Low-power, no-Y capacitor primary adjustment charger design
Power scheme introduction
With the popularity of smartphones and tablets. The requirements for mobile phone chargers are also getting higher and higher. The challenge is mainly derived from two aspects. First, low standby power consumption. Since the charger is usually plugged into the outlet, and charging is not performed most of the time. However, they still consume power, thus wasting energy and user money. How to reduce the standby power consumption of these devices, thereby saving power, meeting government regulations, and saving money for users, is clearly a problem that design engineers must face. IEC five-star energy consumption requires that the power consumed by the equipment must be less than 30mW at no load. Second, EMI performance. Because the charger is very small in size and strict in cost control, the use of the filter is limited. On the other hand, the limitation of the primary and secondary leakage currents has led more and more manufacturers to adopt the Y-free capacitor scheme. This poses a great challenge to the design of EMI.
This scheme adopts the 5V@1A flyback converter controlled by UCC28720, introduces a special transformer structure, and successfully removes the Y capacitor. At the same time, the UCC28720 is a primary feedback converter, which eliminates the pupil and secondary feedback lines, saving cost and improving reliability. The UCC28720 integrates high-voltage start-up and FM-amplitude modes, making the standby power consumption of the entire converter less than 10mW in the full voltage range, which is far superior to the five-star standard.
Figure 1 is a schematic diagram.
Figure 1: Schematic diagram of the 5W no-Y capacitor charger
1 Standby power estimation
In the voltage adjustment control mode, the controller operates in frequency modulation (FM) and amplitude modulation (AM) modes, as shown in Figure 2. As can be seen from the figure, in standby mode, the UCC28720 supports a minimum switching frequency of 680 Hz; and the primary peak current is 1/4 of the full load peak current. Therefore, the standby power consumption can be estimated as follows:
It can be obtained from the above formula that the standby power consumption is independent of the transformer inductance and the specific peak current of the converter, and is only related to the designed maximum operating frequency to the minimum operating frequency ratio of the chip and the maximum design peak current and minimum peak current ratio. According to the chip specification:
In this design, the output power is 5W, and the maximum switching frequency is designed to be 70KHz. Therefore, it can be calculated that the theoretical standby power consumption is:
Since the output needs to add a certain dummy load to ensure the control output voltage is stable, the dummy load is generally about 2mW, then the no-load power consumption of the whole machine can be less than 10mW in the full voltage range.
Figure 2: UCC28720 FM and AM mode diagram
Features of PCB filters
Specially designed for easy and fast PCB hole through mounting, safe and effective;
FT110P/FT110PD series are general purpose one-stage common mode filters, high cost performance;
FT120P/FT120PD series are two-stage common mode filters, excellent common and differential mode filtering effect with very compact structure.
FT1200P/FT1200PD series are two-stage filters comprising one common mode and one differential mode, with differential mode filtering effect enhanced.
Introduction of PCB mounting filters
Rated currents: 0.5 to 6A
Available for AC and DC circuits
Optional medical versions (H type)
Plastic or metal shell optional
Custom specific versions available on request
PCB Filter,PCB Mounting Filter,RFI Noise Filter,EMI Filter DC Power
Jinan Filtemc Electronic Equipment Co., Ltd. , https://www.chinaemifilter.com