MintyUSBoost: A tiny boost converter for low power projects - Page 1
Forum section: electronics / projects

author: nathanpc
author_rank: Unknown
timestamp: February 19, 2016, 07:45:43 pm
content: Recently I decided to try my luck at making a simple DC-DC boost converter for powering my DIY headphone amplifier which requires 9V from the USB. The design is pretty simple, just a PIC modulating the pulse width depending on the output voltage. This is my first attempt at building a switchmode regulator from scratch, so feedback is appreciated.http://currentflow.net/post/139602284263/mintyusboost-a-tiny-boost-converter-for-low-power

author: Kleinstein
author_rank: Super Contributor
timestamp: February 19, 2016, 09:27:13 pm
content: This is not all a tiny solution. There are ready may tiny chips - you might even find one in SOT23 or similar.Also in case of a software fault this could cause a short on the USB or less likely create too much voltage.Thus it usually is not a good idea to use a µC to replace a simple regulator chip, that is way better and more reliable at it. It might be worth is if the µC is more than just making a constant voltage and if size and noise do not matter.For a class A amplifier, even a simple 2 transistor royer converter would be an option.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 19, 2016, 09:43:08 pm
content: Without any kind of current feedback at all, it is possible that the converter self-destructs at certain conditions, such as startup - the output cap is a dead short, inductor easily saturates and current rises too quickly, exceeding the FET rating.Oversized FET, ESR of the caps and resistance in USB power input protects the prototype from said destruction.Driving the FET gate from the microcontroller pin is slowish, possibly reducing efficiency. Smaller FET (with smaller total gate charge) would increase efficiency by speeding up switching, but then again, you depend on the oversized FET because of lack of necessary basic protection. On a converter with specs like this, MCU IO is a good enough FET driver as is, but only with a carefully selected FET.Lack of gate resistor may cause ringing and FET destruction. The "voltage increasing" tip for non-"logic-level" FETs behind the link you give doesn't work at all in this kind of case, 10K output impedance is orders of magnitude too high for even remotely fast switching.Feedback loop implemented is rather slow to load or supply changes, and most probably oscillates at some conditions.These are many reasons why DC/DC controller ICs do exist: they implement all the features that are absolutely necessary in almost all cases, but are missing from this project. Of course it will be an interesting project to implement more of those features, and you can do surprisingly lot on a simple microcontroller. It's definitely not black magic, but it's much more than what you show.The project is the opposite of tiny, it's kinda huge, but that probably doesn't matter, if it's small enough, it's fine. In DC/DC converters, smaller is usually better. Keep everything contained on a small area, over a good ground plane.But DC/DC "proof of concepts" can indeed be easy, and I have seen many people (including myself) start exactly like you, and you don't even need an MCU, I start many DC/DC proof of concepts with only a signal generator and a FET!

author: nathanpc
author_rank: Unknown
timestamp: February 20, 2016, 10:46:20 am
content: Quote from: AcHmed99 on February 19, 2016, 09:21:02 pmYes, I just wanted to build something quick and try it out. I used the PIC12F683 because it was what I had on hand, but I want to buy some of the newer PICs to try all their awesome peripherals and see what projects I can come up with. Thanks very much for the feedback.Quote from: Kleinstein on February 19, 2016, 09:27:13 pmI must agree "tiny" was the wrong word for this, but it's small enough to fit in a Altoids tin. About the software fault, I'm aware of that, but this was just a quick project just to try out building a boost converter with the parts I had on hand.Quote from: Siwastaja on February 19, 2016, 09:43:08 pmI'm aware of those problems, but as you've said this is more of a "proof of concept", just to get a initial understanding on something, make sure it works before moving on to something more complex. Thanks for all of your great advice and feedback!