Need help in a small transistor project please

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shubham123

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I have to make a project on 'Transistor As A Switch' and draw a graph between the input & output voltage showing the cut-off region,saturation & the active region.
I have attached the circuit diagram.The problem is that I dont know what values to take for the various components.

I tried making it with BC547 or BC 548 transistor,100k and 1k as Rb & Rc respectively,3volt for Vbb and Vcc(varied the voltage using a 10k potentiometer),Multimeter as Vi and Vo to measure the input and output voltage.Could not get any significant result,the votage kept varying a lot.

From what I understand,when Vbb will be less than 0.7V then multimeter Vo reading is equal to Vcc.As Vbb increases above 1V,Vo decreases.But as I said there was irregular voltage in the multimeter Vi.
Thanks a lot
 
added footnote:

transistors are about current flow. What is the open loop gain (λ) of the transistor you are using? The resistors turn voltage into current. (Vbb - .7) / RB = Ib. This will set a corresponding Ice (Ie = Ice + Ib). Then, Vo = Vcc - (Ice x RC).

the data sheet calls hfe the open loop gain. See charts for operation.

Also, when a transistor is used for a switch, you assume the gain is 1/10th and set your base current 10x higher than you normally would for a given collector current to make sure the transistor goes into saturation. The transistor gain is also dependent on the collector/emitter voltage. See charts on data sheet...

View attachment BC547.pdf
 
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Just got what I think is the correct readings.I had connected the potentiometer
& transistor wrongly.I have attached the new readings.Let me know if they are correct.Thanks a lot for answering.

View attachment 68607
 
We can't say that they are numerically correct without knowing the current gain (hfe, or β) of the particular transistor, but they look perfectly reasonable and follow the correct pattern.
 
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