Well since we work in digital, common calculation is to multiply by ten the Base current needed.
If 1K to the collector. Ic = 5/1000 = 5mA
HFE = 70 (take the minimum to ensure...
Ib= (Ic/HFE) * 10 = 0.7ma
Rb = (5 - 0.7) / 0.7mA = 6k at minimum
By the Maths, i figure that 5.6k, 5.1k or 4.7K as base resistor can also work.
In many application you'll see 1k to base, 1k to collector too or same base value as collector one.
Last edited by mister_e; - 20th January 2005 at 16:36.
Steve
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