PROGRAMMABLE POWER SUPPLY

Transcription

1 PROGRAMMABLE POWER SUPPLY MATTHIEU L. KIELA HARDWARE DESCRIPTION APRIL 25, 2006 WESTERN WASHINGTON UNIVERSITY ELECTRONICS ENGINEERING TECHNOLOGY ETEC 474, PROFESSOR MORTON

2 INTRODUCTION In laboratory and experimental work, the source of electric energy is very important for the project. Most electronic products require power to function so power supplies are an integral part of any instrumentation system. Sometimes it is difficult to use a power supply when it comes to getting an accurate output value and often the more features on the power supply the more difficult it is to operate. When a power supply has all these different features they also become expensive to purchase. The programmable power supply (PPS) that I am designing will have several advantages over a typical power supply since it will eliminate the problem of trying to get an accurate output value, it will have fewer features making it easier to use, and a smaller size. The size of this power supply will make it easier to carry and it will save space in the working environment. The PPS will be a microprocessor based design in order to process all the information for the user. It will be less expensive compared to the typical power supply due to less features on the user interface. This PPS receives 120 volts alternate current and converts it to a direct current stepping it down from zero to fifteen volts at the current level of one Amp. HARDWARE DESCRIPTION Microcontroller Unit The PPS is controlled by the MC9S12DP256B (9S12), described as U1 in the appended schematic diagram. This 16-bit microcontroller features 256K bytes of Flash EEPROM, 12K bytes of RAM, and 4K bytes of byte-erasable EEPROM. The 9S12 receives data input from the keypad through General I/O Port B. The Analog Device AD 620 amplifier the current drop across the 0.1 resistor, depicted as R10 on the schematic 2

3 diagram, and sends it to 9S12 Analog to Digital converter. A voltage divider network, made up of R11 and R12 is also sent to 9S12 Analog to Digital converter. Port A and Port K control the LCD screen, and the Serial Peripheral Interface (SPI) controls the digital potentiometer to get the desired voltage output from the voltage regulator. LCD Module The ASI-M-204ABS-KJ-BYD/Z, depicted as LCD1 on the schematic diagram, is the 16 pin, 4-line by 20- character backlit LCD module implemented to display PPS output information. The LCD module receives information from 8 pins connected to Port A (PA0 - PA7) and 3 pins connected to Pork K (PK0 - PK2), shown in the LCD Module section of the schematic diagram. The backlit of the LCD module is essentially an LED, a current limiting resistor tied to the source, R16, is placed in series with the anode (pin 15), with the cathode (pin 16) tied to the ground. A voltage source network made up of R8 and C10 connected to LCD inputs VDD (pin 1), VSS, (pin 2), and VO (pin 14), is used to provide a LCD contrast setting. Keypad Module The keypad, depicted as KP1 on the schematic diagram, is the 4 rows by 4 columns, 8 pins. It connected to 9S12 through Port B (PB0 - PB7). The keypad will be responsible to receive the input from the user and sent the information to the microcontroller for the desired output voltage. Source Module The PPS receives 120volts alternate current and passes it to the step down transformer by a contact switch, (S1), and protected by a fuse (F1). A red LED, depicted as LED1 on the schematic diagram, will monitor the presence of the power in the circuit. 3

4 The alternate current is then stepped down to 25 volts through the transformer depicted as RT1 on the schematic diagram. The conversion and rectification are made by the means of diode bridges depicted as B1 on the schematic diagram and the capacitor network made up of C8 and C9. The regulation of the direct current is obtained by the means of the voltage regulator, depicted as REG1 on the schematic diagram. Microcontroller Supporting Circuitry The 9S12 utilizes other resources. As shown in the schematic diagram it includes the reset circuitry, Crystal circuitry, and the BDM connector. The /reset pin of 9S12 is connected to the reset circuitry as a safety precaution to protect the system. The MAX 6314 low-power CMOS microprocessor supervisory circuit (U2) is implemented, shown in the section entitled Reset Circuitry. As stated in the MAX6314 specifications, the reset circuit asserts a reset signal whenever the VCC supply voltage falls below a preset threshold or whenever a manual reset is asserted. The reset remains asserted for an internally programmed interval (reset timeout period) after the VCC has risen above the reset threshold or the manual reset is deserted. The Crystal Circuitry is a 16 MHz oscillator circuit made up of a crystal (X1) and capacitor (C4 and C5) network. This circuit is implemented to clock the 9S12 and is connected the EXTAL, XTAL, and VSSPLL pins of the 9S12. The BDM Connector is a 10 pin male header (J6) used for interfacing with the Noral debugging software. Loading and updating the final program into the 256K byte Flash EEPROM is performed through this connector. 4

5 Programmable Power Supply-Parts List Item Quantity Part Description Designators 1 1 Bridge Rectifier, 2Amp /30V B1 3 1 Cap-Mono, X7R, RAD,10%, 0.1uF/50V C1 5 1 Cap-Mono, X7R, RAD,10%, 0.003uF/50V C2 7 1 Cap-Mono, X7R, RAD,10%, 330uF/50V C3 9 2 Cap-Mono, X7R, RAD,10%, 22pF/50V C4,C Cap-Mono, X7R, RAD,10%, 0.1uF/50V C6, C Cap-Mono, X7R, RAD,10%, 10uF/50V C7, C Cap-Electrolytic, RAD,1uF/35V C Cap-Electrolytic, RAD,1000uF/35V C Cap-Mono, X7R, RAD, 2200uF/35V C Cap-Mono, X7R, RAD, 0.1uF/35V C10,C11, C Connector, Multipurpose Nylon Binding Posts SV Crystal, 16MHz 30PPM CA-301, M-C X Fuse, 120V/ 10Amp F IC, Microcontroller, Motorola MC9S12DP256B, 16-bit U IC, Reset Circuit, Maxim MAX6314 U IC, Amplifier, Analog Devices, AD 620 U IC, Digital Potentiometer, Analog Devices, AD 7376 U Jack, LCD connector, 50Pins J2, P Jack, BDM, 10pin, male header J Keypad, 4X4, 8 Pins KP LCD Module, ASI-M-204ABS-KJ-BYD/Z LCD LED, T1 3/4, 2V/ 20mA, Red LED Regulator, LM317, V Adjustable REG Regulator, UA7805C, 5V Fixed REG Resistor, Metal Film, 1%, 22.1Ω/0.25W R Resistor, Metal Film, 1%, 10KΩ/0.25W R9,R Resistor, Metal Film, 1%, 3.01KΩ/0.25W R Resistor, Metal Film, 1%, 3.99KΩ/0.25W R Resistor, Metal Film(POT), 1%, 10-20KΩ/0.25W R Resistor, Metal Film, 1%, 0.1Ω/0.25W R Resistor, Metal Film, 1%, 1KΩ/0.25W R13, R14, R Resistor, Metal Film, 1%, 240Ω/0.25W R Resistor, Metal Film, 1%, 5KΩ/0.25W R Resistor, Metal Film, 1%, 5.49KΩ/0.25W RG 71 1 Switch, Snap-Action w/ Lever, SPDT, 125/250Vac S Transformer, 120/25.2V AC/ 2 Amp RT1 5