Taiwan Semiconductor Corporation BY251G

Overview

BY251G from Taiwan Semiconductor is a single-die standard silicon rectifier diode rated for 3 A average forward current, 200 V repetitive peak reverse voltage (VRRM), and 150 A non-repetitive surge current (IFSM), used in DC-DC converters and switching-mode power supplies where low forward voltage drop and high reliability are required.

For engineers reviewing the BY251G datasheet, BY251G pinout, BY251G application, or BY251G equivalent, key selection criteria include its DO-201AD package, 1.0 V max VF at 3 A, 5 µA max IR at 25°C, 40 pF junction capacitance, and thermal resistance of 40°C/W - all critical for thermal management and efficiency in high-frequency rectification.

Technical Context

The BY251G operates as a unidirectional, single-junction PN rectifier with no integrated control logic or switching functionality. Its electrical behavior follows standard diode conduction and blocking characteristics, with forward conduction governed by diffusion current and reverse blocking limited by avalanche breakdown at 200 V.

Thermal performance is defined by a junction-to-ambient thermal resistance of 40°C/W under natural convection, and it supports operation across –55°C to +150°C junction temperature range. The device uses pure tin-plated leads compliant with J-STD-002 solderability and JESD 201 Class 1A whisker resistance.

Key Specifications

Pinout & Package

Package: DO-201AD - Axial-leaded, molded plastic case with cathode band marking; UL 94V-0 rated compound; 1.20 g typical weight; lead finish: pure tin, J-STD-002 compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar standard rectifier applications.

Compared with STTH3L06 and 1N5408, the BY251G delivers optimal balance of 200 V rating, 1.0 V VF, and 150 A surge capability - making it more thermally efficient and better suited for space-constrained 24–48 V DC-DC outputs than higher-VRRM alternatives.

Availability

BY251G is available at Aetrix Electronics and suitable for DC-DC converters, switching inverters, and industrial auxiliary power supplies requiring stable component supply, consistent parametric performance, and long-term manufacturing continuity.

Supply support for BY251G 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 analog and discrete semiconductor manufacturer headquartered in Hsinchu, Taiwan, specializing in rectifiers, TVS diodes, MOSFETs, and bipolar transistors since 1979.

The BY251G belongs to TSC's BY25xG standard rectifier family, engineered for high-efficiency, high-reliability AC/DC and DC/DC power conversion in industrial, telecom, and consumer power supplies.

FAQ

What is the maximum junction temperature for the BY251G?

The BY251G has a maximum junction temperature (TJ MAX) of +150°C, verified per absolute maximum ratings in the official TSC datasheet Version D2105. This rating applies under steady-state conditions with proper thermal management. Operation beyond this limit risks permanent degradation of the PN junction. Derating curves in Figure 1 confirm usable current drops linearly above 75°C ambient, and the BY251G must be mounted with adequate copper area or heatsinking to maintain TJ ≤ 150°C at full 3 A load.

Is the BY251G RoHS and halogen-free compliant?

Yes, the BY251G is RoHS compliant per EU Directive 2011/65/EU and halogen-free per IEC 61249-2-21, as explicitly stated in the "FEATURES" section of the TSC datasheet. The device uses lead-free pure tin plating on leads and halogen-free molding compound. These certifications are production-verified and documented in TSC's material declarations - no exemptions or exceptions apply to the BY251G.

What does the "G" suffix in BY251G indicate?

The "G" suffix in BY251G denotes green (halogen-free) compound packaging, consistent with TSC's standardized marking convention across the BY25xG family. Per the "MARKING DIAGRAM" on page 4 of the D2105 datasheet, "G" explicitly identifies halogen-free molding material meeting IEC 61249-2-21. It is not a grade, revision, or packaging variant code - it is a material compliance identifier directly tied to the BY251G ordering code.

Can the BY251G replace a 1N5408 in a 24 V power supply?

The BY251G can functionally replace a 1N5408 in a 24 V power supply *only* if the circuit's peak reverse voltage remains ≤200 V. While both share DO-201AD packaging and 3 A rating, the 1N5408's 1000 V VRRM provides far greater margin. Using BY251G in a 1N5408 footprint risks catastrophic failure if transient spikes exceed 200 V. Verify actual reverse stress - including line surges and inductive kickback - before substituting BY251G for 1N5408.

What is the forward voltage drop of the BY251G at 3 A and 125°C?

The BY251G datasheet specifies VF ≤ 1.0 V maximum at IF = 3 A and TJ = 25°C, but does not provide a guaranteed max value at 125°C. However, Figure 4 (Typical Forward Characteristics) shows VF ≈ 0.85 V at 3 A and TJ = 125°C. Since VF decreases with rising temperature in silicon diodes, the BY251G's actual VF at 125°C will be lower than at 25°C - typically 0.80–0.88 V - improving conduction efficiency under thermal stress.