Vishay Releases New Half-Bridge dc–dc Controller and Synchronous Rectifier

Vishay Intertechnology, Inc. released a new 500-kHz half-bridge dc-to-dc controller and synchronous rectifier driver that work together as a chipset to enable more efficient 25W to 300W telecom and computer power supplies. The new Si9122A half-bridge controller and SiP11203/11204 secondary synchronous rectifier driver offer greater than 90% dc to dc conversion efficiency – even for output voltages below 3.3 V – in power supply modules and network cards for fixed telecom systems, central office switching equipment, distributed power systems, intermediate bus converters, and brick converters.

Designed to operate within the fixed telecom voltage range of 36 to 75V and withstand 100-V, 100-ms transients, the Si9122A is capable of controlling and driving both the low and high-side switching devices of a half bridge circuit and also controlling the synchronous rectifier MOSFETs on the secondary side of the bridge. The Si9122A uses a pulse transformer to drive these low-on-resistance secondary MOSFETs, enabling much better conversion efficiency compared to implementations using Schottky diode rectifiers. On-chip control of the dead-time delays between the primary and secondary synchronous signals keeps efficiencies high and prevents shorting of the power transformer. An external resistor sets the switching frequency from 200 kHz to 500 kHz. Advanced monitoring and control circuitry in the Si9122A enables users to set the maximum current in the primary circuit and allows the system to operate a constant current into a short circuit. This same circuitry also provides constant current into large capacitive loads during start-up or when paralleling multiple power supplies.

The Si9122A is available in TSSOP-20 or MLP65-20 packages. The SiP11203/11204 integrate seven functions typically implemented with discretes in isolated converters: the synchronous rectifier drivers, the error amplifier, the precision voltage reference, the opto-isolator driver, control of the start-up, control of the shutdown, and overvoltage protection. As such, they enable a simpler compact power supply module when used in conjunction with the Si9122A and other isolated dc-to-dc controllers.

The SiP11203/11204 and Si9122A interface via a pulse transformer to provide isolated control of the synchronous MOSFETs. The error signal, supplied by the SiP11203/11204, is fed to the Si9122A via an opto-isolator. Together the transformers and the opto-isolator provide isolation between the input and the output. Samples and production quantities of the Si9122A and SiP11203/4 are available now, with lead times of eight weeks for larger orders. Pricing for U.S. delivery in 10,000 piece quantities is $1.95 for the Si9122A and $1.55 for the SiP11203 or SiP11204.