Design issue with buck converter

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angy

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I have design a Buck converter(LM2576_ADJ) whose input voltage is 24 V and output voltage is 4.2 V. But after putting some load ,the load current is 800mA,but my voltage starts to drop .My doubt is I want to add more load upto 2 A without any drop at output voltage.How can it be achieved .Is there some design issue
 

You need to show your circuit. A common problem with switching regulators is not having an inductor which is capable of handling the peak currents.

Keith
 

In diagram R8= 2.4 K instead of 9K
Inductor is SH50C3.0-100
 

Is that really a 10mH inductor? If so, I think that is your problem. I would expect something around 100uH.

I am not sure of the inductor part number you have given, but if you are actually using a 100uH or something similar, can it take the peak current?

How have you built it? Switching regulators at these sorts of currents can be tricky to breadboard.

Keith.
 

Sorry its not 10uH It is 100uH
Specification is
INDUCTOR :100UH 3.0A 50KHZ CLP

Its not made on breadboard .How can i check the current part of it .The max load current its taking is 700mA at 4V
 

It sounds ok. The datasheet says the current rating should be 1.15xIload.

However, the E.T product is 66Vus which would look more like 150uH should be used from the graphs. I am not sure if that is enough to cause your problem though, but a larger inductance would be worth trying.

Keith.
 

can try 150uH but according to datasheet still the choice is 100UH .
 

angy said:
can try 150uH but according to datasheet still the choice is 100UH .
Click to expand...

That isn't how I interpreted the graphs based on my calculations. However, I am not convinced it will solve the problem. It might be worthwhile looking at the feedback pin with a 'scope. They don't show any filtering which is unusual.

Also measure input power as you load it. It may give a clue as to the problem.

Keith
 

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