Electronics & Software – Tips & Guide


Why is MOSFET better than BJT

Why is MOSFET better than BJT?

This is because the mosfet works faster because it uses metal oxide regardless of the bjt that relies on the electronic hole combination.

mosfet consumes much less power when switching at high frequency because of its faster switching speed. this is due to the fact that the mosfet leads by grid-oxide controlled field effect and not by electron / hole recombination (which is slow) as in bjt. The gate control circuit is much simpler in the mosfets.

There are several reasons that stand out:

lower conduction losses: bjts have a constant saturation voltage drop of about 0.7 V, while mosfets have an on-resistance of up to at 0.001 ohm, leading to very low power losses. of course, it’s only up to a point.

Very high input impedance: Bjts need a low base current to drive a larger collector current. they act as current amplifiers. The mosfets are voltage controlled and have virtually no gate current, the gate acts as a low value capacitor (a few picofarads to several nanofarads). This can be of considerable advantage in switching and high current applications because the power bjts have a medium to low gain, which requires high base currents (sometimes of the order of several amperes!) To generate high currents.

nowadays we use a lot of integrated circuits or chips, and for that we want to put a lot of devices in a small area (order of nano or micro) so fet occupy less area than bjt and it is about 1 / 5th.

  • The operation of bjt is not easy compared to fet.
  • fet can be made easily.
  • even the fets can be used as passive elements rather than as amplifiers


Mosfet has several advantages over bjt

mosfet is much faster than bjt because in a mosfet, only majority carriers are the current. the device switches much faster than bjt and is therefore used for switching smps power.

mosfet does not suffer huge variations of point q, it’s the opposite we see in bjt. because the collector current changes due to changes in temperature, current gain, base voltage of the transmitter. but this huge variation is not found in Mosfet since it is a majority carrier.

mosfet has a very high input impedance in the megohms range while bjt in the kiloohms range .thus making the mosfet very ideal for amplifier circuits.

mosfets are less noisy than bjts. in an electronic context, noise refers to random interference in a signal. When a transistor is used to amplify a signal, the internal processes of the transistor will introduce some of this random interference. Bjts usually introduce more noise into the signal than mosfets. This means that the mosfets are better suited for signal processing applications or voltage amplifiers.

Mosfets can be much smaller than bjts. many more mosfets can be placed in a smaller space than the bjts. for this reason, mosfets constitute the bulk of the transistors used in chips and computer processors. Mosfets are also easier to manufacture than bjts because they take less action.