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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.

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 DC bias poi …
  • 17.7k
0 votes

If two BJT bases are shorted, where does the voltage come from?

If you care about leakage currents, and perhaps the switching speed of the circuit, I would suggest adding pull-down resistors between the base and emitters of each of the 4 H-Bridge transistors. Anyt …
  • 17.7k
0 votes

Influential factors setting the operation point of a bipolar transistor?

You typically bias a transistor to optimize some conflicting, variable, and perhaps unclear goals: 1: To minimize wasted power (current) 2: To allow the AC component of a signal (added to the DC bias …
  • 17.7k
1 vote

Transistor bias circuit

That PNP is biased off. I suspect you really intended to put an NPN there, and exchange the E & C ?
  • 17.7k
4 votes
Accepted

Changing Vbe_on in Pspice - Student capture

There is no 'VBE' parameter in a SPICE model. This is indirectly controlled via the 'IS' parameter. Be aware that a BJR doesn't just "turn on" at a single VBE voltage -- it's all gradual even from VBE …
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0 votes

PN junction voltage drops in a Saturated BJT

The definition of saturation is VBC > 0. Thus VCE is less than VBE. Under normal conditions, VBE is around 0.7 V, and the transistor will operate reasonably predictability until VBC is over 0.3 or 0 …
  • 17.7k
3 votes
Accepted

Gate to Source Resistor turning MOSFET into BJT

A BJT has a very definite relationship between VBE and currents. MOSFETs have lower gm (dI_drain/dVGS) which is not as precise as BJTs. … The current that flows in your R_GS is linear with VGS; a BJT is exponential. There is no definite relationship (like beta) between resistor current and drain current. …
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13 votes
Accepted

NPN transistor resistor from base to GND. Is this useful?

Depending on the MCU, its IO pin may be tri-state at power up (or reset) until it is programmed to either a '0' or a '1'. If it is tri-state, small amounts of leakage (on the transistor, pin, or PC bo …
  • 17.7k
0 votes

Is it possible to make this BJT-based voltage limiter more \$\beta\$-independent and tempera...

This circuit might work in a 'DC' mode; however it will not work well (or at all) in practice because of AC (loop gain) stability. Note that this circuit is not particularly precise -- the clamping po …
  • 17.7k
1 vote

Why does the emitter current increase with an increase in collector to base voltage in the c...

There are two different effects on collector current that happen when VCE is increased. Which one depends on whether the VBE is held constant, or the IB is held constant. Base current is the sum of B …
  • 17.7k
1 vote
Accepted

Can you (theoretically) reverse bias a BJT?

Yes, you can exchange emitter and collector, but the transistor won't work as well. Generally the emitter is doped much higher than the base, and base is doped higher than the collector. This improves …
  • 17.7k
1 vote

What is BF in transistors?

While beta is useful To broadly describe BJT performance, it is not a fundamental parameter of the device. …
  • 17.7k
5 votes
Accepted

BJT Capacitance at RF limmitations

You could use a somewhat higher emitter R -- to get slightly more gain; then add a 2nd stage (which would now be driven from a lower impedance (=re of the BJT, ~ 2.6 ohm @ 20 mA). …
  • 17.7k
1 vote
Accepted

Transistor H-Bridge Help

Yes, you need an additional set of transistors. Basically, for each PNP, connect a R (2 k ?) from base to emitter. Then connect an NPN: collector -> PNP base; base -> GPIO, and emitter to GND via 2 kΩ …
  • 17.7k
2 votes

Transistor to switch low voltages (< 1V)

A MOSFET is easier to use than a BJT in this case, although a BJT would work. …
  • 17.7k

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