Transistor ?

[sundin13]

This is my first post here so go easy on me.  I'm a electrical tech student who is just starting out.  I'm stumped on this question...

For the circuit shown, Vcc = 14 V, BetaDC = 162, and Rc = 543 Ohms

a)  Vce (in Volts) when Vin = 0 V

b) the min value of Ib (in uA) required to saturate the transistor assuming Vce(sat) = 0 V

c)  the max value of Rb (in kohms) for saturation operation if V in = 2.9 V

I'm not asking for anyone to do my home work here I just need some feedback so that I can wrap my head around this stuff so one day I can be answering these types of question with ease.  Thanks in advance.. ;D

View attachment 38467

 

[Staigen1]

Hi there sundin13, velcome to the forum!
Sundin? Sounds like a Swedish name. Are you from Sweden?

Some of the questions cant be answered, because there is a lack of some parameters!
Vbe, for instance.
But asume it is a perfect transistor(such transistor dont exist!) with a Vbe of zero votage and DCbeta=162.

Question a:
Since Vin=0V then Ib=0mA(uA,A), hence also Ic=0mA(uA,A), then the voltage across Rc=0V

Question b:
This one is harder, but it is only math! First you have to calculate the current throu Rc at saturation, then divide that with the beta value. If you calculate the Ic in other values than uA, then you have to convert the answer to uA.

Question c:
Here you can do the math in two ways. First way, divide the Vin voltage with the Ib current in uA, the answer is in Megohm, than convert to Kohm. Second way, convert the Ib current to mA, then divide the Vin voltage with that value, the answer is in mA.

But watch out, there's a trap buildt in in this anwers! The trap only affects the c question. ??? ;D
I belive you see the trap at once, once you have read throu the text once more.

//Staigen

 

[audioguru2]

I'm stumped on this question...

For the circuit shown, Vcc = 14 V, BetaDC = 162, and Rc = 543 Ohms

a)View attachment 38460

 

[Staigen1]

So you like to do others homework, Audioguru?

Well, i belive some of your answers will turn out to be wrong, too, in this teoretical questions! ;D ;D ;D

Hehe

//Staigen

 

[audioguru2]

Hi Staigen,
My answers covered all the bases (and collectors) including the trap.
A transistor doesn't saturate very well with only the tiny base current that is calculated by its beta. ;D

 

[Staigen1]

Yepp, i know that, and you know that, but the guy that wrote the book dont seems to know! Also, we dont know the answer or the facit yet, will you supply us with that, Sundin?

//Staigen

 

[sundin13]

Thanks guys.  And Yeah we use 0.7 V (silicon)  for Vbe  Oops sory :-\

 

[Staigen1]

Than you have to do your math then!

Are you from Sweden?


//Staigen

 

[sundin13]

The closest I've been to Sweden is IKEA.  I'm from Ontario.  First year Tech student with out a clue whats going on in Electronics class!  I'm looking for all the help I can get. 

It turns that I just left out the Vbe.  I've fixed the diagram.  So now because there is no current through Rb  ->  Vce = VCC approx....

I'm still thinking about the next two parts.  I'll check back tommorrow after some more reading.

Thanks everyone for the help so far. ;D