What are the differences between MOSFETs and Triodes when used as switches?

MOSFET and Triode are very common electronic components, both can be used as electronic switches, but also on many occasions to exchange the use of switches, as a switch to use, MOSFET and Triode have a lot of similarities, there are also different places, so the two should be how to choose?

 

Triode has NPN type and PNP type.MOSFET also has N-channel and P-channel.The three pins of MOSFET are gate G, drain D and source S, and the three pins of Triode are base B, collector C and emitter E. What are the differences between MOSFET and Triode?

 

 

N-MOSFET and NPN Triode used as switching principle

 

(1) Different control mode

Triode is a current-type control components, and MOSFET is a voltage control components, Triode on the input voltage requirements of the control side is relatively low, generally 0.4V to 0.6V or more can be realized Triode on, by changing the base limit current resistor can change the base current. The MOSFET is voltage-controlled, the voltage required for conduction is usually about 4V to 10V, and when saturation is reached, the required voltage is about 6V to 10V. In the control of lower voltage occasions, the general use of Triode as a switch, or Triode as a buffer control MOSFET, such as microcontrollers, DSP, PowerPC and other processors I / O port voltage is relatively low, only 3.3V or 2.5V, generally will not directly control the MOSFET, the lower voltage, MOSFET can not be conduction or internal resistance of the large internal consumption In this case, Triode control is usually used.

 

(2) Different input impedance

Triode's input impedance is small, MOSFET's input impedance is large, the junction capacitance is different, Triode's junction capacitance is larger than the MOSFET, the action accordingly on the MOSFET to be faster than the Triode; MOSFET in the stability of the better, is a multi conductor, small noise, thermal stability is better.

MOSFET's internal resistance is very small, and Triode's on-state voltage drop is almost constant, in small current occasions, generally use Triode, and use MOSFET even if the internal resistance is very small, but the current is large, the voltage drop is also very large.