powerZONE Products for the week of July 14, 2003
STMicroelectronics Says . . .
VIPer53: Offline Switcher Cuts Power-Supply Component
Count
Extensive integration improves self-protection
STMicroelectronics has introduced an offline primary power switch for use in applications such as switch-mode power supplies for DVDs, LCD monitors, set-top boxes, games consoles, adaptors and general AC-DC converters.
The VIPer53 combines an enhanced current-mode PWM controller with a high-voltage MDMesh power MOSFET in a single package.
The part has an efficient standby mode, enabled by enhanced pulse skipping, that will help power-supply makers meet increasingly stringent environmental regulations such as those of the Energy Star Program.
The VIPer53 also has a number of self-protection mechanisms. Overload
and short-circuit faults are controlled by feedback monitoring and a delayed
device reset. A high-gain error amplifier provides protection against primary
regulation or secondary loop failures. Over-temperature protection is built
in, removing the need for an external thermal sensor.
analogZONE Says...
The VIPer53 is a part that fits directly into the off-line primary switching supply families that are beginning to be in just about every power management manufacturer's portfolio. In this case there is a rather neat twist to the supply voltage regulation to the part, which means that the optocoupler feedback loop common to these applications, can be avoided.
The VIPer53 is powered by a rectified feed from an auxiliary winding on the coupling transformer. It feeds the VDD pin and is automatically regulated to +15 V by an error amplifier that is a transconductance amplifier. The difference between the voltage on the VDD pin and the trimmed internal reference produces a small current that is integrated by an external capacitor which, at steady state, blocks any dc voltage to the COMP pin holding VDD to +15 V. The unity-gain bandwidth of the error amplifier is about 700 kHz with a voltage gain of about 45 dB. A belt-and-braces optocoupler feedback loop can be added if wanted.
An external resistor/capacitor combination sets the frequency of operation with lower frequencies suggested for lower powers because the sizing of the transformer will be smaller. The highest operating frequency is 300 kHz. The operating supply current (at 100 kHz switching) is a typical 9 mA.
The output power capability depends on the package specified. On universal voltages (85 Vac to 265 Vac) the capability of the DIP-8 is 30 W and the thermally-enhanced SO-8 is 40 W. On European voltage ranges (195 Vac to 265 Vac) the SO-8 can be loaded to 65 W so it is still below the 75 W threshold for Class D products that require special power factor correction.
Also included is adjustable current limitation, soft-start and shutdown. There is also an auxiliary under-voltage lockout system with hysteresis.
The VIPer53 will take its share of primary switch sockets particularly where the OEM can safely eliminate the secondary to primary optocoupler circuitry.
The VIPer53 is in production in, as noted, DIP-8 and thermally-enhanced SO-10.