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onsemi BC238BU
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- Part No.:
- BC238BU
- Manufacturer:
- onsemi
- Category:
- Single Bipolar Transistors
- Package:
- TO-226-3, TO-92-3 (TO-226AA)
- Datasheet:
-
BC238BU.pdf
- Description:
- TRANS NPN 25V 0.1A TO-92-3
- Quantity:
- Payment:
- Shipping:
Inventory:9,014
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Product details
Overview
BC238BU from Fairchild Semiconductor is an NPN epitaxial silicon transistor designed for low-noise amplifier and general-purpose switching applications. It features VCEO = 25 V, IC = 100 mA, PC = 500 mW, hFE = 180–460 (Class B), and fT = 85 MHz at VCE = 5 V, IC = 10 mA - enabling use in audio preamplifiers, signal conditioning stages, and discrete logic interfaces.
For engineers reviewing the BC238BU datasheet, pinout, applications, or equivalent options, key selection considerations include its TO-92 package compatibility, Class B hFE range, low VCE(sat) (0.2 V typical at IC = 10 mA), noise figure of 2 dB at 1 kHz, and verified suitability for linear amplification and medium-speed switching in industrial and consumer electronics.
Technical Context
The BC238BU operates as a discrete NPN bipolar junction transistor with fixed-emitter biasing capability and optimized gain-bandwidth trade-off. Its hFE classification (B: 180–460) ensures predictable DC current amplification across production lots, while fT = 85 MHz supports audio-frequency and low-MHz signal amplification without parasitic oscillation.
Designed for operation at TJ ≤ 150°C and TSTG = –55 to +150°C, it maintains stable VBE(on) = 0.62 V (typ.) and Cob = 3.5–6 pF, making it suitable for temperature-stable bias networks and low-capacitance coupling in multi-stage amplifiers.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCEO | 25 V - maximum safe collector-emitter voltage before breakdown under open-base conditions |
| IC | 100 mA - continuous DC collector current rating defining usable output drive capability |
| PC | 500 mW - thermal power limit at TA = 25°C, requiring heatsinking above ~150 mW in enclosed environments |
| hFE (Class B) | 180–460 - guaranteed DC current gain range enabling consistent bias point design in amplifier stages |
| fT | 85 MHz - unity-gain frequency confirming usable bandwidth up to ~10–15 MHz for small-signal amplification |
| VCE(sat) | 0.2 V (typ. at IC = 10 mA, IB = 0.5 mA) - low saturation voltage minimizing conduction loss in switching mode |
| NF | 2 dB @ 1 kHz - low noise figure critical for high-fidelity audio preamplifier input stages |
Pinout & Package
BC238BU is housed in a standard through-hole TO-92 package (3.60 × 4.58 × 1.02 mm), with lead spacing matching JEDEC TO-92 mechanical specifications and compatible with manual soldering and wave soldering processes.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (Emitter) | Current sink terminal | Reference node for bias network; connects to ground or negative rail in common-emitter configuration |
| 2 (Base) | Control input terminal | Receives forward-biased current to modulate collector current; requires series resistor for current limiting |
| 3 (Collector) | Current source terminal | Delivers amplified output current; connects to load and positive supply via collector resistor or direct drive |
Key Features
| Feature | Design Value |
|---|---|
| Low-noise performance | 2 dB noise figure at 1 kHz enables use in microphone preamps and sensor signal conditioning without added noise degradation |
| Guaranteed hFE classification | Class B (180–460) ensures predictable DC operating point stability across manufacturing batches |
| High fT / low Cob ratio | 85 MHz fT with 3.5–6 pF output capacitance supports wideband small-signal amplification up to 10 MHz |
| Low VCE(sat) | 0.2 V typical saturation voltage reduces power dissipation in switching applications below 100 mA load |
Applications
| Audio Preamp Stage | Discrete Logic Level Shifter |
|---|---|
Use Scenario: Amplifying weak signals from electret microphones or piezoelectric sensors in battery-powered voice recorders. IC Role / Device Role / Timing Role: NPN transconductance amplifier in common-emitter configuration with emitter degeneration. Use Value: 2 dB noise figure and 180–460 hFE ensure high SNR and repeatable gain without trimming resistors. | Use Scenario: Converting 3.3 V logic outputs to interface with 5 V TTL inputs in mixed-voltage embedded systems. IC Role / Device Role / Timing Role: Saturated switch providing level translation with fast turn-on/turn-off (ton/toff < 100 ns). Use Value: VCE(sat) ≤ 0.2 V and IC = 100 mA rating enable reliable 5 V pull-up drive with minimal voltage drop. |
| Industrial Sensor Interface | LED Driver (Medium Current) |
Use Scenario: Conditioning analog output from RTD or thermistor bridges in programmable logic controller (PLC) analog input modules. IC Role / Device Role / Timing Role: Linear amplifier stage with fixed bias for offset compensation and gain scaling. Use Value: Stable hFE and low VBE(on) variation (0.55–0.7 V) support accurate 25°C–85°C calibration over time. | Use Scenario: Driving indicator LEDs or small LED arrays (≤ 50 mA per channel) in HMI panels and instrumentation displays. IC Role / Device Role / Timing Role: Constant-current switch controlling LED brightness via base current modulation. Use Value: 500 mW power rating and 0.2 V VCE(sat) allow efficient LED current regulation without external current-sense resistors. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar NPN transistor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| BC547B | VCEO = 45 V, hFE = 200–450, fT = 300 MHz, TO-92 package | Higher voltage rating and bandwidth; higher leakage (ICEO = 15 nA vs. BC238BU's 0.2 nA) | Preferred when >30 V supply rails or >20 MHz signal paths are required; less optimal for ultra-low-noise audio |
| 2N3904 | VCEO = 40 V, hFE = 100–300, NF = 5 dB @ 1 kHz, TO-92 | Lower noise margin and narrower hFE range; wider availability but higher VCE(sat) (0.2–0.3 V) | Suitable for general-purpose switching where noise and precise gain aren't critical; not recommended for low-noise preamp stages |
Compared with BC547B and 2N3904, the BC238BU offers superior low-noise performance (2 dB vs. ≥5 dB) and tighter hFE control (180–460), making it preferable for precision analog amplification, though its 25 V VCEO limits use in higher-voltage switching circuits.
Availability
BC238BU is available at Aetrix Electronics and suitable for audio preamplifiers, industrial sensor interfaces, and discrete logic level shifters requiring stable component supply, long-term obsolescence management, and traceable sourcing.
Supply support for BC238BU 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 BC238BU belongs to the BC237/238/239 family - engineered for low-noise linear amplification and general-purpose switching in cost-sensitive consumer and industrial electronics.
FAQ
What is the hFE range for BC238BU?
The BC238BU is classified as Class B, with a guaranteed DC current gain (hFE) range of 180 to 460 when measured at VCE = 5 V and IC = 2 mA. This specification is explicitly defined in the Fairchild BC237/238/239 datasheet Rev. A2 (August 2002) and applies directly to the BC238BU variant. Designers can rely on this range for stable biasing in amplifier and switching circuits without post-production sorting.
Is BC238BU suitable for audio amplifier input stages?
Yes, BC238BU is specifically suited for audio amplifier input stages due to its 2 dB noise figure at 1 kHz, low VBE(on) variation, and Class B hFE consistency. These characteristics minimize signal degradation in microphone preamps and sensor front-ends. The BC238BU datasheet confirms its low-noise designation within the BC237/238/239 family, distinguishing it from the higher-noise BC237 and BC239 variants.
What is the maximum collector-emitter voltage rating for BC238BU?
The BC238BU has a maximum collector-emitter voltage rating (VCEO) of 25 V under open-base conditions at TA = 25°C. This value is specified in the Absolute Maximum Ratings table of the official Fairchild datasheet and must not be exceeded to avoid device breakdown. Derating is required above 25°C ambient, with junction temperature limited to 150°C.
Does BC238BU have a documented TO-92 pinout configuration?
Yes, the BC238BU uses the standard TO-92 pinout: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector - as confirmed in the "BC237/238/239" datasheet Figure "Package Dimensions" and marked on the device body (flat side facing viewer, leads down). This configuration is consistent across all members of the BC237/238/239 family and validated by Fairchild's mechanical drawings.
Can BC238BU replace BC238B in existing designs?
Yes, BC238BU is functionally identical to BC238B in electrical and mechanical specifications - both share the same VCEO, hFE Class B range, TO-92 package, and pinout. The "U" suffix denotes tape-and-reel packaging per Fairchild's ordering conventions, not a parametric change. Therefore, BC238BU can be used as a drop-in replacement for BC238B in PCB layouts and schematic designs without modification.
BC238BU 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):
- 25 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
BC238BU FAQ
1.How can I place an order for BC238BU through Aetrix?
Please submit a Request for Quotation (RFQ) for BC238BU 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 BC238BU reliable?
The price and inventory of BC238BU are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BC238BU is usually 5 days.
3.What payment methods are accepted for BC238BU?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BC238BU transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for BC238BU?
BC238BU orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your BC238BU 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 BC238BU?
For technical support, including BC238BU datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BC238BU requirements.
6.How does Aetrix verify that BC238BU is sourced from the original manufacturer or authorized distributors?
All BC238BU 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 BC238BU meets industry standards.
7.What is the process for return or replacement of BC238BU?
All BC238BU units undergo pre-shipment inspection (PSI). If there is an issue with BC238BU, 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 BC238BU part is unused and in its original packaging.
Return procedure for BC238BU:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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