Author Topic: Voltage dropping badly  (Read 2796 times)

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Offline LukeBTopic starter

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Voltage dropping badly
« on: November 02, 2018, 08:51:27 am »
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-charger

Hopefully the link works
 

Offline madires

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Re: Voltage dropping badly
« Reply #1 on: November 02, 2018, 10:55:14 am »
Have you checked the battery voltage when the boost converter's output drops below 5V? What kind of inductor are you using?
 

Offline LukeBTopic starter

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Re: Voltage dropping badly
« Reply #2 on: November 02, 2018, 01:06:07 pm »
The battery is practically full and the inductor is this https://lcsc.com/product-detail/Power-Inductors_22uH-20_C11037.html
 

Offline madires

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Re: Voltage dropping badly
« Reply #3 on: November 02, 2018, 02:15:05 pm »
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.
 

Offline Buriedcode

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Re: Voltage dropping badly
« Reply #4 on: November 02, 2018, 02:23:33 pm »
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?
 

Offline brybot

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Re: Voltage dropping badly
« Reply #5 on: November 02, 2018, 06:00:23 pm »
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.
 

Offline mvs

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Re: Voltage dropping badly
« Reply #6 on: November 02, 2018, 07:38:39 pm »
Why is this happening and how can I fix it.
Li-Ion protection IC has discharge overcurrent detection... With just one FS8205 dual MOSFET it can trip at discharge currents less then 1A.
 

Offline LukeBTopic starter

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Re: Voltage dropping badly
« Reply #7 on: November 03, 2018, 12:29:07 am »
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.
 

Offline MasterT

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Re: Voltage dropping badly
« Reply #8 on: November 03, 2018, 12:47:45 am »
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.
 

Offline LukeBTopic starter

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Re: Voltage dropping badly
« Reply #9 on: November 03, 2018, 12:52:19 am »
The Modules were made myself from part from lcsc.
 

Offline kjr18

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Re: Voltage dropping badly
« Reply #10 on: November 03, 2018, 09:29:23 am »
I did myself something 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.
 

Offline janoc

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Re: Voltage dropping badly
« Reply #11 on: November 03, 2018, 11:05:08 am »
The Modules were made myself from part from lcsc.

The chip still could have been fake.
 


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