Agilent Technologies 6031A Isolation, Secondary Microprocessor, Digital-to-Analog Converters

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.

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