onsemi MPSA18

Overview

MPSA18 from onsemi is an NPN silicon low-noise general-purpose transistor in TO-92 package, rated for V_CEO = 45 V, I_C = 200 mA, and f_T = 100–160 MHz, with h_FE up to 1500 at I_C = 10 mA - widely used in audio preamplifier stages, RF amplifiers, and signal conditioning circuits where low noise and high gain are critical.

For engineers reviewing the MPSA18 datasheet, pinout, applications, or equivalent options, key selection considerations include its 0.5 dB noise figure at 100 Hz (R_S = 1 kΩ), 6.5 nV/√Hz equivalent input noise voltage, TO-92 mechanical compatibility, Pb-free availability (MPSA18RLRPG), and verified performance in low-current, high-gain analog front-ends.

Technical Context

The MPSA18 operates as a discrete NPN bipolar junction transistor optimized for low-noise small-signal amplification. Its design emphasizes high DC current gain (h_FE ≥ 400 at I_C = 10 mA) and minimal broadband noise, supported by low C_cb (1.7–3.0 pF) and C_eb (5.6–6.5 pF) capacitances.

It functions in linear active mode with V_CE(sat) ≤ 0.3 V at I_C/I_B = 10, V_BE(on) ≈ 0.6–0.7 V, and thermal resistance R_θJA = 200 °C/W - enabling stable operation in ambient temperatures from −55°C to +150°C without forced cooling in low-power designs.

Key Specifications

Pinout & Package

Package: TO-92 (Case 29-11, Style 1), through-hole, Pb-free variant available (MPSA18RLRPG). Standard lead configuration with Emitter (Pin 1), Base (Pin 2), Collector (Pin 3).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise NPN transistor applications.

Compared with MPSA18, the 2N5088 offers superior gain at microamp bias but sacrifices bandwidth and voltage rating, while the BC549C provides comparable noise and form factor at lower cost but reduced breakdown margin - making MPSA18 the balanced choice for 45 V, 100+ MHz, low-noise dual requirements.

Availability

MPSA18 is available at Aetrix Electronics and suitable for audio preamplifiers, RF receiver front-ends, and instrumentation signal conditioning requiring stable component supply, long-term manufacturability, and RoHS-compliant sourcing.

Supply support for MPSA18 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

onsemi (formerly ON Semiconductor) is a global semiconductor manufacturer specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The MPSA18 belongs to onsemi's legacy low-noise bipolar transistor family, engineered specifically for high-fidelity analog signal amplification in cost-sensitive, space-constrained applications where TO-92 footprint and proven reliability are essential.

FAQ

What is the maximum collector-emitter voltage rating for the MPSA18?

The MPSA18 has a maximum collector-emitter voltage rating (V_CEO) of 45 Vdc, as specified in the Absolute Maximum Ratings table. This value represents the upper limit before avalanche breakdown occurs with base open. Exceeding this voltage risks permanent device failure, even momentarily. The MPSA18 must be operated within this constraint in all circuit configurations, including transient conditions in audio or RF amplifier designs.

Does the MPSA18RLRPG variant support lead-free soldering processes?

Yes, the MPSA18RLRPG is explicitly designated as a Pb-free (RoHS-compliant) version in the ordering information section, packaged in TO-92 with 2000 units per ammo pack. It meets J-STD-020 moisture sensitivity level (MSL) requirements for standard reflow profiles and is qualified for lead-free soldering at peak temperatures up to 260°C, consistent with IPC-J-STD-020D guidelines.

What is the typical noise figure of the MPSA18 at 1 kHz and how is it measured?

The MPSA18 exhibits a typical noise figure (NF) of 0.5 dB at 1 kHz, measured under conditions of I_C = 100 µA, V_CE = 5.0 Vdc, and source resistance R_S = 10 kΩ. This value reflects its performance as a low-noise amplifier in high-impedance signal paths, such as moving-coil microphone inputs. The MPSA18 achieves this via optimized epitaxial base doping and narrow base width, directly contributing to its 6.5 nV/√Hz equivalent input noise voltage.

Can the MPSA18 be used in switching applications, and what is its saturation voltage?

While optimized for linear amplification, the MPSA18 can operate in switching mode with V_CE(sat) ≤ 0.3 V at I_C = 50 mA and I_B = 5 mA. However, its relatively high storage time (not specified in the datasheet) and lack of guaranteed switching parameters make it less suitable than dedicated switching transistors like the 2N2222A. For reliable digital logic interfacing or power switching, the MPSA18 should only be used where speed and duty cycle are non-critical.

How does the DC current gain (h_FE) of the MPSA18 vary with collector current?

The MPSA18's h_FE varies significantly with I_C: minimum 400 at I_C = 10 mA, rising to 1100 at I_C = 1.0 mA, and peaking near 1500 at I_C = 100 mA. This nonlinearity necessitates careful bias network design - especially in wide-dynamic-range amplifiers - as gain compression or distortion may occur if operating point drifts. Stable biasing around I_C = 1–10 mA is recommended for predictable performance in the MPSA18.