Autotransformer regulator inverts 12V to produce 12V Looking for DataSheets?
|You can create a dc/dc regulator with an internal switching MOSFET that inverts 12V to produce an output of 200 mA at 12V (Figure 1). The IC is a high-efficiency device whose low quiescent current (120 µA maximum) is the product of a CMOS process that limits the absolute-maximum input-to-output voltage to 21V. Thus, to avoid having 24V across its terminals, the IC must isolate itself from the inductor-flyback voltage. It can do so by driving either an external switch in a nonbootstrapped configuration or an internal switch in a flyback-transformer configuration.|
Autotransformer T1, a center-tapped inductor with a 1-to-1 turns ratio, offers a design alternative. Terminal LX flies back to 1/2VOUTplus a diode drop, or approximately 6V. The V+ terminal remains at 12V, yielding 18V maximum between V+ and LX–well within the 21V limit. Because IC1drives the gate of its internal MOSFET between the V+ and OUT voltages, you normally connect OUT to VOUTto ensure sufficient gate drive. (In a typical application, the chip inverts 5V to produce 5V.) In this circuit, the 12V input provides adequate gate drive, so OUT connects to ground. (DI #2067)