5
Theory of operation
The diagram below outlines the topology and major internal components of a fully assembled system. Four output slots are
provided and can be populated by any combination of output modules (OP-A, OP-B, OP-C, OP-D). The remaining components
in the block diagram are housed in the input module.
The input module is responsible for receiving the AC mains line voltage and converting it to an appropriate DC voltage whilst
providing protection from AC line disturbances and preventing excessive EMI emissions and current harmonics. The integrated
EMI filter attenuates high frequency current emissions to levels below EN55022 class B. It also provides single pole fusing in
the live conductor (L) and protection from line disturbances as outlined in EN61000.
Inrush current is controlled by a resistive element upon initial connection to the AC line. Once the internal capacitances have
been charged, the resistive element is bypassed to reduce losses.
Active Power Factor Correction (PFC) is used to ensure an accurate input current waveform with extremely low harmonic
content, exceeding the requirements of EN61000-3-2. This stage also provides active input current limiting which prevents
overloading of the input stage while maintaining high power factor.
The output of the PFC stage charges the hold-up electrolytic capacitors which store enough energy to allow the system to
continue operating during minor line disturbances. These are the only electrolytic capacitors in the entire power supply and to
further increase system reliability, long life and high temperature capacitors are used.
A highly efficient zero voltage switching circuit (ZVS) is used to drive the medically isolated transformer from the hold-up
capacitors. The output modules connect to the transformer secondary and provide safe isolated power to a high performance
synchronous rectifier power converter which is controlled using the latest analog control technology to produce superior output
performance in an extremely reduced size.
A built in fan, which speed is automatically controlled, ensures the unit proper cooling in any operating condition maintaining
at minimum its RPM and, in turn, acoustic noise. The control function directly correlate the fan supply voltage to the control
voltage derived from the half bridge current sense resistor. The secondary control input is derived from a non-linear
temperature sensor located near the rectifiers on the main board.
T
HEORY OF
O
PERATION
