LM317T DROPOUT DATA NEEDED

SIDDHARTH MOHAN

Other Parts Discussed in Thread: LM317M, LM317L, LM317-N, LM317A, LM317, LP3878-ADJ

Hi, i have doubts in LM317T Three-Terminal Adjustable Regulator, can someone provide the dropout voltage versus load current curve or data.

regards Siddharth

over 7 years ago

0 Michael J Schultis over 7 years ago

TI__Mastermind 24485 points

Hello Siddharth,

I am not familiar with LM317T, are you referring to one of the following:

LM317, LM317A, LM317-N, LM317M, LM317L.

Attached you will find typical data for the LM317 over current (up to 1A) and temperature. Please note this is not a guarantee of performance but just a typical spec measured on one device.

Best,
Michael

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael J Schultis

Genius 3205 points

thanks for the reply LM317T/NOPB is IC Voltage-Regulator-Adjustable Positive 1.25/37V 1.5A 3-TO-220, also could you confirm the reason for current limit values in 2 slabs as per attached image

0 Michael J Schultis over 7 years ago in reply to SIDDHARTH MOHAN

TI__Mastermind 24485 points

Hello Siddharth,

The LM317-N device is the one you are referring to. My data previously is for the LM317. I have contacted the appropriate support for the device you are referring to, and they should bet back with you shortly

Best,
Michae

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael J Schultis

Genius 3205 points

Yes perhaps, i am attaching the datasheet and image for reference. 1826-0393.pdf

0 Michael_DeSando over 7 years ago in reply to SIDDHARTH MOHAN

TI__Genius 12630 points

Hello Siddharth,

I have attached the dropout voltage curve for LM317-N found in the datasheet on page 8.

If you need anything else please let me know.

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael_DeSando

Genius 3205 points

thanks but i need the variation of dropout versus load current variation across X axis , the one that you have sent varies temperature across X axis.

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael J Schultis

Genius 3205 points

What is the typical Vin and the typical Vout in the setup? i mean what are the conditions under which these tests have been done?

0 Michael_DeSando over 7 years ago in reply to SIDDHARTH MOHAN

TI__Genius 12630 points

Siddharth,

The dropout voltage curve only shows the difference between Vout and Vin at the point where Vout differs by more than 100mV from the set value. This could be for any Vout (since Vin is in reference to the Vout) within the allowed range of the part. There are various load currents shown across temp but I can get a specific test case in the lab if you can let me know what you need. Do you have a specific output voltage at a specific temp and output current that you would like to see?

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael_DeSando

Genius 3205 points

Request you to please provide the dropout curve at 25 Deg C, for a load current from 0 to 2 Amp,

0 Michael_DeSando over 7 years ago in reply to SIDDHARTH MOHAN

TI__Genius 12630 points

Siddharth,

I have attached the Input - Output voltage differential at which the output voltage varied from the set output voltage more than 100mV for a load current 0A to 1.5A. After 1.5A, the part heats up rather quickly making the dropout voltage hard to measure as the device begins to shut down. The datasheet says this is a 1.5A part but in the EC table shows the typical current limit to be 2.2A for the TO-3 package. I would recommend using a heat sink to operate this part above 1.5A.

Let me know if this data is what you need or if you need anything else!

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael_DeSando

Genius 3205 points

THANK YOU very much, let me try to use this curve and will update you thanks

0 SIDDHARTH MOHAN over 7 years ago in reply to SIDDHARTH MOHAN

Genius 3205 points

Hi Michael, the most recent curve that you sent shows an input-output deviation of 1.5v at no load or IL=0 amp, which appears to be not matching the low deviation% given in the attached curve from datasheet. Even at 0.5A load the deviation is very low as compared to the curve sent recently , kindly advise

0 SIDDHARTH MOHAN over 7 years ago in reply to SIDDHARTH MOHAN

Genius 3205 points

REQUEST FEEDBACK

0 Michael_DeSando over 7 years ago in reply to SIDDHARTH MOHAN

TI__Genius 12630 points

Siddharth,

Sorry for the confusion. The graph I sent uses the Input to Output voltage difference (the input voltage minus the output voltage). The graph you posted shows the output voltage deviation % which is how much the output voltage measured differs from the output voltage set value in a percent form. So they both show something different. For dropout, you typically want to know how much the input voltage needs to be above the output voltage for proper regulation (in this case for the output voltage to be within 100mV of what you set it for). For accuracy or load regulation, you typically want to know how much the output voltage varies from what it should be (what you set it for). I hope this helps clear up any confusion. So to summarize, the dropout curve I posted shows the part will still regulate the output voltage within 100mV of the set value at an input - output difference shown on the graph I posted for dropout. To know how much the output voltage will vary at different load currents for a fixed Vin = 15V and fixed Vout = 10V (which is far above the input voltage needed for that specific output voltage for proper regulation), then you use the load regulation curve that you posted. Please let me know if you have any questions.

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael_DeSando

Genius 3205 points

thanks for the details, can you please let me know what is values for VIN, OUT, R1,R2 used to arrive at this curve. regards

0 Michael_DeSando over 7 years ago in reply to SIDDHARTH MOHAN

TI__Genius 12630 points

Siddharth,

R1 is a 5% 240 ohm and R2 is a 5% 750 ohm. This produces an output voltage of approx. 5.19V but I was measuring around 5.22V during operation. The Vin voltage started several volts above the output voltage (like Vin=8V) and then I decreased Vin until the output voltage dropped by 100mV. So I decreased the input voltage until I measured approx. 5.12V and then recorded that input voltage as the drop out voltage for that specific load current. Then I repeated from a load current from 0A to 1.5A. I also have a 0.1uF input cap and 1uF output cap which is recommended in the datasheet. The purpose of this test is to show how low the input voltage can be in relation to the output voltage for the part to still regulate (regulate within 100mV of the set output voltage).

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael_DeSando

Genius 3205 points

Thanks for the reply. I hope you mean that for every load current value in the plot the Vout is 5.12v and corresponding Vin can be obtained by adding 5.12v to dropout voltage given in the curve, is this correct?

regards

0 SIDDHARTH MOHAN over 7 years ago in reply to Michael_DeSando

Genius 3205 points

HHi Michael, request you to please provide the droput voltage versus load curve for part LP3878-ADJ

0 Michael J Schultis over 7 years ago in reply to SIDDHARTH MOHAN

TI__Mastermind 24485 points

Siddharth,

Please start a new E2E post for your question regarding the LP3878-ADJ.

Best,
Michael

Power management

Power management forum

LM317T DROPOUT DATA NEEDED