onsemi MPSA20

Overview

MPSA20 from onsemi is an NPN silicon general-purpose amplifier transistor in TO-92 package, rated for 40 V_CEO, 100 mA continuous collector current, and 625 mW power dissipation at 25°C ambient - commonly used in low-noise preamplifier stages, signal switching, and interface buffering in consumer audio and industrial control circuits.

For engineers reviewing the MPSA20 datasheet, pinout, applications, or equivalent options, key selection considerations include its 40–400 DC current gain range at 5 mA/10 V, 125 MHz f_T, low 4.0 pF C_obo, and verified noise performance down to 1–10 dB NF across 100 Hz–1 kHz with optimal source impedance matching.

Technical Context

The MPSA20 operates as a medium-speed, low-noise bipolar junction transistor optimized for small-signal amplification and linear switching. Its h_FE spans 40–400 at I_C = 5 mA and V_CE = 10 V, supporting stable biasing across temperature (−55°C to +150°C).

It delivers 125 MHz current-gain bandwidth product under standard test conditions (I_C = 5 mA, V_CE = 10 V, f = 100 MHz), with V_CE(sat) ≤ 0.25 V at I_C/I_B = 10, and exhibits low output capacitance (C_obo ≤ 4.0 pF at V_CB = 10 V) for improved high-frequency stability.

Key Specifications

Pinout & Package

Package: TO-92 (Case 29-11, Style 1), through-hole plastic package with 3.43 mm max height, 4.45–5.20 mm body width, and 2.54 mm lead pitch. Standard marking: "MPSA20" with date code.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN small-signal amplifier applications.

Compared with 2N3904 and BC547B, the MPSA20 offers superior verified noise performance and tighter C_obo specification - making it preferred for analog signal chains demanding <3 dB NF and stable gain up to 10 MHz, while maintaining full pin compatibility in TO-92 layouts.

Availability

MPSA20 is available at Aetrix Electronics and suitable for audio preamplifiers, industrial sensor interfaces, and logic-level switching applications requiring stable component supply, long-term manufacturability, and RoHS-compliant variants (MPSA20G).

Supply support for MPSA20 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 supplier specializing in energy-efficient power management, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The MPSA20 belongs to onsemi's legacy discrete transistor portfolio designed for general-purpose linear amplification and switching - emphasizing reliability, wide temperature operation, and consistent parametric distribution across manufacturing lots.

FAQ

What is the maximum collector-emitter voltage rating for the MPSA20?

The MPSA20 has a maximum collector-emitter voltage (V_CEO) rating of 40 Vdc, as specified in the Absolute Maximum Ratings table. This value represents the highest voltage that can be applied between collector and emitter with the base open before risking device breakdown. Exceeding this rating may cause irreversible damage. The MPSA20 is therefore suited for low-voltage analog and digital circuits operating up to ±20 V supply rails, and must be used with appropriate voltage margin in switching applications where inductive kickback could occur.

Does the MPSA20 have a documented noise figure, and at what conditions is it measured?

Yes, the MPSA20 features documented noise figure contours in its official datasheet (Figure 5–7). At 1 kHz with V_CE = 5 Vdc and I_C = 1.0 mA, the noise figure ranges from ~1.0 dB to 3.0 dB depending on source resistance (R_S). Minimum noise occurs near R_S ≈ 1–3 kΩ. These values are measured with 1 Hz bandwidth and validated per onsemi's standard test setup - making the MPSA20 suitable for low-noise preamplifier stages where signal integrity is critical, such as electret microphone buffers or precision sensor front-ends.

Is the MPSA20 pin-compatible with other TO-92 NPN transistors like the 2N3904?

Yes, the MPSA20 uses the standard TO-92 package with identical pinout: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector - matching the 2N3904, BC547, and most industry-standard TO-92 NPN transistors. However, direct substitution requires verification of electrical parameters: the MPSA20 has lower f_T than the 2N3904 (125 MHz min vs. 300 MHz typ), different h_FE distribution, and superior low-frequency noise. So while PCB layout remains unchanged, circuit performance - especially in high-speed or ultra-low-noise applications - must be revalidated when swapping the MPSA20 into a 2N3904 design.

What is the thermal resistance from junction to ambient (R_JA) for the MPSA20, and how does it affect PCB layout?

The MPSA20 has a thermal resistance of R_JA = 200°C/W when soldered onto a standard FR-4 PCB per datasheet Note 1. This means each watt of power dissipated raises the junction temperature by 200°C above ambient - so at 625 mW, the theoretical rise is 125°C. To maintain safe operation (T_J ≤ 150°C), ambient temperature must stay below 25°C unless heatsinking or copper pour is added. Layout best practices include using ≥1 cm² of 2-oz copper connected to the collector pad, minimizing trace length to reduce thermal impedance, and avoiding placement near heat sources. Derating is required above 25°C at 5.0 mW/°C.

What is the guaranteed minimum DC current gain (h_FE) for the MPSA20 at typical operating conditions?

The MPSA20 guarantees a minimum DC current gain (h_FE) of 40 at I_C = 5.0 mAdc and V_CE = 10 Vdc, with a maximum of 400 under the same conditions. This wide distribution reflects its intended use in applications tolerant of gain variance - such as emitter-degenerated amplifiers or saturated switches where base drive is overdesigned. For bias-critical linear amplifiers, designers should use worst-case h_FE = 40 in calculations and verify stability across the full −55°C to +150°C junction temperature range, where h_FE decreases approximately 0.5%/°C above 25°C.