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

onsemi BC637_L34Z

Name: BC637_L34Z
Brand: onsemi
SKU: BC637_L34Z
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC637_L34Z

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BC637_L34Z.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:2,772

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Product details

Overview

BC637_L34Z from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for general-purpose switching and linear amplification, with V_CEO = 60 V, I_C = 1 A, h_FE = 40–250 (at I_C = 5–150 mA), V_CE(sat) = 0.5 V (I_C = 500 mA, I_B = 50 mA), and TO-92 package. It serves in low-voltage power control, relay drivers, and audio preamplifier stages.

For engineers reviewing the BC637_L34Z datasheet, pinout, applications, or equivalent options, key selection factors include its 60 V V_CEO, 1 A continuous collector current, DC gain range across operating currents, saturation voltage under defined drive conditions, and TO-92 mechanical compatibility in space-constrained PCB layouts.

Technical Context

The BC637_L34Z operates as a medium-power bipolar junction transistor with fixed NPN polarity and epitaxial base construction, enabling stable gain and low leakage (I_CBO ≤ 0.1 µA at V_CB = 30 V). Its f_T of 100 MHz supports high-speed switching up to ~10 MHz in practical circuits with proper drive and load matching.

It features complementary pairing with BC638 (PNP) and shares identical TO-92 outline and terminal assignment (E-C-B) with BC635/BC639, differing only in breakdown voltage grading-BC637_L34Z is specifically rated for 60 V V_CEO and 60 V V_CER, positioning it between BC635 and BC639 in voltage capability.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	60 V - Maximum safe collector-emitter voltage before avalanche breakdown under open-base condition; defines upper rail limit in switch designs.
I_C	1 A - Continuous DC collector current rating; sets thermal design baseline for heatsinking and trace width in PCB layout.
h_FE	40–250 - DC current gain range across I_C = 5 mA to 150 mA; determines required base drive for saturation or linear operation.
V_CE(sat)	0.5 V @ I_C = 500 mA, I_B = 50 mA - Low saturation voltage enables <0.25 W conduction loss at full rated current.
f_T	100 MHz - Current-gain bandwidth product; indicates usable small-signal amplification up to ~10–20 MHz with gain roll-off.
P_C	1 W - Total package power dissipation at T_A = 25°C; derates linearly above 25°C ambient per specified thermal resistance.

Pinout & Package

BC637_L34Z is housed in a standard TO-92 plastic package with 3 leads, lead-free and RoHS-compliant per Fairchild's 2002 specification. The package outline conforms to JEDEC TO-92 variant A (flat side facing viewer, leads down).

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink node	Reference terminal for bias network; connects to ground or low-side return path in common-emitter configurations.
2 (Collector)	Current source node	Primary output terminal carrying switched or amplified load current; requires appropriate voltage margin and trace current rating.
3 (Base)	Control input node	Receives forward-biased drive current to modulate collector current; requires series resistor to limit I_B and ensure saturation.

Key Features

Feature	Design Value
Complementary PNP pairing	Matched performance with BC638 for push-pull and differential amplifier topologies without gain or timing mismatch.
Low leakage	I_CBO ≤ 0.1 µA ensures minimal off-state current in battery-powered or high-impedance sensor interfaces.
High f_T	100 MHz enables reliable operation in pulse-width modulation (PWM) gate drivers and RF predriver stages up to 20 MHz.
TO-92 mechanical standardization	Enables drop-in replacement across BC635/BC637/BC639 family in existing footprints without rework or stencil changes.

Applications

Relay Driver Circuit	DC Motor Speed Control
Use Scenario: Driving 12 V, 500 mA electromagnetic relay coil from microcontroller GPIO. IC Role / Device Role / Timing Role: NPN switch providing current gain to interface low-current logic output with inductive load. Use Value: V_CE(sat) = 0.5 V minimizes coil voltage drop and self-heating; 1 A I_C rating accommodates relay inrush peaks.	Use Scenario: PWM-controlled H-bridge half-bridge stage for 6–24 V brushed DC motors in portable tools. IC Role / Device Role / Timing Role: Low-side switching element handling bidirectional current during freewheeling and active drive phases. Use Value: 100 MHz f_T supports clean edge fidelity at 20 kHz PWM frequency; TO-92 allows compact dual-channel layout.
Audio Preamp Stage	LED Constant-Current Driver
Use Scenario: First-stage voltage amplification in battery-powered microphone preamplifier with 2–5 mV input signal. IC Role / Device Role / Timing Role: Common-emitter linear amplifier biased for low-noise, mid-bandwidth operation (20 Hz–20 kHz). Use Value: h_FE ≥ 40 at I_C = 5 mA ensures stable gain with minimal base current loading on preceding stage.	Use Scenario: Precision constant-current sink for high-brightness white LEDs in signage or indicator panels. IC Role / Device Role / Timing Role: Regulated current source using emitter-degeneration resistor and base voltage reference. Use Value: Tight I_CBO ≤ 0.1 µA prevents drift in LED current over temperature and time; 60 V V_CEO supports multi-LED series strings.

Relay Driver Circuit

DC Motor Speed Control

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

IC Role / Device Role / Timing Role: NPN switch providing current gain to interface low-current logic output with inductive load.

Use Value: V_CE(sat) = 0.5 V minimizes coil voltage drop and self-heating; 1 A I_C rating accommodates relay inrush peaks.

Use Scenario: PWM-controlled H-bridge half-bridge stage for 6–24 V brushed DC motors in portable tools.

IC Role / Device Role / Timing Role: Low-side switching element handling bidirectional current during freewheeling and active drive phases.

Use Value: 100 MHz f_T supports clean edge fidelity at 20 kHz PWM frequency; TO-92 allows compact dual-channel layout.

Audio Preamp Stage

LED Constant-Current Driver

Use Scenario: First-stage voltage amplification in battery-powered microphone preamplifier with 2–5 mV input signal.

IC Role / Device Role / Timing Role: Common-emitter linear amplifier biased for low-noise, mid-bandwidth operation (20 Hz–20 kHz).

Use Value: h_FE ≥ 40 at I_C = 5 mA ensures stable gain with minimal base current loading on preceding stage.

Use Scenario: Precision constant-current sink for high-brightness white LEDs in signage or indicator panels.

IC Role / Device Role / Timing Role: Regulated current source using emitter-degeneration resistor and base voltage reference.

Use Value: Tight I_CBO ≤ 0.1 µA prevents drift in LED current over temperature and time; 60 V V_CEO supports multi-LED series strings.

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
BC637 (no suffix)	Same electrical specs and TO-92 package; L34Z denotes specific Fairchild date/batch coding per internal traceability system.	No functional difference; L34Z is a valid orderable variant of BC637 with identical parametric performance.	Select BC637_L34Z when sourcing from authorized channels requiring lot-specific traceability or legacy BOM alignment.
MPSA13	Higher h_FE (50–250), same V_CEO = 60 V, but lower I_C = 500 mA and P_C = 625 mW; TO-92 compatible.	Not suitable for 1 A continuous loads; preferred where high gain at low current (<100 mA) is prioritized over power handling.	Choose MPSA13 only if circuit operates below 500 mA and benefits from higher gain at microampere base drive levels.

Compared with BC637_L34Z, the base BC637 offers identical functionality with no differentiation in design intent or electrical behavior, while MPSA13 trades current/power capability for enhanced small-signal gain-making BC637_L34Z the optimal choice for 1 A switching or linear applications requiring full-rated dissipation.

Availability

BC637_L34Z is available at Aetrix Electronics and suitable for relay driver circuits, DC motor speed control, audio preamplifier stages, and LED constant-current drivers requiring stable component supply and long-term industrial availability.

Supply support for BC637_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, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The BC637_L34Z belongs to Fairchild's legacy BC63x NPN transistor family, engineered for cost-sensitive, medium-power general-purpose switching and amplification in consumer, industrial, and automotive auxiliary systems.

FAQ

What is the maximum collector-emitter voltage rating for BC637_L34Z?

The BC637_L34Z has a V_CEO rating of 60 V, meaning it can safely block up to 60 V between collector and emitter with the base open. This value is confirmed in the Absolute Maximum Ratings table under "Collector-Emitter Voltage" for BC637, and applies identically to BC637_L34Z as a variant of that part number.

Is BC637_L34Z pin-compatible with BC635 or BC639?

Yes, BC637_L34Z is pin-compatible with BC635 and BC639, sharing the same TO-92 package and terminal assignment (Emitter–Collector–Base, left-to-right with flat side facing). All three parts use identical mechanical footprint and pinout, though their V_CEO ratings differ (45 V, 60 V, and 80 V respectively).

What is the DC current gain (h_FE) range of BC637_L34Z at typical operating conditions?

The BC637_L34Z exhibits h_FE = 40–250 depending on operating point: minimum 40 at I_C = 150 mA, typical 250 at I_C = 5 mA, and minimum 40 again at I_C = 500 mA. These values are explicitly listed in the Electrical Characteristics table for BC637 under h_FE2 and h_FE1 test conditions.

Does BC637_L34Z support high-frequency switching applications?

Yes, BC637_L34Z has an f_T of 100 MHz, indicating usable small-signal amplification and fast switching capability. In practice, it supports clean PWM switching up to 20 kHz with low storage time and consistent V_CE(sat), making it suitable for motor control and SMPS predriver stages where speed and saturation integrity matter.

What is the package type and lead configuration of BC637_L34Z?

BC637_L34Z uses the TO-92 plastic package with three leads arranged Emitter–Collector–Base (pin 1–2–3) when viewed with the flat side facing the user and leads pointing downward. This configuration is standardized across the BC635/637/639 family and documented in the Package Dimensions section of the Fairchild datasheet.

BC637_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):: 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

BC637_L34Z FAQ

1.How can I place an order for BC637_L34Z through Aetrix?

Please submit a Request for Quotation (RFQ) for BC637_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 BC637_L34Z reliable?

The price and inventory of BC637_L34Z are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC637_L34Z is usually 5 days.

3.What payment methods are accepted for BC637_L34Z?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC637_L34Z transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC637_L34Z?

BC637_L34Z orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC637_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 BC637_L34Z?

For technical support, including BC637_L34Z datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC637_L34Z requirements.

6.How does Aetrix verify that BC637_L34Z is sourced from the original manufacturer or authorized distributors?

All BC637_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 BC637_L34Z meets industry standards.

7.What is the process for return or replacement of BC637_L34Z?

All BC637_L34Z units undergo pre-shipment inspection (PSI). If there is an issue with BC637_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 BC637_L34Z part is unused and in its original packaging.

Return procedure for BC637_L34Z:

1.Submit a request within 90 days.

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

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