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| Precondition | Value |
|---|---|
| Vcc | 12v |
| Vbb | 3.3v |
| RL | 155Ω |
| NPN BC337 | |
| Vbe(sat) | 1.2v |
| Vce(sat) | 0.7v |
Ic = Vcc/RL = 12v/155Ω = 78mA
Vb = 3.3v - Vbe(sat) = 3.3 - 1.2 = 2.1v
Calculating using Ib=Ic/10
It is common to assume that base current is 1/10 of the collector current.
Ib = Ic/10 = 78/10 = 7.8mA
Vb = 3.3v - Vbe(sat) = 3.3 - 1.2 = 2.1v
Rb = Vb/Ib = 2.1/0.0078 = 269 Ω
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Tested with 220 Ω and it worked.
Using Hfe in your calculation:
Calculating using hFE
To guarantee that the transistor operates in the saturation region, we multiply the base current by a factor of three.
hFEHfe=100 (@100mA)
Ib = Ic/Hfe = 78/100 = 0.78mA
Rb = Vb/Ib Ibx3 = 2.1/(0.00078 = 2.7 kΩ00078x3) = 897 Ω
Calculating using the online calculator
See reference
hFE=100
Rb = 960 Ω
Why are these all so different??? I gues it would work from 200 to 1KΩ.
References
| Reference | URL |
|---|---|
| Base Resistor Calculator | https://www.petervis.com/GCSE_Design_and_Technology_Electronic_Products/transistor_base_resistor_calculator/transistor_base_resistor_calculator.html |
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