4 - Principles of Operation

The EEPROM (electrically erasable programmable read-only memory) chip on the A2 interface board stores a variety of data and configuration information. This information includes calibration constants, GPIB address, present programming language, and model-dependent data, such as the minimum and maximum values of voltage and current. One of the EEPROM storage locations holds a checksum value which is used to verify the integrity of the EEPROM data. Access to the calibration data in the EEPROM is controlled by the combination of a password and switch settings on A2S201, located on A2 interface board (See Chapter 3 "Inhibit Calibration Switch").

The Dual 12-bit DAC converts the programmed value of voltage and current on the bus into the CV_Prog and

CC_Prog signals, which are sent to the CV control circuits in order to control the magnitude of the output voltage in the CV mode and output current in CC mode. The CV_Prog and CC_Prog signals are in the 0 to -5 V range, which corresponds to the zero to full-scale output ratings of the dc power supply.

The Quad 8-bit DAC converts programmed information for the following circuits into analog format: negative offset trim (OS_Trim_Neg), overvoltage setting (OV_Prog), current measurement range select (Range_Select), and fan speed programming (Fan_Prog). The OS_Trim_Neg signal allows the negative current control circuit to be calibrated at zero. The OV_Prog signal is applied to the OV detect circuit, which compares the programmed overvoltage setting with the actual output voltage. The Range_Select signal selects either the high or the low (20mA) measurement range. The Fan_Prog signal is applied to the fan speed control circuit in order to speed up the fan as temperature increases, and to slow the fan speed down as temperature decreases.

The 16-bit ADC in conjunction with a 4x1 multiplexer returns data from the following measurement signals to the logic array: monitored output voltage (VMon), monitored high-range current (Imon_H), monitored low-range current (Imon_L), and monitored peak current (Imon_P). All measurement signals are in the range of 0 to +5V, which corresponds to the zero to full-scale readback capability of the dc power supply.

The 8-channel, 8-bit ADC returns the following signals to the logic array: high-range output current (Imon_H), high range negative current (Imon_H-), overvoltage (V_Mon), ambient temperature (Temp_Amb), heatsink temperature (HS_Therm), and output fuse state (Fuse). Five of these signals are for fan control. The logic array varies the Fan_Prog signal depending upon the ambient temperature, the heatsink temperature, and the present output voltage and current. The Fuse signal informs the logic array if the output fuse (F300) is open.

A1 Main Board Circuits

Power Circuits

As shown in Figure 4-2, the power circuits consist of: input power rectifiers and filter, current-monitoring resistors, an output stage, a voltage gain stage, an overvoltage SCR, and an output filter.

The ac input rectifier and filter converts ac input to a dc level. The output stage regulates this dc level at the output of the power supply. The output stage has up to four parallel NPN transistors mounted on a heatsink and connected between the +Rail and the +Output. These transistors are driven to conduct by a positive-going signal from driver Q303 (located in the voltage gain stage). The output stage also has up to four parallel PNP transistors mounted on a heatsink and connected between the +Rail and the -Rail. These transistors are driven to conduct by a negative-going signal from driver Q304 (located in the voltage gain stage).

The voltage gain stage is controlled by a signal from the control circuits. A positive-going signal to the voltage gain stage makes the output more positive. A negative-going signal to the voltage gain stage makes the output more negative. The Turn-on control signal to the voltage gain stage simply keeps the output of the unit turned off for about 100 milliseconds at power turn-on while the microprocessor is initializing the unit.

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Agilent Technologies 6633B, 6634B, 66332A, 6632B service manual A1 Main Board Circuits, Power Circuits
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6632B, 6633B, 66332A, 6634B specifications

Agilent Technologies, a leader in electronic test and measurement solutions, offers a range of power supplies designed to meet various application needs. Notable models include the 6632B, 6634B, 66332A, 6633B, and 6612C. Each of these units provides unique features and technologies that cater to researchers, engineers, and technicians in the industry.

The Agilent 6632B is a single-output DC power supply that delivers up to 30V and 3A. It is known for its excellent load regulation and low noise, making it ideal for sensitive electronic testing. The model includes built-in voltage and current measurement capabilities, allowing users to monitor output conditions in real time. The 6632B is commonly used in laboratory environments, educational institutions, and manufacturing lines.

Moving to the 6634B, this model offers dual-output capabilities with a maximum output of 30V and 6A. This versatility enables simultaneous powering of two different devices or circuit sections. It also features parallel and series operation options, allowing users to create a custom power supply configuration for specific applications. With a programmable interface, the 6634B simplifies test automation, ensuring efficiency in extensive testing scenarios.

The Agilent 66332A stands out with its precision and high performance. This power supply provides three outputs—two programmable and one fixed—yielding flexible power configurations. Its intuitive user interface allows easy adjustment of voltage and current settings. The device is equipped with extensive protection features to safeguard both the power supply and the connected load against faults. It is an excellent choice for complex testing setups that require reliable power.

The 6633B model offers a high-performance power supply with dual outputs, similar to the 6634B but with enhanced specifications. It can provide up to 40V and 2A per channel, delivering precision for demanding applications. This model is particularly suited for industries focused on high-reliability applications, such as telecommunications and aerospace.

Lastly, the Agilent 6612C is a compact and lightweight power supply providing single-output up to 60V and 2A. This model is designed for simplicity and ease of use, making it an excellent choice for portable applications. The 6612C’s unique characteristics include a compact design and user-friendly controls, which facilitate operation in field settings.

In summary, Agilent Technologies’ power supply models—6632B, 6634B, 66332A, 6633B, and 6612C—offer an array of features that cater to a wide range of testing and research needs, ensuring reliable power delivery in various contexts.
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