## 3 DC-DC Converters
### Boost Converter  
Boost converters are typically used to boost up the input voltage at the desired voltage level while stepping down the supply current. This converter is categorized as a switched-mode power supply and generally is composed of two semiconductor devices (diode/switching transistor) and storage elements (inductor/capacitor). The boost converter topology is shown in Figure 2.  
A controller is responsible for managing the switch between two states of \"on\" and \"off\". By flowing the current through the inductor during the on state, electrical energy is stored in the magnetic field; then, the capacitor supplies the current to load, and the diode is reverse-biased. During the off state, the diode is forward-biased and allows current to flow through the circuit; then, the stored energy will transfer to the load.  
The boost converter can operate in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM) which is determined by the effect on the current of the inductor [33]. In DCM, all energy stored in the inductor will be consumed in each cycle, there will be no energy and current for part of the time, and the inductor current will reach zero during a switching cycle. In CCM, the inductor current in each cycle is greater than zero, and some parts of the energy of each cycle remain to meet the next cycle. The usage of boost converters offers several benefits:  
* Continuous input current
* Has the smallest possible number of components
* Simple drive circuit due to the grounded switch used in this topology In contrast, this converter has some drawbacks such as [34]:
* Requiring a large capacitor size
* Poor efficiency for very large duty cycles
* Non-isolated input from the output
* High switching noise  
The input and output voltages in the boost converter have a direct relationship with the duty cycle of the pulses which can be described as follows:  
\[\frac{V_{out}}{V_{in}}=\frac{1}{1-D} \tag{17}\]  
where \(V_{out}\), \(V_{in}\), and \(D\) are the output voltage of the converter, the input voltage, and the converter's duty cycle, respectively. Regarding the value of \(0<D<1\), it is clear that the output voltage is always higher than the input voltage.  
For converters that have a high current output, the use of a switch instead of a diode in the output looks quite reasonable. Synchronizing in the power converters means replacing the switch instead of the diode; and here, a synchronous boost converter with two switches is considered for analysis. In cases where the large voltage drop across the diode is not desirable, a synchronous converter can be used to improve efficiency and power losses. If the current level stays the same in both synchronous and non-synchronous topologies, the voltage drop of the switch will be less than the diode, resulting in lower power dissipation and heat generated in the semiconductor [35]. For duty cycles of more than 40%, the efficiency of a synchronous boost converter would be greater than non-synchronous [36]. However, ideal semiconductor devices are considered in this paper, and the power losses and temperatures of this topology would not be different with the nonsynchronous boost converter.  
Figure 2: Circuit diagram of the conventional boost converter.