In this article we look into a simple 220V mains PWM controlled fan or light regulator circuit which does not require a microcontroller or costly triac drivers for the intended operations.
Capacitive Phase Chopping
All Ordinary types fan regulator and 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 regulator 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 regulator 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.
R1, R5 = 1M
R2, R3, R4 R6 = 10K
VR1, C2 = SEE TEXT
OPTO = 4N35 OR ANY STANDARD
C1 = 0.22uF/400v
C3 = 100uF/25V
D1---D5 = 1N4007
Z1 = 12V
IC1 = 4060
TRIAC = BT136
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.
Smart PWM Fan Regulator Using IC 555
Almost all light/fan regulator circuits make use of a silicon-controlled rectifier (triac or SCR).
These devices are switched with a predetermined phase angle which subsequently stays in the conduction mode until the following zero crossing of the mains AC cycle.
This process looks easy, however simultaneously it presents difficulties while controlling smaller loads or which are inductive in nature causing hysteresis and flickering.
The reason of these issues depend on the truth that due to smaller load wattage the current delivered to the devices is inadequate to sustain their conduction.
Therefore a region of the control characteristic is not thoroughly implemented. The outcome further deteriorates for the loads that are inductive.
How the Circuit Works
The proposed AC 220V PWM regulator circuit using IC 555 gives you a simple solution by supplying the triac with a constant gate current, to ensure that loads as nominal as 1 watt is also controlled smoothly.
To have the circuit as compact and straightforward as it can be, we utilize the popular timer IC 555.
The output of the IC 555, which can be typically triggered high, is activated low through a negative potential input.
This negative supply is made available from the stage comprising C1-R3, rectifier D1 -D2, along with stabilizer section D3-C2. BJTs T1 to T3 deliver a initializing pulse on the trigger input pin#2 of the 555 for each of the zero crossings of the mains AC input.
During a PWM period, as decided by the adjustment of P1 and P2, the output of the IC 555 is usually high, and we, therefore, have practically zero voltage difference across pins 3 and pin 8, i.e. the triac remains switched off.
As soon as the set interval is elapsed, pin 3 becomes low and the triac is activated.
For the rest of the half AC cycle, a gate current keeps running, which allows the the triac to continue to conduct.
The lowest point where, let's say, a light bulb need not just illuminate, is determined by carefully adjusting the pot P1. Filter R7 C5 L1 supplies the necessary decoupling for the triac.
As a final point, remember that the absolute maximum power that could be governed by this IC 555 based smart regulator switch should not exceed 600 watts.
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