onsemi BSP50

Overview

BSP50 from ON Semiconductor is an NPN Darlington transistor designed for high-current switching applications requiring extremely high DC current gain (hFE ≥ 1000 at IC = 150 mA, VCE = 10 V) with continuous collector current up to 800 mA, VCEO = 45 V, and SOT-223 package thermal resistance of 125°C/W - used in industrial relay drivers and solid-state output modules.

For engineers reviewing the BSP50 datasheet, pinout, applications, or equivalent options, key selection criteria include verified Darlington saturation performance (VCE(sat) = 1.3 V at IC = 500 mA/IB = 0.5 mA), junction temperature range (–55°C to +150°C), and SOT-223 thermal dissipation capability under sustained load conditions.

Technical Context

The BSP50 implements a monolithic NPN Darlington pair structure optimized for high-current gain at medium collector currents (up to 500 mA), with base-emitter and collector-base breakdown voltages rated at 5 V and 60 V respectively. Its design targets low-input-drive switching where minimal base current must control substantial load current.

Thermal performance is defined by RθJA = 125°C/W in the SOT-223 package, and absolute maximum ratings specify TJ(max) = 150°C with derating above 25°C. The device is not intended for linear amplification but for saturated-switching operation with validated VBE(sat) = 1.9 V at IC = 500 mA/IB = 0.5 mA.

Key Specifications

Pinout & Package

SOT-223 surface-mount package with exposed thermal pad (pin 4), standardized footprint for PCB thermal relief and mechanical stability in high-power switching layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with NSS12500U and DZT5550, the BSP50 uniquely balances high-current capability (800 mA), robust thermal design (125°C/W + exposed pad), and industrial-grade junction temperature (150°C), making it the only option qualified for sustained 500 mA switching in unventilated control cabinets.

Availability

BSP50 is available at Aetrix Electronics and suitable for industrial relay drivers, PLC output modules, and DC motor start circuits requiring stable component supply across multi-year production cycles.

Supply support for BSP50 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 energy-efficient power management, analog, sensor, and logic solutions for automotive, industrial, and cloud infrastructure markets.

The BSP50 belongs to ON Semiconductor's legacy Fairchild bipolar transistor product line, engineered specifically for high-reliability industrial switching applications where Darlington gain and thermal resilience are critical.

FAQ

What is the maximum continuous collector current rating for the BSP50?

The BSP50 is rated for a continuous collector current (IC) of 800 mA at TA = 25°C. This rating assumes proper PCB thermal management using the SOT-223 thermal pad. At higher ambient temperatures or reduced copper area, derating applies per the 8.0 mW/°C specification. Always validate actual operating current in your thermal environment before final design sign-off for the BSP50.

Does the BSP50 have a built-in base-emitter resistor?

No, the BSP50 does not include any integrated base-emitter resistor. It is a bare Darlington transistor requiring external base current limiting - typically via a series resistor driven by a microcontroller GPIO or logic buffer. This allows flexible biasing for varying load currents and ensures precise control over turn-on speed and saturation depth for the BSP50.

Can the BSP50 be used in linear amplifier configurations?

The BSP50 is characterized and specified exclusively for saturated switching operation, not linear amplification. Its hFE variation, thermal instability under bias, and lack of small-signal parameters (e.g., fT, Cobo) in the datasheet confirm its optimization for on/off use. For analog gain stages, select purpose-built general-purpose BJTs - the BSP50 should only be applied as a switch in designs targeting the BSP50's published switching parameters.

What is the function of pin 4 on the BSP50 SOT-223 package?

Pin 4 on the BSP50 is the exposed thermal pad, electrically connected to the collector terminal. It must be soldered to a PCB copper pour for effective heat dissipation. Leaving pin 4 unconnected degrades thermal resistance by >40%, risking premature thermal shutdown or parametric shift. Always include thermal vias beneath pin 4 when routing the BSP50 into production PCBs.

How does the BSP50's VCE(sat) compare to standard single NPN transistors at 500 mA?

At IC = 500 mA, the BSP50 achieves VCE(sat) = 1.3 V - significantly lower than typical single NPN transistors (e.g., 2N2222: ~0.8 V at 150 mA, but >2.0 V at 500 mA due to gain collapse). This advantage stems from Darlington architecture sustaining high hFE at elevated current, enabling efficient high-current switching not achievable with conventional BJTs - a key differentiator for the BSP50 in industrial load control.