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Home > Applications & Technologies > Power Supply Technology
Applications & Technologies

Power supplies are needed for most every bit of electronics equipment with the exception of battery-powered devices. Power supplies always involve power conversion – converting the available power to the type of power required by the electronics equipment.

A power supply takes in the available power, and outputs usable power for the system that needs to be powered. For home use the available power is from the wall socket in the form of AC power. The power supply converts this to a form of power suitable for the end system.

It’s important to match the correct power supply to the system being powered. It starts with understanding if the end system needs AC or DC power at the desired voltage and power requirements. But some systems are more sensitive to fluctuations in power than others and may require a more regulated supply.

Converting the AC or DC input voltage, to the required AC or DC output voltage, involves considering factors like power efficiency, stability over temperature, and how well regulated the output voltage must be.

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AC/DC power supplies are straightforward - connect the input to an AC power source, which can be high voltage mains or a wall outlet. The power supply then converts the AC power into DC power. When selecting an AC to DC power supply, it’s important to determine the output power and voltage required for the system so the correct power supply can be used.

Efficiency is key when selecting an AC to DC power supply. These power supplies take a high-voltage AC voltage and usually step it down to a much lower voltage. Of course the simplest way to do this is with a set of resistors, transformers, and capacitors, but the result would be an adapter that give off waste energy in the form of enough heat to melt an iceberg.

The best AC to DC power supplies have the highest efficiency. A switched-mode configuration increases efficiency, which lowers heat while saving energy. Efficiency is given as a percentage and can be as low as 60% to as high as 94%.

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A DC/DC power supply steps a DC voltage up or down. If the output DC voltage is higher than the input DC voltage, it’s important to note that this output cannot be higher than the input power (Voltage x Current), otherwise we would be rethinking the laws of physics.

A switched-mode power supply (SMPS) is a type of DC/DC power supply that uses a switching regulator to rapidly switch the input voltage On and Off in order to reduce the voltage. The SMPS is a DC to DC converter, which means it takes in a DC voltage and then, very efficiently, converts that voltage to one or more DC output voltages. These DC output voltages can be a lower voltage, or a higher voltage.

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Switched-Mode Power Supply Topologies






AC/AC power supplies are transformers that can step-up or step-down an AC voltage. These can be as simple as the power supplies used in toys and small industrial applications or as large as those used on the line transformers outside of homes, or as gigantic as the huge transformers found at power generation plants such as the Hoover Damn.

When dealing with single-phase AC systems, the most common type of transformer is appropriately enough called a single-phase transformer. These have two coils, one primary and the one secondary. Three-phase transformers are used for three-phase AC systems and contain six coils, one pair for each phase.

Transformers are selected using four common specifications. The Power Rating is the rated power of the transformer’s secondary winding and is represented as Watts. The Maximum Primary Voltage is the highest voltage that can be applied to the transformer’s primary winding. The Maximum Secondary Voltage is the maximum voltage available from the transformer’s secondary winding. Lastly, the Direct Current Resistance is the measured resistance of the transformer’s windings when a test DC current is applied.

It’s crucial that the correct transformer be selected for a given application or the system can be damaged. For example, if a transformer is selected that is rated for more power than the circuit requires, the circuit will not draw more power than it needs but without the proper load on the transformer, the transformer may overheat and fail.

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The most common type of DC/AC power supply are the types used as uninterruptable power supplies (UPS) and also used in cars to convert the car’s DC power to useful AC power that can power some home devices.

A circuit that converts DC to AC power is called an inverter. Modern inverters contain a microcontroller that runs a control loop which manages the conversion process. A DC to AC inverter is usually a modulated full-bridge topology, such as a buck converter. It converts DC current to an AC waveform.

A more modern type of DC/AC converter is the microinverters used inside solar panels. A microinverter is built inside a solar panel and converts the DC power generated by the solar power into AC power usable by the house mains.

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