Keywords:
power supplies, switching regulators, linear regulators, buck converter, boost converter, buck-
boost converter, power supply design, DC-DC converter
APPLICATION NOTE 6726
ADVANTAGES OF SWITCHING REGULATORS
OVER LINEAR REGULATION
Abstract: In this application note, you’ll learn the essentials of switching regulator technology and
understand its benefits over linear regulation. Review basic circuits for some common non-isolated DC-DC
converter topologies. The piece also discusses pulse-width modulation (PWM) concepts used to regulate
the converter output voltage automatically and concludes with a discussion on the current level of
integration available for circuits at the IC level. A similar version of this application note appeared in Power
Systems Design on April 23, 2018.
Introduction
Electronic equipment requires a DC voltage as the supply input at various voltage levels. The AC power line
(utility supply wall outlet) or DC power (batteries, solar panels, etc.) are the main power inputs. Through DC-
DC power conversion technology, these energy sources can be converted to suitable end voltages for
powering ICs and other devices.
For DC-DC step-down conversion without isolation, we can use linear or switching regulator technology. A
linear regulator (
Figure 1) simply inserts an electronically variable resistor (a trans-resistor = transistor) in
series with the input DC to drop the voltage to the desired value. If the input or load current changes, the
resistor is varied by a feedback loop to keep the output voltage constant. The big disadvantage of linear
regulation is power loss, which is when the resistor sees the difference between input and output voltages
continuously while passing the load current. When power is low, this effect is not necessarily an issue.
However, imagine a 5V load at 10A from a DC source of 10V. In this scenario, the power loss through the
resistor is 50W, with a conversion efficiency of only 50%.
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Figure 1. Linear regulator.
Switching regulators, by comparison, offer a significant improvement in conversion efficiency and,
consequently, energy savings. Transistors are employed here as well, but instead of being used in a linear
variable resistor mode, they are utilized in switched mode as switches that are either in the ON or OFF
state. When ON, a switch drops very little voltage across it, and when OFF, it passes very little or no
current. As a result, the power dissipated is low in either condition. In fact, this approach makes it possible
to achieve efficiencies of over 90%. In the previously discussed example, 90% efficiency would mean that
the converter would dissipate just 5.5W versus 50W.
Figure 2
shows the size difference of a heatsink needed to minimize the temperature rise to only 10
degrees. Note that most modern DC-DC converters are efficient enough to eliminate heatsinks altogether
and just rely on the copper planes in the PCB for dissipating the heat.
Figure 2. Comparison of heatsinks for 50W versus 5.5W for 10
℃ rise.
Inside the Step-Down Switching Regulator
Figure 3
shows a buck, or step-down, converter, which converts a given DC input voltage to a lower DC
output voltage. When SW1 is ON, (V
- V ) is applied across the inductor, simultaneously storing energy
in the magnetic field and supplying energy to V
. When SW1 turns OFF, the current through L1 cannot
instantaneously change and continues to discharge its energy to the load, RL and C1. As a result, the
current in L1 falls, reversing the polarity of the voltage across L1. The switching node VLX, between D1 and
L1, ‘flies’ negative until it goes below ground, forward-biasing D1 and setting up the ‘free-wheeling’ path for
IN OUT
OUT
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