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Load effect or load regulation indicates the extent to which the load current changes effect the output voltage. It is expressed as a ratio of the difference between no load voltage to full load voltage and no load voltage. It can be expressed as a fraction or as percentage.

The smaller the percentage the better is the performance of the power supply.

(a) Line Regulation or Source Effect:

It is the extent to which the output voltage of a regulated power supply will be held constant under the influence of the mains voltage variations. Typical value of line regulation is 0.01%.

The point to be noted here is that there must be a reasonable limit to the ability of the regulator to maintain output constant for line voltage variations. Therefore a range will be specified for the input voltage.

Example: 230 V, ± 10%.

That is the output of the regulated power supply will be constant even if the supply voltage has its changes between 207 V and 253 V.

(b) Periodic and Random Deviation:

The periodic and random deviation and ripple factor express the quality of the DC output from a regulated power supply. Periodic and random deviation (PARD) includes all periodic and random variations in the output voltage of the power supply. It is expressed as millivolts RMS or millivolts pp. Typical value is 1 mV RMS.

It describes the ability of fixed and adjustable current limiters employed in the regulator circuit, from protecting the supply, or the circuit under test from excessive current. An overload indicator is usually provided that indicates the overload condition.

(d) Warm up Time and Drift:

Warm up time is the time the supply takes to stabilize its circuits to present a constant output. It is expressed in minutes.

Drift is the deviation from the rated output voltage with respect to time. It is expressed as a minimum percentage of change in the output voltage from the specified voltage over a time period.

Example: less than 3% in 12 hours.