onsemi KSA940TSTU

Overview

KSA940TSTU from onsemi is a PNP epitaxial silicon transistor designed as a vertical deflection output power amplifier in CRT display systems, with −150 V V_CEO, −1.5 A I_C, 25 W P_C (T_C=25°C), h_FE = 40–140 at −500 mA, and TO-220-3LD package. It serves as the complementary device to KSC2073 in high-voltage horizontal/vertical scan driver stages.

For engineers reviewing the KSA940TSTU datasheet, pinout, applications, or equivalent options, key selection criteria include safe operating area (SOA) compliance at −150 V/−1.5 A, thermal derating above 25°C case temperature, saturation voltage ≤ −1.5 V at −500 mA/−50 mA drive, and Pb-free TO-220-3LD mechanical compatibility with heatsink mounting.

Technical Context

This PNP power transistor operates in Class-A or Class-AB linear amplification mode for vertical deflection yoke drive, requiring robust SOA handling of pulsed collector currents up to −1.5 A under −150 V V_CE. Its f_T = 4 MHz supports stable operation within CRT scan frequency bands without oscillation.

Designed for fixed-bias or emitter-follower configurations, it features low V_BE(on) (−0.65 to −0.85 V) and Cob = 55 pF to minimize switching losses and capacitive loading in high-impedance deflection circuits. Junction temperature must remain ≤150°C during continuous DC or pulse operation.

Key Specifications

Pinout & Package

Package: TO-220-3LD (Case 340AT), lead-free, with integral metal tab electrically connected to Collector for direct heatsink mounting.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP high-voltage power amplifier applications.

Compared with MJD127G and 2SA1943, KSA940TSTU provides optimal balance of −150 V rating, 25 W dissipation in TO-220, and 4 MHz bandwidth-making it uniquely suited for legacy CRT vertical output without over-engineering or under-specifying.

Availability

KSA940TSTU is available at Aetrix Electronics and suitable for CRT monitor repair, legacy display system maintenance, and industrial analog video equipment requiring stable component supply with long-lifecycle support.

Supply support for KSA940TSTU 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, and consumer markets.

The KSA940TSTU belongs to onsemi's legacy bipolar power transistor product line, engineered specifically for high-voltage analog video deflection and power switching in CRT-based systems.

FAQ

What is the maximum safe collector-emitter voltage for KSA940TSTU?

The KSA940TSTU has a guaranteed V_CEO rating of −150 V at T_C = 25°C. Operation beyond this voltage risks secondary breakdown, especially under pulsed conditions. Derating is required above 25°C case temperature per the power derating curve in Figure 5 of the official datasheet. The KSA940TSTU must not be used in circuits where transient spikes exceed −150 V without clamping protection.

Is KSA940TSTU pin-compatible with KSC2073?

No, KSA940TSTU is not pin-compatible with KSC2073. While they are complementary devices (PNP vs. NPN), their pinouts differ: KSA940TSTU uses Base–Collector–Emitter (1–2–3), whereas KSC2073 uses Emitter–Collector–Base in TO-220-3LD. Direct substitution without PCB modification will cause circuit failure. The KSA940TSTU must be mounted in its designated orientation with Collector tied to the heatsink tab.

What is the typical DC current gain (hFE) of KSA940TSTU at operating conditions?

The KSA940TSTU exhibits h_FE = 40–140 when measured at V_CE = −10 V and I_C = −500 mA. This wide range reflects process variation across lots and requires base drive design to accommodate the minimum value (40) for reliable saturation. The KSA940TSTU's h_FE remains stable up to I_C = −1.0 A but degrades above that point per Figure 2.

Can KSA940TSTU be used in switching power supplies?

Yes, KSA940TSTU can be used in low-frequency (<100 kHz) switching power supplies such as CRT auxiliary supplies, provided SOA limits are respected during turn-on/turn-off transitions. Its −1.5 V V_CE(sat) and 55 pF C_ob support efficient operation, but the KSA940TSTU lacks optimized switching speed for high-frequency SMPS and should not replace purpose-built MOSFETs or RF transistors.

Does KSA940TSTU require a heatsink in continuous operation?

Yes, the KSA940TSTU requires a heatsink for any continuous DC operation above ~1.5 W dissipation. At its full 25 W rating, the device must be mounted on a thermally rated heatsink with thermal resistance ≤1.2°C/W to maintain T_J ≤150°C. Without heatsinking, the KSA940TSTU exceeds safe junction temperature within seconds under load, risking permanent damage.