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Questions tagged [hfe]

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0
votes
2answers
448 views

How to make amplifier (almost) Beta independent?

There are several ways to bias the quiescent point of transistor, when used as an amplifier. Among which voltage divider is best known for its improvements (improved temperature drift and beta ...
0
votes
2answers
213 views

Collector must be more positive than the emitter

My book (The Art of Electronics by Paul Horowitz and Winfield Hill) is stating something that seems to be the opposite of the example it is using. I am not going to school for my studies so I ...
0
votes
1answer
326 views

Choosing a transistor for a low power application

simulate this circuit – Schematic created using CircuitLab I have looked at a few guides, both on this forum and elsewhere, for choosing a transistor. I know to look for things like HFe and ...
2
votes
2answers
642 views

How does using negative feedback in biasing stabilize the beta of a BJT?

As far as I know the only reason beta is not reliable because it is temperature dependent. I have seen some diagrams about biasing to obtain stable beta. I read the negative feedback provides this ...
3
votes
1answer
382 views

How would a transistor's hFE affect a phase shift oscillator?

I have a phase shift oscillator circuit from a drum machine that I would like to reproduce as faithfully to the original as possible. My problem is that the 40 year old design uses a transistor (...
2
votes
1answer
355 views

How can a transistor lose its gain?

I do a lot of old radio repairs and I have always been told that the way to test a BJT transistor is to check its junctions which should work as diodes. But many times, I noticed that despite the ...
0
votes
2answers
93 views

How much the hFE value decrease at -40C

We are using to the BC856ALT1G on our products Below is datasheet of ON Semiconductor. I'd like to know that How much the hFE value decrease at -40C (low temperature) or How to calculate the hFE ...
0
votes
2answers
4k views

How to calculate actual hfe for low voltage source?

The datasheet for a transistor (said 2N2222) give us the hfe asuming a Vcc in the 30V range. For uses like Arduino projects, the Vcc is usually 5V, and under that conditions, the actual hfe is lower. ...
1
vote
0answers
764 views

hfe of transistor in active region

I've been studying NPN's and I'm trying to calculate the voltages and currents. Consider the following transistor circuit simulate this circuit – Schematic created using CircuitLab with Vb, ...
5
votes
1answer
713 views

Matching transistors for discrete opamp (audio use)

I am building some GAR2520 discrete opamps that require a matched pair of BC550(CTA) NPN transistors. I built a simple emitter follower with a 15V supply, biased at about half that. I input a 1khz ...
0
votes
5answers
740 views

Can you find an analytic expression for the (beta)hfe of a BJT?

I understand there are two models \$Ic=\beta Ib\$ and \$Ic=I_s exp (\frac{V_{BE}}{Vt})\$ for a bipolar junction transistor. However (correct me if I am wrong), I have not seen any textbook ...