# Transistor Sizing

Discussion in 'General Electronics Chat' started by Freenerd, Jan 31, 2009.

1. ### Freenerd Thread Starter New Member

Jan 31, 2009
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I am working on a prototype garage project and stuck on how to select a proper transistor. I am pumping between 12vdc and 240vdc through the circuit depending on jumpers and am frying 2n3055's faster than a hen peckin scratch! I'm a complete novice in electronics but I'm trying hard. HELP!!!

What info is needed beyond the vdc to figure this out. I have know idea how to properly measure voltage & current through the transistor so I could use alittle help there also.

Freenerd

2. ### mik3 Senior Member

Feb 4, 2008
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First, take care with the 240VDC, it is dangerous.

How do you produce 240VDC?

What is the maximum current the load needs?

3. ### Freenerd Thread Starter New Member

Jan 31, 2009
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One goal is to regulate voltage across the range to support variable charge loads to battery banks which are supplying dc input to inverters. The 12 vdc to 240vdc is coming from batteries (and yep - I'm being VERY careful indeed!) I'm just a bit stumped on getting the high power transistors properly proportioned given the voltage range and potential amps. The circuit is divided into 6 parallel paths so I need to address all 6. I am anticipating current in the 0 to 40 - 60amp range spread across the 6 circuits. All goes well on the 2n3055's until I add a load - then... pop!

4. ### beenthere Retired Moderator

Apr 20, 2004
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3055's are not rated for that voltage. If you simply run them as current switches (not in a linear mode), then a couple of IGBT's might be more the thing. They start with voltage ratings of 600 volts.

Tell us more about the circuit.

5. ### Freenerd Thread Starter New Member

Jan 31, 2009
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Unfortunately I can't go into a whole lot of detail (secret stuff...) - I guess the more simple question would be:

~Is there a transistor that maintains the low power characteristics of the 2n3055 while also enabling higher voltages to 300vdc to 600vdc at 30 to 40amp? This would allow for the range I need in a single transistor.

Thanks again!

6. ### studiot AAC Fanatic!

Nov 9, 2007
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I think it likely that you are pushing your transistors beyond their gain capabilities.
They would survive much better with proper drivers.
What current gain are you expecting, at both low and high current?
Yes there are transistors that easily have the sort of voltage rating you are asking, they used to be used in television tube drive circuitry and are now available quite cheaply on the surplus market.
However they have low current gain and need drivers and predrivers.

I recently picked up a pack of BUV47s (850 volts /120 watts/9amp) for a song.

Last edited: Feb 3, 2009

Apr 5, 2008
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Hello,

As beenthere already told you "normal" transistors will not be able to handle that.
A IBGT will. Take a look at the attached datasheet for example.

Greetings,
Bertus

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8. ### beenthere Retired Moderator

Apr 20, 2004
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If you don't have to run in the linear region, an IGBT is just made for that voltage and current. As a for instance, the STGW30N80VD in TO-247 is rated 600 volts @ 80 amps & costs a whole \$5.46 from Digi-Key.

9. ### Freenerd Thread Starter New Member

Jan 31, 2009
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Thanks for the lookups!
The g450hhbk06p2 is an absolute moose! A smaller pkg would work better if possible. I noticed the following spec in the datesheet: Collector Emitter Breakdown Voltage: Min = 600V - sounds to me like this means you cannot go below 600V - True of False?

I'm not finding the STGW30N80VD mentioned by beenthere. The TO-247 case would definitely work better though. Also, how do I know if they are AC or DC powered (I need DC)?

Dec 20, 2007
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11. ### Freenerd Thread Starter New Member

Jan 31, 2009
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I do use mains - they're just attached to my inverters which is managing an abundant volume of electricity coming from my solar array. Almost 'everyone else' is paying through the nose monthly - but I'm free and clear! Zero \$ for electricity is good for me...

I can't find G450HHBK06P2 in digikey to get pricing. Is that were you located it? This is a BIG component 2.5"x4"x1". I need a bigger garage and I'm guessing a bigger wallet for this beast!!!

Beenthere - can you post the link for that STGW30N80VD? Something tells me the price is going to be more to my liking.

Thanks.

12. ### beenthere Retired Moderator

Apr 20, 2004
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It's on page 1252 of the current catalog. You should be able to do a parametric search for IGBT's and get several more hits. International Rectifier makes them, too.

It's worth getting data sheets and application notes to get a better feel for the critters. They are very different from BJT transistors.