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About Non-isolated DC-DC converter

wallpapers News 2021-04-29
The simplest non-isolated DC-DC converter is a series of series resistors, but since the voltage drop varies with the load current, the actual circuit uses transistors to lower the voltage, which is controlled by a feedback circuit to keep the voltage constant. This is a "linear" regulator, usually supplied in a three-pin TO-220 package. The problem is that the voltage can only be lowered, not increased, and the device itself consumes a lot of power, which is the difference between the input and output voltages multiplied by the load current.
The solution to this problem is a "switch mode" regulator, in which the transistor is fully turned on or off, and consumes very little power in both cases, passing a voltage pulse through the inductor and capacitor to the output. The pulse is then "smoothed" back to the DC, where the output voltage is controlled by varying the pulse width. Switch-mode regulators offer a significant increase in efficiency compared to linear circuits. A nice feature of the switch-mode regulator is that it can also be configured to raise the voltage, becoming a "boost" converter. When it is used only to reduce the voltage, it is a "buck" converter.
There are other types of regulators, such as "SEPIC" circuits that can produce negative output voltages (buck and boost) and "SEPIC" circuits that can produce outputs above or below the positive input voltage. This is useful in battery-powered applications, where the load voltage needs to be maintained constant when the battery is discharged.
In many circuits, achieving maximum efficiency with the smallest size is a key consideration in product development and is critical for DC-DC converters. Smaller sizes of inductors and capacitors can be used to increase the pulse frequency of a switch-mode converter. Another factor, however, is that the transistor dissipates some power at each switch edge, and the more edges (frequencies) it switches per second, the more power it dissipates. As a result, efficiency and size are often opposites. Magnetics have made few recent improvements in these areas, but the latest broadband gap semiconductor technologies such as silicon carbide (SiC) and gallium nitride (GaN) allow for lower losses at each switch edge, allowing for the use of higher frequency, smaller size magnetic elements. This technology enables non-isolated DC-DC converters to be more than 95% efficient, with output currents up to 100A or more.

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