Let’s talk regulators

IMG_20140918_193021As you probably know by now, I have released a few of my “old” circuit boards for sale on Tindie. Actually, they’re all revisions of previous boards I’ve shown off on the blog before. The one board you have not seen revised yet is my AMS1117 3.3&5v fixed voltage regulator board, pictured on the left. I’ve been looking over the design, while also straying away from it looking at other low drop out (LDO) regulators.

Functionality of the original board was not a problem. I still use these boards for prototyping and testing, and also in my final project builds like in my 24/7 powered ESP8266 project. The worst part of the board are the capacitors because they’re so close to everything else on the board including each other. I didn’t leave enough room between the larger capacitors so they’re awkwardly pressed up against each other. It’s so bad that I used hot glue to keep them solid in place because some of the capacitors aren’t sitting flat on the board. This can be easily fixed in the next revision by moving to SMD parts, which has been the plan for all of the boards since I decided to revise them all.

IMG_0767With the drop out voltage of the diode (reverse input voltage protection) and the regulator itself, you’re required to supply at least 7v to get 5v out of it. That’s the same thing as everyone’s favorite LM7805 which has a drop out of 7v, without a protection diode which would add another ~0.7v to the total drop out of your regulator. With that said, I pretty much only use 9v batteries with my AMS1117 board because it meets that minimum input voltage without being too much over. I have the ESP8266 project powered 24/7 so I’m obviously not using batteries but a 9v wall power supply.

spx1117circuit
SPX1117 schematic in Eagle – “Improved Ripple Rejection” circuit from datasheet

Speaking of wall power supplies, it introduces another “issue” if you use one with a voltage regulator. I don’t own a bench power supply or oscilloscope so I can’t get down into the fine details of  better monitored current draw or frequency response. You don’t have problems with frequency response with batteries because they output a solid DC voltage. However, with wall power supplies, the power from the wall is a rectified sine wave which is bound to have ripples in the output. I’ve been considering the change to the SPX1117 regulator which has a circuit in the datasheet to reduce the ripple… but then I wonder how much this actually matters to anyone. For hobbyist projects which is what these boards are made for, it’s really not going to have any major affects to it, as demonstrated in my projects that have worked well with the regulator board for extended periods of time.

I’m not really sure which regulator I’m going to go with. The main reason for looking at the SPX regulator is because they’re more readily available from my go-to suppliers than the AMS regulator. I may even just put the regulator circuit on the boards that would need them, like the ATmega328p breakout board. That’s the biggest motivation for designing these regulator board anyway. In that case, I probably wouldn’t need a regulator that can put out as much current (800mA)… We’ll see! Thanks for reading!

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