a lower voltage (around 1 V), suitable for the CPU. Modern CPU power requirements can exceed 200W, can change very rapidly, and have very tight ripple requirements, less than 10mV. Typical CPU power supplies found on mainstream motherboards use 3 or 4 phases, while high-end systems can have 16 or more phases. One major challenge inherent in the multiphase converter is ensuring the load current is balanced evenly across the n phases. This current balancing can be performed in a number of ways. Current can be measured "losslessly" by sensing the voltage across the inductor or the lower switch (when it is turned on). This technique is considered lossless because it relies on resistive losses inherent in the buck converter topology. Another technique is to insert a small resistor in the circuit and measure the voltage across it. This approach is more accurate and adjustable, but incurs several costs—space, efficiency and money. Finally, the current can be measured at the input. Voltage can be measured losslessly, across the upper switch, or using a power resistor, to approximate the current being drawn. This approach is technically more challenging, since switching noise cannot be easily filtered out. However, it is less expensive than having a sense resistor for each phase. Efficiency There are two main phenomenon impacting the efficiency: conduction losses and switching losses. Conduction losses happen when current is flowing through the components and thus depend on the load. They are caused by Joule effect in the resistance when the transistor or MOSFET switch is conducting, the inductor winding resistance, and the capacitor equivalent series resistance. Losses are proportional to the square of the current in this case. Conduction losses are also generated by the diode forward voltage drop (usually or for schottky diode), and are proportional to the current in this case. Switching losses happen in the transistor and diode when the voltage and the current overlap during the transitions between closed and open states. A schottky diode can be used to minimize the switching losses caused by the reverse recovery of a regular PN diode. The switching losses are proportional to the switching frequency. In a complete real-world buck converter, there is also a command circuit to regulate the output voltage or the inductor current. This circuit and the MOSFET gate controller have a power consumption, impacting the overall efficiency of the converter. Impedance matching A buck converter can