What are the differences between MOSFETs and transistors in the ON state?

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A MOSFET is a field-effect transistor that is widely used in both analog and digital circuits. A triode is also known as a bipolar transistor; it is capable of controlling the flow of current and amplifying smaller signals into electrical signals with higher amplitudes. Both MOSFETs and transistors have an ON state; so what is the difference between them when in this ON state? For MOSFETs and transistors in their ON state, MOSFETs are typically characterized by Rds, while transistors are usually described using saturated Vce. So, is it possible to have the opposite situation, where the transistor uses saturation Rce while the MOSFET uses saturation Vds? When a transistor is in the ON state, it operates in the saturation region, and the conduction current Ice is primarily determined by Ib and Vce. Since the base drive current Ib of a transistor generally cannot be kept constant, Ice cannot be simply determined by Vce alone; therefore, saturation Rce cannot be used to represent it (as Rce changes). Since Vce is small in the saturated state, transistors are generally represented by their saturated Vce. When in the ON state, a MOSFET operates in the linear region (equivalent to the saturation region of a transistor). Similar to transistors, the current Ids is determined by Vgs and Vds. However, the drive voltage Vgs of a MOSFET can generally remain constant; thus, Ids is affected only by Vds. That is, with Vgs fixed, the on-resistance Rds remains essentially unchanged, which is why the Rds parameter is used for MOSFETs. Current can flow in both directions through the D and S terminals of a MOSFET. It is this outstanding advantage of the MOSFET that eliminates the concept of DCM in synchronous rectification, allowing energy to be transferred from the input to the output as well as from the output back to the input. It enables two-way energy flow. Since the points D and S of a MOS transistor can be swapped, then why is the term DS defined? For the MOS transistors inside an IC, they are certainly completely symmetric during manufacturing; the definition of D and S serves to facilitate discussions regarding the direction of current flow as well as calculations. Secondly, since D and S have been defined, what is the difference between them? For power MOSFETs, in some special applications—such as for voltage tolerance or other reasons—it may be necessary to create a lightly doped region at the D terminal of the NMOS to ensure voltage tolerance; in such cases, D and S differ from each other. Thirdly, after swapping D and S, what are the differences in the characteristics of the MOS compared to before? For example, Vth, Miller effect, parasitic capacitance, on-resistance, and breakdown voltage Vds. After the DS swap, when Vgs=0, the transistor can still conduct as long as Vds>0.7V, whereas it could not do so before the swap. When Vgs > Vth, an inverted layer channel has been formed, and after inversion the two have identical properties. Determining D and S: We are simply saying that the current can flow from D--to--S, or it can also flow from S----to---D. But this does not mean that the names of the D and S terminals can be swapped. The width of the DS channel is controlled by the GS voltage. Once G is fixed, who S is is determined. If the above is determined as S-side, it is considered D. What was originally D is considered to be S, and a voltage is applied to G and this S; as a result, the channel does not change and remains closed. Before Vgs reaches Vth, Cgs is charged through the drive resistor R; the model for this stage is a simple RC charging process. When Vgs reaches Vth, the DS conductive channel begins to open, and Vd starts to drop sharply. According to I = C*dV/dt, current flows through the parasitic capacitance Cgd in the direction: G --> D. According to KCL at terminal G, the Igd current splits the IR current; most of the drive current flows toward Igd, with only a small portion continuing to flow toward Cgs. Therefore, there is a short section where Vgs changes relatively smoothly. This is the miler platform.