Relays cut on-resistance in half

A spate of power innovations is led by a photovoltaic relay family that drastically reduces on-state resistance, yet still boosts load current by over one-third.

A 50% reduction of ac-dc on-state resistance and 37.5% increase of maximum ac-dc load current rating at full (100%) duty cycle. Those are the claims International Rectifier makes for its new series of photovoltaic relays for applications that range from power supplies and power distribution to audio equipment and instrumentation, as well as computers and computer peripherals (Fig. 1). The PVN012A family is also rated for maximum pulsed (surge) load current.

Compared to traditional electromechanical relays, says IR, the PVN012A family offers a smaller footprint, high input-to-output isolation, bounce-free operation, solid-state reliability, stable on-resistance over life, and greater input sensitivity.

The new 20V, single-pole, normally open, solid-state relays use a HEXFET MOSFET output switch, driven by an integrated photovoltaic generator circuit. The output switch is controlled by radiation from a GaAlAs LED that's optically isolated from the photovoltaic generator. The new series is available in a 6-pin DIP, 6-pin SMT, and tape-and-reel.

MOSFET driver IC
In another development, Allegro MicroSystems Europe's dual, full-bridge, gate-driver IC with integrated microstepping translator circuitry drives a range of industrial bipolar two-phase stepper motors in the 30-500 W power range (Fig. 2). Motor power is provided by external N-channel power MOSFETs at supply voltages from 12 to 50 V.

The A3986 contains two sinusoidal digital/analogue converters that generate the reference voltage for two separate, fixed, off-time, pulse-width-modulated current controllers. These provide current regulation for external power-MOSFET, full-bridge circuits. Motor stepping is controlled by the two-wire step and direction interface, providing complete microstepping control at full-, half-, quarter- and sixteenth-step resolutions.

The fixed off-time regulator can operate in slow-, mixed- or fast-decay modes, which results in reduced audible motor noise, increased step accuracy, and reduced power dissipation.

The translator is the key behind the driver IC's easy implementation. Simply inputting one pulse on the "step" input drives the motor one step (full, half, quarter, or 16th depending on the microstep select input). There are no phase-sequence tables, high-frequency control lines, or complex interfaces to program.

The above-supply voltage required for the high-side N-channel MOSFETs is provided by a bootstrap capacitor. Efficiency is enhanced via synchronous rectification, and the power FETs are protected from shoot-through by integrated crossover control and programmable dead time. In addition to crossover current control, internal circuit protection provides thermal shutdown with hysteresis and undervoltage lockout.

PurePath Digital power stages
Not to be outdone, Texas Instruments introduced two new PurePath Digital power stages. The TAS5261, which offers a single-chip digital amplifier power stage, can drive more than 300W into a 4Ω speaker, while the two-channel TAS5162 digital amplifier power stage can drive 200W per channel at 6Ω and 125W at 8Ω. TI believes the devices enable higher efficiency and sound quality in a variety of audio applications. These include many previously restricted from using digital amplifiers due to power requirements, such as high-end DVD receivers and mid- to high-end audio/video receivers (AVRs).

Precision Op Amps
On another front, Linear Technology recently unveiled a new family of ultra-low power op amps that it claims set a new standard for precision low voltage operation and tiny footprint.

The LT6003 (single), LT6004 (dual) and LT6005 (quad) amplifiers draw less than 1µA and operate from 1.6 to 16V. With its input offset voltage of 500µV max at 25°C and a maximum drift of 5µV/°C, the LT6003 family is able to offer a high-precision, ultra-low voltage ultra low op amp. A tiny 2mm-by-2mm DFN package makes the footprint of the LT6003 the smallest in this class. Inputs and outputs feature rail-to-rail operation.

The LT6003 family aims at battery-operated, handheld instrumentation due to the combination of low supply current, a 1.6 to 16V operating range, and tiny packages.

For many micropower amplifiers, rail-to-rail operation compromises the supply current, with up to a threefold current increase as the output approaches the rails. According to Mike Kultgen, Linear Technology design manager, "The LT6003 family uses unique design techniques to preserve its micropower operation in all normal operating conditions as well as during startup, when the amplifier output is likely to be at the supply rail."

Inductors keep a low profile
Finally, a family of miniature, surface-mount, I-core power inductors is the latest development from C&D Technologies (Fig. 3). They're targeted at designs with restricted pc-board space and height—the ultra-low-profile 8200 series is the smallest package-size inductor introduced by the company.

Typical applications for the 3.2-by-2.5-by-2.3mm high devices include low-power filtering in PCMCIA and ExpressCard products. They can also be used to solve EMI problems in PCs, laptops, handheld devices, and discrete dc-dc converter designs.

Inductance values range from 1.0µH to 470µH, and dc current ratings span 70mA to 2.0A. Operating temperature range is –40 to +85°C.

The RoHS-compliant 8200 series can be exposed to peak reflow solder temperatures of 260°C. Parts are supplied taped and reeled for high-volume, automated assembly.

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