onsemi PN3643_J61Z

Overview

PN3643_J61Z 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_J61Z datasheet, pinout, applications, or equivalent options, key selection considerations include its DC current gain range, saturation voltage under defined drive conditions, thermal resistance (R_θJA = 200 °C/W), and suitability for linear amplification up to 30 MHz.

Technical Context

The PN3643_J61Z operates as a silicon NPN BJT with fixed-emitter configuration and base-controlled conduction. Its small-signal current gain h_fe = 2.5 at 100 MHz confirms usable RF performance up to VHF band, while amplifier power gain G_pe = 10 dB and collector efficiency η = 60% at 30 MHz indicate optimized operation in Class A or AB amplifier stages.

Thermal design is constrained by R_θJA = 200 °C/W and P_D = 625 mW at 25°C, derating linearly at 5.0 mW/°C above ambient. The device supports continuous collector currents up to 500 mA but requires external base current limiting and heatsinking for sustained high-current switching.

Key Specifications

Pinout & Package

PN3643_J61Z is housed in a standard through-hole TO-92 package with 3 leads. Lead identification follows JEDEC TO-92 outline: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector (flat side facing viewer, leads down).

Key Features

Applications

Equivalent & Alternatives

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

Compared with PN3643_J61Z, MMBT3904LT1G offers surface-mount compatibility but reduced power handling, while 2N3904 provides identical packaging and thermal performance with higher voltage margin-making it ideal for drop-in upgrades in existing TO-92 layouts requiring extended breakdown headroom.

Availability

PN3643_J61Z is available at Aetrix Electronics and suitable for audio preamplifiers, relay driver circuits, and DC motor interface applications requiring stable component supply, long-term manufacturability, and through-hole assembly compatibility.

Supply support for PN3643_J61Z 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.

PN3643_J61Z belongs to Fairchild's general-purpose bipolar transistor product line, engineered for cost-effective, robust amplification and switching in industrial controls, consumer electronics, and legacy system replacements.

FAQ

What is the maximum continuous collector current rating for PN3643_J61Z?

The PN3643_J61Z supports a maximum continuous collector current of 500 mA at T_A = 25°C. This rating assumes proper PCB thermal relief and derating per the 5.0 mW/°C slope above ambient. At elevated temperatures or without copper pour, the safe operating current decreases significantly-designers must verify junction temperature using R_θJA = 200 °C/W and actual power dissipation in the PN3643_J61Z application.

Is PN3643_J61Z suitable for RF amplifier use?

Yes, PN3643_J61Z is validated for RF amplifier use up to 30 MHz, evidenced by G_pe = 10 dB and η = 60% under standardized 30 MHz test conditions. Its h_fe = 2.5 at 100 MHz and C_ob = 8.0 pF further support stable gain in VHF front-end stages, though layout parasitics and bias stability become critical above 20 MHz in practical PN3643_J61Z implementations.

What is the pin configuration of PN3643_J61Z in TO-92 package?

PN3643_J61Z uses standard TO-92 pinout: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector (viewed with flat side facing forward and leads pointing downward). This matches JEDEC TO-92 outline and is identical to 2N3904 and PN2222A-enabling direct physical substitution in through-hole sockets and hand-soldered prototypes where PN3643_J61Z is specified.

Does PN3643_J61Z have a documented thermal shutdown mechanism?

No, PN3643_J61Z is a passive bipolar transistor without integrated thermal protection circuitry. Safe operation relies entirely on external thermal design-such as PCB copper area, ambient airflow, and derating per the 5.0 mW/°C slope. Exceeding T_J = 150°C risks permanent degradation; designers must calculate worst-case junction temperature using P_D, R_θJA, and ambient conditions in each PN3643_J61Z deployment.

Can PN3643_J61Z replace 2N2222A in existing designs?

PN3643_J61Z can replace 2N2222A in many cases due to matching TO-92 package, identical pinout, and overlapping specs (V_CEO = 30 V vs. 30 V, I_C = 500 mA vs. 800 mA, h_FE = 100–300 vs. 75–300). However, 2N2222A has higher I_C and P_D = 1 W-so PN3643_J61Z is appropriate only where load current stays ≤500 mA and power dissipation remains ≤625 mW in the final 2N2222A-replaced PN3643_J61Z circuit.