In this paper, practical application, combined with the welding machine control system power embedded system design and debugging process encountered some problems, analyzed and discussed the power embedded system design and debugging methods.
1 system hardware architecture
Embedded systems based Welding Electrode Manufacturer control system design, to AT91RM9200 as the system core microprocessor control system requirements based on expansion of SDRAM, SRAM, Flash, keyboard, LCD display circuit parameters can be adjusted in real time, display and error alarm, RS485 serial interface for data transfer communications, infrared remote control can be. System hardware structure shown in Figure 1.
2 System Power Supply Design
2.1 System Power Works
AT91RM9200 is a complete system built around the ARM920T processor chip. It has a wealth of system and application peripherals and standard interfaces, making low-power, low-cost embedded industrial products. AT91RM9200 offers a full-function power management controller (PMC), to optimize the overall system power consumption, and to support normal, idle, slow clock and Standby mode, to provide different power levels and incident response delay time . In idle mode, ARM processor clock and wait for the next interrupt is disabled (or master reset); slow clock mode is selected after reset mode, in this mode the main oscillator
Oscillator circuit is the basis for sending and receiving equipment, its role is to produce a certain frequency of the AC signal, an energy conversion device - the DC can be converted to a certain frequency AC power. Off to reduce power consumption and PLL; Standby mode is the slow clock mode and idle mode of combination, which enables the processor to quickly respond to wake events, and maintains a low power consumption. When the system outside normal working hours from the DC power supply and battery charging, disconnect the external power supply automatically switches to the internal backup battery.
2.2 Power Circuit Design
AT91RM9200 has five types of power supply pins: VDDCORE pin for power supply to the core, typically 1.8 V; VDDPLL, VDDOSC respectively, to the PLL or oscillator power supply, typically 1.8 V; VDDIOP, VDDIOM were used to the outside set I / O port cable, USB transceiver and the external bus interface I / O port line power supply, usually 3.3 V. In addition, the system's keyboard, display circuit supply voltage of +5 V power supply needs. Therefore, the control system needs to use three groups of power. Through control of the whole control system requirements and performance analysis to determine the system load current is about 3 A. Therefore, the system power supply voltage regulator chips use a series of ON's LM2576 voltage regulator, the external DC power supply voltage regulator into the system needs to +3.3 V and +5 V power supply. As the power supply requirements of the system kernel 1.8 V, so the system should be used two power conversion circuit. This selection of TI's micro-power, low dropout voltage PMOS regulator (LDO chip) TPS72518 chip as the core power conversion, the +3.3 V regulator to +1.8 V, supplies power for the processor core. System power supply circuit shown in Figure 2. Figure 2 shows the power supply decoupling and other embedded systems, PCB design. C3, C6 is the voltage regulator chip electrolytic bypass capacitor in the circuit which enables the circuit to stabilize access to work; C2, C5, C8 and stability for the output capacitor, for reducing the output ripple, noise and output load current change impact good results, according to the regulator's own work requirements, were selected capacitance 10 μF, 100 μF electrolytic capacitor
Electrolytic capacitor is made of two parallel metal plates and the electrolyte is placed between two metal plates that form the capacitor. Capacitors used in accordance with the electrode material. Paid to the type of electrolyte capacitor name. Coated with electrolyte media have polarity, positive and negative points can not be connected correctly.
32-bit microprocessor-based embedded system performance depends largely on the stability and reliability of the clock circuit, the clock circuit depends on the stability of the system phase-locked loop (PLL) stability. Therefore, the analog part of the PLL power supply filter circuit should be used to ensure the stability of power supply . Microprocessor internal clock, power and reset control key components of various modes of operation parameters on the system plays an important or even decisive role. Therefore, in order to ensure that the various modes of operation under the same set of parameters, usually in the embedded system design to provide back-up battery power supply circuit. Shown in Figure 2, using TI BQ24200 battery charger as a back-up power system battery, external power supply when the system is working properly charge it, the external power supply is cut off after the system power by it, in order to save important system parameters.
3 debug system power
3.1 Debugging the content and procedures
A large embedded system hardware circuit, should be sub-module for welding, testing, to avoid the problems encountered can not start checking. Because the system requires access to each circuit block input power, if power input properly, then the output will not correct or even burn IC
IC is the use of semiconductor production process, in a small silicon chip production, many transistors and resistors, capacitors and other components, and multi-layer wiring in accordance with the method or tunnel routing components into a complete electronic circuit . It is in the circuit by the letter "IC" (also useful for text symbol "N", etc.) said. So should the first installation, commissioning and system power supply module. The success of the system power supply circuit debugging module is the hardware circuit debug key to success.
After the welding circuit components based on a good, carefully check whether the Tungsten Welding Electrode is wrong components, circuit boards or welding slag existence Weld short circuit phenomenon, check and correct the power to debug. By the DC power supply
For the load to provide a stable DC power electronic devices. DC power supply power supply mostly AC power, when the AC power supply voltage or load resistance changes, the regulator of the DC output voltage will remain stable. DC power supply with electronic equipment to high precision, high stability and high reliability in the direction of the power supply for electronic equipment put forward higher requirements.
Generator output power access system power module input port (POW1), input power Vin adjusted to +6 V, with an oscilloscope check the system power supply 1.8 V, 3.3 V, 5 V output port, there is no voltage output. Power to re-check the circuit and found that electrolytic capacitor C6 has been burned black, because the C6 positive and negative polarity reversed. A new capacitor for correct welding power debugging, 1.8 V, 5 V output voltage is normal, while the output voltage of 3.3 V voltage less than 3 V. View LM2576 voltage regulator chip data sheet, the regulator input power Vin, simultaneous detection of three groups of system power supply voltage, power output is correct when the three groups, the input voltage Vin is 6.7 V or so. As the load current control system is about 3 A, so by adding the load current in the circuit load resistance of 3 A in order to test the stability of the system power supply. After debugging, capacitors, inductors and other components, the normal heat output voltage value is correct. At this point, the system power supply module debugging success.
Next, step by step installation, commissioning other module circuits. Each installation of a power-detection module, the main power supply voltage detection system and the module's input voltage, the output is correct. When the entire system installed after the hardware power-on circuit debugging and found that the system power supply instability, which often power-down DC input power, resulting in the system power supply is not working properly. Because the system circuits are more difficult to check, has not been resolved. In many power testing, debugging, and found a circuit voltage (boost) converter smoke - the chip was burned. Carefully inspect the chip's data sheet, found that the chip model wrong, positive and negative feedback voltage pin is reversed. After the removal of the chip, the system power supply is working properly.
3.2 Analysis of Debugging
Commissioning of the system power supply circuit and the entire system hardware installation and commissioning process analysis, combined with the installation, the problems encountered during commissioning, the following conclusions:
â‘ chip resistors
Chip fixed resistor, from Chip Fixed Resistor directly translated, commonly known as chip resistors (SMD Resistor), uranium glass, metal resistors in one. Is the uranium metal powder and glass powder mixture, using the screen printing method on a substrate made of printed resistors. Resistant to moisture, high temperature, the temperature coefficient.
Capacitors are mostly used by the collision of the substrate, cracking of the ceramic material, and SMD IC pin quantity, spacing narrow, low hardness, very likely lead solder shorts, cold solder joint, such as failure, so the demolition, temperature control should be mastered welding, preheating, touch and other techniques.
â‘¡ the power module during debugging, you must carefully check the components installed is wrong with a voltmeter the presence Weld detection circuit or short circuit welding slag and so on, to ensure the correctness of the circuit, to avoid burn out components.
â‘¢ If there is not much on the power to grasp, consider using an adjustable band-limiting function of power supply, the power supply's voltage to rise slowly, testing the input current (voltage) and output voltage until the output voltage to meet the requirements.
â‘£ When debugging a relatively large system circuit should be installed and debugging the system power, and then gradually debugging a successful installation, commissioning and other modules. Each module is installed on a power-on tests to ensure correct and then debug the other modules.
In this paper, based on the AT91RM9200 embedded control systems, for example, the focus of the system power supply circuit design ideas, methods, and system power installation and commissioning process, combined with the problems encountered during commissioning, debugging of embedded systems approach and attention to the circuit items were analyzed. With the extensive use of embedded systems, power supply circuit design and debugging is particularly important in this paper the design and debugging ideas worth learning.