This passage describes the fan speed control circuit board that is mainly used for cooling the fan of the electronic instrument circuit CPU(Central Processing Unit). The circuit is as shown.
Circuit Work Principle
The operational amplifier IC1a and the peripheral components C1, R3 in this circuit form an integrator. IC1b and R4, R5 form a comparator with lagging characteristics. IC1a, IC1b and peripheral components R1, R2, R3, etc. form a triangular wave generator. The triangular wave is output from the (1) pin of IC1a and is applied to the inverting terminal (2) of IC2. The non-inverting terminal (3) of IC2 is externally connected to VR1 for the DC control voltage of the waveform output. This control voltage controls the speed of the fan motor M from zero to full power. On VR1, there is a branching resistor R7 connected in parallel to protect the motor M’s speed within the set range.
The operational amplifier IC2 is a comparator circuit, which functions are as a driving circuit of the TR1 triode to directly drive the instrument fan M to rotate. D1 is a protection diode that dampens the anti-peak voltage when the fan motor is operating.
Electronic Component selection
The operational amplifier IC1 is a normal operational amplifier TL062 type, but the IC2 is a 3130 type. The operating voltage of the circuit fan motor is 12V, and the maximum pulse rate of the driving fan motor is 100Hz. At this time, the motor rotates almost without noise. Changing the parameters of R3 and C1 can change the circuit frequency. The values of R3 and C1 are selected in the circuit, and the pulse frequency is 33 Hz.