onsemi PN3643_D75Z

Overview

PN3643_D75Z from Fairchild Semiconductor is an NPN general-purpose bipolar junction transistor (BJT) designed for amplification and switching in low-to-medium power circuits, with V_CEO = 30 V, I_C = 500 mA continuous, h_FE = 100–300 at I_C = 150 mA, and TO-92 package. It is commonly used in audio preamplifiers, relay drivers, and signal conditioning stages.

For engineers reviewing the PN3643_D75Z datasheet, pinout, applications, or equivalent options, key selection considerations include its DC current gain range, collector-emitter saturation voltage of 0.22 V at I_C = 150 mA/I_B = 15 mA, thermal resistance of 200 °C/W, and suitability for linear amplification up to 30 MHz.

Technical Context

The PN3643_D75Z operates as a silicon NPN BJT with fixed emitter-base and collector-base junction structures optimized for general-purpose analog and digital switching. Its h_FE variation across I_C (100–300) supports stable biasing in Class-A amplifiers and robust saturation in logic-level interface circuits.

Thermal design relies on R_θJA = 200 °C/W and P_D = 625 mW at 25°C, derating linearly at 5.0 mW/°C above ambient. Small-signal parameters include f_T ≈ 300 MHz (inferred from h_fe = 2.5 at 100 MHz), C_ob = 8.0 pF, and G_pe = 10 dB at 30 MHz under matched 140 Ω/260 Ω source/load conditions.

Key Specifications

Pinout & Package

PN3643_D75Z is housed in a standard through-hole TO-92 package with 3 leads: Emitter (Lead 1), Base (Lead 2), Collector (Lead 3). The package provides mechanical robustness and adequate thermal dissipation for ≤625 mW operation at ambient temperatures up to 75°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BC547B and MPSA18, PN3643_D75Z uniquely balances 500 mA current delivery, 30 V breakdown, and 30 MHz usable gain-making it optimal for medium-power switching and wideband analog amplification where both headroom and drive strength matter.

Availability

PN3643_D75Z is available at Aetrix Electronics and suitable for audio preamplifiers, relay drivers, and LED current regulators requiring stable component supply, long-term obsolescence management, and traceable lot-controlled sourcing.

Supply support for PN3643_D75Z 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.

The PN3643_D75Z belongs to Fairchild's general-purpose BJT product line, engineered for cost-sensitive, high-volume applications demanding reliability, consistent parametric spread, and broad temperature operation.

FAQ

What is the maximum continuous collector current for PN3643_D75Z?

The PN3643_D75Z supports a maximum continuous collector current of 500 mA at T_A = 25°C, with derating applied above that ambient temperature per the 5.0 mW/°C thermal specification. This rating is validated under steady-state DC conditions and assumes proper PCB copper area for heat dissipation. Exceeding this current risks thermal runaway or permanent degradation of the PN3643_D75Z junction.

Is PN3643_D75Z suitable for switching 24 V loads?

No - PN3643_D75Z has a V_CEO rating of 30 V, which provides only 6 V of margin above 24 V. Transient voltage spikes, inductive kickback, or supply ripple can easily exceed this limit and cause avalanche failure. For 24 V switching, a device with ≥60 V V_CEO, such as the PN3643_D75Z's higher-voltage sibling PN3646, is recommended instead of relying on the PN3643_D75Z.

Does PN3643_D75Z have a documented transition frequency (f_T)?

The PN3643_D75Z datasheet does not explicitly list f_T, but h_fe = 2.5 at 100 MHz implies an f_T ≈ 250–300 MHz. This inferred value aligns with its G_pe = 10 dB and η = 60% performance at 30 MHz. Designers should verify stability margins in RF applications using actual PN3643_D75Z measurements rather than relying solely on extrapolated f_T.

Can PN3643_D75Z replace BC547 in existing designs?

PN3643_D75Z can replace BC547 in many switching applications due to identical TO-92 pinout (E-B-C) and overlapping h_FE range, but caution is needed: BC547's I_C = 100 mA rating is significantly lower than PN3643_D75Z's 500 mA, so thermal design must be re-evaluated. Also, V_CEO differs (45 V for BC547 vs. 30 V for PN3643_D75Z), making PN3643_D75Z unsuitable in higher-voltage circuits originally designed for BC547.

What is the thermal resistance junction-to-ambient for PN3643_D75Z?

The PN3643_D75Z has a specified R_θJA of 200 °C/W under standard JEDEC test conditions (single-layer PCB, 1-inch² copper pad). This value assumes no added heatsinking; real-world performance improves with larger copper areas or thermal vias. At 500 mA and V_CE(sat) = 0.22 V, power dissipation is ~110 mW, resulting in ~22 °C rise above ambient - well within the PN3643_D75Z's −55 °C to +150 °C operating range.