onsemi KSD794AYS

Overview

KSD794AYS from ON Semiconductor is an NPN epitaxial silicon power transistor in TO-126 package, rated for 45 V V_CEO, 3 A DC collector current, and 10 W collector dissipation at T_C = 25°C. It delivers h_FE of 30–70 at I_C = 20 mA and 60–100 at I_C = 0.5 A, with V_CE(sat) ≤ 2 V at I_C = 1.5 A / I_B = 0.15 A, and is specified for audio frequency power amplifier applications.

For engineers reviewing the KSD794AYS datasheet, pinout, applications, or equivalent options, key selection considerations include its complementary pairing with KSB744/KSB744A, safe operating area (SOA) limits up to 100 µs pulse width, junction temperature rating of 150°C, and TO-126 thermal mechanical interface for heatsink mounting.

Technical Context

This device operates as a linear-mode NPN bipolar junction transistor optimized for Class AB audio output stages and low-frequency switching. Its design emphasizes high DC current gain consistency across collector current range (h_FE ≥ 60 at I_C = 0.5 A), low saturation voltage (V_CE(sat) ≤ 0.3 V typical), and stable f_T of 60 MHz at V_CE = 5 V / I_E = 0.1 A - enabling reliable amplification up to mid-audio frequencies.

The KSD794AYS shares the same die and package construction as the KSD794A but is binned to the lower h_FE2 classification (60–120), distinguishing it from higher-gain variants. Its SOA curve is defined by both thermal dissipation limits (10 W at T_C = 25°C) and secondary breakdown constraints, with derating required above 25°C case temperature.

Key Specifications

Pinout & Package

Package: TO-126 - Three-lead plastic power package with metal tab (collector-connected) for direct heatsink mounting and mechanical robustness in industrial/audio power modules.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD127G and 2N5551, the KSD794AYS provides balanced trade-offs for medium-power audio and switching: TO-126 thermal interface enables efficient heatsinking, h_FE binning ensures predictable biasing, and SOA supports both linear and pulsed operation - unlike the high-voltage/low-gain MJD127G or low-power 2N5551.

Availability

KSD794AYS is available at Aetrix Electronics and suitable for audio power amplifiers, DC motor drivers, linear power supply pass elements, and relay driver circuits requiring stable component supply, consistent parametric binning, and long-term industrial availability.

Supply support for KSD794AYS 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 (formerly Fairchild Semiconductor) is a global semiconductor supplier specializing in power management, analog, sensor, and discrete devices for automotive, industrial, and cloud power applications.

The KSD794AYS belongs to ON Semiconductor's legacy audio and general-purpose power transistor family, engineered for reliability in linear amplification and medium-current switching where thermal robustness and gain consistency are critical.

FAQ

What is the maximum continuous collector current for KSD794AYS?

The KSD794AYS is rated for 3 A DC collector current (I_C) at T_A = 25°C with adequate PCB copper area or heatsink. At elevated ambient temperatures or without thermal management, derating applies per the power dissipation curve - for example, at T_C = 75°C, maximum I_C drops to approximately 2.2 A to maintain P_C ≤ 10 W. Always verify thermal design using the KSD794AYS SOA graph and junction-to-case thermal resistance.

Is KSD794AYS pin-compatible with KSD794A?

Yes, the KSD794AYS and KSD794A share identical TO-126 package pinout (Emitter-Collector-Base), mechanical dimensions, and absolute maximum ratings. The primary difference lies in h_FE binning: KSD794AYS is classified in the R group (h_FE2 = 60–120), whereas KSD794A covers broader gain ranges including O (100–200) and Y (160–320). Electrical substitution is permissible if gain tolerance meets circuit requirements.

Does KSD794AYS have a built-in base-emitter resistor?

No, the KSD794AYS is a standard three-terminal bipolar junction transistor with no internal base-emitter resistor. External base biasing must be provided via discrete resistors or active current sources, sized according to target I_C, h_FE, and V_BE(sat) (≤2 V at I_C = 1.5 A). This allows full design flexibility in amplifier bias networks and switching drive circuits.

What is the safe operating area (SOA) limitation for KSD794AYS at 100 µs pulse width?

At 100 µs pulse width and 2% duty cycle, the KSD794AYS supports up to 5 A collector current at V_CE ≤ 45 V, bounded by secondary breakdown limits rather than thermal dissipation. This enables robust transient response in audio clipping protection and motor stall recovery. Refer to Figure 6 in the official KSD794/794A datasheet for the precise SOA boundary curve at this pulse condition.

Can KSD794AYS be used in place of KSD794 in existing designs?

Yes, the KSD794AYS replaces KSD794 directly in most applications, as both share identical V_CEO = 45 V, I_C = 3 A, and TO-126 packaging. The KSD794AYS offers improved h_FE consistency (R-class binning) versus the original KSD794's wider spread, enhancing bias stability in production units. No layout or schematic changes are needed for drop-in use.