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The difference between depletion type and enhanced type MOS tube

date: 2019-08-28
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The main difference between depletion type and enhanced type is that depletion type MOS tube has conductive channels when no voltage is applied at G terminal (Gate), while the enhanced type MOS tube has conductive channels only when it is opened.The two control mode is not the same, depletion type MOS tube VGS (grid voltage) can use positive, zero, negative voltage control on, and the enhanced MOS tube must make VGS>VGS (th) (gate threshold voltage).


The main difference between depletion type and enhanced type is that depletion type MOS tube has conductive channels when no voltage is applied at G terminal (Gate), while the enhanced type MOS tube has conductive channels only when it is opened.The two control mode is not the same, depletion type MOS tube VGS (grid voltage) can use positive, zero, negative voltage control on, and the enhanced MOS tube must make VGS>VGS (th) (gate threshold voltage).


Since a large number of Na+ or K+ positive ions are doped in the SiO2 insulation layer of exhausted n-channel MOS tube (negative ions are doped in the manufacturing of p-channel exhausted MOS tube), when VGS=0, the electric field generated by these positive ions can induce enough electrons in the p-type substrate to form an n-type conductive channel.When VGS>0, a large ID (drain current) will be generated;If VGS is less than 0, it will weaken the electric field generated by positive ions, narrow the N channel, and reduce the ID.


These characteristics make the depletion type MOS tube in practical application, when the device is turned on, the MOS tube may be triggered by mistake, leading to the failure of the whole machine;It is not easy to control, making its application very few.


Therefore, most NMOS and PMOS we see in daily life are enhanced MOS tubes.Among them, PMOS can easily be used as a high-end driver.However, due to the problems of large on-resistance, high price and few replacement types, PMOS are usually replaced by NMOS in high-end drivers, which is the most common and important reason for the enhanced NMOS in the market, no matter for applications or product categories. Especially in the applications of switching power supply and motor drive, NMOS are generally used.


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