High-performance current-mode PWM controller meets green power design requirements

With the development of the market and people's widespread concern about environmental issues, low-cost, low standby power consumption and high-efficiency power ICs are becoming more and more popular. Reducing system standby power consumption and improving system conversion efficiency have become the development direction of green power ICs. Today's power applications are becoming more and more widespread, and in most cases, the power supply is in standby mode. Although the power consumed by a single power supply in standby mode is relatively small, the huge amount of usage in the entire market has resulted in a considerable total power consumption, accounting for 15% or more of the total power consumption of the entire power supply. After the rapid development of power IC technology in recent years, most products on the market can meet the 300mW standby power consumption requirement specified by Energy Star EPS2.0. Today, ultra-low standby power consumption technology has become popular. The minimum standby power consumption can reach 30mW in power supplies below 30W, and it is expected to be lower in the future.

In the fierce market competition environment, Xi'an Xinpai integrates technological advantages and strengthens R&D management to continuously improve the high-performance green power chip product line. Based on the existing SW265X series, SW253G and SW2263, the latest series of high-efficiency, ultra-low standby power consumption green power chips such as SW2273, SW2801 (QR mode) and SW2306 (QR mode) are launched. In order to meet market demand, Xinpai has launched a high-performance, low-cost, current-mode PWM controller ---SW2604. The chip has simple peripheral circuits and flexible system design; its standby power consumption is less than 200mW, which is suitable for adapters, set-top box power supplies, small appliances and LED lighting. This article will focus on the technical characteristics and application design considerations of SW2604.

Figure 1: SW2604 internal circuit reference block diagram

Technical features of SW2604

SW2604内部电路参考框图如图1所示。该电源控制器可工作在典型的反激电路拓扑中，构成简洁的AC/DC 转换器；在85~265V的宽电压范围内可提供高达12W的连续输出功率；借助优化的电路设计并结合高性价比双极型制造工艺，最大程度节约了产品的整体成本。SW2604内部电路如图1所示。芯片内部启动电路被设计成一种独特的电流吸入方式，可利用功率开关管的本身放大作用完成启动（开关管Ic对Ib的放大），从而显著降低了启动电阻的功率消耗。在输出功率较小时，Ic将自动降低工作频率，从而实现了极低的待机功耗；在功率管截止时，内部电路将功率管反向偏置，直接利用双极型晶体管的CB高耐压特性，大幅提高功率管的耐电压能力直到700V高压，这保证了功率管的安全；芯片内部还提供了完善的防过载、防饱和功能，可实时防范过载、变压器饱和、输出短路等异常状况，提高了电源可靠性。SW2604主要特点如下：

A. Adjustable operating frequency

The operating frequency of SW2604 is adjustable by the external CT capacitor. The internal current source of the chip charges the CT capacitor with a constant current of 100μA to form the rising edge of the clock. When the charging voltage reaches 2.5V, the internal circuit will discharge the CT with a pull-down current of 1.9mA to form the falling edge of the clock and complete a clock cycle. For bipolar power switches, the effect of storage time on switching loss needs to be considered, and the switching frequency is usually set below 70KHz.

B Over temperature protection function

The SW2604 chip has an integrated over-temperature protection function. When the temperature inside the chip reaches 140°C, the thermal protection circuit will be activated, pulling down the clock signal, reducing the switching frequency and power consumption. The switching frequency decreases as the temperature increases until the oscillator is turned off. See Figure 2.

Figure 2: The SW2604 chip has an integrated over-temperature protection function.