onsemi PN3638A

Overview

PN3638A from Fairchild Semiconductor is a PNP general-purpose bipolar junction transistor designed for amplification and switching in low-to-medium power circuits, with confirmed 25 V V_CEO, 800 mA I_C, and TO-92 package. It delivers h_FE = 100 at I_C = 50 mA / V_CE = 1.0 V and supports switching applications up to 300 mA collector current with 75 ns turn-on time.

For engineers reviewing the PN3638A datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP polarity, 25 V breakdown rating, thermal resistance of 200 °C/W (junction-to-ambient), saturation voltage of 0.25 V at 50 mA/2.5 mA drive, and suitability for discrete amplifier stages or logic-level interface switches.

Technical Context

The PN3638A operates as a silicon PNP BJT fabricated in Fairchild's Process 63, optimized for general-purpose linear amplification and saturated switching. Its electrical behavior is defined by DC current gain (h_FE) ranging from 30 to 100 depending on bias conditions, and small-signal parameters including h_fe = 1.5 at 100 MHz and C_ob = 10 pF at 10 V V_CB.

Thermal performance is characterized by R_θJA = 200 °C/W and R_θJC = 83.3 °C/W, with maximum junction temperature rated at +150 °C. Absolute ratings specify V_CEO, V_CB, and V_EB all at 25 V, 25 V, and 4.9 V respectively - confirming robustness for rail-referenced PNP switch topologies.

Key Specifications

Pinout & Package

PN3638A is housed in a standard TO-92 plastic package with straight leads and no lead clip. Pin identification follows the conventional TO-92 emitter-collector-base (ECB) layout when viewed with flat side facing outward and leads pointing downward.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA92 and BC557B, the PN3638A offers optimal balance of speed (75 ns t_on), low saturation voltage (0.25 V), and tight gain specification (100 at 50 mA), making it especially suited for medium-speed, medium-current PNP switching where thermal efficiency and predictable gain matter.

Availability

PN3638A is available at Aetrix Electronics and suitable for audio preamplifiers, logic-level interfaces, DC motor control, power supply sequencing, and discrete analog signal conditioning requiring stable component supply and long-term manufacturability.

Supply support for PN3638A 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete components before its acquisition by ON Semiconductor in 2016.

The PN3638A belongs to Fairchild's legacy general-purpose PNP transistor family, engineered for cost-sensitive, high-volume applications demanding reliable amplification and switching performance in TO-92 packaging.

FAQ

What is the maximum continuous collector current rating for PN3638A?

The PN3638A has a maximum continuous collector current (I_C) rating of 800 mA at T_A = 25°C. This value decreases with rising ambient temperature due to its 5.0 mW/°C derating factor above 25°C, and actual usable current depends on PCB copper area, airflow, and thermal interface. The PN3638A must be operated within its 625 mW total device dissipation limit to avoid junction overheating.

How does PN3638A differ from PN3638 in terms of DC current gain?

The PN3638A provides higher and more tightly specified DC current gain than the PN3638: h_FE = 100 (min) at I_C = 50 mA / V_CE = 1.0 V, versus h_FE = 30 (min) for the PN3638 under identical conditions. This makes the PN3638A preferable for low-base-drive applications such as battery-powered sensor interfaces or precision current mirrors where consistent gain matters.

What is the pin configuration of PN3638A in the TO-92 package?

The PN3638A uses the standard TO-92 ECB pinout: when viewing the flat side of the package with leads pointing downward, the leftmost pin is Emitter, center is Collector, and rightmost is Base. This matches JEDEC TO-92 outline and is verified in Fairchild's packaging documentation - critical for correct PCB layout and avoiding reverse-bias damage during assembly.

Can PN3638A be used as a direct replacement for PN2907A?

No, the PN3638A is not a direct replacement for the PN2907A. While both are PNP transistors in TO-92 packages, the PN2907A has V_CEO = 60 V and h_FE = 100–300, whereas the PN3638A is rated at V_CEO = 25 V and h_FE = 100 (min). Substituting PN3638A in a PN2907A design risks overvoltage failure if collector swings exceed 25 V - always verify voltage margins before interchange.

What is the typical output capacitance (C_ob) of PN3638A and why does it matter?

The PN3638A has a typical output capacitance (C_ob) of 10 pF at V_CB = 10 V and f = 1.0 MHz - half that of the PN3638 (20 pF). This lower capacitance improves high-frequency gain stability and reduces Miller effect in amplifier stages, making the PN3638A more suitable for VHF preamplifiers or fast-switching applications where parasitic capacitance directly impacts bandwidth and rise/fall times.