| In recent years, the electronic systems are more and more widely used in many application areas with the rapid development of electronics technology. More and more types of electronic equipment are springing up. People's life and work have deeper ties with these equipments. Power supply is the essential module in any Electronic product. Due to the high demands of the consumer E-products, there is an increasing requirement for the power supply.Aiming at the high requirement of the adapter and charger application of portable E-products, a rapid dynamic response and high-precision CV/CC flyback AC-DC converter, employing primary side regulation (PSR) scheme, is designed in this thesis to improve the output accuracy and response ability. Compared with the conventional secondary feedback converter, the PSR topology omits the optical coupler and precise voltage source, simplifying the circuit structure and the cost are reduced. The proposed converter operates in pulse frequency modulation (PFM) mode. When working in CV mode, the output voltage is sensed by sampling the voltage on the auxiliary winding. The voltage sampled is then compared with a reference voltage by error amplifier. The switching frequency is controlled by the signal generated by comparing the error voltage from EA with the digital exponential wave voltage from the digital assistant CV mode, realizing the constant voltage output. The compensation module detects the switch frequency on real-time by adopting digital technology to generate the compensation current, which is decreasing as the increase of switch frequency. The compensation current is flowed from FB port and injects into the pull-down resistor of auxiliary winding, compensating the output voltage loss caused by the charging cable resistance. Meantime, the compensation current injects the primary current sense resistor from CS port to adjust the primary peak voltage dynamically, improving the CV response ability. In CC mode, the demagnetization time is tested through the auxiliary winding and the CC module adjusts the switching frequency, the product of which and demagnetization time is 1/2. The primary peak voltage is maintained constant simultaneously. Then, the constant output current with inductance compensation is obtained, the output accuracy is immune to the unstable primary inductance. Based on the method, the circuit and layout design of the system controller is proposed in this paper.A control IC for the proposed CV/CC converter has been fabricated in NEC 1?m 5V/650V HVCMOS process and the performance is verified by a 5V/1.2A prototype. The experimental results show that the standby power is lower than 140mW in a wide range of universal-input ac voltage from 85 V to 265 V. In CV mode, the output precision is within ±1.5%, the line regulation is ±0.5% and load regulation is ±0.9%, the conversion efficiency is over 72.3%; when the load steps from idle to heavy, the minimum value of ouput voltage is 4.16V and the maximum undershoot time is 7.4ms. In CC mode, the output precision is ±2.2%, the line regulation is within ±1.8% and load regulation within ±1.1%, the conversion efficiency is above 70.1%. Therefore, the proposed control chip has a promising application in low power CV/CC flyback AC-DC converter. |
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