onsemi PN3638A_D74Z

Overview

PN3638A_D74Z from Fairchild Semiconductor is a PNP general-purpose bipolar junction transistor designed for amplification and switching applications with continuous collector current up to 800 mA and V_CEO = 25 V. It features h_FE = 100 at I_C = 50 mA / V_CE = 1.0 V, V_CE(sat) = 0.25 V at I_C = 50 mA / I_B = 2.5 mA, and TO-92 radial ammo packaging (EOL code D74Z), commonly used in low-voltage power control circuits.

For engineers reviewing the PN3638A_D74Z datasheet, pinout, applications, or equivalent options, key selection criteria include its PNP polarity, 25 V V_CEO, 800 mA I_C rating, 100 minimum h_FE at low-current bias, and TO-92 package compatibility with manual or automated through-hole assembly.

Technical Context

The PN3638A_D74Z operates as a silicon PNP BJT fabricated using Fairchild's Process 63, optimized for general-purpose linear amplification and saturated switching. Its DC current gain spans 30–100 depending on operating point (e.g., h_FE ≥ 100 at I_C = 50 mA/V_CE = 1.0 V; h_FE ≥ 20 at I_C = 300 mA/V_CE = 2.0 V), and it supports fast switching with t_on = 75 ns and t_off = 170 ns under specified pulse conditions.

Thermal performance is defined by R_θJA = 200 °C/W and R_θJC = 83.3 °C/W, enabling operation from –55 °C to +150 °C junction temperature. The device exhibits low output capacitance (C_ob = 10 pF) and input capacitance (C_ib = 25 pF), supporting stable high-frequency small-signal gain (h_fe = 1.5 at f = 100 MHz).

Key Specifications

Pinout & Package

PN3638A_D74Z is supplied in a TO-92 plastic package with radial lead configuration per EOL code D74Z (Ammo pack, flat side up, first wire off is collector). Leads are straight, unclipped, and arranged in standard emitter-base-collector (E-B-C) order when viewed with flat side facing outward and leads 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 BC807-40, PN3638A_D74Z offers optimal balance of moderate voltage rating (25 V), high low-current gain (h_FE = 100), and TO-92 radial ammo (D74Z) compatibility-making it ideal for cost-sensitive, through-hole assembled industrial controls where precision biasing and thermal margin matter more than ultra-high voltage or miniaturization.

Availability

PN3638A_D74Z is available at Aetrix Electronics and suitable for DC power switching, low-frequency amplification, relay driver circuits, and level translation interfaces requiring stable component supply across production lifecycles.

Supply support for PN3638A_D74Z 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 devices before its acquisition by ON Semiconductor in 2016. Its legacy products remain widely deployed in industrial and automotive systems.

The PN3638A_D74Z belongs to Fairchild's general-purpose PNP transistor family engineered for robustness and consistency in amplification and switching roles across consumer, industrial, and automotive auxiliary circuits.

FAQ

What is the maximum continuous collector current rating for PN3638A_D74Z?

The PN3638A_D74Z 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 thermal derating at 5.0 mW/°C above 25 °C. Operation at full 800 mA requires adequate PCB copper area or heatsinking to maintain junction temperature below 150 °C. The PN3638A_D74Z datasheet specifies this limit under steady-state DC conditions-not pulsed operation.

Is PN3638A_D74Z pin-compatible with the original PN3638?

Yes, PN3638A_D74Z shares identical TO-92 pinout (E-B-C) and mechanical dimensions with PN3638, but offers improved electrical parameters: higher minimum h_FE (100 vs. 30 at I_C = 50 mA), lower V_CE(sat) (0.25 V vs. 0.3 V), and reduced C_ob (10 pF vs. 20 pF). These enhancements make PN3638A_D74Z a preferred upgrade in new designs, though legacy PN3638 layouts remain fully compatible.

What does the D74Z suffix indicate for PN3638A_D74Z?

The D74Z suffix identifies the packaging configuration: radial TO-92 ammo pack with flat side up and first wire off as collector. This differs from D26Z (reel, emitter-first) and D75Z (ammo, collector-first with flat side up). D74Z ensures consistent orientation for automated insertion and matches mechanical drawings in Fairchild's TO-92 Tape and Reel Data Rev. B1. PN3638A_D74Z is not interchangeable with non-D74Z variants without verifying tape orientation and lead geometry.

Can PN3638A_D74Z be used in linear amplifier applications?

Yes, PN3638A_D74Z is explicitly characterized for linear amplification, with h_FE = 100 at I_C = 50 mA / V_CE = 1.0 V and h_fe = 1.5 at f = 100 MHz. Its low C_ib (25 pF) and stable h_FE across bias points support Class-A preamplifiers up to ~10 kHz. For higher fidelity, ensure proper emitter degeneration and thermal stabilization, as the PN3638A_D74Z lacks built-in compensation networks found in dedicated audio transistors.

What is the thermal resistance from junction to ambient (R_θJA) for PN3638A_D74Z?

The thermal resistance from junction to ambient (R_θJA) for PN3638A_D74Z is 200 °C/W under standard test conditions (free-air, no heatsink, FR-4 board with 1-inch² copper pad). This value assumes minimal PCB copper; adding thermal vias and extended copper pours can reduce effective R_θJA by 20–40%. The PN3638A_D74Z datasheet specifies R_θJA = 200 °C/W as a worst-case reference for conservative thermal design.