2SC4781 bipolar transistor — Specifications & Equivalents

About the 2SC4781

The 2SC4781 is an NPN bipolar transistor with a collector–emitter voltage (V_CEO) rating of 30 V and a continuous collector current (I_C) of 4 A. It can dissipate up to 0.9 W and is rated to a junction temperature of 150 °C. It is supplied in the TO92 package.

At a glance

• Type: NPN bipolar transistor
• Max collector–emitter voltage (V_CEO): 30 V
• Max collector current (I_C): 4 A
• Transition frequency (f_T): 170 MHz
• Power dissipation (P_D): 0.9 W
• Max junction temperature (T_J): 150 °C
• Package: TO92
• Manufacturer: Multi-source (JIS registered part number)

Typical applications

Judging from its ratings the 2SC4781 is generally applied in RF and high-speed switching stages.

A transition frequency (f_T) of 170 MHz indicates the frequency range over which useful current gain remains available.

Biasing and absolute maximum ratings

Absolute-maximum breakdown limits are V_CEO 30 V, V_CBO 30 V and V_EBO 10 V (magnitudes). The emitter–base rating is the easiest to overlook and is often only a few volts, so protect the junction against reverse drive.

Dissipation is capped at 0.9 W, and that figure assumes the datasheet's mounting and ambient conditions — derate it for your own thermal design.

Choosing a replacement for the 2SC4781

A drop-in substitute for the 2SC4781 must be the same NPN type and offer a collector–emitter rating of at least 30 V, a collector current rating of at least 4 A and a transition frequency of at least 170 MHz for the same bandwidth.

Mechanically, check the replacement against the TO92 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Because 2SC4781 is a JIS-registered part number rather than one vendor's proprietary series, it is produced by several manufacturers. Datasheet figures vary slightly between them, so check the datasheet of the brand you actually buy — this also makes like-for-like sourcing easier.

Where the application switches inductive loads or runs near the voltage limit, keep extra headroom rather than choosing a part that only just meets the original numbers.

Frequently asked questions

What is the 2SC4781?

The 2SC4781 is an NPN bipolar junction transistor (BJT). It is rated for 30 V collector-emitter and 4 A continuous collector current.

What is the maximum voltage of the 2SC4781?

Maximum collector-emitter voltage (Vceo) is 30 V, and collector-base (Vcbo) is 30 V.

How much current can the 2SC4781 handle?

Continuous collector current is rated at 4 A, with dissipation limited to 0.9 W.

What package does the 2SC4781 come in?

It is listed in TO92. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 2SC4781?

This page lists 17 candidate equivalents matched on electrical ratings and package. Any replacement should meet or exceed the original voltage, current and dissipation figures and use a compatible drive level.