University of Pennsylvania
Department of Electrical and Systems Engineering
ESE 205 – Electrical Circuits and Systems Laboratory I
Lab 4b – Soldering a USB Power Charger
Figure 1: Power Charger Board (bigger picture on last page)
USB is an ubiquitous and inexpensive connectivity protocol that is present in almost every
computer. Universal Serial Bus (USB) is a connectivity specification to establish communication
between devices and the host controller (usually personal computers). There are different types of
USB connectors as shown in Figure 2. USB ports on a PC/Laptop can supply 500mA @ 5V DC to
devices (e. g. keyboard, mice, webcams, hard disks) and since several mobile devices are low power
battery driven, the USB power is also used to charge the batteries. However, USB chargers can
support upto 2A (for iPad) or 1A(for iPhone or mobile phones)
Figure 2: Types of USB connectors (http://en.wikipedia.org/wiki/Universal_Serial_Bus)
Making of a USB Charger (i.e. output upto 1.1 A @ 5v)
Figure 3: 120VAC to 5VDC Conversion
Circuit Components:
1.
9v AC Adapter : Converts 110v AC to 9V AC. (image courtesy www.jameco.com)
2.
(How? http://en.wikipedia.org/wiki/Diode_bridge) (image courtesy : www.digikey.com)
3
3.
Capacitor, 2200 uF / 35 volts. IT IS VERY IMPORTANT TO NOTE THE POLARITY OF THE CAPACITOR.
An electrolytic capacitor can burst if connected in reverse. (Why?
http://en.wikipedia.org/wiki/Electrolytic_capacitor, check the “Polarity” section)
4.
Resistors of different values. Resistor values are determined by color bars (see picture on last page)
5.
Voltage Regulator, LM7805 (link to pdf file of specifications).
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage.
Use the heat-sink to allow the voltage regulator to cool down when operating. Assemble the heatsink before soldering them to the board.
(Warning: Heat-sink can become very hot)
6. Voltage dividers :
A device like the iPod touch or iPhone will only charge if it detects presence of data on the usb
cable. The set of voltage dividers (how do they work?) generate the right voltage to make the the
iPod/iPhone “think” that the data is present. Presence of voltage on USB data lines enable the
charging circuitry in the iPhone or iPod. You need to calculate the corresponding values of the
resistors and solder them in the board.
(Note: R3 and R4 – 22k Ohms, R2 – 33k Ohms and R5 – 27k Ohms) 4 Electrical and Systems
Engineering, USB Charger, ESE205 | Univ. of Pennsylvania
7. Led:
Led is used as an indicator which turns on when the board is powered on.
Procedure
1. Measure the resistance values using Digital Multimeter (DMM).
2. Place components on the printed circuit board (pcb) on the top side of the board. This is the side
from which you can read the text.
Figure 4: Printed Circuit Board (PCB)
3. Soldering :
Figure 5: Soldering Iron, a Good Soldering Iron Tip, Soldering method
It requires a bit of skill to solder correctly. Some hints; do not use a lot of solder and make sure the
solder tip is shiny. 5
Tutorial on soldering on ESE Lab web site
http://www.ese.upenn.edu/rca/funstuff/soldering/soldering.html
YouTube
http://www.youtube.com/watch?v=MHNDa2Wvk8I&feature=related
Snip the long leads of the components.
4. Testing :
-First confirm the polarity of the capacitor on the PCB. (Warning: An electrolytic can burst if
connected in reverse polarity)
-Measure the voltage between pins 1 and 4 of the USB.
Figure 5: USB Port Information
5. See picture of finished power charger board on next page
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