A LYTSwitch-4 device monolithically combines a controller and
high-voltage power FET into one package. The controller
provides both high power factor and constant current output in
a single-stage. The LYTSwitch-4 controller consists of an
oscillator, feedback (sense and logic) circuit, 5.9 V regulator,
hysteretic over-temperature protection, frequency jittering,
cycle-by-cycle current limit, auto-restart, inductance correction,
power factor and constant current control.
FEEDBACK Pin Current Control Characteristics
The figure shown below illustrates the operating boundaries of
and below IFB(AR)
Maximum Duty Cycle
Figure 6. FEEDBACK Pin Current Characteristic.
The FEEDBACK pin current is also used to clamp the maximum
duty cycle to limit the available output power for overload and
open-loop conditions. This duty cycle reduction characteristic
also promotes a monotonic output current start-up characteristic
and helps preventing over-shoot.
The REFERENCE pin is tied to ground (SOURCE) via an external
resistor. The value selected sets the internal references,
determining the operating mode for dimming (LYT4311-4318)
and non-dimming (LYT4211-4218) operation and the line
overvoltage thresholds of the VOLTAGE MONITOR pin.
For non-dimming or PWM dimming applications with LYT4211-
4218, the external resistor should be a 24.9 kW ±1%. For phase
angle AC dimming with LYT4311-4318, the external resistor
should be a 49.9 kW ±1%. One percent resistors are
recommended as the resistor tolerance directly affects the
output tolerance. Other resistor values should not be used.
BYPASS Pin Capacitor Power Gain Selection
LYTSwitch-4 devices have the capability to tailor the internal
gain to either full or a reduced output power setting. This allows
selection of a larger device to minimize dissipation for both
thermal and efficiency reasons. The power gain is selected with
the value of the BYPASS pin capacitor. The full power setting is
selected with a 4.7 mF capacitor and the reduced power setting
(for higher efficiency) is selected with a 47 mF capacitor. The
BYPASS pin capacitor sets both the internal power gain as well
as the over-current protection (OCP) threshold. Unlike the
larger devices, the LYT4x11 power gain is not programmable.
Use a 47 mF capacitor for the LYT4x11.
The switching frequency is 132 kHz during normal operation.
To further reduce the EMI level, the switching frequency is
jittered (frequency modulated) by approximately 2.6 kHz.
During start-up the frequency is 66 kHz to reduce start-up time
when the AC input is phase angle dimmed. Jitter is disabled in
The controller includes a soft-start timing feature which inhibits
the auto-restart protection
to distinguish start-up into
afefaatuulrte(sfhoor rtth-ecisrcouftit-)sftraormt paerlaiordge(tSOFT)
output capacitor. At start-up the LYTSwitch-4 clamps the
maximum duty cycle to reduce the output power. The total
soft-start period is tSOFT.
Remote ON/OFF and EcoSmart™
The VOLTAGE MONITOR pin has a 1 V threshold comparator
connected at its input. This voltage threshold is used for
remote ON/OFF control. When a signal is received at the
VOLTAGE MONITOR pin to disable the output (VOLTAGE
MONITOR pin tied to ground through an optocoupler photo-
transistor) the LYTSwitch-4 will complete its current switching
cycle before the internal power FET is forced off.
The remote ON/OFF feature can also be used as an eco-mode
or power switch to turn off the LYTSwitch-4 and keep it in a
very low power consumption state for indefinite long periods.
When the LYTSwitch-4 is remotely turned on after entering this
mode, it will initiate a normal start-up sequence with soft-start
the next time the BYPASS pin reaches 5.9 V. In the worst case,
the delay from remote on to start-up can be equal to the full
discharge/charge cycle time of the BYPASS pin. This reduced
consumption remote off mode can eliminate expensive and
unreliable in-line mechanical switches.
Rev. E 11/14