Pin erratically stays High WITH pulldown R
mikeslaney
Posts: 17
Hi There,
I am using PINx to operate an IRF10 MOSFet that in turn powers a motor. It works fine for about 3-5 cycles but then the pin stays high even when the program/hardware calls for it to go low. I am using a 10k R to pulldown the signal but it still won't go down. I thought that the MOSFet was pulling it up·so·I disconnected the lead that goes between the MOSFet·and the PIN·but the·PIN stayed high.
Reseting the board doesn't work so I need to power-cycle the whole system.
Other times, PINx goes high when it's told to but then all of a sudden goes low after about 3 seconds.
Could the MOSFet be pulling the pin up and keeping it up then causing other problems?
How does one calculate the appropriate·pullup/down R?
What size R should go between the MOSFet and the PIN?
Any help is appreciated.
Oh, and I got my new bs2sx today. Thanks.
·
I am using PINx to operate an IRF10 MOSFet that in turn powers a motor. It works fine for about 3-5 cycles but then the pin stays high even when the program/hardware calls for it to go low. I am using a 10k R to pulldown the signal but it still won't go down. I thought that the MOSFet was pulling it up·so·I disconnected the lead that goes between the MOSFet·and the PIN·but the·PIN stayed high.
Reseting the board doesn't work so I need to power-cycle the whole system.
Other times, PINx goes high when it's told to but then all of a sudden goes low after about 3 seconds.
Could the MOSFet be pulling the pin up and keeping it up then causing other problems?
How does one calculate the appropriate·pullup/down R?
What size R should go between the MOSFet and the PIN?
Any help is appreciated.
Oh, and I got my new bs2sx today. Thanks.
·
Comments
····· I assume your motor/Mosfet circuit is the standard one: Positive voltage on one motor lead, other motor lead to Drain on Mosfet, Source pin of Mosfet to 0v. I also assume your chosen Mosfet will fully turn on with about 5 volts on the gate. ( i.e. its made to work with 'logic levels') I generally use IRL510 and IRL520 and they've worked perfectly on 500 or so controller boards.
··· Gate of Mosfet goes to pin. ( can go through 100 ohm resistor, if you wish.
··· Pulldown resistor of 5K to 15K from Gate to Source, right at mosfet, if possible.
··· Have you got a diode around the motor? ( cathode to + ).
··· When gate is disconnected from pin, the only way for it to change states is if program tells it to. Can you show us the part of the program that should run the motor?
· Regards,
· Tom
·
OK, so I got the erratic behavior corrected but there is another problem. The IRL510 pulled too much current and blew a pin (well, two pins but that was pure stupidity..). I put a meter on it and it shows that it is pulling 500MA, just about the specs for the motor itself. But it even pulled 500MA just to turn an LED on too(?!?).
As an aside, I'm lost on a lot of datasheets. Where would it actually state that the device requires 'x' current to turn on?