NXP Semiconductors BF861B,235

Overview

BF861B,235 from NXP Semiconductors is an N-channel symmetrical junction field-effect transistor (JFET) in SOT23 package, designed for low-noise RF and audio preamplifier stages. It delivers 6–15 mA drain current (IDSS), 16–25 mS forward transfer admittance (|yfs|), and ultra-low input capacitance (Ciss ≤ 10 pF) at 1 MHz, enabling high-gain, broadband amplification in compact car radio AM tuner front-ends.

For engineers reviewing the BF861B,235 datasheet, BF861B,235 pinout, BF861B,235 application, or BF861B,235 equivalent, this device is selected for low-noise small-signal amplification where gate-source cutoff voltage (VGSoff = −0.5 to −1.5 V), thermal resistance (Rth(j-a) = 500 K/W), and reverse transfer capacitance (Crss ≤ 2.7 pF) directly impact noise figure and stability in tuned RF circuits.

Technical Context

The BF861B,235 operates as a depletion-mode N-channel JFET with symmetrical source/drain terminals, supporting common-source and common-gate configurations. Its junction-based structure provides inherent linearity and low 1/f noise, with gate-source breakdown voltage (V(BR)GSS = −25 V) and gate cutoff current (IGSS ≤ −1 nA) ensuring robust DC biasing stability.

Thermal performance is defined for FR4 PCB mounting: total power dissipation is rated at 250 mW up to Tamb = 25 °C, derating linearly above that temperature. The device exhibits typical equivalent input noise voltage of 1.5 nV/√Hz at 1 MHz, making it suitable for high-sensitivity analog signal conditioning where noise floor minimization is critical.

Key Specifications

Pinout & Package

SOT23 plastic surface-mounted package (TO-236AB); 3-lead, 1.3 mm × 2.9 mm footprint; JEDEC-compliant outline with 0.95 mm lead pitch and 1.2 mm body height.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise JFET amplifier applications.

Compared with BF861B,235, the BF862,215 offers higher gain and current drive but tighter VGSoff spread, while the J310 provides higher raw transconductance at the expense of surface-mount compatibility and documented RF capacitance specs.

Availability

BF861B,235 is available at Aetrix Electronics and suitable for automotive AM tuner front-ends, portable RF test equipment, and precision audio preamplifiers requiring stable component supply, consistent parametric performance, and long-term obsolescence management.

Supply support for BF861B,235 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

NXP Semiconductors is a global semiconductor company headquartered in Eindhoven, Netherlands, specializing in secure connectivity solutions for automotive, industrial, and consumer applications.

The BF861B,235 belongs to NXP's discrete RF JFET product line, engineered specifically for low-noise, high-frequency analog signal amplification in space-constrained, cost-sensitive consumer and automotive electronics.

FAQ

What is the gate-source cutoff voltage range for BF861B,235?

The BF861B,235 has a gate-source cutoff voltage (VGSoff) ranging from −0.5 V to −1.5 V, measured at ID = 1 μA. This parameter defines the gate bias required to fully deplete the channel and is critical for establishing stable DC operating points in amplifier designs. The BF861B,235's VGSoff spread ensures reliable turn-off behavior across manufacturing lots while allowing flexibility in bias network design.

Does BF861B,235 support symmetrical source/drain operation?

Yes, the BF861B,235 is a symmetrical junction FET, meaning its source and drain terminals are electrically interchangeable. This symmetry simplifies PCB layout in RF matching networks and enables flexible configuration in common-source, common-gate, or cascode topologies. The BF861B,235 pinout (Pin 1 = source, Pin 2 = drain) reflects this physical symmetry, not functional asymmetry.

What is the maximum drain-source voltage rating for BF861B,235?

The BF861B,235 has a maximum drain-source voltage (VDS) rating of 25 V under DC conditions, as specified in its absolute maximum ratings table. This rating applies with the gate open or properly biased, and operation beyond this voltage risks permanent device failure. The BF861B,235 is not intended for high-voltage switching applications but optimized for low-voltage, low-noise amplification.

How does the input capacitance of BF861B,235 affect RF amplifier design?

The BF861B,235 features an input capacitance (Ciss) of ≤10 pF at 1 MHz, which directly impacts high-frequency gain roll-off and impedance matching. In RF amplifier design, this low Ciss enables stable operation beyond 500 MHz without neutralization, reduces loading on preceding stages, and simplifies input network design. The BF861B,235's Ciss value is tightly specified and process-controlled, ensuring consistent bandwidth across production units.

Is BF861B,235 suitable for automotive applications?

The BF861B,235 is not automotive-qualified per NXP's documentation: it lacks AEC-Q101 certification and was not tested to automotive temperature, reliability, or qualification standards. While it is widely used in car radio AM tuners, system-level qualification-including board-level thermal cycling, vibration, and EMC testing-is the customer's responsibility. The BF861B,235 datasheet explicitly states non-automotive qualification status.