Duty Cycle Calculator – Calculate PWM Duty Cycle

Calculate duty cycle, on-time, and off-time for PWM signals. Essential for motor control and power regulation.

On-Time (s)

Period (s)

Frequency (Hz)

Duty Cycle: 50%

How to Use This Duty Cycle Calculator

Enter on-time and period values

Input the on-time (how long the signal is high) and the total period time. Both values should be in the same units, typically seconds or milliseconds.

Or use frequency and duty cycle

Alternatively, enter the frequency and desired duty cycle percentage. The calculator will determine the on-time and off-time for you.

Click Calculate to see results

You will see the duty cycle percentage, signal frequency, period, and the on-time and off-time durations for your PWM signal.

Common Duty Cycle Applications

Application	Typical Duty Cycle	Purpose	Frequency Range
LED Dimming	1-100%	Brightness control	100 Hz - 1 kHz
DC Motor Speed	10-90%	Speed regulation	1-20 kHz
Servo Control	5-10%	Position control	50 Hz (20 ms period)
Buck Converter	10-90%	Voltage step-down	50-500 kHz
Boost Converter	10-80%	Voltage step-up	50-500 kHz
Class D Audio	Variable	Audio amplification	200-500 kHz

Note: Duty cycle determines the average power delivered. Higher duty cycle means more on-time and higher average output.

Understanding Duty Cycle and PWM

What Is Duty Cycle?

Duty cycle is the percentage of time a periodic signal is in its active (high) state. A 50% duty cycle means the signal is high for half the period and low for the other half. A 25% duty cycle means the signal is high for one-quarter of the period. Duty cycle directly controls average power delivery.

PWM Basics

Pulse Width Modulation (PWM) varies the width of pulses while keeping frequency constant. By changing the duty cycle, you control the average voltage or power without changing the supply voltage. This is highly efficient because the switching element is either fully on or fully off.

Duty Cycle Formula

Duty cycle equals on-time divided by period, multiplied by 100. D = (T_on / T) × 100%. The period is the inverse of frequency: T = 1/f. Off-time equals period minus on-time: T_off = T - T_on.

Frequency Considerations

PWM frequency affects performance. Too low and you get visible flicker in LEDs or audible noise in motors. Too high and switching losses increase. For motors, 1-20 kHz works well. For LEDs, 100 Hz minimum to avoid flicker. Power supplies often use 50-500 kHz.

PWM Design Tips

Choose the Right Frequency

For motor control, use 1-20 kHz to avoid audible noise. For LED dimming, use at least 200 Hz to prevent visible flicker. For power converters, higher frequencies allow smaller components but increase switching losses.

Mind the Dead Time

In H-bridge and half-bridge circuits, add dead time between switching transitions. This prevents shoot-through where both transistors conduct simultaneously, causing high current spikes and potential damage.

Use Proper Filtering

PWM outputs often need filtering. Motors have inherent inductance that smooths current. LEDs may need current-limiting resistors. Power supplies require LC filters to convert PWM to smooth DC voltage.

Consider Minimum On/Off Times

Some loads need minimum on-time or off-time. Motors need minimum pulse width to overcome friction. Switching power supplies have minimum on-time limits. Ensure your duty cycle range accounts for these constraints.

Frequently Asked Questions

What does a 100% duty cycle mean?

A 100% duty cycle means the signal is always high (on) with no off-time. The output delivers full continuous power, equivalent to a direct connection to the supply. There is no PWM effect at 100% duty cycle since the signal never switches off.

How do I calculate duty cycle from frequency?

First find the period: T = 1/frequency. Then duty cycle = (on-time / period) × 100%. For example, at 1 kHz (1 ms period) with 0.25 ms on-time, duty cycle = (0.25 / 1) × 100% = 25%.

What frequency should I use for PWM motor control?

For DC motors, 1-20 kHz is typical. Below 1 kHz, you may hear audible whining. Above 20 kHz, switching losses increase without benefit. Small motors can use higher frequencies. Large motors often work well at 2-8 kHz.

Why does my LED flicker with PWM?

Flicker occurs when PWM frequency is too low. The human eye can detect flicker below about 100 Hz, especially in peripheral vision. Use at least 200 Hz for general lighting, 1 kHz or higher for camera applications to avoid banding in video.

What is the difference between duty cycle and frequency?

Frequency is how many complete cycles occur per second. Duty cycle is what percentage of each cycle the signal is on. You can change duty cycle without changing frequency, which is how PWM controls power while maintaining constant switching rate.

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