onsemi KSC5042FYDTU

Overview

KSC5042FYDTU from ON Semiconductor (formerly Fairchild) is a high-voltage NPN triple-diffused planar silicon transistor designed for dynamic focus and horizontal deflection 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 switching in TV and monitor flyback circuits.

For engineers reviewing the KSC5042FYDTU datasheet, pinout, applications, or equivalent options, key selection criteria include safe operating area (SOA) compliance, low output capacitance for fast switching, saturation voltage under defined drive conditions, thermal derating behavior, and TO-220F package mounting compatibility with heatsink interfaces.

Technical Context

This transistor operates as a high-voltage switch in horizontal deflection output stages, where precise timing and energy recovery demand stable breakdown characteristics and minimal capacitive loading. Its triple-diffused planar structure ensures controlled carrier distribution and improved ruggedness against secondary breakdown.

The device exhibits a DC current gain (h_FE) of ≥30 at V_CE = 5 V and I_C = 10 mA, V_CE(sat) ≤ 5 V at I_C = 20 mA / I_B = 4 mA, and V_BE(sat) ≤ 2 V under the same conditions - supporting reliable turn-on in pulse-driven line output applications.

Key Specifications

Pinout & Package

Supplied in TO-220F package: insulated plastic case with metal tab, vertical mounting orientation, and integral heatsink interface. Pin 1 = Base, Pin 2 = Collector (tab-connected), Pin 3 = Emitter.

Key Features

Applications

Equivalent & Alternatives

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

Compared with KSC5042FYDTU, 2SC5042 offers identical performance and drop-in compatibility, while KSC5027YTA trades 200 V breakdown headroom for higher DC gain - making it viable only where system-level voltage stress remains below 700 V.

Availability

KSC5042FYDTU is available at Aetrix Electronics and suitable for CRT television manufacturing, monitor repair programs, and legacy display system maintenance requiring stable component supply and long-term traceability.

Supply support for KSC5042FYDTU 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 consumer electronics.

The KSC5042FYDTU belongs to Fairchild's legacy high-voltage bipolar transistor family, engineered specifically for reliability-critical horizontal deflection and flyback switching in analog CRT video systems.

FAQ

What is the maximum collector-emitter voltage rating for KSC5042FYDTU?

The KSC5042FYDTU 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 per JEDEC test conditions and defines the absolute upper limit for safe DC or pulse operation in deflection circuits. Exceeding this voltage risks irreversible avalanche failure. The KSC5042FYDTU must be operated within its SOA envelope even below this rating when combined with high current.

Is KSC5042FYDTU pin-compatible with other TO-220F transistors?

Yes - KSC5042FYDTU uses standard TO-220F mechanical dimensions and pinout: Pin 1 = Base, Pin 2 = Collector (tab), Pin 3 = Emitter. It shares footprint and mounting hole alignment with industry-standard TO-220F devices like 2SC5042 and KSC5027YTA. However, electrical compatibility depends on voltage, gain, and SOA matching - physical fit does not guarantee functional substitution.

What is the typical output capacitance (C_ob) of KSC5042FYDTU and why does it matter?

The KSC5042FYDTU exhibits a typical output capacitance (C_ob) of 2.8 pF at V_CB = 100 V and f = 1 MHz. This low value directly reduces switching transition time and associated power loss in horizontal deflection circuits operating near 15.7 kHz. Lower C_ob also improves waveform sharpness and minimizes ringing in flyback transformer primary waveforms - critical for stable EHT generation in CRT systems using KSC5042FYDTU.

Can KSC5042FYDTU be used in surface-mount designs?

No - KSC5042FYDTU is exclusively packaged in through-hole TO-220F format and is not available in surface-mount variants. Its thermal design relies on mechanical mounting to an external heatsink via the collector-tab interface, which is incompatible with standard SMT reflow profiles and board-level thermal management. Any attempt to adapt KSC5042FYDTU for SMT would compromise reliability, electrical isolation, and thermal performance.

Does KSC5042FYDTU require a heatsink in normal operation?

Yes - KSC5042FYDTU dissipates up to 6 W at T_C = 25°C, and its thermal resistance (R_θJC) necessitates heatsinking to maintain junction temperature ≤150°C. Without a properly sized heatsink, even moderate duty-cycle operation causes rapid thermal accumulation. The TO-220F package's insulated tab allows direct mounting to grounded metal chassis, but thermal interface material and sufficient surface area remain essential for sustained KSC5042FYDTU performance.