electronic elementary questions

[vaidhyanathan]

The opeartion of BJT (ON or OFF) is dependent on the value of bias voltage(Vbe). But why it is called a current controlled device?

 

[jeet_asic]

It is a current controlled device because the base current controls the current flow from the emitter to collector.

 

[FoxyRick]

Actually it can be viewed as either current or voltage controlled, and design equations used accordingly.

However, it is generally regarded as a current controlled device because a significant amount of current needs to flow through the base for operation, no matter which 'view' one is taking.

That is in contrast to field effect transistors which have almost no current through the gate. Thus it is 'voltage controlled'.

 

[LvW]

The opeartion of BJT (ON or OFF) is dependent on the value of bias voltage(Vbe). But why it is called a current controlled device?

No, that's wrong. As long as the physical phenomena within a transistor are concerned - it is NOT current controlled (in spite of the common rule that the collector current is a multiple of the base current).
For a detailed description and justification see here:

SCIENCE HOBBYIST: how transistor works, an alternate viewpoint

 

[FoxyRick]

LvW, the description of transistor action in that link is fantastic!

I wish they had used that description when I was at university (a long time ago) because I always hated having to rely on equations when I didn't really know how they described the phenomena at work.

Serioulsy, that is recommended reading to anyone who might use a transistor. It works for me!

 

[LvW]

FoxyRick,
I agree with you.
If you are intererested, read the second part of this contribution (link at the end). Here it is explained that (and why) even the reverse of Ohms law - "a current produces a voltage across resistor" - is just a fiction (from the physical point of view).

 

[FoxyRick]

Yes, I've read it all. I used to be a science teacher (well, head of science) in a high school, and I always prided myself on being able to explain the 'truth' of how things worked, to those willing to learn. At least, when the truth is actually known. I firmly believe that it leads to a much better understanding and ability to take that knowledge further, than simply teaching equations and half-truths.

The resistor explanation is perfectly true. Potential difference is what causes charged particles to move, giving a current. Simples!

 

[Allisonque]

It is currently controlled to adjust the base current flows from the source electrode uses a collector.

___________________________________________________________________________________
PRWeb Coupon Code

 

[ecad]

i want to know which all factors affects the life span of a transistor..?? and how long transistor can be use..?? i mean it's life.??

 

[godfreyl]

A transistor should last almost forever unless it is damaged either physically or due to the voltage, current or temperature limits being exceeded.

 

[ecad]

Any idea About Arduino Software.. ?? if yes then please help me out with "thermistortable.h" ..