Principles Of Operation; Introduction; Overall Block Diagram Description; Ac Input Circuits - Agilent Technologies 6622A Service Manual

2-1

INTRODUCTION

The following paragraphs provide block diagram level
descriptions of the power supply. Differences between the
models are given as required. The descriptions provide a
basic understanding of circuit operation and are intended as
an aid in troubleshooting. It is assumed in the following
discussions that you are familiar with the operating and
programming instructions presented in the Operating
Manual (Agilent Part No. 5957-6377).
2-2 OVERALL BLOCK DIAGRAM
DESCRIPTION (FIGURE 2-1)
Figure 2-1 is a block diagram that illustrates the major
assemblies contained within the power supply. As shown in
the figure, each supply includes ac input circuits, an GPIB
board, front panel display and keyboard, and two or more
output boards.
2-3 AC Input Circuit
The ac input circuit consists of a line module on the rear
panel of the supply, front panel ON/OFF switch S1, power
transformer (T1), located in the front of the chassis, and a
cooling fan located in the rear of the chassis. The line
module contains a voltage selector card that selects the
applicable ac input voltage: 100 Vac, 120 Vac, 220 Vac, or
240 Vac. The voltage card selection must match the nominal
line voltage that is connected to the unit. The line module
also contains the main fuse F1. An 8 A fuse (normal blow)
must be installed for a 100/120 VAC input; a 4 A fuse
(normal blow) must be installed for a 220/240 Vac input.
The ac input is applied to the power transformer when S1 is
ON. Depending on the line module setting, the 120 VAC
cooling fan either runs directly from the line or from the
appropriate transformer tap. The power transformer
provides the main ac inputs to the output boards and also
provides the ac inputs for the bias voltage supplies located
on the GPIB board and each output board. Ac power
distribution is shown in detail in figure 6-1 in the rear of this
manual.
2-4

GPIB Board

The GPIB board contains the GPIB interface, system
microcomputer, output boards interface, and front panel
interface. These circuits provide the interface between the
Section II

PRINCIPLES OF OPERATION

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 GPIB or from
the supply's front panel. The GPIB board interprets
commands from the GPIB or from the front panel to control
the selected output. The GPIB board also processes
measurement and status data received from the output
boards. This data may be read back to the controller over
the GPIB and/or displayed on the supply's front panel.
Also, each output board can be individually calibrated over
the GPIB using calibration commands (See Appendix A in
Operating Manual). Correction factors are calculated during
calibration and are stored in non-volatile memory on the
GPIB board. The GPIB board is described in greater detail in
paragraph 2-7.
2-5
Most of the remote operations that can be performed via the
GPIB can also be performed from the supply's front panel.
In addition to the ON/OFF switch already mentioned, the
front panel contains an LCD display and a keypad. The LCD
display consists of an alphanumeric display and status
annunciators. The LCD normally displays the measured
output voltage and current of the selected output. When
programming an output from the front panel keypad, the
selected output channel, the function being programmed,
and the present value will be displayed. The annunciators
indicate which output channel has been selected and give
GPIB power supply status information. The keypad allows
control of the supply's system functions as well as
individual control of each output channel. Detailed
instructions on using the front panel's display and keypad
are given in the Operating Manual.
2-6
Each power supply model contains two or more (up to four)
output boards. The output combinations that correspond to
each model are shown in Figure 2-1. Each isolated output
can supply power in two ranges as shown in Figure 2-2.
This flexibility allows you to use the same output to power
loads with different voltage and current requirements. The
output ranges and operating characteristics of each output
are described in greater detail in Section IV of the Operating
Manual.
As shown in Figure 2-1, each output board contains a
rectifier/filter, power module, control circuit, secondary
interface circuit, and bias supplies. Note that each 80 W
output board has two power modules connected in parallel.
2-1

Front Panel

Output Boards