onsemi 2SA2126-S-TL-E

Overview

2SA2126-S-TL-E from onsemi is a PNP bipolar junction transistor (BJT) designed for general-purpose amplification and switching in low-voltage, medium-current applications. It features a DC current gain (h_FE) of 120–270 at I_C = 2 mA, V_CE = 2 V; maximum collector-emitter voltage V_CEO = 50 V; continuous collector current I_C = 150 mA; and power dissipation P_D = 200 mW at T_A = 25 °C. It is commonly used in audio preamplifier stages and signal-level switching circuits.

For engineers reviewing the 2SA2126-S-TL-E datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP polarity, TO-92SC (SOT-423) package footprint, guaranteed h_FE range, V_CEO rating, and thermal derating behavior above 25 °C ambient.

Technical Context

This device operates as a standard silicon PNP BJT with epitaxial base construction, optimized for linear amplification and saturated switching. Its h_FE is specified across I_C = 0.1–10 mA and V_CE = 2 V, supporting stable biasing in Class-A and Class-AB small-signal stages.

It exhibits a typical V_CE(sat) of 0.25 V at I_C = 10 mA and I_B = 1 mA, enabling efficient low-loss switching in discrete logic interfaces and driver circuits. Junction-to-ambient thermal resistance R_θJA is 500 °C/W, requiring careful PCB copper area planning for sustained >50 mW operation.

Key Specifications

Pinout & Package

2SA2126-S-TL-E is housed in a TO-92SC (SOT-423) plastic surface-mount package with three leads: Emitter, Base, and Collector. The package measures 2.1 mm × 1.3 mm × 0.9 mm and is compatible with standard reflow soldering profiles.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP small-signal transistor applications.

Compared with 2SA2126-S-TL-E, the 2SA1774EBTLR offers identical electrical specs but less favorable thermal performance in compact layouts, while BC807-25LT1G trades V_CEO margin for wider h_FE range-both require validation of PCB thermal relief and bias stability under target operating conditions.

Availability

2SA2126-S-TL-E is available at Aetrix Electronics and suitable for audio signal conditioning, discrete logic interfacing, and low-power sensor buffering requiring stable component supply across industrial control, consumer electronics, and medical instrumentation programs.

Supply support for 2SA2126-S-TL-E 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 2SA2126-S-TL-E belongs to onsemi's general-purpose bipolar transistor product line, engineered for reliability and consistency in cost-sensitive, space-constrained analog and digital interface circuits.

FAQ

What is the maximum operating temperature for the 2SA2126-S-TL-E?

The 2SA2126-S-TL-E has a maximum junction temperature (T_J) of 150 °C. Its thermal performance depends on PCB copper area and ambient conditions: at 25 °C ambient, it can dissipate up to 200 mW, but this must be linearly derated by 0.4 mW/°C above 25 °C. For reliable long-term operation, keep T_J ≤ 125 °C in continuous use. Always verify actual board-level thermal rise using IR imaging or thermocouple measurement during prototype validation of the 2SA2126-S-TL-E.

Is the 2SA2126-S-TL-E RoHS compliant and lead-free?

Yes, the 2SA2126-S-TL-E is RoHS compliant and fully lead-free, meeting EU Directive 2011/65/EU and China RoHS II requirements. It is qualified to MSL1 per J-STD-020, meaning it can be subjected to unlimited floor life and standard Pb-free reflow profiles without baking. The device marking "S" in the suffix confirms lead-free plating, and the full part number 2SA2126-S-TL-E appears on the tape-and-reel packaging label and die surface.

Can the 2SA2126-S-TL-E replace a 2N3906 in existing designs?

The 2SA2126-S-TL-E shares the same PNP polarity and similar V_CEO (50 V vs. 40 V), I_C (150 mA vs. 200 mA), and h_FE range as the 2N3906, but it uses an SOT-423 package versus the 2N3906's TO-92. Direct replacement requires PCB footprint redesign. Electrically, the 2SA2126-S-TL-E offers higher V_CEO and lower V_CE(sat), but its smaller package has higher thermal resistance-verify thermal performance and solder joint reliability before substituting the 2SA2126-S-TL-E into legacy 2N3906 layouts.

What is the typical noise figure of the 2SA2126-S-TL-E in small-signal amplifier configurations?

The 2SA2126-S-TL-E does not specify a formal noise figure (NF) in its datasheet, as it is not characterized for ultra-low-noise RF or precision audio applications. However, measured spot noise voltage at 1 kHz is approximately 12 nV/√Hz with I_C = 1 mA and V_CE = 5 V-comparable to other general-purpose PNP BJTs. For low-noise design, pair the 2SA2126-S-TL-E with emitter degeneration and proper bypassing; avoid using it in first-stage mic preamps where dedicated low-noise transistors like BC550C are preferred.

Does the 2SA2126-S-TL-E have avalanche rating or ruggedness specifications?

No, the 2SA2126-S-TL-E is not rated for avalanche operation and lacks published secondary breakdown or SOA (Safe Operating Area) curves beyond DC and pulsed I_C/V_CE limits. It must be operated strictly within its absolute maximum ratings: V_CEO ≤ 50 V, I_C ≤ 150 mA, and P_D ≤ 200 mW (derated). Transient overvoltage events exceeding V_CEO risk permanent damage. Use external clamping (e.g., Zener diode from collector to emitter) if inductive loads or voltage spikes are present in the 2SA2126-S-TL-E application circuit.