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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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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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