lnk403 Power Integrations, Inc., lnk403 Datasheet - Page 8

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

turns on pulling down the FEEDBACK pin of U1 and initiating
auto-restart operation. Once in auto-restart the low duty cycle
of operation (~3%) together with the small pre-load on the
output prevents the output voltage rising to a high level. Once
the output load is reconnected normal operation resumes.
Capacitor C12 provides local decoupling for the BYPASS pin of
U1 which is the supply pin for the internal controller. During
start-up C4 is charged to ~6 V from an internal high-voltage
current source tied to the device DRAIN pin. Once the bias
voltage has risen into regulation the operating supply current is
provided via R10. Diode D4 prevents U1 from charging C6
during start-up which would increase the start-up delay time.
Capacitor C12 also selects the output power mode, reduced
power mode (C12 = 10 mF) was selected to reduce device
dissipation and improve efficiency necessary for the thermal
environment of an LED light bulb.
Feedback
The bias winding voltage is proportional to the output voltage
(set by the turns ratio between the bias and secondary
windings). This allows the output voltage to be monitored
without secondary side feedback components. Resistor R15
converts the bias voltage into a current which is fed into the
FEEDBACK pin of U1. The internal engine within U1 combines
the FEEDBACK pin current, VOLTAGE MONITOR pin current
and drain current information to provide a constant output
current over a 2:1 output voltage range.
Output Rectification
The transformer secondary winding is rectified by D2 and
filtered by C4 and C5. A Schottky barrier diode was selected
for efficiency and the combined value of C4 and C5 were
selected to give an acceptable LED ripple current. For designs
where lower ripple is desirable the output capacitance value
can be increased. A small pre-load is provided by R6 which
limits the output voltage under no-load conditions.
Key Application Considerations
Power Table
The data sheet power table (Table 1) represents the minimum
and maximum practical continuous output power based on the
following conditions:
1. Efficiency of 80%
2. Device local ambient of 70 °C
3. Sufficient heat sinking to keep the device temperature
4. For minimum output power column
5. For maximum output power column
Rev. A 080610
8
below 100 °C
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Reflected output voltage (V
FEEDBACK pin current of 165 mA
BYPASS pin capacitor value of 100 mF
(LNK403EG = 10 mF)
Reflected output voltage (V
FEEDBACK pin current of 135 mA
BYPASS pin capacitor value of 10 mF
LNK403-409EG
OR
OR
) of 65 V
) of 120 V
Note that input line voltages above 85 VAC do not change the
power delivery capability of LinkSwitch-PH devices.
Device Selection
Select the device size by comparing the required output power
to the values in Table 1. For thermally challenging designs, e.g.
incandescent lamp replacement, where either the ambient
temperature local to the LinkSwitch-PH device is high and/or
there is minimal space for heat sinking use the minimum output
power column. This is selected by using a 10 mF BYPASS pin
capacitor and results in a lower device current limit and
therefore lower conduction losses. For open frame design or
designs where space is available for heat sinking then refer to
the maximum output power column. This is selected by using a
100 mF BYPASS pin capacitor for all but the LNK403 which has
only one power setting. In all cases in order to obtain the best
output current tolerance maintain the device temperature below
100 °C
Maximum Input Capacitance
To achieve high power factor, the capacitance used in both the
EMI filter and for decoupling the rectified AC (bulk capacitor)
must be limited in value. The maximum value is a function of
the output power of the design and reduces as the output
power reduces. For the majority of designs limit the total
capacitance to less than 200 nF with a bulk capacitor value of
100 nF. Film capacitors are recommended compared to
ceramic types as they minimize audible noise with operating
with leading edge phase dimmers. Start with a value of 10 nF
for the capacitance in the EMI filter and increase in value until
there is sufficient EMI margin.
REFERENCE Pin Resistance Value Selection
LinkSwitch-PH can be programmed via the REFERENCE pin
resistor for dimming or non-dimming applications. Use a
49.9 kW resistor value for dimming applications. This allows the
largest dimming range, however line regulation performance is
reduced. For non-dimming applications (least variation of
output current with AC input voltage changes) use a 24.9 kW
value.
VOLTAGE MONITOR Pin Resistance Network Selection
For widest AC phase angle dimming range, use a 4 MW resistor
connected to the line voltage peak detector circuit. Make sure
that the resistor’s voltage rating is sufficient for the peak line
voltage. If necessary use multiple series connected resistors.
For best line regulation, use a series combination of resistors
that equals 3.909 MW connected to the line voltage peak
detector. In addition, connect a 1 MW in series with a 402 kW
resistor (1.402 MW total) from the VOLTAGE MONITOR pin to
SOURCE pin. Use 1% tolerance resistors for good accuracy.
Line regulation can be further improved by using the PIXls
spreadsheet’s fine tuning section. See the LinkSwitch-PH
Application Note for more information.
Primary Clamp and Output Reflected Voltage V
A primary clamp is necessary to limit the peak drain to source
voltage. A Zener clamp requires the fewest components and
board space and gives the highest efficiency. RCD clamps are
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