im using a TIP120 NPN to switch my 5v 1.1A solenoid, but my solenoid isnt working unless i give it a little push i think its my resistor problem what value of resistor should i use for my base of transistor.
A search for "tip120 base resistor" turns up many hits like this one.
cyborg8274:
im using a TIP120 NPN to switch my 5v 1.1A solenoid, but my solenoid isnt working unless i give it a little push i think its my resistor problem what value of resistor should i use for my base of transistor.
What exactly is the circuit you used and what resistor values have you tried?
Steve
The datasheet states a base:collector current of 1:250 for a TIP120 darlington used as a switch (Figure2, page3).
With 5volt drive, and 1.5volt BE drop, there is ~3.5volt across the base resistor.
Base current needed is 1.1A (solenoid) / 250 = 0.0044A = 4.4mA.
Theoretical base resistor value = 3.5volt / 0.0044Amp = 795ohm.
Practically, anything between 220ohm and 1k will do.
Don't forget the kickback diode across the solenoid.
Not having one could kill the transistor.
Leo..
slipstick:
What exactly is the circuit you used and what resistor values have you tried?Steve
I’ve tried with 1K resistor but solenoid doesn’t seem to work without a push and I tried to use led to see if it’s working and it’s working fine but it’s not working with solenoid.
What is supplying power to the solenoid (volts and amps)?
Is it wired like this?
5 volt 1.1Amp solenoid.
I hope you are not trying to power it from Arduino's 5volt pin.
You need ~6volt external power (~one volt is lost in the TIP120), capable of delivering 1.1Amp.
So how are you powering that solenoid.
Leo..
Wawa:
5 volt 1.1Amp solenoid.
I hope you are not trying to power it from Arduino's 5volt pin.You need ~6volt external power (~one volt is lost in the TIP120), capable of delivering 1.1Amp.
So how are you powering that solenoid.
Leo..
groundFungus:
What is supplying power to the solenoid (volts and amps)?Is it wired like this?
I'm using a wall adapter of 12v to arduino jack and yes im powering it with 5v pin from arduino to solenoid directly
im using a 12v supply to arduino jack and this is how im connecting the solenoid and im using 5v pin from arduino to power the solenoid too
Reread reply #6. If you are going to post a schematic, make it match what YOU are doing, not some generic thing from the web.
cyborg8274:
im using a 12v supply to arduino jack and this is how im connecting the solenoid and im using 5v pin from arduino to power the solenoid too
Can't do that. You will fry the 5volt regulator.
The 5volt regulator on an Uno can't deliver more than 100mA (0.1Amp) when the Uno is powered with 12volt.
Leo..
Don't forget the kickback diode across the solenoid.
No need for it since the TIP120 already has a builtin kickback diode. See the datasheet.
How does the diode from emitter to collector in a TIP120 dissipate current generated by the coil of a relay?
http://www.st.com/content/ccc/resource/technical/document/datasheet/f9/ed/f5/44/26/b9/43/a4/CD00000911.pdf/files/CD00000911.pdf/jcr:content/translations/en.CD00000911.pdf
I would suggest it does not. It only blocks current flow the same as the turned off transistors, and allows high voltage to be created from the coil generated current.
justone:
No need for it since the TIP120 already has a builtin kickback diode. See the datasheet.
Common mistake.
The diode inside the transistor is pointing in the wrong direction.
It needs to go across the load.
Leo..
justone:
No need for it since the TIP120 already has a builtin kickback diode. See the datasheet.
No, that's wrong. The diode has to go across the inductor. You'l fry the TIP120 immediately if you
don't include a diode across the solenoid coil.
Since darlingtons drop 1.1 to 2V, a 5V solenoid needs 6 to 7V power supply to work with a darlington.
Use a logic level MOSFET and this isn't a problem, but you still need the diode.
I had to dig up an old project I worked on to see what I did.
Took a little while to get it back into working order.
I know it doesn't prove anything but I did not use any diodes.
It sounds a little rough but I was playing around with microstepping on a tiny2313.
Out of curiosity why is the diode in there in the first place?
That's an H-bridge - the diodes provide protection for the other arm of the half-bridge in that configuration (which is why the diode is there in the first place), but if you have a single TIP120 its diode does nothing useful.
That's an H-bridge
Are you referring to the driver in the video?
If so then no it isn't an H-bridge but just four tip120s driving each leg of a unipolar stepper.
Those tip120s sure must be pretty rugged since I did not use any flyback diodes.
the diodes provide protection for the other arm of the half-bridge
Yeah that's what I guessed when "complimentary" was used in the def.
Thanks
"Complimentary" (a gift or praise) is a different word from "complementary" (opposite to)!
The TIP120's are probably failing gradually though - inductive kickback is not friendly to semiconductors,
and most devices don't have a datasheet rating for what they can survive. The interference to nearby
circuitry is not nice either!