PWM (Pulse Width Modulation)

Understanding PWM

Pulse Width Modulation is the fundamental technology controlling LED brightness. Understanding PWM helps professionals troubleshoot flicker issues and evaluate panel quality.

How PWM Works

**Basic Principle:** Instead of varying LED current, PWM rapidly switches LEDs between full on and full off.

**Duty Cycle:** The percentage of time the LED is on:

• 100% duty = Full brightness
• 50% duty = Half brightness
• 10% duty = 10% brightness

**Persistence of Vision:** Human eyes average rapid pulses into perceived continuous brightness.

PWM Specifications

**Frequency:** How many on-off cycles per second:

• Low: <10kHz (may flicker)
• Medium: 10-20kHz (safe for most)
• High: 20kHz+ (flicker-free)

**Resolution:** Number of distinct duty cycle levels:

• 8-bit: 256 levels
• 10-bit: 1024 levels
• 12-bit: 4096 levels

Advantages of PWM

**Color Consistency:** LED color remains accurate regardless of brightness.

**Efficiency:** LEDs operate at optimal current when on, maximizing efficiency.

**Precision:** Digital control enables exact, repeatable brightness levels.

PWM and Low Brightness

**Challenge:** At very low brightness, LEDs are mostly off, making pulses more visible.

**Solution:** Higher PWM frequencies reduce visibility of individual pulses at low brightness.

PWM Artifacts

**Camera Flicker:** Camera shutter can capture individual pulses as brightness variations.

**Rolling Shutter:** Different parts of image captured at different times during PWM cycle.

Driver IC Role

**IC Quality:** The LED driver IC determines:

• PWM frequency capability
• Gray scale depth
• Current accuracy
• Flicker performance

**Modern ICs:** High-quality driver ICs enable:

• Very high PWM frequencies
• Excellent low-brightness performance
• Minimal flicker

Specification Interpretation

**Refresh Rate vs. PWM:** These are related but different:

• Refresh rate: Full screen update rate
• PWM: Individual LED switching rate

Both affect flicker visibility.