DC-DC Step Down getting hot & shutting off

Hi guys,

I am using a LM2575T (DC/DC Buck Converter | DC/DC Converter | Overview | Step-Down Buck | TI.com) to go from a 12V DC wall adapter into a 16x2 LCD (http://www.newhavendisplay.com/specs/NHD-0216SZ-FSW-FBW.pdf), Mega, and ethernet shield.

I was originally using a 500mA DC-DC converter, since I only need to draw ~200mA between the screen, Mega, and ethernet shield, but about 10 seconds after plugging it in, the arduino power starting blinking and then shut off. This is when I switched to the LM2575T.

I have no unplugged the Mega and ethernet shield, so the DC-DC is going from 12V wall adapter into the LCD only. The LCD looks to draw only 32.5mA, but for some reason the DC-DC (rated at 1A) is getting super hot and then shutting off.

Any ideas on what's going on here?? I have the proper capacitors, and inductors attached.

You say you have the proper capacitors and inductors, but we can’t check that if you don’t
give more information. Layout is very important for switchmode converters, do you understand
layout issues?

I’m sure that I don’t; hopefully I can get some help working out whatever the issue is here.

Here are the components that I’m using; these were chosen based on the recommendations in DC-DC datasheets. I’m attached some photos of the wiring as well.


One thing I’m definitely unclear of is if the inductor is wired correctly; the datasheet doesn’t really show any direction.

Is this enough information to help troubleshoot? I can provide whatever else is useful; not quite sure what that is at the moment.

Thanks so so much for the help!

The board layout and component selection for a switch mode regulator really is critical and if you haven't been trained how to do it properly, you are wasting your time. Take a look at these inexpensive properly designed and manufactured regulators from Pololu, a reputable U.S. company.

Photo of the layout. In particular the enclosed area of the current switching loop (diode/inductor/output cap)
needs to be as small as possible and right next to the relevant pins of the chip. The feedback connection must also very short.

Inductors are non-polarized.

That kind of circuit is not going to work well on breadboard or protoboard. You need to design a PCB for it.

I can't see the diode D1 in your photos. Is it under the cap or something? The specifications on that diode are quite important too.

Those photos are pretty useless. It took me a minute to work out that they show two different views of different components. But thanks for trying.

Just buy a pre built module from Pololu or wherever. That's how the professionals do it.

It's really hard to get vaguely acceptable performance from a switching power supply (DC-DC or SMPS) built on prototyping board. The layout, and lengths of paths, are really critical.

You also need a good, fast schottky diode - normal crap diodes won't work.

Is that electrolytic capacitor low ESR?

That's why most of us buy from either polulu (nice small converters from pretty reputable vendor), or chinese randoms on ebay (search dc-dc converter in business and industrial -> electrical and test equipment section - there are tons, many at seemingly impossible prices)