Modern Fan Regulator (Phase Control) Explained

 

Modern Fan Regulator (Phase Control)

Modern fan regulators control power instead of just reducing voltage. They use a technique called phase control, which cuts parts of the AC waveform.

Step 1: AC Voltage Equation

v(t) = Vm sin(ωt)

• Vm = peak voltage
• ω = angular frequency

Step 2: Cutting the Wave

A TRIAC turns ON at angle α (firing angle).

• 0 to α → No voltage
• α to π → Voltage passes

Step 3: RMS Voltage

The fan speed depends on RMS voltage:

Vrms = Vm √[ (1 / 2π) ∫(α to π) sin²(θ) dθ ]

After solving:

Vrms = Vm √[ (1 / 2π) ( (π − α)/2 + sin(2α)/4 ) ]

What This Means

• α = 0° → Full speed
• α = 90° → Medium speed
• α → 180° → Very low speed

Step 4: Power Delivered

P ∝ Vrms²

• Small change in α → big change in power
• This allows smooth speed control

Old regulator: reduces voltage by wasting energy as heat.
New regulator: turns ON late in each AC cycle without wasting energy.

How Firing Angle is Controlled

• Uses RC circuit (resistor + capacitor)
• Capacitor charging decides when TRIAC turns ON

Conclusion

The math is about how much of the sine wave is allowed through, and calculating the RMS voltage, which controls the fan speed.