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 Using a transistor as a switch

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amr mohamed
 
 


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PostSubject: Using a transistor as a switch   Wed 16 Mar 2011, 9:28 pm


Using a transistor as a switch


There are three areas of operation of the transistor is an area of ​​segments
Cut OFF in which a
Transistor is turned off completely
Work and the complex stream = Cefromntqp operating active region
And the transistor works
Like a microphone, where the compound stream
Is the enlarged image of the stream Alhadpomntqp saturation Saturation
In which a transistor
Working to full capacity any Fully
ON and the current complex is the largest
Can not be here (ie, stream
Complex) based on stream
Al Qaeda
.


Use
Transistors as the key electrical


When the transistor is used
As the key electrical, it works either
In the blocks or at the
Saturation, in short, be either
Ergonomics, such as matte or key.
When the transistor Ergonomics
(saturation region) is the effort
VCE almost zero and here we say that
Transistor is not saturated any
Can pass more of the stream
Compound. The device that control the
Runs through this
Transistor called pregnancy
(LOAD)


(See figure below).



Very important observation here

Is that the capacity to be dissipated by transistors are very small
You know
Why? Because the effort
VCE is a very small (approximately
Zero) and as we know that the ability
Dissipated by the transistor =
Stream complex IC × voltage VCE.


Mark

When
Any transistor in the case of
Saturation, the voltage
VCE is
Almost zero, and the stream
More complex as possible.



Example

You are using the transistor
2N3904, in Aldcanivet Special
This transistor, we found that
Po = 625 mW that any capacity
That this transistor can
Dissipation (in the form of heat)
Equal to 625 mW. Now
If we assume that the voltage VCE =
0.4 V at saturation, this
Transistor can pass
Stream complex = 1.5 amp
(Approximately the result of dividing power
The voltage VCE, taking into account
Units). But the question now is:
Can this transistor
Pass this much power
Note that the Aldata Special Shit
It says that the highest Ic can
This transistor is a bear
200 mA? Answer
Absolutely not. If the stream was passed
1.5 mA in this
Sitvhm transistor.
cheers
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