AA Battery Charger
ETE 272 Project
Table of Contents
Circuit function: 0
Design Considerations: 1
What I learned: 1
This project idea is to make a small & relatively simple, USB charger for just about any device such as a cell phone, camera, or an ipad, that can be charged by a USB port. The circuitry runs off of 2 AA batteries.
This circuit is based off the typical application for the main IC in this circuit which is the LT1302- “Micropower High Output Current Step-Up Adjustable and Fixed 5V DC/DC Converters”. “It can maintain high efficiency over a wide range of output current. They operate from a supply voltage as low as 2V and feature automatic shifting between Burst Mode operation at light load, and current mode operation at heavy load.”1 In this circuit the mode of operation for the LT1302 is in heavy load. An inductor had to be used that would be able to handle current of 2.5A to 3A it also had to have a low DCR, under 0.05Ω, so that copper loss is kept low while inductance value is not critical, which is why the RLB9012-100KL was used it has a max current rating of 3.4 Amps and a DCR value of 0.045Ω. A Generic 8 pin socket is used to hold the LT1302 just in case it fails it is easy to replace within the circuit. Generic resistors are used to mediate voltages and currents. Ceramic capacitors were used as high frequency bypass capacitors. Electrolytic Capacitors are used as power supply capacitors to keep voltage from fluctuating. The schottky diode 1N5818 was used due to its fast recovery, which is needed for switching regulator applications.
According to the data sheet for the LT1302, the LT1302 mandates careful attention to layout due to its high speed, high current switching. For this reason they have a suggested component placement is for proper operation. The LT1302 is sensitive to noise and so High frequency bypass capacitors must be added and it is recommend that it be placed as close as to the LT1302 as possible to minimize noise. It is said that the ground trace should not carry switch current and to be segregated thus they have a suggested component placement as illustrated in figure 91 below. I tried to my design to resemble this closely however it could not be exact because I had more components to deal with, for the data pins of the USB jack.
Electrical Rules Check, this takes the parameters of the various parts, and checks to see if anything unusual is going on. In my case I had 4 warnings which I approved because parts: 3V, GND, Frame1, and IC1’ do not need a value attached to them, however in the part device it indicates a section for a value thus giving us the warnings.
Design Rule Check, in my board design no DRC errors are to be found.