Paralleling transistors

[ehs dav]

paralleling transistors

Hi all
I wana parallel some power transistors 2 gain higher power(>>350 watts).
The VCC is about 80 VDC. The load is in collector and is inductive.
Emitter is grounded (better with a resistor ). In the base there is a inductive load and a resistor for biasing.

My problem is that transistors are not match exactly and are BOOOMBing(fired,damaged,explosived,....) when i connect them.
How can i connect bases and collectors of them to obtain same hfe and Vbe?

thQ laT

 

[instruite]

irfp460 power amplifier

Can you give the load spec of inductor like inductance and resistance of the inductor?
and also the current requirement?

 

[IanP]

Use very small equalizing resistors connected between emitters and GND. Somethng like 0.05Ω-0.1Ω (rated for proper power) per transistor should do ..
And I think you sould use more than 2 transistors (3 or even 4) ..
Regards,
IanP

 

[echo47]

Yes, try small emitter resistors.

And please wear safety glasses!

Once upon a time, a friend of mine was troubleshooting a 500 watt switching power amplifier. I handed him my safety glasses. He asked "do I need these?". I replied "just in case". He put them on. A few minutes later the amplifier blew up and pelted him in the face with flying FET fragments.

 

[tsanlee]

You must take care the " thermal run away " in bipolar process.

The uniform turn in large BJT or MOS layout is so imrprtant.

The same distance(resistor ) from base driver circuit to NPN (Large NPN)
,but the NPN (large NPN) is so large (area), so you can tune the metal length or add small dummy resistor for uniform turn.

 

[leomecma]

Why do you need use two transistors in parallel? There's some devices that supports this power without you have to put it together. Your load have 350W of power, but transistor have to drive about 350W/80V = 4,38 A... Am I true?

 

[Ante]

Are you switching (off-on) the inductive load or analogy (0-100%) regulating it?

 

[echo47]

He hasn't said if linear or switching, but I would assume linear because he's talking high power and not just high current.

leomecma, he says >> 350W, which means much greater than 350W. He wants bipolar, which eliminates two of your suggestions. The BU931 has mediocre secondary breakdown performance (about 0.6A at 80V), so isn't well suited for this application. Many years ago I used Motorola MJ15024. There are probably even better modern transistors.
https://www.onsemi.com/site/products/summary/0,4450,MJ15024,00.html

 

[ehs dav]

Thanks Everybody
&
Sorry for late(i was so busy and in pressure because of project)

A NEW PROBLEM

at first the wants me to build high voltage (12KV) sine wave.
I built a transformer for this and a sine wave, but i need too power in low volt side of transformer (high current).
So I was need to parallel bipolar transistors.
Then now they say just want 12KV ac.
Now i can use mosfets too and parallel them and use square wave(on and off)instead.
i think irfp460 is good.
If I do, i can use old transformer but i need new circuit.
My question is which circuit is better?
half pole, full pole, using top ics, pwm,using each transistors for half period or...

PLEASE HELP

if this project ends i shoud build inverter 500watt {60~78V DC => 50V 60hz AC}
:roll:


but
tanque weri mach
with ALL your helps :

 

[IanP]

Quite a number of inverters use CT (centre tap) push/pull transformer configuration at low voltage side. Attached is an example of paralleld power mosfets and push/pull transformer ..
IRFP460 can be used to this purpose, although I would try to select MOSFETs with lower low Rds(on).
The IRFP460 has 0.27Ω, but you should be able to find ones with Rds(on) below<< 0.1Ω (lower heat).
BTW, what will be the switching frequency? 50Hz?
Regards,
IanP

 

[ehs dav]

hi
thanx lot IanP and others

Is the lower Rds(on) better or higher maximum power in this application?
What is zn*26v18 (i cant read the name in picture) and what is the usage of it in this circuit?
Please write the full name too. (for replace with other parts)
AND

ALL GUYS
in my country the limitation of existance devices and parts should be considered too.
you can consider me in a deep hole in the center of a desert of MARS or MOON at stormy night
I was joking but i cant find or order many parts.
thanx sooooooooooooooo much

 

[IanP]

You have 15V zener diode at Mosfets' gates, and 24V zener diode in the back-emc protection circuit. The other component in this circuit is bidirectional transient voltage surpressor, ZN-something (I can't read it too), and you can use 1.5KE47CA or equivalents ..
As far as MOSFET's rds(on) is concerned it is obviously better if that resistance is smaller, but if you can't get them use whatever you can get and just increase the size of heatsink on which these MOSFETs will be mounted ..
Regards,
IanP