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LM317 Variable power supply


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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

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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. 
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  • 4 weeks later...

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.
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  • 3 months later...

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.

post-21042-14279142906485_thumb.jpg

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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.

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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?

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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.
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  • 8 months later...

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