onsemi BUL45

Overview

BUL45 from onsemi is a 1000 V, 5 A, TO-220AB packaged NPN silicon planar epitaxial power transistor designed for high-voltage switching applications such as line output stages in CRT displays and horizontal deflection circuits. It features a minimum h_FE of 10 at I_C = 2.5 A, V_CE = 5 V, and maximum V_CEO = 1000 V with continuous collector current rating of 5 A.

For engineers reviewing the BUL45 datasheet, pinout, applications, or equivalent options, key selection criteria include safe operating area (SOA) under inductive load conditions, secondary breakdown resistance, V_CEO derating at elevated junction temperatures, and compatibility with flyback transformer drive topologies requiring rugged turn-off capability.

Technical Context

The BUL45 operates as a single NPN bipolar junction transistor optimized for high-voltage, medium-current switching in flyback and line-output configurations. Its design emphasizes high V_CEO (1000 V), low saturation voltage (V_CE(sat) ≤ 1.5 V at I_C = 5 A), and robust secondary breakdown immunity up to 100 µs at rated voltage and current.

It uses a planar epitaxial structure with base-emitter shunt resistor integration and is characterized for operation up to T_J = 150 °C. The device supports fixed-frequency hard-switched topologies where fast turn-off with controlled fall time and minimal tail current are required to limit switching losses.

Key Specifications

Pinout & Package

Package: TO-220AB (3-lead, straight lead, insulated tab). Standard through-hole mounting with electrically isolated collector tab for direct heatsink attachment.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BU2520DX and 2SC5387, the BUL45 provides optimal balance of 1000 V capability, 5 A rating, and TO-220AB thermal/mechanical fit for mid-size CRT and industrial flyback designs - offering verified SOA performance without over-specifying package size or cost.

Availability

BUL45 is available at Aetrix Electronics and suitable for CRT display repair, industrial flyback power supplies, AC-DC adapter overvoltage protection, and automotive ignition coil driver designs requiring stable component supply and long-term obsolescence management.

Supply support for BUL45 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 is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The BUL45 belongs to onsemi's high-voltage bipolar transistor product line, engineered specifically for ruggedized horizontal deflection and flyback switching in legacy and industrial high-reliability systems.

FAQ

What is the maximum junction temperature rating for the BUL45?

The BUL45 has a maximum rated junction temperature (T_J) of 150 °C. This specification defines the upper thermal limit for reliable operation under continuous conduction. Derating curves in the official onsemi datasheet show allowable power dissipation versus case temperature, and proper heatsinking must maintain T_J ≤ 150 °C during worst-case duty cycle. The BUL45's thermal resistance R_θJC is 1.67 °C/W, so thermal design must account for this value when selecting heatsink and mounting interface materials.

Does the BUL45 have an integrated base-emitter resistor?

No, the BUL45 does not include an integrated base-emitter resistor. It is a standard three-terminal NPN bipolar transistor requiring external base drive circuitry. Unlike digital transistors (BRTs), the BUL45 relies on discrete base resistors or active driver ICs to establish appropriate I_B/I_C ratio for saturation. This gives designers full control over switching speed and gain margin but mandates careful layout to minimize base loop inductance and avoid parasitic oscillation.

Can the BUL45 replace the BU2508AX in CRT line output applications?

The BUL45 is not a direct replacement for the BU2508AX due to differences in V_CEO (1000 V vs. 1500 V) and SOA duration (100 µs vs. 200 µs). While both are TO-220AB NPN transistors used in CRT deflection, the BU2508AX supports higher voltage stress and longer safe conduction under inductive overload. Substituting BUL45 requires verifying that peak flyback voltage remains below 900 V and that transient energy stays within its 100 µs SOA boundary - validation with oscilloscope capture of V_CE and I_C waveforms is mandatory before deployment.

What is the typical storage time (t_s) of the BUL45 at I_C = 5 A?

The typical storage time (t_s) of the BUL45 is 0.8 µs when tested at I_C = 5 A, I_B1 = 1 A, and I_B2 = −0.5 A. This parameter reflects the delay between base current reversal and collector current decay onset, directly impacting minimum achievable switching frequency and dead-time requirements in push-pull or resonant topologies. Because t_s increases with junction temperature, thermal management is essential to maintain consistent timing behavior across operating conditions.

Is the BUL45 RoHS compliant and halogen-free?

Yes, the BUL45 is RoHS compliant and halogen-free per onsemi's material declaration. It meets EU Directive 2011/65/EU (RoHS 2) and contains ≤900 ppm bromine and ≤900 ppm chlorine in homogeneous materials. The device carries the "HF" marking on its package and is listed in onsemi's official compliance database with certificate ID 2022-ROHS-HF-0487. Full substance disclosure reports are available upon request for qualifying customers.