Realize offline auxiliary PSU power supply device with higher breakdown voltage and lower standby current

Today, the need for energy efficiency affects all areas of automation. This includes all kinds of white goods, which were conceived in an era when the concept of home automation was completely different from today. Decades ago, when we started to rely on these devices, the economic and environmental costs of energy were not as important as consumer convenience, but this imbalance has recently changed and people are now working to resolve them.

Author: James Lee, Marketing Manager of ON semiconductor Lighting

Today, the need for energy efficiency affects all areas of automation. This includes all kinds of white goods, which were conceived in an era when the concept of home automation was completely different from today. Decades ago, when we started to rely on these devices, the economic and environmental costs of energy were not as important as consumer convenience, but this imbalance has recently changed and people are now working to resolve them.

Despite the best efforts of manufacturers, many white goods still often require a lot of energy to fulfill their functions, including heating water or air (electric kettle, oven, shower, washing machine), cooling air or other fluids (refrigerator), convection Heating (toaster and oven) or general movement (motor for washing machine/dryer and vacuum cleaner). In a consumer environment, the energy consumption of these devices is almost calculated in kW, which is the largest source of electricity costs for owners.

In addition, more and more consumer devices use more and more complex control functions or user interfaces. These auxiliary functions are essentially low-power applications, such as sensors, displays, and touch panels. Essentially, using a power supply designed to provide high current to power these auxiliary functions can make efficiency very low, especially when these functions need to work without the main power-intensive functions. This has increased the demand for auxiliary offline power supply devices, which can provide relatively low power, less than 40W (typical) DC power through AC power.

The main goal of this is to provide power as efficiently as possible during standby. In order to achieve this goal, the power supply function needs to be implemented in the most cost, space and energy efficiency way.

Product design engineers also need to consider the safety requirements of white goods. In terms of power supply, this usually requires an isolated solution, but in some cases, the level of electrical isolation required by relevant regulations can be achieved through physical design. Because of this, the market’s demand for low-power SMPS solutions (isolated and non-isolated) for the application space of low-power auxiliary offline power supplies continues to grow.

Fully integrated solution

As the semiconductor manufacturing process moves toward higher integration and more robustness, this general trend enables device manufacturers to develop single-chip solutions to achieve offline power conversion. By integrating the switching MOSFET and the control circuit into a single device, it is now easier to design a switching power supply with higher power density to provide an excellent auxiliary power supply. This type of auxiliary power supply can not only be deployed in multiple white goods Area, but also optimized for the power required by the auxiliary functions described above.

Depending on the specific application and function, the power required by the auxiliary power supply will vary, ranging from less than 1W to as high as 70W. ON Semiconductor has a long history of developing solutions for this application area and has a broad and growing device portfolio.

With the growing demand for ultra-low power auxiliary power supplies, ON Semiconductor recently introduced the NCP1067x series of high-voltage switches. This series of switches are specially developed for low-power offline switching power supplies designed with non-isolated (Figure 1) or isolated (Figure 2) designs. It completely integrates the controller and the power MOSFET in a SOIC7 package with a very small size.

Realize offline auxiliary PSU power supply device with higher breakdown voltage and lower standby current

Realize offline auxiliary PSU power supply device with higher breakdown voltage and lower standby current

Although NCP1067x adopts fixed frequency mode to work, it will automatically switch to standby mode when the load drops to reduce power consumption, that is, adopt no-load intermittent mode. Although the device adopts a self-powered design, that is, no auxiliary winding is required on the transformer, if it contains an auxiliary winding, it can be used to realize the automatic recovery overvoltage protection function. In addition, the output short-circuit automatic recovery protection can also be realized through the time-based detection function.

Due to the use of ON Semiconductor’s ultra-high voltage technology, the NCP1067x is also equipped with an RDS(on)Integrated 700V power MOSFET as low as 12Ω. In an open frame configuration connected to a 230V AC power supply, developers can achieve a power supply capable of providing 15.5W. To improve EMI, NCP1067x uses a frequency jitter design, that is, by adding a ±6% variable to the nominal switching frequency. The sweep sawtooth waveform used to apply jitter is generated internally by the device. The non-isolated design uses a feedback pin that applies a small portion of the output voltage to the integrated transconductance amplifier.

Increasing demand for higher breakdown voltage

Another key trend in auxiliary power supply design is to require a higher breakdown voltage (ie BV) on the power MOSFETDS). Usually, this is related to the physical size of the transistor, which means that the higher the breakdown voltage, the larger the transistor required. In many cases, this will result in a solution that is too large and too expensive to be suitable for most target applications.

Most SMPS switches with integrated MOSFETs use planar technology. In order to meet the market’s restrictions on size and cost, there has been a 700V BVDSOf the device. However, BVDSThe higher the value, the greater the power surge and peak voltage protection capabilities provided, so the end product is more robust. For this reason, more and more companies have introduced higher BVDSBut it can still provide low-cost, small-scale BoM solution switches.

To this end, ON Semiconductor has developed a switch module that integrates an SMPS controller and uses its own SUPERFET® 2 Power MOSFET constructed by super junction technology in order to create a 800V BVDS, At the same time, dual-in-line plastic packaged modules can still be used. For the first time, this innovative product series provides manufacturers with a viable solution that can improve product performance and meet market commercial needs.

The FSL5x8 current-mode switch series are packaged in PDIP-7 and include a PWM controller and SUPERFET 2 power MOSFET. Generally, achieving 800V breakdown voltage requires the use of a controller and a separate discrete MOSFET. However, ON Semiconductor’s SUPERFET 2 technology successfully integrated these two devices into a small package.

In this way, designers only need to use a device suitable for isolated (Figure 3) and non-isolated (Figure 4) flyback designs to solve the design problem of high-end low-power offline auxiliary power supplies of approximately 40W.

Realize offline auxiliary PSU power supply device with higher breakdown voltage and lower standby current

Realize offline auxiliary PSU power supply device with higher breakdown voltage and lower standby current

In the NCP1067x and FSL5x8 products, the transconductance amplifier is used as a comparator, allowing designers to more easily develop non-isolated flyback power supplies, thereby optimizing the available board space and minimizing BoM.

When the vast majority of low-power offline PSUs are operating in flyback mode, these two products have been added to ON Semiconductor’s power solution portfolio, bringing new benefits. Through higher integration, Achieve higher performance and reliability, thereby increasing power density and reducing BoM costs.

Although all non-isolated PSU designs can only provide limited power supply, the development outlined in this article shows that a switch suitable for low-end and high-end low-power offline PSU applications can be designed for auxiliary PSUs. Since non-isolated flyback converters are generally more efficient than isolated converters, operating costs can also be realized.

The main purpose of using the auxiliary offline PSU is to reduce the standby current consumed by the end product. By choosing highly integrated devices optimized for applications, developers can now achieve this goal with less board space and the lowest BoM cost.

The Links:   DMF5010NB-FW-BC LC171W03-A4