Zero-voltage switching

The Zero-voltage Switching Quasi-resonant Converter... 

A second type of quasi-resonant converter is the zero voltage switching (ZVS) quasi-resonant family. A ZVS QR buck converter and its waveforms are shown in Figure 4-11. Here the power switch remains on most of the time and performs resonant off periods to decrease the output power. Actually, the ZCS and the ZVS families mirror one another. If you were to compare the switch voltage and current waveforms between the two families, and if one inverts both the voltage and current waveforms in order to reference them to the power switch, the waveforms would have a striking resemblance to one another. 

As with PWM switching power supplies, there are comparable topologies within the zero-current switching (ZCS) and zero-voltage switching (ZVS) quasi-resonant families. You ll immediately recognize the family members upon seeing them. 

A Zero Voltage Switched Quasi-resonant Off-line Half-bridge Converter... 

Using a proper control technique, a full-bridge converter can be operated in a zero-voltage switching (ZVS) mode (Dalai, 1990). This type of operation results in negligible switching losses. At reduced load currents, however, the ZVS property is lost. There has been much effort to overcome this problem, but the converter requires additional components to maintain the ZVS. 

Dalai, D.B. 1990. A 500 kHz multi-output converter with zero voltage switching. In IEEE Applied Power Electronics Conference Record, pp. 265-274, Los Angeles. 

Liu, K.H. and Lee, F.C. 1986. Zero-voltage switching technique in DC/DC converters. In IEEE Power Electronics Specialists Conference Record, pp. 58-70, Vancouver. 

The piezoelectric hysteresis loops have been studied additionally to above dielectric hysteresis. This kind of loop is shown on Fig. 2.17. It has been recorded on PZT nanotube with outer diameter 700 and 90 nm wall thickness with the help of piezoatomic force microscopy (see Refs. [42, 43]). The obtained loop is the direct evidence of ferroelectric properties of the nanotube. Square form of the loop speaks about sharp polarization switching at coercive voltage 2 V. The residual (at zero voltage) piezoelectric coefficient d ff is of the same order as for the thin PZT film. 

This problem can be avoided by using a zero-crossover-fired power controller. This is a time-proportioning system controlled by the temperature controller. Being zero-voltage fired, this controller s circuit is free of RF noise. In other words, the switching occurs when no voltage is on the line. 

Soft-switched converters can be classified as (a) resonant converters, and (b) resonant (zero-current or zero-voltage) transition converters. Similar to the PWM converters, there are two types in each case, namely, single-ended and double-ended. 

ZVS QRCs (Kit Sum, 1988 Liu and Lee, 1986) are similar to ZCS QRCs. The auxiliary LC elements are used to shape the switching device s voltage waveform at off time in order to create a zero-voltage condition for the device to turn on. Figure 10.87(d) shows an example of ZVS QR boost converter implemented using ZV resonant switch. The circuit can operate in the half-wave mode (Fig. 10.87(e)) or in the fuU-wave mode... 

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