Design Win

15W 5V USB adapter

Solution Description

This is a 15 W (5 V-3 A) wide range mains USB power adapter solution based on the STCH03 current-mode quasi-resonant controller, which combines a high-performance, low voltage PWM controller chip with a 650 V HV start-up cell in the same package. The switching controller provides constant output current (CC) regulation through primary-sensing feedback.

This solution maintains accurate output current regulation without the need for a dedicated current reference IC or a current sensor, and provides a full set of protections, including output overvoltage (OVP)  and undervoltage (UVP) protection, transformer saturation and secondary diode short protection, which considerably increases end-product safety and reliability.

The architecture of the solution is based on a single-ended QR Flyback converter consisting of the following stages: (i) an input stage with front-end AC rectifier, low cost EMI filter, fuse and NTC to ensure safe converter operation; (ii) an RCD Snubber network protects the Power MOSFET at turn-off by limiting the leakage inductance voltage spike and dissipating the corresponding energy; (iii) a power and control stage with STD7N80K5 N-channel 800V, 0.95Ω MDmesh K5 Power MOSFET in DPAK package, connected to the HF transformer and driven by the STCH03 PWM controller - constant voltage (CV) and constant current (CC) operation is achieved with minimum number of external components; (iv) an output stage intended to implement high efficiency secondary side rectification based on FERD20U50DJF 50V, 20A Field-Effect Rectifier Diode (FERD) in Power FLAT package and to feed the Primary PWM IC with output voltage feedback signal.

This high power density, high efficiency power supply solution is able to satisfy energy saving recommendations (EuCoC rev. 5 – Tier 2 and EPS of DOE USA), with low standby power (less than 15 mW at 230 VAC), compliance with EN55022-Class-B Conducted noise emissions and immunity compliance according to IEC61000.


  • Key Product Benefits

    STCH03 - high efficiency regulator

    The STCH03 is a current-mode PWM controller with fully integrated primary side constant current output regulation (CC). It is specifically designed for offline quasi-resonant ZVS flyback converters such as this solution, and helps achieve maximum efficiency and very low power consumption. The controller supports three different modes according to the output load level in order to optimize conduction and switching losses and to minimize input power consumption, thereby allowing the solution to comply with even the most stringent energy saving regulations: 

    • QR mode at heavy load 
    • Valley-skipping mode at medium/light load 
    • Burst mode at very light load or with disconnected load 

    The device also offers the output overvoltage protection (OVP), overtemperature protection (OTP), and hiccup-mode protection, which is invoked when the transformer saturates or the secondary diode fails, and output undervoltage protection (UVP) that limits the average output current in case of an output short-circuit.

    STD7N80K5 - 800V Power MOSFET

    The primary side power switch is an N-channel 800V, 0.95 Ω typ. Power MOSFET belonging to MDmesh K5 series of ST’s best-in-class super-junction VHV MOSFET technology, which ensures the best efficiency, robustness and safety margin for flyback converters where the size of the DRAIN snubber circuit can benefit. This revolutionary, avalanche-rugged, high voltage Power MOSFET technology is based on an innovative proprietary vertical structure. The result is a drastic reduction in on-resistance at very high BVdss, an ultra-low gate charge for applications which require high switching speed, superior power density and high efficiency, and unequaled robustness at very high BVdss. The selected DPAK package helps achieve high power density in a slim form factor.

    FERD20U50DJF best-in-class rectifier

    Packaged in PowerFLAT™ 5x6, the FERD20U50 is used in the secondary side rectification. This 50V/20A diode based on a proprietary process achieves the best-in-class VF/IR trade-off for a given chip surface. This diode exhibits much better intrinsic performance than traditional Schottky-structured diodes of equivalent voltage and current ratings. The combination of a lower VF diode, with better control of leakage current, integrated into a smaller die enable designers to reach higher efficiency, implement easier thermal design and use smaller packages, resulting in a higher application compactness, with potential cost benefits.

  • All Features

    • Universal AC Main Input voltage range: 90 VAC to 264 VAC
    • Output range: 5 V-3 A continuous operation
    • Constant voltage (CV) and constant current (CC) operation with CC primary sensing
    • Output overvoltage and short-circuit protection
    • Input power in standby <15 mW at 230 VAC
    • Intelligent power management to maximize efficiency over entire output power range
    • Compliant with stringent energy regulations: EuCoC rev. 5 – Tier 2 and EPS of DOE USA
    • EMI: According to EN55022-Class-B
    • ESD Immunity test: compliant to IEC 61000-4-2
    • Surge immunity test:  compliant to IEC 61000-4-5
    • Burst immunity test: compliant to IEC 61000-4-4
    • Small form factor: 44x35x15 mm