Turn -ON Checkout Procedure

Before applying power to the supply, check the label on the heat sink to make certain that the supply's line voltage option agrees with the line voltage to be used. If the option does not correspond to your line voltage, refer to paragraph "LINE VOLTAGE OPTION CONVERSION" in the service section before applying power.

a.Connect line cord to power source and turn LINE switch on.

b.Push +6V METER switch and, with no load con- nected, vary +6V VOLTAGE control over its range and check that the voltmeter responds to the control setting and the ammeter indicates zero.

c.Set the +6V VOLTAGE control to 6 volts and short the

+6V output terminal to COM (common) terminal

with an insulated test lead. The ammeter should indicate a short-circuit output current of approximately 1.0 A. Remove the short from the output terminals.

d.Push the +20V METER switch and turn Tracking Ratio control fully clockwise to the Fixed position. With no load connected, vary ±20V VOLTAGE control

over its range and check that the voltmeter responds to the control setting and the ammeter indi- cates zero.

e.Set the ±20V VOLTAGE control to 20 volts and

short the +20V output terminal to the COM terminal

with an insulated test lead. The ammeter should indicate a short-circuit output current of 0.55 A ± 5%. Remove the short from the output terminals.

f.Repeat steps (d) and (e) for -20 V output.

g.Adjust the +20V output to 20 volts. Then push -20V METER switch and check the effect of the Tracking Ratio control on the voltage of the -20V output. The - 20V output should be adjustable from less than 0.5 volts to a maximum of 19 to 21 volts.

If this brief checkout procedure or later use of the supply reveals a possible malfunction, see the service information section for detailed test, troubleshooting, and adjustment pro- cedures.

OPERATION

This power supply can be operated individually or in parallel or series with another supply (see Parallel and Series Opera- tion paragraphs). All output terminals are isolated from ground. The ±20V and +6V outputs use a single common out- put terminal. This common (COM) terminal or any one of the other output terminals may be grounded to the chassis at the front panel ground terminal ( in Figure 2), or all outputs may be left floating. Loads can be connected separately between each of the 0 to ±20V output terminals and the COM terminal, or between the -20V and the +20V terminals for a 0 to 40V output. Each output voltage or current can be quickly selected for monitoring with the push-button meter switches. To moni-

tor the 0 to 40V output voltage, add the voltmeter readings of the +20V and -20V output and use either the +20V or the - 20V meter to measure the current.

Tracking Ratio Control

With the Tracking Ratio control in the Fixed position, the volt- age of the -20V supply tracks that of the +20V supply within 1% for convenience in varying the symmetrical voltages needed by operational amplifiers and other circuits using bal- anced positive and negative inputs.

Turn the Tracking Ratio control counter clockwise out of the Fixed position to set the voltage of the -20V supply lower than that of the +20V supply. The negative supply can be set from a minimum of less than 0.5 volts to a maximum within 5% of the +20V supply's output. Once this is done, the ±20V voltage control still controls both outputs and maintains a constant ratio between their voltages.

Overload Protection Circuits

±20-Volt Current Limit. The +20V and -20V outputs are indi- vidually protected against overload or short circuit damage by separate current limit circuits to limit the output current to 0.55 A ± 5%. (This is 110% of the maximum rated output.) If a sin- gle load is connected between the +20V and -20V outputs, the circuit set for the lesser current limit will limit the output. No deterioration of supply performance occurs if the output current remains below the current limit setting.

+6V Current Foldback. The overload and short-circuit pro- tection circuit for the +6V output reduces the output current limit as the output terminal voltage decreases. (The operating region of the +6V output is enclosed by heavy lines in Figure 4.) The maximum rated output current is 2.5 A and the current limit is factory-adjusted to operate at 2.75 A ± 5% when the output is 6 volts. At lower output voltages, the circuit reduces the maximum obtainable output current linearly until 1 A ± 15% flows when the output is shorted. The short-circuit cur- rent can not be adjusted.

During the actual operation of the ±20V and +6V outputs, if a load change causes the current limit to be exceeded, the OL LED is lighted. If overload conditions occur, the ±20V supplies will protect the load by limiting the current to 0.55 A and the +6V supply will protect the load by reducing both voltage and current simultaneously along the foldback locus as shown in Figure 4. The ±20V and +6V supplies are self restoring; that is, when the overload is removed or corrected, the output voltage is automatically restored to the previously set value.

Operation Beyond Rated Output

The supply may be able to provide voltages and currents greater than its rated maximum outputs if the line voltage is at or above its nominal value. Operation can be extended up to 5% over the rated output without damage to the supply, but performance can not be guaranteed to meet specifications in

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