Today's theme: "Why buy it when you can build it for 10x the cost?" Let me back up a bit. Here's a readily available DC-DC buck (step-down) converter found on eBay for a little as $1. It's nothing fancy, more a breakout for the IC; however, the convenience of the module cannot be overstated. I use this to drop the incoming supply (12V DC) for my arcades to 5V. 5V is the critical voltage for the Raspberry Pi. Bringing 12V into the arcade allows more flexibility to power other electronics, but we still need to drop 12V down for the Raspberry Pi.
The core of component of this step down converter is the LM2596; an adjustable switch regulator. The adjustable part is where we hint at the flexibility. Say you need 5.00VDC? done. What about 8.5V? Easy, just turn that trim pot.
Alright, so a board with an easily adjustable DC supply is great, but how's the current output? The datasheet states
we can get 3A from this thing (a decent heat sink is needed, but that comes later).
We have established this LM2596 is an excellent solution for producing a wide array of lower DC voltages (with enough current) for many consumer electronics, but getting the most out of the LM2596 requires more from the PCB design and its surrounding components. In particular, more than what this affordable eBay hobby board can provide.
So why not build one? Suuuure. Why not. The datasheet for the LM2596 (especially from On Semiconductor) shows not only a typical diagram for the adjustable dc-dc step-down, but a typical PCB layout. I had my way with eagle CAD to layout essentially the same thing, but got carried away with adding a switch (for standby mode), screw terminals, USB ports (no more butchering USB cables:) and a fixed 5v linear regular just because. Since this is the switching power supply, the design is heavily suggestive of using short traces and ideally single-point grounding or ground plane construction should be used. Why? Rapidly switching currents associated with wiring inductance, stay capacitance, and parasitic inductance of the PCB traces can generate voltage transients. These voltage transients can generate electromagnetic interference (EMI) and affect the desired operation negatively. Some care needs to be taken in the layout.
In the end I ended with a adjustable DC supply that can double as a powerful dual USB charger ( rev 2 will have settable data +/- lines for fast charge devices like iPhone, Samsung, PS4 controllers...) and enough terminal points to make wiring a Porta Pi or JAMMArCADE easy. (Yes, to charge certain USB devices the data + and - lines need to be set to either 1.2V, 2.0 or a combination of 2.0 and 2.7V..... uhhhhggg)
But it doesn't stop there. I have a few PS2 Slims that are missing a PSU. This supply is rather unusual needing 8.5V at 4amps. Measuring the actual current draw of the PS2 Slim (the silver version in this case which is spec'd to use less power than the black body version) I only see about 1.8A draw SO why not use this regular as an universal DC supply for game consoles? Well, the ones that need an external power supply. Aside from matching the right DC barrel connector, we can power consoles like:
Revision 2 is a work in progress, to add more room for a suitable heat sink and fixing my mistake of putting the switch on the wrong PCB layer.
If you want rev 1 of this PCB, It's available for $0.50/ea as there are a few mistakes in rev 1 that were pointed out in the article.
If you do not solder the switch, the buck converter is always on. The switch was to put the LM2596 into standby mode, but having placed the switch layout on the wrong side, not populating is no big deal. Having no switch does not cripple the board's useability.
About 17x the eBay version right now. Buying robust parts in small quantities is brutal on the buget. But, eh.
|Arcade Power Block||Revision_IDEA||Jan 10 2017||Ryan Bates|
|Item||Part||QTY||Value||Description||Digikey P/N||Bulkrate/ea @10||Bulk Line Cost @10|
|1||LM2596||1||ADJ||DC-DC Switching Regulator Adjustable||LM2596TVADJGOS-ND||$ 2.18||$ 2.18|
|2||Cout, Cin||2||220uF 50V||CAP ALUM 220UF 20% 50V RADIAL||399-6123-ND||$ 0.37||$ 0.74|
|3||D1||1||60V 3A||Diode Schottky 60V 3A Through Hole DO-201AD||MBR360RLGOSTR-ND||$ 0.43||$ 0.43|
|4||L1||1||33uH, 7.4A||UnShielded Toroidal Inductor 5.0A||M8852-ND||$ 2.18||$ 2.18|
|5||R1||1||1.21k||Resistor 1.21 kOhms ±1% 0.25W, 1/4W||RNF14FTD1K21CT-ND||$ 0.07||$ 0.07|
|6||R2||1||50K, 0.50W||Trim Potentiometer Cermet 25 Turn Top Adjustment||3296W-503LF-ND||$ 2.12||$ 2.12|
|7||USB-A||1||USB-A||USB - A USB 2.0 Receptacle Connector 4 Position||UE27AC54100-ND||$ 0.38||$ 0.38|
|8||C2||1||100uF||CAP ALUM 100UF 20% 35V RADIAL||1189-1300-ND||$ 0.21||$ 0.21|
|9||L2||1||22uH||FIXED IND 22UH 4.1A 36 MOHM TH||732-7157-ND||$ 1.80||$ 1.80|
|10||Cff||1||2200pF||CAP CER 2200PF 1KV RADIAL||445-16006-ND||$ 0.26||$ 0.26|
|11||Sw1||1||DPDT||$ 0.20||$ 0.20|
|12||R3||1||2k||$ 0.50||$ 0.50|
|13||C1,C2,C3,C4||4||CAP ALUM 1-47uF 16V||$ 0.11||$ 0.44|
|14||LM7805||2||$ 0.95||$ 1.90|
|15||LED1, LED2||2||Red, Green||$ 0.10||$ 0.20|
|16||PCB||1||$ 2.65||$ 2.65|
|17||Heatsink||1||$ 0.97||$ 0.97|
Revision is here! Made the layout to fit a real heatsink (reason to follow) and added resistors to make a voltagae divider on the USB data + and - lines. That way I can charge my Samsung phone, PS4 controller and pretty much any high current USB device that looks for a voltage on the data lines for charge.
Want a PCB? Add one to any order. Why isn't this item in the shop? I'm still experimenting and refining the idea.
REVISION 3 and a video to talk about this long journey.
Final version! Available here.