《功率因数校正开关电源的研究与设计》外文翻译..doc

《功率因数校正开关电源的研究与设计》外文翻译 Switching Power Supply Design(开关电源设计) CHAPTER 3 Half- and Full-Bridge Converter Topologies 3.1 Introduction Half-bridge and full-bridge topologies stress their transistors to a voltage equal to the DC input voltage not to twice this value, as do the push-pull, single-ended, and interleaved forward converter to pologies. Thus the bridge topologies are used mainly in offline converters where supply voltage would be more than the switching transistors could safely tolerate. Bridge topologies are almost always used where the normal AC input voltage is 220 V or higher, and frequently even for 120-V AC inputs. An additional valuable feature of the bridge topologies is that primary leakage inductance spikes (Figures 2.1 and 2.10) are easily clamped to the DC supply bus and the energy stored in the leakage inductance is returned to the input instead of having to be dissipated in a resistive snub -ber element. 3.2 Half-Bridge Converter Topology 3.2.1 Basic Operation Half-bridge converter topology is shown in Figure 3.1. Its major advantage is that, like the double-ended forward converter, it subjects the “off” transistor to only V dc and not twice that value. Thus it is widely used in equipment intended for the European market, where the AC input voltage is 220 V. First consider the input rectifier and filter in Figure 3.1. It is used universally when the equipment is to work from either120-VACAmerican power or 220-V AC European power. The circuit always yields roughly 320-V rectified DC voltage, whether the input is 120 or FIGURE 3.1 Half-bridge converter. One end of the power transformer primary is connected to the junction of filter capacitors C1, C2 via a small DC locking capacitor Cb . The other end is connected to the junction of Q1, Q2, which turn “on” and “off” on alternate half cycles. With S1 in the closed position, the circuit is a voltage doubler ; in the open position, it is a full-wave rectifier. In either case, the rectified output is