Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Lm317

Status
Not open for further replies.

EN0

Member
Is there a difference in the function of LM317 and LM117? Or is it just the specs that are different? They can both do current regulation?

Also on the LM317 datasheet:

https://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS009063.PDF

What does the section " current limit" mean. Because it says typical 2.2Amps but everything I read says it can output 1.5 amps or less. So what is "Current Limit"?

Axro,

Here is the datasheet I pulled up:

https://www.electro-tech-online.com/custompdfs/2009/07/LM117.pdf

Notice on the top of the page is says "LM117/LM317A/LM317 3-Ternimal Adjustable Regulator." There is no difference between them. Usually, you see the "A" at the end of a part stating that it can withstand a wider temperature range but it still carries out the same purpose.
 

MikeMl

Well-Known Member
Most Helpful Member
Is there a difference in the function of LM317 and LM117? Or is it just the specs that are different? They can both do current regulation?

The 117 has tighter specs, and is spec'd over a wider temperature range.
Yes.

...
What does the section " current limit" mean. Because it says typical 2.2Amps but everything I read says it can output 1.5 amps or less. So what is "Current Limit"?

Current limit is built-in protection against a sudden short-circuit; it is not the maximum current that the 317 will deliver under normal use.

You have to read the spec sheet carefully to determine what current you can actually draw. The 1.5A spec presupposes that the device is mounted on a very large heatsink, and the temperature of the device itself is kept below a specified limit. If it gets hotter than that, it shuts down to protect itself.

There have been lots of posts on this forum from people who did not understand that. They typically complain that they expect the 317 to supply 1.5A, it doesn't due to thermal shutdown, but they didn't mount it on a heatsink!
 
Last edited:

MikeMl

Well-Known Member
Most Helpful Member
Please! correct me if I'm wrong, but I thought the LM317 had a higher amp rating than the LM117, other than that, they are the same.
Kinarfi

Off the spec sheet!

317-png.31454
 

Attachments

  • 317.png
    317.png
    12.5 KB · Views: 2,684
Last edited:

kinarfi

Well-Known Member
Thank you, I did some reading and saw the errors in my thinking and decided to delete, but it did appear the out put was limit by case size also, heat dissipation is suppose.
Kinarfi
 
Last edited:

k7elp60

Active Member
Another difference that sometimes is not noticed is that the minimum load current for the LM117 is 5MA, while the LM317 is 10MA. When using them as regulators where the load may be removed the value of R1 needs to be considered. The LM117 can use 240Ω, while in the LM317 needs to use a 120 to ensure the minimum load current is 10MA.
 

axro

New Member
Current limit is built-in protection against a sudden short-circuit; it is not the maximum current that the 317 will deliver under normal use

Is there somewhere that has definitions or commonly used terms in datasheets. Some of the terminology can be tricky sometimes.
 

MikeMl

Well-Known Member
Most Helpful Member
Read the "test conditions" that go with each line item in the spec sheet.
 

EN0

Member
Right, the only difference will usually be in temperature range, maximum current, or maximum voltage.
 

axro

New Member
In this section:

vivo-jpg.31457


Under conditions on the second line. Does that mean if Voltage In/out is greater than or equal to 3 and less than or equal to 40.

Or does it mean If voltage in is greater than Voltage in MINUS Voltage out.

Is that a minus sign or a dash.
 

Attachments

  • vivo.jpg
    vivo.jpg
    14.3 KB · Views: 2,101

audioguru

Well-Known Member
Most Helpful Member
The spec lists the voltage across the regulator from its input to its output. It is from 3V to 40V.
 

crutschow

Well-Known Member
Most Helpful Member
In this section:

vivo-jpg.31457


Under conditions on the second line. Does that mean if Voltage In/out is greater than or equal to 3 and less than or equal to 40.

Or does it mean If voltage in is greater than Voltage in MINUS Voltage out.

Is that a minus sign or a dash.
To amplify on audioguru's comment, it's a minus sign, thus it's the input voltage minus the output voltage.
 

MikeMl

Well-Known Member
Most Helpful Member

Attachments

  • 317c.png
    317c.png
    75.7 KB · Views: 323

axro

New Member
To amplify on audioguru's comment, it's a minus sign, thus it's the input voltage minus the output voltage.

So does that mean you could put 50V into it and have 30V Output? Because 50 - 30 is 20 which is under the 40V they have listed.
 

audioguru

Well-Known Member
Most Helpful Member
The LM317 does not have a ground connection.
If you limit the voltage between its input and output to 40V then its input could be 50V and its output could be 10V to 47V.
But then it gets fried if the output is shorted to ground.
 

wealth210

New Member
Does anyone use LM317 for regulator output 5v+/-1% @load current 1.0A+/-30%.The working ambient temperature range is 10℃~40℃.I find it when the output is 5v@1.3A in 40℃,the surface of LM317 is very heat and the output become unstable.Maybe I need to consider mounting very large heatsink.
 

audioguru

Well-Known Member
Most Helpful Member
The chip temperature must be within the limits. Its case is much cooler than its chip temperature by the amount shown in the calculation of its "thermal resistance" in its datasheet. A heatsink also has a datasheet that shows its "thermal resistance".
 

axro

New Member
The LM317 does not have a ground connection.
If you limit the voltage between its input and output to 40V then its input could be 50V and its output could be 10V to 47V.
But then it gets fried if the output is shorted to ground.

So the "conditions" sections of a datasheet are just the test conditions at which they get the result numbers. I assume though that the test's numbers that are posted are usually done at the minimum and maximum specs of the chip?
 

audioguru

Well-Known Member
Most Helpful Member
Yes, the test numbers posted in the datasheet are usually the guaranteed minimum and maximum spec's. The "typical" is also posted and most graphs show the typical numbers.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top