1、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
2、 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 fre
3、quently 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 dissipat
4、ed 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 i
5、s 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 r
6、oughly 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 “o
7、n” 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 about 308 to 336 V dc. 220 V AC. It does this when switch S1 is set to the open position for 220-V AC i
8、nput, or to the closed position for 120-V AC input. The S1 component is normally not a switch； more often it is a wire link that is either installed for 120 V AC, or not for 220 V AC. With the switch in the open 220-V AC position the circuit is a full wave rectifier, with filter capacitors C1 and C2
9、 in series. It produces a peak rectified DC voltage of about (1.41220) 2 or 308 V. When the switch is in the closed 120-V AC position , the circuit acts as a voltage doubler. One half cycle of the input voltage when A is positive relative to B, C1 is charged positively via D1 to a peak of (1.41 120)
10、 1 or 168 V. On a half cycle when A is negative with respect to B, capacitor C2 is charged positively via D2 to 168 V. The total voltage across C1 and C2 in series is then 336 V. It can be seen in Figure 3.1 that with either transistor “on,” the “off” transistor is subjected to the maximum DC input
11、voltage and not twice that value. Since the topology subjects the “off” transistor to only Vdc and not 2Vdc, there are many inexpensive bipolar and MOSFET transistors that can support the nominal 336 DC V plus 15% upper maximum of 386 V. Thus the equipment can be used with either 120- or 220-V AC line inputs by making a simple switch or linkage change. Assuming a nominal rectified DC voltage of 336 V, the topology works as
