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Theory Of Operation 61
4
Theory of Operation
This chapter provides a brief theory of operation for the Agilent 6610xA Power Modules. Figure 4-1 is a block diagram of
the primary circuit functions of the power modules. The diagram references the schematic sheets where the circuits are
located.
AC Input and Bias Supplies
AC input power is distributed to each module through the backplane connector board on the mainframe. A turn-on relay
inside the module applies ac power from the mainframe to the power module. This relay receives its bias power from the
mainframe and is opened and closed by a control signal from the mainframe.
The ac input is rectified and filtered in the power module, producing the + and - dc rail. In addition to the dc rail, the ac
input is also applied to a bias transformer, which provides the following bias voltages:
+ 15V (primary)
+ 5V (secondary)
±
12V (secondary)
Microprocessor Circuits
All communication between the modules and the controller or keyboard except for the trigger signals is processed by U44
on the mainframe. The primary function of this microprocessor is to distribute the digital signals from controller or
keyboard to the correct module slot in the mainframe.
Microprocessor Ul on the modules communicates with U44 through two data lines -a transmit and a receive line (Tx and
Rx). Associated with Ul is ROM chip U2, RAM chip U3, and EEPROM chip U22.
At turn-on, microprocessor Ul first transfers the calibration constants that are stored in the EEPROM chip of each module
into RAM. It then applies the calibration correction factors in RAM to the voltage or current setting information and
calculates a bit count that it sends to the DACs. The microprocessor directs the data either to the CV or the CC DAC. It is
able to send sixteen data bits to each DAC by first strobing in the upper byte, and then strobing in the lower byte.
CV/CC DACs
Upon receiving data from the microprocessor, the CC and CV DACS output the correct analog output voltage. Both the CC
and the CV DACs output an analog signal in the range of 0 to minus 6 volts (calibrated), which corresponds to the zero to
full-scale output range of the power module’s voltage and current. The DACs are referenced to a regulated 7V bias.