Author Topic: Smoothing VCC with cap - conceptual question  (Read 1435 times)

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Offline Erwin Ried

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Smoothing VCC with cap - conceptual question
« on: July 07, 2017, 06:42:58 am »
Hi everybody, I need some theorical tips about my issue. I am making a simple dock for a raspberry pi zero. The usb of the zero is quite simple, directly connected to almost everything so when I hot plug a load in the usb (100mA) it reboots the Pi 1 of every 10 tries.

What can I do to prevent this? Should adding a 10uF cap between vcc and gnd be enough? Will adding a bigger cap bring some undesired counter effect?

Thanks
My website: http://ried.cl
 

Offline OiD

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Re: Smoothing VCC with cap - conceptual question
« Reply #1 on: July 07, 2017, 02:53:02 pm »
IS it always the same device that causes this to fail? What device is it? If its not one single device is there anything in common that does not cause this effect? Maybe a very low value resistor in series with the power line for the specific device
 

Offline Erwin Ried

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Re: Smoothing VCC with cap - conceptual question
« Reply #2 on: July 07, 2017, 11:39:37 pm »
Yes it is the same. I discovered that the inductor in the pi had a crack so maybe that is the cause of the reboot.

How do I put the resistor by the way?
My website: http://ried.cl
 

Offline OiD

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Re: Smoothing VCC with cap - conceptual question
« Reply #3 on: July 08, 2017, 11:28:16 am »
Maybe the inductor has something to do with it, maybe not. If you can fix it you'll know ;)

The resistor Idea was if it only happened with one device. But if it happens with all  then its on the raspy side or the power supply... or the Kernel?
 
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Offline Erwin Ried

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Re: Smoothing VCC with cap - conceptual question
« Reply #4 on: July 09, 2017, 11:22:43 pm »
Well, I only want to use that device. Could adding 1 ohm resistor in vcc between the device and the pi do something bad at the long run?
My website: http://ried.cl
 

Offline OiD

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Re: Smoothing VCC with cap - conceptual question
« Reply #5 on: July 11, 2017, 05:11:10 pm »
That would depend on the device, it's current rating and voltage tolerance. Maybe your devices has a large capacitance and no power control IC so all it does is draw as much current as possible. Try with a lower or higher value resistor, maybe an NTC if you can find one rated at the current required.

If you have acces to a scope you could also probe the pi and see if there are current spikes when you plug the device in. Or you could also try a dummy conector, one with only the power pins and no data to make sure it's not a communication issue/bug.
 


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