LED Driver with Integrated Spread Spectrum Reduces EMI without Adding Flicker

February 03, 2015 // By Keith Szolusha, Linear Technology

Odds are good that something will fall into the AM band. One way to minimize EMI peaks is to allow the switch mode power supply (SMPS) operating frequency to cover a range of values, namely spread spectrum switching. The desired effect of spread spectrum switching is to push down the EMI peaks that would occur at the SMPS fundamental operating frequency and harmonics, spreading the EMI energy over a range of frequencies instead.

Automotive LED drivers should be compact, efficient and support flicker-free PWM dimming. They should not produce significant conducted EMI at and around the AM radio band. Unfortunately, low EMI is not in the nature of high power switch mode power supplies—the constant switching frequency produces a significant EMI signature at a number of frequencies, including the power supply's fundamental operating frequency and its harmonics.
Linear Technology, LT3795, LED Driver