Virtually every piece of electronics equipment requires some sort of power conversion. Technical training manager, Murata Power Solutions, Trinidad Lawrie, explains the basics Whether converting AC mains power to DC or, conditioning DC to suit load requirements, the power supply and conversion element of a product is key. In its simplest form, the power system comprises the power source, power converter and the load.
Most components require specific levels of DC voltage in order to function. With the bandwidth and high levels of functionality present in modern equipment, it is often the case that more than one DC voltage is needed to support the various loads. These could include devices such as processors, ASICs, FPGAs and memory as well as fans and disk drives.
The most important decision to be made in the design of a power system is the selection of the power architecture to meet its application needs. This analysis typically involves the trade-off of conflicting requirements: cost, efficiency, size and flexibility.
Types of conversion
There are two product groups to consider when discussing power conversion. The stage that takes AC input voltage and produces a DC output voltage is known as the power supply. A front end power supply provides a single regulated DC bus voltage typically used in a distributed bus architecture. Common configurations include: CompactPCI, cable TV (CATV) and dimensions such as three by five inches or 1U rack unit height.
Modules that take the DC voltage feed from a battery, front end power supply or another DC/DC converter and convert it to a DC level required to power the load are known as DC/DC converters. Many designs have multiple loads with different power requirements so several DC/DC converters may be required in a single design. Both isolated and non-isolated DC/DC converters are available.
Isolated converters provide electrical separation of the input supply from the output load. The transformer used in an isolated DC/DC converter provides a safety barrier as the input and output grounds are isolated. Non-isolated DC/DC converters can take their input from an isolated DC/DC bus converter and are used at the point-of-load to limit voltage distribution losses in distributed power and intermediate bus architectures. Their output voltage is typically programmable by an external resistor or voltage source.
Talking terminology
Input voltage range These are the maximum and minimum limits that the power supply or converter can accept at its input. A wide range enhances design flexibility.
Output voltage This is the nominal or typical DC voltage at the output terminals of a power converter. Devices may have single or multiple outputs. A high degree of output voltage stability ensures the load being supplied does not have its operation, life expectancy or reliability adversely impacted by fluctuations in supply.
Power loss Expressed in Watts, is the difference between the input and output power. Losses can comprise heat, noise, light or other forms of energy expended during conversion. Minimising losses improves energy efficiency in response to environmental, legislative and end user demands.
Efficiency Expressed as a percentage, this is the ratio of total output power to input power.
Line regulation This states as a percentage, the variation of an output voltage due to a change in the input when all other factors remain constant. Load regulation is the variation of the output voltage due to a change in the output (load) with all other factors held constant and is also expressed as a percentage.
Voltage adjustment or trimming This is where the output voltage can be adjusted within a given range. This is often implemented to optimise the output voltage for specific applications and can compensate for static losses when the load current is constant.
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