Importance of input and output capacitance for LDOs

[Falcon69]

okay, makes sense.

Each regulator may not draw full power both at same time, in fact it is VERY unlikely I will even pull close to half of the rated values I stated.  I haven't yet calculated it. I just calculated up everything as if it had all turned on (which is impossible, as for example, only one LED is on while the other is switched off, and vice versa).

So, I should get a switching regulator that can handle about 4A (to be on the safe side), then get a low drop out voltage regulator that only has a drop-out of like 0.3-0.4 volts so it can produce the 5 volts from the 5.4 volts the switching regulator will put out?

Now, these will be on the PCB, the walwart (12 volt wall plug) gets plugged into the wall, then via a barrel connector on the PCB board, it connects to the PCB supplying power to the switching regulator, then to the circuit and the LDO regulator.

SO, just reading up on all these buck converters, it looks like the majority of them don't even use Tantalums. It seems almost all of them are asking for the Ceramic Caps.

Heh, I was just looking at that Diodes AP65403SP one. .86 per 100 from Mouser. that's under a buck! (lol, get it, a buck?!)

And yes, been reading about that frequency stuff. The Vishay Data sheets are very informative on it and explains where each of the components should go...I think if I use those same methods and apply to the Diodes chip..I should be okay...however, this is not a 4-layer board, it's only a 2-layer.

http://www.mouser.com/ds/2/427/sip12116-364719.pdf  <--- Page 12

[DimitriP]

Capacitor discussions are all fun and great, but for just under $11 you can get 10 of these and have some spares too...

http://www.ebay.com/itm/10-PCS-LM2596-DC-DC-3A-Buck-Converter-Adjustable-Step-Down-Power-Supply-Module-/182202896686?hash=item2a6c23912e:g:AzwAAOSwAPlXhEYE

[Falcon69]

yup. I know, but I want these on the pcb board themselves with the rest of my circuit. And I'm finding out that the LM2596 is not very efficient, why I am here. Try and find a better solution, using only ceramics (no tantalums for obvious reasons, or electrolytics because of size), and also lower the cost and reduce heat from the IC chip when operating at almost full 3amps or so my circuit may draw.

Those on eBay are also fakes. They do not conform to the actual specs the LM2596s is suppose to conform to. There's a video on it.

[amitchell]

Have you played around with TI WEBENCH? The power architect may interest you.

http://www.ti.com/lsds/ti/analog/webench/overview.page?DCMP=sva_web_webdesigncntr_en&HQS=sva-web-webdesigncntr-vanity-lp-en

[Falcon69]

yes, I played around with that for awhile. But it seems you can only use Ti's chips? Unless I'm missing something. I tried to figure out how to change it to use the Vishay or Diodes regulators, but couldn't figure out how.

The chip blueskull mentioned on previous page is about $3 each when purchased in 100. That's too much for this application. I will need to use the cheaper Diodes ones at 86 cents each if I can.