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.

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.

 

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.

 

Your first regulator on the left has the Adj pin going to the 15V supply!!

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

 

Your first regulator on the left has the Adj pin going to the 15V supply!!

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

My first ckt(top-left) in Image is LM7805 and Second one is (Center-right) is LM338 And pin is Adj, out, IN.

 

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.

 

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.

 

What voltages do you have across R1, R2, R3...?

 

You arbitrary use of capitals make your text hard to read. Could you avoid it, please?

 

What voltages do you have across R1, R2, R3...?

nearby 15.68V.

What voltages do you have across R1, R2, R3...?

I am getting around 15.64 V across resistors.

 

You arbitrary use of capitals make your text hard to read. Could you avoid it, please?

Sorry, I won't do it again.

 

nearby 15.68V.


I am getting around 15.64 V across resistors.

Measure them individually,, what is across R3...?

 

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.

 

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

 

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?

 

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

No.
You need to determine what's wrong and get it to working on the breadboard first.

 

No.
You need to determine what's wrong and get it to working on the breadboard first.

Sir, No offence but if I know what's wrong in this I would have not posted this query. That's why I am asking here for help.

 

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.

 

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.

Ok, Sir, I will make the measurement now and post it here. Schematic is the same as shown above.

 

Schematic is the same as shown above.

Okay.
Write all the voltages for every node on the schematic and repost it.

 

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.

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.