A Step·Down Switching Regulator Design Exercise With TL497A

The schematic of a basic step-down regulator is shown in Figure 6-34.

Figure 6-34. Basic Step-Down Regulator

We selected CF to be 120µF, the next higher standard value. Figure 6-35 illustrates the regulator with the calculated values applied to it. A 150µF filter capacitor may be used as a prefilter as well as a 0.01µF disc capacitor to take care of any transients on the incoming VI rail. For peak currents greater than 500mA, it is necessary to use an external pass transistor and diode. Such a technique is illustrated in Figure 6-36 which is an automotive power supply. With a 12 V battery, this stepdown regulator supplies 5V at 2 A output current. Figure 6-37 illustrates a basic step-up regulator. This design steps up the output voltage from 5V to 15V. The equations for determining the values of the external components are provided in Figure 6-31.