Voltage dropping badly - Page 1
Forum section: electronics / beginners

author: LukeB
author_rank: Contributor
timestamp: November 02, 2018, 08:51:27 am
content: Hello,I have been working on this battery charge, boost and protect circuit. I have had many various issues with it along the way and I have found another. I have everything working nearly properly however when I load the circuit with over 350ish milliamps the voltage drops below 5v. Why is this happening and how can I fix it. I was hoping to get up near 1 amp or at leas 700 800 milliamps.https://easyeda.com/maxibrandon3/5v-boost-protect-and-chargerHopefully the link works

author: madires
author_rank: Super Contributor
timestamp: November 02, 2018, 10:55:14 am
content: Have you checked the battery voltage when the boost converter's output drops below 5V? What kind of inductor are you using?

author: LukeB
author_rank: Contributor
timestamp: November 02, 2018, 01:06:07 pm
content: The battery is practically full and the inductor is thishttps://lcsc.com/product-detail/Power-Inductors_22uH-20_C11037.html

author: madires
author_rank: Super Contributor
timestamp: November 02, 2018, 02:15:05 pm
content: What I've meant is the input of the boost converter to figure out if there's sufficient power. The inductor seems to be suitable but its datasheet is broken unfortunately. If you have a scope you could observe the switching while increasing the load.

author: Buriedcode
author_rank: Super Contributor
timestamp: November 02, 2018, 02:23:33 pm
content: What board are you using? Switching power supplies can be sensitive to layout. Was this a pre-built module or one you've designed yourself?

author: brybot
author_rank: Contributor
timestamp: November 02, 2018, 06:00:23 pm
content: The datasheet for your switching regulator is a bit sparse. It may be that your inductor is too large for this application. Try dropping down to 10uH or 4.7uH. I checked your inductor spec sheet and it didn't list the saturation current. Have you checked it? If the saturation current is low, you definitely won't get proper operation.

author: mvs
author_rank: Frequent Contributor
timestamp: November 02, 2018, 07:38:39 pm
content: Quote from: LukeB on November 02, 2018, 08:51:27 amLi-Ion protection IC has discharge overcurrent detection... With just one FS8205 dual MOSFET it can trip at discharge currents less then 1A.

author: LukeB
author_rank: Contributor
timestamp: November 03, 2018, 12:29:07 am
content: Thanks for the responses,I dont think it is triggering over current as the voltage on the output only slowly lowers as the load increases. This module is one that I have designed myself so the layout seems like it could be the problem. With regards to the inductor i used a 22uh one as recommended in the datasheet. I do have an oscilloscope available too.

author: MasterT
author_rank: Frequent Contributor
timestamp: November 03, 2018, 12:47:45 am
content: Very likely your MT3608 is a fake. I bought a few modules from ali in the past, had to throw all of them in the garbage can after preliminary check-up, non of them outputs more than 200 mA, 2 out of 4 modules failed with magic smoke during tests.

author: LukeB
author_rank: Contributor
timestamp: November 03, 2018, 12:52:19 am
content: The Modules were made myself from part from lcsc.

author: kjr18
author_rank: Regular Contributor
timestamp: November 03, 2018, 09:29:23 am
content: I did myselfsomething like that, small charger, protection boost and switching circuit. Even though my coil and diode are on the small side, it can deliver about 1A for a short time (diode gets hot, very hot. I might try to overload one, just to see what pops first). Originally I made this to power some not very power hungry projects, so it won't see much action.It looks like it's really might be a layout issue. Have you tried populating only boost part and powered it from some power supply? Just to make sure if that MT3608 is at fault here.

author: janoc
author_rank: Super Contributor
timestamp: November 03, 2018, 11:05:08 am
content: Quote from: LukeB on November 03, 2018, 12:52:19 amThe chip still could have been fake.