LM3450AEV230V30/NOPB National Semiconductor, LM3450AEV230V30/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM3450AEV230V30/NOPB
• Description: LM3450A EVAL BOARD 230V30
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3450AEV230V30/NOPB

• Current - Output / Channel: 700mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 50V
• Features: -
• Voltage - Input: 180 ~ 265VAC
• Utilized Ic / Part: LM3450A
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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PHASE DIMMER OPERATION
A simplified schematic of a phase dimmer is shown in
8. An RC network consisting of R1, R2, and C1 delay the turn-
on of the triac until the voltage on C1 reaches the trigger
voltage of the diac. Increasing the resistance of the poten-
tiometer (wiper moving downward) increases the turn-on de-
lay which decreases the on-time or “conduction angle” of the
triac (θ). This reduces the average power delivered to the
load.
Phase dimmer voltage waveforms are shown in
Figure 9a shows the full sinusoid of the input voltage. Even
when set to full brightness; few dimmers will provide 100%
conduction angle.
Figure 9b shows a waveform from a forward phase dimmer.
The off-time can be referred to as the firing angle and is simply
180° – θ.
Figure 9c shows the waveform of a reverse phase dimmer
(also called an electronic dimmer in the lighting industry).
These typically or more expensive, microcontroller based
dimmers that use switching devices other than triacs. Note
that the conduction angle starts from the zero-crossing, and
terminates some time later. This method of control reduces
the noise spike at the transition.
Any form of phase dimming modulates the incoming AC
waveform by chopping part of the sinusoid, reducing the av-
erage power to the load. These dimmers work very well with
standard incandescent bulbs, but not with power converters.
A converter attempts to regulate the load in with presence of
any input, effectively ignoring the phase angle. To implement
a dimmable converter, the angle must be sensed at the input,
decoded and used to properly control the LED current regu-
lator.
FIGURE 8. Basic Forward Phase Dimmer
Figure
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Figure
9.
16
PRECISION VOLTAGE REFERENCE
The LM3450 provides a 3V voltage reference (V
asing the V
regulated once V
for the reference. A 10nF ceramic bypass capacitor should be
placed from V
LOW POWER SHUTDOWN
The LM3450 can be placed into a low power shutdown by
grounding the V
power shutdown, the device will turn on the GATE for one
cycle followed by a fixed off-time of 42µs and the cycle re-
peats. During shutdown, the DIM output will be high (zero light
output) since the buffer rail at FLT1 will be at or near zero.
This feature is designed to hold up the PFC output voltage
while removing the load (turning the LEDs off).
THERMAL SHUTDOWN
Internal thermal shutdown circuitry is provided to protect the
IC in the event that the maximum junction temperature is ex-
ceeded. The threshold for thermal shutdown is 160°C with a
20°C hysteresis. During thermal shutdown GATE is disabled.
FIGURE 9. Phase Dimming Waveforms
ADJ
REF
pin as well as any external circuitry. V
ADJ
CC
to GND.
pin (any voltage below 75mV). During low
exceeds 3V. There is a 2mA current limit
REF
) for bi-
30127430
REF
is