LNK454/456-458/460
DES
DZOV
ROV
RES
AC
IN
LinkSwitch-PL
D
S
CONTROL
BP
FB
CF
RF
RSENSE
PI-5837-060710
Figure 4. Typical Application Schematic.
Functional Description
Auto-restart protection is triggered by a FEEDBACK pin voltage
in excess of 2 V. This feature can be used to provide output
overvoltage protection (via DZOV and ROV, in Figure 4), which
triggers the IC to enter auto-restart.
The LinkSwitch-PL combines a high-voltage power MOSFET
switch with a power supply controller in one device. The IC
provides a single-stage power factor correction plus LED
current control. The LinkSwitch-PL controller consists of an
oscillator, feedback (sense and logic) circuit, 5.85 V regulator,
hysteretic over-temperature protection, frequency jittering,
cycle-by-cycle current limit, loop compensation circuitry, auto-
restart, switching on-time extension, power factor and constant
current control.
Auto-Restart
In a direct LED current sensing configuration, the average
FEEDBACK pin voltage is a replica of the LED current, scaled
by the sense resistor (RSENSE in Figure 4). A small low-pass filter
(RF and CF in Figure 4) reduces high frequency noise at the
FEEDBACK pin.
2 V
Cycle Skipping
Mode
Figure 5 illustrates the operating regions of the FEEDBACK pin
voltage. The LinkSwitch-PL sets its operating point such that
the average FEEDBACK pin voltage in steady-state operation is
290 mV. This threshold is set low to minimize the sensing
resistor dissipation. The internal MOSFET switching frequency
and on-time are updated once every input AC half-cycle to
regulate the output current and maintain high power factor.
550 mV
Normal Operation
If the FEEDBACK pin peak voltage exceeds 550 mV, cycle
skipping mode is triggered and the power processed by the
integrated power MOSFET is clamped on a cycle-by-cycle
basis. Switching frequency may vary during an input voltage
half-cycle to reduce thermal stress on the output LEDs.
290 mV
PI-5838-060111
Figure 5. FEEDBACK Pin Operational Voltage Thresholds.
3
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Rev. C 10/11
POWERINT [ Power Integrations ]
