Vega Customer Applications Manual
Section 9 - Functional Notes
Rev. A3: October 2003
Page 29 of 48
Section 9 - Functional Notes
The aim of this application note is to describe and explain the function of the Vega 450W and 650W converters and the
function of Vega modules. It is not a description of the circuits and topologies, but purely a description of practical
functionality.
This application note does not contain the specifications of the converters and modules themselves but aims to expand
and explain them. Please refer to the "Vega Specification" documents themselves for each module and converter.
Outline.
Each Vega power supply consists of a case containing a 450W or 650W primary converter and a number of power
modules. The power modules can be fitted in thousands of possible combinations or configurations.
The Primary converter can be fitted with a number of options (primary options). The output modules can also be fitted
with a number of options (secondary options).
Please refer to Vega specifications to see the available modules and allowed configurations and to see how to order
the right line-up of modules for your application. The Vega specification also shows the primary and secondary
options available and how to order them.
Overview function.
The primary converter (450W and 650W) :-
Mains is fed to a power factor correction circuit via an input filter. The Power factor correction (boost converter)
reduces the harmonic distortion of the mains supply. Current is drawn sinusoidally, rather than in sudden burst at the
peak of each mains cycle as it would be if simple rectification was used. The boost converter and bulk capacitors
provide rectified and smoothed DC to the forward converter. The forward converter chops the DC at 200Khz using a
power switching device controlled by a Pulse width modulator. The waveform is then applied to the primary of a
transformer.
The primary converter is protected against current limit and has thermal protection.
The output modules :-
The secondary of each module fits within the primary windings of the forward converter transformer. Each output
module rectifies, smooths the secondary waveform and regulates the voltage using a Magnetic-Amplifier (saturable
reactor). Smooth, stable, safety isolated, DC voltage at the required current level is thus provided.
The modules monitor their output current via a current transformer and in event of current exceeding a set point keeps
the current to a safe level via the control circuit.
The modules also monitor their output voltage level and in event of an overvoltage being detected feeds the
information to the primary converter which is shut down (see "Overvoltage" later).
Input Voltage.
Vega functions from 85-264 VAC 47-63Hz. Active power factor correction is always present to ensure Vega meets the
requirements for distortion of the mains (EN61000-3-2).
Inrush current.
At initial turn on a surge of input current will flow to charge the internal capacitors. At turn on, the current flows through
a thermistor which offers high resistance and impedes the flow of current to <40A. When the voltage of the bulk
