Buck Regulator for Raspberry Pi

5V buck regulator/charger

DSCN0191

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

Buck%20Charger

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.

Specifications

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,

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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

—          ———                    —–

Resistors

———

1        R1                              47R

2        R2,R4                         75k

2        R3,R5                         49.9K

Capacitors

———-

1        C1                              100uF

1        C2                              1000uF

Integrated Circuits

——————-

1        U1                               LM2576

Diodes

——

2        D1,D2                         1N4004

1        D3                              LED

Miscellaneous

————-

1        J1                              TBLOCK-I2

1        J2                              USBCONN

1        L1                              100uH