“Modern product regulations require lower standby power consumption and higher efficiency. The strategy to meet these requirements may be to use complex power sequence control to shut down part of the power system to improve light-load efficiency. In addition, shutting down parts of the power system such as PFC requires the downstream power converter to be designed for a wide input voltage range. Features such as the UCC28056 architecture and burst mode enable the design to meet these modern power requirements, keeping the PFC stage on in all power modes.

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Summary

Modern product regulations require lower standby power consumption and higher efficiency. The strategy to meet these requirements may be to use complex power sequence control to shut down part of the power system to improve light-load efficiency. In addition, shutting down parts of the power system such as PFC requires the downstream power converter to be designed for a wide input voltage range. Features such as the UCC28056 architecture and burst mode enable the design to meet these modern power requirements, keeping the PFC stage on in all power modes.

1 Introduction

As product regulations continue to require improved performance in these key areas, efficiency and standby power consumption have become the focus of attention in offline applications. This concern requires the use of complex power strategies to meet these requirements, such as turning off the PFC in a low-power mode. Although this strategy is effective, it greatly increases the complexity of the system design and also increases the burden of the DC/DC converter design downstream of the PFC, making it unable to handle a wider input voltage range. The UCC28056 device is specifically designed to solve this problem and can maintain high efficiency over the entire load range, allowing designers to keep the PFC on even in low power mode. This application note describes the design decisions for using UCC28056 to optimize the transition mode PFC design to improve efficiency and standby power consumption.

2 Power consumption standard

Table 1 and Table 2 summarize the power consumption requirements of the US Department of Energy (DOE) Class VI for applications with a nameplate output power of 50 mW and above.

Table 1. DOE Class VI (50 W to 249 W)

Table 2. DOE Class VI (>250 W)

Table 3 summarizes the power consumption requirements of the “European Code of Conduct” (CoC) Level II for applications with a nameplate output power of 50 W to 250 W. At the time of writing, the requirement for a nameplate output power greater than 250 W was not known.

Table 3. CoC II level power consumption requirements

It should be noted that the CoC II level considers the light load efficiency point at 10% load, and the efficiency under this load is usually affected by static losses and lower output power. The efficiency is lower at 10% load, so higher efficiency is required at the other four regulation efficiency points to meet the minimum average efficiency.

3 Optimize efficiency and standby power consumption

To illustrate the method of optimizing standby power consumption and efficiency, consider the following 85 VAC to 265 VAC, 165 W design, as shown in Figure 1.

Figure 1. UCC28056 design example

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UCC28056 is used in offline applications to optimize efficiency and standby power consumption.doc