STR-X6757 - Off-Line Quasi-Resonant Switching Regulators - Features and Benefits

Oct 12, 2026

STR-X6757 is a quasi-resonant topology IC for SMPS applications, engineered to reduce EMI noise versus conventional PWM solutions, especially above 2 MHz. It enables soft switching by turning on the internal MOSFET near zero voltage using the resonant behavior of the primary inductance and a resonant capacitor. A molded TO-3P package integrates the controller chip and MOSFET, supporting up to 320 W at 230 VAC. It includes bottom-skip operation to avoid light-load frequency increases, plus auto and manual standby modes that lower input power. Protection features include pulse-by-pulse drain overcurrent limiting, latched overvoltage and overload protections, maximum on-time limiting, and an avalanche-energy guaranteed MOSFET for improved reliability.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages11

Reading Time28 min

AccessFree to download

Features and Benefits

Typical Application

Description (continued)

Selection Guide

Absolute Maximum Ratings

Functional Block Diagram

Terminal List Table

Thermal Derating Curves

STR-X6757 | Off-Line Quasi-Resonant Switching Regulators | | | | --- | --- | --- | | Features and Benefits
▪ Quasi-resonant topology IC 􀂟 Low EMI noise and soft switching
▪ Bottom-skip mode 􀂟 Improved system efficiency over the entire output load by avoiding increase of switching frequency
▪ Auto-Standby mode 􀂟 Lowers input power at very light output load condition
▪ Avalanche-guaranteed MOSFET 􀂟 Improves system-level reliability and does not require VDSS derating
▪ 650 VDSS / 0.62 Ω RDS(on)
▪ Various protections 􀂟 Improved system-level reliability
▫ Pulse-by-pulse drain overcurrent limiting
▫ Overvoltage Protection (bias winding voltage sensing), with latch
▫ Overload Protection with latch
▫ Maximum on-time limit
Package: 7-Pin TO-3P | | Description
The STR-X6757 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 320 W at 230 VAC and 165 W at universal input. The bottom-skip mode skips the first bottom of VDS and turns on the MOSFET atthe second bottom point, to minimize an increase of operating frequency at light output load, improving systemlevel efficiency over the entire load range. There aretwo standbymodesavailabletoreducetheinputpower under very light load conditions. The first is Auto-Standby mode, which is internally triggered by periodic sensing, and the other is a manual standby mode, which is executed by clamping the secondary output. In general applications, the manual standbymodereducestheinputpowerfurthercompared to Auto-Standby mode.
Continued on the next page… | | Not to scale | | | Typical Application | STR-X6757 | Off-Line Quasi-Resonant Switching Regulators | | --- | --- | Description (continued) The soft-startmodeminimizes surgevoltageandreducespower 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-energyguaranteed MOSFET secure good system-level reliability. Applications include the following: ▪ Set Top Box ▪ LCD PC monitor, LCD TV ▪ Printer, Scanner ▪ SMPS power supplies Selection Guide | Part Number | Package | | --- | --- | | STR-X6757 | TO-3P | Absolute Maximum Ratings at TA = 25°C | Parameter | Symbol | Conditions | Rating | Unit | | --- | --- | --- | --- | --- | | Drain Current1 | IDpeak | Single pulse | 18 | A | | Maximum Switching Current2 | IDmax | TA = –20°C to 125°C | 18 | A | | Single Pulse Avalanche Energy3 | EAS | Single pulse, VDD = 30 V, L = 50 mH, ILpeak = 3.53 A | 326 | mJ | | Input Voltage for Controller (MIC) | VCC | | 35 | V | | SS/OLP Terminal Voltage | VSSOLP | | –0.5 to 6.0 | V | | FB Terminal Inflow Current | IFB | | 10 | mA | | FB Terminal Voltage | VFB | IFB within the limits of IFB | –0.5 to 9.0 | V | | OCP/BD Terminal Voltage | VOCPBD | | –1.5 to 5.0 | V | | MOSFET Power Dissipation4 | PD1 | With infinite heatsink | 44 | W | | | | Without heatsink | 2.8 | W | | Controller (MIC) Power Dissipation | PD2 | VCC × ICC | 0.8 | W | | Operating Internal Leadframe Temperature | TF | Recommended operation temperature, see cautions | –20 to 125 | °C | | Operating Ambient Temperature | TOP | | –20 to 125 | °C | | Storage Temperature | Tstg | | –40 to 125 | °C | | Channel Temperature | Tch | | 150 | °C | 1Refer to MOSFET ASO curve 2IDMAX is the drain current determined by the drive voltage of the IC and the threshold voltage, Vth, of the MOSFET 3Refer to Avalanche Energy Derating curve 4Refer to MOSFET Ta-PD1 curve All performa

FAQs

What switching behavior does STR-X6757 provide to reduce stress on the MOSFET?

It uses a soft-switching mode that turns on the internal MOSFET close to zero voltage (near the VDS bottom point) through the resonant characteristics of the primary inductance and resonant capacitor.

How does bottom-skip mode improve efficiency at light load?

Bottom-skip mode skips the first VDS bottom and turns on the MOSFET at the second bottom point, minimizing an increase in operating frequency and improving system efficiency over the full load range.

Which protection functions are included in STR-X6757?

It provides pulse-by-pulse drain overcurrent limiting, latched overvoltage protection (bias winding voltage sensing), latched overload protection, maximum on-time limiting, and an avalanche-energy guaranteed MOSFET to enhance system reliability.

Oct 12, 2026

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