DC Power Supply Specifications

- summary or overview about the key DC power supply specifications detailing what they mean and their importance.

When choosing any DC power supply, the specification is of key importance. A variety of DC power supply specifications will be quoted, each detailing a different element of the performance of the power supply.

For different applications, different power supply specifications will be important. However each one needs to be considered when choosing or specifying a suitable power supply.

Power supply voltage and current specification

The voltage and current are the two most important parameters and will naturally be quoted in volts and amps. Sometimes the output power in watts may be quoted.

Line regulation specification

Line regulation is the variation in output voltage when the input or line voltage changes. It is normally quoted in millivolts variation or as a percentage of the output voltage and should be a few millivolts (e.g. 5 mV) or around 0.01% of the maximum output voltage for most supplies for a change of line voltage anywhere within the operating range.

Power supply specification for load regulation

Load regulation is the variation in output voltage for a change in the load. It is normally quoted as a in millivolts variation or as percentage of the maximum output voltage It might typically be a few millivolts (e.g. 5 mV) or 0.01% for a step load change from 0 to 100% load. It is normally quoted for a constant line voltage and steady temperature.

Power supply specification for ripple and noise

The ripple and noise on the output is combined as a single measurement. For linear supplies, ripple frequency will normally be at twice the line frequency. For switching supplies ripple and spikes will arise from the switching action of the supply. The ripple components are often given as rms figures, but for switching supplies a peak to peak measurement is more useful because it shows the extent of the spikes arising from the switching. Most good supplies should offer noise and ripple figures of better than 10 mV rms and for switching supplies figures of 50mV or less should be achievable in many cases, although very high current supplies may have slightly higher values.

Power supply stability specification

Stability of the output voltage is important for some applications and is quoted for many supplies. Typically the output voltage will be measured over a period of time under constant load and input voltage and the voltage drift measured. Typically, this will be a few millivolts (e.g. five to ten) over a period of ten hours.

Temperature stability specification

The temperature stability might also be important. This is measured as a percentage or absolute voltage change per degree C. Typically, this might be in the region of 0.02% / degree C or 2 mV / degree C.

By Ian Poole

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