Reducing EMIDesigners creating circuits switching medium to high currents need to be concerned about Electromagnetic Interference (EMI). The LEDs and the CCR switch extremely fast, less than 100 nanoseconds. To help eliminate EMI, a capacitor can be added to the circuit across R2. (Figure 11) This will cause the slope on the rising and falling edge on the current through the circuit to be extended. The slope of the CCR on/off current can be controlled by the values of R1 and C1.The selected delay / slope will impact the frequency that is selected to operate the dimming circuit. The longer the delay, the lower the frequency will be. The delay time should not be less than a 10:1 ratio of the minimum on time. The frequency is also impacted by the resolution and dimming steps that are required. With a delay of 1.5 microseconds on the rise and the fall edges, the minimum on time would be 30 microseconds. If the design called for a resolution of 100 dimming steps, then a total duty cycle time (Ts) of 3 milliseconds or a frequency of 333 Hz will be required
Please somebody help me understand how to work out the value of capacitor I need to add to my PWM CCR circuit. I read that the Arduino's PWM frequency is at about 500Hz, and that I will have 255 dimming steps. But the recommendation for adding a capacitor in my CCR datasheet leaves me very confused:
Do you really care about a little EMI?
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