Chapter 4 Theory of Operation

AC Input and Bias Supplies

AC Input and Bias Supplies

Referring to the schematic shown on page 127, 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 T1 is energized. The transformer secondary windings are connected to the main pc board through connectors.

The bias supplies are consists of four sections; ±15 Vdc for the +6V power circuits; ±15 Vdc, +5 Vdc and -5.1 Vdc for the ±25V power circuits and floating logic; ±16.4 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 ±15 Vdc for the +6V power circuits are produced by rectifiers CR15 and CR16, filter capacitors C43 and C44, and voltage regulators U24 and U25 on the bottom board. These supplies provide bias voltages for the +6V power circuits.

The ±16.4 Vdc for the display circuits are produced by rectifier CR20, filter capacitors C44 and C45, and voltage regulators U24 and U25 on the top board. A separate winding of T1 provides a center tapped 6 Vrms filament supply for the display.

The ±15 Vdc for the ±25V power circuits are derived from ±16.4 Vdc by diodes CR15 through CR18 on the top board. These supplies provide bias voltages for the ±25V power circuits.

The floating +5 Vdc and -5.1 Vdc supplies are produced from ±16.4 Vdc supplies. VR2 on the top board forms a clamp circuit to provide over voltage protection in the event of a regulator failure. The ADC 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 R73 on the top board is not detected. The TURN_ON RESET signal holds the main controller and other logic in a reset state until after 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 CR3, filter capacitor C15, and regulator U11 on the bottom board. The GPIB (IEEE-488) and RS-232 computer interfaces are powered from this supply.

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Agilent Technologies E3631A manual Theory of Operation AC Input and Bias Supplies