SMA/SMAF/SMB/SMC: Introduction to the DO-214 Series Diode Package

SMB

SMB (DO-214AA) is an SMT‑compatible, low‑profile, medium‑power package, designed for 2–3 A of moderate power with enhanced surge‑current handling and improved thermal performance. Larger and more robust than SMA, it is well suited for industrial power supplies, automotive electronics, DC‑DC converters, and other applications. It is not compatible with SMA/SMAF footprints, so board modifications are required.

Dimensions are approximately 5.4 × 3.6 × 2.6 mm, with a pin pitch of 2.6 mm (wider than the 1.27 mm pitch of SMA/SMAF connectors). The color code indicates the cathode side. RoHS‑compliant and lead‑free, rated for MSL 1, and capable of withstanding reflow soldering at 260°C.

The thermal resistance RθJA is approximately 80–120 °C/W (without heat sinking); with a GND copper pad of at least 10 mm × 10 mm, it can be reduced to 50–70 °C/W, offering superior thermal performance compared to SMA/SMAF packages.

Average forward current IF (AV): 2–3 A; Reverse breakdown voltage VRRM: 50–1200 V; Reverse recovery time trr: 25–75 ns; Forward voltage drop VF: 1.1–1.5 V (at IF); Reverse leakage current IR ≤ 5 μA (at room temperature); Maximum junction temperature TJ max: 150–175 °C; Surge current IFSM: 30–100 A (8.3 ms).

SMA

Ultra-fast recovery diodes in the SMA (DO-214AC) package are characterized by a reverse recovery time of trr ≤ 75 ns, targeting medium‑low power, high‑frequency switching applications in the 1–2 A range. Designed for SMT mounting and compact layouts, they are a popular choice for switch-mode power supplies, DC‑DC converters, and LED drivers.

Ultra-fast recovery: Reverse recovery time trr ≤ 75 ns (with some ultra‑high‑speed variants as low as 25–50 ns), significantly faster than fast recovery diodes (trr 150–300 ns), making them well suited for high‑frequency switching (≥50 kHz).

Package and Thermal Resistance: SMA (DO-214AC) flat‑wing package, measuring approximately 4.5 × 2.5 × 1.1 mm; junction–ambient thermal resistance is about 150 °C/W (without a heat‑sink pad), which can be reduced to 80 °C/W with an additional copper pad.

Average forward current IF (AV): 1–2 A; reverse voltage rating VRRM: 50–1200 V; forward voltage drop VF: 1.1–1.7 V (at IF); maximum junction temperature TJ: 150–175 °C.

SMAF

SMAF is not part of the standard series; it is an ultra‑thin, enhanced package developed based on SMA (DO‑214AC). Its key advantages include an ultra‑low profile—approximately 1.1 mm in height, 50% thinner than SMA—pad compatibility with SMA, and a reverse recovery time (trr) of ≤75 ns. It is optimized for medium‑to‑low‑power, high‑frequency applications in the 1–2 A range, making it ideal for space‑constrained designs such as ultra‑thin power supplies, LED drivers, and portable devices. While delivering performance comparable to SMA, it offers significant height‑saving benefits.

SMAF (DO-214AD) is a flat, ultra-thin SMT package measuring approximately 3.3 × 2.4 × 1.1 mm, with a height nearly half that of the SMA (DO-214AC). It features a 1.27 mm lead pitch and is compatible with SMA pads, allowing for direct substitution. The color code indicates the cathode end. RoHS‑compliant and lead‑free, it meets MSL 1 and can withstand reflow soldering at 260°C.

Selection logic: Consistent with SMA, prioritize components in the following order: “trr ≤ 75 ns → VRRM ≥ 1.2–1.5 times the peak reverse voltage → IF (AV) ≥ 1.5 times the actual average current → thermal resistance / heat dissipation → surge protection / reliability.”

Pad and Heat Dissipation: Retain the SMA pad configuration (1.27 mm pitch), with copper coverage of at least 5 mm × 5 mm; ensure TJ ≤ 125°C, and derate by 10% for every 10°C above ambient.

SMC

SMC (DO-214AB) is an SMT‑compatible, low‑profile, high‑power package that delivers 3–5 A of high current while maintaining low power consumption and excellent thermal performance. Its footprint and power-handling capability exceed those of SMA, SMB, and SMAF packages, making it well suited for high‑power switching power supplies, UPS systems, PFC circuits, on‑board chargers (OBC), and other applications. However, its lead‑frame configuration is incompatible with the pads of the preceding three package types, necessitating a custom PCB design.

The SMC (JEDEC DO-214AB) package measures approximately 7.9 × 6.5 × 2.8 mm, with a lead pitch of 5.08 mm—significantly wider than the 1.27 mm or 2.6 mm pitches of SMA and SMB packages, respectively. It features a cathode‑side band, is RoHS‑compliant and lead‑free, rated for an MSL 1 condition, and can withstand reflow soldering at 260°C.

Selection logic: IF(AV) ≥ 1.5 × actual current → VRRM ≥ 1.2 × peak reverse voltage → trr ≤ 75 ns → thermal resistance / thermal management design → surge protection / reliability (automotive applications require AEC‑Q101).

PCB Design: Pad center-to-center spacing of 5.08 mm, pad dimensions of 3.0 × 4.0 mm, GND copper pour ≥15 mm × 15 mm, and at least four thermal vias (φ0.5 mm) to reduce thermal resistance.