On Thu, 5 Mar 2015 22:41:16 -0800 (PST), you wrote: >I wired up a circuit with an LED strip, 3 N-channel MOSFETs, and a separate >12V power supply, with the gate pins on the MOSFETS connected to I/O pins >on the Beaglebone.
some mosfets have protective diodes on the gate inputs. > >When I didn't connect the circuit to the Bone ground, I apparently fried 2 >boards. Neither will boot up. One gives a flicker on the power light and >then goes off, and on the other the power light turns on, but the other >LEDs don't flash and I can't get into either board. If I assume that the ground on the circuit didn't have a connection to the BBB ground, and that the 12 volt supply was connected to the circuit +12 and gnd, then you put floating lines on the BBB outputs, and any leakage in the power supply to ground (or the BBB ground) could put any voltage on the output pins of the BBB. The gates were floating, which is why the circuit was unstable. BTW: these had to be enhancement mode FETs for this to work. > >Here is the thread on the Adafruit forum with a photo of the circuit: >http://forums.adafruit.com/viewtopic.php?f=8&t=69691&p=353330&sid=eff0f5bd69bba9338e6f0ec2d7fa70c4#p353330 >*The Adafruit support said that setup should not have hurt the board. * If connected properly. > >I checked the voltage on the gate pin on each MOSFET that was connected to >the Bone and it was nominal (~200mA). > Voltage is not measured in ma, do you mean 200 mv? The meter you used loaded the circuit, and would not show the true voltage. It's not a matter of current into the chip, it's a matter of voltage (period). The voltage can cause nasty things in the chip transistors driving the pin, and the power supply of the chip itself then does the damage. >Does anyone have any ideas on this? How could this have fried 2 boards? A suggestion for you. Next time, do not make single connections to pins on the BBB (or anything else unless you're quite certain of what you're doing). Best to take a ribbon connector that makes connections to everything at once, run it to a breakout board, and then hard wire your connections to that. A frequent problem in breadboards is wires coming loose. This way the ground is automatically made to the chips on the breadboard. Another option would be to use a darlington transistor array, such as the ULN2803 or the ULN2003 instead of the FETS. Again, the same warning about grounding is in effect. Since you have two non-functional BBB's I'd suggest taking a meter and checking the voltages at the various regulators on the board. You have a schematic, and it may be possible that you have a bad regulator somehow. That's better than a fried CPU. Harvey > >Thanks for any help. > >And PS I posted this earlier today but didn't see it show up in the forum. >Sorry if it needed to be approved and you are getting a duplicate. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
