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Topic: Transistors in parallel (Read 4971 times) previous topic - next topic

tomasi

Hi. I have a high current load to control with Arduino (25 amps approx.).
My idea is to join cheap and easy to find  NPN transistors in parallel to control the current (pwm current control) capable of 40 amps or more for safety reasons.
Here is my idea:


Will this work?

Thanks in advance.

winner10920

I haven't actually tried it so don't take this as 100%, but I believe due to the fact that no matter what each transistor setup will have slightly different resistances and flow which will overload some more than others, which would cause a cascading pop of your well spent money as they fail :  /

tomasi

hmm... should i go for a single power mosfet then?

Thanks in advance.

Grumpy_Mike

FETs will shair current when put in parallel. Transistors will not.

winner10920

Yeah I believe you can get a decent mosfet that will work and be cheap, that's what most people do

Saad Khalil

Yes try MOSFET.. i'm sure it will work for you..
Saad Khalil

terryking228

Hi,
Back in the Dark Ages when I first touched power transistors there were no power FETs.

Many high-power power supply designs DID parallel junction transistors. They typically added small resistors in series with the collector of every paralleled transistor, a resistance that would drop about .1 volt at normal operating current. So like .1 ohms for 10 amps, etc.

This equalized the current across multiple transistors. 

Also the transistors should be same type, same manufacturer, best if same date code...
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

tomasi

Thank you all for the infos.I googled a little and this is what i found:

  STP80NE06-10

  http://www.datasheetcatalog.org/datasheet/stmicroelectronics/5632.pdf

VDS Drain-source Voltage (VGS=0)60V
VDGR Drain-gate Voltage (RGS=20k?)60V
VGS Gate-source Voltage  ±20V
ID Drain Current (continuous) at Tc=25C  80A
ID Drain Current (continuous) at   Tc=100C  57A

  Im not familiar with MOSFETs.One thing that concerns me regarding this MOSFET is VGS value of 20V.Does it means that i must have 20V on gate for switching?
Sorry for all these questions.Thank you all.





Grumpy_Mike

Quote
Many high-power power supply designs DID parallel junction transistors.

Yes an in those days many many designs failed. I was on a team that tried that in my first job, I was only an apprentice then but none of the grown ups could make it work. I still remember the pings as they went one after another. In those days just one of these 5A power transistors cost the same as my weeks wages.

Quote
One thing that concerns me regarding this MOSFET is VGS value of 20V.Does it means that i must have 20V on gate for switching?

No that is the maximum voltage it will take before you damage it. However you do need 10V to turn this FET on fully. Look at the Rds (on) conditions.

tomasi

humm.. 10v for switching. Will this work?


took from other topic: http://arduino.cc/forum/index.php?topic=75747.0

(need to learn about mosfets...i think it will took a year).


... in series with the collector ...



A small resistance in  series with the emitter would be far more effective and would balance the load on each transistor naturally through adjusting the base current.

In a previous life I was part of a team that designed DC motor drives.  The biggest I worked on was a 10KW drive that used banks of over a hundred 2N3055s with .1 ohm resistors in series with the emitter.  I believe some of them are still in service today.



Facts just don't care if you ignore them.

terryking228

Quote
A small resistance in  series with the emitter would be far more effective


Oh. Yeah.. they were in the Emitter for sure..

Hey it was only 45 years ago, how could I forget?
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

Grumpy_Mike

Quote
humm.. 10v for switching. Will this work?

Yes that would be fine.

tomasi

Thanks Grumpy Mike.
Im still studying about FETS. Can I sugest to you more experienced ppl a complete tutorial on playground? As Arduinos are related to robotics and LED arrays, it might be a good start point.
I found this FET.
http://www.datasheetcatalog.org/datasheet/irf/irlz44n.pdf

It´s a logic level FET, so I think a "pre transistor" to achieve RDs(on) won´t be necessary. Am I right?


cheers from Brazil

Edsoncan

Work but:
You must have a small reistence in emissor  and a resistence in base too.
Semicondutor never have the same polarization voltage.

Problem:
The current is not equal in each transistor and you must project with more than 20A.
Edson

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