4 Theory of Operation
102 Keysight E3633A and E3634A Service Guide
AC Input and Bias Supplies
The ac mains are connected by a fused power module. This module incorporates
the functions of mains connection, fusing, and line voltage selection (100/115/
230 Vac). The line voltage selection function of the module selects which primary
winding of power transformer is energized. The transformer secondary windings
are connected to the main pc board through connectors.
The bias supplies are consists of three sections; +5 Vdc and -5.1 Vdc for the power
circuits and floating logic; ±17.4 Vdc for the display; and +5 Vdc for the earth
referenced logic. Power-on reset signals are provided by the +5 Vdc supply of the
floating logic.
The ±17.4 Vdc for the display circuits are produced by rectifier CR8, filter
capacitors C18 and C19, and voltage regulators U12 and U16. A separate winding
of transformer provides a center tapped 6 Vrms filament supply for the display.
The floating +5 Vdc is produced from the separate winding of transformer. The
+5_REF signal is derived from +15 Vdc supply and the TURN_ON RESET signal is
derived from +5 Vdc supply. The FAN FAIL signal is asserted when the fan current
through R20 is not detected. The TURN_ON RESET signal holds the main
controller and other logic in a reset state until the +5 Vdc logic power is fully
operational. This signal is generally active only following application of line power
to the instrument.
The +5V dc earth referenced supply is produced by rectifier CR4, filter capacitor
C23, and regulator U9. The GPIB (IEEE-488) and RS-232 computer interfaces are
powered from this supply.
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