As people pay more and more attention to air quality, air purifiers have become standard equipment in homes and offices. It integrates technologies from multiple fields. Common types include: pure physical filtration type, which relies on HEPA filters to intercept dust and other particles; electrostatic dust collection type, which uses static electricity to absorb charged particles; and photocatalyst purification type, which uses ultraviolet rays to activate catalysts to decompose harmful gases, creating a fresh environment indoors.

 Application of MOSFET in air purifier circuit

 In the air purifier circuit, VBE1206N is recommended, and its parameters are:

 - Unipolar N-type

- VDS(V): 200
- VGS(±V): 20
- Vth(V): 3
- On-resistance at VGS=10V(mΩ): 55
- ID (A): 30
- Technology: Trench
Package: TO252

Precise fan motor drive : The fan drives the air circulation, and the MOSFET uses PWM to control its speed. When the air quality is good, the PWM duty cycle is reduced, and the fan rotates slowly to save energy; when the pollution is heavy, the duty cycle is increased, and the fan rotates quickly to purify the air. The 30A current carrying capacity and 200V withstand voltage of VBE1206N ensure stable operation of the fan. 

Fine control of negative ion release : Negative ions can absorb dust, and MOSFET controls the high-voltage circuit of the negative ion generator. It quickly conducts to produce negative ions when turned on, and quickly cuts off when turned off. It also finely controls the output according to the air quality, and its fast switching characteristics ensure accurate control.

Sensor system power supply protection and signal conversion : PM2.5, VOC and other sensors monitor air quality, and MOSFET powers them and converts signals. It controls the power supply on and off to reduce power consumption, and also conducts at regular intervals to convert the sensor's weak current signal into a voltage signal, helping the purifier to accurately control air quality and achieve intelligent and efficient operation.

Selection points

1. Voltage level

The MOSFET drain-source breakdown voltage (Vds) must exceed the maximum operating voltage of the circuit, leaving a 20% - 30% margin to prevent voltage fluctuations. The gate-source voltage (Vgs) must be adapted to the drive circuit to ensure reliable conduction without exceeding the limit.

(ii) Current capability

The fan motor current changes with the speed, and the MOSFET drain current (Id) parameter is determined according to the motor rating and maximum current. A 30% - 50% margin is reserved to ensure that it can cope with the startup impact and pulse current and stably drive the motor.

(III) On-resistance

The smaller the on-resistance (Rds (on)), the lower the MOSFET on-power consumption, which is beneficial to the energy saving of the fan motor drive circuit. When the heat dissipation is good, it is also necessary to ensure that the resistance changes little after the temperature rises to maintain energy saving and system stability. Generally, it is best to choose less than 50mΩ at room temperature.

4. Switching speed

Because fan speed regulation and negative ion control often use PWM technology, MOSFET switching is required to be fast to reduce losses and improve response. However, too fast switching can easily cause electromagnetic interference, so it is necessary to combine the drive circuit to adapt the MOSFET output resistance and capacitance parameters to achieve fast and stable conduction and cutoff.

(V) Packaging form

The internal space of the purifier is limited. TO-220 package is used for high current and high power, which has good heat dissipation but occupies a large area; TO-263 is used for medium power; SOT-23 is used for low power and tight space. Considering both cost and reliability, a package with high cost performance is selected.

 MOSFET plays an irreplaceable and important role in the fan motor drive, negative ion generator control, sensor power supply and signal processing of air purifiers, significantly improving the performance and quality of air purifiers and providing people with a more comfortable and healthy indoor air environment. With the continuous development of semiconductor technology, the performance of MOSFET will be further improved, and its application prospects in air purifiers and other types of electrical equipment will be broader.