LM1084 it5.0

LM1084 5A Low Dropout Positive Regulator

I don't see any reference design for a Constant Current application in the LM1084 data-sheet. Which Typical Application circuit are you referencing?

Details of your circuit would be most helpful, otherwise I can only guess.

Extrapolating from the one given point (Rload= 2.1V /0 .85A = 2.5 ohms), for 5A output the output voltage is (5A x 2.5ohms) 12.5V and the minimum input voltage will need to be Vout+Vdo+Vref = 14.9V

A few alternate possibilities could be:

 Vin-Vout differential is too high, or too low. Either end of the range can limit the available current for different reasons.

 Circuit is designed OK but thermal dissipation is causing the output to go into thermal limiting.

Donald Thanks for your reply I have inserted reference design. Input voltage is 13.8.

Hi,

The design is not for constant current but for constant voltage of 5V with load current of up to 5A

Hi Avi,

It was by mistake that I wrote constant current. I am getting 5V output without load but it drops as soon as load is connected.

Your input voltage is way too high. At 5A, it would need to dissipate 40W. Cant you provide a lower Vin?

Avi I am not a technical guy. Will try to do it I think placing few resistors before the regulator will help?

Rajesh, if you are not a technical guy please get or hire one. This is quite a high power supply and must be handled with due care. However, I dont intend to leave you without an answer. Power must be dissipated in any linear solution, and dissipating it in resistors or the LDO is an unacceptable waste. 

If you cant have a lower Vin the correct way to go is to put a first switching DC DC stage. And this gets me to what I already told you. You need help from a power professional.

Thanks Avi, I am trying to help my kid with his school assignment. Let's see if I can make it for him.