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BJT stands for Bipolar Junction Transistor. It is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications.

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In a diode-connected BJT like this, the BJT is kept right at the edge of active vs saturated mode and so only a small base current is required. Most of the "diode current" flows via the collector to …
answered Mar 29 '18 by jonk
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By assuming that Vbe=0.7V it's easy to progress, however no such thing is stated (the only data given is that β is very large), so i was wondering if there is a way to find Ic without that assu …
answered Jun 3 '18 by jonk
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}\$ from your DAC, too. You should use beta matched BJT pairs for \$Q_3\$, \$Q_5\$, \$Q_4\$, and \$Q_6\$ -- such as the BCM61 and BCM62. (I didn't add beta-mismatch compensation to the circuit … like 24 bits of linearity, precision, or accuracy (no one can provide that kind of accuracy.) But you are just using this for driving a base current, I gather. It should be okay for BJT parameter extraction and curve tracing. …
answered Nov 20 '16 by jonk
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}&=V_{CC}\frac{R_2}{R_1+R_2}\\\\ R_{TH}&=\frac{R_1\:R_2}{R_1+R_2} \end{align*}$$ A very simple KVL yields: $$V_{TH}-I_B\cdot R_{TH}-V_{BE}-I_E\cdot R_E=0\label{kvl}\tag{$KVL$}$$ Assuming the BJT is … through some basic "sanity checks." If the sanity checks fail, then the BJT would instead almost certainly be saturated and therefore the assumption above (that \$I_E=\left(\beta+1\right)\cdot I_B …
answered Nov 12 '17 by jonk
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I'm sorry for the delay. I've been busy. I hope you won't mind if I take a moment now to expand on my earlier comment about an approach to the \$\uparrow\$ transition voltage calculation. You can deci …
answered Jun 6 '18 by jonk
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are asking, the collector is often said to be approximately "a current source" (in a PNP case; or "current sink" for an NPN.) Current sources/sinks are ideally infinite impedance. (Of course, a BJT is … are true. If you are thinking about a specific situation where a certain, known base current is being supplied (or \$V_{BE}\$ is known) and if the BJT is in its active region of behavior (\$\beta …
answered Oct 27 '17 by jonk
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Supposing your load is \$5\:\textrm{A}\$ and you are interested in learning about BJTs, you have two options for the final power stage BJT -- NPN or PNP. Sometimes, this is determined by things like … this current compliance range, you should be thinking about a TO-220 style package (or better.) A power BJT will drop some \$V_{CE}\$ across the switch, no matter what you do about it, and all of …
answered Dec 12 '16 by jonk
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Then let's just ignore the equations, then. The base current doesn't cause collector current. It permits collector current. In the PNP BJT you show in your circuit (I'm ignoring all of your circuit …
answered Sep 2 '16 by jonk
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, \$V_{BE}\$, which is somewhat impacted by the collector current and very much impacted by temperature... so that's important... and \$V_{CE}\$ is immediately related to whether or not the BJT is … about is the Ebers-Moll model. It's level 1 model includes three distinct ways of looking at the BJT: transport, injection, and hybrid-pi. They are equivalent views, but they have different areas …
answered Aug 13 '16 by jonk
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. I hope that helps a little in trying to understand the differences (there is a difference of sorts, but it is usually not something anyone dwells on.) The take-away here is that: Average BJT … current gain is remarkably flat over a wide range of collector currents. This allows for some planning regarding a circuit design. BJT current gain can vary by a factor 1.5 or more between parts within a …
answered Jan 9 '18 by jonk
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the answer is "yes," but with all those caveats about reality and actual variations with real BJT parts. In general, in the forward active region, the relationship between the collector current … V_{BE_{CAL}}+V_T\cdot\operatorname{ln}\left(\frac{I_C}{I_{C_{CAL}}}\right)$$ So, if I know that my BJT exhibits \$V_{BE_{CAL}}=700\:\textrm{mV}\$ at \$I_{C_{CAL}}=5\:\textrm{mA}\$, then I would find …
answered May 31 '17 by jonk
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your question as well as Neil managed to read it. The BJT physics is pretty interesting. If you want to understand one of the better models for it, look up the MEXTRAM model. That will give you some … : simulate this circuit – Schematic created using CircuitLab The whole point of arranging the voltage source polarities as shown is that the BJT is either in active mode, or saturated. It's not possible to …
answered Jan 31 '18 by jonk
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Your circuit has the basic structure of an NPN \$V_\text{BE}\$ multiplier. Typically, a \$V_\text{BE}\$ multiplier is operated with a current source (or sink, as in your case) and they provide a predi …
answered Jun 7 by jonk
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quantities will be anywhere near as accurate given actual parts. All of the inputs to these calculations are, at best, approximate. The value of \$\beta\$, assuming that the BJT is in an active region … design, reasonable variations in supply rails, variations around nominal resistor values, and BJT variations around \$V_{BE}\$ and forward \$\beta\$ values should be bracketed during the analysis and …
answered May 28 '17 by jonk
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BJT model}\\ \textrm{ignoring the Early Effect:} \\ I_C&=I_S\cdot\left(e^{\cfrac{V_{BE}}{V_T}}-1\right) \\ \textrm{move }I_S\textrm{ over to the other side,}\\ \cfrac{I_C}{I_S}&=\left(e^{\cfrac{V_{BE …
answered Dec 29 '16 by jonk

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