TIP3055 as a solid state relay

Hey guys, I built a few of these http://www.arduino.cc/playground/uploads/Main/relays.pdf - a while ago to control 12v relays... Works great. Can I use the same circuit setup but with a TIP3055 http://www.futurlec.com/Transistors/TIP3055.shtml - to run a device at 12vdc @ 3.5a continuous (7 amp at start up)? From my limited knowledge I think so... Seems that the TIP3055 can handle 10a continuous and dissipates up to 75w @ 150 celcius...


Yes. 15 A and 90 W. Don't forget heat-think

Right, I'm hitting up the electronics store tomorrow for TO-220 heat sinks. I will just unsolder the TIP120's I have on the circuit board now and replace them with the TIP3055.

Thanks so much!

Doesn't seem to work... It's supplying the ground signal, and it will work to trip a relay, but when I connect the 3.5a load the ground signal degrades and it won't work... But the TIP120 works! Any idea's?

Hfe is low, according to data sheet min=20, max=70. What is the base resistor, can you try with 220 Ohm ?

I don't know much (lol), but I was looking at the hfe and wondering if that isn't my problem... The R1 is 1Kohm. I have a 220ohm resistor, I'm going to try that but it's only like an 1/8w... that ok?

Yes, P = U ^2 / R = 5^2 / 220 = 0.11 W. Should be o’k with 1/8 watts.
Sorry, I’ve missed out low hfe yesterday, when checked on power and current rating of the tranistor. Better alternative is TIP140.
You can make it work with TIP3055 soldering two of them in Darlington configuration, but try if it works with 220 resistor.

No workie with 220ohm R1. I have these TIP120's... Will they work with a heat sink? http://www.futurlec.com/Transistors/TIP120.shtml

They are only 5A (8A impulse) , and you saying your load 7A at startup.

I'm not sure if it's 7a or more or less... It's a ballast for a light. I did fire one up using the TIP120 and it worked... Whether or not it'll keep working I don't know. Guess I can just try it out.

What kind of ballast, is it an inductor for fluorescent lights?

No, automotive HID.

I'm ordering some TIP140's... They're super cheap. I won't have the rest of the components I need to finish this until Monday anyway, so no huge rush that I can't wait for the proper transistors.

Forget about using a transistor or a darlington, for switching 3.5 to 7A you'd be much better off using a logic level mosfet. The voltage drop will be much less, and with the right mosfet you won't even need a heatsink. OTOH, using a darlington you will need a large heatsink because of the high saturation voltage of the darlington (it will probably drop at least 2 volts).

Well, I'm a noob lol, so can you point me in the right direction, please?

OK, you need to pick an N-channel logic level power mosfet that has a low enough Rds(on) quoted at 7A or more at Vgs around 4.5v, and that has a Vds rating of at least your maximum supply voltage (you mentioned 12v). There are lots to choose from. I use type STP40NF10L as a general purpose power mosfet, and that will certainly do for your application, however there are others costing less that would also be suitable.

Connect the mosfet like this:

  • Source terminal to Arduino ground and to the -ve side of your 12v supply
  • Gate terminal to the Arduino output pin through a 120 ohm resistor
  • Drain terminal to the -ve side of your load
  • +ve side of your load to +12v
  • also connect a 10K resistor from the Arduino output pin to ground (this makes sure the mosfet stays off while the Arduino starts up)
  • if the load is inductive, don't forget to connect a kickback diode in parallel with it (although power mosfets are tolerant of slightly inductive loads anyway)

I just read this page… http://brunningsoftware.co.uk/FET.htm

Looks like it’s pretty simple, and pretty much the same setting up a MOSFET as it is the transistor… Basically the same circuit as… http://www.arduino.cc/playground/uploads/Main/relays.pdf

Apply 5V to the gate, it opens and allows current to flow between the drain/source pins (I think that is the right terminology and idea?)

Any thoughts on the appropriate mosfet’s to use? I’d like 10a continuous to be safe, 15a peak is plenty.

Thanks so much for the advice dc42!

Oop, see that you just responded before I posted this :slight_smile:

Ok, I found that mosfet you mentioned on a supplier page, http://www.newark.com/stmicroelectronics/stp40nf10l/n-channel-mosfet-100v-40a-to-220/dp/26M3697?Ntt=STP40NF10L

Will I need a heat sink and can I operate that right off an arduino pin?

Ah, what about this one? http://www.newark.com/fairchild-semiconductor/mtd3055vl/n-channel-mosfet-60v-12a-to-252/dp/63K5835

Speaking of kickback -- if I have a very high potential ring when turning off, and my controlling transistor has a filter electrolytic capacitor that only likes 12V, should I put a Zener across it? The Zener would conduct forward in the "backwards" direction, and it would start conducting (bringing voltage down to 12V) in the forward direction if there's a large forward voltage.

FlyingSteve: Ok, I found that mosfet you mentioned on a supplier page, http://www.newark.com/stmicroelectronics/stp40nf10l/n-channel-mosfet-100v-40a-to-220/dp/26M3697?Ntt=STP40NF10L

Will I need a heat sink and can I operate that right off an arduino pin?

You will not need a heatsink. The Rds of that mosfet is quoted as 0.036 ohms at 5v Vgs and 20A, so at 3.5A continuous the power dissipated will be (3.5 * 3.5 * 0.036) = 0.441 W. You can drive it straight from the Arduino although a series resistor of about 120 ohm is recomended.

FlyingSteve: Ah, what about this one? http://www.newark.com/fairchild-semiconductor/mtd3055vl/n-channel-mosfet-60v-12a-to-252/dp/63K5835

That one has a much higher Rds(on) so it will dissipate more power and need a heatsink. Newark have several other suitable ones. Look for MOSFET - Single, N channel, Rds(on) test voltage 4.5v or 5v, Rds(on) not more than 0.05 ohm, and the voltage and current rating you want.