TP120 vs TP102

Whoo hoo, just soldered up my first arduino shield (SparkFun MIDI shield) this AM and it works swimmingly well! Now, to the next part:

I'm hoping to drive a 24VDC solenoid from my Arduino. I've been looking at the schematic in the playground ( I have collected the 1N4004, a 2.2k-Ohm resistor, but my Radioshack doesn't have a TP102.

They do have a TP120.

Is there an issue with using a TP120? I saw reference to using it in the forums at;start=all; I can pick up the heat sink et al to use it. But I'm confused on how to figure the power formula. Throwing in transistors and resistors throws me for a loop.

So, to summarize my questions: can I use the TP120? If yes, how to I calculate what power is needed to drive the solenoid?

Thanks! Ralph

How do the transistor specs compare on their respective data sheets?

The TIP120:

Power dissipation: 65W Collector emitter voltage: 60V Collector base voltage: 60V Emitter base voltage: 5.0V collector current (continuous): 5.0A collector current (peak):8.0A Base current: 120mA unclamped inductive load energy: 50mj

The TIP102:

Transistors designed for your electronic needs. Power dissipation of 360mW. Case Type: TO-92. V(GS):.8V. BV(G35): 2.5V. I(DSS) Min.: 2.0mA.I(DSS) Max: 20mAh.Y(FS) (min.):16.00.

V(GS): .8V BV(G35): 2.5V I(DSS) Min.:2.0mA I(DSS) Max: 20mAh Y(FS) (min.): 16.00

I hope that helps clarify it - also, the parts are TIP102 & TIP120, not TP120 & TP102.


Lemme rephrase that: is the TIP102 the same as Radioshack part MPF102?

It looks to me like a TIP102 and a TIP120 should be interchangeable for this sort of application.


The TIP102: Power dissipation of 360mW. Case Type: TO-92. V(GS):.8V. BV(G35): 2.5V. I(DSS) Min.: 2.0mA.I(DSS) Max: 20mAh.Y(FS) (min.):16.00.

that is NOT a TIP102!!! It's not even close.

is the TIP102 the same as Radioshack part MPF102?


You all are an encouraging, helpful lot. Thanks for helping me dig deeper into the deep sea of electronics!

Yes, I have a handful of solenoids I want to drive, each off a different output on the arduino.

I have 2 24vdc pull-types:

and 2 24vdc rotary solenoids:

westwf - thanks for the note re: TIP120 / TIP102. I'm basing this off the schematic in the Playground, referenced above. I'll proceed cautiously!

Thanks to both westwf & Richard Crowley re: the MPF102. I'd seen a note on where they mentioned buying a RS MPF102 while discussing the TIP102, and I thought perhaps Radioshack had used a different part number to refer to the TP102. Now I know! :)

Hrm. Well, I don't need a lot of pull force, so I'll try it at 12 vdc. Better yet, while I'm still figuring this out I'll just wire up 1 solenoid - the rotary one. What's the formula you're using to figure out the watts? I've been plugging values into my spreadsheet (full of I = V/r, P = V*I etc formulas), but I don't know how to get ohms & volts to figure the amps & watts.

I know this is googleable, but I'm swimming in a lot of new information and struggling to take it in. Your patience is appreciated!

Ooh! I like that calculator! Thanks for that!

Okay, off to wire up a solenoid successfully, or possibly blow myself up. Time will tell.


It works, but it's a little weak - not strong enough to flip the solenoid over, just click a little bit.

So going by the calculator, I need a power supply that puts out 24vdc at 750 mA, is that right? The only Ohms I need to calculate are from the solenoid? I guess I'm confused as to how to incorporate the values for the TIP120 transistor. I need more juice, but I don't know the formula to calculate it with the transistor in play.

That makes sense. Thank you very much for the explanation!

The solenoid, connected directly, snaps right over and back. The resistor is a 2.2k-Ohm, 1/4 watt, 5% tolerance. Wouldn't a resistor with a lower Ohm rating (say, 1k) would allow more power to the ... well, never mind. That doesn't make sense. What is the resistor doing between the transistor and the Arduino's digital out?