Chapter 4 Theory of Operation
Block Diagram Overview
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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.
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