PWM Duty Cycle Calculator

Pulse Width Modulation (PWM) controls power to a device with a digital signal that switches rapidly between fully on and fully off.
Varying the ratio of on-time to off-time sets the effective voltage the load sees. The reason to do it this way is efficiency: a transistor that is either saturated or cut off dissipates almost nothing, while a linear regulator burns the difference as heat.

Key PWM Parameters

Period (T): The total time of one complete on/off cycle T = 1 / f (where f is frequency in Hz)

Duty Cycle (D): The percentage of the period when the signal is HIGH (on) D (%) = (t_on / T) × 100

On-Time (t_on): How long the signal is HIGH in each cycle t_on = D × T / 100

Off-Time (t_off): How long the signal is LOW in each cycle t_off = T − t_on

Average Voltage: For a digital signal with amplitude V_high: V_avg = V_high × D / 100

Practical Applications

Servo Control Special Case

Servo motors use a fixed 50 Hz (20 ms period) signal where:

• 1 ms on-time = 0° (or minimum position)
• 1.5 ms on-time = 90° (center)
• 2 ms on-time = 180° (or maximum position)

The duty cycle for servo control is only 5–10%, but the pulse width controls position.

LED Dimming and Flicker

For LED dimming, frequencies below 100 Hz can cause visible flicker, especially in video. Frequencies above 1 kHz are generally safe. Many LED dimming systems use 10–50 kHz to avoid any perceptible flicker even with high-speed cameras.

Arduino/Microcontroller PWM

Most Arduino boards have built-in PWM on pins 3, 5, 6, 9, 10, 11. The default PWM frequency is:

• Pins 5 and 6: ~980 Hz
• Pins 3, 9, 10, 11: ~490 Hz

The analogWrite() function takes 0–255 where 0 = 0% and 255 = 100% duty cycle.