As a high-frequency electric product, hair dryer usually consists of heating wire, high-speed small fan and circuit board. There are usually metal blowers and plastic blowers, and the centrifugal airflow formed by the rotation of the blades driven by the motor drives the rotor to blow out to achieve the purpose of drying and shaping. In this issue, Heketai introduces the application of MOS and rectifier in hair dryer products.

A hair dryer usually consists of a shell, a handle, blades, a motor, an electric heating element, etc. Its working principle mainly depends on the cooperation of the motor and blades and the heating effect of the electric heating element. The following is a circuit board on an ordinary hair dryer product disassembled by an engineer. It is also the core component to realize the whole machine function. It uses main control chip, power module, drive module, sensor module, display module and other auxiliary devices.

As the brain of the product, the main control chip is the core component of the circuit board, which is responsible for controlling the whole workflow of the hair dryer, including wind speed and heating power. The sensor module is used to detect various state parameters of the hair dryer, such as temperature and humidity, and it feeds back the data to the main control chip, so that the main control chip can adjust the working mode of the hair dryer according to the real-time state and ensure the safe and stable operation of the hair dryer.

In addition, the power module is responsible for providing stable power input for the circuit board to ensure that the blower can work normally. The power module is usually composed of rectifier, filter and other components, and can convert alternating current into stable direct current for the circuit board. The display module is mainly used to display the working state of the blower, such as wind speed gear and heating power. The display module is usually composed of LED indicator, LCD screen, discrete devices and other components, which can intuitively display the current state of the hair dryer.

In addition, the driving module is responsible for controlling the rotating speed of the fan and the heating power of the electric heating element. The driving module usually includes power transistor, driving circuit and other elements, which can realize accurate control of the fan and electric heating elements. MOS can play the role of starting and stopping the motor in the motor driving circuit. MOS tube is usually used as a switching element to drive the motor to start and stop by controlling its on and off. By adjusting the on-time (i.e. duty ratio) of MOS tube, the average current of the motor can be controlled, so as to adjust the speed of the motor. In the H-bridge driving circuit, four MOS transistors form an H-shaped circuit structure. By controlling the simultaneous conduction of the two MOS transistors on the diagonal, the current can pass through the motor, thus driving the motor to rotate. By changing the combination of the conducting MOS transistors, the forward and reverse rotation of the motor can be realized.

Other auxiliary components that the hair dryer may use include capacitors, inductors, voltage regulators and protective devices, such as overcurrent protection and temperature protection.

Discrete devices mainly play the role of rectification, switching and voltage stabilization in this circuit, and rectifier and MOS tube may be used. On the circuit of this blower, MOS tubes that can be used on this board include HKTD7N65 or HKTD5N50 produced by Heketai, and four rectifier bridges S5M can be used. HKTD7N65 with TO-252 package can withstand the drain-source voltage as high as 650V and the continuous drain current of 7A, which can meet the demand of high-power blower. S5M can withstand the maximum DC reverse voltage of 1000V and forward current of 5A, which can play an important role in this rectifier circuit.