User manual

SNS

PWM

I-LIM

1.27V

SNS

PGND

FILTER

750 mV

125 ns

LEADING EDGE BLANKING

Nearly a constant on-

time as the line varies

The PWM reference increases

as the line voltage increases.

As line voltage increases, the voltage across the

inductor increases, and the peak current increases.

D x LED Current

Circuit Analysis and Explanations

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For this evaluation board, the following resistor values are used:

R2 = R7 = 309kΩ

R15 = 3.48kΩ

Therefore the voltages observed on the FILTER pin will be as follows for listed input voltages:

For VIN = 90V

RMS

, V

FILTER

= 0.71V

For VIN = 120V

RMS

, V

FILTER

= 0.95V

For VIN = 135V

RMS

, V

FILTER

= 1.07V

Using this technique, a power factor greater than 0.99 can be achieved without additional passive active

power factor control (PFC) circuitry.

Figure 25. Typical Operation of FILTER Pin

AN-2082 LM3444 -120VAC, 8W Isolated Flyback LED Driver SNVA454E–September 2010–Revised May 2013

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