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

onsemi BC638BU

Name: BC638BU
Brand: onsemi
SKU: BC638BU
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC638BU

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BC638BU.pdf

Description:: TRANS PNP 60V 1A TO-92-3

Quantity:: RFQ Add To RFQ list

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Inventory:7,618

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Product details

Overview

BC638BU from onsemi is a PNP epitaxial silicon transistor designed for medium-power switching and linear amplification, with −60 V V_CEO, −1 A continuous collector current, 100 MHz f_T, and TO-92-3 (Case 135AR) package. It serves as a complement to BC637 in push-pull output stages and discrete logic interface circuits.

For engineers reviewing the BC638BU datasheet, pinout, applications, or equivalent options, key selection criteria include its −60 V breakdown rating, −500 mA saturation performance at −50 mA base drive, DC current gain range of 25–160 across operating currents, and RoHS-compliant Pb-free construction.

Technical Context

This PNP bipolar junction transistor operates in common-emitter configuration with specified V_CE(sat) = −0.5 V at I_C = −500 mA / I_B = −50 mA and V_BE(on) = −1 V under same conditions. Its f_T of 100 MHz supports audio-frequency amplification and fast-switching digital loads up to ~100 kHz.

The device exhibits three distinct h_FE regions: 25 at 5 mA, 40–160 at 150 mA, and 25 again at 500 mA - indicating optimized gain stability across mid-current switching ranges. Thermal resistance R_JA is 125 °C/W on standard FR-4 PCB land pattern.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	−60 V: Maximum safe collector-emitter voltage before avalanche breakdown in open-base condition.
I_C (cont.)	−1 A: Continuous DC collector current rating defining maximum sustained load-handling capability.
f_T	100 MHz: Current-gain bandwidth product enabling stable small-signal amplification up to audio and low-RF frequencies.
V_CE(sat)	−0.5 V @ I_C = −500 mA / I_B = −50 mA: Low saturation voltage ensures minimal conduction loss in switching applications.
h_FE	25–160: DC current gain range across 5 mA to 150 mA collector currents, supporting both bias-sensitive analog and robust digital drive.
P_D	1 W @ T_A = 25°C: Maximum power dissipation on standard PCB layout; derates 8 mW/°C above ambient.

Pinout & Package

BC638BU is housed in TO-92-3 plastic package (Case 135AR), with standardized leadform: Emitter (pin 1), Collector (pin 2), Base (pin 3). Leads are bent per JEDEC TO-92 outline.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink terminal for PNP operation	Connected to higher potential rail in switching configurations; sets reference for base bias network.
2 (Collector)	Main output current path	Drives load to ground when saturated; requires heatsinking above ~300 mW dissipation.
3 (Base)	Control input for minority-carrier injection	Receives negative-going drive signal; typical series resistor ≥1 kΩ limits I_B to safe −100 mA max.

Key Features

Feature	Design Value
Complementary pairing	Matched electrical characteristics with BC637 NPN for balanced push-pull stage design and reduced crossover distortion.
RoHS compliance	Pb-free, halogen-free/BFR-free construction meets EU Directive 2011/65/EU and industrial environmental requirements.
High V_CEO rating	−60 V breakdown enables use in 48 V automotive subsystems, industrial 24/48 V DC control, and relay driver circuits.
Stable h_FE over current range	Gain remains ≥40 from 10 mA to 150 mA, simplifying bias network design for consistent switching thresholds.

Applications

Relay Driver Circuit	DC Motor Control Stage
Use Scenario: Driving 12 V/24 V electromagnetic relays requiring 50–100 mA coil current in PLC I/O modules. IC Role / Device Role / Timing Role: PNP switch providing high-side current sourcing to relay coil with fast turn-off via base pull-up. Use Value: −60 V V_CEO prevents breakdown during inductive kickback; −0.5 V V_CE(sat) minimizes power loss and heat rise in sealed enclosures.	Use Scenario: Controlling bidirectional brushed DC motors in battery-powered tools using H-bridge half-bridge sections. IC Role / Device Role / Timing Role: High-side PNP switch in complementary pair with BC637, enabling full bridge conduction without shoot-through risk. Use Value: Matched h_FE and V_CE(sat) between BC638BU and BC637 ensures symmetrical on-resistance and timing in motor commutation.
Linear Voltage Regulator Pass Element	Discrete Logic Level Shifter
Use Scenario: Acting as series pass transistor in adjustable 3–15 V linear regulators delivering up to 800 mA output. IC Role / Device Role / Timing Role: Medium-power PNP pass element controlled by error amplifier feedback loop. Use Value: 1 W power rating and 125 °C/W thermal resistance allow regulated output under moderate load and ambient temperature.	Use Scenario: Translating 3.3 V logic signals to 5 V or 12 V domains in mixed-voltage microcontroller interfaces. IC Role / Device Role / Timing Role: Inverting level shifter with emitter-follower or common-emitter topology depending on bias configuration. Use Value: 100 MHz f_T supports clean edge transitions up to 10 MHz clock rates; −5 V V_EBO protects against reverse-bias damage during hot-plug events.

Relay Driver Circuit

DC Motor Control Stage

Use Scenario: Driving 12 V/24 V electromagnetic relays requiring 50–100 mA coil current in PLC I/O modules.

IC Role / Device Role / Timing Role: PNP switch providing high-side current sourcing to relay coil with fast turn-off via base pull-up.

Use Value: −60 V V_CEO prevents breakdown during inductive kickback; −0.5 V V_CE(sat) minimizes power loss and heat rise in sealed enclosures.

Use Scenario: Controlling bidirectional brushed DC motors in battery-powered tools using H-bridge half-bridge sections.

IC Role / Device Role / Timing Role: High-side PNP switch in complementary pair with BC637, enabling full bridge conduction without shoot-through risk.

Use Value: Matched h_FE and V_CE(sat) between BC638BU and BC637 ensures symmetrical on-resistance and timing in motor commutation.

Linear Voltage Regulator Pass Element

Discrete Logic Level Shifter

Use Scenario: Acting as series pass transistor in adjustable 3–15 V linear regulators delivering up to 800 mA output.

IC Role / Device Role / Timing Role: Medium-power PNP pass element controlled by error amplifier feedback loop.

Use Value: 1 W power rating and 125 °C/W thermal resistance allow regulated output under moderate load and ambient temperature.

Use Scenario: Translating 3.3 V logic signals to 5 V or 12 V domains in mixed-voltage microcontroller interfaces.

IC Role / Device Role / Timing Role: Inverting level shifter with emitter-follower or common-emitter topology depending on bias configuration.

Use Value: 100 MHz f_T supports clean edge transitions up to 10 MHz clock rates; −5 V V_EBO protects against reverse-bias damage during hot-plug events.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP medium-power transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC638TA	Same die, identical electrical specs; differs only in packaging - tape-and-reel vs. bulk (BU); TO-92-3 case code identical.	No functional difference; BU denotes bulk packaging for prototyping or low-volume assembly; TA used for automated SMT placement.	Select BC638BU for manual soldering, evaluation, or small-batch builds where reel handling is unnecessary.
MPSA92	Higher V_CEO (−300 V), lower f_T (50 MHz), similar I_C (−500 mA), different h_FE profile (25–100).	Better suited for high-voltage flyback snubbers or CRT deflection circuits; less optimal for high-speed switching above 50 kHz.	Choose MPSA92 only when >−100 V breakdown is required; BC638BU preferred for general-purpose 24–48 V switching with tighter gain control.

Compared with BC638TA, BC638BU offers identical electrical behavior but simplified logistics for bench use; versus MPSA92, BC638BU delivers superior small-signal bandwidth and tighter gain consistency at medium voltages, making it more suitable for precision switching and audio amplification.

Availability

BC638BU is available at Aetrix Electronics and suitable for relay driver circuits, DC motor control stages, linear voltage regulator pass elements, and discrete logic level shifters requiring stable component supply and long-term industrial availability.

Supply support for BC638BU 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, serving automotive, industrial, cloud, and IoT markets with discrete, analog, and power management solutions.

The BC638BU belongs to onsemi's legacy bipolar transistor family designed for cost-sensitive, medium-power linear and switching applications where reliability, manufacturability, and RoHS compliance are essential.

FAQ

What is the maximum continuous collector current rating for BC638BU?

The BC638BU has a maximum continuous collector current (I_C) rating of −1 A at T_A = 25°C. This rating assumes adequate PCB copper area for thermal dissipation; derating applies above 25°C ambient at 8 mW/°C. At I_C = −500 mA, the device maintains V_CE(sat) ≤ −0.5 V with −50 mA base drive, confirming robust conduction capability within its safe operating area.

Is BC638BU pin-compatible with BC637?

No, BC638BU is not pin-compatible with BC637 - they are complementary PNP/NPN devices with identical TO-92-3 package outlines but reversed polarity and internal structure. Pin 1 is Emitter for BC638BU and Collector for BC637. Their circuit roles differ fundamentally, though they are electrically matched for push-pull pairing in the same footprint.

Does BC638BU support high-frequency switching applications?

Yes, BC638BU supports high-frequency switching up to approximately 100 kHz due to its 100 MHz f_T and low V_CE(sat). However, it is not optimized for RF or MHz-range switching; its primary strength lies in audio amplification and fast digital switching where gain-bandwidth trade-offs favor stability over ultra-high speed. For >500 kHz applications, consider RF-optimized transistors.

What is the junction-to-ambient thermal resistance (R_JA) of BC638BU?

The BC638BU has a thermal resistance R_JA of 125 °C/W when mounted on a standard FR-4 PCB (76 mm × 114 mm × 1.57 mm) with minimum land pattern. This value assumes no added heatsink; doubling copper area reduces R_JA by ~15–20%. At 1 W dissipation, junction temperature rises ~125°C above ambient - limiting practical continuous operation to ≤25°C ambient unless actively cooled.

Can BC638BU be used in linear amplifier configurations?

Yes, BC638BU is qualified for linear amplifier use, with documented h_FE linearity across 5–150 mA collector currents and V_CE = −2 V. Its 100 MHz f_T and low noise characteristics (not explicitly specified but consistent with epitaxial PNP process) support Class-A audio preamplifiers and low-distortion signal buffering. Bias networks must ensure stable Q-point given h_FE variation across units.

BC638BU Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

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

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 1 A

Voltage - Collector Emitter Breakdown (Max):: 60 V

Vce Saturation (Max) @ Ib, Ic:: 500mV @ 50mA, 500mA

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

DC Current Gain (hFE) (Min) @ Ic, Vce:: 40 @ 150mA, 2V

Power - Max:: 1 W

Frequency - Transition:: 100MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

BC638BU FAQ

1.How can I place an order for BC638BU through Aetrix?

Please submit a Request for Quotation (RFQ) for BC638BU 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 BC638BU reliable?

The price and inventory of BC638BU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC638BU is usually 5 days.

3.What payment methods are accepted for BC638BU?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC638BU transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC638BU?

BC638BU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC638BU 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 BC638BU?

For technical support, including BC638BU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC638BU requirements.

6.How does Aetrix verify that BC638BU is sourced from the original manufacturer or authorized distributors?

All BC638BU 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 BC638BU meets industry standards.

7.What is the process for return or replacement of BC638BU?

All BC638BU units undergo pre-shipment inspection (PSI). If there is an issue with BC638BU, 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 BC638BU part is unused and in its original packaging.

Return procedure for BC638BU:

1.Submit a request within 90 days.

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

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