Because of wrong saturation equation relating the base current and collector current.1. How am I getting a different equation than yours pls?
Because you do not know if the transistor you are going to buy has the max beta, min beta or any value in between. You want to ensure saturation for whatever transistor you buy, which leads to calculate for the worst case.2. In the first expression, why are we considering Bmin than Bmax.
Vbe(sat) max.3. For calculation purpose, which value of Vbe should I use: Vbesat. Or Vbeon (min, typical, max) ?
No. Is more difficult to achieve saturation with little collector current or with a lot of collector current?4. Also should the calculations not be done for Icmin to ensure that the tx. remains in saturation for least current?
Because of wrong saturation equation relating the base current and collector current.
No. Is more difficult to achieve saturation with little collector current or with a lot of collector current?
See how they defined saturation state:
IC = 10mA , Ib = 0.5mA --> B = 20
IC = 100mA, IB = 5mA --> again B = 20.
So in your case: 48mA (Yes. I was wrong with may "6 times" assumtion) --> / 20 = 2.4mA.
microcontroler voltage drop high for driving 2.4mA: maybe 0.3V --> look into the datsheet
base resistor --> to be calculated
Klaus
Post #3, which is the conclusion of post #9. If the datasheet is using forced beta of 20 in their datasheet, then use that as minimum beta, or lower.Pls. inform me of the right equation relating base current and saturation current in an npn bjt for saturation in this case pls. And thanks again.
You didn't read thoroughly. There's figure 4 for Ic/Ib = 10 and a Vce(sat) specification in the electrical characteristics table for Ic/Ib = 20. Strictly speaking, Ic/Ib in saturation isn't current gain B. It's an externally enforced current ratio, sometimes called "forced beta". Obviously forced Ic/Ib can be arbitrarily smaller than B but not larger.Sorry... could not find this on the given link of the datasheet.
I already told you to read the datasheet on this. Look for VOH.Why should there be an additional voltage drop of 0.3v.
Surely, the transistor is even more saturated at lower Ic.Do you suppose the resistor Rb value which was calculated for Ic corresponding to current from 8 segments will still keep the transistor in saturation for such low current?
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