Off-Line Quasi-Resonant Switching Regulators
Features and Benefits
▪ Quasi-resonant topology IC Low EMI noise and soft
▪ Bottom-skip mode Improved system efficiency over
the entire output load by avoiding increase of switching
▪ Standby mode Lowers input power at very light output
▪ Avalanche-guaranteed MOSFET Improves system-level
reliability and does not require VDSS derating
▪ 450 VDSS / 0.189 Ω RDS(on)
▪ Various protections Improved system-level reliability
▫ Pulse-by-pulse drain overcurrent limiting
▫ Overvoltage Protection (bias winding voltage sensing),
▫ Overload Protection with latch
▫ Maximum on-time limit
Package: 7-Pin TO-3P
Not to scale
The STR-X6729 is a quasi-resonant topology IC designed for
SMPS applications. It shows lower EMI noise characteristics
than conventional PWM solutions, especially at greater than
2 MHz. It also provides a soft-switching mode to turn on the
internal MOSFET at close to zero voltage (VDS bottom point)
by use of the resonant characteristic of primary inductance
and a resonant capacitor.
The package is a fully molded TO-3P, which contains the
controller chip (MIC) and MOSFET, enabling output power
up to 460 W at 120 VAC input. The bottom-skip mode skips
the first bottom of VDS and turns on the MOSFET at the second
bottom point, to minimize an increase of operating frequency
at light output load, improving system-level efficiency over
the entire load range.
Astandby mode is executed by clamping the secondary output.
In general applications, standby mode reduces input power.
The soft-start mode minimizes surge voltage and reduces power
stress to the MOSFET and to the secondary rectifying diodes
during the start-up sequence.
Various protections such as overvoltage, overload, overcurrent,
maximum on-time protections and avalanche-energy guaranteed
MOSFET secure good system-level reliability.
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