Snubber Circuits : Theory , Design and Application

Passive Snubber Types The basic function of a snubber is to absorb energy from the reactances in the power circuit. The fIrst classification of snubber circuits is whether they absorb energy in controlling a voltage or a current. A capacitor placed in parallel with other circuit elements will control the voltage across those elements. An inductor placed in series with other circuit elements will control the current through those elements. Figure I shows this concept. A voltage snubber (Fig. la) has energy storage capacitors in it and a current snubber (Fig. Ib) has inductors for energy storage. The networks associated with the inductor and capacitor shown in Figure I determine how energy is passed to the storage element and how the energy is removed from it All of the other classifications of snubberg relate to the ways in which the energy is transferred to and from the snubber. If the energy stored in the snubber is dissipated in a resistor the snubber is classed as dissipative but if the energy is moved back to the input or ahead to the output the snubber is classed as non-dissipative even though there may be some small losses. A snubber is classed as polarized or non-polarized depending on Introduction Snubbers are an essential part of power electronics. Snubbers are small networks of parts in the power switching circuits whose function is to control the effects of circuit reactances. Snubbers enhance the performance of the switching circuits and result in higher reliability, higher efficiency, higher switching frequency, smaller size, lower weight, and lower EMI. The basic intent of a snubber is to absorb energy from the reactive elements in the circuit. The benefits of this may include circuit damping, controlling the rate of change of voltage or current, or clamping voltage overshoot. In performing these functions a snubber limits the amount of stress which the switch must endure and this increases the reliability of the switch. When a snubber is properly designed and implemented the switch will have lower average power dissipation, much lower peak power dissipation, lower peak operating voltage and lower peak operating current. This article describes some of the various types of snubbers, where they are used, how they function, how they are designed and what their limitations are. Snubbers may be either passive or active networks. This article is limited to the main types of passive snubbers. Passive snubber network elements are limited to resistors, capacitors, inductors and diodes. Active snubbers include transistors or other active switches, often entail a significant amount of extra circuitry and introduce another level of parasitics which must be dealt with (usually with a passive snubber). However, active snubbers are appropriate in some applications. A good example of an active snub is what you would like to say to your boss when he or she decides not to give you a raise. Fig. lb