LLC Control Card

KEY FEATURES

  • Compact circuit block with built-in isolate gate drivers and full functionality for control of 3-level isolation stage using LLC operating mode
  • Enable usage of low voltage (150V) MOSFETs allowing high switching frequencies > 250kHz
  • Allows smaller transformer and EMI filters
  • Control of Synchronous Rectifiers from Primary Side
  • Supports low-power burst-mode operation
  • Minimal current consumption (<100uA) in pre-start-up operating mode
  • UVLO (typically set at 400V) so as to allow clean start of PFC stage and subsequent start of isolation stage.

 

FUNCTIONALITY

The ICERGi LLC controller card (IC93-002) provides low-cost isolated gate drivers and full-functionality control for the isolation stage in AC-DC power conversion.  This implementation is suited to operation of four sets of series-stacked 150V FETs to provide a three-level implementation as shown in Fig. 1.

It may be used independently or in association with a an ICERGi PFC stage.

Line sensing is undertaken to effect UVLO and OVLO functionality, with overcurrent detection allowing rapid response to short-circuit events. A conservative design approach also raises the frequency immediately on detection of an overcurrent conduction. This provides protection against capacitive-mode operation, and also the low voltage devices have inherently better reverse-recovery characteristics which makes them much more tolerant to capacitive mode conditions.

Pins are also provided for signalling with a Power Factor Correction stage, allowing transmission of a power-fail warning signal. Standard Enable, Feedback and Overvoltage protection functionality is also implemented using optocouplers.

Drive to the primary devices is integrated at low cost using ICERGi gate driver ICs (IC70-001).  A small transformer can be used to provide the isolation as needed for drive of secondary-side rectifiers.

The circuit block is implemented in a 26.3 x 35.3 mm PCB, with pinout as shown.  This is intended for side mounting on to a main PCB board and for usage in association with another card housing power switching devices.

Fig. 1  LLC Control Card and application circuit