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Figure 8 shows a practical circuit using the boost topology formed with the MAX1932. This IC is an integrated controller with an onboard programmable digital-to-analog converter (DAC). The DAC sets the output voltage digitally through a serial link. R5 and R8 form a divider that meters the output voltage. R6 is effectively out of circuit when the DAC voltage is the same as the reference voltage (1.25V). This is because there are zero volts across R6 and so zero current. When the DAC output is zero (ground), R6 is effectively in parallel with R8. These two conditions correspond to the minimum and maximum output adjustment range of 40V and 90V, respectively. 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). A switching regulatoris a circuit that uses a power switch, an inductor, and a diode to transfer energy from input to output.
Boost converters are widely utilized in consumer electronics to raise and stabilize the sagging voltage of Lithium-ion batteries under load. A new and growing consumer market is the Internet of Things (IoT), a ‘cloud’-based network of wirelessly interconnected devices that frequently include audio, video, smart home and wearable applications. The IoT trend, combined with green energy (the drive to reduce wasted power and move to renewable forms of energy generation), demands that small devices operate autonomously for long periods of time while consuming little power. The MAX17222nanoPower synchronous boost converter fits the bill. The MAX17222 offers a 400mV to 5.5V input range, a 0.5A peak inductor current limit, and an output voltage that is selectable using a single standard 1% resistor. A novel True Shutdown ™ mode yields leakage currents in the nanoampere range, making this a truly nanoPower device! 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)
Figure 15. In discontinuous mode the inductor fully discharges and then the inductor voltage rests at zero. To minimize this loss, switching regulators can use Schottky diodes that have a relatively low forward-voltage drop and good reverse recovery. For maximum efficiency, however, you can use a MOSFET switch instead of the diode. This design is known as a "synchronous rectifier" (see Figures 12, 13 and 14). The synchronous rectifier switch is open when the main switch is closed, and the same is true conversely. To prevent cross-conduction (both top and bottom switches are on simultaneously), the switching scheme must be break-before-make. Because of this, a diode is still required to conduct during the interval between the opening of the main switch and the closing of the synchronous-rectifier switch (dead time). When a MOSFET is used as a synchronous switch, the current normally flows in reverse (source to drain), and this allows the integrated body diode to conduct current during the dead time. When the synchronous rectifier switch closes, the current flows through the MOSFET channel. Because of the very low-channel resistance for power MOSFETs, the standard forward drop of the rectifying diode can be reduced to a few millivolts. Synchronous rectification can provide efficiencies well above 90%. The True Shutdown feature disconnects the output from the input with no forward or reverse current, resulting in very low leakage current. The input quiescent current (I QINT) for MAX17222 is 0.5nA (Enable open after startup) and the output quiescent current (I QOUT) is 300nA. The power switch was the key to practical switching regulators. Prior to the invention of the Vertical Metal Oxide Semiconductor (VMOS) power switch, switching supplies were generally not practical.
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There are, admittedly, disadvantages with switching regulators. They can be noisy and require energy management in the form of a control loop. Fortunately, the solution to these control problems is integrated in modern switching-mode controller chips. Charge Phase
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