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Nexperia USA Inc. BF821,235
- Part No.:
- BF821,235
- Manufacturer:
- Nexperia USA Inc.
- Category:
- Single Bipolar Transistors
- Package:
- TO-236-3, SC-59, SOT-23-3
- Datasheet:
-
BF821,235.pdf
- Description:
- TRANS PNP 300V 0.05A TO-236AB
- Quantity:
- Payment:
- Shipping:
Inventory:6,446
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Product details
Overview
BF821 from Nexperia is a PNP high-voltage bipolar junction transistor in SOT23 package, rated for −300 V VCEO, −50 mA IC, and 50 minimum hFE at −25 mA. It operates as a high-voltage switching or amplification element in off-hook detection, ring signal handling, and line interface circuits within telephony infrastructure.
For engineers reviewing the BF821 datasheet, BF821 pinout, BF821 application, or BF821 equivalent, key selection criteria include verified −300 V collector-emitter blocking capability, low leakage (−10 nA ICBO at −200 V), SOT23 thermal resistance (500 K/W), and compatibility with telephony line voltage transients per ITU-T K.20/K.21.
Technical Context
The BF821 is a silicon PNP BJT optimized for high-voltage linear and switching operation in analog telephony interfaces. Its design centers on sustaining −300 V across C–E with open base and maintaining stable hFE (50–150) under −20 V VCE bias at −25 mA IC.
It exhibits low feedback capacitance (1.6 pF Cre) and 60 MHz fT, enabling stable performance in ringing-frequency signal paths. Thermal design relies on PCB-mounted 1 cm² copper pad to achieve Rth(j-a) = 500 K/W, limiting continuous dissipation to 250 mW at Tamb ≤ 25 °C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCEO | −300 V - supports full telephone line ringing voltage (−170 V peak) with ≥1.8× safety margin |
| IC | −50 mA - sufficient for loop current sensing and relay drive in analog line cards |
| hFE | 50 min @ −25 mA - ensures reliable base drive in low-current off-hook detection circuits |
| VCE(sat) | −800 mV max @ −30 mA/−5 mA - minimizes power loss during active switching in line feed circuits |
| Cre | 1.6 pF - limits capacitive coupling in high-impedance AC-coupled ring detector stages |
| fT | 60 MHz - enables stable gain in 20 Hz–20 kHz audio band without phase shift issues |
| Rth(j-a) | 500 K/W - requires defined 1 cm² copper pad for thermal compliance in sustained line monitoring |
Pinout & Package
SOT23 plastic surface-mount package: 3-terminal, 1.9 mm pitch, 2.9 mm × 1.3 mm × 1.0 mm body; collector-connected tab for thermal conduction to PCB.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Base (B) | Current-controlled input node; requires series resistor to limit IB ≤ −50 mA peak |
| 2 | Emitter (E) | Common reference terminal; connected to negative rail or ground in high-side switch configuration |
| 3 | Collector (C) | High-voltage output node; electrically and thermally tied to PCB copper pad per datasheet layout guidance |
Key Features
| Feature | Design Value |
|---|---|
| High-voltage blocking | −300 V VCEO enables direct connection to POTS line without external voltage clamping |
| Low leakage current | −10 nA ICBO at −200 V ensures minimal standby current in always-on line monitoring |
| Thermal robustness | 150 °C Tj rating with defined PCB pad allows operation in sealed telecom enclosures |
| Fast transition frequency | 60 MHz fT supports clean response in 20 Hz–20 kHz voice-band signal conditioning |
Applications
| Telephony Line Interface | Ringing Signal Detection |
|---|---|
Use Scenario: Monitoring analog PSTN line for on-hook/off-hook state and loop closure in VoIP gateways. IC Role / Device Role / Timing Role: PNP high-side switch controlling current-sense path between line and ground reference. Use Value: −300 V rating withstands −170 V ringing peaks while −50 mA IC handles typical 20–50 mA loop current. | Use Scenario: Detecting presence of 20 Hz AC ringing voltage superimposed on −48 V DC line. IC Role / Device Role / Timing Role: High-impedance AC-coupled amplifier stage biased into linear region for envelope detection. Use Value: 1.6 pF Cre and 60 MHz fT preserve ringing waveform integrity without distortion or attenuation. |
| Off-Hook Supervision | Line Feed Circuit Protection |
Use Scenario: Confirming subscriber handset lift-off by measuring DC loop current change in central office line card. IC Role / Device Role / Timing Role: Current-mirror reference transistor in precision current-sensing branch. Use Value: 50 min hFE ensures predictable base current scaling across temperature for ±5% current measurement accuracy. | Use Scenario: Isolating sensitive control logic from high-voltage transients induced by lightning or load switching on telecom lines. IC Role / Device Role / Timing Role: Clamping element in overvoltage protection network, conducting only above −300 V threshold. Use Value: −300 V VCBO and −10 µA ICBO at 150 °C provide fail-safe transient suppression without false triggering. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar PNP high-voltage transistor applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| BF820 | NPN complement; +300 V VCEO, same package and gain profile | Requires circuit topology inversion; not drop-in for PNP-based bias networks | Select when NPN high-side configuration simplifies existing schematic layout |
| BC807-40 | Lower VCEO (−45 V); higher hFE (250–630); same SOT23 footprint | Unsuitable for direct line voltage exposure; limited to internal board-level signals | Choose only for low-voltage sub-circuits where −45 V rating is sufficient and high gain is prioritized |
Compared with BF821, BF820 offers polarity reversal without sacrificing voltage rating, while BC807-40 trades critical −300 V capability for higher gain and lower cost-making BF821 uniquely suited for primary-line interface roles where absolute voltage endurance is non-negotiable.
Availability
BF821 is available at Aetrix Electronics and suitable for telephony line interface, ringing detection, off-hook supervision, and line feed protection requiring stable component supply across industrial telecom equipment lifecycles.
Supply support for BF821 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
Nexperia is a global semiconductor expert focused on high-volume, high-reliability discrete and logic devices, headquartered in Nijmegen, Netherlands.
The BF821 belongs to Nexperia's high-voltage bipolar transistor product line, engineered specifically for analog telephony, alarm systems, and industrial line-powered sensors where sustained −300 V operation is essential.
FAQ
Is BF821 automotive-qualified?
No. Per Nexperia's revision history (v.4, October 2024), BF821 is explicitly designated as non-automotive. It lacks AEC-Q101 qualification, automotive-grade screening, and extended temperature validation beyond −65 °C to +150 °C ambient. Use in automotive applications is unsupported and voids warranty.
What is the maximum safe continuous power dissipation for BF821?
250 mW at Tamb ≤ 25 °C, provided the device is mounted on a single-sided 1 cm² tin-plated copper pad as specified in Table 6. Derating is required above 25 °C at 0.5 mW/°C due to Rth(j-a) = 500 K/W. Exceeding this limit risks junction temperature exceeding 150 °C.
Can BF821 replace BC857 in a −48 V line interface?
No. While both are PNP SOT23 transistors, BC857 has only −65 V VCEO-insufficient for telephony line surge immunity. BF821's −300 V rating is mandatory for surviving ITU-T K.20/K.21 transients; substituting BC857 would cause catastrophic failure during ringing or lightning events.
Does BF821 require a heatsink in standard telephony designs?
No external heatsink is required. The SOT23 package achieves thermal compliance via PCB copper pad conduction. Nexperia specifies a 1 cm² mounting pad for collector; no additional thermal interface material or mechanical heatsink is needed for ≤250 mW operation at ≤25 °C ambient.
BF821,235 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Nexperia USA Inc.
- Series:
- -
- Package/Case:
- TO-236-3, SC-59, SOT-23-3
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Transistor Type:
- PNP
- Current - Collector (Ic) (Max):
- 50 mA
- Voltage - Collector Emitter Breakdown (Max):
- 300 V
- Vce Saturation (Max) @ Ib, Ic:
- 800mV @ 5mA, 30mA
- Current - Collector Cutoff (Max):
- 10nA (ICBO)
- DC Current Gain (hFE) (Min) @ Ic, Vce:
- 50 @ 25mA, 20V
- Power - Max:
- 250 mW
- Frequency - Transition:
- 60MHz
- Operating Temperature:
- 150°C (TJ)
- Grade:
- Automotive
- Qualification:
- AEC-Q101
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- TO-236AB
BF821,235 FAQ
1.How can I place an order for BF821,235 through Aetrix?
Please submit a Request for Quotation (RFQ) for BF821,235 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 BF821,235 reliable?
The price and inventory of BF821,235 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BF821,235 is usually 5 days.
3.What payment methods are accepted for BF821,235?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BF821,235 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for BF821,235?
BF821,235 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your BF821,235 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 BF821,235?
For technical support, including BF821,235 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BF821,235 requirements.
6.How does Aetrix verify that BF821,235 is sourced from the original manufacturer or authorized distributors?
All BF821,235 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 BF821,235 meets industry standards.
7.What is the process for return or replacement of BF821,235?
All BF821,235 units undergo pre-shipment inspection (PSI). If there is an issue with BF821,235, 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 BF821,235 part is unused and in its original packaging.
Return procedure for BF821,235:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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