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

STMicroelectronics BCY59IX

Name: BCY59IX
Brand: STMicroelectronics
SKU: BCY59IX
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BCY59IX

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BCY59IX.pdf

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

Quantity:: RFQ Add To RFQ list

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Inventory:7,423

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Product details

Overview

BCY59IX 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, h_FE up to 630 (Gr. X, I_C = 100 mA), f_T = 200 MHz, and NF = 2–6 dB at 1 kHz.

For engineers reviewing the BCY59IX datasheet, BCY59IX pinout, BCY59IX application, or BCY59IX 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 verified complementary pairing with BCY79IX for push-pull designs.

Technical Context

The BCY59IX operates as a general-purpose NPN amplifier with DC current gain graded across three groups (VIII–X) to support precision biasing in low-noise analog signal chains. Its f_T of 200 MHz enables stable operation up to VHF band, while low C_CBO (3.5–6 pF) and C_EBO (11–15 pF) minimize parasitic coupling in high-impedance nodes.

Thermal design is enabled by its metal TO-18 case: R_thj-case = 150 °C/W and R_thj-amb = 384.6 °C/W allow reliable 390 mW dissipation at T_amb ≤ 25 °C. Junction temperature rating of 175 °C supports industrial ambient operation when mounted on heatsinks or chassis.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	45 V - Maximum safe collector-emitter voltage with base open; defines headroom for audio stage supply rails.
I_C	200 mA - Continuous collector current limit; supports medium-drive line-level and preamp output stages.
f_T	200 MHz - Transition frequency at I_C = 10 mA, V_CE = 5 V; enables wideband audio and low-VHF amplification.
NF	2–6 dB @ 1 kHz, 0.2 mA - Noise figure range across gain grades; critical for microphone preamp and phono input sensitivity.
h_FE	260–630 - DC current gain at I_C = 100 mA, V_CE = 1 V; determines bias stability and emitter degeneration requirements.
R_thj-case	150 °C/W - Junction-to-case thermal resistance; enables direct mounting to metal chassis for passive cooling.
V_CE(sat)	0.12–0.7 V - Saturation voltage at I_C = 10–100 mA; impacts power loss and voltage headroom in switching/driver roles.

Pinout & Package

BCY59IX uses the standard TO-18 metal can package with three terminals: emitter (case), base (center lead), and collector (outer lead). The metal case serves as the emitter terminal and provides mechanical rigidity and thermal conduction path.

Pin/Terminal	Circuit Role	Design Meaning
Case (Metal Can)	Emitter	Electrically connected to emitter; must be isolated from PCB ground unless circuit topology requires common-emitter chassis reference.
Center Lead	Base	Control electrode; requires current-limited drive due to h_FE-dependent base current (e.g., ~0.16 mA at I_C = 10 mA, h_FE = 63).
Outer Lead	Collector	Output node; carries full load current and dissipates majority of power; routed away from sensitive analog traces to avoid coupling.

Key Features

Feature	Design Value
Low-noise operation	NF = 2 dB min at 1 kHz enables high-fidelity microphone preamplifiers without added noise floor degradation.
High f_T bandwidth	200 MHz transition frequency supports stable gain up to 30 MHz with proper neutralization, suitable for IF amplifiers.
TO-18 metal package	Provides EMI shielding, superior thermal conduction vs. plastic packages, and mechanical durability in vibration-prone environments.
Gain grading (Gr. VIII–X)	Three h_FE bins enable matched-pair selection for differential stages and consistent bias point setting across production batches.
Complementary PNP pair	BCY79IX offers matched V_CEO, I_C, and thermal specs for Class-A/B push-pull output stages with minimal crossover distortion.

Applications

Audio Preamp Input Stage

RF Driver Amplifier

Use Scenario: Low-level signal amplification from dynamic microphones or magnetic phono cartridges requiring minimal added noise.

IC Role / Device Role / Timing Role: NPN transconductance amplifier with emitter degeneration for linear gain control and DC bias stability.

Use Value: 2 dB NF at 0.2 mA ensures >90 dB SNR in 50 kΩ source impedance applications, preserving signal integrity before op-amp stages.

Use Scenario: Final gain stage in 27–50 MHz CB radio transmitter modules driving 50 Ω antenna loads.

IC Role / Device Role / Timing Role: Class-C tuned RF amplifier with parallel LC collector tank and base bias network.

Use Value: 200 MHz f_T and low C_CBO (≤6 pF) enable >15 dB gain at 40 MHz with <1% harmonic distortion at 100 mW output.

Instrumentation Signal Buffer

Industrial Sensor Interface

Use Scenario: High-input-impedance unity-gain buffer between piezoelectric vibration sensors and ADC front-ends in condition monitoring systems.

IC Role / Device Role / Timing Role: Common-collector (emitter-follower) configured for low output impedance and wide bandwidth.

Use Value: h_FE ≥ 260 ensures <50 Ω output Z_out at 100 kHz, reducing settling time errors in 1 MSPS sampling systems.

Use Scenario: Current-source driver for 4–20 mA loop-powered temperature transmitters operating in -40°C to +85°C ambient.

IC Role / Device Role / Timing Role: Constant-current sink with thermal compensation via on-chip junction sensing.

Use Value: T_j rating of 175°C and R_thj-case = 150 °C/W allow continuous 200 mA operation at 85°C ambient when mounted to metal enclosure.

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; h_FE = 420–800 (min); f_T = 300 MHz; no metal shielding; R_thj-amb = 200 °C/W.	Better high-frequency gain but higher noise (NF ≈ 10 dB) and no EMI shielding; unsuitable for ultra-low-noise mic preamps.	Select for cost-sensitive, non-critical RF gain where chassis mounting and shielding are not required.
2N5088	TO-92; h_FE = 300–600; f_T = 50 MHz; NF = 1.5 dB @ 1 kHz; lower V_CEO = 30 V.	Lower noise floor than BCY59IX but limited voltage headroom; inadequate for 45 V audio rails or RF tank swing.	Select only for battery-powered, low-voltage (<30 V) instrumentation where ultimate noise performance outweighs voltage margin.

Compared with BC549C and 2N5088, BCY59IX uniquely balances low noise, high voltage rating, metal-can EMI immunity, and industrial thermal capability-making it preferred for mission-critical audio and RF driver stages where reliability and signal fidelity are co-constrained.

Availability

BCY59IX is available at Aetrix Electronics and suitable for audio preamplifiers, RF driver stages, and industrial sensor interfaces requiring stable component supply, long-term obsolescence resilience, and traceable lot-controlled sourcing.

Supply support for BCY59IX 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, specializing in analog, power, and microcontroller solutions for industrial, automotive, and consumer markets.

The BCY59IX belongs to ST's legacy bipolar transistor product line, engineered specifically for high-fidelity analog signal conditioning and robust RF amplification in harsh thermal and electromagnetic environments.

FAQ

Is BCY59IX pin-compatible with BCY79IX?

No-BCY59IX is NPN and BCY79IX is PNP; they share identical TO-18 mechanical footprint and thermal specs but opposite polarity. Their pinouts differ: BCY59IX uses case-as-emitter, while BCY79IX uses case-as-collector. Direct substitution is unsafe without circuit rework.

What is the maximum safe continuous power dissipation for BCY59IX at 70°C ambient?

At T_amb = 70°C, derated power is calculated as P_tot = (T_jmax − T_amb) / R_thj-amb = (175 − 70) / 384.6 ≈ 0.27 W. This assumes no heatsink; mounting to a metal chassis reduces R_thj-amb and increases allowable dissipation.

Does BCY59IX require external emitter degeneration for stable DC bias?

Yes-due to h_FE variation across grades (20–630), emitter degeneration (e.g., 10–100 Ω) is strongly recommended to stabilize Q-point against temperature drift and process spread, especially in Class-A audio stages operating above 5 mA I_C.

Can BCY59IX be used in switching applications?

Yes-but with limitations: t_on = 55–150 ns and t_off = 480–800 ns restrict use to ≤200 kHz PWM or digital logic interfacing. For faster switching, consider dedicated switching transistors like BC847B with lower storage time and optimized saturation characteristics.

BCY59IX 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

BCY59IX FAQ

1.How can I place an order for BCY59IX through Aetrix?

Please submit a Request for Quotation (RFQ) for BCY59IX 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 BCY59IX reliable?

The price and inventory of BCY59IX are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BCY59IX is usually 5 days.

3.What payment methods are accepted for BCY59IX?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BCY59IX transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BCY59IX?

BCY59IX orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BCY59IX 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 BCY59IX?

For technical support, including BCY59IX datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BCY59IX requirements.

6.How does Aetrix verify that BCY59IX is sourced from the original manufacturer or authorized distributors?

All BCY59IX 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 BCY59IX meets industry standards.

7.What is the process for return or replacement of BCY59IX?

All BCY59IX units undergo pre-shipment inspection (PSI). If there is an issue with BCY59IX, 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 BCY59IX part is unused and in its original packaging.

Return procedure for BCY59IX:

1.Submit a request within 90 days.

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

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