STMicroelectronics DB4

Overview

DB4 from STMicroelectronics is a bidirectional trigger diode (DIAC) designed for gate triggering of triacs and SCRs in AC phase-control circuits. It features a typical breakover voltage of 40 V (35–45 V range), ≤3 V breakover voltage symmetry, ≤50 µA breakover current, and operates across –40 °C to +125 °C junction temperature. It is used in CFL/LED lamp ballast startup and motor/light dimmer trigger stages.

For engineers reviewing the DB4 datasheet, DB4 pinout, DB4 application, or DB4 equivalent, key selection criteria include its 40 V nominal V_BO, low I_BO (≤50 µA), tight V_BO symmetry (≤3 V), SOT-23-3L surface-mount package, and compatibility with triac-based zero-crossing or phase-angle control topologies.

Technical Context

The DB4 functions as a symmetrical, two-terminal, bidirectional avalanche switch that conducts only after both forward and reverse voltages exceed its specified breakover threshold. Its operation is defined by V_BO (35–45 V), ΔV (dynamic V_BO ≥5 V), and rise time ≤2 µs - enabling fast, repeatable triggering in high-noise AC line environments.

It requires no external bias and exhibits matched forward/reverse characteristics due to monolithic construction. The device sustains repetitive peak on-state current up to 2.0 A (tp = 20 µs, 120 Hz), with leakage current ≤10 µA at 0.5×V_BO max, ensuring stable quiescent behavior in RC-trigger networks.

Key Specifications

Pinout & Package

SOT-23-3L surface-mount package: compact, lead-free, ECOPACK®2-compliant, optimized for automated pick-and-place assembly. Pin 1 and Pin 3 must be shorted externally per application circuit requirements.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar DIAC trigger applications.

Compared with DB3 and SMDB3, the DB4 offers higher and more stable breakover voltage (40 V vs. 32 V), greater surge current capability (2.0 A vs. 1.0–2.0 A), and identical thermal and symmetry specs - making it optimal for mains-powered lighting and motor control where robust, repeatable 40 V triggering is required.

Availability

DB4 is available at Aetrix Electronics and suitable for motor dimmers, LED lamp ballasts, AC phase-control circuits, and fluorescent starter modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for DB4 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, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The DB4 belongs to ST's legacy DIAC product line, engineered specifically for robust, low-cost AC line triggering in lighting, appliance, and power control applications - emphasizing symmetry, temperature stability, and high-volume manufacturability.

FAQ

What is the correct pin configuration for DB4 in a triac gate trigger circuit?

DB4 uses a three-terminal SOT-23-3L package with Pins 1 and 3 functionally identical (MT1/MT2) and Pin 2 as the common trigger node. Per ST's application guidance, Pins 1 and 3 must be shorted externally in PCB layout to form a true two-terminal device. This ensures symmetrical conduction and matches the internal die structure.

Can DB4 replace DB3 directly in an existing design?

No - direct replacement is not recommended without circuit validation. DB4 has a higher V_BO (35–45 V vs. 28–36 V), which delays triac turn-on in each AC half-cycle. This shifts phase angle, reduces output power, and may cause instability in RC-timed dimmers or oscillators calibrated for 32 V triggering.

Is DB4 compliant with RoHS and REACH requirements?

Yes - DB4 is ECOPACK®2-compliant, meeting EU RoHS Directive 2011/65/EU and REACH Regulation (EC) No. 1907/2006. ST confirms lead-free terminations, halogen-free molding compound, and full substance declaration per ST's published environmental compliance documentation.

What is the maximum allowable continuous power dissipation for DB4 at 85 °C ambient?

DB4 does not specify a standalone power derating curve, but its absolute maximum ratings limit junction temperature to +125 °C. With θ_JA ≈ 300 °C/W (SOT-23-3L, standard JEDEC pad), max continuous power at 85 °C ambient is ~0.13 W. However, in normal operation, DB4 conducts only transiently (<2 µs), so average power remains <1 mW - thermal design focuses on peak pulse handling, not steady-state dissipation.