PWM input frequency and practicable resolution for LED Dimming

[Ingmar_Biovt]

Dear Community,

using the STEVAL-ILL089V1 board we would like to power a string of 12 LEDs (Cree XLamp Element G LED Data sheet) and use the PWM dimming function. While the respective raising and falling DIM treshold voltages are clearly stated in the ALED6000 datasheet, I am not sure about the practicable PWM input frequency and resolution. As I am not that experienced in the electronics field yet, I would highly appreciate if you could give me recommendations for the PWM input frequency and practicable resolution (minimal increment / step size).

Thanks in advance and best regards,

Ingmar 

[AScha.3 · Accepted solution]

Hi,

The limits are in the data sheet,  so you can choose...

Usually basic driving frequency is > 100 Hz, to avoid visible flickering. But on LEDs you might still see some flickering, so I would recommend a frequency about 2khz to start with.

Then question is: what you want to do with it?

Need a very wide range for dimming?

Our eyes get the impression of brightness almost on a logarithmic scale, so reducing the pwm from 100% to 90% changes almost nothing in brightness. To get it to visible low light levels, you need to go to 1% pwm or lower.

So maybe useful to have a pwm with 1024 ticks and dimming is just always half or double the pwm width, from min to max.

Just try it to see, how it looks. Then you know.