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

onsemi BSR18B

Name: BSR18B
Brand: onsemi
SKU: BSR18B
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BSR18B

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-236-3, SC-59, SOT-23-3

Datasheet:: BSR18B.pdf

Description:: TRANS PNP 40V 0.2A SOT-23-3

Quantity:: RFQ Add To RFQ list

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Product details

Overview

BSR18B from Fairchild Semiconductor is a PNP general-purpose bipolar junction transistor (BJT) designed for amplification and switching in low-power analog and digital circuits, with V_CEO = 40 V, I_C = 200 mA, h_FE = 60–220 (at I_C = 0.1–100 mA), V_CE(sat) = 0.25 V (I_C = 10 mA, I_B = 1 mA), and SOT-23 package. It is used in signal conditioning stages of portable audio amplifiers and discrete logic-level translators.

For engineers reviewing the BSR18B datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP polarity, DC current gain range across operating currents, saturation voltage at defined drive conditions, thermal resistance (550 °C/W), and suitability for low-duty-cycle switching or linear amplification in space-constrained PCB layouts.

Technical Context

The BSR18B is a silicon PNP BJT fabricated on Fairchild's Process 23, optimized for general-purpose linear amplification and saturated switching. Its electrical behavior follows standard Ebers-Moll modeling with confirmed breakdown voltages (V_CEO, V_CBO, V_EBO) and cutoff leakage (I_CBO, I_EBO ≤ 50 nA).

Switching performance is characterized by t_d = 35 ns, t_r = 35 ns, t_s = 225 ns, and t_f = 75 ns under specified test conditions (V_CC = 3.0 V, I_C = 10 mA, I_B(on/off) = 1.0 mA), confirming suitability for medium-speed digital interface buffering and pulse generation.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	40 V - Maximum collector-emitter voltage before breakdown; defines safe operating range in common-emitter amplifier or switch configurations.
I_C (DC)	200 mA - Continuous collector current limit; sets upper bound for load-driving capability in relay drivers or LED sinks.
h_FE	60–220 - DC current gain spanning I_C = 0.1–100 mA; enables predictable biasing across varying signal amplitudes.
V_CE(sat)	0.25 V @ I_C=10 mA/I_B=1 mA - Low saturation voltage reduces power loss and heating in switching applications.
R_θJA	550 °C/W - Junction-to-ambient thermal resistance on FR-4 PCB (1.6″ × 1.6″); informs derating requirements above 25 °C ambient.
C_cb	4.5 pF @ V_CB=5 V - Collector-base capacitance impacts high-frequency gain roll-off and stability in RF-adjacent stages.

Pinout & Package

SOT-23 plastic surface-mount package with gull-wing leads; compact footprint (2.9 mm × 1.3 mm × 1.0 mm) suitable for high-density routing.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Current-controlled input terminal	Receives forward-biased base current to enable conduction; polarity requires negative drive relative to emitter for PNP operation.
2 (Emitter)	Major current source terminal	Connected to higher potential rail in PNP switch; serves as reference node for bias network and current return path.
3 (Collector)	Major current sink terminal	Drains load current to lower potential; voltage swing limited by V_CEO rating and saturation behavior.

Key Features

Feature	Design Value
Process 23 fabrication	Ensures consistent h_FE distribution and low leakage (I_CBO/I_EBO ≤ 50 nA) across production lots.
Low V_CE(sat)	0.25 V at I_C/I_B = 10/1 mA enables efficient switching in battery-powered logic interfaces.
Controlled C_eb and C_cb	10 pF and 4.5 pF respectively support stable gain up to ~100 MHz in small-signal amplifiers.
Specified switching times	t_s = 225 ns dominates turn-off delay; critical for timing-critical level-shifting in microcontroller I/O expansion.

Applications

Audio Signal Amplifier	Discrete Logic Level Shifter
Use Scenario: Boosting weak microphone signals in portable voice recorders before ADC sampling. IC Role / Device Role / Timing Role: PNP BJT configured in common-emitter topology providing 20–30 dB voltage gain with minimal distortion. Use Value: h_FE consistency across 0.1–10 mA ensures stable gain without manual trimming; low V_CE(sat) preserves dynamic range near supply rails.	Use Scenario: Translating 5 V TTL outputs to 3.3 V logic inputs in mixed-voltage MCU systems. IC Role / Device Role / Timing Role: PNP switch operating in saturated mode to pull 3.3 V bus low when 5 V input is active. Use Value: Verified t_s = 225 ns and t_f = 75 ns meet 1–5 MHz digital interface timing budgets without added propagation delay.
LED Current Sink Driver	Low-Power Relay Control
Use Scenario: Driving indicator LEDs in handheld medical devices powered by single-cell Li-ion batteries. IC Role / Device Role / Timing Role: Linear current regulator using emitter-degeneration resistor; operates in active region for precise brightness control. Use Value: V_CEO = 40 V accommodates transient spikes during battery charging; I_C = 200 mA supports multi-LED strings.	Use Scenario: Activating 12 V coil relays from 3.3 V microcontroller GPIO pins via discrete driver stage. IC Role / Device Role / Timing Role: High-gain PNP switch providing >10× current amplification to drive relay base with minimal GPIO loading. Use Value: h_FE ≥ 110 at I_C = 10 mA ensures reliable turn-on with <1 mA base drive; R_θJA = 550 °C/W allows continuous operation at 50 mW dissipation.

Audio Signal Amplifier

Discrete Logic Level Shifter

Use Scenario: Boosting weak microphone signals in portable voice recorders before ADC sampling.

IC Role / Device Role / Timing Role: PNP BJT configured in common-emitter topology providing 20–30 dB voltage gain with minimal distortion.

Use Value: h_FE consistency across 0.1–10 mA ensures stable gain without manual trimming; low V_CE(sat) preserves dynamic range near supply rails.

Use Scenario: Translating 5 V TTL outputs to 3.3 V logic inputs in mixed-voltage MCU systems.

IC Role / Device Role / Timing Role: PNP switch operating in saturated mode to pull 3.3 V bus low when 5 V input is active.

Use Value: Verified t_s = 225 ns and t_f = 75 ns meet 1–5 MHz digital interface timing budgets without added propagation delay.

LED Current Sink Driver

Low-Power Relay Control

Use Scenario: Driving indicator LEDs in handheld medical devices powered by single-cell Li-ion batteries.

IC Role / Device Role / Timing Role: Linear current regulator using emitter-degeneration resistor; operates in active region for precise brightness control.

Use Value: V_CEO = 40 V accommodates transient spikes during battery charging; I_C = 200 mA supports multi-LED strings.

Use Scenario: Activating 12 V coil relays from 3.3 V microcontroller GPIO pins via discrete driver stage.

IC Role / Device Role / Timing Role: High-gain PNP switch providing >10× current amplification to drive relay base with minimal GPIO loading.

Use Value: h_FE ≥ 110 at I_C = 10 mA ensures reliable turn-on with <1 mA base drive; R_θJA = 550 °C/W allows continuous operation at 50 mW dissipation.

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP general-purpose amplifier applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
MMBT3906	V_CEO = 40 V, I_C = 200 mA, h_FE = 100–300 (I_C = 10 mA), but C_cb = 5.5 pF and R_θJA = 405 °C/W.	Higher h_FE improves low-current bias stability; lower thermal resistance allows higher continuous power in same layout.	Select MMBT3906 when tighter h_FE tolerance or improved thermal performance is required; verify pinout compatibility (same SOT-23, but pin 1 = emitter for MMBT3906 vs. base for BSR18B).
BC807-40	V_CEO = 45 V, I_C = 500 mA, h_FE = 250–630 (I_C = 100 mA), R_θJA = 350 °C/W, but larger SOT-323 footprint.	Higher current and gain support heavier loads; smaller package not directly interchangeable due to different pad layout.	Choose BC807-40 for higher drive capability where board area permits SOT-323; avoid in space-constrained designs requiring SOT-23.

Compared with MMBT3906 and BC807-40, the BSR18B offers balanced gain linearity across 0.1–100 mA, verified switching timing for digital interfacing, and SOT-23 compatibility with legacy Fairchild designs-making it optimal for cost-sensitive, space-limited amplification where moderate current and thermal margin suffice.

Availability

BSR18B is available at Aetrix Electronics and suitable for audio signal conditioning, discrete logic level translation, and low-power relay driving requiring stable component supply and long-term obsolescence management.

Supply support for BSR18B 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 designer and manufacturer of analog and discrete semiconductors, acquired by ON Semiconductor in 2016; known for robust process technologies and broad portfolio of power and signal devices.

The BSR18B belongs to Fairchild's general-purpose bipolar transistor product line, developed for cost-effective, reliable amplification and switching in consumer, industrial, and computing applications where SOT-23 packaging and predictable DC characteristics are prioritized.

FAQ

What is the maximum continuous collector current rating for the BSR18B?

The BSR18B has a maximum DC collector current (I_C) rating of 200 mA, validated under steady-state conditions at T_A = 25 °C. This rating assumes proper PCB thermal relief and derating per the 1.84 mW/°C slope above ambient. Exceeding this value risks thermal runaway or permanent degradation of the BSR18B's junction integrity.

Does the BSR18B support switching applications, and what are its key timing parameters?

Yes, the BSR18B is qualified for switching use with documented delay time (t_d) = 35 ns, rise time (t_r) = 35 ns, storage time (t_s) = 225 ns, and fall time (t_f) = 75 ns at V_CC = 3.0 V and I_C = 10 mA. These values confirm suitability for digital interface buffering up to ~2 MHz, provided base drive meets specified I_B conditions in the BSR18B datasheet.

What is the pin configuration of the BSR18B in the SOT-23 package?

The BSR18B uses standard SOT-23 pinout: Pin 1 = Base, Pin 2 = Emitter, Pin 3 = Collector. This configuration is explicitly shown in the "1. Base 2. Emitter 3. Collector" diagram on page 2 of the BSR18B Rev. A datasheet. Misalignment with alternate PNP SOT-23 variants (e.g., MMBT3906) may cause circuit failure if substituted without verification.

How does the BSR18B's DC current gain (h_FE) vary with collector current?

The BSR18B's h_FE is specified across five test points: 60 (I_C = 0.1 mA), 80 (1 mA), 110 (10 mA), 60 (50 mA), and 30 (100 mA). This non-monotonic profile reflects typical BJT behavior-peak gain near 10 mA-enabling stable bias design in both low-current sensor interfaces and moderate-drive switching stages using the same BSR18B device.

Is the BSR18B RoHS compliant and halogen-free?

Yes, the BSR18B Rev. A datasheet confirms compliance with RoHS Directive 2011/65/EU and halogen-free status per IEC 61249-2-21. The device contains no lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB), or polybrominated diphenyl ethers (PBDE), and bromine/chlorine content is below 900 ppm-verified for use in environmentally regulated industrial and consumer products requiring the BSR18B.

BSR18B Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-236-3, SC-59, SOT-23-3

Packaging:: Tape & Reel (TR)

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 200 mA

Voltage - Collector Emitter Breakdown (Max):: 40 V

Vce Saturation (Max) @ Ib, Ic:: 400mV @ 5mA, 50mA

Current - Collector Cutoff (Max):: 50nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 110 @ 10mA, 1V

Power - Max:: 230 mW

Frequency - Transition:: -

Operating Temperature:: -55°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-3

BSR18B FAQ

1.How can I place an order for BSR18B through Aetrix?

Please submit a Request for Quotation (RFQ) for BSR18B 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 BSR18B reliable?

The price and inventory of BSR18B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BSR18B is usually 5 days.

3.What payment methods are accepted for BSR18B?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BSR18B transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BSR18B?

BSR18B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BSR18B 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 BSR18B?

For technical support, including BSR18B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BSR18B requirements.

6.How does Aetrix verify that BSR18B is sourced from the original manufacturer or authorized distributors?

All BSR18B 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 BSR18B meets industry standards.

7.What is the process for return or replacement of BSR18B?

All BSR18B units undergo pre-shipment inspection (PSI). If there is an issue with BSR18B, 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 BSR18B part is unused and in its original packaging.

Return procedure for BSR18B:

1.Submit a request within 90 days.

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

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