[Guide]The continuous and rapid development of Electronic products has continuously improved the requirements for high-efficiency power supply design. The high-efficiency conversion circuit defined in the textbook can no longer meet the actual needs of the market, and achieving high efficiency under rated operating conditions is only one of the requirements of the modern market. A truly competitive power supply design must maintain high efficiency over the entire load and operating voltage range, including under light load and standby conditions.
In this regard, mainstream energy efficiency regulatory agencies (such as the European Commission, ErP / EuP Ready, 80 Plus and Energy Star) have established standards for product power consumption and efficiency (see Figure 1).
Figure 1: Mainstream energy efficiency regulators
Most standards have proposed average efficiency requirements in the range of 10% to 100% of the rated load current, as well as the maximum power consumption requirements allowed under no-load or standby conditions. In practice, different market segments usually have specific requirements based on their final applications.
The following are some examples:
● Desktop computers usually need to run for a long time under light load, so there are specific efficiency requirements for them to run under 10% of the full load. The requirements are also different for specific brands and models.
● For the TV power supply, the most important thing is the efficiency in standby mode. Taking some basic Display and remote control functions into consideration, power consumption of less than 300mW is usually required.
● Since the power adapter can be completely disconnected from the load, it is most important to minimize the no-load power consumption. The no-load power consumption of some mobile phone adapters can even reach below 10mW.
However, in product-level power supply design, efficiency is only one of many performance considerations and trade-offs for designers. Any attempt to improve efficiency must consider its impact on other performance factors, such as ripple, transient performance, noise, and EMI. In the actual product design process, this may require a lot of optimization work to meet the specific requirements of different projects in different markets.
Faced with such complex and diverse needs, it has become increasingly difficult to design power solutions for continuously updated products. Many traditional analog power solutions do not have the flexibility and adjustability required by modern standards, and making full use of digital multi-mode solutions has become the key to high-efficiency power supply design.
HR121x series products are MPS’s second-generation digital PFC + LLC integrated controllers, which provide multiple control modes and excellent design flexibility, which can fully meet the efficiency and performance requirements of various market applications and power levels (see Figure 2) .
Figure 2: Typical application circuit of HR1210 in HR121x series products
The HR121x series products integrate a high-voltage current source, a safety-certified X capacitor discharge circuit and a high-voltage PFC + LLC drive circuit. Compared with competing solutions, its circuit is very simple and hardly requires external components.
In addition, the HR121x series products adopt digital-analog hybrid chip design, so they also inherit the advantages of traditional analog chips in certain aspects, such as corresponding speed, real-time peak current protection, capacitive protection, automatic dead zone adjustment and other functions in the switching cycle .
The digital control core of HR121x combined with re-editable memory provides great flexibility for the overall solution. Through the UART communication port configuration, you can easily control the cooperation between the PFC and LLC two-stage circuits, the switching between different control modes, the switching frequency of key operating points, and the threshold time and recovery method of the protection function. Therefore, the power supply design using HR121x series products can flexibly adapt to the performance requirements of different applications under any load conditions (see Figure 3).
Figure 3: PFC control mode of HR121x series products
The PFC control part of HR121x series products can realize CCM and DCM mixed mode operation:
● HR121x series products can fully work in CCM mode under heavy load conditions to minimize the peak current.
● Under medium load or high input voltage conditions, the CCM and DCM hybrid mode can be used in the same power frequency cycle to achieve the best balance of switching loss and peak current.
● Under light load conditions, HR121x series products can operate in low-frequency DCM or adjustable burst mode to further reduce switching losses.
The switching points of different modes can be adjusted through the internal digital registers of the HR121x series products, so that each part of the efficiency curve can be optimized for different input voltage and load conditions.
The LLC control part of HR121x series products adopts advanced current mode, which has better stability and response speed than traditional voltage mode. In addition, HR121x devices are divided into three different operating modes according to load conditions (see Figure 4).
Figure 4: LLC control mode of HR121x
● Under heavy load conditions, continuous resonant mode is used to ensure zero voltage conduction and minimize RMS current.
● If the device enters the frequency hopping mode under relatively light load conditions, the dead time will be inserted to reduce the equivalent switching frequency and avoid switching to the audible frequency range.
● It can enter the burst mode with adjustable frequency under extremely light load conditions. In this way, while further reducing the switching loss, the influence of audible noise can also be adjusted through frequency control.
Similarly, the switching point and working status of each mode can also be digitally adjusted to achieve the best balance between efficiency and audible noise.
The HR121x product family provides excellent solutions that can meet the efficiency requirements of many applications today, while also providing first-class performance and integration. Its digital core provides designers with the flexibility to further optimize the design, fully meet today’s power efficiency standards, and meet the challenges brought about by the new requirements of next-generation equipment.
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