EEVblog Electronics Community Forum
EEVblog => EEVblog Specific => Topic started by: DarkPrince on October 07, 2012, 03:57:23 pm
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EEVblog #366 - USB PSU Troubleshooting (https://www.youtube.com/watch?v=QL0KnXDPbe8#ws)
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Hey Dave,
So you were measuring between the two terminals of the inductor. I was wondering if there was enough load on the boost converter, so it wasn't running in discontinuous conduction mode. Figure the duty cycle is going to be very small to generate those output voltages if no load is present. I only ask because you measured across the inductor the second to last time declaring it non-operational, than the output terminals on the last test when declaring it operational. Video magic (behind on the scenes) measuring the output voltage?
Of course if that were true than with a resistor connected rather than the capacitor the first time you would have seen a little boost of voltage, so truly could have been a package flow issue.
Anyway, once again a wonderful video. Keep up the troubleshooting videos, may have embarrassing moments (do'h moments!) but non the less they are educational/entertaining/food-for-thought.
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Wrong components on manual assembled prototypes, classic mistake and good for a lot of wasted engineering time :(
My method to reduce this type of mistakes somewhat is to count the number of parts before placing them.
This provides a simple verification that the correct quantity of a certain part ended up on the PCB. Have one left over, or one short, means a mistake has been made.
Does not eliminate the problem entirely, but with this PCB, this approach would have raised a flag with both the 10k resistor (one left) and the 100p cap (one short).
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Dear Dave,
I would just like to say thanks for the progress of this series. Electronics design tutorials are very useful.
Kind regards,
Marius
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My method to reduce this type of mistakes somewhat is to count the number of parts before placing them.
This provides a simple verification that the correct quantity of a certain part ended up on the PCB. Have one left over, or one short, means a mistake has been made.
I like that one, extremely simple yet very effective (and I probably would never think of it myself). Thanks for sharing.
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Hey Dave,
Take youself a video of Sagan hitting you on the head and giggling, so you can link to it any time you do something especially stupid.
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Thank you Dave for letting everyone learn from your mistakes instead of hiding them.
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Dave leaves them in to show all how to do it, warts and all. You need to get experience, and it only comes from making mistakes.
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Hi Dave, I was looking at designing my own battery operated USB power supply using a single cell Lipo. The USB was only for charging so not isolation needed (correct me if I am wrong).
MCP73837/8 - Battery Management 1A USB/DC input auto-swich
LM2623MM/NOPB - DC/DC Switching Controllers GEN PURP,GATED OSC DC/DC BOOST CONVRTR (this mongrel at least has legs to solder, but only goes to 14V)
Maybe this will give you some ideas.
Rutger
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you would still need isolation if you planned to use it while it charging, or if you have the output connected to a voltage, pretty much if you do not close the earth loop your fine,
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What if you disable the output while charging via the USB and only activate the output when you are charging via an isolated DC power supply or when you use it in battery mode? A small relay should do the trick, right?
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i am not sure if this is a just for you or a commercial product, if just for you, then, it doesnt even need to be isolated on the product if your external supply is isolated,
my point was, if your output "ground" is not at the same ground as your input you have a problem,
if you are aware of this then your not too likely to go and blow the thing up,
or you design a physical switch for the output that disconnects the ground aswell so your safe as long as the output is off,
it just comes down to what range of senarios you want to cover, something i have been beating myself up about on my own higher power varient,
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Are you ever going to finish this thing?
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Relay on the outputs, driven form USB input voltage? Or for more security, relay on the outputs, driven by the battery via a tac switch that gets depressed when you push in the usb plug?
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Hey Dave,
So you were measuring between the two terminals of the inductor. I was wondering if there was enough load on the boost converter, so it wasn't running in discontinuous conduction mode. Figure the duty cycle is going to be very small to generate those output voltages if no load is present. I only ask because you measured across the inductor the second to last time declaring it non-operational, than the output terminals on the last test when declaring it operational. Video magic (behind on the scenes) measuring the output voltage?
Of course if that were true than with a resistor connected rather than the capacitor the first time you would have seen a little boost of voltage, so truly could have been a package flow issue.
Anyway, once again a wonderful video. Keep up the troubleshooting videos, may have embarrassing moments (do'h moments!) but non the less they are educational/entertaining/food-for-thought.
yep, i also think there were no soldering problem with the QFN chip, it is not a good idea to measure between the inductor when there is no load at the output, always try to measure after the diode with the filtering cap
Great video!
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Dave,
I look forward to seeing the design process and the schematics.
I indicated that you were waiting on, or having trouble getting the USB to serial converter. I was wondering why you did not use a micro controller with USB built in. I know there are several. I think that I would lean to the atmega16u2. The only reason is that the Arduino Uno uses this chip as a USB to serial and the code is open source so I would have an easy starting point. You don't need to actually convert the USB to serial, just keep the interface so the PC software thinks it is talking to a serial port. You could use the UART serial port on the chip to talk to another serial device or just use the pins for more I/O.
I guess I will learn the answer to these and many other questions when the design blog comes out.
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Uart isolation is easy usb is not, seeing as these power supplys could be hooked up to anything you dont want your pc getting fried if anything goes wrong ;)
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Uart isolation is easy usb is not, seeing as these power supplys could be hooked up to anything you dont want your pc getting fried if anything goes wrong ;)
Are you expecting something like optoisolaters on the RX and TX lines between the microcontroller and the USB-to-serial chip? I didn't see that in the previous design (the bench supply) but it could happen.
I was looking at lowering the chip count, board space and maybe the cost, I did not take into account isolation.
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Uart isolation is easy usb is not, seeing as these power supplys could be hooked up to anything you dont want your pc getting fried if anything goes wrong ;)
Are you expecting something like optoisolaters on the RX and TX lines between the microcontroller and the USB-to-serial chip? I didn't see that in the previous design (the bench supply) but it could happen.
I was looking at lowering the chip count, board space and maybe the cost, I did not take into account isolation.
Yes the USB version offers opto-isolation on Rx and Tx.
Another reason to use the FTDI is that it means dave doesn't need to worry about VID and PID stuff