2SC478 bipolar transistor — Specifications & Equivalents

About the 2SC478

The 2SC478 is an NPN bipolar transistor with a collector–emitter voltage (V_CEO) rating of 25 V, a continuous collector current (I_C) of 0.12 A and a DC current gain (h_FE) of minimum 20. It can dissipate up to 0.3 W and is rated to a junction temperature of 200 °C. It is supplied in the TO18 package.

At a glance

• Type: NPN bipolar transistor
• Max collector–emitter voltage (V_CEO): 25 V
• Max collector current (I_C): 0.12 A
• DC current gain (h_FE): minimum 20
• Transition frequency (f_T): 100 MHz
• Power dissipation (P_D): 0.3 W
• Max junction temperature (T_J): 200 °C
• Package: TO18
• Manufacturer: Multi-source (JIS registered part number)

Typical applications

Judging from its ratings the 2SC478 is generally applied in RF and high-speed switching stages and small-signal amplification and general-purpose switching.

A transition frequency (f_T) of 100 MHz indicates the frequency range over which useful current gain remains available.

The quoted current gain of minimum 20 determines the base drive needed: divide your target collector current by the minimum h_FE, not the typical figure, when sizing the base resistor.

Biasing and absolute maximum ratings

Absolute-maximum breakdown limits are V_CEO 25 V, V_CBO 50 V and V_EBO 1 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 0.3 W, and that figure assumes the datasheet's mounting and ambient conditions — derate it for your own thermal design.

Choosing a replacement for the 2SC478

A drop-in substitute for the 2SC478 must be the same NPN type and offer a collector–emitter rating of at least 25 V, a collector current rating of at least 0.12 A, current gain in the same ballpark as minimum 20 and a transition frequency of at least 100 MHz for the same bandwidth.

Mechanically, check the replacement against the TO18 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.

Because 2SC478 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 2SC478?

The 2SC478 is an NPN bipolar junction transistor (BJT). It is rated for 25 V collector-emitter and 0.12 A continuous collector current.

What is the maximum voltage of the 2SC478?

Maximum collector-emitter voltage (Vceo) is 25 V, and collector-base (Vcbo) is 50 V.

How much current can the 2SC478 handle?

Continuous collector current is rated at 0.12 A, with dissipation limited to 0.3 W.

What is the hFE of the 2SC478?

DC current gain (hFE) is quoted as minimum 20. Size base drive from the minimum value so the transistor saturates fully across production spread.

What package does the 2SC478 come in?

It is listed in TO18. Verify the pinout of the specific variant, as one outline can carry different pin assignments.

What can I use to replace the 2SC478?

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.