The FS6X1220RT Fairchild
Power Switch (FPS), from Fairchild Semiconductor International (San
Jose, CA, U.S.), is a highly integrated off-line power switch designed
for appliances that use an internal medium-voltage d.c. bus for distribution
of power (48 V to 72 V d.c.). Possible applications include digital
feature phones, VOIP (Voice Over Internet Protocol) phones, and telecom
central office power supplies.
According to the company, the new power switch integrates a fully avalanche-rated
SenseFET (200-V minimum breakdown rating) with a current mode PWM (pulse
width modulation) IC––a unique combination that minimizes external components,
simplifies designs, and lowers cost in target applications.
Madhu Rayabhari, Fairchild's strategic marketing director of Integrated
Circuits Group, explains, "SenseFET is a special power MOSFET that has
a single gate and drain but two sources - one for the main power path and
another that provides a proportional current output. This proportional
current output feeds our PWM IC directly on chip. Hence, designing for
an external current sense resistor is eliminated, which, in turn, minimizes
external components and simplifies designs. As this approach eliminates
the use of a precision, high-power resistor, it also reduces the cost."
Designs based on the integrated FS6X1220RT are also said to achieve a
higher performance than offered by discrete MOSFET/controller or RCC switching
converter solutions while benefiting from reduced board space and improved
"VOIP phones, for example, require extremely compact power supplies that
feature high reliability and efficiency," Mr. Rayabhari tells APPLIANCE. "The
FS6X1220RT enhances system reliability by minimizing the number of components
needed and providing a variety of protection features such as overload
and overcurrent protection. High performance is provided by the current
mode PWM function. It also enhances system efficiency through optimized
An integrated 300-kHz oscillator helps to further increase system efficiency
and allows for the use of smaller transformers. "This device has optimized
gate drivers and internal SenseFET that minimize the switching losses for
the 300-KHz frequency. This combination of frequency choice and internal
component performance enhances efficiency," Mr. Rayabhari explains. "By
employing a higher switching frequency than conventional PWM ICs, the size
of the transformer - and also, associated capacitors - is reduced."
The FS6X1220RT also features line-under voltage detection, remote sleep
on/off, under-voltage lock out, and an optimized blanking and gate turn-on/turn-off
driver. In addition, the device has temperature-compensated, precision
current sources for loop compensation and fault protection circuitry.