How do I calculate the average voltage from PWM?

The average voltage of a PWM signal is Vavg = Vpeak × (Duty / 100). For example, a 5V signal at 50% duty cycle gives 2.5V average. This is why PWM is used as a simple DAC — adding a low-pass RC filter smooths the square wave into a DC voltage.

What PWM frequency should I use for motor control?

For DC motors, 1–20 kHz is typical. Below 1kHz you may hear audible noise from the motor. Above 20kHz reduces audible noise but increases switching losses. For servo motors, use 50Hz (20ms period) with 1–2ms pulse width for position control.

What is the difference between duty cycle and PWM frequency?

Frequency determines how fast the signal switches (e.g. 1 kHz = 1000 cycles/second). Duty cycle determines the ratio of ON time to total period (e.g. 25% duty = signal is high for 25% of each cycle). Frequency sets the speed; duty cycle sets the average power or voltage.

PWM Calculator

Calculate PWM period, on/off times, and average voltage from frequency and duty cycle — or find the duty cycle needed to achieve a target average voltage.

PWM Parameters

Frequency

Duty Cycle (%)

Peak Voltage (Vpeak)

Results

Period (T)1.000 ms

tON500.0 µs

tOFF500.0 µs

Average voltage (Vavg)2.500 V

Vavg = Vpeak × D/100

Common PWM Frequencies by Application

Application	Typical Frequency
DC motor speed control	1–20 kHz
Servo motor control	50 Hz
LED dimming	100 Hz – 20 kHz
Switching power supply	20 kHz – 2 MHz
Class D audio amplifier	40 – 400 kHz
Piezo buzzer tone	1 – 20 kHz

How PWM Works

Pulse-Width Modulation (PWM) is a technique for encoding analog information in a digital signal by varying the fraction of time the signal is high (the duty cycle). The average voltage seen by the load equals the peak voltage multiplied by the duty cycle.

A low-pass filter on the output converts the PWM waveform to a true DC analog voltage equal to Vavg. Without a filter, the load itself may integrate the switching (e.g., a motor's inductance or an LED's phosphor persistence).

Average Voltage

Vavg = Vpeak × D / 100

Period and Timing

T = 1 / f | tON = T × D/100

Key Points

Higher frequency: smoother output but higher switching losses
D = 0% = always off; D = 100% = always on
Motor control: higher frequency reduces audible noise (>20 kHz)
Servos use 50 Hz with 1–2 ms pulse width to encode angle
LED dimming: >100 Hz prevents visible flicker
PWM resolution: an N-bit timer gives 2ᴺ steps of duty cycle

Applications

Motor speed and direction control
LED brightness dimming
Servo position control
Switching power supply duty cycle
DAC via RC low-pass filter

PWM Formulas

D = t_on / T = t_on × f | Vavg = D × Vhigh + (1–D) × VlowFor Vlow=0: Vavg = D × Vcc | f = 1/T | T = t_on + t_offResolution: n bits → 2ⁿ steps, step size = Vcc/2ⁿArduino 8-bit: f = F_CPU / (prescaler × 256)

Arduino PWM Reference

Timer	Pins	Default freq	Prescaler options	Notes
Timer0	D5, D6	976 Hz	1,8,64,256,1024	millis() uses this
Timer1	D9, D10	490 Hz	1,8,64,256,1024	16-bit timer
Timer2	D3, D11	490 Hz	1,8,32,64,128,256	tone() uses this
ESP32	Any GPIO	1Hz–40MHz	configurable	LEDC peripheral
RP2040	Any GPIO	1Hz–62.5MHz	configurable	Flexible PWM

Practical Examples

DC motor speed control (Arduino, D9)

analogWrite(9, 128): D = 128/255 = 50.2%, Vavg = 0.502×12V = 6.02V → ~50% speed

Frequency = 490Hz. For smoother motor control, increase to 20kHz (above audible).

LED dimming at 1kHz (ESP32)

ledcSetup(0, 1000, 8): 1kHz, 8-bit → 256 steps

ledcWrite(0, 64): D = 64/256 = 25% → LED at 25% brightness

At 1kHz: no visible flicker (human eye flicker threshold ~60Hz)

Design Tip

For motor control, use f > 20kHz to avoid audible whine. For LED dimming: f > 200Hz is sufficient (100Hz minimum to avoid flicker on camera). High-frequency PWM increases switching losses in MOSFETs (P_sw = ½×Vds×Id×(tr+tf)×f). RC low-pass filter converts PWM to analog: τ = RC >> 1/f for smooth DAC output.

Did you know? PWM dimming of LEDs is preferred over analog current reduction because LED colour temperature shifts at lower currents. By switching the LED fully on and off rapidly (>100 Hz), PWM maintains consistent colour while varying average brightness — the technique used in all quality LED dimmers.