Controller with 600V Half Bridge Driver
STMicroelectronics' L6598 simplifies design of efficient power supplies, replacing both single-ended and multi-chip solutions.
 Applying a proprietary high voltage IC technology called BCD-Offline, STMicroelectronics is the first to integrate a resonant converter control circuit with high voltage half bridge driver circuits capable of operating at voltages up to 600V. By integrating these drivers the new L6598 reduces the component count of resonant converters, making them more attractive in TVs, monitors, ac-dc adapters and dc-dc modules.
High frequency resonant converters have become increasingly popular with power supply designers because they can achieve very high efficiency, especially at frequencies above 150kHz. This high efficiency is mainly due to the absence of switching losses in the power switch and the rectifiers. This results in lower losses and thus smaller heatsinks and a reduction in the overall size and weight of the unit. In addition resonant converters reduce EMI/RFI interference and offer good reliability.
Using the ST L6598 all of these benefits can be obtained with a simpler circuit since all of the controller features and all the driver circuits are integrated in one SO16 or DIP16 package. The L6598 includes a voltage controlled oscillator, soft start frequency shift timer, bootstrap diode, enables and undervoltage lockout functions. Operating at up to 350kHz it can be used with compact external filter components, contributing to a further reduction in size. The half bridge driver section has a current capability of 250mA source and 450mA sink, providing enough to drive efficiently high power MOS or IGBT discrete transistors at high frequencies. Though the chip is rated up to 600V it can also operate at much lower voltages.
An L6598 solution can replace half bridge resonant converters made using two chips, reducing the component count. It can also be used to replace simpler single ended resonant converters, improving performance. In a half bridge solution the transformer is used 'bidirectionally", so it is not necessary to flux reset mechanisms. Moreover, the voltage rating of the output transistor is halved. This reduced voltage significantly reduces turn on losses -- zero current switching only reduces turn-off losses -- and the half bridge configuration also has the lowest turn off losses.
Transformer size is smaller for the half bridge because a forward resonant converter 'wastes' half the period with no power transfer while the core flux is being reset. Also, all the windings have half the number of turns compared to a forward converter, and this could significantly reduce the leakage inductance in certain designs.
The L6598 is offered in two versions: type L6598 is assembled in a DIP16 package; L6598D in a SO16N package.
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