PAGE 084 OF 150 · TIMERS, FLASHERS & DIMMING
Choosing a PWM Frequency
Too low a rate shows visible flicker.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Too slow causes flicker
Below about 100 Hz many people see flicker, and slow-moving eyes or cameras can notice more. A frequency of a few hundred hertz to a few kilohertz is common for LEDs.
Guidelines
- 500 Hz to 1 kHz: suitable for ordinary indicator dimming.
- Several kilohertz: smoother with cameras and moving views.
- Above about 20 kHz: out of hearing range, which avoids whining in inductors and some drivers.
Very high frequency raises switching losses in MOSFETs, so choose a balance for the job.
REMEMBER
Switching an LED on and off quickly can look like steady dimmer light.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
Explore LED clocks, stopwatches and electronics at cosycom.com.