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Thursday, 29 August 2019

Testing of Regulated Power Supply

Testing of Regulated Power Supply:


For testing the specifications of a regulated power supply the following procedure is adopted.

(a) Output: 

The output of the power supply can be measured using a Digital Volt Meter (D.V.M.). This voltage should tally with the specified voltage when the line voltage is within the tolerance expressed by the manufacturer. A dimmer stat (variac) of the same power rating as that of the power supply is  taken in order to check whether the output voltage is constant within the tolerance values of the mains voltage., The line voltage input to the power supply is to be given from the output of the variac. The output voltage from the variac is first adjusted to the lower limit of mains voltage measuring the output of the variac using a D.V.M. in its AC. volts range. Now the D.C. voltage of the power supply is to be measured. Then the AC. from the variac is to be adjusted to the normal voltage and the D.C. output is to be measured. Finally the output of the variac is to be increased to the upper limit specified by the manufacturer and the D.C. output is to be measured. In all the three measurements the output must be constant.



(b)  Load Regulation:

The load regulation is done in the following way. The current limiting control must be set to the maximum current limit value in the regulated power supply control panel. An adjustable load resistance unit is to be taken. In the output of the Regulated Power Supply the load is to be connected through a D.C. ammeter of appropriate range that covers the maximum current offered by the power supply. A voltmeter is to be connected across the output terminals of the power supply. The no load voltage is to be measured and recorded disconnecting the load resistor unit. Then the load resistor unit is to be connected and adjusted to the maximum resistance position such that the load current is at its minimum. The output voltage and the magnitude of the load current are to be measured and recorded. Adjusting the load resistance for convenient current setting output voltage and load current readings are to be measured and recorded. The last observation must be while drawing the maximum current specified by the manufacturer. Taking the full load voltage from the observations, the regulation can be calculated. The calculated value should match with the specification offered.

(c) Ripple:

A capacitor of 0.1 μ F is to be connected in series with test terminals of the D.V.M. The D.V.M. is to be kept in the AC. volts range. Now the voltmeter is to be connected across the D.C. output terminals of the regulated power supply. The voltage indicated by the AC. voltmeter is the ripple output of the power supply. It should be very low of the order of 1 mV R.M.S. or as is specified.

(d) Overload Protection:

The overload protection can be tested as: A load resistance unit is to be taken first. It is to be connected in series with a D.C. ammeter of proper range that covers double the maximum current limit of the power supply. The load current is to be initially brought to the maximum limit by reducing the value of resistance of the load resistance unit. Now the load resistance value is to be further decreased such that current more than the limit is drawn by the load circuit. Upon making the adjustments the overload indicator of the power supply along with overload alarm if provided have to work indicating the overloading on the power supply.

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