AN4130 datasheet(9/41 Pages) STMICROELECTRONICS

9 / 41 page

AN4130

Theory of operation

Doc ID 023315 Rev 1

9/41

line voltage, and is a compromise for all others. But it's “good enough”. The small capacitor

across the lower resistor is only there to keep switching noise out of the circuit.

Figure 6.

Voltage and current waveforms with AC injection

The current waveform at the “nominal line” above actually has the lowest harmonic content

due to the input current distortion inherent in the PFC-flyback converter. The HVLED815PF

clamps the voltage on the ILED pin between about 0.2 V on the low end, and at about 1.5 V

on the high end. If the injected waveform wants to swing below 0.2 V, the peak current in the

FET is set to zero, so no input current flows. The scope images in Figure 7, 8, and 9 show

how well the AC injection works.

Figure 7.

Waveforms with 90 V input

Figure 8.

Waveforms with 110 V input

Trace colors:

Yellow = line voltage

Magenta = line current, 50 mA/div ref -3div

Blue = voltage at ILED pin, ref -3 div

Green = LED current, 50 mA/div ref -3div

Trace colors:

Yellow = line voltage

Magenta = line current, 50 mA/div ref -3div

Blue = voltage at ILED pin, ref -3 div

Green = LED current, 50 mA/div ref -3div

AN4130 Datasheet(PDF) 9 Page - STMicroelectronics