TOP225YN is a power supply switching IC manufactured by Power Integrations. It belongs to the TOPSwitch-II series, designed for AC-DC switched-mode power supplies (SMPS) used in many electronic devices. 

This IC combines several circuits into one chip, including a high-voltage MOSFET, PWM controller, startup circuit, and protection circuits, making power supply design simpler and more efficient. 

Main Specifications

• Type: Offline PWM switching regulator (SMPS controller)

• Series: TOPSwitch-II

• Package: TO-220-3

• Input voltage: 85 V – 265 V AC

• Breakdown voltage: 700 V

• Switching frequency: about 100 kHz

• Output power: up to ≈100 W depending on design

• Operating temperature: -40 °C to +150 °C 

Key Features

• Built-in 700 V power MOSFET

• Auto-restart protection

• Current limiting

• Thermal shutdown protection

• High efficiency (up to ≈90%)

• Works with flyback, forward, buck, or boost SMPS circuits 

Typical Applications

Devices where you may find TOP225YN:

• TV power supply boards

• DVD / receiver power supplies

• Battery chargers

• Audio equipment power supplies

• Industrial SMPS power modules 

✅ Simple explanation:
TOP225YN is the main switching chip that converts 220 V AC into low-voltage DC inside many power supplies.

✔️ If you want, I can also show:

• TOP225YN pin configuration (3 pins explanation)

• How to test TOP225YN with a multimeter

• Difference: TOP224YN vs TOP225YN vs TOP248YN (very useful for repair).