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Base voltage divider question?
What is this formula R1 / R2 = ~1 / 1.17?
Why did he multiply 75kΩ with 2.17 / 1.17 to get R1?
Where did you get the 6.9V value?
Oh 7.5V - 0.6V
Oh 15V - 8.1V
1 Answer
- billrussell42Lv 73 years agoFavorite Answer
That is a strange way of calculating bias. Not one I would ever use.
ratio of voltage across those two resistors is 6.9v/8.1v according to the schematic.
and that is 1/1/17
ratio of R1+R2 to R2 is (1+1.17)/1.17 = 2.17/1.17
skip all that, here is how you calculate R1 and R2.
Take HFE of transistor and divide Ic by that to get Ib. In this case 1000µa/100 = 10µA.
You want the bias current thru R1,2 to be higher than that, say 10 x, 100 µA.
R2 = 8.1/100µA = 81kΩ
R1 = 6.9/100µA = 69kΩ
those values will work as well as the ones from that utube video.
he used a different ratio, looks like 5x, 50µA, which gives you 160k and 140k, essentially what he has.