audio/videoZONE Products for the week of April 29, 2002
STMicroelectronics Says . . .
STV9380/90: Class D deflection booster can deliver
efficiencies of 80-95% compared to 20-30% for Class AB
STMicroelectronics has introduced a family of TV vertical deflection boosters
that use Class D amplification to deliver a significant reduction in power
consumption compared to existing linear devices. The new STV9380/90 devices
not only provide a more cost-effective solution than linear boosters but
also allow the power consumption of a TV set to be reduced by as much as
7W.
Vertical boosters are power amplifiers used to drive the deflection yoke that controls the vertical position of electrons in the CRT tube. The traditional approach uses a linear power amplifier (Class AB) to generate a sawtooth current waveform in the coil. Class D amplifiers use switching techniques in conjunction with a simple external filter. The advantage of the class D technique is that the circuit is more efficient, with efficiencies of 80-95% achievable in practice, compared to 20-30% for linear boosters.
Apart from the saving in energy, the benefit of this higher efficiency is that less heat is generated inside the amplifier, so bulky power packages and heatsinks can be eliminated, making the devices suitable for automatic insertion. Further cost savings can also result from the reduced demand on the power supply, which can be made smaller, lighter and cheaper. In addition, the LC filter protects the IC against arcing, eliminating the need for additional protection devices.
The STV9380/90 devices integrate a voltage reference, comparator, precision
PWM (Pulse Width Modulation) generator and power output stage, and are offered
with integrated fly-back generator. Unlike linear boosters, where increasing
the fly-back voltage to reduce fly-back time increases power dissipation,
the Class D boosters allow fly-back voltage to be increased with no impact
on power consumption.
analogZone Says . . .
My colleague, Lee Goldberg, is the more environmental and he will love this part. It is so totally logical to take the technology developed for Class-D audio work and to apply it to a fixed 50 Hz or 60 Hz deflection amplifier. ST notes that if all the 125 million TV receivers produced every year, running 5 hours a day, were to use these parts there would be a savings of 1260 GW-hr, equivalent to a coal-power station emitting a million metric tonnes of CO2 into the atmosphere. The parts combine processes with bipolar, CMOS and DMOS all on the same die.
Drive to the part continues to be a sawtooth at frame rate to be amplified and applied as a current through the vertical deflection yoke. A small sense resistor is in series with the yoke to measure the current passing to use as a feedback voltage. The Class-D switching frequency is nominally at 150 kHz (set by an external resistor) and the flyback is formed by an external capacitor being switched in series with the output stage's power rail (internal flyback), a system that offers very fast flyback times. An external filter is required, of course, to restore the analog waveform but this can be formed with just one small inductor, three resistors and a couple of small value capacitors.
The data sheet for the STV9380 characterizes the part at +/-12 V but it can be used up to +/-18 V, has a quiescent of 14 mA and can drive up to +/-1.25 A through a 5.5 ohm, 7 mH yoke. The STV9381 increases output capability to +/-1.5 A. PSRR is a typical 82 dB of both rails. There is overcurrent, overvoltage and undervoltage protection included in the parts. overvoltage and overcurrent conditions.
The STV9380 and STV9381 are both in DIP-20 packages and are in production.
Parts for lower-end equipment will be the STV9390 (+/-1 A, in production)
and the STV9391 (+/-0.75 A) which will be offered in the 4th quarter. Both
the STV9390 and STV9391 will be in SO-20. No prices were quoted.