Design of fan drive circuit speed control voltage

　　The circuit is driven by optocoupler isolation; the input end of optocoupler is driven by PWM pulse wave signal input by MCU; the electrolytic capacitor of the output end of optocoupler is pulsed and discharged; then the continuously adjustable VSP is obtained. PWM wave is generated by MCU programming control. The higher the PWM carrier frequency is, the more accurate the adjustment of VSP voltage is. It depends on the needs and MCU resources. The carrier frequency of 4011 is 80Hz.

　　Each end of cN1 connector corresponds to each function outgoing line of DC fan? The motor power supply voltage vs and the control circuit power supply voltage 15V must be treated together.

　　The IC1 sampling optocoupler tlp521 realizes the strong and weak current isolation drive.

　　R1 is the chip current limiting resistor, and the output end of the optocoupler should get enough driving current.

　　R2 and R3 are 15V partial resistance. When the duty cycle of PWM output is 100 and the optocoupler is fully on, the voltage on resistor R2 shall be ensured to be within the specification of the technical parameters of the DC fan, so as to protect the built-in circuit of the fan.

　　E1 electrolytic capacitor is a filter rectifier capacitor; the PWM voltage waveform on R2 resistor is shaped into a relatively smooth DC voltage waveform VSP; it is used for sampling and controlling the fan speed by the built-in drive circuit of DC fan. The selection of capacitance value should be appropriate; too large will lead to slow charging and discharging; too small will lead to slow speed adjustment; too small will lead to uneven rectified VSP voltage; large ripple will cause fan speed change; instability. According to the chip data of built-in drive circuit, the typical value of VSP ripple is 10mV, and the ripple range should be within ~ 40 (60mV). Therefore, when selecting electrolytic capacitor, the range of voltage ripple of VSP should be controlled within the range specified by the chip. Here, 47 μ f / 25V is selected, which was originally 47 μ f / 35V:; it has been used in V-type frequency converter, and the effect is ideal.

　　C1 is 0.1 μ f ceramic capacitor, which is used to filter high frequency clutter.

　　DZ1 is a 5.6v regulator; the voltage on R2 is clamped at the highest 5.6v; the built-in circuit of fan is protected. The voltage range of VSP in DC fan specification is generally within 0 (6.5V). Only 5.6v is suitable for Midea. When the VSP input is 5.6v, it can meet the requirements of the system wind speed, so 5.6v is selected. This is just a reference value; the specific design depends on the specific requirements.

　　R4 current limiting resistance; protection of fan built-in circuit; can also play a role in anti-interference.

　　The outdoor unit is placed outdoors; the fan power supply circuit is composed of fuse, D1, E2 and R9; the unidirectional conduction characteristic of D1 can effectively prevent the wind turbine from rotating in case of power failure; the indoor fan can also prevent the fan from rotating in case of power failure to make the indoor chip work.