Schottkey Diode

[mantha3]

Hi,

I am building a boom box that can run on a Battery or a 75 watt power supply. I want to run a diode inline to protect the power supply from the battery and vice versa. So I want to run a one directional diode to ensure power only flows OUT of either the battery or Power Supply. I want to buy the diode that cuts voltage the least. Ideally it would be 12Volt in and 12 Volt out... Which I don't think I'll find.

From what I've read it seems a Schottkey Diode is the best option for me. Any advice? I'm thinking of buying 2 rated at 3 AMP 12 Volt or 5AMP 12 Volt. Overkill i know.

Thanks,
ATM

[FFF]

Like a Low-Drop type : STPS40L15CW (insulated type) CT=metal tab.
Or a STPS30L40CW
Expensive though....5 euro a piece.
Hotter=lower voltage drop >> mount it on the regulator heatsink of the amp6....down to 0.33V
And why a new thread?!

[mantha3]

FFF,
My bad on the new thread. This is more an extension to one I had previously started. I'll knock that off going forward. I appreciate the specs you just provided me with.

[mantha3]

I updated my design so I can get a handle on the (+) and GND. I'm going to protect the power supply but on the battery I'm just going to make sure I don't have it in while not in use.

The STPS30L40CW. It looks like the power In flows in the middle pin and then the diodes are runnign the same way to the outer pins.. so the Right and Left Pin both have (+) flowing out? Do I run wire to both and then have a back up like I have in the pic?

What does a Volt Regulator that has a 12 Volt out do when 12 Volts run into it (see my diagram.



Uploaded with ImageShack.us

[Scratchy]

You need a minumum of 13VDC in to get 12V out of that regulator, any less and you will get nothing out (1V dropout).
It seems you are adding complexity to this amp, just for complexity sake and increasing component count?

There are millions of devices rated at 12V running at 14.2V every day in automobiles.
The typical charging voltage in a car is 13.8 - 14.2VDC, so you really don't have anything to be concerned about running a fan and some LEDs at 13.5 Volts.

Actually you should be concerned about how you are going to charge the SLA.
I would instead put the schottky diode in series with the positive lead from the battery going to the amplifier (replace the switch with the diode).
This would prevent the SMPS from charging/overcharging the SLA.

You should then just get an external charger for the SLA.
http://talkingelectronics.com/projec...er-12vSLA.html

[FFF]

Yes, I agree, this is getting much too complex and just not really needed. Even the extra 10mF cap.

Just the STPS30L40CW (anodes (plus) on outsides, current -runs- to and out the middle) will do, to block smps from battery.
Even a normal diode will do really, when speakers are sensitive enough. (+1dB on them is enough)
And a bit bigger heatsink to avoid the fan?
A charger can be had (in a not electronics related store) for 6 Euro also.

So you only -need- that:
-charger,
-a normal, cheap 5A-diode,
-a switch to switch feed of amp/LED between sla/smps (single, middle to amp/LED),
-a switch to turn LED on/off.

But you could use a handwound pot of say, 200ohms to set the brightness of the LED?

[mantha3]

Thanks for the advice people. I was starting to confuse myself with the diagram I had. I think I was just having fun plugging stuff in for the sake of plugging stuff in.

This boom box I'd like to run on AC Switching Power Supply on a book shelf while at home. I'd not put a battery in it. Then if I'm out at a cabin or something I'd put a battery in it. The Power Supply is not to charge really. I have a 12 Volt/9Amp battery and little charger for it. I use this for ice fishing in Minnesota USA. I may bring this boom box on the ice to party in the ice shack!

Here is what I think I'll build. More simple.

Is this a good Pot to buy? -
http://search.digikey.com/scripts/Dk...ords=ct2159-nd

Here is what I'll build I think -
URL=http://img178.imageshack.us/i/components.png/][/URL]

[mantha3]

PS - I'll build a little trap door on the back to put the batter in our take it out. I'll just have the (+) wire and GND wire in that with Alligator clips

[FFF]

OK.
No, a 10k pot? Better a ca. 500 = CT2156-ND
http://search.digikey.com/scripts/Dk...name=CT2156-ND
(I found those 3mm, blue, >2000mcd leds: they take 20mA-3.2V. so 12xLED could be 3x 4 leds =60mA)
http://www.okaphone.com/artikel.asp?id=464373

Even a 250 pot will do nicely.
http://search.digikey.com/scripts/Dk...name=CT2155-ND

Is this a good Pot to buy? -
http://search.digikey.com/scripts/Dk...ords=ct2159-nd

[Scratchy]

You can buy some really good Pot here in BC.

BTW, you must ensure your alligator clips don't get shorted together while it is powered from the SMPS.
Better to use some insulated "faston" connectors:
ampfastonreceptacl_66.jpg