Astrodyne RS75 75 Watt Switch Mode Power Supplies 13.5 volt down to 12 volts

[mantha3]

I have a question on running an Astrodyne RS75 75 Watt Switch Mode Power Supply at 13.5 volt down to 12 volts. Would I just run 1,2 or maybe 3 diodes to get down to 12 volt? Any specs on good diodes I should buy

some background:
I am building a boom box/book shelf stereo. I will have some 12 Volt components in this (12 Volt Fan, 12 Volt LED light strip) that I'd like to run so I thought it was a good idea to get the 13.5 volt down to 12 volt for these items… I'd like to run the AMP6 at the full 13.5 Volt
I am building a boom box/book shelf stereo. I plan to run this on a 12 volt battery and also have this 13.5 volt power supply for when in the home.

I am going to put in the main compartment a 12 volt set of LED lighting to light the inner electronics area so people can see what is inside. I also will run a 12 volt PC fan (not needed but I have it, why not)
Here is the specs on the power supply:


Model Number Output Voltage Output Amps Load Regulation Ripple and Noise Over Voltage Protection DC Voltage Adjust (typ.) Efficiency
RS75-15 15 Volts(DC) 5.0 Amps ±0.5% (Note 4) 120mV pk-pk (Note 1) 17.25 ~ 20.25Volt(DC) Hiccup mode, auto recover 13.5~16.5Volt(DC) 0.82

This is what I was thinking of building and the yellow box is where I'd put the diodes:



Uploaded with ImageShack.us

[FFF]

Y. is ok. Will also prevent current from battery>smps. And a low drop diode to prevent the reverse might be useful too. (smps>battery), unless the smps is supposed to charge the battery of course.

[mantha3]

Would you recomend any particular Diode or Diode spec? I go online and look at places selling Diodes and I'll see 85,000 different types to choose from. I'm just learning. I was looking for input on the voltage reducer diode(s) mostly but I think your idea of doing a diode to protect the batter is also a good idea!

Thanks for taking the time to respond to this! I'm a newbie.

[FFF]

For leds+fan:
- 1N4001, glass-type 50V,1A 15 eurocent each. (I assume 1A is plenty)
- 1N4002, non-glass-type, rest=same
- 1N4007, 1000V, rest=same

Else just use 3x inline to Fan + same to LEDs (separate feed)
If using more serious Fan and LEDs for whole home, then: 1N5404, 3A, 400V, 45 eurocent here.

Try a bit, you can get 10x1N4001/2/7 for 1 euro.

All types should do.

[mantha3]

I'm reading some online content on "Zener diodes" and "General purpose signal diodes such as the 1N4148 are made from silicon and have a forward voltage drop of 0.7V. "

I think I'd go General Purpose and use 2 of these or so. I could dial up the Power supply to 4.1 volt output and use 3 of these General Purpose.

Time to buy a voltage meeter.

This is fun stuff.

[tuo]

Well, yes, they do. But 1N4148 is a general purpose signal diode, whose current rating is only 200 mA. This is not enough for a power amplifier, so if you use these, they will blow eventually. FFF has listed better options, and those diodes are still very cheap and do have similar ~0.7 V forward voltage drop.

[Scratchy]

It's great to see you are planning ahead for your build.
However, there is really no need for the fan. This is just adding noise (both electrical and mechanical).
If you feel you must use the fan, then there is really no need for those diodes. This is just adding complexity.
A 12V fan will run fine at 13.5V (just a little faster).

As for the LEDs, technically there is no such thing as a 12V LED.
LEDs have current limiting resistors designed to limit the current according to the input voltage.
There is a great LED resistor calculator linked in this post:
http://www.41hz.com/forums/showthrea...tor-for-an-LED

[FFF]

Yes. Scratchy is right....no real need....shame, can be fun playing with the diodes.

Did you plan the fan for the amp? ...but you still can make the fan run more silent with lower voltage! = diodes!
And diodes for reverse current smps<>battery.

[mantha3]

Hey FFF! Thanks for the detail you just added. I looked these up and clear as day. Thank you for the response.

[mantha3]

This is the 12 Volt LED light that I was thinking of. This is pretty bright. This is 12 volt strip of LEDs. I should have been more specific on what I was talking about. So I'm thinking of doing the single run of diodes to get the 13.5 down to 12 volt and then split the 12 volt out to the fan and LED strip.

URL=http://img180.imageshack.us/i/ledtubew400x300.jpg/][/URL]


Or this from the same place-

http://besthongkong.com/product_info...roducts_id=751