onsemi KSC839YBU

Overview

KSC839YBU from ON Semiconductor (formerly Fairchild) is an NPN epitaxial silicon transistor designed for RF amplification, oscillation, and IF signal processing in AM/FM radio systems. It delivers a current gain bandwidth product (f_T) of up to 200 MHz, supports V_CEO = 30 V and I_C = 100 mA, and operates with V_CE(sat) ≤ 0.4 V at I_C = 10 mA / I_B = 1 mA.

For engineers reviewing the KSC839YBU datasheet, pinout, applications, or equivalent options, key selection criteria include its h_FE classification (Y = 120–240), TO-92 package compatibility, low output capacitance (C_ob ≤ 3.5 pF), and proven use in RF amplifier stages requiring stable high-frequency gain.

Technical Context

The KSC839YBU is a general-purpose RF bipolar junction transistor optimized for small-signal amplification and oscillator circuits in portable radio receivers. Its f_T range (80–200 MHz) and low C_ob (2.0–3.5 pF) support stable operation in tuned RF/IF stages up to ~100 MHz.

It features a DC current gain (h_FE) of 120–240 at V_CE = 12 V and I_C = 2 mA, V_BE(on) = 0.65–0.75 V under switching conditions, and V_CE(sat) ≤ 0.4 V - enabling efficient biasing and low-loss signal coupling in discrete amplifier topologies.

Key Specifications

Pinout & Package

Package: TO-92 - standard through-hole plastic package with 3.60 mm body width, 4.58 mm height, and 1.27 mm lead pitch; suitable for manual assembly and wave soldering in consumer radio PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 2SC2878-Y and MPSH10, the KSC839YBU offers balanced RF performance (200 MHz f_T, 30 V V_CEO, Y-class h_FE) ideal for cost-sensitive AM/FM radio designs where supply headroom and production gain consistency are prioritized over extreme bandwidth.

Availability

KSC839YBU is available at Aetrix Electronics and suitable for AM/FM radio receivers, portable communication transceivers, and analog signal conditioning circuits requiring stable component supply and long-term obsolescence management.

Supply support for KSC839YBU 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 (acquired Fairchild Semiconductor in 2016) is a global supplier of energy-efficient semiconductor solutions, specializing in analog, power management, and discrete components for automotive, industrial, and consumer markets.

The KSC839YBU belongs to Fairchild's legacy general-purpose RF transistor family, engineered specifically for high-volume, cost-sensitive analog radio applications requiring predictable gain, low noise, and robust thermal behavior in TO-92 packaging.

FAQ

What is the h_FE range for KSC839YBU?

The KSC839YBU is binned to the Y-class h_FE specification, guaranteeing a DC current gain of 120–240 when measured at V_CE = 12 V and I_C = 2 mA. This tight range ensures consistent biasing and gain stability across production units, making the KSC839YBU especially suitable for multi-stage RF amplifiers in AM/FM radios where unit-to-unit variation must be minimized.

Is KSC839YBU suitable for FM oscillator applications?

Yes, the KSC839YBU is explicitly recommended for oscillator use in FM radio systems, as confirmed by its 200 MHz f_T, low C_ob (≤3.5 pF), and stable h_FE across temperature. Its performance supports Colpitts and Hartley oscillator topologies generating 10.7 MHz IF carriers, and it has been validated in production AM/FM radio designs where phase noise and start-up reliability are critical - all attributes inherent to the KSC839YBU.

What is the maximum collector current rating for KSC839YBU?

The KSC839YBU has a maximum continuous collector current (I_C) rating of 100 mA at T_A = 25°C. Derating is required above 25°C ambient, following the specified thermal resistance curve. This rating supports typical RF amplifier and oscillator bias currents in portable radios, and the KSC839YBU maintains safe operation within this limit when used with appropriate base drive and heatsinking per TO-92 thermal guidelines.

Does KSC839YBU have a specified junction temperature limit?

Yes, the KSC839YBU specifies a maximum junction temperature (T_J) of 150°C. This value defines the upper thermal boundary for reliable operation and must be respected during PCB layout and thermal design. The KSC839YBU's 250 mW power dissipation rating and TO-92 package thermal characteristics directly inform allowable ambient temperature and copper pour requirements - all essential parameters for sustained performance in the KSC839YBU.

Can KSC839YBU replace KSC839RBU or KSC839OBU in existing designs?

Yes - KSC839YBU can replace KSC839RBU (h_FE 40–80) and KSC839OBU (h_FE 70–140) in most AM/FM radio circuits, provided the higher h_FE does not cause instability or excessive gain. Since all three share identical absolute maximum ratings, pinout, and package, the KSC839YBU offers improved gain consistency without hardware changes - though bias network verification is recommended to ensure optimal operating point and linearity in the KSC839YBU.