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EEPROM
The primary microprocessor determines the power supply ID, start-up parameters, calibration constants and scale factors by
reading the factory-initialized EEPROM.
Isolation
Two optical isolators transmit serial data between the primary and secondary microprocessors while maintaining electrical
isolation between the controller/user-interface and the power mesh.
Secondary Microprocessor
The secondary microprocessor translates the serial data from the primary microprocessor into a parallel data bus and other
control signals. Values are loaded into the voltage, current, and readback DAC via the data bus. The secondary
microprocessor also controls the analog multiplexer, which is used when reading back the actual output.
Digital-to-Analog Converters
Output voltage and current are controlled by two 12-bit DACs whose digital inputs are directly connected to the secondary
microprocessor. The microprocessor programs the DACs according to data received over the GPIB or from the front panel
rotary pulse generator. The DAC circuits also include buffers and compensation amplifiers.
The 12-bit readback DAC is connected to the input of a comparator where it's output is compared to the unknown voltage
output of the analog multiplexer. The secondary microprocessor programs the output of the readback DAC starting with the
MSB and continuing down to the LSB. Each bit is programmed either on or off until the output of the DAC is closest to the
unknown voltage output of the multiplexer. At this point, the microprocessor returns the programmed value of the readback
DAC.
Analog Multiplexer
The analog multiplexer selects one of five input voltages to be compared to the readback DAC. This comparison allows the
microprocessor to determine the value of the input voltage. The five inputs of the multiplexer are: CV_PROG and
CC_PROG, which are only used during selftest, at power-on, or in response to the TEST? query when the supply is
disabled; OV_MON, which represents the overvoltage trip setting; and I_MON and V_MON, which represent the measured
values of output current and voltage.
Status Inputs
The status inputs from the main board provide the following status information to the secondary microprocessor. They are:
CC, which is set when the supply is operating in constant current mode; CV, which is set when the supply is in constant
voltage mode; AC_FAULT, which signals that ac power has dropped below the minimum operating voltage of the supply;
OT, which indicates an overtemperature condition has occurred on the supply; and OV, which indicates an overvoltage has
occurred on the supply.