Chapter 4 Theory of Operation
AC Input and Bias Supplies
AC Input and Bias Supplies
Referring to the schematic shown on page 121 and 122, 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 four sections; +5 Vdc and
The ±17.4 Vdc for the display circuits are produced by rectifier CR4, filter capacitors C19 and C24, 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 R15 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 CR7, filter capacitor C21, and regulator U10. The GPIB
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