onsemi BCX70G

Overview

BCX70G from ON Semiconductor is an NPN epitaxial silicon general-purpose transistor in SOT-23 package, rated for 45 V V_CEO, 200 mA I_C, and 350 mW P_C, with DC current gain (h_FE) of 120–220 at 2 mA and 60–220 at 50 mA, used in low-power switching and amplification circuits such as signal buffering in portable audio and sensor interface stages.

For engineers reviewing the BCX70G datasheet, pinout, applications, or equivalent options, key selection considerations include its 125 MHz f_T, 4.5 pF C_ob, 0.35 V V_CE(sat) at 10 mA/0.25 mA drive, 6 dB noise figure at 1 kHz, and SOT-23 footprint compatibility with space-constrained PCB layouts.

Technical Context

The BCX70G operates as a discrete NPN bipolar junction transistor optimized for linear amplification and digital switching in low-voltage, low-current applications. Its design supports stable h_FE across I_C = 2 mA to 50 mA and V_CE = 1 V to 5 V, with guaranteed breakdown voltages of 45 V (V_CEO, V_CBO) and 5 V (V_EBO).

It features low saturation voltage (0.35 V min at I_C/I_B = 10 mA/0.25 mA), fast switching performance (t_ON = 150 ns, t_OFF = 800 ns under defined R_L/R₁/R₂ conditions), and low noise (6 dB NF at I_C = 0.2 mA, f = 1 kHz), making it suitable for audio preamplifier stages and precision analog front-ends.

Key Specifications

Pinout & Package

SOT-23 plastic surface-mount package with 3-pin configuration, 1.3 mm × 2.9 mm footprint, 1.1 mm height, and gull-wing leads compatible with standard reflow soldering profiles.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar general-purpose transistor applications.

Compared with BCX70G, BC847B offers higher DC gain but reduced bandwidth, while MMBT3904 delivers faster switching and lower saturation voltage at the cost of 5 V lower breakdown rating-selection depends on whether gain stability, RF response, or switching efficiency dominates the design requirement.

Availability

BCX70G is available at Aetrix Electronics and suitable for portable audio interfaces, industrial sensor signal conditioning, and low-voltage logic-level translation requiring stable component supply and long-term obsolescence management.

Supply support for BCX70G 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

ON Semiconductor is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and communication markets.

The BCX70G belongs to ON Semiconductor's general-purpose bipolar transistor product line, designed for cost-sensitive, space-constrained applications requiring reliable amplification and switching performance at low to medium frequencies.

FAQ

What is the maximum collector-emitter voltage rating for BCX70G?

The BCX70G has a maximum collector-emitter voltage (V_CEO) rating of 45 V at T_A = 25°C. This rating is confirmed in the Absolute Maximum Ratings table and applies under continuous DC conditions. Exceeding this voltage risks avalanche breakdown and permanent device failure. Designers should maintain at least 20% derating margin in safety-critical applications, especially at elevated ambient temperatures where V_CEO decreases.

Does BCX70G support high-frequency amplification, and what is its usable bandwidth?

Yes, BCX70G supports high-frequency amplification with a current gain bandwidth product (f_T) of 125 MHz measured at V_CE = 5 V and I_C = 10 mA. Its usable small-signal bandwidth extends reliably to ~10 MHz in common-emitter configurations, limited by parasitic capacitances (C_ob = 4.5 pF) and package inductance. For stable gain above 5 MHz, proper RF layout practices-including short traces and ground plane coupling-are required.

What is the typical saturation voltage of BCX70G, and how does it affect switching efficiency?

The BCX70G exhibits a typical collector-emitter saturation voltage (V_CE(sat)) of 0.35 V at I_C = 10 mA and I_B = 0.25 mA. At higher currents (e.g., 50 mA/1.25 mA), V_CE(sat) rises to 0.55 V. This low saturation voltage directly reduces conduction losses in switching applications-e.g., a 10 mA load dissipates only 3.5 mW in the BCX70G versus >10 mW in higher-V_CE(sat) alternatives-improving thermal performance and battery life in portable designs.

How is the BCX70G marked on the package, and what do the markings indicate?

The BCX70G is marked "AG" on the top surface of its SOT-23 package. This two-character code corresponds to the Fairchild/ON Semiconductor internal lot and process identification system and uniquely identifies the BCX70G variant among other BCX70-series transistors (e.g., BCX70A, BCX70J). The marking is laser-etched and visible under 10× magnification; orientation follows standard SOT-23 pin 1 indicator (notch or dimple), with pin 1 (Base) at the left when the marking is read left-to-right.

Can BCX70G be used in low-noise audio preamplifier stages, and what parameter confirms this capability?

Yes, BCX70G is suitable for low-noise audio preamplifier stages, confirmed by its specified noise figure (NF) of 6 dB at I_C = 0.2 mA, V_CE = 5 V, f = 1 kHz, and R_S = 2 kΩ. This value reflects its ability to amplify weak signals-such as electret microphone outputs-with minimal added noise. To achieve this performance, designers must operate the BCX70G within its recommended bias point, use low-noise passive components, and avoid grounding loops that introduce external interference into the BCX70G signal path.