[SOLVED] Need help for choosing a linear voltage regulator

[zeeekay]

Hi folks! I am currently designing a GSM based design needs 5V 650 mA current for charging interface . The design is size critical and we are using KTT version of LM317 for providing 5V-650 mA . The heat sinking is done by a solder masked pad on PCB. We need to power up design by 26V.
The problem we are facing is enormous heat generation. I understand that (Vi -Vo) is high enough and it is reasonable for heat to generate. However, I am unable to find another linear regulator with small form factor + SMD that we can use to meet my requirement.

Kindly help, if you have any info about a linear regulator which can stay "cool" and can meet our requirements.

 

[FvM]

In the described design form factor, the regulator's junction-to-ambient thermal restance will be almost independent of the specific regulator chip and rarely below 30 to 50 K/W. I leave it to your detail engineering work to calculate the resulting chip overtemperature at 26V input and 650 mA.

In a short, you simply must give up the idea of a linear regulator for the application.

 

[pwdixon]

This is a perennial problem, you can only dissipate the energy with a heatsink if you want to use a linear regulator. If you can tolerate a switching regulator you should look at a dc/dc convertor they can be quite efficient and needn't generate excessive heat. The size of a switching regulator will inevitably be bigger than a linear regulator but it would be smaller than a linear regulator including a heatsink.

 

[zeeekay]

Thanks everyone for help.. It seems a classical problem of its type.

I will try to find a high frequency switching regulator to minimize inductors/ capacitors size.

What is your suggestion ? Do you see any drawback of using a 1 MHz switching regulator. Can you specify any idcutor-less regulator that can suit my application.

Regards !

 

[IanP]

Thanks everyone for help.. It seems a classical problem of its type.

I will try to find a high frequency switching regulator to minimize inductors/ capacitors size.

What is your suggestion ? Do you see any drawback of using a 1 MHz switching regulator. Can you specify any idcutor-less regulator that can suit my application.

Regards !

Google for: 7805 switching replacement ..
Here is one example:
https://www.murata-ps.com/data/meters/dms-78xxsr.pdf

:wink:
IanP

 

[crutschow]

..........................................
What is your suggestion ? Do you see any drawback of using a 1 MHz switching regulator. Can you specify any idcutor-less regulator that can suit my application.

A 1 MHz regulator should be fine as long as you don't have anything in the GSM receiver that's sensitive to that signal.

Such a regulator will require an inductor but it will be quite small because of the high switching frequency. Inductor size is inversely proportional to frequency for a given current output.