Design of Snubbers for Power Circuits（对权力的缓冲器电路的设计）.pdfVIP

DESIGN OF SNUBBERS FOR POWER CIRCUITS By Rudy Severns What’s a snubber? Power semiconductors are the heart of power electronics equipment. Snubbers are circuits which are placed across semiconductor devices for protection and to improve performance. Snubbers can do many things: · Reduce or eliminate voltage or current spikes · Limit dI/dt or dV/dt · Shape the load line to keep it within the safe operating area (SOA) · Transfer power dissipation from the switch to a resistor or a useful load · Reduce total losses due to switching · Reduce EMI by damping voltage and current ringing There are many different kinds of snubbers but the two most common ones are the resistor- capacitor (RC) damping network and the resistor-capacitor-diode (RCD) turn-off snubber. This appli- cation note will show you how to design these two snubbers. Switching waveforms Before getting into the design of snubbers it is important to understand the waveforms which occur naturally in power circuits. These provide both the motivation for using snubbers and the infor- mation needed for their design. There are many different types of circuits used in power converters, motor drives, lamp ballasts and other devices. Fortunately all of these different circuits have a common network and waveforms associated with the switches. Figure 1 shows four widely used circuits. All of these circuits, and in fact most power electronics circuits, have within them the same switch-diode- inductor network shown within the dotted lines. The behavior of this network is the same in all these circuits which means that we only have to solve the snubber design problem for one circuit to apply it to all of the others. This tremendously simplifies the problem and allows generalized snubber design tech- niques. A typical boost converter is s