The substitution of the load resistor requires adding a load switch to open and short the load in the CC or CV load regulation tests. The load transient recovery time test procedure cannot be performed using load resistors.
An electronic load is considerably easier to use than a load resistor. It eliminates the need for connecting resistors or rheostats in parallel to handle the power, it is much more stable than a carbon-pile load, and it makes easy work of switching between load conditions as is required for the load regulation and load transient-response tests.
Current-Monitoring Resistor Rm. To eliminate output current measurement error caused by voltage drops in the leads and connections, connect the current-monitoring resistor between -OUT and the load as a four-terminal device. Figure 2-2 shows correct connections. Select a resistor with stable characteristics: 0.001, 1% accuracy, 30 ppm/°C or lower temperature coefficient and 20W power rating (20 times actual power if other than 0.001Ω is used).
Figure 2-2. Current-Monitoring Resistor Setup
Constant Voltage (CV) Tests
CV Setup. If more than one meter or a meter and an oscilloscope are used, connect each to the + S and - S terminals by a separate pair of leads to avoid mutual coupling effects. Connect only to + S and -S (except for peak-to-peak PARD) because the unit regulates the output voltage between + S and - S, not between + OUT and - OUT. Use coaxial cable or shielded 2-wire cable to avoid pickup on test leads. For all CV tests set the output current at full output to assure CV operation.
Load Effect (Load Regulation). Constant-voltage load effect is the change in dc output voltage (Eo) resulting from a load-resistance change from open-circuit to full-load. Full-load is the resistance which draws the maximum rated output current at voltage Eo. Proceed as follows:
a.Connect the test equipment as shown in Figure 2-3. Operate the load in constant resistance mode (Amps/Volt) and set resistance to maximum.
b.Turn the unit's power on, and turn up current setting to full output.
c.Turn up output voltage to: 7.0Vdc (6023A) 20.0Vdc (6028A)
as read on the digital voltmeter.
