30-04-2012, 01:23 PM
DC-DC CONVERTER
DC_DC report.docx (Size: 429.96 KB / Downloads: 53)
INTRODUCTION
DC-DC converters are electronic devices used whenever we want to change DC electrical power efficiently from one voltage level to another. They are needed because unlike AC, DC can’t simply be stepped up or down using a transformer. In many ways, a DC-DC converter is the DC equivalent of transformer DC energy performs the conversion with the highest possible efficiency. An important point to remember about all DC-DC converters is that like a transformer, they essentially just change the input energy into a different impedance level. So whatever the output voltage level, the output power all comes from the input, there is no energy manufactured inside the converter. Quite the contrary, in fact, some is inevitably used up by the converter circuitry and components, in doing their job. We can therefore represent the basic power flow in a converter with this equation:
PROJECT DESCRIPTION
DC-DC converter consists of following components:
Printed Circuit Board (PCB)
LT1374 Switching Regulator
Filtering
Input Protection
Output Voltage
Printed Circuit Board (PCB)
It has trough-hole plating and electrical tracks on the bottom and top of PCB, has dimension: 56mm long X 54mm wide.
LT1374 switching regulator
The LT®1374 is a 500KHz monothilic buck-mode switching regulator. A 4.5A switch is included on the die along with all the necessary oscillator, control and logic circuitry. High switching frequency allows a considerable reduction in the size of external components. The topology is current mode for fast transient response and good loop stability. Both fixed output voltage and adjustable parts are available. A special high speed bipolar process and new design techniques achieve high frequency at high switching frequency. Efficiency is maintained over a wide output current range by using output to bias the circuitry and by utilizing a supply boost capacitor to saturate the power switch. The LT1374HVIR s used, this has a maximum input voltage of 32V and has a temperature range of -40’C to 125’C in a 7-LEAD PLASTIC DD package. Full cycle-by-cycle short-circuits protection and thermal shutdown is provided. Standard surface mount external parts are used, including the inductor and capacitor.
Filtering
The DC-DC converter operates on a frequency near 500 Khz, the exact frequency depends on the load, temperature and input voltage. Because of the high frequency it is relatively easy to filter the input and output voltages from switching noise. Particular care has been given to the input filter because most switching noise is produced on the input of the DC-DC converter. The filter consists of C16, C23 and C27 to filter the high frequency noise (fundamental and higher harmonics). C14 andC15act as energy buffers. C31, C11 and inductor L2 make a low pass filter towards he power-supply. This filter reduces the switching noise on the input of the DC-DC converter from 500mV to 20mv under full load (4A). A “of the board” ferrite inductor on the output of the DC-DC converter is added to stop the 500KHz signal from entering the radio and frequency modulating the transmitter VCO.