Buck regulator for the Raspberry Pi/charging apple devices using the LM2576
It’s often handy to have a power supply around that provides a powered USB port for running a raspberry pi or charging up ipads and iphones.
This supply has a high input voltage range of upto 40V allowing use from a number of sources such as wall warts or to be able to be powered from a 12V or 24V Lead acid in a car boat or caravan.
The circuit shown below uses the simple switcher the LM2576 from TI
Power is supplied via D1 to the LM2576 which is a TO220 5 pin package, this drives a 100uH inductor in a standard buck configuration.
Resistors R2 to R5 are set up as in the adafruit tutorial to allow charging of apple devices.
Input Voltage 7-40V
Output Voltage 5V
Output Current 3A
Ordering the PCB’s a new supplier
For initial prototypes I usually use PCB pool once I have a a few designs ready to go I combine them all into one job lot and send them off and get PCB’s back in 8 days, with a free SMT stencil, it’s a good deal if your doing some surface mount boards as well. You tend to get 2 copies of each board back as well to allow for mistakes. The fact they take proteus files directly is really nice as it stops me making a mistake transferring to Gerbers…
Then I tend to debug the boards and when I have enough boards working, I’ll put a 1000 sq cm panel with multiple designs(they allow up to 6) together and send an order to gold pheonix. It’s a good deal on pricing and the boards usually arrive in Ireland in 2-3 weeks and good quality, also you tend to get more boards than requested.
However when doing this design I was in the middle of doing a bunch of debug and hadn’t finished up enough other new designs to make a PCB pool order worth while.
As this was purely a through hole board and not particularly complex I thought I would give dangerous prototypes new dirty cheap PCBS which worked out great,
It really nice you can get different coloured boards and in this case as you can see from the pictures I decided on a red board. Boards took around 5 weeks to arrive by post in Ireland, and I got 14 boards so $1 a board… impressive. The quality looks great so if you can afford the wait and the fixed size restriction I’d recommend them.
PCB’s from dirty cheap PCB’s 14 5 cm x 5 cm boards for $14….
For proteus users rather than eagle users I just exported the gerber files into a single zip file and renamed the layers as requested on the website, seemed to work fine.
The BOM for this project is below:
QTY PART-REFS VALUE
— ——— —–
1 R1 47R
2 R2,R4 75k
2 R3,R5 49.9K
1 C1 100uF
1 C2 1000uF
1 U1 LM2576
2 D1,D2 1N4004
1 D3 LED
1 J1 TBLOCK-I2
1 J2 USBCONN
1 L1 100uH