This design note describes power management techniques implemented in the VIPerPlus series of AC-DC converter ICs that can be used to reduce the standby power consumption of home appliances. By using the VIPerPlus converter, designers of home appliance switching power supplies (SMPS) can meet the most demanding energy-saving regulations in the following ways:
Advanced light load management
Zero power mode (ZPM) automatically turns off the appliance at the end of the operating cycle
We use two VIPerPlus high voltage converter evaluation boards to demonstrate examples of implementing these techniques.
Advanced light load management
As a product of the VIPerPlus series, VIPer01 integrates an 800V avalanche rugged power MOSFET with a fixed frequency PWM current mode controller in a single chip. It integrates high-voltage startup, sense FETs, error amplifiers, and oscillators with frequency jitter. Flyback, buck or buck-boost topologies, as well as a few external components can be used to implement a complete AC-DC converter application.
VIPer01's important features help users comply with energy-saving regulations for light-load power consumption:
Low thresholds for power MOSFETs and internal logic allow ICs to be as low as 4.5V power supply works.
Low gate charge of power MOSFETs and low power consumption of internal logic It tastes very low quiescent current.
Pulse frequency modulation (PFM) reduces the switching frequency at light loads, minimizing frequency-dependent losses.
The following sections describe how these specifications affect actual performance in the real world and report performance measurements of the VIPerPlus board under light load conditions.
VIPer01 application performance
The ST application engineering team tested the operation of the VIPer01 converter using the STEVAL-ISA177V1 evaluation kit, which is a wide input range flyback converter that provides 4.25W for a single 5V output.
Under no-load conditions, the board consumes less than 10mW at 230V AC, and when powered for 250mW loads, its efficiency is higher than 60%, as shown in Figure 1.
Figure 1: No-load and light-load performance of the STEVAL-ISA177V1 evaluation kit
Advanced zero-power architecture
Another VIPerPlus device, VIPer0P, can be used to design switching power supplies for periodic working home appliances, such as washing machines that contain a limited number of operating cycles and usually remain closed between cycles. VIPer0P automatically places the switching power supply in shutdown mode at the end of the operating cycle, and consumes less than 5mW in the off state.
This eliminates the need for bistable electromechanical switches that are commonly used in this design, improves system reliability, and reduces system cost. In fact:
The SMPS can be turned off by a microcontroller that monitors the operation of the appliance and enters a special state where no power is supplied to its output.
Once in this state, the switching power supply is ready to be manually restarted by the user, and the power consumption under the 230V AC power supply is less than 5mW.
This function is a zero-power function, as shown in Figure 2: That is, it enables the system to achieve the zero power consumption defined in Section 4.5 of the IEC 62301 standard. It contains a special idle state ZPM, which is completely off except for the circuit required to exit the ZPM. The only part of the control IC that keeps working is the zero-power logic block, and the 4V regulator that supplies the bias voltage to it.
Figure 2: Zero-Power Functionality of the VIPer0P Converter IC
The overall power consumption of the ZPM consists of two parts: power consumption on the branches ZD1, RG, ZD2, M3; and approximately 1.5 μA quiescent current Iq absorbed by the 4 V regulator and zero-power logic block, plus output to an external circuit The power consumption of the output current.
The power consumption can be estimated as follows:
At an input voltage of 230V AC, the worst-case value is assumed to be RG = 28MΩ VZD1 + VZD2 = 20V, Iq = 2μA, ZPM power dissipation is 4.2mW plus 0.325mW/μA current output to the external circuit.
Example of a zero-power architecture
The demo board STEVAL-ISA174V1 is based on the VIPer0P converter IC and implements a wide input range, non-isolated, dual output flyback converter that provides 6.8W of total power, as shown in Figure 3.
Figure 3: STEVAL-ISA174V1 Evaluation Board for the VIPer0P Converter
It provides 4W power through the -5V output, which is tightly regulated by a voltage divider connected to the non-inverting input of the error amplifier on the feedback pin; it also provides 2.8W to the 7V output, which is passed through the two output windings. The magnetic coupling of the turns ratio is semi-regulated.
ST's application note AN4836 describes this fully-characterized circuit board. The application described here complies with the most stringent regulations for energy-saving design, such as the requirements for external power supply in the European Code of Conduct (CoC) version 5.
The data shown in Figure 4 shows that the application has zero input power in the ZPM state and complies with IEC 62301 Section 4.5. No-load operation meets five-star energy-saving standards.
Figure 4: ZPM input power and no-load input power for the STEVAL-ISA174V1 board
The data in Figure 5 shows that the equivalent 12V/6.8W SMPS formed by connecting the loads on the Vout1 and Vout2 lines meet the ErP Lot 6 Tier 2 requirements in the off mode and has a 10% load efficiency to meet the European Code of Conduct (CoC) Version 5 envisioned goals.
Figure 5: Light Load Performance of the STEVAL-ISA174V1 Board
summary
Today's power supply units require more sophisticated methods to improve performance to meet the latest energy-saving regulations. STMicroelectronics' VIPerPlus high-voltage converters use advanced technology and smart power architectures to meet the growing demand for high-efficiency power supplies for smart appliances that must interface with advanced user interfaces.
The VIPer01 application shows how to easily meet the most stringent energy regulatory requirements for continuous home appliances such as refrigerators. On the other hand, the VIPer0P application demonstrates how to build a clever standby architecture that includes simple interactions with the MCU to reduce the material costs of power for appliances that operate on a periodic basis, such as washing machines.
This SMPS design also provides high reliability and flexibility with only a few components.
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