Switch-mode Operation
All power converter circuits (step-up, step-down, etc.) fall into one of two major architecture categories: linear and switching. Linear regulators represent an older technology that has been traditionally chosen due to simplicity of implementation and, in some cases, lower cost. However linear regulators have a significant drawback: inefficiency. Depending on system configuration a linear regulator can have a power conversion efficiency well below 50%. Compare that to the 85%-95% typical conversion efficiency of most switching regulators. This difference in efficiency is manifested simply as wasted power in the form of dissipated heat.

In the past the power loss of linear regulators was usually ignored in AC wall-powered devices because simplicity and low-cost took precedence. However, as power levels grew the thermal problems presented by linear regulators were too much to ignore and slowly a transition has been taking place to switch-mode regulators. On the other hand, portable devices have used switch-mode regulators widely, sometimes exclusively, for a long time. Obviously, if you want the best battery run-time you cannot afford to waste 30%-50% of the battery’s power.

One notable exception to this widespread use of switching regulators in portable and handheld equipment is in the battery charging function. The charge control IC in most cell phones todayis a linear mode device that wastes 30%-50% of the input power. Presumably this “sloppiness” in design is somewhat due to not caring that the power is wasted. After all, the device is typically plugged into the AC wall adapter which an “infinite” source of power.

The power-saving benefits of switch-mode regulators are shown in the example below powering a 1W typical digital load at 1.5V from a 5V input supply:

For any power converting regulator:

Efficiency (η) = P_OUT/P_IN
Power dissipated (P_D) = (1-η)*P_IN = (1-η)*(P_OUT/η)

For a Linear Regulator:
η = V_OUT/V_IN
P_OUT = 1W
V_IN = 5V
V_OUT = 1.5V
P_D = (1-1.5/5)*(1/(1.5/5)) = 2.3W


For a Switching Regulator:
h = 90% (typical and relatively constant)
P_OUT = 1W
V_IN = 5V
V_OUT = 1.5V
P_D = (1-0.9)*(1/(.9)) = 0.11W

For each watt delivered by the linear regulator an additional 2 watts are immediately wasted as heat. This requires proportionately more power to be drawn from upstream sources and is magnified by the inherent losses in the power distribution grid (typically 8% to 10%). By contrast it is observed that the switching regulator only dissipated about 110mW (20 times less!). The net result is less power load on the input supply and less power drawn from the grid, thereby reducing electricity generation. If all digital electronic systems used this technology it is estimated the global power savings would be on the order of gigawatts which represents multiple power generating plants and millions of tons of CO₂ emissions each year.

Summit’s Programmable Power management devices almost exclusively use switching regulator technology and it is featured in the following products:

SMB135
SMB122
SMB120
SMB117
SMB113A
SMB112
SMB111
SMB110