DC/DC Converters
(31 675)DC/DC converters are usually small-size components used to change direct current (DC) to DC with different parameters. They can be found in various packages (housings): as a single block adapted to THT (through-hole technology) mounting, e.g. in packages compliant with DIP standards (Dual In-line Package) or SIP (Single In-line Package), adapted to SMD (surface-mount device) mounting technology, but also in LGA packages (Land Grind Array) or in a brick standard of various sizes, e.g. half brick or quarter brick. Especially hobbyists, who do not create complex electronic circuits, will associate them with ready-made modules soldered onto PCBs or devices in packages for building-in or mounting on a DIN rail. The last type of mounting technology is mainly used in industrial control and electrical cabinets. The variety of packages in which DC/DC converters can be found results from their common use. Except for AC motors, direct current (DC) is used to power most electrical and electronic devices. For this reason, these components can be found, for example, as integrated circuits in computer power supplies, motherboards, or graphics cards, where they generate different DC voltages for the individual electronic components.
The main distinction among DC/DC converters is a result of the ratio of output voltage to their input voltage, so it is possible to find converters reducing voltage, called step-down converters, those increasing voltage, i.e. so-called step-up converters, or those that can produce at the output voltage that is both higher and lower than the input voltage, i.e. step-up/step-down converters. Very often, they feature adjustable output voltage, which allows to obtain a very wide range of its parameters. In such cases, it is usually set using a small potentiometer, integrated with the electronic circuit of the converter.
DC/DC converters – safeguards
Many DC/DC converters manufactured nowadays feature galvanically separated input and output. Such systems are often called isolated converters. This provides additional protection of the powered system against overvoltage and power surges, which could damage the converter itself as well as the powered device, resulting in permanent damage. Galvanic isolation of the input and output is required for safety reasons e.g. in medical devices. Of course DC/DC converters, as well as most other power supply devices, also offer other protections, among which we can distinguish continuous short-circuit protection, overload protection, overvoltage protection, reverse polarity protection, overheating protection or protection in the event of a drop in supply voltage. Simply put, the more protections a given device has, the lower the chance of a malfunction or permanent damage to the powered devices and the converter itself.
How to choose a DC/DC converter
While choosing the right DC/DC converter for your application, it is important to take a look at a few aspects. The first is the input voltage value, which is given in volts [V]. The input voltage range of a converter must contain the value of the voltage it will be supplied with. Applying too low voltage can cause converter malfunction, while applying too high input voltage can permanently damage it. Another parameter is the output voltage. The value that the user wants to obtain at the output of the converter should be determined depending on the devices that it will power. It must be identical with the value specified by the manufacturer of a given device in its technical documentation. The output voltage of DC/DC converters is often adjustable within a given range, thanks to which they can supply power to devices with different power supply parameters.
Another parameter which you must properly choose before buying the DC/DC converter is the maximum output current, given in amperes [A], often defined as the current efficiency. It represents the maximum electrical current that a given device can produce while still operating properly. The DC/DC converter current efficiency should be higher than the current required by the system being powered (in extreme cases equal to it). A power device operating within the limits of its maximum current efficiency will generate a significant amount of heat, which, if operated for a long time in such conditions, may lead to damage. This situation is particularly likely if the converter does not have any overload or overheat protection. It is good practice to choose a converter with a higher current efficiency than required. It is mainly to avoid work at the upper limit of its current efficiency, but also so as not lead to a situation where it is necessary to replace the currently installed converter with a new one, with a higher current efficiency, when the system undergoes slight expansion. Often, to compare which converter is more efficient, the power of a given converter is considered, which is given in watts [W]. Power is the product of voltage and current, so with equal voltage values it is easy to compare which device will be able to generate more current.
Another aspect that is sometimes important is the temperature range in which a given converter can operate. Some applications may require operation in sub-zero temperatures or in an environment where the temperature will be much higher than the room temperature. There are converters that are designed for temperatures as low as -50°C, but also for as extreme temperatures as 150°C. The temperature difference is significant, and when choosing a converter for a specific application, this aspect must not be overlooked in order not to damage the converter.
Some DC/DC converters can have more than one output. Then, each output has a different voltage value. Of course, in addition to the number of outputs, there can also be a larger number of electrical connections, e.g., in the form of a terminal strip integrated in the system. Sometimes DC/DC converters have integrated cables for electrical connection. When choosing this type of a device, you can also pay attention to its efficiency. The higher it is, the lower the power losses which most often occur as a conversion of electrical energy into thermal energy. To sum up, all DC/DC converter parameters should be selected depending on the target application and the criteria imposed by the cooperating elements, i.e., those supplying the converter and those that will be powered by it.
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