Sunday, August 24, 2014

Put an inductor to cheap DC/DC dropdown regulator.

Keep Voltage High, and Drop It Down When It is Needed

LM2596 is packaged into a very popular module to drop voltage at your circuit endpoints. When your circuit needs fairly large energy, you should keep the voltage high over all the circuit except for the endpoints where the power is actually consumed, and LM2596 works as an “energy distributor”.

Evernote Snapshot 20140525 183252

This is my humble module that controls 12 LEDs and 4 servos simultaneously. It draws at maximum 2A at 6V (12W). This induces heavy noise both on the voltage and the ground lines, which results in total mess on digital signals.

Then, I put an inductor at the entrance of the LM2596 module after cutting the pattern (voltage line before the first rectifier). Its inductance is 100uH with temporal torelance 3A. This halved the noise especially outside of of the module, as shown below.


The noise inside the module.


The noise outside the module.

This is very important when you use these modules in a parralel manner. The inductor blocks the noise and prevents the noise from being transmitted to the other circuit. Otherwise the noise inside is going to be multiplied.

P.S. To Get Beyond Tutorials

In many examples and tutorials over the Internet, this kind of signal integrity and noise stuff is ignored because those are very simple and work with low evergy. But such small curcuit just works as long as you follow its datasheet.

However, decent application may need a lot of power and suffer noise problems. At this time, I was stuck and I didn’t know how to solve it. I spend a lot of time, and bought cheap digital oscilloscope and logic analyzer myself to solve what’s happening in my circuit. I should have done this long ago already.

That’s why I wrote this post. If you got stuck because you don’t know what’s happening in your electric circuit, just buy your oscilloscope and logic analyzer first, these cost under $100 nowadays.