TOP224Y

PMIC - AC DC Converters, Offline Switchers: TOP224Y Application Field and Working Principle

Introduction

TOP224Y is a vertically integrated primary-side regulation flyback converter by Power Integrations. It is designed for off-line applications such as adapter, LED driver, and other power supplies. In fact, it enables high-efficiency and low-cost system design with a single-stage configuration and primary-side control. This mostly eliminates the cost and complexity of secondary-side circuitry, allowing for better system performance.

Application Field

TOP224Y is mainly used for universal input of AC mains, as well as open-frame switched-mode power supplies. Its performance is ideal and reliable for applications such as AC adapters, consumer electronics, white goods, medical products, LED drivers and more. Moreover, it features user-friendly control, high efficiency, and low electromagnetic emission and noise level.

Features

• Optimized for flyback applications
• Operates from universal AC input
• Primary-side regulation
• Input voltage range from 55 V to 440 V
• Low standby power
• Low noise operation
• Built-in antenna for interference monitoring
• Undervoltage lockout (UVLO) circuitry
• Fail-safe protection against open-loop operation
• Linear post-regulation simplifies output voltage setting
• Built-in slope compensation

Working Principle

TOP224Y is a highly integrated, off-line flyback converter with a primary-side control. It has internal startup and controlling circuitry, including an integrated linear post-regulation stage. The device accepts a universal AC input and provides a regulated DC output.

TOP224Y uses a flyback transformer for current sensing and voltage conversion. An internal FET switch is used in the primary circuit. A feedback winding on the transformer is used to sense the output voltage (or current) and detect its regulation point. The control circuitry then adjusts the duty of the internal FET switch to maintain the output voltage or current.

The main components of the TOP224Y operating circuit, from top to bottom, include the voltage rectification circuit, the startup circuit, the MPL-loop control circuit and the overload protection circuit.

The voltage rectification circuit uses the AC input to charge the capacitor C2; when the capacitor is discharged, the capacitor will be recharged and the internal FET is turned off. The startup circuit utilizes the charge of C2 to determine the charging voltage at the beginning of the cycle, when the voltage is higher than the rated voltage, the protector launch the starting circuit. The MPL loop control circuit consists of an optocoupler U1, a UVLO, an overcurrent sample and an output voltage comparator. Its main effect is to achieve output voltage regulation, overcurrent protection and soft switching.

The overload protection circuit is connected to the output voltage sense feedback winding of the flyback transformer. When the output voltage is abnormal, the overload protection circuit will open the FET by the voltage divider network. Finally, the soft-start circuit and the linear post-regulator circuit affect the steady-state output voltage of the converter.

Conclusion

TOP224Y is an integrated single-stage flyback converter with primary-side control for off-line applications, designed for universal AC input applications that require primary-side regulation. It has optimized performance and improved system efficiency, allowing for more cost-effective and reliable designs. In addition, it supports a variety of functions, such as low input standby power and linear post-regulation, as well as built-in Automatic Overtemperature Protection, Under Voltage Lock Out (UVLO), and soft-start circuit.