Buck/Boost power supply outputting wrong voltage and climbing - Page 1
Forum section: electronics / beginners

author: Count Zero
author_rank: Newbie
timestamp: September 16, 2019, 01:55:17 am
content: Hi Everyone, first time poster and whatnot. I'm trying to build a power supply circuit I found onlin. It's supposed to output a steady 3.3 volts but when I connect a lithium battery it outputs about 3.5 volts and slowly climbs from there. After a couple of minutes it's putting out 3.8 volts but the battery holder is me and a couple of breadboard leads so I don't know if there's a limit to how high it will go. It will also continue outputting voltage (according to the multimeter) well after it's been disconnected from the battery, ten minutes typing this post and the multi-meter is reading around 0.92Here's the board I'm using:https://www.bernebeer.nl/3v3-buck-boost-regulator-great-1-cell-lithium/And here is my list of components:TI Buck/Boost chip:http://www.mouser.com/ProductDetail/texas-instruments/tps63031dskr/?qs=ptj1V1atRApEDiB8KPHu8g%3d%3d&countrycode=US&currencycode=USDInductor:http://www.mouser.com/ProductDetail/coilcraft/lps3015-153mrb/?qs=QQJxVsr8EGbi5e%2ftD15nHw%3d%3d&countrycode=US&currencycode=USD10uF capacitor:http://www.mouser.com/ProductDetail/taiyo-yuden/jmk212ab7106kght/?qs=CNQs48zzdnpTzaa%2fvSgl3Q%3d%3d&countrycode=US&currencycode=USD0.1uF capacitor:http://www.mouser.com/ProductDetail/yageo/cc0603jrx7r7bb104/?qs=AgBp2OyFlx8tkr7yadKwIw%3d%3d&countrycode=US&currencycode=USDI bought enough components to build five, when the first acted strangely I built a second to make sure I didn't mess up while soldering and it acted exactly the same. I'm checking my soldering work with a microscope so I have some confidence that everything is connected. The fact that it's "kind of" working is throwing me through a loop, my suspicions so far are:1.) I made a mistake selecting my passive components. I wasn't able to find an exact match for the capacitors so I approximated, maybe I missed something.2.) I've made a mistake in placing my passive components,2.) My hand soldering is leaving some sort of electrical slop in the system that is allowing the voltage to build up.3.) I've got things connected incorrectly4.) I scraped some of the solder mask off the bottom of the board so I could reflow the big central pad through the vias, it's possible this messed something upHere are some pictures of the whole setup, behaving poorly:And some pictures of the second board I assembled:My understanding of buck/boost converters is hazy at best so any advice/insights to why this is happening would be greatly appreciated.

author: ledtester
author_rank: Super Contributor
timestamp: September 16, 2019, 02:56:51 am
content: What happens if you put a load on the output? Try some different loads, e.g. 10 mA, 100 mA, 500 mA.

author: JackJones
author_rank: Regular Contributor
timestamp: September 16, 2019, 03:33:27 am
content: It looks like there's some flux residue on the board. It can cause all sorts of problems, cleaning it off would be my first step.

author: Count Zero
author_rank: Newbie
timestamp: September 17, 2019, 01:12:52 am
content: Quote from: ledtester on September 16, 2019, 02:56:51 amThank you! I think that fixed it. I put a nine 4.7k resistors (because that's what I had sitting around) in series in between the output leads and it's sitting here outputting a steady 3.35 volts. I googled "buck boost supply with no load" and found this:Quote from: https://www.researchgate.net/post/How_do_DC_DC_buck_converters_works_in_no_load_conditionsIf I'm understanding correctly it was working all along, that's just how it acts with no load load.

author: soldar
author_rank: Super Contributor
timestamp: September 17, 2019, 09:39:35 am
content: I can't even get the pictures to load. Please show some consideration to bandwidth and those of us with little of it.