Design issue with buck converter

[angy]

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

 

[keith1200rs]

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

 

[angy]

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

 

[keith1200rs]

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.

 

[angy]

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

 

[keith1200rs]

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.

 

[angy]

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

 

[keith1200rs]

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

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