hello all, i got a question, can i simulate the transistor junction in this way?

and also why the circuit doesnt work as i expect?, like when i use a normal transistor npn as emitter follower this happens:
I connect collector vcc, lets say im using a square wave to drive the transistor as on-off ( saturation and interdiction mode )

during the phase where its in saturation, the transistor is conducting, and vcc is tied to gnd via a resistor ( in this way there is no shortcircuit, but we can "remove the D.C" in order to see only the signal i give in input ( at its base - 0.7V )

Now i tried to simulate to do exactly the same thing, but i didnt obtain this result, why so? what i wanted to do is to see in output a square wave in output ( since it should work as the transistor, vcc is pulled to gnd via the resistor, and what i get is the pulse wave - the drop of the diode )

Can someone explain me? thanks.

 

The output voltage node is clamped to 4V by V1, which is a perfect voltage source with zero resistance.
Disconnect V1 and you should get the output you are expecting.
Note that, in the circuit shown, the diode current is over 600 Amps!

 

The output voltage node is clamped to 4V by V1, which is a perfect voltage source with zero resistance.
Disconnect V1 and you should get the output you are expecting.
Note that, in the circuit shown, the diode current is over 600 Amps!

but i wanna simulate when im giving a d.c voltage into it too, what i can do? i can add a series resistor?

 

The output voltage node is clamped to 4V by V1, which is a perfect voltage source with zero resistance.
Disconnect V1 and you should get the output you are expecting.
Note that, in the circuit shown, the diode current is over 600 Amps!

whats a good value that can i assign to a real generator? 100 ohm is fine?

 

i wanna simulate when im giving a d.c voltage into it too

Into what?

 

Explain your circuit. Why do you think there should be a 4V source across the resistor?

A diode does act very much like a transistor BE junction when the collector is unconnected, but where does the 4V source come from?

 

hello all, i got a question, can i simulate the transistor junction in this way?

and also why the circuit doesnt work as i expect?, like when i use a normal transistor npn as emitter follower this happens:
I connect collector vcc, lets say im using a square wave to drive the transistor as on-off ( saturation and interdiction mode )

during the phase where its in saturation, the transistor is conducting, and vcc is tied to gnd via a resistor ( in this way there is no shortcircuit, but we can "remove the D.C" in order to see only the signal i give in input ( at its base - 0.7V )

Now i tried to simulate to do exactly the same thing, but i didnt obtain this result, why so? what i wanted to do is to see in output a square wave in output ( since it should work as the transistor, vcc is pulled to gnd via the resistor, and what i get is the pulse wave - the drop of the diode )

Can someone explain me? thanks.

You are making very little sense.

Your circuit in no way resembles any kind of transistor circuit.

Consider the following circuit.



In this circuit, we are driving two 1 kΩ loads with a ramped signal that goes from -5 V to +5 V. One load, R1, is being driven via a series diode. The other is being driven by an NPN transistor configured as an emitter-follower.

We expect the voltages across the two loads to be very similar and, indeed, they are, as shown by the following simulation results:



What is very different between the two is where the current in each load comes from. In the case of R1, all of the current must come from the signal source. But in the case of R2, most of the current comes from the 9 V power supply and very little comes from the signal source.



At a signal voltage of 4 V, the current into the diode is 3.37 mA, but the current into the base of the transistor is only 10.6 µA. About 99.6% of the current in R2 is not coming from the signal source, but from the 9 V supply.

 

You are making very little sense.

Your circuit in no way resembles any kind of transistor circuit.

Consider the following circuit.

View attachment 347420

In this circuit, we are driving two 1 kΩ loads with a ramped signal that goes from -5 V to +5 V. One load, R1, is being driven via a series diode. The other is being driven by an NPN transistor configured as an emitter-follower.

We expect the voltages across the two loads to be very similar and, indeed, they are, as shown by the following simulation results:

View attachment 347423

What is very different between the two is where the current in each load comes from. In the case of R1, all of the current must come from the signal source. But in the case of R2, most of the current comes from the 9 V power supply and very little comes from the signal source.

View attachment 347424

At a signal voltage of 4 V, the current into the diode is 3.37 mA, but the current into the base of the transistor is only 10.6 µA. About 99.6% of the current in R2 is not coming from the signal source, but from the 9 V supply.

I meant the BE junction basically, in this way i simulate whats happening inside that part of transistor by applying "VIN" to base and VDC to emitter which is cathode of a diode

 

The diode only mimics a BE junction when the collector is left unconnected. Not particularly useful.

 

I meant the BE junction basically, in this way i simulate whats happening inside that part of transistor by applying "VIN" to base and VDC to emitter which is cathode of a diode

No, you don't. As I said, your circuit in no way resembles any kind of transistor circuit.