Adding MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) to circuit design can bring significant advantages in various aspects, making them a ubiquitous key component in modern electronic devices. Its main benefits include:
Excellent switch performance:
High speed switch: MOSFET is a voltage controlled device. Control the conduction between the source (S) and drain (D) by applying or removing a voltage relative to the source (S) at the gate (G). The gate input impedance is extremely high (can be regarded as a capacitive load), and it hardly draws steady-state current. This enables them to switch between ON and OFF states at extremely high speeds, with much lower switching losses than traditional bipolar junction transistors (BJTs).
Low switching loss: Fast switching speed means that devices consume less energy during state transitions, which is crucial for applications that require frequent switching such as switch mode power supplies (SMPS), motor drives, inverters, etc., and can significantly improve overall system efficiency.
Extremely low driving power consumption:
Due to the fact that the gate consumes almost no DC current in steady state (after being turned on or off) (only needing to overcome minimal leakage current), the driving circuit only needs to provide transient current to charge and discharge the gate capacitance to control the switching state. This makes the driving circuit very simple (such as directly driving with GPIO pins of microcontrollers), and the driving power consumption itself is very low, especially suitable for battery powered devices and systems that pursue high efficiency.
Low on resistance:
For power MOSFETs (especially low-voltage devices), the drain source resistance (Rds (on)) in their conducting state can be made very low (as low as milliohms). This means that when fully conductive, the voltage drop between the source and drain is very small, resulting in extremely low power loss (I ² Rds (on)) in the conductive state, thereby reducing heat generation and improving energy conversion efficiency (especially in the power transmission path).
Monopolarity and thermal stability:
MOSFET is a majority carrier device (N-channel relies on electrons, P-channel relies on holes). This unipolar working mode avoids the switching speed limitation caused by the minority carrier storage effect in BJTs.
Its on resistance (Rds (on)) has a positive temperature coefficient: as the temperature increases, the channel resistance increases. This characteristic enables MOSFETs to have natural current sharing characteristics when used in parallel, and is less prone to "thermal runaway" like BJTs (a vicious cycle of higher current, higher temperature, stronger conduction, and higher current until burnout). Working at high temperatures is relatively more stable and reliable.
Good linear working ability:
In the variable resistance region (also known as the linear region or ohmic region), the drain current (Id) of MOSFET can be continuously and linearly controlled by the gate source voltage (Vgs). This makes MOSFETs not only suitable for switching applications, but also for linear amplification, analog switching, voltage controlled resistors, and constant current sources, providing better linearity and simpler bias circuits than BJTs in certain situations.
Inherent body diode:
Most power MOSFETs (especially vertical structures such as VDMOS) naturally form a parasitic body diode during the manufacturing process, with the cathode connected to the drain (D) and the anode connected to the source (S). Although this diode typically does not perform as well as an external fast recovery diode in terms of reverse recovery time, it can provide a freewheeling path in certain applications (such as H-bridge motor drives, Buck/Boost converters) to protect MOSFETs from reverse voltage spikes caused by inductive load shutdown. Sometimes, an external freewheeling diode can be omitted to simplify the design.
Easy to integrate:
The planar structure of MOSFETs is highly suitable for large-scale integrated circuit (IC) manufacturing processes. CMOS (Complementary MOS, a combination of N-channel and P-channel MOSFETs) technology is the absolute mainstream foundation of modern digital circuits (CPUs, memory, logic chips, etc.) and analog/mixed signal integrated circuits, because it has the advantages of extremely low static power consumption (ideally no static current), high integration density, and strong anti-interference ability.
The core advantages of adding MOSFETs in circuits are their high efficiency, ease of use, and flexibility. It achieves high-speed and low loss switching through voltage control, with simple driving and extremely low power consumption; Having low resistance during conduction reduces energy loss; Its unipolar and positive temperature coefficient characteristics provide good thermal stability and parallel capability; Simultaneously possessing the potential for linear operation and the built-in body diode providing additional protection/functionality; Most importantly, it is the cornerstone of modern integrated circuits. These characteristics collectively make MOSFETs an ideal choice for a wide range of electronic applications, from micro watt level digital logic to kilowatt level power conversion.