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2-1
INTRODUCTION
The following paragraphs provide block diagram level
descriptions of the power supplies. 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. 06626-90001).
2-2
OVERALL BLOCK DIAGRAM DESCRIPTION
(FIGURE 2-1)
Figure 2-1 is a block diagram that
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 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; a4 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 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.
GPIB Board
2-4
GPIB board contains the GPIB interface, system
The
microcomputer, output boards interface, and front panel
interface. These circuits provide 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 GPIB or from
the supply's front panel. The GPIB board
commands from the GPIB
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
Section II
PRINCIPLES OF OPERATION
illustrates the major
inte r prets
or from the front panel to
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 stored in non-volatile memory on the GPIB
board. The GPIB board is described in greater detail in
paragraph 2-7.
2-5
Front Panel
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 and 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
Output Boards
The Agilent 6625A and 6628A contain two output boards
and the Agilent 6626A and 6629A contain 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.
The ac input to each output board is rectified, filtered, and
applied to the power module regulator. Each output board
employs series regulation techniques. The regulator element
is connected in series with the load and operates in the linear
region (between saturation and cutoff) of the transistor
characteristic curve. Regulation is achieved by varying the
conduction of the series element in response to changes in
the line voltage or the load. The constant voltage CV control
circuit compares the voltage at the output with a reference
voltage and generates a control signal which varies the
conduction of the series regulator to raise or lower the
output voltage as required. The constant current CC control
2-1
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Troubleshooting
