Agilent Technologies E3633A, E3634A manual AC Input and Bias Supplies

Chapter 4 Theory of Operation

AC Input and Bias Supplies

AC Input and Bias Supplies

Referring to the schematic shown on pages 129 and 130, 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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