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Chapter 5 Theory of Operation
Main Power Supply
4
5
Power Supplies
The line input voltage is filtered, and then applied to the main power
supply. The main power supply provides all power to the instrument.
Secondary power supplies are contained on the main circuit board.
The secondary supplies control the fan, create the –2.1 V and +3.3 V
voltages, and provide the isolated +5 V supply.
Main Power Supply
The main power supply is a switching supply. No schematic is given for
this supply since it should be replaced as a unit. It features a universal
input, eliminating the need to set power line voltage or frequency.
The main supply provides the following voltages to the main board:
• +5 V (for logic and analog circuitry)
• +16 V, –16 V (for analog circuitry)
• –5.2 V (for ECL logic and analog circuitry)
• +12 V isolated (for fan and earth-referenced logic)
• +12 V standby (for power switch and over-temperature shutdown
circuitry)
The main supply uses an electronic power switch, controlled by logic on
the main board, to turn the supplies on or off. The +12 V standby power
is always available when line power is applied. All the power supply
outputs can be checked on the main board.
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