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

onsemi BC639_L34Z

Name: BC639_L34Z
Brand: onsemi
SKU: BC639_L34Z
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC639_L34Z

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BC639_L34Z.pdf

Description:: TRANS NPN 80V 1A TO-92-3

Quantity:: RFQ Add To RFQ list

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Inventory:2,175

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Product details

Overview

BC639_L34Z from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for medium-power switching and linear amplification, with V_CEO = 80 V, I_C = 1 A, P_C = 1 W, h_FE ≥ 40 at I_C = 150 mA, and f_T = 100 MHz - used in relay drivers, power supply control stages, and audio preamplifier circuits.

For engineers reviewing the BC639_L34Z datasheet, pinout, applications, or equivalent options, key selection criteria include collector-emitter breakdown voltage (80 V), DC current gain at high current (h_FE ≥ 40 @ I_C = 150 mA), saturation voltage (V_CE(sat) ≤ 0.5 V @ I_C = 500 mA, I_B = 50 mA), thermal rating (T_J = 150°C), and TO-92 package compatibility.

Technical Context

The BC639_L34Z operates as a general-purpose bipolar junction transistor with fixed NPN polarity and epitaxial base construction, supporting both active-region amplification and saturated-switching modes. Its design targets stable DC current gain across I_C = 5–500 mA and low V_CE(sat) under moderate base drive.

It features complementary pairing with BC640 and shares absolute maximum ratings and test conditions with BC635/BC637 family members, though V_CEO, V_CER, and V_CES are uniquely rated at 80 V, 100 V, and 100 V respectively - confirming its higher-voltage capability within the series.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	80 V - Maximum collector-emitter voltage before breakdown under open-base condition; defines safe operating voltage in switching applications.
I_C	1 A - Continuous collector current rating; sets upper limit for steady-state load handling in driver or amplifier stages.
P_C	1 W - Total power dissipation at T_A = 25°C; determines thermal derating requirements on PCB without heatsink.
h_FE	≥40 @ I_C = 150 mA - Minimum DC current gain at mid-range current; ensures reliable base drive sizing for saturation.
V_CE(sat)	≤0.5 V @ I_C = 500 mA, I_B = 50 mA - Low saturation voltage enables efficient switching with <0.25 W conduction loss.
f_T	100 MHz - Transition frequency at V_CE = 5 V, I_C = 10 mA; supports RF amplification up to ~10–20 MHz with gain margin.

Pinout & Package

BC639_L34Z is housed in a standard TO-92 plastic package with 3 leads: Emitter (Lead 1), Collector (Lead 2), Base (Lead 3), aligned to JEDEC TO-92 outline and compatible with manual or wave soldering processes.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current exit path for majority carriers	Connected to ground or low-impedance return; requires low-inductance trace in switching layouts.
2 (Collector)	Current entry path under forward-active or saturation bias	Drives inductive loads (e.g., relays) or feeds next stage; routed away from sensitive analog nodes.
3 (Base)	Control terminal modulating collector current	Driven via current-limiting resistor; susceptible to noise - often bypassed with 10–100 nF to emitter.

Key Features

Feature	Design Value
High V_CEO (80 V)	Enables use in 24–48 V industrial control systems without cascading transistors or voltage clamping.
Low V_CE(sat) (≤0.5 V)	Reduces conduction losses below 250 mW at 500 mA, improving efficiency in battery-powered switch-mode interfaces.
Stable h_FE ≥40 @ 150 mA	Allows predictable base resistor calculation for consistent turn-on across production lots and temperature ranges.
TO-92 package	Supports hand-soldering, prototyping, and space-constrained through-hole designs while maintaining thermal performance up to 1 W.

Applications

Relay Driver Stage	DC-DC Converter Switch
Use Scenario: Driving 12 V/500 mA electromagnetic relay coil from microcontroller GPIO. IC Role / Device Role / Timing Role: NPN switch operating in saturation mode to sink relay coil current. Use Value: V_CE(sat) ≤ 0.5 V minimizes coil voltage drop, ensuring full actuation; h_FE ≥ 40 allows 12 mA base drive for robust margin.	Use Scenario: Low-side switch in 24 V input, 5 V output buck converter operating at 100 kHz. IC Role / Device Role / Timing Role: Power switch controlling energy transfer into output inductor during ON phase. Use Value: 80 V V_CEO provides 2× safety margin over 24 V rail; 1 A I_C supports peak currents up to 1.5 A with derating.
Audio Preamp Input Stage	Linear Voltage Regulator Pass Element
Use Scenario: First-stage small-signal amplification of microphone-level signals in portable audio recorder. IC Role / Device Role / Timing Role: Common-emitter amplifier biased in active region for voltage gain. Use Value: f_T = 100 MHz ensures flat gain response up to 20 kHz; low ICBO (0.1 µA) prevents DC offset drift in high-Z input networks.	Use Scenario: Series pass transistor in adjustable 3–12 V linear regulator delivering up to 800 mA. IC Role / Device Role / Timing Role: Continuously variable resistance element controlled by error amplifier feedback. Use Value: 1 W P_C and 150°C T_J allow operation at 1.5 W dissipation with proper PCB copper area; V_BE(on) = 1 V simplifies bias network design.

Relay Driver Stage

DC-DC Converter Switch

Use Scenario: Driving 12 V/500 mA electromagnetic relay coil from microcontroller GPIO.

IC Role / Device Role / Timing Role: NPN switch operating in saturation mode to sink relay coil current.

Use Value: V_CE(sat) ≤ 0.5 V minimizes coil voltage drop, ensuring full actuation; h_FE ≥ 40 allows 12 mA base drive for robust margin.

Use Scenario: Low-side switch in 24 V input, 5 V output buck converter operating at 100 kHz.

IC Role / Device Role / Timing Role: Power switch controlling energy transfer into output inductor during ON phase.

Use Value: 80 V V_CEO provides 2× safety margin over 24 V rail; 1 A I_C supports peak currents up to 1.5 A with derating.

Audio Preamp Input Stage

Linear Voltage Regulator Pass Element

Use Scenario: First-stage small-signal amplification of microphone-level signals in portable audio recorder.

IC Role / Device Role / Timing Role: Common-emitter amplifier biased in active region for voltage gain.

Use Value: f_T = 100 MHz ensures flat gain response up to 20 kHz; low ICBO (0.1 µA) prevents DC offset drift in high-Z input networks.

Use Scenario: Series pass transistor in adjustable 3–12 V linear regulator delivering up to 800 mA.

IC Role / Device Role / Timing Role: Continuously variable resistance element controlled by error amplifier feedback.

Use Value: 1 W P_C and 150°C T_J allow operation at 1.5 W dissipation with proper PCB copper area; V_BE(on) = 1 V simplifies bias network design.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN switching and amplification applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC639 (no suffix)	Same electrical specs and TO-92 package; L34Z denotes specific date/batch code per Fairchild traceability system.	No functional difference - L34Z is a valid orderable variant of BC639 with identical performance and footprint.	Select BC639_L34Z when lot traceability or legacy BOM compliance is required; otherwise BC639 is functionally interchangeable.
MPSA42	Higher V_CEO (300 V), lower h_FE (min 40 @ I_C = 10 mA), same TO-92 package.	Better suited for high-voltage flyback snubbers or AC line sensing; less optimal for high-current switching due to lower I_C rating (500 mA).	Choose MPSA42 only when >100 V blocking is essential; BC639_L34Z remains preferred for 24–48 V switching with higher current capability.

Compared with BC639 (base variant), BC639_L34Z offers identical electrical behavior and mechanical fit, while MPSA42 trades current capacity for higher voltage tolerance - making BC639_L34Z optimal for medium-voltage, medium-current linear and switching roles where gain stability and saturation efficiency are prioritized.

Availability

BC639_L34Z is available at Aetrix Electronics and suitable for relay drivers, DC-DC converter switches, audio preamplifiers, and linear voltage regulator pass elements requiring stable component supply and long-term industrial availability.

Supply support for BC639_L34Z 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, signal conditioning, and discrete components before its acquisition by ON Semiconductor in 2016.

The BC639_L34Z belongs to Fairchild's legacy BC63x NPN transistor family, engineered for cost-sensitive, high-reliability general-purpose switching and amplification in industrial, automotive, and consumer equipment.

FAQ

What is the maximum collector-emitter voltage rating for BC639_L34Z?

The BC639_L34Z has a V_CEO rating of 80 V, meaning it can safely block up to 80 V between collector and emitter with the base open. This value is confirmed in the Absolute Maximum Ratings table under "Collector-Emitter Voltage" for BC639. Exceeding this voltage risks avalanche breakdown and permanent device failure.

Is BC639_L34Z pin-compatible with BC637 or BC635?

Yes, BC639_L34Z shares the same TO-92 package and pinout (Emitter-Collector-Base) with BC635 and BC637. However, it is not electrically interchangeable: BC639_L34Z has higher V_CEO (80 V vs. 60 V for BC637), so substituting it into a BC637 design is safe, but replacing BC639_L34Z with BC637 may cause overvoltage failure.

What is the typical DC current gain (hFE) of BC639_L34Z at 500 mA collector current?

Per the datasheet, BC639_L34Z guarantees h_FE ≥ 40 at V_CE = 2 V and I_C = 150 mA. At I_C = 500 mA, h_FE is not specified in minimum form, but typical curves show h_FE ≈ 25–35. For robust design, assume h_FE ≥ 25 at 500 mA when calculating base drive requirements for saturation.

Does BC639_L34Z require a heatsink in 1 W continuous operation?

No - BC639_L34Z is rated for 1 W total power dissipation at T_A = 25°C in free air with standard TO-92 mounting. At full 1 W, junction temperature reaches ~150°C, which is its absolute maximum. For reliability, operate below 0.7 W without heatsink; add minimal copper pour if sustained >0.5 W is required.

Can BC639_L34Z be used as a direct replacement for BC640 in a circuit?

No - BC640 is a PNP transistor, while BC639_L34Z is NPN. Their polarities are opposite, so they cannot be interchanged without reversing biasing, swapping supply rails, and redesigning the surrounding network. They are complementary devices, not substitutes.

BC639_L34Z 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:: NPN

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

Voltage - Collector Emitter Breakdown (Max):: 80 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

BC639_L34Z FAQ

1.How can I place an order for BC639_L34Z through Aetrix?

Please submit a Request for Quotation (RFQ) for BC639_L34Z 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 BC639_L34Z reliable?

The price and inventory of BC639_L34Z are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC639_L34Z is usually 5 days.

3.What payment methods are accepted for BC639_L34Z?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC639_L34Z transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC639_L34Z?

BC639_L34Z orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC639_L34Z 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 BC639_L34Z?

For technical support, including BC639_L34Z datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC639_L34Z requirements.

6.How does Aetrix verify that BC639_L34Z is sourced from the original manufacturer or authorized distributors?

All BC639_L34Z 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 BC639_L34Z meets industry standards.

7.What is the process for return or replacement of BC639_L34Z?

All BC639_L34Z units undergo pre-shipment inspection (PSI). If there is an issue with BC639_L34Z, 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 BC639_L34Z part is unused and in its original packaging.

Return procedure for BC639_L34Z:

1.Submit a request within 90 days.

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

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