LM338 Voltage regulator ck. Why this is not working?

Thread Starter

Raj Pandey

Joined May 27, 2019
62
fitttttt.PNG Hi all,

I have created an LM338 ckt for getting 5.1 Voltage and max 2.2 A but I am not Getting it Please help me I have created ckt as in the datasheet.

Center -right circuit is LM338 one. and at node R1, R2, and R3 I am getting 9.92V, 12.03V and 15.68 respectively. at the load resistor, it keeps getting burnt so I have placed 2 1K resistors and there also I am getting 15.68V.

Here's the datasheet of LM338 :http://www.ti.com/lit/ds/symlink/lm338.pdf Please refer to Page no.12.
IMG20190521133601.jpg IMG20190521133548.jpg
Below are the Images of ckt.

my Load acting resistors are being burnt and I am getting 15.98 V without Load resistors and with also. please Help me regarding this.
 
Last edited:

crutschow

Joined Mar 14, 2008
24,302
Are you sure the pin=out is correct for the LM338 package you have?
Double check all the wiring.

If it still doesn't work, measure all the node voltage in the circuit, write them on the schematic, and then post that here.
 

Thread Starter

Raj Pandey

Joined May 27, 2019
62
Are you sure the pin=out is correct for the LM338 package you have?
Double check all the wiring.

If it still doesn't work, measure all the node voltage in the circuit, write them on the schematic, and then post that here.
I have checked more than enough times still it isn't working.
 

Thread Starter

Raj Pandey

Joined May 27, 2019
62
Your first regulator on the left has the Adj pin going to the 15V supply!!

Pinout left to right is. ADJ, OUT,,IN

Top left IC in the image is LM7805 and center-right one is LM338 and I am providing external power to them. So and the pinout of LM338 is as you said and I have connected as same.
 

danadak

Joined Mar 10, 2018
3,878
Minimum load LM338 is 5 mA, whenever you measure output you have to have that min
load present, right ?

Your load R's, if 5V out, have to be P = E^2/ Rload = 25/3 = ~ 8W, I do not see any
8W resistors on your breadboard ? If you are using 1/2W resistors for Rload poof !

Regards, Dana.
 

bertus

Joined Apr 5, 2008
20,317
Hello,

Even when you get it working, it will never deliver the 2.2 A.
The LM338 will need a huge heatsink, as there is a 10 volt difference (15 Volt in - 5 volt out) with 2.2. A = 22 watts to be dissipated.
Also the breadboard will not be able to carry 2.2 A.


Bertus
 

Thread Starter

Raj Pandey

Joined May 27, 2019
62
Hello,

Even when you get it working, it will never deliver the 2.2 A.
The LM338 will need a huge heatsink, as there is a 10 volt difference (15 Volt in - 5 volt out) with 2.2. A = 22 watts to be dissipated.
Also the breadboard will not be able to carry 2.2 A.


Bertus
Hi Sir,

So what is the Solution here? and Without the load resistors, it should provide 5.1 V right. But I am not getting it so this means does I have to create it on PCB and test it then on the breadboard. And if possible can you provide me a better an improved schematic of this or just suggest changes.

And If I work with LM2576 12-V variant and drop it to 5.1 Volts with 2.2 A will it be fine?
 

crutschow

Joined Mar 14, 2008
24,302
When you make all the voltage measurements I requested in my post #2 and put the on the schematic, then we will be better able to help.
Otherwise it's just a guessing game. :rolleyes:
 

Thread Starter

Raj Pandey

Joined May 27, 2019
62
When you make all the voltage measurements I requested in my post #2 and put the on the schematic, then we will be better able to help.
Otherwise it's just a guessing game. :rolleyes:
Ok, Sir, I will make the measurement now and post it here. Schematic is the same as shown above.
 

Thread Starter

Raj Pandey

Joined May 27, 2019
62
When you make all the voltage measurements I requested in my post #2 and put the on the schematic, then we will be better able to help.
Otherwise it's just a guessing game. :rolleyes:
HI Sir, I have checked the voltage around R1, R2, and R3. R1=9.92V , R2 = 12.03V and R3 = 15.68V.
R1, R2, and R3 are the one connection between the ceramic cap and electrolytic cap with LM388.
 
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