500W Zener TVS in a DO-214AC footprint
The SMAJ18E3/TR13 is a unidirectional Zener TVS diode from Microchip Technology, rated for 500W peak pulse power per the 10/1000µs waveform. It clamps at 32.2V max with a 15.5A peak pulse current, and its 18V reverse standoff voltage makes it a fit for protecting 12V or 15V rails where the nominal line stays below 18V.
Minimum breakdown voltage is 20V, giving a 2V guard band above the 18V standoff — enough headroom to avoid nuisance triggering from normal line ripple or load transients. The 32.2V clamp sets the maximum voltage the downstream circuitry sees during a surge event; a 12V rail with a 30V absolute-max input would be at risk if the clamp exceeds that ceiling.
Microchip lists the SMAJ18E3/TR13 as Active.
Single-channel unidirectional — polarity matters
This is a single unidirectional channel. It protects one DC rail with the cathode toward the positive supply. For AC signal lines or bidirectional clamping, a different part from the SMAJ family would be needed. The DO-214AC (SMA) package is a common surface-mount footprint; the copper pad area under the cathode tab influences thermal resistance during repetitive surge events.