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Charge your iPOD without connecting it to a computer!
Build a charger for your
or MP3 player
By JOHN CLARKE
This Charger can be used to charge your
iPOD™ or MP3 player without connecting
to your computer’s USB port. It can be
powered using a DC plugpack or from 12V
DC in your car and it can also be used to
power any accessory normally run from a
USB port.
U
SING THE USB PORT on your
computer to charge your player’s
batteries is not always practical. What
if you do not have a computer available
at the time or if you do not want to
power up a computer just for charging?
Or what if you are travelling?
Chargers for iPODs and MP3 players
are available but they are expensive
and you need separate models for
charging at home and in the car. SILICON CHIP’s new charger can be used
virtually anywhere.
While we call the unit a charger, it
really is nothing more than a 5V supply that has a USB outlet. The actual
charging circuit is incorporated within
the iPOD or MP3 player itself, which
only requires a 5V supply.
As well as charging, this supply can
run USB-powered accessories such
as reading lights, fans and chargers,
particularly for mobile phones.
The supply is housed in a small
plastic case with a DC input socket
at one end and a USB type “A” outlet
at the other end, for connecting to an
iPOD or MP3 player when charging.
A LED shows when power is available
at the USB socket.
Maximum current output is 660mA,
more than adequate to run any USBpowered accessory. (The specification
for the computer USB 2.0 port requires
the USB port to deliver up to 500mA
at an output voltage between 5.25V
and 4.375V).
Circuit details
The circuit is based around an
Fig.1(a): the basic scheme for a switchmode power supply. Voltage
regulation is achieved by rapidly switching S1.
36 Silicon Chip
MC34063 switchmode regulator. This
has high efficiency so that there is very
little heat produced inside the box,
even when delivering its maximum
output current. The circuit is more
complicated than if we used a 7805
3-terminal regulator but since the input
voltage could be 15V DC or more, the
voltage dissipation in such a regulator
could be 5W or more at 500mA. and
5W is far too much for a 7805, even
with quite a large heatsink.
Hence, we have taken the switchmode approach. This is illustrated in
Fig.1(a) and involves a switch (S1),
inductor L1, diode D1 and capacitor
C1. When the switch is closed, current flows through inductor L1 into
the load. The current (Path 1) slowly
builds up from zero to the peak value,
as shown in Fig.1(b).
When this peak current is reached,
the switch opens and current from
the inductor flows through diode D1
to discharge the inductor energy into
the load. This current path is shown
as Path 2. Capacitor C1 is included to
act as a reservoir of power to smooth
out the voltage produced across the
load.
The output voltage is dependent
on the load and the ratio of time that
switch 1 is closed to when it is open.
siliconchip.com.au
iPOD
It is also dependent on the peak current through L1
and the input voltage. This type of circuit can be
very efficient because voltage control is achieved by
rapidly switching the input. The small amount of
power dissipated is mainly due to voltage losses in
the switching device and diode D1.
Fig.2 shows the full supply circuit, which is based
on an MC34063 switchmode controller IC. Its internal
schematic is shown in Fig.3. The switching function
of S1 [in Fig.1(a)] is provided by the internal transistor
(Q1). The internal oscillator sets the switching period,
while the “Ipeak sense” limits the current flowing in
inductor L1 by controlling the on-time for transistor
Q1. The 1.25V reference and comparator provide a
feedback arrangement to monitor and control the
output voltage.
Power from the DC socket passes through diode D2
and slide switch S1 to IC1. D2 protects against reverse
Fig.1(b): this diagram shows the current through L1
when S1 is closed (blue) and opened (red).
siliconchip.com.au
Fig.2: the complete circuit is based on a dedicated MC34063
switchmode controller IC.
February 2006 37
Fig.3: inside an MC34063 switchmode controller IC.
The internal oscillator sets the switching period, while
transistor Q1 does the switching.
polarity and the adjacent Trans
ient
Voltage Suppressor (TVS1) clamps
any fast spikes which may be riding
on the input supply. Further filtering
is provided by a 470mF low-ESR (Effective Series Resistance) capacitor.
As previously described, current
is switched to L1 using the internal
transistor in IC1. In operation, the three
paralleled 1W resistors between pins 6
& 7 monitor the current through L1.
When the current reaches 1A, pin 7
becomes 300mV lower than pin 6 and
the internal transistor switches off. The
energy stored in L1 is then dumped into
capacitor C1 via Schottky diode D1.
The resulting output voltage is
filtered using a 1000mF low-ESR capacitor.
Output voltage control
Pin 5 of IC1 monitors the output
via a voltage divider consisting of a
Fig.4: this switching waveform was measured across the
output with an 8W resistive load, resulting in a current of
625mA. Note how the switching shows signs of “hunting”,
as the circuit constantly maintains a 5V output.
1kW resistor, trimpot VR1 and a 560W
resistor to ground. VR1 sets the output
voltage to 5V.
Zener diode ZD1 and the 10W resistor are included to catch any output
overshoot voltages which can occur if
the output load is suddenly reduced.
As explained, the switching of L1
controls output regulation. If the load
is suddenly reduced, the only way IC1
can stop any voltage rise is to prevent
any switching of power to L1 and let
capacitor C1 drop back to 5V. So, to
prevent voltage overshoot, ZD1 begins
to conduct when the voltage reaches
5.1V, with the current through it limited by its series 10W resistor.
In normal circumstances, when
the output voltage is correctly set to
5V, ZD1 will not conduct unless the
voltage rises momentarily. However,
if VR1 is set so that the output voltage is higher than 5V, ZD1 conducts
Specifications
Output voltage............................................................................................ 5V
Output current.................................................... 660mA maximum for 5V out
Input voltage range.................................................................9.5V to 15V DC
Input current requirement................. 500mA for 9V in, 350mA for >12V input
Input current with output shorted.................120mA at 9V in, 80mA at 15V in
Output ripple...................................................14mV (from no load to 660mA)
Load regulation..............................................25mV (from no load to 660mA)
Line regulation..........................20mV change at full load from 9 to 18V input
No load input current............................................................................. 20mA
38 Silicon Chip
continuously. Because of this, the
range of adjustment for VR1 has been
deliberately restricted to limit the
output to be no more than 6.5V, under
worst-case conditions.
This worst-case setting occurs when
VR1 is set fully clockwise (towards the
560W resistor) and when VR1 is 20%
high in value and the reference for IC1
is at its maximum at 1.32V (typically,
IC1’s reference is 1.25V but this could
be anywhere within the range of 1.18V
to 1.32V).
With 6.5V at the output, there will
be 140mA through ZD1 and the 10W
resistor. Dissipation in ZD1 will be
0.7W (below its 1W rating), while dissipation in the 10W 0.5W resistor will
be 0.2W. When VR1 is set correctly, the
output is protected against producing
transients above 5V.
Should the output become shorted,
the fault current will be limited to
a safe value at or below 120mA, as
set by the paralleled current sense
resistors.
Construction
All the components for the charger
are mounted on a PC board coded
14102061 and measuring 79 x 47mm.
This board is mounted upside down
in a small plastic case measuring 83 x
54 x 31mm.The screw covers for the
lid then serve as rubber feet.
Begin construction by checking the
PC board for breaks or shorts between
the copper tracks. Repair these as necessary. That done, make sure the holes
are the correct size for each component
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Fig.5: install the parts on the PC board as shown here.
Inductor L1 is secured using cable ties.
Fig.6: the full-size etching pattern for the PC board.
and check that the PC board clips neatly
into the integral side pillars in the box.
The component overlay for the PC
board is shown in Fig.5. First, insert
and solder the resistors, links and
trimpot. You should check the resistor values with a digital multimeter.
Make sure IC1 is mounted with the
orientation shown.
The two electrolytic capacitors are
mounted on their side to allow clearance in the box; make sure they are
mounted with the correct polarity.
LED1 is mounted with cranked leads
so that it can poke through a hole in
the side of the case. Again, take care
with its polarity.
There are four diodes on the PC
board, including the zeners and TVS.
Take care to ensure that all polarised parts (ie, the
IC, diodes and electrolytic capacitors) are correctly
oriented when building the PC board.
Make sure you insert the correct ones
in each position and with the correct
orientation. Once they are in, insert
and solder in the two PC stakes followed by slide switch S1. The latter
is mounted so that the top of its body is
10mm above the PC board surface.
Inductor L1 is wound on a powdered iron toroid with 0.5mm enamelled copper wire. Wind on 75 turns in
two layers spaced evenly around the
core. The wire ends must be scraped
clean of enamel and tinned, before
soldering.
Alternatively, if the wire is coated
with red enamel, this can normally be
melted off with the tip of your soldering iron. The toroid is secured to the
PC board with two cable ties. These
Table 1: Resistor Colour Codes
o
o
o
o
o
o
siliconchip.com.au
No.
1
1
1
1
3
Value
1kW
560W
470W
10W
1W
4-Band Code (1%)
brown black red brown
green blue brown brown
yellow violet brown brown
brown black black brown
brown black gold gold
pass through holes in the PC board.
Fig.7 shows the drilling details for
the case. You have to drill holes for
the DC socket and LED in one end, the
switch at the top and the USB socket in
the other end of the box. Mark these out
and drill and file as necessary.
Testing
Initially wind VR1 fully anticlockwise. That done, set your multimeter to
read DC volts and connect it between
terminals TP1 and GND. Apply power
to the input, switch on and adjust VR1
so that the voltage is 5V.
This can generally be set to within
Table 2: Capacitor Codes
Value μF Code EIA Code IEC Code
100nF 0.1µF
104
100nF
470pF NA
471
470p
5-Band Code (1%)
brown black black brown brown
green blue black black brown
yellow violet black black brown
brown black black gold brown
NA
February 2006 39
Par t s Lis t
1 PC board, code 14102061, 79
x 47mm
1 UB5 transparent blue plastic
case, 83 x 54 x 31mm (Jaycar
HB-6004 or equivalent)
1 12V DC plugpack fitted with a
2.5mm DC plug and rated at
350mA minimum
1 fused cigarette lighter socket
lead with 2.5mm DC plug
1 SPDT slider switch (S1) (DSE
P7602 or equivalent)
1 USB PC-mount “A” socket
1 PC-mount 2.5mm DC socket
1 powdered iron toroidal core
measuring 14.8 x 8 x 6.35mm
(Neosid 17-732-22, Jaycar
LO-1242 or equivalent)
1 2m length of 0.5mm enamelled
copper wire
1 50mm length of 0.7mm tinned
copper wire
1 M3 x 12mm countersunk screw
1 M3 tapped x 12mm Nylon
spacer
2 100mm cable ties
2 PC stakes
1 1kW horizontal trimpot (VR1)
Fig.7: here are the drilling details for the plastic case. The square cutouts
are made by drilling small holes around the inside perimeter, knocking
out the centre pieces and filing to shape.
Semiconductors
1 MC34063 switchmode controller (IC1)
1 1N5819 1A Schottky diode
(D1)
1 1N5404 3A diode (D2)
1 P6KE27A 600W transient
voltage suppression diode
(27V) (TVS1)
1 5.1V 1W zener diode (ZD2)
1 3mm green LED (LED1)
Capacitors
1 1000mF 16V low-ESR PC
electrolytic
1 470mF 25V low-ESR PC
electrolytic
1 100nF MKT polyester
1 470pF miniature ceramic
Resistors (0.25W, 1%)
1 1kW
1 10W 1/2W
1 560W
3 1W 1/2W 10%
1 470W
20mV of 5V (ie, 4.98V to 5.02V) using
the trimpot.
Check that LED1 lights. If it doesn’t,
check that it is the right way around. If
there is still no power indication, use
a multimeter to check for voltage at
40 Silicon Chip
The PC board is
clipped upside down
into the bottom of the
case and is secured
using an M3 tapped
Nylon spacer. This
spacer ensures that
the board doesn’t
move when the slide
switch is operated.
pin 6 of IC1 and for a similar voltage
at pins 1, 7 & 8. If there is no voltage
here, perhaps the DC socket plug has
the wrong polarity. The plug should
have the positive to the centre hole and
the negative to the outer case.
When testing is complete, the PC
board can be clipped into the case,
making sure the LED protrudes from
its hole in the side of the case. The
section of PC board directly below the
switch will need supporting so it is not
pushed out of position when the slide
switch is operated. We used an M3
tapped Nylon spacer in the side of the
case to support the PC board and this
is secured using an M3 screw.
To do this hold the spacer tightly
against the PC board directly below
the switch and mark out the position of
the hole for the screw. The transparent
box makes positioning of this hole easy.
Now drill out the hole and secure the
spacer. Finally, fit the lid and insert the
rubber feet into the screw holes. SC
Footnote: iPod is a trademark of Apple Computer, Inc.
siliconchip.com.au
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