Question about the beta value in BJT

[Audioguru]

dependence of beta on temperature in bjt

Yes of course we can use the datasheet's minimum base current to saturate a transistor, provided that it's available... but some datasheets I encounter (most of them) has no such information.....
take for example on the datasheet link I've provided before:
**broken link removed**

All datasheets list the max saturation voltage loss at a fairly high base current.
This one that you posted also does.

 

[pinoy]

bjt hfe beta

... yeah... that's what's I'm talking about... Ic/Ib of that VCEsat is 20... just like in the graph, right? I use the graph from the datasheet (VCEsat vs Ic at a certain beta, Ic/Ib = 20), then I can calculate my required Ib in order to make sure that my transistor is saturated at certain Ic...

For example: My transistor collector current Ic=100mA....
then the base current that can saturate the transistor is: Ib=100mA/(20) = 5mA

then in my design, I should bias my transistor's base to have a base current of not less than 5mA to make sure that my transistor will operate at saturation region...

 

[Audioguru]

beta hfe mid

Yes!
That is why they publish datasheets.
So you make a circuit that works properly.

Added after 8 minutes:

The written spec's are guaranteed.
The graphs are for "typical" transistors and many are much worse.

If you design a circuit for typical transistors then most will work but many will not.
But if you design circuits using the guaranteed minimum and maximum spec's then ALL your circuits will work pefectly.

 

[electronics_kumar]

bjt 2n3904 beta

yeah right... we all know about that... "there's no such thing as ideal in this world"
...note: beta in saturation is different from the beta in active region.... in saturation, beta is small (around 10~20) and in active, beta is higher (around 100~400).....

how to strike this relation any equation or graph to quote

 

[Audioguru]

typical values for beta of bjt

Quote the written guaranteed spec's from the datasheet.
For the 2N3904 they are:
1) hFE, DC Current Gain, IC= 10mA, VCE= 1.0V, 100-300
2) Collector-Emitter saturation Voltage, IC= 10mA, IB= 1.0mA, 0.2V max

The graphs show the typical values, not minimum and not maximum.