onsemi BC517_L34Z

Overview

BC517_L34Z from ON Semiconductor (formerly Fairchild) is an NPN Darlington transistor optimized for high-current switching applications up to 1.2 A, featuring a minimum DC current gain (h_FE) of 30,000 at 20 mA, V_CEO = 30 V, and V_CE(sat) = 1.0 V at I_C = 100 mA / I_B = 0.1 mA - used in relay drivers, lamp drivers, and low-frequency power switches.

For engineers reviewing the BC517_L34Z datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed high h_FE, TO-92 package thermal resistance (R_θJA = 200 °C/W), safe operating area at 1.2 A continuous collector current, and emitter-base breakdown voltage (V_EBO) of 10 V.

Technical Context

The BC517_L34Z integrates two cascaded NPN transistors in a single TO-92 package to achieve ultra-high current gain without external biasing components. Its Darlington configuration inherently exhibits higher V_BE(on) (1.4 V) and V_CE(sat) (1.0 V) versus standard NPNs, trading voltage headroom for gain and drive simplicity.

Designed for DC and low-frequency (<100 kHz) switching, it operates across –55°C to +150°C junction temperature range with 625 mW total dissipation at 25°C, derating linearly at 5.0 mW/°C above ambient - requiring careful thermal management in sustained 1 A operation.

Key Specifications

Pinout & Package

BC517_L34Z is housed in a standard TO-92 plastic package with 3 leads: Collector (lead 1), Base (lead 2), Emitter (lead 3), compliant with JEDEC TO-92 outline dimensions (14.47 mm length, 4.58 mm width, 3.86 mm height).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN Darlington transistor applications.

Compared with BC517-100 and MPSA14, BC517_L34Z delivers the highest guaranteed current gain and full 1.2 A rating in TO-92, making it optimal for designs requiring deterministic base drive and robust 1 A switching without derating or thermal compromise.

Availability

BC517_L34Z is available at Aetrix Electronics and suitable for relay drivers, lamp drivers, DC motor controls, and industrial sensor interfaces requiring stable component supply and long-term manufacturability.

Supply support for BC517_L34Z 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, sensors, and discrete devices, with heritage from Fairchild Semiconductor's portfolio.

The BC517_L34Z belongs to ON Semiconductor's general-purpose bipolar transistor product line, engineered for cost-sensitive, high-reliability switching applications in industrial automation, building controls, and legacy automotive subsystems.

FAQ

What is the guaranteed minimum h_FE for BC517_L34Z?

The BC517_L34Z guarantees a minimum DC current gain (h_FE) of 30,000 at V_CE = 2.0 V and I_C = 20 mA, as specified in the official ON Semiconductor datasheet Rev. A. This value is binned and tested per unit, ensuring consistent low-base-drive performance across production lots. The BC517_L34Z achieves this via its monolithic Darlington structure, distinguishing it from standard NPN transistors.

Can BC517_L34Z replace BC547 in a circuit?

No - BC517_L34Z is not a drop-in replacement for BC547. While both are TO-92 NPN transistors, BC547 is a standard BJT (h_FE ≈ 110–800), whereas BC517_L34Z is a Darlington with h_FE ≥ 30,000, higher V_BE(on) (1.4 V vs. ~0.7 V), and higher V_CE(sat) (1.0 V vs. ~0.2 V). Substituting BC517_L34Z for BC547 would disrupt biasing and increase power loss unless circuit re-optimization is performed.

What is the maximum continuous collector current for BC517_L34Z?

The BC517_L34Z supports a maximum continuous collector current (I_C) of 1.2 A at T_A = 25°C, as defined in its Absolute Maximum Ratings table. Sustained operation near this limit requires adequate PCB copper area or forced airflow to manage junction temperature, given its R_θJA of 200 °C/W. Derating is mandatory above 25°C ambient per the 5.0 mW/°C specification.

Does BC517_L34Z have built-in base-emitter resistors?

No, BC517_L34Z does not include internal base-emitter resistors. It is a bare Darlington pair requiring external base current limiting - typically a series resistor between the driving source and pin 2 (Base). Unlike "digital transistors" (e.g., NSD12001), the BC517_L34Z offers no integrated bias network, preserving design flexibility but mandating external component selection for stable turn-on/turn-off behavior.

Is BC517_L34Z suitable for PWM motor control?

The BC517_L34Z is rated for low-frequency switching only (typically <100 kHz), due to inherent Darlington storage time and minority-carrier delays. While usable for basic on/off or slow PWM (e.g., <5 kHz) of small DC motors, it is not recommended for high-efficiency or high-frequency PWM drive. For such applications, MOSFETs or dedicated motor driver ICs provide faster switching, lower conduction loss, and better thermal performance than BC517_L34Z.