onsemi BD435S

Overview

BD435S from ON Semiconductor is a medium-power NPN epitaxial silicon transistor in TO-126 package, rated for 32 V V_CEO, 4 A continuous collector current, and 36 W power dissipation at T_C = 25°C. It serves as a linear amplifier or switching device in industrial power supplies, motor drivers, and relay drivers where robust DC gain (h_FE = 40–130) and low saturation voltage (V_CE(sat) ≤ 0.5 V @ I_C = 2 A, I_B = 0.2 A) are required.

For engineers reviewing the BD435S datasheet, pinout, applications, or equivalent options, key selection considerations include its 32 V breakdown rating, TO-126 thermal performance, complementary pairing with BD436, and suitability for medium-current switching in non-life-critical industrial control circuits.

Technical Context

The BD435S operates as a single NPN bipolar junction transistor with epitaxial base construction, optimized for stable DC current gain across I_C = 10 mA to 2 A and V_CE = 1–5 V. Its f_T of 3 MHz supports moderate-speed switching up to ~100 kHz in hard-switched topologies.

Thermal design relies on case-to-heatsink conduction via the metal tab (Pin 2), with maximum junction temperature limited to 150°C and derating beginning at T_C > 25°C per Figure 6. Safe operating area (SOA) curves confirm pulsed capability up to I_C = 7 A with PW ≤ 300 μs and duty cycle ≤ 1.5%.

Key Specifications

Pinout & Package

BD435S uses the TO-126 package: molded plastic case with metal tab (collector) mounted to heatsink, 3 leads in-line, lead spacing 2.54 mm, total length 10.16 mm. The metal tab is electrically connected to Pin 2 (Collector).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD435S, MJD44H11G offers greater voltage headroom but demands board space reallocation, whereas BD437S delivers direct package- and pin-compatible voltage scaling-enabling rapid design iteration without requalification of thermal or mechanical interfaces.

Availability

BD435S is available at Aetrix Electronics and suitable for industrial motor drives, relay interface modules, and linear power supplies requiring stable component supply, long-term manufacturability, and consistent parametric performance across production lots.

Supply support for BD435S 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

ON Semiconductor is a global semiconductor manufacturer specializing in power management, analog, sensor, and logic devices for automotive, industrial, cloud, and consumer markets.

The BD435S belongs to Fairchild's legacy medium-power bipolar transistor family, designed for cost-effective, thermally robust switching and linear amplification in industrial control and power conversion equipment.

FAQ

What is the maximum continuous collector current rating for BD435S?

The BD435S is rated for 4 A continuous collector current (I_C) at case temperature T_C = 25°C. This rating assumes adequate heatsinking; current must be derated linearly above 25°C per the power derating curve in the datasheet, reaching zero at T_C = 175°C. At T_C = 100°C, the usable I_C drops to approximately 2.2 A. BD435S must not exceed this limit in sustained operation to avoid thermal runaway or junction failure.

Is BD435S pin-compatible with BD433S or BD437S?

Yes, BD435S shares identical TO-126 package dimensions, pin assignment (Emitter-Collector-Base), and mechanical footprint with BD433S and BD437S. All three devices have the same pinout: Pin 1 = Emitter, Pin 2 = Collector (metal tab), Pin 3 = Base. This allows direct physical substitution on PCBs, though electrical differences-especially V_CEO (22 V / 32 V / 45 V) and h_FE ranges-must be verified for functional compatibility in each circuit.

What is the typical V_BE(on) of BD435S under rated conditions?

The BD435S exhibits a typical base-emitter on voltage (V_BE(on)) of 1.1 V when V_CE = 1 V and I_C = 2 A. This value is confirmed across production lots and remains stable within ±0.1 V over temperature (25°C to 125°C). Designers should use 1.2 V in worst-case base resistor calculations to ensure sufficient drive margin under high-temperature, low-h_FE conditions.

Does BD435S require a heatsink in standard operation?

Yes, BD435S requires a heatsink for any application drawing >1.5 A continuously or dissipating >5 W. With R_θJA ≈ 50°C/W (no heatsink), junction temperature would exceed 150°C at just 0.7 W. Even at 2 A and V_CE(sat) = 0.4 V (0.8 W), ambient temperatures above 40°C necessitate heatsinking. A 10°C/W heatsink keeps T_J < 100°C at full 4 A load with proper mounting.

What is the safe operating area (SOA) limitation for BD435S in pulse applications?

The BD435S SOA permits pulsed collector currents up to 7 A (I_CP) only under strict conditions: pulse width ≤ 300 μs and duty cycle ≤ 1.5%. Exceeding either parameter risks secondary breakdown or localized hot-spot formation. For 100 μs pulses, peak current may reach 5.5 A; for 1 ms pulses, it must be reduced to ≤ 2.5 A. These limits are defined in Figure 5 of the BD433/435/437 datasheet and must be validated per actual board layout and thermal environment.