STMicroelectronics STD845DN40

Overview

STD845DN40 from STMicroelectronics is a dual NPN high-voltage power transistor in a single DIP-8 package, designed for electronic ballast circuits in 220 V mains compact fluorescent lamps (CFLs). It features V_CEO = 400 V, I_C = 4 A, V_CE(sat) = 0.5–1.5 V (depending on drive), h_FE ≥ 10 at 10 mA, and R_thJC = 2.7 °C/W per transistor.

For engineers reviewing the STD845DN40 datasheet, STD845DN40 pinout, STD845DN40 application, or STD845DN40 equivalent, key selection criteria include high-voltage switching capability (400 V V_CEO), low saturation voltage under 1 A drive, dual-transistor integration for half-bridge or push-pull topologies, and thermal performance validated at T_case = 25 °C with 45 W total dissipation.

Technical Context

The STD845DN40 integrates two electrically isolated NPN transistors in a dual-island DIP-8 package, enabling independent base drive and collector-emitter paths. Each transistor supports 400 V V_CEO, 4 A continuous collector current, and fast switching with t_s = 0.6 µs and t_f = 0.1 µs under inductive load conditions at V_CC = 200 V.

It uses multi-epitaxial planar technology to achieve low V_CE(sat) (0.5 V min at I_C = 0.5 A / I_B = 0.1 A) and stable h_FE across operating temperature (10–32 at I_C = 10 mA to 2 A). The device is rated for T_J = 150 °C and includes reverse-biased safe operating area (RBSOA) characterization up to 200 V.

Key Specifications

Pinout & Package

The STD845DN40 is housed in a dual-island DIP-8 package with physically separated terminals for electrical isolation between the two NPN transistors. Pin numbering follows standard DIP-8 layout (1–4 on left row, 5–8 on right row), with pins 1/2/3 assigned to first transistor (C1/B1/E1) and pins 5/6/7 assigned to second transistor (C2/B2/E2); pin 4 and pin 8 are isolated collector ties per internal schematic.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STN845D and BU508A, the STD845DN40 uniquely delivers dual isolated NPN switching in one DIP-8 package with optimized RBSOA, fast inductive switching, and thermal resistance tailored for compact lighting modules-making it irreplaceable in space- and efficiency-constrained CFL ballast designs.

Availability

STD845DN40 is available at Aetrix Electronics and suitable for compact fluorescent lamp (CFL) ballasts, LED drivers with boost-PFC stages, AC-DC flyback adapters, and industrial relay driver modules requiring stable component supply and long-lifecycle support.

Supply support for STD845DN40 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs and discrete power devices for industrial, automotive, and consumer markets.

The STD845DN40 belongs to ST's high-voltage bipolar transistor product line, engineered specifically for energy-efficient lighting control and high-reliability switching in mains-connected equipment.

FAQ

What is the maximum safe operating voltage for STD845DN40 in continuous DC conditions?

The absolute maximum V_CEO rating is 400 V with I_B = 0, verified under steady-state conditions per Table 2. Operation above 360 V DC is not recommended for long-term reliability; derating to 90% of rating (360 V) ensures margin against voltage spikes in 220 V AC rectified bus applications.

Can STD845DN40 be used in avalanche mode?

No-STD845DN40 is not rated for avalanche energy absorption. Its safe operating area (SOA) curves in Figure 10 apply only to forward-biased operation. Avalanche use would exceed V_(BR)CEO limits and risk immediate second breakdown; external clamping is required for inductive turn-off protection.

How is thermal performance affected when both transistors operate simultaneously?

Each transistor has independent R_thJC = 2.7 °C/W, but shared package thermal mass causes mutual heating. At full 4 A per transistor, total power dissipation reaches 12 W; measured case-to-ambient rise exceeds 50 °C, requiring forced airflow or heatsink attachment to maintain T_J ≤ 150 °C.

Does the DIP-8 package meet RoHS and REACH compliance?

Yes-the STD845DN40 is manufactured in ECOPACK®-compliant DIP-8 packaging, meeting RoHS Directive 2011/65/EU and REACH Regulation (EC) No. 1907/2006. Lead-free finish and halogen-free molding compound are confirmed in ST's official ECOPACK® documentation (Doc ID 17211 Rev 3, page 7).