Switch Mode Power Supply
Led Strip Lights, Switch Mode Power Supply, dc power conversions
Abstract: Switch-mode power supplies are a popular and sometimes necessary choice for DC-DC power conversion. These circuits offer distinct benefits and tradeoffs when compared to alternative methods of converting DC power. This article presents a brief summary of the advantages and tradeoffs of switch-mode power supplies, and also offers a simple review of their operation and theory.
The majority of electronic DC loads are supplied from standard power sources. Unfortunately, standard source voltages may not match the levels required by microprocessors, motors, LEDs, or other loads, especially when the source voltage is not regulated. Battery-powered devices are prime examples of the problem: the typical voltage of a standard Li+ cell or NiMH stack is either too high/low or drops too far during discharge to be used in conventional applications.
Fortunately, the versatility of SMPSs solves the problem of converting a standard source voltage into a usable, specified output voltage. There are numerous SMPS topologies, which are classified into fundamental categories—these power supplies step up, step down, invert, or even step up and down the input voltage. Unlike linear regulators, which can only step down an input, SMPS are attractive because a topology can be selected to fit nearly any output voltage.
Additionally, modern SMPS ICs are designed with varying levels of integration, allowing the engineer to choose among topologies with more or less of the standard SMPS features brought into the IC. In doing so, manufacturers ease the design burden for commonly used, application-specific power supplies or offer the engineer basic SMPS ICs for custom projects, thereby enhancing the versatility of these widely used devices.
Engineers also face the other common problem of how to convert DC power efficiently. For instance, it is often required to step down an input voltage to achieve a lower output voltage. A simple solution implements a linear regulator, as this device requires only a few capacitors and adequate thermal management. However, where such simplicity ends, inefficiency begins—even to unacceptable levels if the voltage differential is large.
The efficiency of a linear regulator is directly related to the power dropped across its pass transistor. This power drop can be significant because dissipated power is equal to ILDO × (VIN - VOUT). For example, when stepping down a 100mA load from a 3.6V battery to a 1.8V output, 0.18W is dropped across the linear regulator. This power drop yields a low 50% efficiency, which reduces battery longevity by 50% (assuming ideal operation).
Understanding this efficiency loss, the dutiful engineer is driven to achieve an improved solution, and here is where the SMPS excels. A well-designed SMPS can achieve 90% efficiency or more, depending on load and voltage levels. As in the previous example, using the step-down SMPS of Figure 1 instead of a linear regulator, 90% efficiency is observed. This is an efficiency improvement of 40% over the linear regulator. The advantage of the step-down SMPS is apparent, and similar or better efficiencies are observed in other SMPS topologies.
dc power conversions
, electronic dc loads
, Led Strip Lights
, source voltage
, step down power supply
, step up and step down input voltage
, step up power supply
, Switch Mode Power Supply