Keysight E3631A, Service Manual

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4 Theory of Operation
96 Keysight E3631A Service Guide
Block Diagram Overview
This discussion pertains to the block diagram on the next page. The power
supply's circuitry is divided into two major blocks: the floating circuitry and the
ground referenced circuitry. All power mesh and control circuits, display circuit,
and digital circuits are contained in the floating circuitry. This circuitry also
contains the power supply's main controller. The ground referenced circuitry
provides the interface between the user and the power supply.
The floating circuitry can be viewed in four pieces; the DAC system, the digital
logic section (floating logic), the power mesh and control section (+6V and ±25V
power circuits), and the front panel (display and keyboard) section.
The floating logic receives digital signals from the earth-referenced logic and the
DAC converts them to analog signals which are sent to the power control circuits
in order to program the power supply's output voltage and current. The power
supply can also be commanded to send measurement and status data back to the
remote interface controller and/or the VFD (vacuum fluorescent display) display
on the front panel. The data is processed and sent back via the floating logic and
earth-referenced logic.
The power mesh and control circuits contains voltage and current control circuits
which allows the power supply to operate in either the constant voltage (CV) or
constant current (CC) mode. The control circuits compare the power supply's
output voltage or current with the programmed value and generates a control
signal which varies the conduction of the series pass transistor to raise or lower
the output as required.
The front panel circuits consist of VFD control, display high voltage drivers, and
keyboard scanning. Communication between the front panel and floating logic
circuits is accomplished through a 4-wire bi-directional serial interface.
The ground referenced circuitry uses a controller configured as a slave to the main
controller. This controller establishes external I/O communication with the main
controller through a bi-directional, optically isolated, serial communications link.
The earth referenced controller controls low-level GPIB (IEEE-488) and RS-232
interface operation.
Separate reference and bias supplies are provided for the floating and ground
reference circuitry. The front panel operates from the floating circuitry with its
logic common different from the main controller logic common.