onsemi BUH51G

Overview

BUH51G from onsemi is an NPN silicon planar power transistor designed for switchmode operation in 50 W halogen electronic transformers. It sustains high inrush current during startup and short-circuit load conditions, with V_CEO = 500 V, I_C = 3.0 A continuous, P_D = 50 W at T_C = 25°C, and TO-225 package. Its key role is as a primary-side switching transistor in low-cost, high-reliability AC/DC transformer drivers.

For engineers reviewing the BUH51G datasheet, pinout, applications, or equivalent options, this page delivers verified electrical ratings, thermal behavior under pulsed inductive loads, dynamic saturation voltage (V_CE(dsat) ≤ 6.0 V at 125°C), safe operating area limits, and real-world switching timing data for halogen lamp driver design validation.

Technical Context

The BUH51G employs a state-of-the-art die optimized for ruggedness in repetitive inductive turn-off stress, featuring V_CES = 800 V and reverse-biased SOA validated under clamped 300 V conditions. Its forced gain (h_FE) remains stable across temperature - 5.0–7.5 at I_C = 2.0 A, 125°C - enabling predictable base drive design.

Switching performance is characterized for both resistive (t_on = 110 ns, t_off = 3.5 μs at 25°C) and inductive loads (t_si = 3.4 μs, t_c = 350 ns at 25°C), with dynamic saturation voltage rising to 15 V at 125°C under 2.0 A/0.4 A drive - critical for thermal margin analysis in sealed transformer enclosures.

Key Specifications

Pinout & Package

BUH51G is housed in a TO-225 package (Case 77, Style 3), epoxy-molded with UL 94 V-0 flammability rating at 0.125 inch thickness. The package features three leads in inline configuration, with defined mechanical dimensions per ON Semiconductor's CASE 77-09 drawing.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN high-voltage switch applications.

Compared with BUH515G and MJE13005, the BUH51G provides optimal voltage margin (500 V) and thermal efficiency (R_θJC = 2.5°C/W) for 230 VAC halogen transformer designs without requiring package or drive circuit changes.

Availability

BUH51G is available at Aetrix Electronics and suitable for halogen lamp drivers, AC-DC auxiliary supplies, inductive ballast replacements, and DC-DC boost converters requiring stable component supply across industrial lighting and power conversion programs.

Supply support for BUH51G 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and IoT applications.

The BUH51G belongs to onsemi's SWITCHMODE™ planar power transistor family, engineered specifically for high-reliability, cost-sensitive switchmode power conversion in lighting and power supply applications.

FAQ

What is the maximum junction temperature rating for BUH51G?

The BUH51G has a specified operating junction temperature range of –65°C to +150°C. This wide range supports deployment in sealed outdoor lighting fixtures where ambient temperatures may exceed 85°C and internal self-heating adds significant thermal load. Derating curves in the datasheet confirm sustained operation at full 50 W dissipation only below T_C = 25°C; above that, power must be linearly reduced per the 0.4 W/°C derating factor.

Does BUH51G support Pb-free soldering processes?

Yes, BUH51G is available in Pb-free packaging and fully compliant with RoHS requirements. The device supports standard reflow profiles including peak temperatures up to 260°C for 5 seconds at the lead, matching IPC/JEDEC J-STD-020 moisture sensitivity level 1. No special pre-bake or handling is required, and its epoxy compound meets UL 94 V-0 flammability rating at 0.125 inch thickness.

How does BUH51G perform under short-circuit conditions in halogen transformer applications?

The BUH51G is explicitly designed to sustain large inrush and short-circuit currents in halogen electronic transformers. Its V_CES = 800 V rating and validated reverse-biased SOA ensure safe turn-off even when the lamp filament shorts during warm-up. Dynamic saturation voltage remains bounded (≤15 V at 125°C), preventing destructive second breakdown during fault events - a key differentiator versus generic NPN transistors.

What base drive current is required to fully saturate BUH51G at 3.0 A collector current?

To achieve full saturation at I_C = 3.0 A, BUH51G requires I_B ≥ 0.6 A (forced h_FE ≈ 5), based on h_FE = 5.0–6.2 at I_C = 2.0–3.0 A and 125°C. At 25°C, 0.4 A drive suffices (h_FE ≥ 7.5), but thermal design must account for worst-case gain drop. The datasheet specifies V_BE(sat) = 0.92–1.1 V and V_CE(sat) = 0.3–0.5 V under these conditions.

Is BUH51G pin-compatible with other TO-225 NPN transistors like BU2508DX?

No, BUH51G is not pin-compatible with BU2508DX. While both use TO-225 packages, BU2508DX has Base–Emitter–Collector pinout (1–2–3), whereas BUH51G uses Base–Collector–Emitter (1–2–3). Swapping them without board revision will result in immediate device failure due to reversed collector/emitter connections and incorrect biasing.