INTRODUCTION
Programmable power supplies are digitally controlled power sources that provide accurate and adjustable levels of voltage, current and frequency. They include a processor, voltage/current programming circuits, current shunt and voltage/current read-back circuits. Remote sensing functions compensate for voltage drops in the load leads by providing feedback of the actual voltage at the load. Overvoltage and overcurrent protection modes are available. Comparators continuously monitor the overvoltage against a program reference value. If the output voltage exceeds the reference value a trigger signal is sent to a silicon controlled rectifier (SCR) across the output, shutting off the source to the load. Most programmable power supplies are subjected to extensive testing and burn-in period o ensure long-term performance.
Programmable power supplies can provide AC, DC or both AC and DC outputs. Typically AC outputs are single phase or three phase. Single phase is used for low voltage applications. Three phase is used with high voltage power supplies. Waveforms include sine waves, square waves and triangular waves. Important AC output specifications include output voltage, voltage accuracy, output frequency and output current. Important Dc output specifications include output voltage, voltage accuracy, current and power. Apparent power is the root mean square (RMS) current and the RMS voltage of AC output. Efficiency is the AC output power divided by the input apparent power.
Programmable power supplies are available with a variety of special features. Computer interfaces provide remote monitoring and control. Overcurrent protection in internal circuitry that limits or shut down the voltage output during overvoltage conditions. Typically, overvoltage protection is provided for the primary output. Pure sine output produces a very high quality, pure sine waveform output. Short circuit protection may include electronic current limiting and thermal resets with automatic recovery. Temperature-compensated devices balance changes in temperature that can result in undesirable outputs.
Programmable power supplies are used in a variety of automated equipment testing, certification, and calibration applications. Devices that are capable of following complex output profiles are also used in highly specialized applications such as crystal growth and differential thermal analysis (DTA) at high pressures. Some programmable power supplies are modular, board-mounted, or include a floor-standing cabinet. Others are wall mounted, floor mounted or sit in a desktop or shelf. Open frame and enclosed units are also available. Programmable power supplies can include can include serial interface such as general-purpose interface bus (GPIB) as well as integral software.
BLOCK DIAGRAM
IMPLEMENTATION
The line voltage is passed through bridge rectifier. A diode bridge or bridge rectifier is an arrangement of four diodes connected in a bridge circuit as shown below, that provides the same polarity of output voltage for any polarity of the input voltage. When used in its most common application, for conversion of alternating current (AC) input into direct current (DC) output, it is known as a bridge rectifier. The bridge recitifier provides full wave rectification from a two wire AC input (saving the cost of a center tapped transformer) but has two diode drops rather than one reducing efficiency over a center tap based design for the same output voltage.
The voltage is now passed through LM2678. It provides an output voltage of 5V. Its output is connected to TPS7xx series of ICs. They are controlled by a 32 bit controller. A microcontroller (or MCU) is a computer-on-a-chip. It is a type of microprocessor emphasizing self-sufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor. The output of the 32 bit controller can be used to provide the feedback and boost signals.
There is more than one LM or TPS. These different controllers or power ICs are used to control separate devices or groups of devices in case finite precision of each device is not required. The TPS IC has internal shutdown feature to power down its feeding devices. They can be controlled by the 32 bit controller for precise shut down features.
The 32 bit controller also has built-in DSP algorithms developed using software that can be used for predictive load scheduling and power supply features. It uses switched mode power supply features for power control. A switched-mode power supply or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator — an internal control circuit that switches power transistors (such as MOSFETs) rapidly on and off in order to stabilize the output voltage or current. Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated and their switching currents can cause noise problems if not carefully suppressed. The power output to cost crossover point between SMPS and linear regulating alternatives has been falling since the early 1980s as SMPS technology was developed and integrated into dedicated silicon chips. There are also provisions in the microcontroller to generate different voltage and current levels etc.
FLEXCON-3000
Flexcon-3000 is a versatile, programmable, web-enabled, application-independent process controller that can provide solutions to a wide range of process control applications. It forms the platform where the power supply is made. Easy-to-use web user interface allows setting up multi-loop process control and programmable logic control with minimum level of expertise. The FlexCon-3000 uses a modular architecture and self-stacking hardware design that enables users to customize its feature sets to develop an application-specific process controller easily. It is very compact and offers many sophisticated features which are:
• Scalable and modular hardware architecture
• Low power consumption
• Configurable analog and digital input/output
• Selectable number of control loops with dual output (heat and cool)
• Manual/Automatic/Cascade/Ratio/Differential loop capability
• PID Control with auto-tuning option
• Independently selectable ON/OFF, Time-proportionate, Distributed Zero Crossing and DAC control output types
• Easy-to-use web-based interface (10/100BaseT) to monitor, configure and control
• No software installation needed
• Real-time graphical representation of loop variables
• Optional alarm notification via Email
• Optional FTP support
• Remote firmware updating
• 20-25% less costly than currently available products
Web Based User Interface
FlexCon-3000 provides simple to use web based user interface. The controller has an integrated Web Server that dynamically updates the embedded web pages. The web interface allows remote configuration and control of the system. It also allows the user to get the status of processes and events in the plant. Status web pages are updated at specified intervals to give the user a real-time view of the process. It also incorporates feature to view logged data as well as historical/real-time trending for data analysis. It also provides role-based access of users to the system.
Setting UpFlexCon-3000 for Web Connectivity
Hardware Settings
Connect one end of an RJ-45 straight through Ethernet cable to the RJ45 socket on the front plate of the controller and the other end to the RJ45 socket on the hub. The controller can also be directly connected to the PC’s RJ45 socket using a crossover Ethernet cable. Make sure the power LED (Red LED (D4)) and the Ethernet LEDs (Green) are active. There are three Green LEDs on the front plate for indicating Ethernet connection. The LED D1 indicates Ethernet connection established. LED D2 indicates byte transmission and D3 indicates byte reception.
Network Settings
For accessing FlexCon-3000, via web user interface, user has to properly configure the network settings of his computer. The default factory set IP address and subnet mask of the FlexCon-3000 is 192.168.0.1, and 255.255.255.0 respectively.
The IP address of user’s computer must be set to 192.168.0.X (where “X” is a number between 2 and 254.) Once accessed the Network configurations can be changed to the desired setting by configuring the IP Setup page in the web interface .
Accessing FlexCon-3000 via Web Interface
The FlexCon-3000 provides an embedded Web-based user interface, which is platform independent. User can configure FlexCon-3000 using any ubiquitous web browsers like Netscape Communicator, Internet Explorer etc.
Start up and Log in
Open any web browser and enter the default IP address into the address field location of the web browser. After the connection is established, the user authentication window will pop up. To log in, enter the factory default username of “Administrator” and the default password “Administrator”. This default user has Administrative privilege. Once the username and password is validated, the Home page of the user interface will appear
NetBurner Network Development Kit
Programming Guide
Using the NetBurner IDE to Create the Template Program
This section serves as both an introduction to the IDE as well as describing how to create a simple network application program that can be used as a template for more complex applications. By the end of this section you will know how to create a project, compile and application and download the application to your NetBurner device. If you prefer command line tools, you can do all of your development using the make utility.
Traditionally called the “Hello World” program, the “Template Program” will specify a minimal code base from which you can write your future applications. The objective of this template program is to print the characters “Hello World” out the debug port of your NetBurner device. In addition, this template program will enable network services so that it can be downloaded over a network connection instead of through a serial port or a BDM (Background Debug Mode) port.
The Debug Monitor
The NetBurner device contains a flash memory boot sector loaded with a boot program called the “Debug Monitor”. This program is designed to be very small and takes up less than 16 Kbytes of memory space. The Debug Monitor is not designed to provide full TCP network communications, although it does support the TFTP protocol.
The full TCP/IP Stack functionality is compiled as part of your application. If you download an application that immediately crashes when it boots, full network services will not be available. In this case, the NetBurner Debug Monitor comes to the rescue. Once in the Debug Monitor (at the NB> prompt), you can download a working application through the serial debug port.
IDE Overview
The Integrated Development Environment (IDE) enables you to create, edit, compile and download applications to your NetBurner device.
Features include:
An Application wizard for creating new applications
The ability to create new projects for existing applications
Project Manager
Customizable syntax highlighting
Compile, link and download applications in one easy step
Class browser
Function Listing
CONCLUSION
The programmable power supply is constructed on the Flexcon module. On the web page, the duty cycle for the PWM input is given. Depending on the duty cycle provided, different output voltages are obtained. The PWM module working condition is displayed. Thus, the programmable power supply can be programmed to provide different voltages to many devices simultaneously.
REFERENCES
· Microcontrollers and Programming, Douglas V Hall,3rd edition