PWM fan speed controller. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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PWM fan speed controller. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Computers

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This device is based on the PIC18F25K20 controller, which allows you to adjust the fan speed using PWM (pulse width modulation). This provides such advantages as: smooth adjustment of engine speed, low noise level, high durability, greater reliability, lower energy consumption and starting current.

PWM fan speed controller

The microcontroller receives temperature data from a temperature sensor D18B20 and after converting the values to degrees Celsius, it outputs a PWM signal on PORTC.2 with 6 different levels:
PWM Temperature
Present in several = 15% <= 49°
Present in several = 30% 50°
Present in several = 40% 51°
Present in several = 50% 52°
Present in several = 75% 53°
Present in several = 100%
> 54 °

(click to enlarge)

The PWM signal from the MK is fed to transistor Q1. The circuit uses two transistors so that the current I_к on transistor Q2 was enough to start the fan. Since the MCU can supply a maximum of 3.6V, and 15% of 3.6V will be 0.5V, 1V is needed to open Q0.7.

How to calculate Q1 and Q2:

V_cc-V_ba-(r_б*i_б) = 0

Fan control between 5V and +/-12V is possible. The maximum current load for the BC338 transistor is 800 mA, so it is possible to use two or more fans, but so that the total current does not exceed this value. The output of the MK is connected to Q1 and Q2, which act as a switch. D3 is used to protect against magnetic fields of the fan, without it, after turning off the device, the reverse current can go to Q2 and break through it.

PWM controller circuit. Location of elements on the PCB

Download printed circuit boards in PDF and firmware

Publication: cxem.net

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