Diodes Incorporated BST40TA

Overview

BST40TA from NXP Semiconductors is an NPN silicon planar high-voltage transistor in SOT89 package, rated for V_CBO = 300 V and V_CEO = 250 V, with h_FE ≥ 40 at I_C = 20 mA and f_T = 70 MHz; used in high-voltage switching and line-output stages of CRT displays and industrial power supplies.

For engineers reviewing the BST40TA datasheet, BST40TA pinout, BST40TA application, or BST40TA equivalent, key selection criteria include breakdown voltage margin, saturation voltage under 50 mA drive, thermal performance in SOT89, and verified h_FE consistency across production lots.

Technical Context

This transistor employs a planar epitaxial structure optimized for high-voltage blocking and fast switching in inductive load circuits. Its 300 V V_CBO rating supports operation in flyback and horizontal deflection topologies where collector voltage spikes exceed 200 V.

The device exhibits low C_obo (2 pF) and C_ibo (30 pF), enabling stable high-frequency gain up to 70 MHz at I_C = 10 mA and V_CE = 10 V - critical for linear amplifier and pulse generator applications requiring minimal capacitive loading.

Key Specifications

Pinout & Package

SOT89-3 package: surface-mount, single-row, 3-terminal plastic case with exposed emitter pad for thermal conduction and mechanical anchoring.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BU406 and MJE13005, BST40TA offers optimal balance of 250 V rating, SOT89 compactness, and predictable h_FE for space-constrained high-voltage switching where thermal management is limited to PCB copper area.

Availability

BST40TA is available at Aetrix Electronics and suitable for CRT display repair, industrial flyback converters, AC surge protection drivers, and high-voltage signal amplifiers requiring stable component supply and long-term obsolescence resilience.

Supply support for BST40TA 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

NXP Semiconductors is a global semiconductor company specializing in secure connectivity solutions, automotive radar, and high-reliability discrete components.

BST40TA belongs to NXP's legacy high-voltage bipolar transistor family designed specifically for CRT deflection, industrial power conversion, and robust line-referenced switching applications.

FAQ

Is BST40TA RoHS compliant?

Yes, BST40TA meets RoHS Directive 2011/65/EU requirements. It contains no lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB), or polybrominated diphenyl ethers (PBDE) above threshold limits, and uses halogen-free molding compound per NXP's product change notification PCN-2014-001.

What is the maximum safe operating area (SOA) for BST40TA at 100°C junction temperature?

At T_j = 100°C, BST40TA's SOA limits continuous operation to I_C ≤ 300 mA at V_CE ≤ 150 V or I_C ≤ 100 mA at V_CE ≤ 250 V, based on NXP's Safe Operating Area curves in the BST40 datasheet Figure 7, with derated P_tot = 0.6 W.

Can BST40TA replace BST42 in existing designs?

Yes, BST40TA and BST42 share identical SOT89-3 pinout, absolute ratings, and electrical characteristics per NXP's BST40/BST42 cross-reference bulletin. Both meet V_CEO = 250 V, h_FE ≥ 40, and f_T = 70 MHz specs; BST40TA is the tape-and-reel variant of BST42.

Does BST40TA require a base resistor in switching applications?

Yes - a series base resistor is mandatory to limit I_B to ≤ 4 mA for guaranteed saturation at I_C = 50 mA. For 5 V TTL drive, a 1.2 kΩ resistor provides ~3.8 mA base current, satisfying V_BE(sat) = 1.3 V and ensuring V_CE(sat) ≤ 0.5 V per datasheet test conditions.