In this article we look into a simple 220V mains PWM controlled fan or light dimmer circuit which does not require a microcontroller or costly triac drivers for the intended operations.

Capacitive Phase Chopping

All Ordinary types fan dimmers which rely on capacitive phase chopping technology have one drawback in common, these generate a lot of RF noise and require bulky inductors for controlling them partially.

Furthermore, the switching or the phase chopping being done using ordinary capacitor diac technology lack accuracy and sharpness.

The proposed mains transformerless PWM controlled fan dimmer circuit designed by me is free from all such possible issues normally accompanied with traditional fan or light dimmers since it uses an advanced CMOS IC based circuit and an accurate zero crossing detector stage.

No MCUs Used

The best thing about this circuit is that it does not require microcontrollers and programming, and also a triac driver has been eliminated making the circuit extremely easy to build even for the new hobbyists.

Let's learn the configuration in detail, which is rather too straightforward:

Referring to the circuit, IC1 which is a 4060 timer chip is configured to produce a delayed positive pulse for the triac each time the phase crosses the zero line of its phase angle.

The entire circuit is powered from an ordinary capacitive power supply using C1, D5, Z1 and C3.

IC1 is configured in its standard form for generating a delayed switch ON or a high every time its pin12 goes through a reset action.

Zero Crossing Switching for the Triac

The dimming action or the phase control action is achieved by making the triac to conduct after a predetermined delay each time a zero crossing is detected.

If this delay is short, it means the triac gets an opportunity to conduct for a greater amount of time for the phase angles, causing the connected fan to spin faster or the light to shine to brighter.

As this delay is increased, the triac is forced to conduct for proportionately shorter durations across the phase angles producing a proportionate amount of reduction over the speed or the brightness of the connected fan or the light respectively.

The zero crossing operation is simply enforced by using an ordinary opto coupler, as can be witnessed in the given diagram.

The bridge D1---D4 transforms the alternating phase angle into equivalent 100 Hz positive pulses.

The LEd and the transistor inside the opto coupler responds to these positive 100Hz pulses and stays switched ON only for so long as the pulses are 0.8V above the zero mark and switches OFF instantly as the pulses reach the zero crossing point.

While the opto transistor is in the conducting phase, the IC pin12 is held at ground level allowing a delay or a predetermined negativestarting pulse for the triac gate.

However at the zero crossing levels the opto switches OFF, resetting the pin12 of the IC such that the IC pin3 restarts a fresh or a new delay for the triac to respond for that particular phase angle.

PWM Phase Control

The length or the pulse width of this delay pulse can be varied by suitably adjusting VR1 which also becomes the speed control knob for the discussed PWM controlled fan dimmer circuit.

VR1 and C2 must be selected such that the maximum delay produced by these should not exceed the 1/100 = 0.01 second timing in order to ensure a linearly incrementing 0 to full calibration over the given control knob.

The above could be implemented by some trial error or by using the standard formula for IC 4060.

For the above you may also experiment the other outputs of the IC.

 Circuit Diagram

Parts List

R1, R5 = 1M
R2, R3, R4 R6 = 10K
C1 = 0.22uF/400v
C3 = 100uF/25V
D1---D5 = 1N4007
Z1 = 12V
IC1 = 4060

Waveform Simulation

The delay waveform image below shows how the phase for the fan may be delayed at every zero crossing, for the various settings of VR1 and C2.


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