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Topic: another transistor quesiton (Read 3188 times) previous topic - next topic

TomGeorge

Hi,
Can you post a picture of your project please, so we can see your component layout and power supply?

Thanks..  Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

robkiller

I need to build it off to the side so you can see it but this is a weekend project so i wont have time until next weekend.  Thanks for the help and i will post next weekend what i have.

Jiggy-Ninja

Voltage is always measured between two points. Since it's already been shown that you don't know the common conventions, whenever you make a voltage measurement mention specifically which points you have each of the multimeter leads probing. "To the motor" is ambiguous, and might mean "across the two motor terminals" or "between one motor terminal and ground". The normal convention is to specify the red lead's point first. For example the "base-emitter" voltage of a transistor means that it is measured with the red lead on the base and the black lead on the emitter.

With the motor running, make and record the voltage between the following points. Expected voltages are given in parentheses. If you measure anything significantly different than there's a problem.

5V - GND (4.5-5)
12V - GND (12)
Arduino pin - GND (4.3-5)
transistor base - GND (1.2-1.5)
transistor base - transistor emitter (1.2-1.5)
transistor collector - GND (1-2)
transistor collector - transistor emitter (1-2)
motor terminal 1 - motor terminal 2 (10-11)

Since you weren't using a diode though, it's likely you've hammered the transistor with a nasty inductive spike and broke it. Replace it with a new part and see if you get the above measurements with the diode in the circuit.
Hackaday: https://hackaday.io/MarkRD
Advanced C++ Techniques: https://forum.arduino.cc/index.php?topic=493075.0

robkiller

#33
Feb 25, 2017, 06:08 am Last Edit: Feb 25, 2017, 06:15 am by robkiller
So i did switch out the Transistor and now i am not getting the motor to run.  I will try to check out the voltages above but in the mean time this is what my project looks like.

stuart0

So i did switch out the Transistor and now i am not getting the motor to run.  I will try to check out the voltages above but in the mean time this is what my project looks like.
Post a schematic.

TomGeorge

#35
Feb 25, 2017, 02:30 pm Last Edit: Feb 25, 2017, 02:36 pm by TomGeorge
Hi,
Are you sure you know the Base, Collector and Emitter pins of your TIP120?
Still can't see how most of your connections are made.
OPs pic..

Can you post a drawing of how you have identified  E B and C on the transistor?
Hint; Collector is the middle pin...

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

stuart0

#36
Feb 25, 2017, 02:45 pm Last Edit: Feb 25, 2017, 02:46 pm by stuart0
Are you sure you know the Base, Collector and Emitter pins of your TIP120?
Still can't see how most of your connections are made.
Good call Tom. I also found it very difficult to see exactly where all the connections go from that photo, however zooming and looking very closely I now believe that op has the TIP120 connected as follows.

1. Base - connected to ground.
2. Collector - connected to through a resistor to +5 (presumably this was supposed to be the base drive).
3. Emitter - connected to the motor return (other motor lead to +V)

Theoretically this should bust the transistor due to base emitter reverse breakdown with insufficient current limiting. Maybe it will survive, maybe not.

robkiller

I got it when you stated how was i determining the base collector and emitter i re checked that on the data sheet and found i had not gotten those correct the first time.  Now it works!!  Thanks so much!!

stuart0

Now it works!!  Thanks so much!!
It's good if that transistor still works, but just be aware that you've had a lot more base-emitter reverse voltage applied than what that device is rated for, actually more than double its ABSOLUTE MAXIUM rating.

From here it's impossible to say for sure, but it may operate a bit below par or the reliability might be compromised.

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