DEPARTMENT OF ELECTRICAL AND SYSTEMS ENGINEERING
ESE UNDERGRADUATE LABORATORY, ESE 205: Electrical Circuits and Systems I
USB (http://en.wikipedia.org/wiki/Universal_Serial_Bus) Charger
(go to last page to see finished printed circuit board)
USB is ubiquitous and inexpensive connectivity that is present in almost computer. Universal Serial Bus (USB) is a
connectivity specification to establish communication between devices and host controller (usually form
personal computers). There are different types of USB connectors as shown in Figure 1. Very conveniently,
USB 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.
Figure 1. Types of USB connectors (http://en.wikipedia.org/wiki/Universal_Serial_Bus)
Making of a USB Charger (i.e. output upto 500 mA @ 5v)
Figure 2, AC to DC power supply
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Electrical and Systems Engineering, USB Charger, ESE205 | Univ. of Pennsylvania
Circuit Components:
1.
2.
3.
4.
5.
9v AC Adapter : Converts 110v AC to 9V AC. (image courtesy www.jameco.com)
4 x rectifier diodes, 1N40004. Converts AC to DC (how ?, http://en.wikipedia.org/wiki/Diode_bridge)
(image courtesy : www.digikey.com)
Capacitor, 1000 uF / 25 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)
Resistors of different values. Resistor values are determined by color bars.
(http://www.ese.upenn.edu/rca/calcjs.html).
Voltage Regulator, LM7805 (link to pdf file of specifications).
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage.
Please use the heatsink to allow the voltage regulator to cool down when operating.
6. Voltage dividers :
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Electrical and Systems Engineering, USB Charger, ESE205 | Univ. of Pennsylvania
A device like 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 believe” the
iPod/iPhone” that the data is present. This enables the charging circuitry in iPhone or iPod.
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 3, Mounting components on the top side.
3. Soldering :
Figure 4, Solder iron in ESE Lab, an example of a good solder iron tip, soldering method.
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Electrical and Systems Engineering, USB Charger, ESE205 | Univ. of Pennsylvania
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.
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. An electrolytic capacitors will burst if connected
in reverse.
-Measure the voltage between pins 1 and 4 of the usb connector using the DMM.
Figure 5, measuring voltages on usb connector
PLEASE SEE NEXT PAGE FOR FINISHED PRINTED CIRCUIT BOARD
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Electrical and Systems Engineering, USB Charger, ESE205 | Univ. of Pennsylvania
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Electrical and Systems Engineering, USB Charger, ESE205 | Univ. of Pennsylvania