LM3445-120VFLBK/NOPB National Semiconductor, LM3445-120VFLBK/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM3445-120VFLBK/NOPB
• Description: PROGRAMMERS, DEVELOPMENT SYSTEMS
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3445-120VFLBK/NOPB

• Current - Output / Channel: 365mA
• Outputs And Type: 1, Isolated
• Voltage - Output: 20V
• Features: Dimmable, TRIAC Dimmable
• Voltage - Input: 90 ~ 135VAC
• Utilized Ic / Part: LM3445
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Circuit Analysis and Explanations
INJECTING LINE VOLTAGE INTO FILTER-2 (achieving
PFC > 0.95)
If a small portion (750mV to 1.00V) of line voltage is injected
at FLTR2 of the LM3445, the circuit is essentially turned into
a constant power flyback as shown in Figure 6.
The LM3445 works as a constant off-time controller normally,
but by injecting the 1.0V rectified AC voltage into the FLTR2
FIGURE 6. Line Voltage Injection Circuit
FIGURE 8. Typical Operation of FLTR2 Pin
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pin, the on-time can be made to be constant. With a DCM
Flyback, Δi needs to increase as the input voltage line in-
creases. Therefore a constant on-time (since inductor L is
constant) can be obtained.
By using the line voltage injection technique, the FLTR2 pin
has the voltage wave shape shown in Figure 7 on it with no
triac dimmer in-line. Voltage at V
below 1.25V. At 1.25V current limit is tripped. C11 is small
enough not to distort the AC signal but adds a little filtering.
Although the on-time is probably never truly constant, it can
be observed in Figure 8 how (by adding the rectified voltage)
the on-time is adjusted.
For this evaluation board, the following resistor values are
used:
R2 = R7 = 309kΩ
R15 = 3.48kΩ
Therefore the voltages observed on the FLTR2 pin will be as
follows for listed input voltages:
For VIN = 90V
For VIN = 120V
For VIN = 135V
Using this technique, a power factor greater than 0.95 can be
achieved without additional passive active power factor con-
trol (PFC) circuitry.
FIGURE 7. FLTR2 Waveform with No Dimmer
RMS
RMS
RMS
, V
, V
, V
FLTR2
FLTR2
FLTR2
= 0.71V
= 0.95V
= 1.07V
FLTR2
peak should be kept
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