DC-DC Converter |
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Switching regulators offer higher efficiency than
linear regulators. In addition,
they
can step-up, step-down and invert the input voltage. This article outlines the different types of switching
regulators used in DC-DC conversion. It
also reviews and compares the various control techniques for these converters. What Is a Switching Regulator?
A
switching regulator is a circuit that uses an inductor, a transformer, or a
capacitor as an energy-storage element to transfer energy from input to output
in discrete packets. Feedback
circuitry regulates the energy transfer to maintain a constant voltage within
the load limits of the circuit. The
basic circuit can be configured to step up (boost), step down (buck), or invert
output voltage with respect to input voltage.
Why Use a Switching Regulator?
For battery management, the only other choice is a linear regulator. Linear regulators only step down, and efficiency is equivalent to the output voltage divided by the input voltage. On the other hand, switching regulators operate by passing energy in discrete packets over a low-resistance switch, so they can step up, step down, and invert. In addition, they offer higher efficiency than linear regulators. Using a transformer as the energy-storage element also allows the output voltage to be electrically isolated from the input voltage. The one disadvantage of the switching regulator is noise. Any time you move charge in discrete packets, you create noise or ripple. But the noise can often be minimized using specific control techniques and through careful component selection. Charge Phase A
basic boost configuration is depicted in Figure 1.
Assuming that the switch has been open for a long time, the voltage
across the capacitor is equal to the input voltage. During the charge phase, when the switch closes the input
voltage is impressed across the inductor and the diode prevents the capacitor
from discharging to ground. Because
the input voltage is DC, current through the inductor rises linearly with time
at a rate that is proportional to the input voltage divided by the inductance.
The energy stored in the inductor for the duration shown is equal to
one-half the inductance times the square of the peak current. Figure 1. Charge
phase: When the switch closes,
current ramps up through the inductor. |
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