Quasi resonant flyback converter design specifications and test results

This is especially true for street lighting. Resonant converter can improve the efficiency of power supply, is one of the most popular power supply topology. Due to the improvement of the high power conversion efficiency and the low voltage stress of the secondary rectifier, the LLC resonant converter has attracted much attention. Compared with the traditional light source, LED has the characteristics of high efficiency and long service life. Therefore, it has become the first choice for reducing indoor and outdoor energy consumption. This is especially true for street lighting.

Resonant converter can improve the efficiency of power supply, is one of the most popular power supply topology. Due to the improvement of the high power conversion efficiency and the low voltage stress of the secondary rectifier, the LLC resonant converter has attracted much attention. However, the complexity of the design and high production costs make the LLC resonant converter difficult to quickly put into the market. LLC also faces the problem that it is a large toroidal current, the need to use zero voltage switching power supply. The LLC resonant converter will result in relatively high power loss in light load. When the performance of MOSFET diode is poor, there will be a lot of potential faults and problems in LLC resonant converter. Dual transistor flyback converter is designed to solve the problem of LLC resonant converter, as an alternative. As a switch is added on the high side, the leakage inductance energy is applied to the input current to improve the efficiency. Snubber circuit and loss. Dual flyback topology suitable for 120W switching power supply.

Details of design specifications and test results will be presented below. The double closed quasi resonant flyback topology double switching quasi resonant flyback topology is actually reducing the loss of clamping circuit. In addition, the quasi resonant operation mode of FL6300A reduces the switching losses and guarantees the high efficiency Figure 1 is a brief illustration of the proposed dual resonant flyback converter.

FL7930B is an active power factor correction (PFC) controller, FL6300A is a quasi resonant mode current mode PWM controller for lighting. FAN7382 can drive two high side and low side MOSFETs. The new 600V385 ohm junction, D-PAK package MOSFET is used in the PFC switch and flyback switch. The traditional single switch flyback converter using RCD clamp circuit, the leakage inductance energy into heat loss. Double closed quasi resonant flyback expansion and then use the leakage inductance energy to the input current, the maximum MOSFET voltage into the input voltage. Limiting the maximum voltage of the MOSFET, clamping the input voltage is beneficial to the reliability.

In single stage flyback converter, it is very difficult to control the maximum voltage value of MOSFET, so it often appears to exceed the voltage value, resulting in short circuit or overload fault. The maximum voltage of the MOSFET is limited, and the power ratio of the clamping circuit can be increased without increasing the power consumption of the clamping circuit, so as to improve the low voltage stress of the secondary rectifier.

Figure 1 Schematic diagram of the proposed conversion

Design and evaluation

Here are the specifications for the application of dual tube quasi resonant flyback converters. The range of input voltage should be broad, so as to achieve high efficiency. Rated power of 120W, in order to comply with the specific requirements of LED street lamps. Design indicators are also possible to remove bulky radiators. All power devices are surface packaging, packaging models with D-PAK or D2-PAK.

The minimum switching frequency is set to 45kHz. In order to leave room for the DC input voltage range from 300V to 430V. Considering the drop time of drain source voltage, the maximum value of the input voltage of MOSFET under the working condition is 0.45 300V. This ensures that the magnetizing current is properly reset, and the drain source voltage drops to the input voltage, triggering the MOSFET conduction.