Switch Mode Altoids iPOD Charger using 3 'AA' batteries

Step 3 PCB

NOTE there are two PCB versions, one for a zener/stabistor voltage reference, and one for a MCP1525 voltage reference. The MCP version is the "preferred" version that will be updated in the future. Only one USB version, using the MCP vref, was made.

This was a difficult PCB to design. There is limited space left in our tin after the volume of 3 AA batteries is deducted. The tin used is not a genuine altoids tin, it is a free box of mints promoting a website. It should be about the same size as an altoids tin. There were no Altoids tins to be found in the Netherlands.

A plastic battery holder from the local electronics shop was used to hold the 3 AA batteries. Leads were soldered directly to the clips on it. Power is supplied to the PCB through the two jumper holes, making battery placement flexible. A better solution might be some sort of nice PCB mountable battery clips. I haven't found these.

The LED is bent at 90 degrees to go out a hole in the tin. The TIP121 is also bent at 90 degrees, but not set flat!!!** A diode and two resistors are run under the transistor to save space. In the picture you can see that the transistor is bent, but soldered such that it floats one centimeter over the components. To avoid accidental shorts, cover this area with hot glue or a hunk of that rubbery stickie tack stuff. The MCP1525 voltage reference is located under the TIP121 in the MCP version of the PCB. It makes a very effective spacer. 3 components were put on the back side: the decoupling cap for the PIC, and the two large zeners (24 volt and 5.1volt). Only one jumper wire is needed (2 for the MCP version).

Unless you want to run the device continuously, put a small switch in-line with wire from the battery power to the circuit board. A switch was not mounted on the PCB to save space and keep placement flexible.

**Eagle has a routing restriction on the to-220 package that interrupts the ground plane. I used the library editor to remove the b-restrict and other layers from the TIP121 footprint. You could also add a jumper wire to solve this problem if you, like me, hate the eagle library editor. Inductor coil and modified to-220 footprint are in the Eagle library included in the project archive.

Part list (Mouser part number provided for some parts, others came out of the junk box):
Part Value (voltage ratings are minimum, bigger is okay)

C1 0.1uF/10V
C2 100uF/25V
C3 0.1uF/50V
C4 47uF/63V (mouser #140-XRL63V47, $0.10)

D1 Rectifier Diode SF12 (mouser #821-SF12 ), $0.22 -or- others
D2 1N4148 small signal diode (mouser #78-1N4148, $0.03)
D3 (Firewire) 24 Volt Zener/1 W (mouser #512-1N4749A , $0.09)
D3 (USB) 5.6 Volt Zener/1 W (mouser #78-1N4734A, $0.07)
D4 5.1 Volt Zener/1W (mouser #78-1N4733A , $0.07)

IC1 PIC 12F683 & 8 pin dip socket (socket optional/recommended, ~$1.00 total)

L1 (Firewire) 22R684C 680uH/0.25 amp inductor coil (mouser # 580-22R684C , $0.59)
L1 (USB) 22R224C 220uH/0.49amp inductor coil (mouser # 580-22R224C , $0.59)

LED1 5mm LED

Q1 TIP-121 Darlington driver or similar

R1 100K
R2 (Firewire) 10K
R2 (USB) 22K
R3 100K
R4 22K
R6 330 OHM
R7 10K
R8 1K

VREF1 Microchip MCP1525 (MCP version PCB) (mouser #579-MCP1525ITO, $0.55) -or-
2.7 volt/400ma zener with 10K resistor (R3) (zener reference version PCB) -or-
2 volt stabistor with 10K resistor (R3) (zener reference version PCB)

X1 Firewire/IEEE1394 6 pin right angle, horizontal PCB mount connector:
Kobiconn (mouser #154-FWR20, $1.85) -or-
EDAC (mouser #587-693-006-620-003, $0.93)