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PreconditionValue
Vcc12v
Vi3.3v
RL155Ω
NPN BC337
Vbe(sat)1.2v
Vce(sat)0.7v
hFE (@100mA)100


Calculations for Ic:

Ic = (Vcc-Vce)/RL = 12v11.3v/155Ω = 78mA73 mA


Calculation for Vb

Vb = Vi - Vbe(sat) = 3.3 - 1.2 = 2.1v

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It is common to assume that base current is 1/10 of the collector current.


Ib = Ic/10 = 7873/10 = 7.8mA3mA

Rb = Vb/Ib = 2.1/0.0078 0073 = 269 Ω288 Ω


Tested with 220 Ω and it worked.

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hFE=100 (@100mA)

Ib = Ic/Hfe = 7873/100 = 0.78mA73mA

Rb = Vb/Ibx3 = 2.1/(0.00078x300073x3) =  897 959 Ω


This would be the max value for Rb.

Calculating using the online calculator

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hFE=100

Rb = 960 Ω 

This would be the max value for Rb.Why are these all so different??? I gues it would work from 200 to 1KΩ.


Formulas

Ic=(V-Vce)/RL

Ib=Ic/hFE

Rb=(Vi-Vbe)/(3*Ib)


References

ReferenceURL
Base Resistor Calculatorhttps://www.petervis.com/GCSE_Design_and_Technology_Electronic_Products/transistor_base_resistor_calculator/transistor_base_resistor_calculator.html
Discussion Forumhttps://forum.allaboutcircuits.com/threads/calculating-base-resistor-for-transistor.78483/

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