onsemi KSP77BU

Overview

KSP77BU from Fairchild Semiconductor is a PNP epitaxial silicon Darlington transistor optimized for high-current switching and amplification in low-frequency analog and power control circuits, featuring V_CEO = −60 V, I_C = −500 mA, P_C = 625 mW, h_FE ≥ 10,000 at I_C = −10 mA, and V_CE(sat) = −1.5 V at I_C = −100 mA. It is commonly used in relay drivers, lamp dimmers, and industrial logic-level interface stages.

For engineers reviewing the KSP77BU datasheet, pinout, applications, or equivalent options, key selection considerations include its −60 V collector-emitter breakdown rating, Darlington current gain architecture, TO-92 package thermal limits, and base-emitter on voltage of 2 V under load - all critical for reliable high-gain switching in 24 V DC control systems.

Technical Context

The KSP77BU implements a two-stage monolithic PNP Darlington configuration with integrated emitter resistor to stabilize bias and suppress leakage. Its high h_FE (≥10 k) enables microampere-level base drive for milliampere collector loads, while V_CE(sat) remains ≤−1.5 V up to −100 mA, supporting efficient low-voltage switching.

Designed for operation at T_J ≤ 150°C and storage between −55°C and +150°C, it meets industrial ambient requirements. The device exhibits I_CBO ≤ −100 nA at V_CE = −50 V and I_EBO ≤ −100 nA at V_CE = −10 V, confirming tight leakage control essential for standby-sensitive applications.

Key Specifications

Pinout & Package

Package: TO-92 (3-lead plastic through-hole), lead spacing 1.27 mm, body height 4.58 mm max, standard JEDEC TO-92 outline with EBC pin order.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA56 and BCP56-16, the KSP77BU delivers Darlington-level current gain in a proven TO-92 package, enabling ultra-low base drive and simplified interface design - a functional distinction that cannot be replicated by standard PNP transistors without added active components.

Availability

KSP77BU is available at Aetrix Electronics and suitable for relay drivers, lamp dimmers, industrial logic interfaces, and DC motor control circuits requiring stable component supply across long-lifecycle embedded programs.

Supply support for KSP77BU 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 power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The KSP75/76/77 series belongs to Fairchild's general-purpose bipolar transistor family, designed specifically for cost-sensitive, high-reliability linear and switching applications in industrial controls and appliance electronics.

FAQ

What is the maximum collector-emitter voltage rating for the KSP77BU?

The KSP77BU has a guaranteed minimum collector-emitter breakdown voltage (V_CEO) of −60 V at I_C = −100 µA and T_A = 25°C. This rating allows safe operation in 48 V DC systems and provides margin against inductive kickback in relay and motor control applications. Derating applies above 25°C ambient per the device's thermal characteristics.

Is the KSP77BU a Darlington transistor, and how does that affect its drive requirements?

Yes, the KSP77BU is a monolithic PNP Darlington transistor with h_FE ≥ 10,000 at I_C = −10 mA. This architecture reduces required base current by two orders of magnitude versus a standard PNP - for example, only ~10 µA base drive is needed to sustain 100 mA collector current. This makes the KSP77BU ideal for direct interfacing with low-current logic outputs without additional buffering stages.

What package type does the KSP77BU use, and are there lead-free variants?

The KSP77BU uses the standard TO-92 plastic through-hole package with E-B-C pinout (Emitter = Pin 1, Base = Pin 2, Collector = Pin 3). Per the original Fairchild documentation, this part was manufactured in leaded (SnPb) finish; no official lead-free variant (e.g., KSP77BU-LEADFREE) was released prior to Fairchild's acquisition. RoHS-compliant alternatives require verification with ON Semiconductor's current portfolio.

Can the KSP77BU replace the KSP76BU or KSP75BU in an existing design?

Yes, the KSP77BU is a direct upgrade within the KSP75/76/77 family: it shares identical pinout, package, and electrical test conditions, but offers higher V_CEO (−60 V vs. −50 V for KSP76BU and −40 V for KSP75BU). No circuit changes are needed unless the design already operates near the lower-rated breakdown limits of those predecessors.

What is the typical V_CE(sat) of the KSP77BU under rated load conditions?

The KSP77BU exhibits a maximum V_CE(sat) of −1.5 V when I_C = −100 mA and I_B = −0.1 mA, per the official Fairchild datasheet. At lighter loads (e.g., I_C = −10 mA), V_CE(sat) drops further - typically below −0.8 V - making it suitable for both switching and linear amplification roles where low conduction loss is critical.