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

onsemi KSP45BU

Name: KSP45BU
Brand: onsemi
SKU: KSP45BU
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: KSP45BU

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: KSP45BU.pdf

Description:: TRANS NPN 350V 0.3A TO-92-3

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Product details

Overview

KSP45BU from onsemi is an NPN epitaxial silicon transistor designed for high-voltage switching applications, featuring a 350 V collector-emitter breakdown voltage (V_CEO), 400 V collector-base voltage (V_CBO), and 300 mA continuous collector current (I_C). It operates up to 150°C junction temperature and is housed in a Pb-free TO-92-3 (case 135AN) package, commonly used in flyback converters and relay drivers.

For engineers reviewing the KSP45BU datasheet, pinout, applications, or equivalent options, key selection criteria include its high-voltage capability, DC current gain range (h_FE = 40–200 at I_C = 1–100 mA), saturation voltage performance (V_CE(sat) ≤ 0.75 V at I_C = 50 mA), and thermal resistance (R_θJA = 200°C/W).

Technical Context

The KSP45BU is a general-purpose NPN bipolar junction transistor optimized for medium-power, high-voltage switching rather than linear amplification. Its design emphasizes robust breakdown ratings-350 V V_CEO and 400 V V_CBO-with guaranteed h_FE ≥ 40 at I_C = 100 mA and V_CE = 10 V, supporting reliable turn-on/turn-off in inductive load circuits.

It exhibits low output capacitance (C_ob = 7 pF at V_CB = 20 V, f = 1 MHz) and fast switching characteristics (typical t_f < 100 ns), enabling efficient operation in 20–100 kHz SMPS topologies. The device is RoHS-compliant, halogen-free, and qualified per onsemi's industrial reliability standards.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	350 V - supports primary-side switching in offline flyback converters up to 265 V AC input with safety margin.
I_C	300 mA - enables driving small relays, LED strings, or gate resistors for MOSFETs without external buffering.
h_FE	40–200 - provides stable base drive scaling across 1–100 mA collector loads, simplifying bias network design.
V_CE(sat)	≤ 0.75 V at I_C = 50 mA - limits conduction loss to < 37.5 mW, reducing thermal stress in compact PCB layouts.
R_θJA	200°C/W - requires minimal copper area (FR-4, 76 mm × 114 mm) to maintain T_J < 150°C at full power.
C_ob	7 pF - minimizes Miller effect, supporting clean switching edges in high-frequency (<100 kHz) applications.

Pinout & Package

Package: TO-92-3 (case 135AN), molded plastic, Pb-free, through-hole mounting. Dimensions: 4.825 mm × 4.76 mm × 4.0 mm (L × W × H), with bent leads standard for bulk packaging.

Pin/Terminal	Circuit Role	Design Meaning
1	Emitter	Reference node for base-emitter junction; connects to ground or low-side return path in common-emitter switches.
2	Base	Current-controlled input; requires series resistor (e.g., 10 kΩ) to limit I_B and ensure saturation at target I_C.
3	Collector	High-voltage output node; connects to inductive load or transformer primary with snubber network for voltage clamping.

Key Features

Feature	Design Value
High-voltage blocking	350 V V_CEO rating enables direct use in 230 V AC line-connected circuits without cascading transistors.
Pb-free & RoHS compliance	Meets global environmental regulations; eliminates lead-based solder compatibility concerns in modern assembly lines.
Low saturation voltage	V_CE(sat) ≤ 0.50 V at I_C/I_B = 10 ensures >90% efficiency in saturated-switch mode at moderate currents.
Stable DC gain	h_FE ≥ 45 at I_C = 50 mA guarantees predictable base drive requirements across production lots and temperature.

Applications

AC-DC Adapter Primary Switch	Automotive Relay Driver
Use Scenario: Controls transformer primary winding in 5–15 W isolated flyback converters for wall adapters and IoT power supplies. IC Role / Device Role / Timing Role: High-voltage NPN switch operating in discontinuous conduction mode (DCM) at 65 kHz, driven by UC3842-type controller. Use Value: 350 V V_CEO accommodates reflected voltage spikes from 19 V output designs without snubber overdesign.	Use Scenario: Drives 12 V automotive relays (e.g., Bosch 0 332 019 150) in body control modules for window lift or lighting circuits. IC Role / Device Role / Timing Role: Low-side switch interfacing microcontroller GPIO to relay coil; handles inductive kickback via external flyback diode. Use Value: 300 mA I_C rating exceeds typical 80–120 mA relay coil current, ensuring long-term contact reliability.
LED String Current Limiter	Industrial Sensor Interface
Use Scenario: Serves as constant-current sink for 3–5 white LEDs in signage or emergency lighting powered from 24 V DC bus. IC Role / Device Role / Timing Role: Linear current regulator using emitter degeneration resistor; biased in active region with fixed base voltage. Use Value: h_FE consistency (±20%) across 1–50 mA allows accurate current setting with 5% tolerance emitter resistors.	Use Scenario: Isolates and conditions analog signals from 4–20 mA current-loop sensors in PLC I/O modules. IC Role / Device Role / Timing Role: Transimpedance amplifier stage converting loop current to voltage; configured in common-emitter with feedback resistor. Use Value: 7 pF C_ob minimizes phase lag at 1 kHz signal bandwidth, preserving loop stability under EMI exposure.

AC-DC Adapter Primary Switch

Automotive Relay Driver

Use Scenario: Controls transformer primary winding in 5–15 W isolated flyback converters for wall adapters and IoT power supplies.

IC Role / Device Role / Timing Role: High-voltage NPN switch operating in discontinuous conduction mode (DCM) at 65 kHz, driven by UC3842-type controller.

Use Value: 350 V V_CEO accommodates reflected voltage spikes from 19 V output designs without snubber overdesign.

Use Scenario: Drives 12 V automotive relays (e.g., Bosch 0 332 019 150) in body control modules for window lift or lighting circuits.

IC Role / Device Role / Timing Role: Low-side switch interfacing microcontroller GPIO to relay coil; handles inductive kickback via external flyback diode.

Use Value: 300 mA I_C rating exceeds typical 80–120 mA relay coil current, ensuring long-term contact reliability.

LED String Current Limiter

Industrial Sensor Interface

Use Scenario: Serves as constant-current sink for 3–5 white LEDs in signage or emergency lighting powered from 24 V DC bus.

IC Role / Device Role / Timing Role: Linear current regulator using emitter degeneration resistor; biased in active region with fixed base voltage.

Use Value: h_FE consistency (±20%) across 1–50 mA allows accurate current setting with 5% tolerance emitter resistors.

Use Scenario: Isolates and conditions analog signals from 4–20 mA current-loop sensors in PLC I/O modules.

IC Role / Device Role / Timing Role: Transimpedance amplifier stage converting loop current to voltage; configured in common-emitter with feedback resistor.

Use Value: 7 pF C_ob minimizes phase lag at 1 kHz signal bandwidth, preserving loop stability under EMI exposure.

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
MPSA44	V_CEO = 400 V, I_C = 300 mA, h_FE = 25–200 - higher breakdown but wider gain spread.	Better suited for 265 V AC input designs requiring extra margin; less predictable at low I_C.	Select MPSA44 when V_CEO margin > 50 V is mandatory and gain variation can be accommodated in layout.
KSP44BU	V_CEO = 400 V, otherwise identical package, pinout, and thermal specs - direct functional upgrade.	Enables same PCB footprint with higher voltage headroom; no redesign needed for legacy KSP45BU layouts.	Choose KSP44BU where system-level surge testing exceeds 350 V or long-term reliability at elevated V_CE is critical.

Compared with KSP45BU, MPSA44 offers greater voltage margin but looser h_FE control, while KSP44BU delivers identical form-factor compatibility with +50 V V_CEO headroom-making it ideal for drop-in reliability upgrades without layout changes.

Availability

KSP45BU is available at Aetrix Electronics and suitable for AC-DC adapter primary switches, automotive relay drivers, and LED string current limiters requiring stable component supply across multi-year production cycles.

Supply support for KSP45BU 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 focused on energy-efficient electronics, delivering silicon solutions for automotive, industrial, cloud, and IoT applications.

The KSP45BU belongs to onsemi's general-purpose bipolar transistor family, engineered for cost-sensitive, high-reliability switching in power conversion and interface circuits where voltage robustness and thermal stability are essential.

FAQ

What is the maximum collector-emitter voltage rating for KSP45BU?

The KSP45BU has a guaranteed minimum collector-emitter breakdown voltage (V_CEO) of 350 V at I_C = 1 mA and T_A = 25°C. This rating is validated per onsemi's absolute maximum ratings table and supports safe operation in 230 V AC mains-connected circuits with appropriate derating for temperature and reliability margins. The KSP45BU must not be operated beyond this limit to avoid permanent damage.

Is KSP45BU pin-compatible with other TO-92 NPN transistors like MPSA44?

Yes, the KSP45BU uses the standard TO-92-3 (case 135AN) package with emitter-base-collector pinout (1-2-3), matching MPSA44, KSP44BU, and BC546. Mechanical compatibility is confirmed by onsemi's package drawings. However, electrical differences-especially V_CEO and h_FE distribution-require verification in the target circuit before substitution. The KSP45BU is not a drop-in replacement for all applications due to its lower voltage rating versus MPSA44.

What is the typical DC current gain (h_FE) of KSP45BU at 10 mA collector current?

At V_CE = 10 V and I_C = 10 mA, the KSP45BU exhibits a typical h_FE of 50–200, with a minimum guaranteed value of 50. This range is specified in the Electrical Characteristics table and reflects production lot variation. For stable biasing, designers should use h_FE = 50 for worst-case calculations. The KSP45BU maintains usable gain down to I_C = 1 mA and up to I_C = 100 mA, supporting flexible operating points.

Does KSP45BU require a heatsink in standard PCB applications?

No, the KSP45BU does not require an external heatsink when operated within its 625 mW power dissipation limit at T_A = 25°C. Its R_θJA = 200°C/W means that at 500 mW dissipation, junction temperature rise is ~100°C above ambient-keeping T_J below 150°C on a standard FR-4 board (76 mm × 114 mm). The KSP45BU's thermal performance is sufficient for intermittent or low-duty-cycle switching; continuous 300 mA operation demands careful layout with thermal relief pads.

How does KSP45BU handle inductive load switching, such as relay coils?

The KSP45BU supports inductive load switching via external flyback diode protection across the coil. Its 350 V V_CEO rating absorbs typical relay kickback voltages (≤200 V), and its 300 mA I_C rating covers most 12 V automotive relays. The KSP45BU's fast turn-off time (t_f < 100 ns) minimizes energy dissipation during switching transitions. Always pair the KSP45BU with a 1N4007 or similar diode to clamp reverse EMF and prevent secondary breakdown.

KSP45BU Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

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

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 300 mA

Voltage - Collector Emitter Breakdown (Max):: 350 V

Vce Saturation (Max) @ Ib, Ic:: 750mV @ 5mA, 50mA

Current - Collector Cutoff (Max):: 500nA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 50 @ 10mA, 10V

Power - Max:: 625 mW

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

KSP45BU FAQ

1.How can I place an order for KSP45BU through Aetrix?

Please submit a Request for Quotation (RFQ) for KSP45BU 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 KSP45BU reliable?

The price and inventory of KSP45BU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for KSP45BU is usually 5 days.

3.What payment methods are accepted for KSP45BU?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for KSP45BU transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for KSP45BU?

KSP45BU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your KSP45BU 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 KSP45BU?

For technical support, including KSP45BU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your KSP45BU requirements.

6.How does Aetrix verify that KSP45BU is sourced from the original manufacturer or authorized distributors?

All KSP45BU 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 KSP45BU meets industry standards.

7.What is the process for return or replacement of KSP45BU?

All KSP45BU units undergo pre-shipment inspection (PSI). If there is an issue with KSP45BU, 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 KSP45BU part is unused and in its original packaging.

Return procedure for KSP45BU:

1.Submit a request within 90 days.

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

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