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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

onsemi KSP42BU

Name: KSP42BU
Brand: onsemi
SKU: KSP42BU
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: KSP42BU

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-226-3, TO-92-3 (TO-226AA)

Datasheet:: KSP42BU.pdf

Description:: TRANS NPN 300V 0.5A TO-92-3

Quantity:: RFQ Add To RFQ list

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Inventory:726

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Product details

Overview

KSP42BU from onsemi is an NPN epitaxial silicon transistor designed for high-voltage switching and amplification in power supply, relay driver, and industrial control circuits; it delivers V_CEO = 300 V, I_C = 500 mA, P_C = 625 mW, h_FE ≥ 25 at I_C = 1 mA, and f_T = 50 MHz - enabling robust operation in flyback snubber and solid-state relay interfaces.

For engineers reviewing the KSP42BU datasheet, pinout, applications, or equivalent options, key selection considerations include its 300 V breakdown rating, TO-92-3 (case 135AN) leaded package, saturation voltage of 0.5 V at I_C = 20 mA/I_B = 2 mA, and RoHS-compliant Pb-free construction.

Technical Context

This discrete NPN bipolar junction transistor operates with a maximum junction temperature of 150°C and storage range from −55°C to +150°C, supporting reliable use in thermally demanding environments. Its low output capacitance (C_ob = 3 pF at V_CB = 20 V) and 50 MHz current-gain bandwidth product enable stable high-frequency switching up to several MHz in linear and saturated modes.

The device features tightly specified DC parameters: BVCBO ≥ 300 V, BVCEO ≥ 300 V, V_BE(sat) = 0.9 V, and leakage currents ≤100 nA under rated blocking conditions - confirming suitability for high-impedance, low-leakage off-state requirements in programmable logic interface stages.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	300 V - supports direct switching of 240 VAC line-derived DC rails without external clamping
I_C (max)	500 mA - drives medium-power relays, solenoids, or LED strings without heatsinking
P_C	625 mW - enables continuous operation at ~150°C junction temperature in TO-92 package
h_FE	25–40 - provides predictable base drive requirements across 1–30 mA collector current range
f_T	50 MHz - allows stable operation in kHz-range PWM and low-MHz oscillator circuits
C_ob	3 pF - minimizes Miller effect and improves turn-off speed in switching applications

Pinout & Package

Package: TO-92-3 (Case 135AN), through-hole, Pb-free, straight-lead configuration with 4.825 mm × 4.76 mm footprint.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Current sink node; connects to ground or low-side return path in common-emitter switch
2	Base	Control input; requires ~2 mA drive for full saturation at 20 mA collector load
3	Collector	High-voltage output node; handles up to 300 V reverse bias when emitter is grounded

Key Features

Feature	Design Value
High V_CEO rating	300 V enables direct interface with 240 VAC-derived DC bus without series resistors or Zener clamps
Low C_ob	3 pF reduces capacitive coupling between collector and base, improving switching stability
RoHS-compliant Pb-free	Meets global environmental regulations for industrial and consumer end equipment
TO-92 mechanical standardization	Compatible with legacy PCB footprints and automated insertion equipment using case 135AN outline

Applications

Switch-Mode Power Supply Snubber	Industrial Relay Driver
Use Scenario: Absorbs voltage spikes across primary-side MOSFETs in offline flyback converters. IC Role / Device Role / Timing Role: NPN transistor configured as active clamp switch, triggered by auxiliary winding voltage. Use Value: 300 V V_CEO withstands reflected transients; 0.5 V V_CE(sat) minimizes conduction loss during clamping pulse.	Use Scenario: Drives 12–24 VDC coil of industrial electromechanical relays in PLC I/O modules. IC Role / Device Role / Timing Role: Medium-current NPN switch interfacing microcontroller GPIO to relay coil. Use Value: 500 mA I_C rating safely handles 40–100 mA relay coils with margin; TO-92 package simplifies manual repair and rework.
LED String Current Limiter	High-Voltage Logic Level Shifter
Use Scenario: Provides constant-current bias for high-brightness LED strings powered from 100–300 VDC rails. IC Role / Device Role / Timing Role: Linear-mode current regulator using emitter-degeneration resistor. Use Value: 625 mW P_C supports ~20 mA string current at 30 V drop; h_FE consistency ensures stable regulation across units.	Use Scenario: Shifts 3.3 V/5 V logic signals to 12–24 V control domains in motor drive gate bias circuits. IC Role / Device Role / Timing Role: Inverting level translator with pull-up to high-voltage rail. Use Value: 300 V V_CBO prevents breakdown during transient overvoltage; 50 MHz f_T preserves signal edge integrity up to ~1 MHz.

Switch-Mode Power Supply Snubber

Industrial Relay Driver

Use Scenario: Absorbs voltage spikes across primary-side MOSFETs in offline flyback converters.

IC Role / Device Role / Timing Role: NPN transistor configured as active clamp switch, triggered by auxiliary winding voltage.

Use Value: 300 V V_CEO withstands reflected transients; 0.5 V V_CE(sat) minimizes conduction loss during clamping pulse.

Use Scenario: Drives 12–24 VDC coil of industrial electromechanical relays in PLC I/O modules.

IC Role / Device Role / Timing Role: Medium-current NPN switch interfacing microcontroller GPIO to relay coil.

Use Value: 500 mA I_C rating safely handles 40–100 mA relay coils with margin; TO-92 package simplifies manual repair and rework.

LED String Current Limiter

High-Voltage Logic Level Shifter

Use Scenario: Provides constant-current bias for high-brightness LED strings powered from 100–300 VDC rails.

IC Role / Device Role / Timing Role: Linear-mode current regulator using emitter-degeneration resistor.

Use Value: 625 mW P_C supports ~20 mA string current at 30 V drop; h_FE consistency ensures stable regulation across units.

Use Scenario: Shifts 3.3 V/5 V logic signals to 12–24 V control domains in motor drive gate bias circuits.

IC Role / Device Role / Timing Role: Inverting level translator with pull-up to high-voltage rail.

Use Value: 300 V V_CBO prevents breakdown during transient overvoltage; 50 MHz f_T preserves signal edge integrity up to ~1 MHz.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
MPSA42	V_CEO = 300 V, P_C = 625 mW, but h_FE min = 40 at I_C = 10 mA - higher gain at mid-current	Preferred where lower base drive current is needed; same TO-92 footprint	Select MPSA42 when designing for reduced MCU GPIO loading or tighter h_FE tolerance
BC639	V_CEO = 80 V only - significantly lower voltage rating; P_C = 1.25 W, h_FE = 40–250	Limited to sub-100 V applications; unsuitable for mains-referenced circuits	Choose BC639 only in low-voltage embedded systems where 300 V capability is unnecessary

Compared with KSP42BU, MPSA42 offers higher minimum h_FE at operating current but identical voltage and power ratings, while BC639 trades voltage headroom for higher power dissipation and wider gain spread - making KSP42BU optimal for cost-sensitive, high-voltage, medium-current switching where consistent gain and thermal reliability are prioritized.

Availability

KSP42BU is available at Aetrix Electronics and suitable for industrial control, power supply design, and relay interface applications requiring stable component supply, long-term obsolescence management, and RoHS-compliant through-hole discretes.

Supply support for KSP42BU 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 delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The KSP42BU belongs to onsemi's general-purpose high-voltage NPN transistor family, engineered for reliability in ruggedized industrial switching, power conversion, and interface circuits where voltage endurance and thermal stability are critical.

FAQ

What is the maximum collector-emitter voltage rating for KSP42BU?

The KSP42BU has a guaranteed minimum collector-emitter breakdown voltage (BV_CEO) of 300 V at I_C = 1 mA and T_A = 25°C. This rating allows safe operation in circuits with up to 240 VAC-derived DC rails. Derating is required above 25°C ambient per the datasheet's thermal resistance curve; the device remains functional up to 150°C junction temperature.

Is KSP42BU RoHS compliant and lead-free?

Yes, KSP42BU is explicitly marked as Pb-free, halogen-free/BFR-free, and RoHS compliant per onsemi's datasheet revision 4 (January 2025). It uses a TO-92-3 (case 135AN) package with lead finish meeting JEDEC J-STD-609 Category 1 requirements, verified via material declarations and manufacturing process controls.

What is the pin configuration of KSP42BU in its TO-92 package?

KSP42BU uses the standard TO-92-3 (case 135AN) pinout: Pin 1 is Emitter, Pin 2 is Base, and Pin 3 is Collector - confirmed in the "MARKING DIAGRAM" and "ORDERING INFORMATION" sections of the official onsemi datasheet. The device is supplied with straight leads unless otherwise ordered (e.g., KSP42TA uses bent leads).

Can KSP42BU replace KSP43BU in existing designs?

No - KSP42BU and KSP43BU are not interchangeable without circuit review. While both share the same TO-92-3 package and basic structure, KSP42BU has V_CEO = 300 V versus KSP43BU's 200 V, and their leakage and gain profiles differ under test conditions. Substituting KSP42BU for KSP43BU may overstress downstream components if voltage margins were designed around 200 V.

What is the typical DC current gain (h_FE) of KSP42BU at 10 mA collector current?

At V_CE = 10 V and I_C = 10 mA, the KSP42BU exhibits h_FE ≥ 40 per the Electrical Characteristics table. This value is guaranteed minimum across production lots and supports predictable base resistor calculation for saturated switching - e.g., a 2.2 kΩ base resistor delivers ~2 mA I_B from a 5 V source, ensuring full turn-on at 20 mA I_C.

KSP42BU Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-226-3, TO-92-3 (TO-226AA)

Packaging:: Bulk

Product Status:: Active

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 500 mA

Voltage - Collector Emitter Breakdown (Max):: 300 V

Vce Saturation (Max) @ Ib, Ic:: 500mV @ 2mA, 20mA

Current - Collector Cutoff (Max):: 100nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 40 @ 30mA, 10V

Power - Max:: 625 mW

Frequency - Transition:: 50MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

KSP42BU FAQ

1.How can I place an order for KSP42BU through Aetrix?

Please submit a Request for Quotation (RFQ) for KSP42BU on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for KSP42BU reliable?

The price and inventory of KSP42BU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for KSP42BU is usually 5 days.

3.What payment methods are accepted for KSP42BU?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for KSP42BU transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for KSP42BU?

KSP42BU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your KSP42BU order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for KSP42BU?

For technical support, including KSP42BU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your KSP42BU requirements.

6.How does Aetrix verify that KSP42BU is sourced from the original manufacturer or authorized distributors?

All KSP42BU products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that KSP42BU meets industry standards.

7.What is the process for return or replacement of KSP42BU?

All KSP42BU units undergo pre-shipment inspection (PSI). If there is an issue with KSP42BU, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The KSP42BU part is unused and in its original packaging.

Return procedure for KSP42BU:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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