What is the different between BJT and mosfet transistor

Posted in BJT
at 2019.12.17

What is the different between BJT and mosfet transistor?

I think a BJT transistor is different because there is always power going on all the time . Being turned on or off when used in a circuit.

Mosfet device is very different, so that almost no current flows when it is off . it can be fully activated or deactivated by a tiny amount of grid voltage ..

A mosfet bjt are two types of transistors. They have many similarities and also some key differences.

Therefore, one or the other may be better suited to specific applications.

The physics of the device of the operation is beyond a few paragraphs but the devices work differently at the physical level. In terms of device behavior, which I think is more in line with the specific question, here is a high-level summary.

Mosfet:

  • Very high input resistance, purely capacitive in most cases.
  • The input impedance (gate) does not change in the drain / source bias conditions.
  • much better switch than bjt (no load storage problem in the triode)
  • much better to produce digital logic than bjt (see previous comment)
  • Lower transconductance (gm) per unit current.
  • Output resistance (rds) per unit of current less than bjt.
  • Intrinsic gain lower vs bjt (see the two previous comments).
  • More “mainstream” process technology. The numerical logic is superior in cmos (complementary mosfet).
  • Dominate the type of transistor ever produced.

Bjt:

  • good analog features:
  • less noise in most applications than the mosfet
  • better linearity in most amplifier structures than the mosfet
  • better intrinsic gain than the mosfet
  • less resistance input as the mosfet
  • current leaks as a function of the collector-emitter current
  • Bjt Saturation has characteristics that limit certain circuits.
  • low input resistance
  • Memory load is not as efficient as digital logic.

Both devices are effectively modeled with the same small signal circuit.

Both operate as voltage-controlled power sources.

It is the critical nature of the transistor. The input voltage controls the output current . It is a transconductor.

The BJT is often described as a device controlled by the current.

The beta describes a relationship between the base current and the collector current and a handful of applications use this effect, but that’s not the norm.

The reality is that the base-emitter voltage (vbe) controls the current in the emitter which in turn defines the base current leak.

This vision of the device’s operation is much more useful in 99% of applications and will improve the understanding and design of circuits.

None of the conventional amplifier circuits show beta as a significant term in the gain of the amplifier.