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From large and cumbersome to small and light, the power adapter is also changing.
When using laptops and smartphones, users want to charge as fast as possible, and the charging power is as small as possible, so equipment manufacturers and power chip manufacturers are struggling to achieve this goal. However, the power adapter also faces many challenges in the miniaturization process. For example, each charger is expected to achieve high energy efficiency at full load, half load, light load and standby. How can we improve energy efficiency for light load? As the number of components increases, the density becomes higher, the arrangement becomes compact, and interference is easily generated. How to achieve high performance, low EMI, and small number of components at the same time? In addition, it can cover the widest range of charging applications from mobile phones to notebooks, and more importantly, the price/performance ratio is high.
To help users solve these problems, ON Semiconductor has introduced the adaptive active clamp flyback controller NCP1568 and 700V half-bridge driver NCP51530, which have been adjusted in terms of topology and performance parameters. According to Jiang Jialiang, senior marketing manager of AC-DC power management at ON Semiconductor's Analog Solutions Division, "The NCP1568ACF controller has advanced features and flexible operation to help provide superior energy efficiency while using SJ FETs or GaN FETs. High-density design is achieved with a small number of external components. The NCP51530 driver is a high-speed, high-performance, rugged power solution that includes AEC Q-100 certification options for automotive applications."
Active Clamp Flyback Topology for Energy Efficient, Low EMI
In a traditional flyback topology, the switch contains a transformer and a Mosfet. Ringing occurs during switching, which produces high frequency EMI, which causes the transformer to leak and dissipate in the buffer or clamp circuit, making it difficult to control and minimize in production. For Mosfet losses, the Rd(on) FET should be chosen to reduce high voltage losses, and a better heat sink may be needed at 90V to reduce energy efficiency. If you don't want to generate EMI, you need the surrounding ringing circuit to absorb it. If you absorb it, it will be lost. Therefore, the more the high frequency, the more the loss, so the traditional flyback topology can't run to high frequency.
In contrast to the active clamped flyback architecture, add a Mosfet and a capacitor on top. Where there is also energy absorption, when Mosfet is off, all energy is stored in the capacitor and reused when needed. As long as the Mosfet's switching voltage is set to zero volts, the lower Mosfet is equal to a zero volt voltage switch, equal to no loss. When Mosfet is turned off, all the energy of EMI loss can be reused and transmitted to the diode, which means that there will be no loss in the whole power conversion process, so that it can be used for high frequency or low EMI while maintaining high energy efficiency. This is the advantage of the active clamp flyback architecture.
Greatly reduce the size of the power adapter
The NCP1568 has three control modes: first, the control mode has an adaptive zero-voltage switching (ZVS) frequency modulation, supports variable Vout, integrated adaptive dead time, and can perform peak current mode control. Second, discontinuous conduction Pass mode and light load mode, optional transition to DCM mode, frequency return, minimum 31kHz frequency clamp, silent jump to eliminate audible noise, standby power consumption less than 30mW; third, high voltage (HV) start, 700V HV start JFET, integrated high voltage switch node detection to optimize ZVS, built-in undervoltage and X2 discharge.
Regarding the adaptive zero-voltage switching frequency, this feature can be adjusted. Jiang Jialiang explained, “For USB Type-C and USB PD applications, you can charge 5V for mobile phones or 20V for notebooks. In addition, depending on the power, the load point The switch will be optimized to reduce the switch conduction loss; the adaptive dead time is also to ensure the best switching state per cycle. The IC needs to adjust the cycle to the light load, standby part, the previous counterattack to achieve very low standby, there may be Sound, you can mute more. When a frequency returns, we can adjust the frequency from 29K to 800Hz, and the middle can change from 29K to 20K or more than ten K. This is not good, so it is the middle frequency. Skip. How to run from the 29K switching frequency to 800Hz? 1K, 2K, 3K, 5K, 10K These people are more likely to hear the frequency skipped, and immediately run to 800Hz, you can also achieve very bass effect, this is Silent jump eliminates the effect of audible clicks