onsemi BUV21G

Overview

BUV21G from onsemi is an NPN silicon power transistor in TO-204 (TO-3) metal package, designed for high-speed, high-current, high-power switching applications such as horizontal deflection circuits in CRT displays and SMPS primary-side switching. It delivers 40 A continuous collector current, 200 V V_CEO(sus), and 250 W total device dissipation at T_C = 25°C.

For engineers reviewing the BUV21G datasheet, pinout, applications, or equivalent options, this page provides verified electrical parameters, thermal resistance (R_θJC = 0.7°C/W), switching times (t_f = 0.4 µs), DC current gain (h_FE ≥ 20 at I_C = 12 A), and safe operating area boundaries - all critical for flyback transformer drive and high-voltage pulse amplification design validation.

Technical Context

The BUV21G operates as a single NPN bipolar junction transistor with base-emitter and base-collector junctions optimized for fast turn-on/turn-off under high-current pulsed conditions. Its second breakdown limit is defined at I_S/B = 12 A (V_CE = 20 V, t = 1 s) and 0.15 A (V_CE = 140 V, t = 1 s), indicating robust ruggedness for inductive load switching.

It features low saturation voltage (V_CE(sat) ≤ 0.6 V at I_C = 12 A, I_B = 1.2 A) and high f_T = 8.0 MHz, enabling stable gain in active-region amplifier stages while maintaining fast switching capability in hard-switched topologies.

Key Specifications

Pinout & Package

BUV21G is housed in a TO-204 (TO-3) metal package with case-isolated collector, rated for high-voltage isolation and mechanical robustness in industrial power systems. The package uses a 2-pin configuration with integral mounting flange for direct heatsink attachment.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN power transistor applications.

Compared with BUV21G, BUV22G offers +50 V blocking headroom at minor speed cost, while MJE13009 trades current capacity and thermal performance for extreme voltage tolerance - making BUV21G optimal for balanced 200 V / 40 A switching where speed and dissipation are co-critical.

Availability

BUV21G is available at Aetrix Electronics and suitable for CRT deflection circuits, industrial SMPS, motor starter modules, and capacitor discharge ignition systems requiring stable component supply, long-lifecycle availability, and traceable Pb-free sourcing.

Supply support for BUV21G 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 power management, analog, sensor, and discrete devices for automotive, industrial, and consumer applications.

The BUV21G belongs to onsemi's Switch-mode Series of high-power bipolar transistors, engineered specifically for horizontal deflection and high-current switching in legacy and industrial power electronics where ruggedness and repeatable SOA performance are essential.

FAQ

What is the maximum junction temperature rating for the BUV21G?

The BUV21G has an operating junction temperature range of −65°C to +200°C. This wide rating supports use in high-ambient environments such as enclosed industrial power supplies or under-hood automotive auxiliary systems. Derating begins above 25°C case temperature per the published power derating curve, and thermal design must ensure T_J remains within this limit during peak-load operation. The BUV21G datasheet specifies T_J = 200°C as absolute maximum.

Does the BUV21G require a heatsink, and what thermal resistance is needed?

Yes, the BUV21G requires a heatsink for any sustained power dissipation above ~25 W. With R_θJC = 0.7°C/W and maximum T_J = 200°C, a 75°C ambient design requires R_θCA ≤ 1.17°C/W total (including interface resistance). For example, using a 0.5°C/W heatsink with 0.1°C/W thermal pad yields safe operation at 125 W dissipation. The BUV21G's metal TO-3 case must be electrically isolated if the heatsink is grounded.

What is the safe operating area (SOA) limitation that most commonly affects BUV21G designs?

The second breakdown limit - not thermal limit - is the dominant SOA constraint for the BUV21G in pulsed high-voltage applications. At V_CE = 140 V, the device sustains only 0.15 A for 1 s, meaning designs driving inductive loads like CRT yokes must avoid simultaneous high V_CE and high I_C during turn-off. The BUV21G's SOA curve in Figure 2 shows this boundary clearly, and snubber networks are often required to suppress voltage spikes before they intersect this region.

Can the BUV21G be used in linear amplifier applications?

The BUV21G can operate in Class-A or Class-AB linear amplifiers due to its 8 MHz f_T and h_FE stability up to 25 A, but its high power dissipation and thermal sensitivity make it impractical for audio output stages without massive heatsinking. It is primarily characterized and qualified for switching - not linear - operation. For linear use, the BUV21G would require strict V_CE/I_C derating per Figure 2, and its SOA must be continuously monitored. Most designs prefer dedicated audio transistors over the BUV21G.

Is the BUV21G pin-compatible with older non-Pb-free versions like BUV21?

Yes, the BUV21G is a direct Pb-free replacement for the legacy BUV21, sharing identical TO-204 (TO-3) package dimensions, pinout (Base = Pin 1, Emitter = Pin 2, Collector = Case), and electrical specifications. The "G" suffix denotes only the lead-free finish; no changes were made to die design, ratings, or SOA. Designers may substitute BUV21G for BUV21 without layout or thermal redesign, provided RoHS compliance is required.