onsemi KSC5042FTU

Overview

KSC5042FTU from ON Semiconductor (formerly Fairchild) is a high-voltage NPN triple-diffused planar silicon transistor designed for dynamic focus and horizontal deflection switching in CRT display systems. It delivers BV_CEO = 900 V, V_CBO = 1500 V, I_C = 100 mA DC, P_C = 6 W at T_C = 25°C, and C_ob = 2.8 pF (typ), enabling robust high-voltage pulse handling in TV and monitor flyback circuits.

For engineers reviewing the KSC5042FTU datasheet, pinout, applications, or equivalent options, key selection criteria include verified 900 V collector-emitter breakdown, low output capacitance for fast switching, TO-220F package thermal performance, safe operating area (SOA) compliance for pulsed loads, and documented base-emitter saturation voltage of 2 V at I_C = 20 mA / I_B = 4 mA.

Technical Context

This transistor employs triple-diffused planar construction to achieve high primary breakdown voltages and stable gain under high-voltage transient stress. Its design emphasizes wide SOA, low C_ob, and controlled saturation characteristics-critical for horizontal output stages where voltage overshoot and capacitive loading directly impact focus stability and deflection linearity.

The device operates with fixed DC current gain (h_FE ≥ 30 at V_CE = 5 V, I_C = 10 mA) and exhibits defined saturation behavior: V_CE(sat) ≤ 5 V and V_BE(sat) ≤ 2 V under I_C = 20 mA / I_B = 4 mA drive, ensuring predictable switching thresholds and minimal conduction loss in hard-switched applications.

Key Specifications

Pinout & Package

Supplied in TO-220F package: insulated flange, vertical mounting, 3-lead through-hole configuration with integral heat sink tab. Flange electrically isolated from collector terminal per standard TO-220F construction.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN switching applications.

Compared with KSC5042FTU, BU2520DX offers higher voltage and thermal headroom at the cost of increased output capacitance, while 2SC5387 trades 100 V breakdown margin for marginally lower C_ob-making KSC5042FTU the balanced choice for mid-size CRT horizontal output stages requiring proven reliability and SOA robustness.

Availability

KSC5042FTU is available at Aetrix Electronics and suitable for CRT television repair, legacy monitor refurbishment, and industrial HMI maintenance requiring stable component supply, long-lifecycle availability, and traceable sourcing of discontinued semiconductor parts.

Supply support for KSC5042FTU 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 high-performance silicon solutions for automotive, industrial, cloud computing, and IoT applications.

The KSC5042FTU belongs to Fairchild's legacy high-voltage bipolar transistor family, engineered specifically for analog video display systems requiring precise timing, high-voltage integrity, and long-term parametric stability in thermally demanding environments.

FAQ

What is the maximum collector-emitter voltage rating for KSC5042FTU?

The KSC5042FTU has a guaranteed minimum collector-emitter breakdown voltage (BV_CEO) of 900 V at I_C = 5 mA and I_B = 0. This rating is validated under standard test conditions and defines the absolute upper limit for DC or repetitive pulse voltage applied between collector and emitter in the KSC5042FTU's off state. Exceeding this value risks irreversible avalanche failure.

Does KSC5042FTU have an insulated package?

Yes, the KSC5042FTU is packaged in TO-220F, which features an electrically insulated flange. The metal tab is isolated from the collector terminal, allowing direct mounting to a common heatsink without additional insulating hardware-critical for safety and noise immunity in high-voltage CRT applications where the collector connects to flyback transformer primaries.

What is the typical output capacitance (C_ob) of KSC5042FTU and why does it matter?

The KSC5042FTU exhibits a typical output capacitance (C_ob) of 2.8 pF at V_CB = 100 V and f = 1 MHz. This low value directly impacts switching speed and focus waveform fidelity in CRT horizontal deflection circuits: lower C_ob reduces Miller effect, shortens turn-off delay, and preserves signal integrity during rapid retrace transitions-key for maintaining sharp raster edges in KSC5042FTU-based designs.

Can KSC5042FTU replace KSC5027 in existing CRT designs?

KSC5042FTU can serve as a functional upgrade for KSC5027 in many CRT horizontal output applications, offering higher BV_CEO (900 V vs. 700 V) and improved SOA. However, designers must verify that the 2.8 pF C_ob and 5 V V_CE(sat) align with existing base drive and snubber network parameters-KSC5042FTU is not a drop-in mechanical or electrical replacement without validation of timing and thermal margins in the target KSC5042FTU implementation.

What is the junction temperature limit for KSC5042FTU and how does it affect thermal design?

The KSC5042FTU has a maximum rated junction temperature (T_J) of 150°C. This limit governs thermal design: with 6 W collector dissipation at T_C = 25°C, effective heatsinking must maintain case temperature below ~85°C under full-load operation to preserve margin against thermal runaway. Derating curves in the original Fairchild datasheet show linear power reduction above 25°C case temperature-essential for reliable long-term operation of KSC5042FTU in sealed TV chassis.