Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

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

STMicroelectronics BCY59X

Name: BCY59X
Brand: STMicroelectronics
SKU: BCY59X
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

Compare

Part No.:: BCY59X

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-206AA, TO-18-3 Metal Can

Datasheet:: BCY59X.pdf

Description:: TRANS NPN 45V 0.2A TO-18

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:5,155

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

BCY59 from STMicroelectronics is a silicon planar epitaxial NPN small-signal transistor in TO-18 metal package, designed for low-noise audio input stages, driver stages, and preamplifier circuits. It features V_CEO = 45 V, I_C = 200 mA, f_T = 200 MHz, h_FE up to 630 (Gr. X), and NF = 2–6 dB at 1 kHz.

For engineers reviewing the BCY59 datasheet, BCY59 pinout, BCY59 application, or BCY59 equivalent, key selection criteria include low-noise performance at 0.2 mA, high f_T for RF/audio amplification, TO-18 thermal robustness (R_thj-case = 150 °C/W), and complementary pairing with BCY79 for push-pull designs.

Technical Context

The BCY59 operates as a general-purpose NPN amplifier with optimized noise figure and transition frequency for analog signal conditioning. Its planar epitaxial structure ensures stable h_FE across temperature, and pulsed test conditions (300 µs, ≤1% duty) validate switching performance under transient loads.

Designed for discrete low-noise front-end use, it supports DC-coupled gain stages with V_BE(sat) ≤ 0.7 V at 10 mA/0.25 mA and V_CE(sat) ≤ 0.35 V - enabling efficient biasing in battery-powered audio preamps and sensor interface circuits.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	45 V - supports rail voltages up to ±22 V in dual-supply audio stages without breakdown
I_C	200 mA - sufficient for line-driver and medium-current preamp output stages
f_T	200 MHz - enables stable gain up to VHF band in RF buffer or wideband amplifier applications
NF	2–6 dB @ 1 kHz - meets low-noise requirements for microphone preamplifiers and sensor signal chains
h_FE	260–630 (Gr. VIII–X) - allows precise DC bias design with predictable current gain across production lots
R_thj-case	150 °C/W - enables reliable operation at T_j ≤ 175 °C with minimal heatsinking in TO-18 metal can

Pinout & Package

TO-18 metal package with hermetically sealed construction, 3-pin configuration (Emitter, Base, Collector), diameter 5.3 mm, height 12.7 mm, axial lead form. Designed for through-hole mounting and high-reliability thermal conduction to chassis or heatsink.

Pin/Terminal	Circuit Role	Design Meaning
1 (Emitter)	Current sink terminal	Connected to ground or negative rail in common-emitter amplifiers; defines reference for V_BE bias
2 (Base)	Control input	Accepts low-current drive (≤50 mA max) to modulate collector current; requires series resistor for stable biasing
3 (Collector)	Current source terminal	Delivers amplified output current; mounted to metal case for thermal path in high-power analog stages

Key Features

Feature	Design Value
Low-noise operation	NF = 2 dB min @ 1 kHz enables clean signal amplification in microphone and piezoelectric sensor interfaces
High f_T	200 MHz transition frequency supports broadband gain up to 30 MHz with stable phase margin
TO-18 metal can	Hermetic sealing and direct case-to-collector connection provide EMI immunity and 150 °C/W thermal resistance
Graded h_FE bins	Three gain groups (VIII–X) allow matched-pair selection for differential amplifiers and push-pull drivers

Applications

Microphone Preamplifier

Audio Line Driver

Use Scenario: Amplifying weak signals from condenser microphones with minimal added noise.

IC Role / Device Role / Timing Role: Low-noise NPN transconductance stage with emitter degeneration for stable gain and bandwidth.

Use Value: 2 dB NF at 0.2 mA enables >70 dB SNR in portable recording systems without active cooling.

Use Scenario: Driving 600 Ω balanced audio lines over distances up to 10 m.

IC Role / Device Role / Timing Role: Class-A common-emitter output buffer with low V_CE(sat) and high h_FE.

Use Value: 0.35 V saturation voltage at 100 mA reduces power loss and distortion in line-level output stages.

RF Signal Buffer

Sensor Interface Amplifier

Use Scenario: Isolating VHF oscillator outputs from variable load impedance in test equipment.

IC Role / Device Role / Timing Role: Common-emitter broadband amplifier with 200 MHz f_T and low C_CB (3.5 pF).

Use Value: 3.5 pF collector-base capacitance minimizes feedback instability in 50 Ω source-terminated configurations.

Use Scenario: Amplifying low-level thermocouple or strain gauge outputs in industrial data loggers.

IC Role / Device Role / Timing Role: DC-coupled NPN gain stage with low I_CES (0.1 nA) and stable h_FE over temperature.

Use Value: 0.1 nA collector cutoff current prevents offset drift in high-impedance sensor bridges at ambient temperatures.

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
BC549C	Plastic TO-92 package, R_thj-amb = 200 °C/W, f_T = 300 MHz, NF = 4–10 dB	Limited thermal dissipation and higher noise floor; unsuitable for chassis-grounded low-noise designs	Prefer when cost-sensitive PCB space is constrained and thermal load < 150 mW
2N5088	TO-92, h_FE ≥ 300 (min), NF = 1.5 dB @ 1 kHz, but V_CEO = 30 V	Lower breakdown voltage restricts use in ±15 V audio rails; no metal-can EMI shielding	Select only for single-supply ≤24 V systems where ultra-low noise dominates over ruggedness

Compared with BC549C and 2N5088, the BCY59 uniquely combines TO-18 metal-can EMI immunity, 45 V breakdown, and sub-3 dB noise - making it irreplaceable in high-fidelity, chassis-grounded, or thermally demanding analog front-ends.

Availability

BCY59 is available at Aetrix Electronics and suitable for microphone preamplifiers, audio line drivers, and RF signal buffers requiring stable component supply, long-term obsolescence management, and traceable military-grade packaging.

Supply support for BCY59 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, power, and microcontroller solutions for industrial, automotive, and consumer markets.

The BCY59 belongs to ST's legacy bipolar transistor family targeting high-reliability analog signal conditioning - emphasizing low noise, thermal stability, and hermetic packaging for mission-critical audio and instrumentation applications.

FAQ

Is BCY59 suitable for surface-mount assembly?

No. The BCY59 uses a TO-18 metal can with axial leads intended for through-hole mounting. It lacks SMD-compatible terminations or thermal pad design. For SMT alternatives, consider ST's SMBT series or consult Aetrix for qualified drop-in replacements with matching electrical specs and thermal profiles.

What is the maximum continuous collector current at 100°C case temperature?

At T_C = 100°C, derating applies per R_thj-case = 150 °C/W. With T_j(max) = 175°C, allowable ΔT = 75°C → P_tot = 75 / 150 = 0.5 W. Since P_tot = V_CE × I_C, and typical V_CE ≥ 1 V in linear operation, max I_C ≈ 500 mA - but absolute rating remains 200 mA per datasheet limits to ensure reliability and SOA compliance.

Can BCY59 be used in complementary symmetry amplifier stages?

Yes - the BCY79 is its designated PNP complement, sharing identical TO-18 package, voltage ratings (V_CEO = 45 V), and thermal characteristics. Both devices are binned for matched h_FE and V_BE, enabling balanced push-pull output stages in Class-AB audio amplifiers without thermal runaway risk.

Does BCY59 require external base resistors in common-emitter configuration?

Yes. The BCY59 has no internal base resistors. External base biasing (e.g., voltage divider or emitter degeneration) is mandatory to set I_C and stabilize Q-point against β variation and temperature drift. Typical designs use R_B1/R_B2 networks or constant-current sources for precision DC operating point control.

BCY59X Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-206AA, TO-18-3 Metal Can

Packaging:: Bulk

Product Status:: Obsolete

Transistor Type:: NPN

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

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

Vce Saturation (Max) @ Ib, Ic:: 700mV @ 2.5mA, 100mA

Current - Collector Cutoff (Max):: 10nA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 180 @ 2mA, 5V

Power - Max:: 390 mW

Frequency - Transition:: 200MHz

Operating Temperature:: 175°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-18

BCY59X FAQ

1.How can I place an order for BCY59X through Aetrix?

Please submit a Request for Quotation (RFQ) for BCY59X 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 BCY59X reliable?

The price and inventory of BCY59X are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BCY59X is usually 5 days.

3.What payment methods are accepted for BCY59X?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BCY59X transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BCY59X?

BCY59X orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BCY59X 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 BCY59X?

For technical support, including BCY59X datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BCY59X requirements.

6.How does Aetrix verify that BCY59X is sourced from the original manufacturer or authorized distributors?

All BCY59X 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 BCY59X meets industry standards.

7.What is the process for return or replacement of BCY59X?

All BCY59X units undergo pre-shipment inspection (PSI). If there is an issue with BCY59X, 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 BCY59X part is unused and in its original packaging.

Return procedure for BCY59X:

1.Submit a request within 90 days.

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

Tech Hub

2026-09-08 Obsolete Electronic Components: How to Source and Evaluate Replacements

A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.

2026-09-07 TTL vs CMOS Logic Levels: 74HC and 74HCT Compatibility Explained

TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.

2026-09-04 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-02 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…

2026-08-21 What Is an LED Driver? Types, Circuits, Dimming, and Selection

An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…