Questions tagged [hfe]

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111 views

Have I understood transistors correctly?

These are what I know and what I've concluded about transistors. Correct me if I'm wrong: It's all about current. When we have a determined voltage differential source, BJTs are used to boost the ...
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0answers
57 views

Maximum Current Gain Possible for a 100 mA PNP transistor

I have a pulse charging circuit where the maximum current is limited by the hFE of the PNP transistor (DTA144EE). The typical hFE at room temperature is ~220 as shown in the plot below. There is of ...
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2answers
105 views

How to interpret the hFE of a datasheet?

How to interpret the hFE of a datasheet? How should I interpret this data, the image is extracted from a PN2222A datasheet With Vce = 10v and Ic = 150ma I can obtain an hfe between 100 and 300 I ...
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1answer
89 views

Is the hFE of a bipolar transistor independent of Vce?

In the datasheet they express the hFE for a fixed Vce, sometimes they put 1v other times 10v, but if the gain is independent of Vce this data is not really important, the hFE indicated in the ...
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1answer
49 views

hFE value (a.k.a β or gain factor) for transistor, at different voltage

I've been looking into the BC337 NPN transistor, and I saw in the hFE graph on page 3 of the datasheet, that the graph was at 1V from the collector to emitter. Is there any way to find out the hFE ...
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1answer
63 views

Calculating base current without knowing current amplification

So I'm currently doing an assignment where I'm meant to design my own common emitter. I'm supposed to choose the Q-point of my collector current and choose my own signal amplification (Av). During ...
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3answers
147 views

effects of hFE in emitter follower?

There are multiple hFE options for BD139s, with the higher hFE being slightly more expensive. What advantages or disadvantages, if any, would the higher hFE parts have in emitter follower circuit?
4
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4answers
629 views

Will a BJT blow up if there isn't any load/resistance either in collector or emitter?

Taking NPN BJT as example. When an NPN BJT is operating in the active mode, \$I_C = \beta I_B\$. That means we can fully control the current pass through the BJT by controlling \$I_B\$ only. In such ...
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2answers
1k 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 ...
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2answers
427 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 ...
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1answer
2k 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 ...
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2answers
2k 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 ...
5
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1answer
619 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
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1answer
895 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 ...
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2answers
117 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 ...
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2answers
8k 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. ...
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1answer
1k 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, ...
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1answer
1k 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 ...
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5answers
1k 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 ...