If a DC-DC converter has a regulation rating of 1%, then the output voltage will not deviate more than 1% from the nominal value over the specified input voltage range and output current range.ĭC-DC converters use closed feedback loops to provide a regulated output. This figure of merit is related to how tightly the output is controlled over input voltage and load current. Be sure that a buck converter’s voltage ripple rating meets your needs. This rating is a measure of how much ripple voltage is on the output. If pushed past this safety limit, the DC-DC converter may overheat and be damaged, or may shut down as a protective measure.
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This is the maximum ambient temperature that the DC-DC converter should run in under full load. The DC-DC converter may provide more than this amount of current, but will get hot, and may fail. This is the maximum amount of current that a user should try to have the DC-DC converter provide to a load. Efficiency may be lower at lower power outputs, where the amount of power required to power the circuit is comparable to the load power. Efficiency for DC-DC converters is typically specified in curves, with peak efficiency achieved at certain load current. For example, if a 4 W load is needed, use a 4 W DC-DC, driven by a 5W source. A good rule of thumb is assume a DC-DC converter is 80% efficient, and then use a source with 125% the load power. When using a DC-DC converter, it is good practice to make sure that the source providing power to the DC-DC converter can provide enough power to account for the inefficiency. Some DC-DC converters are 90%+ efficient.
The following are some important characteristics to consider in designs.Įfficiency is the fraction of input power that reaches the load. See figure 5 for examples of creating positive and negative output voltages with isolated DC-DC converters.įigure 5: Using isolated DC-DC converters to create positive and negative output voltagesĭC-DC converter datasheets have key parameters that describe their important characteristics. This can be used to produce positive and negative voltages depending on how you connect the output terminals. Isolated power converters are those in which the input ground and output ground are not connected. The flyback is an isolated boost converter. The forward converter is an isolated buck converter. Important examples of isolated DC-DC converters are the forward and flyback converter. A SEPIC is used for similar applications as the buck-boost, but provides some advantages in some applications. There are buck-boosts that produce positive and negative voltages.Ī SEPIC converter also steps a voltage up or down, producing a voltage equal to or higher or lower than the input voltage. A lithium battery cell can vary between 2.5 and 4.2 V.
A buck boost could also power an LED from a single cell. A 12V battery’s voltage can vary between 10 V and 14.7 V. A buck boost could be used to provide a 12 V output from a 12 V battery. A boost converter could be used to drive a string of LEDs from a lithium cell, or provide a 5 V USB output from a lithium cell.Ī buck-boost converter steps a voltage up or down, producing a voltage equal to or higher or lower than the input voltage. A buck converter could be used to charge a lithium ion battery to 4.2 V, from a 5 V USB source.Ī boost converter steps a voltage up, producing a voltage higher than the input voltage.
Isolation is determined by whether or not the input ground is connected to the output ground.įour common topologies that makers might find useful are the buck, boost, buck-boost, and SEPIC converters.Ī buck converter steps a voltage down, producing a voltage lower than the input voltage. Their disadvantages are noise and complexity.ĭC-DC converters come in non-isolated and isolated varieties. At 90% efficiency, they are generally much more efficient and smaller than linear regulators. Closed feedback loops maintain constant voltage output even when changing input voltages and output currents. This paper briefly introduces DC-DC converters, notes common examples, and discusses important datasheet parameters and applications of DC-DC converters.ĭC-DC converters are high-frequency power conversion circuits that use high-frequency switching and inductors, transformers, and capacitors to smooth out switching noise into regulated DC voltages. DC-DC converters are widely used to efficiently produce a regulated voltage from a source that may or may not be well controlled to a load that may or may not be constant.
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