SMAJ40CA-M3/61

The SMAJ40CA-M3/61 from Vishay is a bidirectional transient voltage suppressor (TVS) diode from the TransZorb SMAJ series, designed to protect sensitive electronic equipment from electrostatic discharges (ESD) and electrical overstress (EOS) transients. The bidirectional configuration makes it ideal for protecting AC signal lines or differential communication buses where the signal can swing both positive and negative relative to ground. With a standoff voltage of 40V, the device is optimized for 24V-36V power rails commonly found in industrial and automotive systems. Under normal operating conditions (voltage below VRWM), the TVS presents a high impedance with typical leakage of only 0.2uA at 25C, ensuring negligible impact on circuit performance. When a transient exceeds the breakdown voltage (44.4V minimum), the device clamps the voltage to a maximum of 64.5V at the rated peak pulse current of 6.2A, diverting the surge energy away from protected components. The 400W peak pulse power rating (8x20us waveform up to 2.3kW) provides robust protection against lightning-induced surges, switching transients, and ESD events up to 30kV per IEC 61000-4-2. The M3/61 suffix indicates Vishay’s halogen-free, RoHS-compliant construction with improved environmental compliance. The compact DO-214AC (SMA) surface-mount package occupies minimal board space and is compatible with standard SMT assembly processes.

The SMAJ40CA-M3/61 operates as a bidirectional avalanche diode TVS protection device. Key operating principles include: (1) Normal Operation – when the voltage across the device is below the standoff voltage (VRWM=40V), the TVS behaves as a very high impedance element with leakage current of only 0.2uA; in the bidirectional CA configuration, this applies for both positive and negative voltages relative to the midpoint; (2) Avalanche Breakdown – when a transient pushes the voltage above the breakdown voltage (VBR=44.4V minimum), the PN junction enters avalanche breakdown; the device presents a low impedance path, clamping the voltage across its terminals; (3) Clamping Action – at the rated peak pulse current of 6.2A (8x20us or 10x1000us waveform), the device clamps the voltage to a maximum of 64.5V; this clamping voltage represents the maximum voltage the protected circuit will see during the transient event; (4) Bidirectional Operation – the CA suffix denotes a bidirectional device constructed with two back-to-back Zener diodes in a single package; this symmetrical clamping characteristic is essential for protecting AC or differential signals where both polarities of transient must be suppressed; (5) Energy Dissipation – the TVS absorbs the transient energy and converts it to heat; the 400W rating (10x1000us) specifies the maximum pulse power the device can safely absorb without failure; the planar die technology ensures uniform current distribution and high junction temperature capability (up to 150C) for long-term reliability.

• RS-485 bus protection: bidirectional TVS across A/B lines clamps common-mode and differential surges to 64.5V max
• 24V industrial supply: 40V standoff protects 24V rails with margin; clamps load-dump and switching transients
• Automotive 24V systems: protects ECUs from ISO 7637 pulse transients and jump-start events
• Sensor signal lines: bidirectional clamping for 4-20mA current loop or +/-10V analog inputs
• Power supply output: protects downstream regulators from reverse voltage and inductive kickback