Ruben Laguna’s blog

Sudden Voltage Drop on MAX756

I got the MAX756 that I was waiting for from Futurlec. The idea was to implement the very same circuit that comes in the MAX756 datasheet. In my first try I got very strange results which I posted to ladyada forum hoping to get some advice on how to solve. Eventually I set up the circuit in another breadboard and got it working the way I expected or at least I thought so.


Now I have the SMPS laid out on a breadboard. I’m powering this SMPS based on MAX756 with a 1.5V battery and I get 3.3V output with no load. If I connect a load (1led+220ohm) I still got 3.3V. That’s ok. I even connected three leds in parallel (24mA). Still working, I get a sound 3.3V reading in my DMM.

But when I connect this 3.3V output to my arduino project (mounted on a breadboard too) things change, and they change in a bad way. It seems to work perfectly for 5 or 6 seconds, 3.3V the green led mounted in the Arduino Pro Mini blinks as it should (because the sketch loaded does that) and the power red led in on and shining bright. But after 5 seconds the voltage drops from 3.3V to 1.7V, the red led still on but dimmed and the green led goes off. This lasts 1 sec maybe 2, and then the voltage goes up to 3.3V again. the arduino resets and the whole process begins again.

I don’t know what happening, but I decided to give up on the SMPS for a while. I will power my design using two coin cells and the LDO regulator already mounted in the Arduino Pro Mini. Less efficient but much easier to use.

I’ll come back to the SMPS when I have more time to investigate and read more about SMPS design and troubleshooting.