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General Information 13
Storage and recall of programmed voltage and current values for all outputs.
Queries of programmed functions or settings.
Output enable or disable.
Programming syntax error detection.
Programmable delay time for service request and OCP mask.
Voltage, current, and overvoltage calibration.
HP-IB interface selftest.
Message display capability on the front panel.
Output connections are made to rear panel screw terminals. Either the positive or negative output terminal can be
grounded, or the output can be floated up to ± 240 Vdc (including output voltage) from chassis ground. Output voltage
can be locally or remotely sensed, and identical outputs can be operated in series or parallel combinations for increased
output voltage or current capability. As shipped from the factory, the power supply is jumpered for local sensing.
Your power supply can be calibrated without having to remove the cover or even having to remove it from your system
cabinet. This feature allows you to calibrate the supply at its normal operating temperature. The recommended calibration
interval is one year. Refer to Appendix A of this manual for complete calibration details. A calibration security jumper is
available inside the unit. Access is described in the service manual.
Basic Operation
Figure 1-2 is a block diagram that illustrates the major assemblies contained within the power supply. As shown in the
figure, each supply includes a power transformer, two or more output boards, an HP-IB board, and front panel (display
and control keys).
Output Low Range Values High Range Values
80 W Low, Voltage 7 V @ 10 A 20 V @ 4 A
80 W High Voltage 20 V @ 4 A 50 V @ 2 A
40 W Low Voltage 7 V @ 5 A 20 V @ 2 A
40 W High Voltage 20 V @ 2 A 50 V @ 0.8 A
Figure 1-1. Output Operating Ranges for HP Models 6621A, 6624A and 6627A.
The appropriate ac input voltage is applied to each output board where it is converted to a raw dc voltage which is
subsequently linearly regulated to become the dc output voltage. The magnitude of the output and the mode of operation
are determined by the load and the data received from the HP-IB computer or from the front panel.
Each power supply model contains one output board for each output that it provides. Models 6624A and 6627A contain
four 40 watt output boards; Model 6623A contains two 40 watt output boards and one 80 watt output board; Models
6621A and 6622A each contain two 80 watt output boards.
HP-IB Board
The HP-IB board provides the interface between the user and the multiple outputs of the power supply. Each output board
is actually an output channel that can be individually selected and controlled over the HP-IB or from the supply's front
panel. Circuits on the HP-IB board interpret commands from the HP-IB or from the front panel to control the selected
output.