DC42 said:
I've done some sums, and from the datasheet I think the PWM frequency of the TLC5947 should be around 1kHz (based on 4MHz nominal internal clock and 4096 clocks per PWM cycle). If you use a 100uF decoupling capacitor, that will give an impedance of 1.6 ohms to ground. To get a 10-fold reduction in the amplitude of the unwanted signal, the impedance of the inductor should be 16 ohms, which implies an inductance of about 3.3mH
How did he arrive at 3.3mH? I can't figure out how you take 1000hz and 16 ohms and arrive at a value of 3.3.
Elsewhere he suggested that a 1000uf capacitor may be be better and I need to know how to adjust the mH for the larger capacitor.
(In case it matters, the maximum current that will flow through this inductor would be 480mA. 20mA max per LED for 24 leds.)