C945 (2SC945) — 50V 150mA General-Purpose NPN Audio/Switching BJT (TO-92)

Overview

The C945 (officially 2SC945 or KSC945) is a general-purpose NPN bipolar junction transistor originally developed by NEC and Toshiba, and manufactured globally by onsemi (Fairchild) and UTC. Housed in a through-hole TO-92 plastic package, it is the undisputed "workhorse" NPN transistor of Asian electronics manufacturing — the Eastern hemisphere counterpart to the Western 2N3904 and European BC547.

Featuring a collector-emitter voltage ( $V_{CEO}$ ) of $50\text{V}$ , continuous collector current of $150\text{ mA}$ , high transition frequency of $300\text{ MHz}$ , and ultra-low noise figure ( $NF \approx 0.5\text{ dB}$ ), the C945 is found in virtually every imported Chinese electronics assortment kit, PC ATX power supply auxiliary circuit, consumer AM/FM radio, LED flasher, and DIY hobbyist project.

Quick reference


Transistor Type	General-Purpose Audio / High-Frequency Switching NPN BJT
Package	TO-92 (3-pin through-hole) / SOT-23
Collector-Emitter Voltage ( $V_{CEO}$ )	$50\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$60\text{ V}$ max
Continuous Collector Current ( $I_C$ )	$150\text{ mA}$ max
DC Current Gain ( $h_{FE}$ )	$70$ to $700$ (Classified by gain rank: R, O, Y, GR, BL)
Transition Frequency ( $f_T$ )	$300\text{ MHz}$ typ ( $150\text{ MHz}$ min)
Noise Figure ( $NF$ )	$0.5\text{ dB}$ typ ( $3.0\text{ dB}$ max at $1\text{kHz}$ )
Total Power Dissipation ( $P_D$ )	$400\text{ mW} \dots 625\text{ mW}$
Complementary PNP Pair	A733 (2SA733)
Pinout Standard (Japanese JIS)	`E - C - B` (Pin 1: Emitter, Pin 2: Collector, Pin 3: Base)

Pinout (TO-92 Package - Japanese JIS Standard)

Looking at the flat front face with leads pointing downward:

text

        ┌─────────┐
        │  TO-92  │
        │  C945   │
        └─┬───┬───┬─┘
          1   2   3
          E   C   B

Pin	Name	Type	Description
1	`EMITTER`	Emitter Terminal	Emitter (Connect to ground or emitter degeneration resistor)
2	`COLLECTOR`	Collector Terminal	Collector (Center lead; connected to load or supply rail)
3	`BASE`	Base Terminal	Base control input (Right lead; driven with base current)

(Note: Standard Japanese 2SC945 parts follow E-C-B. However, certain Western-targeted variants like Fairchild's KSC945C with a "C" suffix use E-B-C. Always check with a multimeter or component tester).

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Breakdown	$V_{(BR)CEO}$	50	—	—	V	$I_C = 1.0\text{mA}, I_B = 0$
Collector-Base Breakdown	$V_{(BR)CBO}$	60	—	—	V	$I_C = 100\ \mu\text{A}, I_E = 0$
Emitter-Base Breakdown	$V_{(BR)EBO}$	5.0	—	—	V	$I_E = 10\ \mu\text{A}, I_C = 0$
Collector Cutoff Current	$I_{CBO}$	—	—	100	nA	$V_{CB} = 60\text{V}, I_E = 0$
DC Current Gain ( $h_{FE}$ )	$h_{FE}$	70	200	700	—	$I_C = 1.0\text{mA}, V_{CE} = 6.0\text{V}$
Collector Saturation Voltage	$V_{CE(sat)}$	—	0.10	0.30	V	$I_C = 100\text{mA}, I_B = 10\text{mA}$
Transition Frequency	$f_T$	150	300	—	MHz	$I_C = 10\text{mA}, V_{CE} = 6.0\text{V}$
Noise Figure	$NF$	—	0.5	3.0	dB	$I_C = 0.1\text{mA}, V_{CE} = 6\text{V}, f = 1\text{kHz}$

$h_{FE}$ Classification Ranks

Rank	$h_{FE}$ Range	Common Identifier
R	$40 \dots 80$	Red
O	$70 \dots 140$	Orange
Y	$120 \dots 240$	Yellow (Most Common)
GR	$200 \dots 400$	Green (High Gain Audio)
BL	$350 \dots 700$	Blue (Super High Gain)

Common mistakes

Swapping with 2N3904 or BC547 without checking pinout:
- C945 (2SC945 JIS): Emitter - Collector - Base (Pin 1: E, Pin 2: C, Pin 3: B)
- 2N3904 (USA): Emitter - Base - Collector (Pin 1: E, Pin 2: B, Pin 3: C)
- BC547 (Europe): Collector - Base - Emitter (Pin 1: C, Pin 2: B, Pin 3: E) Directly plugging a C945 into a PCB designed for 2N3904 connects the Base to the Collector line, preventing the circuit from functioning.

Notes

Suffix Guide: 2SC945 is the full Japanese Industrial Standard (JIS) part number; C945 is the standard top-mark abbreviation printed on the physical TO-92 body; KSC945 is the onsemi/Fairchild part number.