Mastero MK-4 ATX PSU with features. - Page 6

rando · 05-06-2004, 11:50 AM

Quote: Originally Posted by MrPerfectionest

Your equations look fine, but in the case of a linear regulator it doesn't have a set efficiency, and you assumed 80% to make your equation work. Have a look in the data sheets and see if you can see anywhere that it quotes a specific efficiency?

You're right, it doesn't. I mistakenly interpreted "high efficiency linear regulators" in the data sheet as a characteristic of the device rather than one of its applications. Not finding any efficiency plots, I simply inserted a conservative 80% estimate into the equation to demonstrate how the equation worked (not to make it work). I now see that the value wasn't conservative since the regulator is apparently terribly inefficient (a property of linear regulators that often drives the use of switching regulators instead).

Thanks for your help. I'll go hop back into my hole.

Mastero · 05-07-2004, 06:00 AM

MBR745's has to be isolated on the heatsink .....

It is always better if you isolate all chips on the Heatsink.

Mastero

ashbosh · 05-07-2004, 02:00 PM

Hey Mastero
Any idea when the MK-4 ATX kit will be available?

Mastero · 05-08-2004, 01:38 AM

Its up for sale
http://www.mp3car.com/vbulletin/showthread.php?t=25909

check it out
Mastero

MrPerfectionest · 05-08-2004, 04:27 AM

I am curious about the 12V regulation peice of the design. It looks to me that you used the 2587T as a boost regulator and the LM1084 as a post regulator to this to fix the voltage at 12V. I am curious about what voltage you are boosting to because if my calculations are correct it looks like you are boosting to ~23.8V then regulating back to 12V. Is this correct?

For the 2587T-ADJ the equation from the data sheet to set the output voltage is Vout = Vref(1+R1/R2), where Vref = 1.23V.

If we use the values you have indicated on the component layout where R1 = 33k and R2=1.8k, this will give the programmed voltage of 23.78V. Is this correct how you calculated it?

Mastero · 05-08-2004, 09:24 AM

ashbosh · 05-09-2004, 08:00 PM

guys, i need some suggestion on what can i use for the heatsinks for MK4. I have old psu. But the heat sinks are too tall and short. where can i get some strip aluminium 5mm thick? Home depot??

Sinorm · 05-09-2004, 08:43 PM

Quote: Originally Posted by ashbosh

guys, i need some suggestion on what can i use for the heatsinks for MK4. I have old psu. But the heat sinks are too tall and short. where can i get some strip aluminium 5mm thick? Home depot??

You can get pieces of aluminium at Home Depot, yes, although I would recommend using something slightly better for your heatsink if possible. Maybe cutting down those old heatsinks you have with a dremel?

mp3hombre · 05-09-2004, 08:47 PM

So no schematics huh?

ashbosh · 05-09-2004, 09:55 PM

Quote: Originally Posted by Sinorm

You can get pieces of aluminium at Home Depot, yes, although I would recommend using something slightly better for your heatsink if possible. Maybe cutting down those old heatsinks you have with a dremel?

I sure can cut down the height, but what abt the width and the thickness? Is 3mm thick and 80mm wide heatsink good enough??

eden · 05-10-2004, 10:02 AM

Mastero,
Sorry to interrupt your topic, it's my first post on this forum and I hope my question won't be too stupid.
Is it possible to have a scope trace of the net "Switch output" (pin1 of your LM2678-3.3V) ?
I'm currently using this switcher and the ringing on this net generates spikes on the ouput over +/-300mV.
Seing your layout, I quite sure your overshoot will be in the same range...

Regards
Eden

MrPerfectionest · 05-10-2004, 10:20 AM

There are going to be overshoots on this line. I am not sure how much specifically is acceptable but overshoots on this line don't necessarily translate into overshoots at the output. What type of load are you testing with that the overshoots are occuring? Also, what is your Cout setup, that is, how many capacitors, capacitance value, and ESR rating?

eden · 05-10-2004, 11:50 AM

Concerning my setup :
Cout : 2 * 470µF AVX TPS serie3 (SMD tantalum). ESR max = 45mOhms.
LC filter = 10µH + 470µF AVX TPS serie3 + 2200µF electrolytic 32mOhm (measured)
Load = Resistor of 1.5ohm (ie about Iout = 2A).

I've tried to avoid overshoot by using snubbers (cf AN1135). The effects are reduced but still present. I've also add 10ohms in serie with the boost capacitor, no improvement.

Output cap cant' avoid this 2nde order oscillation. The only way for me is to slow down the rise edge of the switch output.

Mastero, could you check if you've got oscillations ?

MrPerfectionest · 05-10-2004, 12:30 PM

What Vin are you using, and I assume you are doing this developement on a real PCB?

slboytoy · 05-10-2004, 06:29 PM

Powers up EPIA boards (jumper Setting onboard)

What's that all about??