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THEORY OF OPERATION
E-5 E-5
INVERTEC STT
FIGURE E.5 – MAIN TRANSFORMER, OUTPUT RECTIFICATION AND CHOKE
MAIN TRANSFORMER, OUTPUT
RECTIFICATION AND CHOKE
Each switch board works as a switch pair. Each board
feeds a separate, oppositely wound primary winding of
the main transformer. The opposite directions of cur-
rent flow through the main transformer primary and the
offset timing of the switch boards induce an AC square
wave output signal at the secondary of the main trans-
former.
The DC current flow through each primary winding,
which is monitored by the current transformer T3, is
redirected or "clamped" back to each respective input
capacitor when the FETs are turned off. This is need-
ed due to the inductance of the transformer primary
windings. The cross coupling of the primaries along
with the clamping action of the diode maintain capaci-
tor balance when they are connected in the series (high
voltage) input configuration.
The firing of both switch board pairs occurs during
halves of 50 microsecond intervals, creating a constant
20 KHZ output.
The AC output from the main transformer secondary is
rectified to a DC output and is applied through a stabi-
lizer output choke, current sensor, IGBT module and
remote protection board to the output terminals.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
