AC to DC adapter. - Page 1
Forum section: electronics / projects

author: Fabiosapplou
author_rank: Newbie
timestamp: April 25, 2017, 10:35:09 pm
content: Hi,im currently using lots of ESP8266 chips to kind of make a smart home, and each and very one of them need a power supply to run, most of the time with a small circuit attached...I don't like to use modules on my designs and so i'd like to incorporate on the main board a steep down adapter from mains to about 5v.So the question is, how practical it is to use capacitive reactance to steep down the voltage and is there anything preventing me from using it safely to power an microcontroler with no down time at all?Or do you think I'd be better of using a small smps or even a regular small transformer with appropriate regulation? Thank you for the help...By the way, these is my first day here... I've been watching Jones for years but only now I decided to join the "clube" cause my English was not good enough.

author: Fabiosapplou
author_rank: Newbie
timestamp: April 25, 2017, 11:55:33 pm
content: I don't really need it to be certified as long as its safe, it's a project for personal use only, so does problems don't apply in these case.I just wanted to try and make it as small as possible of a circuit in order to be able to fit it in the electrical boxes were the the wiring for the switches are made in order to control them remotely.The problem is that there is only mains on the box, and i wanted a way of steeping down the voltage in order to use it on the low voltage circuit.I really anted to avoid transformers completely as the circuit only requires a low amount of power. But i don't know if its a good idea to use Resistive reactance to do it. I don't see way not, but it also does not feel right for some reason.

author: nctnico
author_rank: Super Contributor
timestamp: April 25, 2017, 11:59:16 pm
content: There are special switching chips for this purpose which only need a few components but I very strongly advice to use a small module with isolation and the appropriate safety ratings for your own protection. Messing with mains voltages isn't to be taken lightly and you won't be the first to die.

author: Fabiosapplou
author_rank: Newbie
timestamp: April 26, 2017, 01:09:00 am
content: Do you know a parte number for something like that? I'd be very thankful...About the mains don't worry, i don't have any qualification regarding electronics, but i'm in fact qualified to deal with mains voltage as an electrician.Thank you very much for the help guys.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2017, 05:34:13 am
content: It depends on how much current you need. Up to about 10mA or so a capacitor dropper transformerless supply works fine, though obviously you have to make sure that your entire circuit is enclosed and cannot be touched.Your English seems fine, if you hadn't mentioned I don't think anyone would know it was not your native language.

author: DaJMasta
author_rank: Super Contributor
timestamp: April 26, 2017, 05:56:43 am
content: The modules should be available a lot of places, just look for an AC to DC converter and there should be plenty of options, and many on the PCB. I generally prefer wall warts (external wall mount power supplies that just give you a DC output) because it lets you keep all the mains off board and out of your box. You can even use DC-DC converters to get a wide variety of voltage rails (including negative voltages) within your device after a single input voltage.In the case of just 5V though, a cheap and reliable way would be just to stick a USB port on it. Then you need a USB host/hub device or just a phone charger and you can get a good amount of 5V without any issue (to 0.5-1A or so with normal chargers and cables, more with special ones).While I don't think there's a huge amount of danger in learning to homebrew your own basic mains power supplies (like linear regulators on secondary transformer taps) and an electrician could likely do a good job managing the risks of it... there's a lot to be said for the application. When it's going to be something always-on and that other users can use, like this one, there is much more of a safety concern and much more importance on efficiency.... and you can find both of this cheaply in commercially made power supplies. Either board-mount small packages or separate metal-caged power supply units which have been tweaked for high efficiency and which come with all the safety certs you'd expect out of a commercial product.And the only thing I noticed about the English was the occasional e at the end of a word, no big deal.

author: sanwal209
author_rank: Regular Contributor
timestamp: April 26, 2017, 09:14:43 am
content: Hi,I would prefer to buy off the shelf adapter, But if you really want to implement it on PCB I would suggest SR086 IC(1.18USD on Digikey). With very few components it can give you 9.0 - 50VDC@100mA and also it has internal 3.3V regulator.http://ww1.microchip.com/downloads/en/DeviceDoc/SR086%20D080613.pdfCheck the attached Image

author: Fabiosapplou
author_rank: Newbie
timestamp: April 26, 2017, 11:24:07 am
content: Brilliant guys! I think I'm set! Thank you very much for the kind comments and for the help. I believe I'll be sticking to the SR086. It appears to be the optimal solution i can make it small and provides the the current i need (about 100mA).Thank you very much.

author: sanwal209
author_rank: Regular Contributor
timestamp: April 26, 2017, 12:05:03 pm
content: No Problem. Enjoy Designing

author: rdl
author_rank: Super Contributor
timestamp: April 26, 2017, 06:27:55 pm
content: I like the newer AC outlets that include USB power. They are still a bit expensive, but not too bad. I can see these becoming more common and maybe standard in some household locations.

author: sanwal209
author_rank: Regular Contributor
timestamp: April 26, 2017, 06:32:48 pm
content: You are right but it will not feasible for OP's application. It would nice if his module and power supply fit in a small box(3D Printed) same size as of wall adapter.

author: rdl
author_rank: Super Contributor
timestamp: April 26, 2017, 06:52:32 pm
content: You can find enclosures like that but internal volume is limited. If the device can be made to fit it might be useful.One example:http://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeyPPB-11861-BK