This post explains for the transistor 2SC3998.

The Part Number is C3998.

The function of this semiconductor is 800V, 25A, NPN transistor.

The package is TO-3PBL Type

Manufacturer: Sanyo Semicon Device

Preview images :

Description

C3998 is 800V, 25A, NPN Triple Diffused Planar Silicon Transistor. 

1. Forward Biased: In order to operate, the base-emitter junction of an NPN transistor must be forward biased, meaning that the base must be connected to a positive voltage relative to the emitter.

2. High Input Impedance: NPN transistors have a high input impedance, which means that they are less likely to draw current from the input source, and are therefore less likely to cause a drop in voltage across the source.

3.. Inverted Output: NPN transistors are known for producing an inverted output relative to their input. That is, if the input signal is high, the output signal will be low, and vice versa. This behavior is due to the way the transistor is designed and is an important characteristic for many electronic applications.

Features:

1. High speed (tf=100ns typ).

2. High breakdown voltage (VCBO=1500V).

3. High reliability (adoption of HVP process).

4. Adoption of MBIT process.

Applications:

1. Ultrahigh-Definition CRT Display

2. Horizontal Deflection Output

Absolute maximum ratings ( Ta=25°C )

1. Collector to Base Voltage: Vcbo = 1500 V

2. Collector to Emitter Voltage: Vceo = 800 V

3. Emitter to Base Voltage: Vebo = 6 V

4. Collector Current: Ic = 25 A

5. Collector Dissipation : Pc = 3.5 W

6. Junction Temperature: Tj = 150°C

7. Storage Temperature: Tsg = -55 ~ +150°C

C3998 PDF Datasheet