctly and has a capacitor connected to its ADJ terminal to ground.

The circuit you posted depends on the minimum amount of regulation its LM117 has. It has the added gain of the external opamp which would make its continuous regulation better, but its regulation with quickly changing input voltage or output current would probably have wild swings. 

[Staigen]

Oops! The diodes!

D1=D2= 1N5401

Hope i dont forgot anything moore ;D


//Staigen

[audioguru]

It looks like when the load draws too much current or is shorted, then the extra current through the diodes causes the LM317 to current-limit or shutdown. Good. ;D

[Staigen]

The transistors need a good heatsink! But it is simple and easy, and it work! ;D


//Staigen

[Staigen]

Hi Zeppelin

Yes, i can, but i leave it up to you to figure out and tell us how it work!
Hint, the forward drop over each 1N5401 is about 0.7V at full output.

//Staigen

[autir]

Hi Autir,
I also built my LM317 variable supply on stripboard. I had the load connected to the heatsink tab, with a terminal screwed on with the same bolt that attaches it to the heatsink, then connected the current-setting resistor to the output pin without any load current in it. Then the output "star" connection is inside the IC.

I connected the supply's ground, the load's ground and the pot's ground all together in one spot, called a ground "star"connection.

It works perfectly. ;D

Hi
is the circuit of this guy
http://casemods.pointofnoreturn.org/vregtut/tutorial-full.html
a good example of star topology?
any ideas on how to connect the LM317K (TO3 package), mounted on a huge heatsink?

also

Hi Autir,
If you have it wired so that load current travels through a wire or pcb trace to which R2  (the pot) is connected to ground and the resistance of the wire or trace develops a voltage across it, then the regulation is much poorer.
National Semi explanes a similar problem that is caused when load current travels in a wire or pcb trace between the regulator's output and the current setting resistor R1:

I have comprehended the problem with the resistance between the 317's output pin and R1. But not the problem with the resistance between ground and R2 (the pot).

Care to explain both a little bit more?

Thanks.

[JuniorHP]

Hi,

I am building a power pack for a laptop... reason being we make recordings on the laptop of sermons, but the power in the building where it is done is very "Noisy"? resulting in terrible recordings.

What we did was using a 6V and 12V car battery in series, connecting the original power to the batteries and getting perfect(clean DC) power into the laptop, which results in beautiful recordings.  This is a temporary solution.  I am planning to use 3x 6V batteries in series, a few diodes and the input and output connectors. I have attached a picture of a drawing i planned, this may be incorrect in which case please let me know.  I am open for any suggestions.

[audioguru]

Your batteries are shown wired in parallel, not in series.
There is not a current-limiting resistor from the power input to the batteries. Therefore they will charge with an extremely high current.
The diodes to the output are backwards and are not needed anyway.

[JuniorHP]

Like this then?

What should the value be of the resistor, is 1k fine?

[audioguru]

Your revised circuit is much better.
1k is so high that the batteries will get hardly any charging current.
The resistor's value is calculated from the input voltage when loaded, the battery's recommended charging current and time. We can assume that the lead-acid batteries each have an average voltage of 6.6V.

[JuniorHP]

Just a few more questions:

The supply is 18V, the batts spesifies less than 1.20A and say the sermons lasts at most 2 hours the resistor will be 30 ohms, correct?

If the batts specify 6V4.0AH/20HR each how quickly will the batteries run down by the laptop?

What are the risks, if any with the way we want to use this?

[audioguru]

The supply is 18V

18VDC is too low to charge an "18V" lead-acid battery. The battery needs at least 21.6V to fully charge.

the batts spesifies less than 1.20A

What spec is that? Charging current?

the sermons lasts at most 2 hours the resistor will be 30 ohms, correct?

No. The supply voltage is too low to charge the battery.

If the batts specify 6V4.0AH/20HR each how quickly will the batteries run down by the laptop?

You calculate the time only if you know the current drain of the laptop.

What are the risks, if any with the way we want to use this?

Just make sure that the battery is never connected backwards.

[allvol]

Having recently acquired a PIC development board that requires 16 v., I decided to build this LM317 PSU from the projects section of this board.

It took less than two hours to construct, using junk box parts, (including the LM317 already on hand).

[audioguru]

I also made a variable supply with an LM317 IC.
Its regulation is extremely good and its output doesn't have any ripple.

[allvol]

Yes, audioguru.

[audioguru]

Yes, audioguru.

[JuniorHP]

What spec is that? Charging current?

Initial Current

[audioguru]

Initial Current

Then calculate a current-limiting resistor with the supply voltage that you have so that the max current spec is not exceeded.

[x_dadu]

I just made the power suply with LM317 - TO220 and the multi-mmeter from the 0-30Vcc power suplply link. I want to know if I can put two LM317 in paralel for more curent, if I need it and how can I connect them, pin to pin or how ...