DC-DC converters are widely used in portable electronic devices like mobile phones and laptops and are primarily powered with batteries. These applications consist of many sub-circuits which provide different voltage levels to different modules of the system. DC-DC converters also make solar harvesting easier and there are such converters that maximize energy harvesting for solar cells, wind turbines, and more. They are known as power optimizers. With V L {\displaystyle V_{\text{L}}} equal to V i − V o {\displaystyle V_{\text{i}}-V_{\text{o}}} during the on-state and to − V o {\displaystyle -V_{\text{o}}} during the off-state. Therefore, the increase in current during the on-state is given by: The inductor's main function is to limit the current slew rate through the power switch. This action limits the otherwise high-peak current that would be limited by the switch resistance alone. The key advantage for using an inductor in switching regulators is that an inductor stores energy. This energy can be expressed in Joules as a function of the current by: A switching regulatoris a circuit that uses a power switch, an inductor, and a diode to transfer energy from input to output. Figure 15. In discontinuous mode the inductor fully discharges and then the inductor voltage rests at zero.

Switching regulators offer three main advantages compared to linear regulators. First, switching efficiency can be much better. Second, because less energy is lost in the transfer, smaller components and less thermal management are required. Third, the energy stored by an inductor in a switching regulator can be transformed to output voltages that can be greater than the input (boost), negative (inverter), or can even be transferred through a transformer to provide electrical isolation with respect to the input (Figure 4).The "increase" in average current makes up for the reduction in voltage, and ideally preserves the power provided to the load. During the off-state, the inductor is discharging its stored energy into the rest of the circuit. If the switch is closed again before the inductor fully discharges (on-state), the voltage at the load will always be greater than zero. When the switch is opened (bottom of figure 2), the diode is forward biased. The voltage across the inductor is V L = − V o {\displaystyle V_{\text{L}}=-V_{\text{o}}} (neglecting diode drop). Current I L {\displaystyle I_{\text{L}}} decreases. The circuit in Figure 10 uses CMC with the MAX668controller. This boost circuit is similar to Figures 7 and 8 except that R1 senses the inductor current for CMC. R1 and some internal comparators provide a current limit. R5 in conjunction with C9 filters the switching noise on the sense resistor to prevent false triggering of the current limit. The MAX668's internal current-limit threshold is fixed; changing resistor R1 adjusts the current-limit setting. Resistor R2 sets the operating frequency. The MAX668 is a versatile integrated circuit that can provide a wide range of DC-DC conversions.

A linear regulator uses a resistive voltage drop to regulate the voltage, losing power (voltage drop times the current) in the form of heat. A switching regulator's inductor does have a voltage drop and an associated current but the current is 90 degrees out of phase with the voltage. Because of this, the energy is stored and can be recovered in the discharge phase of the switching cycle. This results in a much higher efficiency and much less heat. What is a Switching Regulator? Figure 6. Discharge phase: when the switch opens, current flows to the load through the rectifying diode.In the above circuit, when the switch is open, the inductor is charged with the energy with the help of the generated magnetic field. Now when the switch is closed, the current is reduced because load impedance is higher and the magnetic field is no longer there. So, a series connection is made that causes a higher voltage at the output. One of the largest power-loss factors for switchers is the rectifying diode. The power dissipated is simply the forward voltage drop multiplied by the current going through it. The reverse recovery for silicon diodes can also create loss. These power losses reduce overall efficiency and require thermal management in the form of a heat sink or fan.

Another commonly used type of control is current-mode control (CMC). This method regulates the output current and, with infinite loop gain, the output is a high-impedance source. In CMC, the current loop is nested with a slower voltage loop, as shown in Figure 9; a ramp is generated by the slope of the inductor current and compared with the error signal. So, when the output voltage sags, the CMC supplies more current to the load. The advantage of CMC is its ability to manage the inductor current. In VMC the inductor current is not metered. This becomes a problem because the inductor, in conjunction with the output filter capacitor, forms a resonant tank that can ring and even cause oscillations. Current mode control senses the inductor current to correct for inconsistencies. Although difficult to accomplish, carefully selected compensation components can effectively cancel out this resonance in VCM. Next, the divider signal is subtracted from the internal 1.25V reference and then amplified. This error signal is then output on pin 8 as a current source. This, in conjunction with the differential input pair, forms a transconductance amplifier. This arrangement is used because the output at the error amp is high impedance (current source), allowing the circuit's gain to be adjusted by changing R7 and C4. This arrangement also provides the ability to trim the loop gain for acceptable stability margins. The error signal on pin 8 is then forwarded to the comparator and output to drive the power switch. R1 is a current-sense resistor that meters the output current. When the current is unacceptably high, the PWM circuit shuts down, thereby protecting the circuit.

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Given the advantages of switching regulators, one might wonder where can linear regulators be used? Linear regulators provide lower noise and higher bandwidth; their simplicity can sometimes offer a less expensive solution.