Circuit Explanation [ PICS ] [ Q ] - Page 1
Forum section: electronics / projects

author: jMrL
author_rank: Newbie
timestamp: August 14, 2017, 09:51:36 am
content: Hello,First off id like to say hi. My name is Jeremy. I've been a DIY tweaker for a little time now. I have started to ravage through all used electronics I can get my hands on just to stock pile my component inventory. I ran across this board and was curious what is the implementation of such. I'm assuming it has something to do with voltage conversion and possible an up/down also.I have done some research on some of the parts and some don't have labels so I'm stuck with the google search atm.http://www.mouser.com/ProductDetail/ON-Semiconductor/FQPF5N60C/?qs=%2fha2pyFadugJAM1sHG7DOqc7IemPvgRwrlXP8hvmbIw%3dhttp://www.alldatasheet.com/datasheet-pdf/pdf/68338/IRF/IRF9952.htmlhttp://www.alldatasheet.com/datasheet-pdf/pdf/257613/WINGS/TL431A.htmlAny explanation would be awesome. Also To hook up I would Use the Circled sections for in and out?Link to Gallery <http://diy.yolodigi.com/imgs/pcb/>Thanks,Jeremy

author: Rerouter
author_rank: Super Contributor
timestamp: August 14, 2017, 09:59:45 am
content: Looks like a dodgy AC - DC power supply.http://tri-heros.net/uploads/news/2013_01/untitled_119.png

author: Paul Rose
author_rank: Regular Contributor
timestamp: August 14, 2017, 07:32:45 pm
content: This is a typical switchmode power supply.The 8 pin chip on is a UC3843 pwm controllerhttp://www.alldatasheet.com/datasheet-pdf/pdf/25562/STMICROELECTRONICS/UC3843.htmlThe 4 pin chip beside the yellow transformer is an optocouplerThe in and out labels you drew on the foil side picture are reversed.Think of the board divided into two isolated regions with the yellow transformer and opto-coupler separating the high voltage/low current side ( larger area with more parts ) from the low voltage/high current side ( smaller area with fewer parts ).The high voltage side rectifies ( likely mains voltage 50/60 Hz ) AC and chops it up into pulses with the IRF9952 under control of the UC3843.The high frequency pulses are transformed to a lower voltage/higher current by the transformer. These low voltage pulses are rectified by the large diode and smoothed by the small electrolytic. The TL431 monitors this voltage and drives the "send" side of the opto-coupler. The "receive" side of the opto-coupler is used by the UC3843 to adjust the pulse width of the high voltage pulses.When the output voltage is too low, the pulses are widened, which in turn raises the output voltage.When the output voltage is too high, the pulses are narrowed, which in turn lowers the output voltage.

author: VoltJesus
author_rank: Contributor
timestamp: August 19, 2017, 05:18:32 pm
content: That board looks eerily familiar. Looks like it came out of either a convection oven or range.I am thinking it is going to be 24v output. Try it with 110-120v input first and see what you get. Some of them do convert 208-220v down, but most I've seen run off 110.Paul Rose gave a much better explanation of how the circuit actually operates than I could even attempt to give.

author: floobydust
author_rank: Super Contributor
timestamp: August 19, 2017, 05:40:41 pm
content: The IC datasheet and app notes can tell more about the basic architecture of the circuit. Most of these AC-DC power supplies are copied from the datasheet.But remember... It is typical cheap stuff from china that has no safety approvals. It has no primary-side fuse, so I don't use these in my home.Solder balls and flux residue, it's a pretty dirty PCB. I would give it a wash in IPA and toothbrush scrub.