Need Help Choosing NPN Transistor

[GeneralBones]

Hey guys! Im building slayer exciters and I've used 2n2222 and mj3055t transistors to make them. What would be the strongest/most powerful NPN transistor I could buy to make a slayer exciters?

 

[CDRIVE]

You're probably better off using a power MOSFET.

Chris

 

[(*steve*)]

The things you need are:

1. High current capability
2. High breakdown voltage
3. Fast switching (specifically switching off)

You might investigate using an IGBT but you'll need for gate drive to get the fast switching speed you require.

At the low voltage you're looking at (9V) the voltage drop across the IGBT will probably be a drawback.

Edit: an IGBT probably can't handle the frequency used in most simple drivers.

 

[CDRIVE]

I didn't see anything in GB's post that mentioned 9V. Where is that Steve?

Chris

 

[(*steve*)]

Where is that Steve?

In my head.

(i.e. not in reality)

 

[CDRIVE]

I heard a rumor that that can be a scary place!

Chris

 

[GeneralBones]

I do plan to move on to MOSFETS soon although the I just wanna make the most powerful single transistor design for now, And maybe a double transistor design if I learn to read circuit diagrams properly

 

[CDRIVE]

Transistors can be paralleled but to compensate for nonidentical Beta's a small Emitter resistor is used to help balance them. The problem with this is a substantially higher Collector - GND on state voltage drop.

Chris

 

[GeneralBones]

Care to explain what that means?

 

[CDRIVE]

Hold tight I'll draw a picture.

Chris

 

[(*steve*)]

Can you get an MJ10021?

 

[CDRIVE]

Can you get an MJ10021?

With the exception of Vce(Sat) those are impressive specs. Though not surprising that Vce(Sat) is so high, as it is a Darlington.

Chris

 

[GeneralBones]

I could shoot for that MJ10021 In the future, thanks alot! Anymore transistors equivalent or better that's not in a t03 package so I can manage heat better?

 

[GeneralBones]

Also can someone make it a bit more clear as to why one would put transistors in parallel?

 

[(*steve*)]

The main magic with the MJ 10021 is the diode connected between the base of the second transistor and the base of the first transistor. There is no reason why you can't do that with your discrete design. I would recommend a Schottky diode.

You put transistors in parallel in order to switch more current than a single transistor of that type of capable of.

 

[GeneralBones]

So if I have a car battery charger that can be switched from 12V2A to 12V10A, and 12V50A, and I use one mj3055t and it works at 12V2A but blows a couple seconds after switching it to 12V10A, then two mj3055ts would be able to handle it?(Since I think the max current for that transistor is 6A)

 

[GeneralBones]

Also, idk how a diode plays into this. But I did lookup "Schottky diode" and found out that I have four MBR2045CTGs that I think are those types of diodes. How would I use them?

 

[(*steve*)]

Connect the diode as shown in the datasheet for the MJ10021

It provides a path to discharge the base emitter junction capacitance.

 

[GeneralBones]

Okay. Does that increase performance?

 

[(*steve*)]

It should significantly improve the speed at which the transistor turns off. This is where most power is likely dissipated in the transistor (so it should run cooler) and a faster turn-off should also give you a higher output voltage.

Because this is not run from a fixed frequency but operated at some Reiner frequency, I can't say with any certainty that the new equilibrium point will be be then the of one. However, the change is simple and cheap and with a try.