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

onsemi BC237A

Name: BC237A
Brand: onsemi
SKU: BC237A
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BC237A

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

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

Datasheet:: BC237A.pdf

Description:: TRANS NPN 45V 0.1A TO-92-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BC237A from Fairchild Semiconductor is an NPN epitaxial silicon transistor optimized for low-noise amplifier and general-purpose switching applications, with hFE 120–220, V_CEO = 45 V, I_C = 100 mA, P_C = 500 mW, and f_T = 150 MHz (typ). It operates in audio preamplifier stages and signal conditioning circuits where stable gain and low noise are required.

For engineers reviewing the BC237A datasheet, pinout, applications, or equivalent options, key selection criteria include DC current gain classification (Class A), collector-emitter saturation voltage at 10 mA/0.5 mA (0.07 V typ), noise figure (2 dB at 1 kHz), TO-92 package compatibility, and thermal limits up to 150°C junction temperature.

Technical Context

The BC237A is a discrete bipolar junction transistor with epitaxial base construction enabling high f_T and low noise performance. Its hFE classification A (120–220) ensures predictable DC gain in linear amplification stages, while V_CEO = 45 V and V_CE(sat) ≤ 0.2 V support reliable switching in low-voltage logic interfaces.

Designed for operation at T_a = 25°C with derating above, it features Cob = 3.5 pF and Cib = 8 pF - values critical for RF-coupled amplifier stability and bandwidth control. The device's V_BE(on) = 0.62 V (typ) at I_C = 2 mA enables accurate bias network design in Class-A small-signal stages.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	45 V - maximum safe collector-emitter voltage before breakdown in common-emitter configuration
hFE (Class A)	120–220 - guaranteed DC current gain range for consistent bias point setting in amplifiers
f_T	150 MHz (typ) - usable small-signal bandwidth limit for audio and low-RF amplification
V_CE(sat)	0.07 V (typ) at I_C=10 mA/I_B=0.5 mA - low saturation loss for efficient switching in digital interface circuits
NF	2 dB at 1 kHz - verified low-noise performance for microphone preamp and sensor signal conditioning
P_C	500 mW - maximum continuous power dissipation at 25°C ambient, derated linearly above 25°C
Cob	3.5 pF - output capacitance affecting high-frequency roll-off and stability in tuned amplifier designs

Pinout & Package

BC237A is housed in a standard TO-92 plastic package with 3 leads, lead-free compatible per RoHS Directive, and rated for operation from –55°C to +150°C storage temperature.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink terminal in common-emitter configuration	Connected to ground or low-impedance return path; defines reference for V_BE and I_C control
2 (Base)	Control input for minority-carrier injection	Receives bias current to set operating point; sensitive to ESD and requires current-limiting resistor
3 (Collector)	Current source terminal in common-emitter configuration	Drives load or next stage; voltage swing limited by V_CEO and thermal dissipation

Key Features

Feature	Design Value
Low-noise amplifier grade	2 dB noise figure at 1 kHz enables use in microphone preamps and precision sensor front-ends
High f_T / low C_ob combination	150 MHz f_T with only 3.5 pF Cob supports stable gain up to ~10 MHz without compensation
Controlled hFE classification	Class A (120–220) ensures batch-to-batch consistency for production amplifier gain matching
Low V_CE(sat) at moderate drive	0.07 V typical at I_B = 0.5 mA allows efficient switching in 5 V logic-level interfaces
TO-92 mechanical standardization	Compatible with legacy through-hole assembly tooling and PCB footprints used across BC237/238/239 family

Applications

Audio Preamp Stage	Signal Switching Interface
Use Scenario: Low-level analog signal amplification from electret microphones or piezoelectric sensors before ADC sampling. IC Role / Device Role / Timing Role: NPN small-signal amplifier in common-emitter configuration with emitter degeneration. Use Value: 2 dB noise figure and 120–220 hFE ensure high SNR and repeatable gain calibration across production units.	Use Scenario: Level-shifting and inversion of 3.3 V/5 V digital control signals driving relays or LEDs. IC Role / Device Role / Timing Role: Saturated switch with base-driven turn-on and passive pull-down. Use Value: 0.07 V V_CE(sat) minimizes power loss and heat generation during sustained ON-state operation.
DC Bias Reference Generator	Current Mirror Active Load
Use Scenario: Stable current source for op-amp bias networks or LED constant-current drivers. IC Role / Device Role / Timing Role: Fixed-base biased transistor operating in active region as two-terminal current source. Use Value: Tight hFE classification (120–220) and low V_BE(on) variation (0.55–0.7 V) enable predictable current output within ±5%.	Use Scenario: High-impedance active load in differential pair amplifiers for rail-to-rail output swing. IC Role / Device Role / Timing Role: Collector-connected transistor configured as cascode current source. Use Value: 45 V V_CEO and 150 MHz f_T support wide dynamic range and bandwidth in analog front-end ICs.

Audio Preamp Stage

Signal Switching Interface

Use Scenario: Low-level analog signal amplification from electret microphones or piezoelectric sensors before ADC sampling.

IC Role / Device Role / Timing Role: NPN small-signal amplifier in common-emitter configuration with emitter degeneration.

Use Value: 2 dB noise figure and 120–220 hFE ensure high SNR and repeatable gain calibration across production units.

Use Scenario: Level-shifting and inversion of 3.3 V/5 V digital control signals driving relays or LEDs.

IC Role / Device Role / Timing Role: Saturated switch with base-driven turn-on and passive pull-down.

Use Value: 0.07 V V_CE(sat) minimizes power loss and heat generation during sustained ON-state operation.

DC Bias Reference Generator

Current Mirror Active Load

Use Scenario: Stable current source for op-amp bias networks or LED constant-current drivers.

IC Role / Device Role / Timing Role: Fixed-base biased transistor operating in active region as two-terminal current source.

Use Value: Tight hFE classification (120–220) and low V_BE(on) variation (0.55–0.7 V) enable predictable current output within ±5%.

Use Scenario: High-impedance active load in differential pair amplifiers for rail-to-rail output swing.

IC Role / Device Role / Timing Role: Collector-connected transistor configured as cascode current source.

Use Value: 45 V V_CEO and 150 MHz f_T support wide dynamic range and bandwidth in analog front-end ICs.

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN small-signal transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC546B	Higher hFE (200–450), same TO-92, V_CEO = 65 V, f_T = 300 MHz	Better high-frequency gain but higher noise (5 dB)	Select when wider bandwidth or higher voltage margin is needed; avoid in ultra-low-noise mic preamps
2N3904	Same hFE Class B range (~100–300), V_CEO = 40 V, f_T = 300 MHz, NF = 5 dB	Lower voltage rating and higher noise than BC237A	Acceptable for general switching; not recommended where <3 dB noise or >45 V V_CEO is required

Compared with BC546B and 2N3904, the BC237A delivers superior low-noise performance (2 dB) and tighter hFE binning (120–220) at the expense of lower f_T, making it optimal for precision audio and sensor signal chains where noise dominates design constraints.

Availability

BC237A is available at Aetrix Electronics and suitable for audio preamplifier design, sensor signal conditioning, and industrial control interface circuits requiring stable component supply and long-term obsolescence management.

Supply support for BC237A 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 components before its acquisition by ON Semiconductor in 2016.

The BC237A belongs to Fairchild's BC237/238/239 family of general-purpose NPN transistors engineered for low-noise amplification and reliable switching in consumer, industrial, and instrumentation applications.

FAQ

What is the hFE classification of BC237A?

The BC237A is classified as Class A, with a guaranteed DC current gain (hFE) range of 120 to 220 when measured at V_CE = 5 V and I_C = 2 mA. This tight binning ensures predictable biasing in production amplifier designs and distinguishes BC237A from BC237B (180–460) and BC237C (380–800). The BC237A datasheet explicitly confirms this classification under "hFE Classification".

Does BC237A support low-noise audio applications?

Yes, BC237A is specifically characterized for low-noise operation with a noise figure of 2 dB at 1 kHz, V_CE = 5 V, I_C = 0.2 mA, and R_G = 2 kΩ. This value is documented in the "Electrical Characteristics" table and confirmed in the "Typical Characteristics" section of the BC237A datasheet. Its low Cob (3.5 pF) and controlled hFE further support stable, high-SNR audio preamplifier implementation.

What is the maximum collector-emitter voltage rating for BC237A?

The BC237A has a maximum collector-emitter voltage rating (V_CEO) of 45 V under standard test conditions (I_C = 2 mA, I_B = 0). This value is specified in both the "Absolute Maximum Ratings" and "Electrical Characteristics" tables of the BC237A datasheet. Exceeding this voltage risks avalanche breakdown and permanent device failure.

Is BC237A packaged in TO-92?

Yes, BC237A uses the standard TO-92 plastic package with three leads arranged as Collector (pin 3), Base (pin 2), and Emitter (pin 1), as shown in the "Package Dimensions" drawing and "Pin Configuration" diagram of the BC237A datasheet. The physical dimensions - including body length (4.58 mm), lead spacing (1.27 mm), and lead diameter (0.38 mm) - match JEDEC TO-92 specifications.

What is the typical current gain-bandwidth product (fT) of BC237A?

The BC237A has a typical current gain-bandwidth product (f_T) of 150 MHz when tested at V_CE = 3 V, I_C = 0.5 mA, and f = 100 MHz. This value is listed in the "Electrical Characteristics" table and supported by Figure 6 ("Current Gain Bandwidth Product") in the BC237A datasheet. At higher currents (e.g., I_C = 10 mA), f_T drops to 85 MHz.

BC237A 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):: 100 mA

Voltage - Collector Emitter Breakdown (Max):: 45 V

Vce Saturation (Max) @ Ib, Ic:: 600mV @ 5mA, 100mA

Current - Collector Cutoff (Max):: 15nA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 120 @ 2mA, 5V

Power - Max:: 500 mW

Frequency - Transition:: 250MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

BC237A FAQ

1.How can I place an order for BC237A through Aetrix?

Please submit a Request for Quotation (RFQ) for BC237A 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 BC237A reliable?

The price and inventory of BC237A are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC237A is usually 5 days.

3.What payment methods are accepted for BC237A?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC237A transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BC237A?

BC237A orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BC237A 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 BC237A?

For technical support, including BC237A datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC237A requirements.

6.How does Aetrix verify that BC237A is sourced from the original manufacturer or authorized distributors?

All BC237A 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 BC237A meets industry standards.

7.What is the process for return or replacement of BC237A?

All BC237A units undergo pre-shipment inspection (PSI). If there is an issue with BC237A, 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 BC237A part is unused and in its original packaging.

Return procedure for BC237A:

1.Submit a request within 90 days.

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

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