Do you need to supply higher voltage to a solenoid if using a flyback diode

Hello everyone, so I am trouble shooting a 5v solenoid not working when plugged to an external source, and when I use my DMM the voltage across the diode/ the solenoid is around 2.6V. The diode is a 1n4007 and the transistor is a tip120. Below is the circuit schematic, please ignore that its shown to be powered by arduino. It isnt, it has a 2 pin barrel jack (1 for -ve and 1 for +ve).
So my question is do I need to supply more than 5v to the solenoid because of voltage drop of the diode?

Thanks in advance.
Dean.

What’s powering the transistor and solenoid…
Hopefully not the Arduino…

a 12v external source, stepped down to 5v with a regulator

According to it's datasheet, the TIP120 has a built-in flyback diode.
Maybe your base resistor is too high, or your regulator is too weak, to power a solenoid.
Providing the exact components and schematic of your setup, may enable providing better answers.

No.
The diode is in parallel with the solenoid and is reverse biased. It will make no diferance to the voltage you need.

So that is due to something else. Maybe lack of power from your source or the Darlington pair not turning on fully.
It is fine saying it is not an Arduino Uno but what is it?

its a 12v, 2amp voltage external voltage source, that is connected to the breadboard with a 2pin barrel jack.

I looked into what you said about the tip120 having an internal flyback diode but the consensus is that an external one is normally used aswell, as the rating of the internal one isnt known

So, sounds inadequate to me. Bread boards should not be asked to carry more than 1A tops and what is the coil resistance of your solenoid?

I ask again what is the Arduino type?

You're kidding! :astonished:

The consensus amongst people who know what they are talking about, is that the tip120 does not have an internal flyback diode.

To do so it would necessarily have to have four pins. There may be such a device available somewhere, but I have not come across it. :astonished:

In any case it is obsolete. Note that the obsolete ULN2x03 octal Darlingtons do include "flyback" diodes and the necessary terminal for them, while the TPIC6x595 series use Zeners to implement the same function more effectively.

The place I bought the coil (amazon) didnt give a data sheet and only a few specifications so, I dont know what the coil resistance is.
And I am using an arduino uno

Please tell me what the diode on the right side of the equivalent circuit is. I interpret that as a built in flyback diode, and if I am wrong, I would like to understand.

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You state it's a "5V solenoid", but you're using it conn'd to 'VIN' or describing a 12V supply to the breadboard.
That seems an issue.

It passes through a 5v regulator, so the solenoid does receive 5v.

So the "5v regulator" output is going to the breadboard and "VIN"?

That's not a flyback diode. It's a body diode. Different thing, different function, different connection.

Also, is the GND from the 5V regulator also going to the Arduino board?

This once more proves the importance of posting a schematic that accurately represents the circuit as built.

The diagram that i showed is the same for mine except it doesnt use the arduino for power and it has a 12v external source that is stepped down to 5v from the regulator.
When i am able to I will make a schematic and post it, thanks everyone again for your continued input.

That's the thing. No exceptions! :wink:
You may think "oh, this picture pretty much shows what I've made, this should do", but you don't realize that there are maybe 5 or 10 details (in your perception) that turn out to be crucial.

Making a schematic isn't very difficult; try with a pencil and paper, and snap a smartphone pic to post here when you're done. Yes, there are many conventions etc., but even a poor schematic that matches your actual circuit is better than a very nice schematic that's not exactly your situation.

Yes thats fair ive learnt my lesson on that I will make a schematic when im in a place where i can do that. Thanks for the advice.

I think you have a misunderstanding of what a flyback diode is. Yes the TIP120 has a diode shown connected cathode to collector and anode to the emitter. This is not a "flyback" diode.

By definition (or at least convention) a flyback diode handles the voltage generated by some inductive element being turned off.

General question:

Is someone having a fire sale of TIP120's? Or do they come with some "Kit"? If the latter the kit mfg should be told the TIP120 is not useful in such a kit.