9
votes
Accepted
Will a bipolar transistor have gain, even if the collector has no curent?
There's only one relationship between currents in the transistor which is always true; it's an application of Kirchhoff's Current Law (KCL):
$$I_E = I_C + I_B$$
Everything else is conditional, ...
- 10.4k
8
votes
Will a bipolar transistor have gain, even if the collector has no curent?
When there is no collector current all the emitter current is from the base and all base current flows "out of" the emitter.
If you define current gain as Ic/Ib then there is by definition ...
- 785
8
votes
Accepted
What are the limits of the Ebers-Moll model for large currents?
In general, DC BJT models include a lot more than some simple Shockley diode model that you show.
One factor that I discuss here is the knee that occurs due to the increasing importance of minority ...
- 72.8k
6
votes
Accepted
Converting Open-Drain to Active-Low
An open drain just means that a MOSFET internally connects the pin to ground inside the IC:
simulate this circuit – Schematic created using CircuitLab
The output being Hi-Z just means that the ...
- 7,499
5
votes
Why use emitter current from DC response in calculations?
In "small signal AC" analysis, you assume that the amplitude of the AC signal is negligibly small compared to the DC bias current. Therefore the AC signal doesn't significantly perturb the ...
- 16.5k
4
votes
Finding the Q-point of a transistor: disambiguation
In other words, 'find the Q-point of this transistor' does not mean 'find the optimal way of biasing this transistor', but rather, it means 'find how this transistor has been biased'.
Is that correct?...
- 3,559
3
votes
Accepted
Finding the Q-point of a transistor: disambiguation
It depends whether you are doing analysis or synthesis.
Analysis is easier, so it's what students are given as an exercise. With these components, work out what's happening.
What engineers really need ...
- 145k
3
votes
BJT circuit with totem pole output
When the emitter-base junction of the input transistor is reverse biased, then the base-collector diode conducts from base to collector, thus applying current to the base of the circled transistor, ...
- 3,559
3
votes
What happens when Vce is more than the value in the datasheet?
Sometimes the datasheets give curves which also give a good indication of the comparable scale of different effects, and one of the important ones is temperature.
The following is from OnSemi's 2n2222 ...
- 3,722
3
votes
Accepted
What happens when Vce is more than the value in the datasheet?
I want to know what happen to hfe when Vce is more than 10 V or lower
The voltage of 10 volts is just a nice handy figure that guarantees the BJT is in its active (non-saturated) region: -
So, if ...
- 396k
3
votes
Will a bipolar transistor have gain, even if the collector has no curent?
A bipolar transistor is a current-controlled current limiter.
The base-emitter current is the input and can be chosen at will. The collector-emitter current is the output where the current limiting ...
- 831
2
votes
Will a bipolar transistor have gain, even if the collector has no curent?
However large the base current happens to be, all of it will flow in the emitter circuit irrespective of how much collector current there is. If the collector is left unconnected then Ie = Ib.
- 6,969
2
votes
Accepted
Is there a typo in this question because I don't think the emitter node of Q2 should be grounded?
Yes, that's a typo, but you don't have to go that far in your reasoning. "because then the current source from Q1 would be between two nodes that are grounded" -- maybe that's true, maybe ...
- 38.8k
2
votes
What is the meaning of Vce in DC current gain?
The simplifies model of a transistor is that you can multiply Ib by hFE to get Ice. But if you look at the datasheet you'll find graphs with curves that show, that hFE is not constant.
hFE depends on ...
- 1,967
1
vote
Is there anywhere I can download BJT Transistor I-V data?
I am interested in writing some simulations involving BJTs which
requires more information than can be obtained from the typical
transistor equations.
Get a simulator (which uses dozens of parameters ...
- 396k
1
vote
BJT circuit with totem pole output
The input part of the TTL logic gate above can be easily explained at low input voltage (logic 0) by the phenomenon of current steering, the essence of which is: If we connect two diodes with ...
- 9,518
1
vote
What is the actual input resistance of a BJT transistor (amplifier circuit especially)?
The datasheet of a 2N3904 transistor has a graph of its typical input impedance vs collector current:
- 2,581
1
vote
Why in the output characteristic graph of BJTs, within the saturation region, is the collector current positive?
The behavior in the deep saturation region is not correctly shown in that diagram.
Here is a simulation for Ib = 10mA, 0 < Vc < 100mV and a 2N4401:
If the collector voltage is less than about ...
- 342k
1
vote
Why aren't the majority charge carriers attracted by terminals of a battery when the p n junction is reverse biased?
why will the free electrons not move toward the battery's positive terminal instead? at least to some extent, it should happen: free electrons from the n side go to the positive terminal of the ...
- 13.7k
1
vote
Why use emitter current from DC response in calculations?
When Re (the external emitter resistor) is not large compared to re (the intrinsic emitter resistance), the variation in Ie (the emitter current) as the input moves up and down causes distortion of ...
- 6,969
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