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A Simple PWM Generator for Fan Speed Control

Many Nidec cooling fans and blowers are available with pulse-width modulated speed control. The standard control profile varies fan speed in a quasi-linear manner from a low level of 1500 rpm at 0% duty cycle to full speed operation at 100% duty cycle.

Following is a simple circuit for a PWM generator that can be quickly assembled and directly attached to a fan's control and ground leads for parametric evaluation of it at a variety of operating points, and for assessment of its range of thermal performance in equipment prototypes during design cycles. <More>

A Simple PWM Generator for Fan Speed Control

A Simple PWM Generator for Fan Speed Control

A Simple PWM Generator for Fan Speed Control—Notes
1. Component values shown in the PWM generator circuit set the modulation frequency at about 20 kHz under load, but fan speed as a function of duty cycle is independent of frequency over a very broad range. Nearly identical transfer functions are produced at frequencies over the recommended operational range of 300 Hz to 60 kHz.

2. The duty cycle range of the PWM generator is 2% to 98%. If duty cycles of 100% and 0% are required, the circuit's output can be switch-selected with alternate contact positions at 5V and ground potential.

3. A CMOS version of the 555 integrated circuit was used to build the PWM generator. Other types will work as well, but they may produce output pulses with lower amplitude.

4. Pulse-width modulation of dc operating voltage to modify fan speed is not recommended. Transients generated by that approach can irreversibly damage motor commutation and control electronics and dramatically shorten the life of a fan.

5. Custom PWM transfer functions are available for high-volume production projects. Among programmable variations are the following response profiles: <Back> <More>

A Simple PWM Generator for Fan Speed Control

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