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### TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 9:38 am
This transistor is rated as high speed switching and power amplifier. My problem is that it will only support a .7 amp load going thru it from a 12 volt car battery. If I hold the gate high directly from the battery , the amps are the same as when pulsed with a 555 timer. The real amp load is 2.12 A when hooked in series with amp meter to the battery.
The specs indicate 60 V coll to emmit and 70 V coll to base and collector current of 10 amps.
Question :: is the voltage too low to push 10 amps on a device rated for 60 to 70 vlots??
Is there an easier way to build a % time on controller?

Roger

Posted: Fri Nov 14, 2008 10:47 am
Try getting another transistor of the same type and putting it in a darlington configuration.

The specs for this NPN (you confused me for a moment by mentioning a Gate) does seem to have adequate current , gain and voltage specs for your application (perhaps more than necessary WRT Vceo and Ic). Sounds like you're just not getting enough base current to turn it on all the way. A darlington device or array should boost the base current to the output device and gain so that it acts better as an on off switch.

Note Vce(sat) is 1V at Ib=-400mA, Ic=4A so you should have less than 1V across the transistor if you have it turned fully on and conducting less than 10A. It should work at Vce=12V, Ic=2.12A just fine

If you include a circuit diagram, perhaps we can comment on the exact method you are using to bias the base

### Re: TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 11:24 am
Oxford wrote:My problem is that it will only support a .7 amp load going thru it from a 12 volt car battery.
Oxford wrote:If I hold the gate high directly from the battery , the amps are the same as when pulsed with a 555 timer. The real amp load is 2.12 A when hooked in series with amp meter to the battery.
A bipolar transistor does not have a GATE.
Oxford wrote:Question :: is the voltage too low to push 10 amps on a device rated for 60 to 70 vlots??
Oxford wrote:Is there an easier way to build a % time on controller?
Power MOS Fets are much easier to use, and are
rated to high currents for load switch applications.
The 2N3055 has been around for decades and was
very good back in the day.

A bipolar power transistor requires a lot of base
current to operate, and if not driven to saturation
will dissipate power (heat).

What load are you trying to drive?

### TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 11:33 am
You were exactly right about base current. Initially I used the bench power supply which is +12 @2.5 amps and got the same .7 amp turn on that I was getting from the pulses of the 555 timer.
When I used the 12 v battery direct to the gate I got 1.9 amps +thru the transistor.
Very shortly It will be on battery power BUT..
I should not expect the 555 timer to supply the necessary amps from/thru pinout #3!?
All I can think of now is to bias the gate of the transistor with 12 V+ thru a variable resistor to bring it up to point where the 555 output will turn it completely on.
Radio Shack has some darlingtons. Could you suggest one that the timer can pulse to deliver battery current to the gate of my TIP3055 and avoid using a pullup resistor?

Roger

### TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 11:43 am
Bigglez,
I am running two 10 ohm cartridge heaters in parallel requiring 2.12 amps. The bipolar transistor is cooking the air around it but I only run it briefly until I get the bugs out. A heat sink is mandatory.
You just said that completely on disapates less heat???
When I get there, fully on will help. I'm working to achieve full on just a % of the time.
Base is more appropriate than gate.

Roger

Posted: Fri Nov 14, 2008 12:41 pm
Lose the Biploar transistor and go to a MOSFET with a low Rds. If you are driving it from a uC, use a Logic level MOSFET.

### Re: TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 12:43 pm
Oxford wrote:I am running two 10 ohm cartridge heaters in parallel requiring 2.12 amps. The bipolar transistor is cooking the air around it but I only run it briefly until I get the bugs out. A heat sink is mandatory.
A correctly designed high current switch (with
PMOSFet transistors) will dissipate virtually no
power, at least not enough to feel warm to the
touch in free air.
Oxford wrote:You just said that completely
on disapates less heat???
I did. Also, by ohm's law you can see that a
switch with zero voltage drop would produce
zero power, regardless of current.

If you are married to using old school 2N3055
power transistors you can expect the on voltage
(VCEsat) to be 1.1V typ, so at IC = 2.12Amps
the transistor will dissipate 2.34Watts.

For the TO-3 package in free air the thermal
resistance is 1.52 degC per watt, so the case will
be only 3.59 degC above ambient.

Did I mention, a schematic would be helpful?

Posted: Fri Nov 14, 2008 12:44 pm
philba wrote:Lose the Biploar transistor and go to a MOSFET with a low Rds. If you are driving it from a uC, use a Logic level MOSFET.
I don't think he's listening...

Also, the OP is using an LM555 to drive it, but
hasn't shown the schematic.

### TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 1:10 pm
Ok, I will try the mosfet again on battery power. It didn't work at all on 2.5 amps supply (12 v) the first time.
A drawing (BMP) later when it works.

Roger

Posted: Fri Nov 14, 2008 1:27 pm
I agree the MOSFET is a good alternate but you don't need a "darlington transistor" just use two of the ones you already have connected in the configuration you see when you look up "darlington pair" on google. Heck the first transistor in the pair could be almost any NPN with Ic large enough to bias the gate of the second to an Amp or so. A 2n2222 might even serve the purpose. I guess I assumed you bought more than one transistor.

http://www.technologystudent.com/elec1/transis2.htm

The fact that the transistor is so hot prooves that it is not in saturation. The 555 can't source much current but the 7555 (A cmos part) can source and sink a much larger load. You may just be running into the limitations of the output on the bipolar NE555. You might want to brush up on (by googling and reading) "Transistor Biasing"

### Re: TIP3055 NPN transistor thru put

Posted: Fri Nov 14, 2008 2:24 pm
Oxford wrote:Ok, I will try the mosfet again
This is the first I've heard of a mosfet?
You do know that a 2N3055 is a bipolar device
(and doesn't have a "gate")?
Oxford wrote:A drawing (BMP) later when it works.
Huh? The schematic is to find out why the design
doesn't work, not a record once the problems are solved.
(You may want a drawing for you records, but to

Posted: Fri Nov 14, 2008 3:17 pm
Hi Roger,

It sounds like you are trying to drive a 2N3055 from the output
of a 555 timer ic, and control 2 amps or so.
This could easily NOT work very well simply because the 555 can
not put out enough current to properly drive the 2N3055.

One thing about 2N3055's is that they dont have much gain,
maybe you can count on a gain of 10 but that's about it.
With a gain of 10 and 2 amps collector current, you need to
drive the base with 200ma of current, which the 555 can not
do.

Also keep in mind that if you burn out the transistor it may never
work again no matter how you connect the circuit. I mention this
(which i take to mean 'base') directly to the battery. This can
quickly blow out the transistor in a common emitter configuration.
If you were lucky you had it connected in a common collector
config and so it didnt blow out, but if not, i hope you have more
2N3055's laying around you can try next.

We will be waiting on your schematic so we can tell you exactly
why it is not working.

Posted: Fri Nov 14, 2008 3:52 pm
Its not clear if you need a high or low side driver. If the transistor is between the load and the ground, it's a low side driver. If it's between V+ and the load, it's a high side device. Use an N MOSFET for low side, P MOSFET for high. Since you are using an NPN transistor, I'd guess that you can use an N MOSFET but a schematic will help us understand that better.

Here's an example of an N channel MOSFET http://www.fairchildsemi.com/ds/FD/FDP3682.pdf

The FDP3682 will handle the current no problem and if you can drive the gate at 10V or higher it will have a resistance of .036 ohms. This means there will be about 80 mV drop in the MOSFET at 2 AMPs and thus around 160 mW of heat generated - basically nothing. Your 3055 will see around 2 Watts of heat which will put the part at around 100C. I would use a heat sink though you wouldn't absolutely have to. Just don't touch it. Your 555 can drive the MOSFET no problem.

Posted: Fri Nov 14, 2008 5:28 pm
Reference TIP3055, if this helps the "design team".

CeaSaR

Posted: Fri Nov 14, 2008 5:31 pm
CeaSaR wrote:Reference TIP3055 if this helps the "design team".
We're trying to ween the OP away from bipolar hogs (like '3055).