ESP8266 Community Forum

- Sun Dec 25, 2016 8:51 am #59934

A problem is the use of a linear regulator which will just waste energy and dissipate heat. Get some buck boost converters for your toolbox http://www.ebay.co.uk/itm/LM2596S-ADJ-3 ... SwKtVW0-6u.

If you do the math difference between what you suggest compared to a linear regulator you will find that they are the same as far as efficiency. Because of the low starting voltage you don't get much efficiency gain with a switcher and the switching power supply you suggested is horrible. Because of the voltage drop in the catch diode and the low output voltage the efficiency will be under 70%. A linear regulator's efficiency is 3.3/5=0.66. And if the input voltage was a little low, due to series resistances, then the switcher would have even worse efficiency and the linear would have higher.

The output of the linear regulator is constant where the switcher's output is a sawtooth waveform and the average voltage output is what you read with a meter, but the ESP8266 is sensitive to the lowest voltage available and that is the value that matters.

9.1.6 Output Voltage Ripple and Transients
The output voltage of a switching power supply operating in the continuous mode will contain a sawtooth ripple voltage at the switcher frequency, and may also contain short voltage spikes at the peaks of the sawtooth waveform.

As I said, that is a horrible switcher for low input voltage and low output voltage use. A mosfet synchronous switcher would be far better but it still is a switcher and still has upper and lower trip points so the above quote still will apply. There would need to be additional LC filtering to get rid of it.

A good low drop linear regulator is your best and easiest option. The regulator you used is claimed to be low drop but it really is marginal for a 5 volt supply input. While the voltage is listed at 5 volt the actual voltage can vary. And as stated in the first reply, series resistance due to the interconnecting cables may also be a factor.

With what you have shown you should be able to get it working properly with what I suggested.

- Sun Dec 25, 2016 1:22 pm #59940 Hi Rudy,

Merry Christmas.

I agree the efficiencies with a 5V supply are similar but if driven with a higher voltage the buck boost converter advantages are clear. The modules I pointed to have pretty good filtering and certainly better than the breadboard setup in the photo.

Speaking of the photo, I must admit I only just looked at the photo in the original post and it looks like the input capacitor (arrowed) is probably 0.1uF or even 10nF and not 10uF. If this was 100uF that would give the linear regulator more chance. Also with those long wires and breadboard the current capacitor will be virtually useless.

It is still important to understand if the USB port is on a PC or a charger.

David

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- Sun Dec 25, 2016 3:26 pm #59945 Merry Christmas David.

Yes there are problems with the setup. Jumper wires like those are convenient, the breadboard is convenient. The problem is that with digital circuits like the ESP8266 these things can really cause significant issues. And a marginal setup can work a lot of the time but when it doesn't work properly then you are scratching your head over possible code issues when the problem really is elsewhere.

I design electronics for a living and have for the past 32 years. I have used the "National's Simple Switchers" in many designs. They are a reliable design if you layout the pcb well. They are cheap but they are not efficient compared to some newer designs.

I tend to prefer using a linear regulator to go from 5v down to 3.3v. The power loss is acceptable. Often they are capable of responding faster than a switcher to dynamic changes in current. Even so you need to be careful when you pick a low drop regulator. Scope testing is important but not so easy to do unless you have a good digital scope.

As you had said in your first post, there are more measurements that need to be done in order to point to what may be the most significant factor. From my experience I still think the changes I suggest will go a long way to making the circuit functional.

- Sun Dec 25, 2016 5:53 pm #59957 Rudy,

Totally agree. The eBay switchers are cheap, flexible and ideal to have a few to use in a prototype when you run it from a RC battery or similar.

If powered from a single PC USB2 port it is likely to current limit. Powering from multiple ports or an USB3 (blue) may fix the problem. Powering from a charger may work but the inrush current could be a problem which is why more information is required.

I would use a bench PSU to supply regulator (linear or switcher), get everything working and then look at powering from USB. I rarely use breadboard as the wiring gets horrendous very quickly, I prefer to build prototypes on pad board with wiring pencil http://uk.farnell.com/roadrunner/rrp-10 ... /dp/145223.

David