缓冲电路参数选取.ppt

Switching trajectory with and without turn-on snubber. Turn-on Snubber isw vsw Vd Io L s disw dt Without snubber With snubber Turn-on Snubber Turn-on Snubber Operating Waveforms Small values of snubber inductance (LsLs1) tri trr Irr Io Vd vsw isw di dt Ls Fig. 27-17 (c) Turn-on Snubber Turn-on Snubber Operating Waveforms Large values of snubber inductance (LsLs1) (disw/dt) limited by circuit to (Vd/Ls)(Io/tri) Irr reduced when LsLs1 because Irr proportional to Io V d vsw isw Irr reduced ton- tri+ trr LsIo Vd Fig. 27-17 (d) Turn-on Snubber Switch waveform at Turn-off with Turn-on Snubber in circuit During switch turn-off, the turn-on snubber will generate an overvoltage of (IoRLs) across the switch Time of (2.3Ls/RLs) requirede for inductor current to decay to 0.1Io Off-time of switch must be (2.3Ls/RLs) vsw isw Vd IoRLs Io trv IoRLsexp(-RLst/Ls) Turn-on Snubber Design Trade-offs Turn-on Snubber Selection of inductor Turn-on Snubber Selection of resistor RLs Chapter 27：Snubber Circuits 27-1 Function and Types of snubber Circuits 27-2 Diodes Snubber 27-3 Snubber Circuits for Thyristors 27-4 Need for Snubbers with Transistors 27-5 Turn-off Snubber 27-6 Overvoltage snubber 27-7 Turn-on Snubber 27-8 Snubbers for Bridge Circuit Configurations 27-9 GTO Snubber Considerations 27-1 Overview of Snubber Circuits for Hard-Switched Converters Function: Protect semiconductor devices by: Limiting device voltages during turn-off transients Limiting device currents during turn-on transients Limiting the rate-of-rise (di/dt) of currents through the semiconductor device at device turn-on Limiting the rate-of-rise (dv/dt) of voltages across the semiconductor device at device turn-off Shaping the switching trajectory of the device as it turns on/off Types of Snubber Circuits 1. Unpolarized series R-C snubbers ? Used to protect diodes and thyristors 2. Polarized R-C snubbers ? Used as turn-off snubbers to shape the turn-off switching trajectory of controlled switc