Surge protection for 40V rails
The SMCJ40E3/TR13 is a unidirectional Zener TVS diode from Microchip Technology, rated for 1500W peak pulse power at 10/1000µs waveform. It clamps transients on a 40V nominal rail, with a breakdown voltage of 44.4V min and a clamping voltage of 71.4V max at 21A peak pulse current. The 40V reverse standoff voltage means the diode does not conduct at normal operating levels up to 40V, only clamping when a surge pushes the line above the breakdown threshold.
Clamping voltages and pulse current
The 44.4V minimum breakdown ensures the diode starts clamping before the protected circuit's absolute maximum rating is reached. The 71.4V clamping voltage at 21A peak pulse current defines the worst-case voltage the downstream components see during a surge event. For shorter pulses (e.g., 8/20µs), the peak power capability is higher, but the 1500W figure is the conservative baseline for derating calculations.