onsemi BD434S

Overview

BD434S from Fairchild Semiconductor is a PNP epitaxial silicon transistor in TO-126 package, rated for -22 V V_CEO, -4 A I_C, 36 W P_C, with h_FE = 40–140 at I_C = -10 mA to -2 A, and V_CE(sat) ≤ -0.5 V at I_C = -2 A / I_B = -0.2 A. It serves as a medium-power switching and linear amplifier device in industrial power supplies and motor control stages.

For engineers reviewing the BD434S datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, TO-126 thermal capability, guaranteed V_CEO = -22 V rating, DC current gain range across operating currents, and saturation voltage performance under high-current switching conditions.

Technical Context

The BD434S operates as a single PNP bipolar junction transistor with epitaxial base construction, optimized for medium-power linear amplification and hard-switching applications. Its design supports continuous collector current up to -4 A and pulsed current to -7 A, with junction temperature limited to 150°C and safe operating area defined per Figure 5 of the datasheet.

It functions as a complement to the NPN BD433 transistor, enabling push-pull and complementary symmetry circuits. Electrical behavior is characterized at T_C = 25°C, with derating applied above 25°C case temperature per the 0.48 W/°C power derating curve.

Key Specifications

Pinout & Package

BD434S is housed in a TO-126 plastic package with three leads, designed for through-hole mounting and moderate power dissipation with external heatsink attachment via the collector tab.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP medium-power transistor applications.

Compared with BD434S, BD436S offers higher V_CEO (-32 V vs. -22 V) with identical package and drive requirements, while MJD44H11T4 provides greater voltage/current headroom in a surface-mount package-requiring board redesign but enabling higher-reliability 48 V applications.

Availability

BD434S is available at Aetrix Electronics and suitable for industrial power supplies, DC motor controllers, and relay interface circuits requiring stable component supply and long-term manufacturing continuity.

Supply support for BD434S 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in discrete power devices, analog ICs, and interface solutions before its acquisition by ON Semiconductor in 2016.

The BD434S belongs to Fairchild's legacy medium-power PNP transistor family, engineered for robust linear regulation and switching in industrial and automotive auxiliary systems where thermal stability and parameter consistency are critical.

FAQ

What is the maximum continuous collector current rating for BD434S?

The BD434S has a maximum continuous collector current (I_C) rating of -4 A at T_C = 25°C. This rating assumes proper heatsinking; derating is required above 25°C case temperature at 0.48 W/°C. The BD434S also supports -7 A pulsed collector current under specified duty cycle conditions, making it suitable for intermittent high-load applications.

Does BD434S have a documented pin-compatible alternative within the same family?

Yes, BD436S is a documented alternative with identical TO-126 package, pinout, and thermal characteristics, differing only in higher -32 V V_CEO rating. Both BD434S and BD436S share the same base-emitter and collector-emitter saturation behavior, allowing BD436S to serve as a higher-voltage drop-in option without circuit modification.

What is the typical DC current gain (h_FE) range for BD434S across operating conditions?

The BD434S exhibits h_FE = 40–140 depending on test conditions: minimum 40 at V_CE = -5 V, I_C = -10 mA; minimum 30 at V_CE = -1 V, I_C = -500 mA; and minimum 85 at V_CE = -1 V, I_C = -2 A. This wide gain range supports both small-signal amplification and high-current switching with predictable base drive requirements.

Can BD434S be used in complementary pair configurations with NPN transistors?

Yes, BD434S is explicitly designed as the PNP complement to the NPN BD433 transistor. Datasheet features confirm this pairing for push-pull amplifier outputs and complementary symmetry switching stages, ensuring matched thermal and electrical characteristics for balanced performance in dual-rail designs.

What is the safe operating area (SOA) limitation for BD434S at elevated temperatures?

The BD434S safe operating area is defined in Figure 5 of its datasheet and contracts with increasing case temperature. At T_C = 100°C, the maximum continuous I_C drops to approximately -1.5 A at V_CE = -10 V due to thermal constraints. Designers must apply the published SOA curve and derating slope (0.48 W/°C) to ensure reliable operation under worst-case thermal conditions.