Taiwan Semiconductor Corporation BZW04-78B

Overview

BZW04-78B from Taiwan Semiconductor is a unidirectional transient voltage suppressor (TVS) diode in DO-204AL (DO-41) package, rated for 400W peak pulse power at 10/1000μs, with 78.0V working stand-off voltage, 86.5–95.5V breakdown voltage at 1mA, and 125V maximum clamping voltage at 3.2A peak impulse current. It protects automotive and industrial power rails against ESD and inductive switching transients.

For engineers reviewing the BZW04-78B datasheet, BZW04-78B pinout, BZW04-78B application, or BZW04-78B equivalent, key selection criteria include clamping voltage margin relative to system rail, leakage current below 1μA at 78V, AEC-Q101 qualification status, thermal resistance (R_θJL = 60°C/W), and DO-41 lead-form compatibility with legacy PCB layouts.

Technical Context

The BZW04-78B operates as a unidirectional avalanche diode, triggered when reverse voltage exceeds its 86.5–95.5V breakdown range under 1mA test current. Its low dynamic impedance ensures rapid clamping response to fast transients such as EFT (IEC 61000-4-4) and ISO 7637-2 pulses.

Designed for surface-mount or through-hole mounting with pure tin-plated leads, it sustains 400W non-repetitive surge energy while maintaining junction temperature ≤175°C and exhibits <1μA reverse leakage above 10V - critical for low-power standby circuits.

Key Specifications

Pinout & Package

Package: DO-204AL (DO-41), axial-leaded, epoxy-molded case with cathode band marking for unidirectional polarity. Lead finish: pure tin, solderable per J-STD-002. Weight: ~0.300g.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar transient voltage suppression applications.

Compared with SMBJ78A and P6KE78A, the BZW04-78B provides optimal balance of DO-41 mechanical compatibility, 1μA leakage, 60°C/W junction-to-lead thermal resistance, and optional AEC-Q101 qualification - making it ideal for space-constrained, thermally demanding, or automotive-compliant designs.

Availability

BZW04-78B is available at Aetrix Electronics and suitable for automotive ECU protection, industrial PLC input hardening, and LED driver overvoltage clamping requiring stable component supply and long-term lifecycle support.

Supply support for BZW04-78B includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Taiwan Semiconductor Corporation (TSC) is a vertically integrated semiconductor manufacturer specializing in discrete power devices, TVS diodes, rectifiers, and thyristors, with global manufacturing and quality certifications.

The BZW04 series was developed specifically for high-reliability transient suppression in automotive and industrial environments, emphasizing AEC-Q101 compliance, tight parametric tolerances, and robust surge endurance in axial-leaded packages.

FAQ

What is the polarity configuration of the BZW04-78B?

The BZW04-78B is a unidirectional TVS diode, with cathode marked by a band on the DO-41 package. It conducts only when the cathode is biased positively relative to the anode - i.e., it clamps positive transients on a line referenced to ground. This configuration matches standard 72V automotive battery rail protection schemes where the protected line is positive and ground is the return path. The BZW04-78B does not conduct in forward bias beyond typical diode drop.

Is the BZW04-78B AEC-Q101 qualified?

The BZW04-78B itself is not automatically AEC-Q101 qualified; qualification applies only to variants marked with "H" suffix (e.g., BZW04-78BH). Per TSC ordering information, the "H" denotes AEC-Q101 compliance. Standard BZW04-78B meets all electrical and mechanical specs but lacks the extended reliability test documentation required for automotive qualification. For automotive applications, specify BZW04-78BH to ensure full AEC-Q101 coverage.

What is the maximum clamping voltage of the BZW04-78B at rated surge current?

The BZW04-78B has a maximum clamping voltage (V_C) of 125 V at peak impulse current (I_PP) of 3.2 A, tested with the standard 10/1000μs double-exponential waveform. This value is guaranteed across the full operating temperature range and represents the upper limit of voltage seen by downstream components during a worst-case surge event. Designers must verify that 125 V remains below the absolute maximum voltage rating of protected ICs or MOSFETs.

How does the BZW04-78B compare to bidirectional variants like BZW04-78BB?

The BZW04-78B is unidirectional, while BZW04-78BB is bidirectional - meaning the latter clamps both positive and negative transients symmetrically around 0 V. The BZW04-78B's breakdown occurs only in reverse bias (cathode positive), making it unsuitable for AC line or floating-signal protection. Use BZW04-78B for DC rail protection where polarity is fixed; choose BZW04-78BB only when protecting differential or AC-coupled signals subject to bipolar transients. Their V_BR, V_C, and P_PK values are otherwise identical.

What is the thermal resistance profile of the BZW04-78B, and how does it affect PCB layout?

The BZW04-78B has a junction-to-lead thermal resistance (R_θJL) of 60°C/W and junction-to-ambient (R_θJA) of 100°C/W when mounted on 10 mm leads per JEDEC standards. To maintain safe junction temperatures during repeated surges, PCB layout should use ≥5 × 5 mm copper pads per lead, minimize trace length, and avoid thermal isolation. Exceeding 175°C junction temperature risks parametric shift or permanent degradation - especially critical in automotive engine-bay applications where ambient may reach 125°C.