Controlling 4V solenoid with MOSFET

Hi!

I am totally new to arduino and electronic hobby in general. I just can remember some basic theories I learnt in school.
I am going to make my second project. I want to control a small solenoid ( http://amzn.to/1Nza5ui ) by using a MOSFET (and an arduino of course).
The link of the solenoid is in Japanese, so I'll provide the basic specs: the solenoid works on DC3-4.5V, 0.17-0.28A.

I got the project idea from this http://www.g7smy.co.uk/?p=595 and Solenoid Circuit – mikeandakshay

My questions are,

  1. what is the ideal circuit to make this works? In the first link it only uses a mosfet and a diode. In the second there are several resistors too.

  2. since the specs of my solenoid is a bit different from the example, could somebody also tell me the right component specs for this? Which MOSFET, diode, and resistors should I use?

  3. If TIP102 or TIP120 is the ideal MOSFET for this, is there any equivalent to that? I could not find it in local shop or amazon. I heard any general purpose logic level MOSFET will work, but I am not sure what to look for in the shop.

Your help is really appreciated!

In the first link it only uses a mosfet and a diode. In the second there are several resistors too.

I only see one schematic... I see a link to the part, which I can't read because I only speak/read English, and and another link to a schematic. The schematic looks good except of course, you'll be using 4V instead of 12V.

You need the diode and both resistors. The purpose for the resistors is explained in the text.

  1. since the specs of my solenoid is a bit different from the example, could somebody also tell me the right component specs for this? Which MOSFET, diode, and resistors should I use?

Yes. Probably any logic-level N-Channel MOSFET will work.

Most MOSFETs require more than 5V at the gate to turn them fully-on. A logic-level MOSFET will turn-on with the 5V output from the Arduino. Otherwise the MOSFET just needs to handle 4V (any MOSFET can do that) and the 280mA current.

  1. If TIP102 or TIP120 is the ideal MOSFET for this, is there any equivalent to that?

Those are NOT MOSFETS. :wink: Those are NPN Darlington Transistors, which is two "regular" bipolar transistors in one package for more current gain than you can get from a single bipolar transistor.

[u]Here's[/u] a circuit using a regular (or Darlington) transistor. It's basically the same as the MOSFET, but there's one less resistor. Regular transistors turn-on with about 0.7V so you don't have to worry about the "logic level" stuff. (With 5V applied to the base-resistor, about 4.3V is dropped across the resistor.)

P.S.
Why are you using a 4V solenoid? That's an odd voltage...

Darlington transistors have a high ON voltage drop. That's okay for driving a 4V solenoid from a 5V supply, but the transistor consumes more power than a FET.

Hi Thanks for the reply! :slight_smile:

DVDdoug:
P.S.
Why are you using a 4V solenoid? That’s an odd voltage…

Well, I was looking for an as-low-as-possible-voltage solenoid, so I found this at the store (3-4.5V)

So, is this circuit fine? (picture attached)
Is it safe to power the solenoid itself from the 5v Vcc pin of arduino? or should I use external power source such as battery?

When you use a FET, 5V is higher than the allowed solenoid voltage. Power the solenoid from another power supply of 3-4.5V, or add a resistor or diode(s) to reduce the current or effective voltage.

It's always a good idea to power motors or solenoids from a separate power supply, i.e. all components which deserve a transistor for switching their high operating current. Such components also can exceed the maximum current of the USB port, so that powering the entire circuit and Ardunino from additional power supplies is recommended.

I'd use a power supply of at least 7V, so that it's sufficient to power the Arduino, and use a solenoid of matching operating voltage, to eliminate the need for another solenoid supply. This makes your device independent from a PC.