Pspice simulation

[bakkis]

Hi,
Am trying to learn a simple circuit simulation with Pspice. The circuit is attached. All the base, collector and emitter resistors are 1K. And supplies are 5V. With this i expect the base current to be 42 microamp. But somehow Pspice seems to show 1.19 mA. Am i right in my calculation or there is something i need to do with the Pspice ?
The transistor i use is Q2N3416. Somebody kindly help me asap.

 

[ericgibbs]

hi,
This is what LTspice shows..

 

[bakkis]

Exactly, how does I(R3) turn out to be 1.19 mA ? Cause if we apply KVL on the input side and having Beta=100(I hope am right here), I(R3) should be 42 microAmp.

 

[ericgibbs]

Exactly, how does I(R3) turn out to be 1.19 mA ? Cause if we apply KVL on the input side and having Beta=100(I hope am right here), I(R3) should be 42 microAmp.

hi,
What do you calculate the input impedance to the Base ???

also the approx Gain of that configuration.??

 

[bakkis]

Thank you eric for trying to help me out with this! Input impedance is 1k . The gain i.e Beta is 100 what i suppose it is.
So, with: 5 -IbRb - 0.7 - (Beta = 100)IbRe = 0 yields me Ib = 42 microAmp.

 

[ericgibbs]

Thank you eric for trying to help me out with this! Input impedance is 1k . The gain i.e Beta is 100 what i suppose it is.
So, with: 5 -IbRb - 0.7 - (Beta = 100)IbRe = 0 yields me Ib = 42 microAmp.

Hi,
Show me the formula for the DC gain with those values of Emitter and Collector resistors....

 

[bakkis]

Am not sure what you mean. Does the gain depend on the resistor values i select. I thought they are transistor dependent.

 

[ericgibbs]

Am not sure what you mean. Does the gain depend on the resistor values i select. I thought they are transistor dependent.

hi,
The circuit gain is a function of the transistor and the Emitter/Collector values

 

[bakkis]

True, i agree. But the beta am speaking of is not the circuit gain but the transistor gain.

 

[ericgibbs]

True, i agree. But the beta am speaking of is not the circuit gain but the transistor gain.

hi,
As its homework we do not give a direct answer, try this ,,, reduce the Vinput to say 2V and the see what the Ibase measures..

Hint: has your class work covered transistors in saturation ????

EDIT:
Look at this LTS plot note the Vce, the transistor is saturated.

 

[ericgibbs]

hi,
This pdf gives a worked example of your problem.

EDIT:
This Sim shows whats happening to the Ib as the Vce falls

 

[bakkis]

Hi eric, thanks for making me realize that i have put the transistor in the saturation. However i still have doubts: My class has started with transistor only a day back, so i dont know if i have come across the saturation conditions yet.
My doubt is : At saturation Ic should be just Vcc/Rc . So should Ie be. i.e Ie = Ic. but at according to the equation at the input Ib doesnt equal to 1.19 mA as suggested by Pspice.

 

[ericgibbs]

Hi eric, thanks for making me realize that i have put the transistor in the saturation. However i still have doubts: My class has started with transistor only a day back, so i dont know if i have come across the saturation conditions yet.
My doubt is : At saturation Ic should be just Vcc/Rc . So should Ie be. i.e Ie = Ic. but at according to the equation at the input Ib doesnt equal to 1.19 mA as suggested by Pspice.

hi,
Did you go thru that pdf I posted, it has a worked example for the circuit type you posted.

Also hint, for the saturation conditions in your circuit you must include the voltage drop across the emitter resistor.

Look at this image, see the RED line showing how the gain falls off at saturation.

 

[bakkis]

Am sorry for the repeated message. I didnt see the PDF though.

 

[bakkis]

Thanks a lot eric. That explains my mistake !!! I owe you just too much