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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. 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. 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. 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). When the switch pictured above is closed (top of figure 2), the voltage across the inductor is V L = V i − V o {\displaystyle V_{\text{L}}=V_{\text{i}}-V_{\text{o}}} . The current through the inductor rises linearly (in approximation, so long as the voltage drop is almost constant). As the diode is reverse-biased by the voltage source V, no current flows through it;
The point is, for both cases, some hind of higher-than-logic voltage gate driver is needed. Additionally, for NMOS that gate drive (Vgs) must be higher than the Vin supply by at least one gate-source threshold; preferably even more than that to minimize on resistance Rds(on) and reduce losses. How to do that? Read on. In the OFF state, the inductor is directly connected to the load and energy to the load is provided by the two energy storage elements in the circuit. Hence, our DC component is directly proportional to the duty cycle of switching but inverted.
Figure 16 shows that skip mode offers improved light-load efficiencies but at the expense of noise, because the switching frequency is not fixed. The forced-PWM control technique maintains a constant switching frequency, and varies the ratio of charge cycle to discharge cycle as the operating parameters vary. Because the switching frequency is fixed, the noise spectrum is relatively narrow, thereby allowing simple lowpass or notch filter techniques to greatly reduce the peak-to-peak ripple voltage. Because the noise can be placed in a less-sensitive frequency band, PWM is popular with telecom and other applications where noise interference is a concern. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. 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.
Although switching techniques are more difficult to implement, switching circuits have almost completely replaced linear power supplies in a wide range of portable and stationary designs. This is because switching circuits offer better efficiency, smaller components, and fewer thermal management issues. 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. There is a more efficient version of DC-DC converters — switch-mode DC-DC converters. Here, the switch-mode technique is used to convert the DC voltage to varying voltage, then rectifying and filtering is done to get the desired voltage. This approach is cheaper and more efficient and it is widely used in almost all portable DC devices and it comes integrated into some chips for direct utilization.This section may be written in a style that is too abstract to be readily understandable by general audiences. Please improve it by defining technical terminology, and by adding examples. ( December 2022) Being similar in its arrangement, it also works in such a way that the output voltage is adjustable based on the duty cycle of the switch.
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