CCFL Push-Pull Snubber Circuit

Abstract: 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.