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What is the difference between a transistor and a MOS tube?


      1, the nature of the work: the transistor tube current control, MOS tube belongs to the voltage control.
      2, the cost of the problem: the transistor is cheap, MOS tube expensive.
      3, power consumption problems: transistor loss.
      4, driving power: MOS tube is often used to power switches, and large current local switching circuit.
      Three transistors are relatively inexpensive, easy to use, commonly used in digital circuit switch control.
The MOS tube is used for high frequency, high speed circuit, high current situation, and sensitive to the control current of the or the drain electrode.
      MOS tube not only can do the switch circuit, also can do the analog amplification, because the gate voltage in a certain range of change will cause the change of the resistance between source and drain.
      The main difference between the two is: Bipolar tube current control device (control is the larger collector current through the current small), MOS tube voltage control device (by controlling the gate voltage between source and drain resistance).
      MOS tube (FET) conduction voltage drop, conduction resistance is small, does not need the gate drive current, low loss, simple drive circuit, self protection diode, good thermal properties, suitable for high power parallel faults, the switching speed is not high, more expensive.
      Three transistor switching speed, large transistor Ic can do a lot, the disadvantage of large losses, large drive current, drive complex.
      Generally low cost occasions, the general application of the first consideration with the transistor, not to consider the MOS tube.
      In fact, it is wrong to say that the current control is slow and the voltage control is fast. To really understand the work of the bipolar transistor and MOS transistor to understand. A transistor is to work by the carrier motion, using NPN tube emitter follower for example, when the add voltage, composed of the and emitter of PN node for multi block ( for hole emitter for electron diffusion) movement, this PN junction will induce the electrostatic by launching area to its area (i.e., in the construction field) as the point is applied voltage of the point to the launch area, when the of electric field voltage is greater than the built-in electric field, carrier (Electronic) is likely to launch from the to the voltage of the the value of the positive guide of the PN junction voltage (engineering generally 0.7V). But the two sides each PN node will have charge, if the collector emitter voltage is added, in the electric field, the electron emission region to the motion (in fact is all electronic move in the opposite direction), the width is very small, it is easy to reach across the electronic collector region here, with PN hole composite (near the collector), in order to maintain the balance of electron acceleration outside the collector collector region is in motion under the action of the electric field, and the hole is PN junction, this process is like an avalanche. Collector of the electron back to the emitter through the power supply, which is the principle of the transistor. Transistor, two PN node will induce charge, as the switch is turned on, the transistor in the saturation state, if the transistor to charge PN junction induction should be restored to a state of equilibrium, this process takes time. And the MOS transistor working way is different, there is no recovery time, so it can be used as a high speed switch tube.
      (1) the field effect transistor is the voltage control element, and the transistor is the current control element. Field effect transistors should be chosen in the case of only allowing less current to be taken from the signal source, while the signal voltage is lower and the transistor should be used in the condition of taking more current from the source signal source.
      (2) the field effect transistor is the use of majority carrier conduction, so called unipolar devices, and the transistor is the majority carrier, but also the use of minority carrier. Bipolar devices are called.
      (3) some of the source and drain of the field effect tube can be used, and the grid voltage can also be negative, and the flexibility is better than that of the transistor.
      (4) FET can work in a very small current and low voltage conditions, and its manufacturing process can easily put a lot of FET integrated on a silicon chip, so the field effect tube has been widely used in large scale integrated circuit.
      (5) the field effect transistor has the advantages of high input impedance and low noise, so it has been widely used in various electronic devices. In particular, the input stage of the whole electronic device can be obtained by the use of the field effect tube, and the performance of the general transistor is difficult to achieve.
      (6) the field effect tube is divided into two major types: junction type and insulated gate type, and the control principle is the same.
Other comparison:
      1, the transistor is a bipolar tube, that is, the work of the tube by the hole and free electrons two kinds of carriers involved.The field effect tube is a single pole type tube, that is, the work of the tube is only a hole, or only a free electron to participate in conductive, only one carrier.
      2, the transistor is a current control device, there is an input current output current.The field effect tube belongs to the voltage control device, and the output current is not provided with the input current.
      3, the input impedance of the transistor is small, and the input impedance of the field effect tube is large.
      4, some field effect transistor source and drain can be exchanged, the collector and emitter of the transistor can not be exchanged.
      5, the frequency characteristics of the field effect transistor is not as well as the transistor.
      6, the noise figure of the field effect tube is small, which is suitable for the low noise amplifier.
      7, if the signal source current is small should choose the field effect tube, on the contrary, the choice of the transistor is more appropriate.

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