In the last few decades, electricity has become very important as a renewable energy. This energy has not only contributed greatly to the development of technology; Rather, it has played a significant role in industry as well as household usages. One of the basic needs of these areas is supplying voltage for the equipment. Power electronic converters are responsible for this task and are used in various applications. Battery chargers, uninterruptible power supplies, and LED drivers are all applications that require very low voltages, and due to their preva‎lence, high-step-down structures have gained a lot of attention. At low voltages, these converters must meet important, challenging and strict standards and requirements in order to be widely used. Few semiconductor elements, low output current ripple, low volume and weight, simple structure and easy control, and high efficiency are among these requirements. Different techniques, to achieve the stated features, have been introduced so far. Using a transformer to reduce the gain is one of these techniques. This method increases the weight, volume and cost of the circuit when isolation is not required. Step-down converters can be used in series to reduce the gain; But this reduces the efficiency of the structure, and for this purpose, two structures are merged together by using a switch. Although the voltage and current stress of this method is high. Other techniques include the use of series capacitor or switched capacitor. But one of the effective techniques in high-step-down structures is the use of coupled inductors, which also gives soft switching potential to the structure, and it is also used in the proposed converter of this thesis. In this thesis a non-isolated high-step-down converter is proposed, which is derived from the zeta converter and provides very low gain using the coupled inductor technique. Although this converter is similar to the zeta converter; But it works very differently. In fact, by reducing the size of the intermediate capacitor in the zeta converter, soft switching is provided for the main switch, both at turning on and off. This feature is true in a wide range of output power. This converter uses minimal magnetic and semi-conductor elements and in its structure there is only one core, one switch, one diode and one magnetic core, and for this reason the structure has very little weight and volume and has a high power density. Also, this structure can be easily designed and easily controlled. Contrary to similar structures, the gain of the proposed converter is controlled by changing the duty cycle, switching frequency, and the value of circuit elements. Also, the efficiency and density of this circuit is very high. To increase the efficiency as much as possible, the diode is replaced with a synchronous rectifier. Because the forward voltage of a diode is higher than its MOSFET counterpart, this substitution increases the efficiency of the structure. The only drawback of this ripple converter is its high output current, which has been tried to be improved. A current reduction cell is added to the output, which causes a very low ripple current to be supplied to the output. This cell is placed in parallel with the output load. This cell consists of a large capacitor and a branch of coupled inductors. This cell does not complicate the structure and does not reduce efficiency. By examining the efficiency of this structure, in the entire output power range, the efficiency of this converter remains more than 96%.

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