1. Thyristor (SCR) Overview
A thyristor is a four-layer (p-n-p-n) semiconductor device with three terminals: anode, cathode, and gate. Once triggered into conduction by a gate pulse, it remains conducting until the current falls below the holding level. This latching characteristic makes thyristors suitable for high-power AC control applications where they switch at AC zero crossings.
| Package Type | Current Range | Mounting Style | Application Areas |
|---|---|---|---|
| Stud-type / hockey-puck | 100A – 5000A+ | Press-fit / clamp | HVDC, steel mills, traction |
| Capsule / disc type | 500A – 8000A+ | Water/air cooled stack | High power rectifiers, HVDC valves |
| TO-220 / TO-247 | 4A – 40A | Through-hole PCB | Motor control, power supplies |
| TO-65 / TO-83 stud | 12A – 100A | Stud mount | Industrial controls, welders |
| Surface mount (DPAK, etc.) | 0.8A – 8A | SMD PCB | Consumer, low power |
• Thyristor Operating Principles
• Package Types and Form Factors
• Key Electrical Characteristics
2. Major Application Areas
Thyristors are used extensively in applications requiring controlled power delivery in AC circuits.
2.1 Power Rectification
• Controlled rectifiers for DC power supplies
• Battery charging systems
• Electroplating and electrolysis power
• Welding power sources
• Motor drive front-end converters
2.2 AC Power Control
• Light dimming and heating control
• Motor speed regulation (AC phase control)
• Soft-start for motors and transformers
• Static VAR compensation
• AC voltage regulators
2.3 HVDC and Power Transmission
• High voltage DC transmission converters
• Line-commutated converter stations
• Static compensators (STATCOM with thyristors)
• 6-inch and 8-inch high power thyristors
• Series-connected valve assemblies
2.4 Industrial Applications
• Steel mill drives and rolling mills
• Induction heating and melting furnaces
• Crowbar and protection circuits
• Pulse power and capacitor discharge
• Welding and cutting equipment
3. Selection Criteria
Selecting the right thyristor requires careful evaluation of application requirements.
• Average or RMS current rating based on load current
• Repetitive peak off-state voltage (Vdrm / Vrrm)
• Non-repetitive surge current (Itsm) rating
• di/dt and dv/dt withstand capability
• Gate trigger current and voltage requirements
• Thermal resistance and cooling method
• Turn-off time (tq) for fast-switching types
• Isolation voltage and creepage requirements
4. Thyristor Part Number Guide
Thyristor part numbers typically encode key parameters. While conventions vary, the following general patterns are commonly observed.
| Part Number Element | Indicates | Common Examples |
|---|---|---|
| Series prefix | Device type and series | KP, KK, KA, BT, 2N, TIC, ST, C |
| Current rating | Average / RMS current | Numbers indicating current class |
| Voltage grade | Blocking voltage class | Numeric suffix with voltage code |
| Package / type | Package style and speed | Letter suffix for type |
| Grade / class | Performance grade | Industrial, telecom, automotive |
• Chinese-made thyristors often use KP (phase-control thyristor), KK (fast switching thyristor), KA (high-frequency) prefixes
• Voltage grade codes typically indicate hundreds of volts
• Disc-type and stud-type use different numbering systems
• Always verify parameters from official datasheets
