Malvern, Penna.—Vishay's 500-kHz half-bridge chip set, comprising a DC/DC controller and synchronous rectifier driver, offer an efficiency of greater than 90 percent for isolated DC/DC converters—even for output voltages below 3.3 volts—in power supply modules and network cards for fixed telecom systems, central office switching equipment, distributed power systems, intermediate bus converters, and brick converters.
Working from a 36-75 volt input, and designed to
withstand 100-volt, 100-ms transients, the Si9122A half-bridge controller drives both the low- and high-side switching devices of a half-bridge circuit and also controls 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 to achieve much better
conversion efficiency that designs using Schottky
rectifiers, according to the company.
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 to 500 kHz. Monitoring and control circuitry in the Si9122A enables users to set the maximum current in the primary circuit. This same circuitry also delivers a constant current into large capacitive loads during start-up or when paralleling multiple power supplies.
The SiP11203/11204, which offer users a choice of synchronous rectifier turn-off (SiP11203) or turn-on (SiP11204) in the event of an over-voltage condition,
integrate seven functions typically implemented with discretes in isolated converters. These include the synchronous rectifier drivers; error amplifier; precision voltage reference; opto-isolator driver; start-up circuitry; shutdown circuitry; and over-voltage
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. Both ICs can be powered by conventional bias supplies (output inductor winding or power transformer winding), or from the same pulse transformer supplying the gate timing signals, and both parts generate a regulated supply for powering the error amplifier and control circuitry.
During power-up, the SiP11203/11204 ensure that the synchronous rectifiers are held off until the supply voltages are sufficient to guarantee effective operation of the driver circuits. During the soft-start interval,
they ensure a gradual ramp-up of the synchronous rectifier. The ICs also allow control of the discharge rate of the synchronous rectifier's driver outputs during power-down.
The SiP11203/11204, which can be powered from a 5.5- to 13-volt source, feature a regulated internal logic voltage of 5 volts and provide a 2.2-amp source and 4-amp sink drive capability. They are designed for high-current applications in any topology requiring secondary-side drivers.
Click here for the Si9122A datasheet here for the SiP11203 and SiP11204. Samples and production quantities of the Si9122A (TSSOP-20 or MLP65-20 packages) and SiP11203/4 (MLP44 16 package) 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 each for the Si9122A and $1.55 each for the SiP11203 or SiP11204.