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Posted on 10 July 2019

A New Generation of Lower Power Consumption Power ICs

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Reducing switching frequency at no load for lower power consumption

Today's environmental concerns are more complex, far-reaching and interconnected than in the past, and using energy more efficiently has become a global mandate. In recent years, consumer power supplies are encouraged to abide by energy-saving specifications, such as California Energy Commission (CEC) energy-saving specifications, ENERGY STAR®, etc.

By Peter Hsieh, Wesley Hsu; Fairchild Semiconductor

 

Meanwhile, lower standby power consumption is also becoming an area of focus. According to industry research, the overall standby power consumption of electronic devices was about 3% to 13% of global energy usage; making it even more important to regulate standby power consumption. Leading mobile phone makers already announced a new cell phone charger standby specification in year 2009 with asterisk marking to identify different level of standby power consumption. For this requirement Fairchild Semiconductor has developed a new PSR controller, the FSEZ1317 with new features such as high-voltage startup circuitry, low operating frequency, low operating voltage and current at no-load and a primary side regulation (PSR) method for reducing the secondary-side feedback circuitry. By using these methods FSEZ1317 not only meets CEC and Energy Star energy-efficiency specifications but also provides less than 30mW standby power consumption. This solution meets the five star rating for powersavings requirements in cell phone chargers.

Introduction

Last year's high oil prices and economic crisis has once again brought the need for energy efficiency in all aspects of electronics as a key focus for global sustainability. In recent years, consumer power supplies must abide by energy-saving specifications, such as California Energy Commission (CEC) energy-saving specifications, ENERGY STAR®, etc., especially in terms of standby losses. Power consumption starts once an electronic is plugged in, even if most of the time, they are in the standby mode. Overall standby power consumption of electronic devices was about 3% to 13% of the total global energy usage. From July 2001 the United States government agencies established a specification for electrical products in that they must not exceed 1W standby consumption for electrical appliances. These new energy-saving standards not only regulate the power supply at different loads outside of the required average efficiency but also defined the minimum standby losses. Table 1 shows the efficiency specifications of ENERGY STAR standards and the acceptable standby losses. One of the most remarkable is that this year leading phone manufacturers announced a new cell phone charger standby specification, a clear definition of a different stand-by loss of a different mark an asterisk. Table 2 shows that for a new cell phone chargers standby losses must be reduced to 30mW below and low standby power converter losses will be an essential requirement for power supply designs in the future.

Energy Start requirement (Energy Star EPS V2.0, 2008)

New Power Consumption Regulation for charger

Analysis the Source of standby losses and New Lower Power Consumption Solution by using Primary Side Regulation Controller FSEZ1317.

Based on the current power system, how to achieve lower power consumption from 0.3W to 30mW could be analyzed from conversional flyback topology of each component in terms of standby losses. Figure 1 shows a 40W flyback topology. For this converter, power consumption is 110mW at 230Vac input. The result is shown as Figure 2.

40W flyback converter schematic

Each components power loss at no load

From this result; standby power loss can be divided into:

Start-up resistor loss (56%): because of start-up resistor for PWM IC turn-on.

1. In order to get a proper start-up for PWM IC from AC line, usually using start-up technology for PWM IC, once PWM IC powered-up, internal start-up circuitry will be disabled. However, there still exist a voltage on start-up resistor and this causes power losses during standby. How to reduce power consumption with high-voltage startup circuit becomes more and more important for the PWM IC.

2. EMI filter capacitor discharge resistor (15%): In order to quick discharge EMI filter capacitor voltage, in case of high-Wattage application usually adds extra discharge resistor parallel to EMI filter capacitor, but for small-watt application the EMI filter capacitor usually no in use.

3. Device switching losses of main loop (13%): In order to stabilize the output voltage, PWM IC must control the duty cycle and frequency, but in standby mode in order to reduce the losses on MOSFET, transformer, secondary side output rectifier and dummy load. PWM IC also reduces duty cycle and frequency in standby mode .Therefore, how to design PWM signal in standby time is also one of the functions for PWM IC.

4. PWM IC's standby consumption (9%): During standby mode, in order to keep PWM IC working, a proper voltage on auxiliary power is necessary. How to work at a lower voltage and operating current for PWM IC during standby mode to reduce power consumption must also be considered.

5. Standby losses of secondary side feedback circuitry (4%): A proper voltage divider at secondary side for feedback loop is necessary but power losses were about 4% of standby losses. For low wattage application by using primary-side regulator technology could help to reduce power consumption.

From above descriptions, some of these challenges could be improved by IC it self. Therefore, improving power IC performance for efficiency, lower cost and power consumption becomes a new milestone for green energy.

A 5W (5V/0.7A) charger using Fairchild Semiconductor’s FSEZ1317 integrated with 700V MOSFET could provide extra low power consumption at charger application. Due to the built-in 500V high-voltage start-up circuit, When the power IC reach the turn-on voltage, this HV start-up circuit will disable and hence, reduce power losses on the start-up circuit. To minimize standby power losses, the green-mode function provides off-time modulation to decrease the PWM frequency linearly at light-load and the minimum frequency is 370Hz at no load condition, while reduce the operation current and permit lower operation voltage, which through using the new technology can easily meet the most of power consumption requirement.

In addition, this new innovative technology uses a Primary Side Regulation (PSR) control method, the use of detection of the voltage waveform from the auxiliary winding, to control the output of a constant voltage and constant current, it cannot only provide a substantial reduction in secondary-side feedback circuit but also reduce the secondary side of the power losses and cost. Since this chip is packaged in SOP8 with a built-in 700V rating MOSFET, the layout for the MOSFET can be eliminated, the device count can be reduced, and the layout space can be greatly saved. Protection to adopt autorestart function includes Output Short Protection (OSP), VDD overvoltage protection (OVP) and Over Thermal Protection (OTP). A builtin frequency hopping function further improves EMI performance. Furthermore, a cable compensation function compensates the voltage drop at the output cable significantly improves the load regulation. Figure 3 is a circuit diagram 3.75W.

Application circuit of 3.75W charger by using FSEZ1317

All the experimentation results are shown in Figure 4~6, the Figure 4 shows the no load power consumption at different AC input voltage. From these results one can see even in the 264VAC AC line, the no load standby power consumption still can be less than 30mW, meet the best five star level of ENERGY STAR’s new power consumption regulation for chargers. Figure 5 shows the output voltage and current characteristic curve. From the result, CV regulation achieves 1.38% @ 90V VAC – 264 VAC input and no load to full load. The CC regulation can achieve 3.6% with fold-back voltage @ 1.5V. The CC regulation range is controlled by 5V~24V VDD range. This CC output performance prevents an unregulated output current when the output voltage is low. The average efficiency is 71.61%@115V and 70.01%@230V that meets Energy Star 2.0 Level V specification (65.5% average efficiency). It offers an enough margin for the mass production tolerances.

Standby mode power consumption at 90Vac~264VAC

Out voltage and output current characteristic

Efficiency at 115Vac and 230Vac

New challenge of Power IC: Lower Power consumption

For green energy, the efficiency usage improvement could help to reduce power losses. An integrated power IC becomes a key feature for efficiency improvements in power management. This could help to reduce total costs, switching losses and improve EMI performance for ‘light, slim and smaller’ power supply designs. This article shows how the FSEZ1317 with internal high-voltage startup circuitry reduces switching frequency at no load for lower power consumption. A novel primary side regulation (PSR) technology could help to reduce the losses at secondary side feedback loop. The alternative method, the Ringing Choke Convertor (RCC) method, has more components, higher cost and a more complex design. Fairchild’s FSEZ1317 reduces components, has lower Bill of Material (BOM) costs, easier design and could become the best solution for charger applications.

 

 

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