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Hi everyone, I'm experiencing some troubles with my MBLC that I suspect happen because of my 6V/2.5A toroidal not capable of make my MBLC stuffed with 2 2x40 LCDs and nearly 200 leds. After running for some seconds, it suddenly resets. What do you think?  to have 3A I built the psu according to a schematic to connect in series 7805's which Smash kindly showed me. The reason for my suspect is that if I'm not wrong, the voltage decreases as the load increase over the capability of the transformer. The fact is that if I connect the secondary outputs of the transformer in series to duplicate the capability to 5A, the problem still occurs. The 7805 have a big heatsink and they don't become very hot, so I suppose they don't shutdown. Any idea?

P.S.: I forgot to say the most important thing, that this happens with the maximum number of possible leds on ^_^

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The 7805 have a big heatsink and they don't become very hot, so I suppose they don't shutdown.

Hmm, a few seconds aren't enough time to heat up the outside or even the heatsink, but the temperature inside (Tj) will reach the maximum very fast and the 7805 will reduce the output voltage.

Have you tried it with less LEDs? Does the heatsink get hot then? And can you meassure the output voltage of the 7805's when you increase the load by switching on more and more LEDs??

Raphael

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The 7805 have a big heatsink and they don't become very hot, so I suppose they don't shutdown. Any idea?
Just to be sure: do you have all the 7805 tabs/heatsinks isolated from each other and from ground? (sorry, I have slept/forgot since we talked about this last)  ;) 

....my 6V/2.5A toroidal....
Remember, you must feed regulators with at least 2 volts more than the rated output voltage for them to work right....anything from 7 to 30 volts is acceptable for 5v regs but the magic number seems to be 9vac.  (more or less than 9 gets things a bit hot depending on load)

The fact is that if I connect the secondary outputs of the transformer in series to duplicate the capability to 5A
-Most- of the time this will give you 12vac @ 2.5A...are you doing a phase trick?...Check out http://sound.westhost.com/xfmr2.htm for some info on transformers. (anyone have a better link?)

Best

Smash

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Quote

....my 6V/2.5A toroidal....

Remember, you must feed regulators with at least 2 volts more than the rated output voltage for them to work right....anything from 7 to 30 volts is acceptable for 5v regs but the magic number seems to be 9vac.  (more or less than 9 gets things a bit hot depending on load)

hi; i just remembered i had something similar with my mbseq with only step buttons and 2 2x40 backlit lcds connected, my adapter/wall wart was on 7 volts at the time.

in my case it hung even before the app is loaded, when i put my wall wart on 9 volts; no problem

so i think you need more volts not amperes

good luck, marcel

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yep Illogik, I think that is the problem indeed, Smash don't worry no ground on the heatsink. Because it's very hard that all the leds will be turned on at the same time, I think it will be no problem. At least as soon as I can buy a new transformer ^^ Thanks everyone

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