What are common issues when using 2N2222 in a BJT NPN amplifier?

[Ivan Antunovic]

Hello people,

I am working on a BJT NPN amplifier the model that I've choosen is 2N2222 : http://www.e-voron.dp.ua/files/pdf/tranzistor/2N2222.pdf

I am having 3 problems here:

1) am not having any AC voltage at output Vce seems like I have set wrong operating point?

2) I am trying to figure out how to determine hoe resistance of this transistor from the graph hybrid output resistance hoe=dIc/dUce at operating point Q

3)Is my schematics for the small signal analysis wrong?

I hope pictures are not blur.

 

[Ivan Antunovic]

Okay they are blur

http://postimage.org/

 

[Ivan Antunovic]

Okay they are blur

and Xce should be in parallel with Re my bad

http://postimage.org/

 

[rude man]

Hello people,

I am working on a BJT NPN amplifier the model that I've choosen is 2N2222 : http://www.e-voron.dp.ua/files/pdf/tranzistor/2N2222.pdf

I am having 3 problems here:

1) am not having any AC voltage at output Vce seems like I have set wrong operating point?

What's your frequency and amplitude? Your RC and RT are both very low.

2) I am trying to figure out how to determine hoe resistance of this transistor from the graph hybrid output resistance hoe=dIc/dUce at operating point Q

forget about h_oe. It's negligible.

3)Is my schematics for the small signal analysis wrong?

No idea. Depends on your software. Your schematic in post 2 does not show a signal source ...

 

[Ivan Antunovic]

What's your frequency and amplitude? Your RC and RT are both very low. forget about h_oe. It's negligible.
No idea. Depends on your software. Your schematic in post 2 does not show a signal source ...

Okay forgotten to say about voltage source it's sinus with amplitude 100 mV and frequency 50Hz

 

[Ivan Antunovic]

Okay forgotten to say about voltage source it's sinus with amplitude 100 mV and frequency 50Hz

I know that hoe is so small but I am trying to do things atleast as correct as I can I do this for my soul.There is Ic-Uce curve in the link that I've given but it's in logaritmic paper how to I convert it from dB to Ampers and Volts?

 

[rude man]

Due to C1 being so large you should be seeing a horribly distorted sine wave at the collector of about 200 mV.
At the output there is very little ac since the time constant formed by RC, RT and CV2 is very low (cutoff freq. about 2 KHz).

This is a really bad design so worrying about h_oe is a total waste of time.
What does your simulator say?

.

 

[Ivan Antunovic]

Due to C1 being so large you should be seeing a horribly distorted sine wave at the collector of about 200 mV.
At the output there is very little ac since the time constant formed by RC, RT and CV2 is very low (cutoff freq. about 2 KHz).

This is a really bad design so worrying about h_oe is a total waste of time.
What does your simulator say?

.

I have taken schematics from the internet,voltmeter shows no voltage at output and oscilloscope shows no signal at output

 

[NascentOxygen]

Okay forgotten to say about voltage source it's sinus with amplitude 100 mV and frequency 50Hz

For a signal frequency of 50Hz your coupling capacitors are way too small; they are attenuating the signal more than the 2222 is amplifying it. What is the reactance of a 1uF capacitor at 50Hz?

 

[Ivan Antunovic]

For a signal frequency of 50Hz your coupling capacitors are way too small; they are attenuating the signal more than the 2222 is amplifying it. What is the reactance of a 1uF capacitor at 50Hz?

it's 3813 ohms.Okay then make it 10kHz so the reactance goes down by 200

 

[Ivan Antunovic]

Forget about this task it has very bad resistances.

I got a new task from my professor:

Compile common emmiter amplifier(NPN) with the following default parameters:

VCC = 12V, power transistor 50 mW max. output signal between 3-5V, VRE = 1V.

Determine Computing and measuring AV, AI, Rin, Rout, the upper and lower limit frequency, THD.

Then, instead of RL connect the speaker and try something heard on the speaker.

I have choosen transistor BC547.

I assumed that the voltage at RL is 5V and from PRL=VRL^2 / RT I get that RL=250 ohms.I measured that Vbe=0.68V.

I am trying to figure out what should be resitances R1 and R2

image upload no limit

 

[rude man]

Forget about this task it has very bad resistances.

I got a new task from my professor:
Compile common emitter amplifier(NPN) with the following default parameters:
VCC = 12V, power transistor 50 mW max. output signal between 3-5V, VRE = 1V.
Determine Computing and measuring AV, AI, Rin, Rout, the upper and lower limit frequency, THD.
Then, instead of RL connect the speaker and try something heard on the speaker.
I have choosen transistor BC547.
I assumed that the voltage at RL is 5V and from PRL=VRL^2 / RT I get that RL=250 ohms.I measured that Vbe=0.68V.
I am trying to figure out what should be resitances R1 and R2

R1 and R2 are chosen to give you the required 1V at the emitter. Consider the base dc current also.
The professor meant to limit your dissipation to 50 mW, not that the transistor cannot sustain more than 50 mW, probably.
EDIT:
I didn't see the 1V V_RE requirement. So this will not be a real common-emitter circuit.
What are your upper and lower frequencis?
You can probably connect the speaker in series with the collector resistor.

 

[NascentOxygen]

I got a new task from my professor:

Compile common emmiter amplifier(NPN) with the following default parameters:

VCC = 12V, power transistor 50 mW max. output signal between 3-5V, VRE = 1V.

The specs say V_cc = 12V, yet your calculations use V_cc of 15V. Why?

 

[Ivan Antunovic]

The specs say V_cc = 12V, yet your calculations use V_cc of 15V. Why?

My bad I was really tired at evening when doing this that I didn't even notice it was 15 V.

 

[Ivan Antunovic]

How do you mean it won't be real common emitter circuit when it has a resistor RC connected directly to the collector electrode?R1 and R2 are voltage dividers I know that they are used to set Quiescent Point.If R1 and R2 are voltage dividers of Vcc and if I want 13.35 V at R1 and 1.65 V at R2,R1 should be 8.09 times larger than R2.

Edit(after drinking a coffee :D):
Btw I am using BC547 for this circuit https://www.fairchildsemi.com/datasheets/BC/BC547.pdf maybe I should take some data from the datasheet and try calculating resistances.For example there is a Ic-Vce curve and I tried to make load line and then it's a piece of cake for finding the resistances.

Load line equation is:
Ic=-Uce/Rc+Re + Ucc/Rc+Re (Asumming that Ic=Ie)the maximum Vce voltage is Vcc which is 12 volts ,maximum current Ic will flow when Ucc/Rc+Re and therefore it's y-intercept of the curve.But still I don't know Rc and Re so therefore I can't find y-intercept...maybe I should consider a worst case scenario and take values for Vce ,Ic and Ib from the datasheet?

 

[NascentOxygen]

If you're aiming for 50mW dissipation, and you bias for V_CE of around 6-7V, then what will be the DC value of I_C?

 

[Ivan Antunovic]

If you're aiming for 50mW dissipation, and you bias for V_CE of around 6-7V, then what will be the DC value of I_C?

Well I don't know since I am trying to figure out how to find R1 and R2 since they determine the bias IB and then IC.If I assume that Vce is around 6 V then VRC=VCC-VCE-VRE=12-1-6= 5 V but still I don't know the value of the resistance RC?

 

[NascentOxygen]

power dissipation = voltage x current

- which voltage?
- which current?

Remember that power into the base is a negligible fraction of total power, for these small signal amplifiers.

 

[Ivan Antunovic]

power dissipation = voltage x current

- which voltage?
- which current?

Remember that power into the base is a negligible fraction of total power, for these small signal amplifiers.

I think he meant power dissipated at the output load resistance

 

[Ivan Antunovic]

Yes power into the base is negligible but I didnt understand first part of your post?