current greater than that available from one supply. Auto-Parallel operation permits equal current sharing under all load conditions, and allows complete control of the output current from one master power supply. The output current of each slave will be approximately equal to the master’s output current regardless of the load conditions. Because the output current controls of each slave are operative, they should be set to maximum to prevent the slave reverting to constant current operation; this would OCCur if the master output current setting exceeded the slave’s.
3-48 Additional slave supplies may be added in parallel with the master/slave combination as shown in the bottom half of Figure 3-10.All the connections between the master and slave #1 are duplicated between slave #1 and the added slave supply. In addition, the strapping pattern of the added slave should be the same as slave #1. Remote sensing and programming can be used, though the strapping arrangements shown in Figure 3-10show local sensing and programming.
3-49Overvoltage protection is controlled by the crowbar circuit in the master supply which monitors the voltage acress the load and fires the SCR's in both units if an overvoltage condition occurs. The firing pulses are fed to the slave supply from transformer T90 (winding 5-6) of the master supply
"
through the “ EXT. CROWBAR TRIGGERterminals on the rear panel of the master supply. Correct polarity must be observed in connecting the crowbars to- gether. The overvoltage trip point is adjusted on the master supply, The OVERVOLTAGE ADJUST potentiometer on the slave supply should be set to maximum [clockwise) so that the master crowbar will control the slave.
3-50AUTO-SERIES OPERATION (Figure 3-11)
3-51 Two or more power supplies can be operated in Auto-Series to obtain a higher voltage than that available from a single supply. When this connection is used, the output voltage of each slave supply varies in accordance with that of the master supply. At maximum output voltage, the voltage of the slaves is determined by the setting of the front panel VOLTAGE controls on the master. The master supply must be the most positive supply of the series. The output CURRENT controls of all series units are operative and the current limit is equal to the lowest control setting. If any of the output CURRENT controls are set too low, automatic crossover to constant current operation will occur and the output voltage will drop. Remote sensing and programming can be used, though the strapping arrangements shown in Figure 3-11show local sensing and programming.
3-52 In order to maintain the temperature coeffi-
TM 11-6625-2958-14&P
Figure 3-11.Auto-Series Operation,
Two and Three Units
cient and stability specifications of the power sup- ply, the external resistors (Rx) shown in Figure
3-11should be stable, low noise, low temperature coefficient (less than 30ppm per degree Centigrade) resistors. The value of each resistor is dependent
