Step 4: Calculating R1
You can find the value of hfe in your datasheet:
Mine says for BC548 its 75 at 10mA at 10V. Its not very precise cause its very difficult to build transistor with a accurate hfe.
hfe = Ic / Ib
We know hfe and Ic so lets calculate Ib:
Ib = Ic / hfe
For BC548:
Ib = 0.03 A / 75
Ib = 0.0004 A => 0.4 mA
Due to Ohms Law:
R1 = U / Ib
R1 = 5V / 0.0004 A
R1 = 12500 Ohm
This is not very accurate to so we use 10kOhm.
Mine says for BC548 its 75 at 10mA at 10V. Its not very precise cause its very difficult to build transistor with a accurate hfe.
hfe = Ic / Ib
We know hfe and Ic so lets calculate Ib:
Ib = Ic / hfe
For BC548:
Ib = 0.03 A / 75
Ib = 0.0004 A => 0.4 mA
Due to Ohms Law:
R1 = U / Ib
R1 = 5V / 0.0004 A
R1 = 12500 Ohm
This is not very accurate to so we use 10kOhm.
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