lnk403 Power Integrations, Inc., lnk403 Datasheet - Page 9

• Manufacturer Part Number: lnk403
• Description: Led Driver Ic With Triac Dimming, Single-stage Pfc And Primary-side Constant Current Control
• Manufacturer: Power Integrations, Inc.

also acceptable however the peak drain voltage should be
carefully verified during start-up and output short-circuit as the
clamping voltage varies with significantly with the peak drain
current.
For the highest efficiency, the clamping voltage should be
selected to be at least 1.5 times the output reflected voltage,
V
When using a Zener clamp in a universal input or high line only
application, a V
for the absolute tolerances and temperature variations of the
Zener. This will ensure efficient operation of the clamp circuit
and will also keep the maximum drain voltage below the rated
breakdown voltage of the MOSFET. An RCD (or RCDZ) clamp
provides tighter clamp voltage tolerance than a Zener clamp.
The RCD clamp is more cost effective than the Zener clamp but
requires more careful design to ensure that the maximum drain
voltage does not exceed the power MOSFET breakdown
voltage. These V
internal MOSFET, a V
designs, giving the best PFC and regulation performance.
Series Drain Diode
An ultra-fast or Schottky diode in series with the drain is
necessary to prevent reverse current flowing through the
device. The voltage rating must exceed the output reflected
voltage, V
average primary current and have a peak rating equal to the
maximum drain current of the selected LinkSwitch-PH device.
Line Voltage Peak Detector Circuit
LinkSwitch-PH devices use the peak line voltage to regulate the
power delivery to the output. A capacitor value of 1 mF to 4.7 mF
is recommended to minimize line ripple and give the highest
power factor (>0.9), smaller values are acceptable but result in
lower PF and higher line current distortion.
Operation with Phase Controlled Dimmers
Dimmer switches control incandescent lamp brightness by not
conducting (blanking) for a portion of the AC voltage sine wave.
This reduces the RMS voltage applied to the lamp thus
reducing the brightness. This is called natural dimming and
LinkSwitch-PH devices when configured for dimming utilize
natural dimming by reducing the LED current as the RMS line
voltage decreases. By this nature, line regulation performance is
purposely decreased to increase the dimming range and more
closely mimic the operation of an incandescent lamp. Using a
49.9 kW REFERENCE pin resistance, selects natural dimming
mode operation.
Leading Edge Phase Controlled Dimmers
The requirement to provide flicker-free output dimming with low
cost, TRIAC-based, leading edge phase dimmers introduces a
number of trade-offs in the design.
Due to the much lower power consumed by LED based lighting
the current drawn by the overall lamp is below the holding
current of the TRIAC within the dimmer. This causes undesirable
behaviors such as limited dimming range and/or flickering. The
relatively large impedance the LED lamp presents to the line
www.powerint.com
OR
, as this keeps the leakage spike conduction time short.
OR
. The current rating should exceed two times the
OR
OR
of less than 135 V is recommended to allow
limits are based on the BV
OR
of 60 V to 100 V is typical for most
DSS
rating of the
Figure 8.
allows significant ringing to occur due to the inrush current
charging the input capacitance when the TRIAC turns on. This
too can cause similar undesirable behavior as the ringing may
cause the TRIAC current to fall to zero and turn off.
To overcome these issues two circuits, the Active Damper and
Passive Bleeder, are incorporated. The drawback of these
circuits is increased dissipation and therefore reduced efficiency
of the supply so for non-dimming applications these
components can simply be omitted.
Figure 8(a) shows the line voltage and current at the input of a
leading edge TRIAC dimmer with Figure 8(b) showing the
resultant rectified bus voltage. In this example, the TRIAC
conducts at 90 degrees.
Figure 9 shows undesired rectified bus voltage and current with
the TRIAC turning off prematurely and restarting.
If the TRIAC is turning off before the end of the half-cycle
erratically or alternate half AC cycles have different conduction
angles then flicker will be observed in the LED light due to
variations in the output current. This can be solved by including
a bleeder and damper circuit.
-150
-250
-350
350
250
150
-50
350
300
250
200
150
100
50
50
0
0.5
0
(a) Ideal Input Voltage and Current Waveforms for a Leading Edge
TRIAC Dimmer at 90° Conduction Angle. (b) Resultant Waveforms
Following Rectification of TRIAC Dimmer Output.
50
50
100
100
Conduction Angle (°)
Conduction Angle (°)
150
150
200
200
Voltage
Current
LNK403-409EG
250
250
300
300
PI-5983-060810
Voltage
Current
PI-5984-060810
350
350
Rev. A 080610
400
400
0.35
0.25
0.15
0.05
-0.05
-0.15
-0.25
-0.35
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
9