How can EPS buffer circuits reduce switching spikes?

The snubber circuit in an EPS (Electric Power Controller) is mainly used to suppress voltage spikes and ringing generated when power devices are turned off. The common RCD snubber circuit works as follows: when the switching transistor is turned off and the voltage rises rapidly, the snubber capacitor (Cs) is charged through the snubber diode (Ds), absorbing the energy stored in the parasitic inductance of the line, thus limiting the voltage peak. Subsequently, the snubber resistor (Rs) dissipates the energy stored in Cs as heat.

Design considerations:

1. Cs capacitance: Calculated based on the energy to be absorbed (0.5*Lp*Ipk²) and the allowable voltage overshoot. A small capacitance results in weak absorption, while a large capacitance results in high losses and a large size.

2. Rs resistance: It needs to be small enough so that Cs can discharge completely before the next turn-off (usually calculated as 3-5 times the RC time constant less than the minimum dead time), but it cannot be too small to avoid excessive discharge current peaks.

3. Layout: The RCD network must be placed as close as possible to the C/E or D/S pins of the IGBT/MOSFET to minimize the parasitic inductance of the buffer circuit itself; otherwise, the effect will be greatly reduced.