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Topic: TIP120 transistor base current from arduino (Read 1 time) previous topic - next topic

sebb898

Hello!

im using a TIP 120 transistor to drive a solenoid 12v and 1.5A

Cant get it to work when i use an analog pin directly to the base to close the transistor?

 The only thing that works is if i have a smaler transistor that helps the TIP 120 to "close".

 Do i need 2 transistors to drive the solenoid? I have tested to use a flyback diode and without resistor and that doesnt work either when i only have the TIP120.

The smal transistor is a s8050


This wiring works


photo host

This wiring doesnt work


how do i print screen

Grumpy_Mike

#1
Jan 23, 2015, 12:04 am Last Edit: Jan 23, 2015, 12:06 am by Grumpy_Mike
Quote
Cant get it to work when i use an analog pin directly to the base to close the transistor?
Well it should, so you must be doing something wrong. Have you set the pin to be an output in the setup function?

I am surprised that the circuit that you say works actually works. There is no pull up resistor on the smaller transistor so there is no where to source current for the base. So again you must be doing something other than you show in that first diagram.


Quote
Do i need 2 transistors to drive the solenoid?
No.

Quote
I have tested to use a flyback diode
Put it back you need it.

Quote
and without resistor
Put it back or you will damage your arduino.

DVDdoug

#2
Jan 23, 2015, 12:09 am Last Edit: Jan 23, 2015, 12:13 am by DVDdoug
Your wiring looks OK.  (It looks like you've got the emitter & collector figured-out, and I'm guessing you had the resistor to the base correctly before you added the "extra" transistor.)

You shouldn't need the extra transistor.  The TIP120 is a Darlington and it already has two transistors and a current gain of at least 1000.

You do need a resistor to prevent damage to the Arduino and/or the transistor.  What's the value of the resistor?  Have you double-checked?  Have you measured it with a multimeter?

Quote
ant get it to work when i use an analog pin directly to the base to close the transistor?
How about just digital on/off without "analog" PWM?  (That's a software change.  You can use the same I/O pin.)

Or, try disconnecting the resistor from the Arduino, and connect it directly to 5V to turn-on the transistor.

The TIP120 also has a built-in "flyback" diode, so you shouldn't need an external one.

sebb898

Software fault i guess!

I tried to uppload arduino blink example and now my wiring with just the darlington resistor works.

Thanks guys&girls

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