Friday, March 27, 2009

Push-Pull Snubber Circuit

The DS3984, DS3988, DS3881, DS3882, DS3992, and DS3994
are cold-cathode fluorescent lamp (CCFL) controllers that use a
push-pull architecture to create the high-voltage AC waveforms
needed to drive the lamps. In a push-pull drive scheme, the
parasitic inductance of the step-up transformer, together with the
parasitic capacitance of the output of the n-channel power
MOSFETs, form a resonant circuit that can create unwanted
voltage spikes. High-voltage spikes can increase the stress on
the power MOSFETs and can also increase the electromagnetic
interference (EMI) created by the system. This application note
describes how to suppress the voltage spikes with a simple
resistor-capacitor (RC) network.

Push-pull drain snubber circuit.