STMicroelectronics – Integrated AC-DC converter IC with PFC achieves excellent light-load efficiency

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STMicroelectronics has introduced the STCMB1, an AC-DC converter IC with Power Factor Correction (PFC) capability built in. It provides an output voltage up to 19V and supports loads of up to 90W.

The STCMB1 consists of a transition-mode PFC stage, a high-voltage double-ended controller for an LLC resonant half-bridge, an 800V high-voltage power stage, and the glue logic which supervises the operation of these three blocks.

While supporting a wide mains-voltage input range from 90V to 264V AC, it offers very low power consumption at light loads to enable users to comply with the latest European Union Code of Conduct (CoC) regulations for external power adapters.

The PFC section uses a proprietary constant on-time control methodology which requires no sinusoidal input reference, thereby reducing system cost and external component count. The LLC section is based on a proprietary time-shift control method with simple compensation, which improves dynamic behaviour and input-ripple rejection. This produces a cleaner output voltage.

The STCMB1 also embeds a high-voltage start-up generator, an x-capacitor discharge circuit and a complete set of protection functions:
• cycle-by-cycle over-current protection
• output over-voltage protection
• latch-mode feedback-failure protection
• AC brown-out protection
• boost inductor-saturation and in-rush current detection

The half-bridge section provides two complementary outputs which drive the high-side and low-side MOSFETs 180° out of phase. The dead time inserted between the turn-off of one switch and the turn-on of the other is automatically adjusted to maintain zero-voltage switching and high efficiency at both low and full loads.

FEATURES

  • PFC controller includes optimiser for harmonic distortion
  • Half-bridge operation at up to 750kHz
  • Synchronous burst-mode operation with PFC enhances light-load efficiency

APPLICATIONS

  • AC-DC adapters
  • Switch-mode power supplies
  • LED street lighting

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The EVLCMB1-90WADP demonstration board is a 19V, 90W AC-DC converter matching the typical specifications of an AC-DC adapter for laptops and notebooks.

Orderable Part Number: EVLCMB1-90WADP

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