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.
3.1 概述
半橋和全橋拓撲開關管的穩(wěn)態(tài)關斷電壓等于直流輸入電壓，而不像推挽、單端正激或交錯正激拓撲那樣為電壓的兩倍。所以橋式拓撲廣泛用于直接電網(wǎng)的離線式變換器。而對推挽等拓撲來說，兩倍的電網(wǎng)整流電壓將超過其開關管的安全耐壓容限。為此，輸入網(wǎng)壓為220V或更高的場合幾乎都使用橋式拓撲。當輸入網(wǎng)壓為120V時也有使用橋式拓撲的情況。
橋式拓撲的另一優(yōu)點是，能將變壓器初級側的漏感尖峰電壓（如圖2.1和圖2.10所示）箝位于直流母線電壓，并將漏感儲存的能量歸還到輸入母線，而不是消耗于電阻元件。