Timeline for Multiple Buck Converters kills dead Pi Pico?
Current License: CC BY-SA 4.0
30 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jul 11 at 3:48 | vote | accept | ashbygeek | ||
| Jul 3 at 1:48 | answer | added | Math Keeps Me Busy | timeline score: 2 | |
| Jul 2 at 21:11 | comment | added | Math Keeps Me Busy | Please don't modify the schematic in your question. In general, once you have received an answer, you should not make modifications to your question that change the substance of your question. | |
| Jul 2 at 20:52 | comment | added | ashbygeek | Let me try revising my current schematic to see if I can get it right. Also, 19V is not a hard requirement. I have some old 12V power bricks (and ATX power supplies) laying around that should work too | |
| Jul 2 at 2:38 | comment | added | Math Keeps Me Busy | A concern I have is that the 19 V supply is quite close to the max Vgs of most MOSFETs (i.e. 20 V). A slight spike will kill your MOSFETs. Adding a Zener between gate and source, and a resistor between ate and the potential 19 V may be in order. Do you need a schematic for that? | |
| Jul 2 at 2:06 | comment | added | ashbygeek | Cool, cool. Many thanks for the questions and suggestions. I found an instructables that suggests using an N-Channel MOSFET on the ground side: instructables.com/…. Worth a think? I'm just not in general very comfortable with MOSFETs yet. | |
| Jul 2 at 1:54 | comment | added | Math Keeps Me Busy | OK, good information. But unfortunately, the ground on your computer is your mains AC ground, but the ground on your Pi Pico differs from that by one Schottky diode drop. Depending upon current through the diode, it could be around 0.5 V. Switching to "ideal" diodes might solve your problem, but there may be another solution. Let me give it some thought, or perhaps someone else has an idea and can chime in. | |
| Jul 2 at 1:12 | history | edited | ashbygeek | CC BY-SA 4.0 | Answered a bunch of questions, add new information |
| Jul 1 at 23:56 | comment | added | ashbygeek | That dock arrangement is why I need the 6 diode bridge. Each dock leg contacts a copper bar on my blinky LED device, one leg has power, one leg has ground, one does nothing. I'm in the US, so the 19V power brick uses 3 prong 120V 60hz power input, as does my desktop computer. Both are plugged into the same power strip. Multimeter indicates the ground out of the power brick has continuity with the redundant ground of the AC input. | |
| Jul 1 at 23:45 | comment | added | ashbygeek | @MathKeepsMeBusy yes, the pico was powered only by BC6 and it was hooked up only through BC6. My multimeter indicates continuity from that module's input ground to it's output ground though. Measured 0.4 Ohms of resistance. Nothing except the diode bridge is connected to the 19V ground. This blinky LED device has a triangular dock and I wanted a simple way to provide power without end users having to worry about which way it gets set in the dock | |
| Jun 27 at 23:21 | comment | added | tomnexus | Ground ground ground ground ground and more ground. Lace that thing up with 16 gauge ground wire. Find a way to ground Battery- too. Without a common ground who knows what voltages are appearing on the GPIOs. | |
| Jun 27 at 23:01 | answer | added | Peter Green | timeline score: 1 | |
| Jun 27 at 21:48 | comment | added | Math Keeps Me Busy | @ashbygeek Correct me if I'm wrong. The PICO is powered soley by the buck converter BC6, and it's ground is connected to the ground of BC6, not the ground associated with the 19V in the upper left hand corner feeding the 6 diode bridge. Is there anything connected to that latter ground? You diagram doesn't show any USB connection, but this is connected to a computer. Is your computer grounded? Is it grounded to the 19V supply's ground? Is it a laptop or desktop? If laptop, does the power brick have 3 prongs? What is your locality? | |
| Jun 27 at 21:18 | comment | added | ashbygeek | @MathKeepsMeBusy Checked with my o-scope and it doesn't look like my buck converters are straying above 5V. However, as per Update 2, this does seem to be happening when I connect a microcontroller to USB and my circuit simultaneously. Would this cause power to be transmitted ovedr ground due to my diodes? | |
| Jun 27 at 21:16 | history | edited | ashbygeek | CC BY-SA 4.0 | New information added |
| Jun 25 at 19:58 | history | edited | ashbygeek | CC BY-SA 4.0 | Updated with information requested in comments |
| Jun 9 at 21:16 | history | edited | Math Keeps Me Busy | CC BY-SA 4.0 | added links to datasheets |
| Jun 9 at 20:41 | comment | added | Math Keeps Me Busy | @ashbygeek if you have an oscilloscope, just observe the outputs of the converters with no load (other than the oscilloscope). Observe the voltage from when they are first powered until they settle at a voltage. if you perform multiple tests, drain the output capacitors between tests by putting a resistor across the outputs while the converter is unpowered. The exact resistance is not important. The larger the resistance, the longer it takes, but the smaller the current. Something around 1 k\$\Omega\$ should be good for both speed and safety. | |
| Jun 9 at 19:57 | comment | added | ashbygeek | @vir I've updated my post, if you have some additional thoughts I would appreciate it | |
| Jun 9 at 19:56 | comment | added | ashbygeek | @MathKeepsMeBusy I added some details about my buck converters. What would I look at in the specs to figure out if they would have problems at low currents? Or would it be simpler to just test them? I'm assuming that would be a case of rigging some kind of variable load (potentiometer?) while hooked up to an scope to check for voltage spikes? | |
| Jun 9 at 19:47 | history | edited | ashbygeek | CC BY-SA 4.0 | Reworded to be clearer that multiple microcontrollers were killed in the making of this post. |
| Jun 9 at 15:08 | history | edited | ashbygeek | CC BY-SA 4.0 | added 869 characters in body |
| Jun 9 at 14:07 | comment | added | ashbygeek | Thanks for the comments. Can confirm that I wasn't able to upload the pictures, thanks for confirming that wasn't just my problem! I'll try to edit my post later today to embed those pictures and add more details about converters | |
| Jun 7 at 1:58 | comment | added | SamGibson♦ | @vir - Hi, Just FYI I've posted this on our meta: electronics.meta.stackexchange.com/questions/10215/… | |
| Jun 7 at 0:23 | comment | added | vir | As @MathKeepsMeBusy notes, the schematic is mostly black boxes connected together so this is more of a block diagram than a full schematic. Could be a miswiring, I'm not seeing a global ground on the output side of the converters so if they're isolated types you could have high voltages on the I/O pins, etc. | |
| Jun 6 at 23:37 | comment | added | Andy aka | How can you kill a dead Pi Pico. I mean, isn't it already dead? Or maybe you made a tautology? | |
| Jun 6 at 23:28 | comment | added | SamGibson♦ | @vir - Hi, FYI I've just noticed that the SE image server uploads aren't working, so the OP can't upload the images onto the usual place. And since it's Friday night, SE staff have gone home :( I'm seeing if I can find anyone but even if I find someone to tell, they would have to find an SRE or similar person to actually investigate. TL;DR - we may be stuck in this situation for a while :( | |
| Jun 6 at 23:20 | comment | added | Math Keeps Me Busy | We don't know anything about your buck converters. It is possible they lose regulation at low output currents, and thus could possibly give overvoltage to your pi pico. But we don't have hard info on that. | |
| Jun 6 at 23:15 | comment | added | vir | Please embed the schematic as an image in your post instead of a Google drive link that could go anywhere and could become non-functional at some later time. | |
| Jun 6 at 23:00 | history | asked | ashbygeek | CC BY-SA 4.0 |