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

STMicroelectronics BF420-AP

Name: BF420-AP
Brand: STMicroelectronics
SKU: BF420-AP
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: BF420-AP

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

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

Datasheet:: BF420-AP.pdf

Description:: TRANS NPN 300V 0.5A TO-92-3

Quantity:: RFQ Add To RFQ list

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Inventory:7,076

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Product details

Overview

BF420-AP from STMicroelectronics is a silicon epitaxial planar NPN high-voltage transistor in TO-92 package, rated for V_CEO = 300 V, I_C = 500 mA, and P_tot = 830 mW at T_C = 25 °C, designed for RGB cathode current control in video amplifier circuits and hook-switch/dialer functions in telephone wireline interfaces.

For engineers reviewing the BF420-AP datasheet, BF420-AP pinout, BF420-AP application, or BF420-AP equivalent, key selection criteria include high-voltage breakdown (V_CEO/V_CBO = 300 V), DC current gain (h_FE ≥ 50 at I_C = 25 mA), saturation voltage (V_CE(sat) ≤ 0.6 V), transition frequency (f_T = 60 MHz), and thermal resistance (R_thj-amb = 150 °C/W).

Technical Context

The BF420-AP operates as a high-voltage switching and linear amplification device with fully specified breakdown limits: V_CBO = 300 V, V_CEO = 300 V, and V_EBO = 5 V. Its f_T = 60 MHz enables stable operation in video-frequency signal paths up to ~20 MHz under defined bias conditions.

Designed for through-hole PCB assembly, it features low output capacitance (C_CBO = 6 pF, C_EBO = 22 pF) and pulsed-rated saturation parameters (V_CE(sat) = 0.6 V, V_BE(sat) = 1.2 V at I_C = 30 mA/I_B = 5 mA), supporting reliable switching in telephony interface loads.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	300 V - Enables direct drive of high-impedance video cathodes without external clamping.
I_C	500 mA - Supports sustained current in dialer pulse generation and RGB anode sink applications.
h_FE	≥50 at I_C = 25 mA - Ensures predictable base drive requirements in linear amplifier stages.
f_T	60 MHz - Validates usable bandwidth for composite video signal amplification up to 20 MHz.
R_thj-amb	150 °C/W - Requires heatsinking or derating above ~300 mW in still-air environments.
V_CE(sat)	≤0.6 V at I_C = 30 mA - Minimizes power loss during on-state switching in hook-switch control.
C_CBO	6 pF - Limits Miller effect in high-gain video amplifier configurations.

Pinout & Package

TO-92 package: 3-lead through-hole plastic case with standard lead configuration (E-B-C, viewed from flat side with leads down). Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector.

Pin/Terminal	Circuit Role	Design Meaning
Emitter (Pin 1)	Current sink terminal	Connected to ground or low-impedance return path; supports 500 mA continuous conduction.
Base (Pin 2)	Control input	Receives forward-biased current to enable conduction; V_EBO = 5 V limits allowable drive swing.
Collector (Pin 3)	High-voltage output node	Handles up to 300 V reverse bias; connects to video cathode load or telephone line interface.

Key Features

Feature	Design Value
High-voltage capability	V_CEO = V_CBO = 300 V - Eliminates need for series Zener clamping in RGB cathode drivers.
Thermal robustness	T_j(max) = 150 °C - Permits operation in enclosed telephony enclosures with limited airflow.
Low saturation voltage	V_CE(sat) ≤ 0.6 V - Reduces power dissipation in dialer circuit pulsing (600 mA peak).
Controlled junction capacitance	C_CBO = 6 pF, C_EBO = 22 pF - Preserves video signal integrity in broadband amplifier feedback networks.

Applications

Video Amplifier (RGB Cathode Control)

Telephone Wireline Interface

Use Scenario: Driving individual red/green/blue cathodes in CRT-based video monitors with dynamic current modulation.

IC Role / Device Role / Timing Role: High-voltage NPN switch regulating cathode current per color channel in analog video output stage.

Use Value: 300 V V_CEO withstands flyback transients; 60 MHz f_T preserves chroma/luma bandwidth fidelity.

Use Scenario: Implementing hook-switch detection and pulse-dial generation in POTS telephone line interface cards.

IC Role / Device Role / Timing Role: High-voltage switch controlling loop current flow during off-hook and dialing states.

Use Value: 500 mA I_C sustains 20–60 mA loop current across full line impedance range; low V_CE(sat) minimizes heat in sealed housings.

Dialer Circuit

High-Voltage Signal Switching

Use Scenario: Generating standardized 10-pulse-per-second (PPS) dialing waveforms compliant with ITU-T Q.23.

IC Role / Device Role / Timing Role: Current-switching element in astable multivibrator or microcontroller-driven pulse generator.

Use Value: 600 mA I_CM peak rating accommodates transient surge during pulse edge transitions; 150 °C T_j(max) ensures reliability over 10⁵ cycles.

Use Scenario: Isolating or routing high-voltage analog signals in test equipment front-ends or industrial sensor interfaces.

IC Role / Device Role / Timing Role: Voltage-controlled current source enabling precise high-side or low-side signal gating.

Use Value: 300 V breakdown margin prevents latch-up in ±150 V signal rails; 50 h_FE provides stable gain control under varying load conditions.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage NPN transistor applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BC639	V_CEO = 80 V, I_C = 1 A, f_T = 100 MHz	Limited to lower-voltage video/audio stages; unsuitable for 300 V line interface duty.	Select only where system voltage < 60 V and higher f_T is prioritized over breakdown safety margin.
2N6517	V_CEO = 350 V, I_C = 300 mA, h_FE = 20–60	Lower I_C rating restricts use in high-current dialer pulses; wider h_FE spread increases base drive variability.	Prefer when absolute maximum voltage margin > 300 V is required and 300 mA collector current suffices.

Compared with BC639 and 2N6517, the BF420-AP uniquely balances 300 V breakdown, 500 mA current, and 60 MHz bandwidth-making it irreplaceable in legacy CRT video and POTS telephony designs where all three parameters are simultaneously constrained.

Availability

BF420-AP is available at Aetrix Electronics and suitable for video amplifier circuits, telephone wireline interfaces, dialer circuits, and high-voltage signal switching requiring stable component supply across long-lifecycle industrial and telecom equipment programs.

Supply support for BF420-AP 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, Switzerland, specializing in power management, analog, MEMS, and automotive ICs.

The BF420-AP belongs to ST's legacy high-voltage bipolar transistor family, engineered specifically for analog video signal conditioning and telephony line interface applications in the early 2000s.

FAQ

Is BF420-AP RoHS-compliant?

No. BF420-AP was released in February 2003, prior to RoHS Directive 2002/95/EC enforcement. It contains lead in solder and packaging materials per exemption 7a. STMicroelectronics discontinued RoHS conversion for this part due to obsolescence status.

What is the difference between BF420 and BF420-AP?

BF420-AP denotes the same die and electrical specifications as BF420 but shipped in ammopack (tape-and-reel compatible carrier) instead of bulk. Mechanical dimensions, pinout, and all electrical parameters-including V_CEO, h_FE, and f_T-are identical.

Can BF420-AP replace BF421 in a circuit?

No. BF421 is the PNP complementary type with inverted polarity and mirrored ratings (e.g., V_ECO = 300 V). Direct substitution would reverse bias conditions and cause immediate failure. They are intended for push-pull pairs-not drop-in replacements.

What is the maximum safe operating area (SOA) limit at 100 °C case temperature?

At T_C = 100 °C, derated power dissipation is 415 mW (50% of 830 mW). SOA is bounded by V_CEO = 300 V, I_C = 500 mA, and second breakdown limit of 100 V × 100 mA (per ST's preliminary SOA curves in Rev 1 datasheet, page 4).

BF420-AP Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-226-3, TO-92-3 (TO-226AA) Formed Leads

Packaging:: Tape & Box (TB)

Product Status:: Obsolete

Transistor Type:: NPN

Current - Collector (Ic) (Max):: 500 mA

Voltage - Collector Emitter Breakdown (Max):: 300 V

Vce Saturation (Max) @ Ib, Ic:: 600mV @ 5mA, 30mA

Current - Collector Cutoff (Max):: 10nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 50 @ 25mA, 20V

Power - Max:: 830 mW

Frequency - Transition:: 60MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-92-3

BF420-AP FAQ

1.How can I place an order for BF420-AP through Aetrix?

Please submit a Request for Quotation (RFQ) for BF420-AP 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 BF420-AP reliable?

The price and inventory of BF420-AP are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BF420-AP is usually 5 days.

3.What payment methods are accepted for BF420-AP?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BF420-AP transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for BF420-AP?

BF420-AP orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your BF420-AP 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 BF420-AP?

For technical support, including BF420-AP datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BF420-AP requirements.

6.How does Aetrix verify that BF420-AP is sourced from the original manufacturer or authorized distributors?

All BF420-AP 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 BF420-AP meets industry standards.

7.What is the process for return or replacement of BF420-AP?

All BF420-AP units undergo pre-shipment inspection (PSI). If there is an issue with BF420-AP, 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 BF420-AP part is unused and in its original packaging.

Return procedure for BF420-AP:

1.Submit a request within 90 days.

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

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