Power supply question (again sorry)

[SuperBad]

My core module lives :)  So now I am forced to work on a power solution for my MBFM.  I discovered that I have a wall wart supply that has both a 12V 500ma line and a 12.5V 200ma line.  I would like to use the 12V line to power the core, and the 12.5V line to power the OPL board.  Is this possible?  is it a bad idea?  If it is doable..  Where should I start?  My other option will be to make the whole transformer power supply as shown on here, but I don't understand the mods I would need to do to get 5v to j1 on the core.  My core module is a Rev 2 from smash TV.

Bobby

[illogik]

8) too hot...., but must answer.....

no no; for the OPL3 board you need a 12 V bipolar power supply.

Bipolar PSU's provide both positive and negative voltages (compared to a shared ground of 0V) which gives you 3 pins/poles/voltages; in this case;  -12V, 0V, +12V

You can make this by using a transformer which makes 2x12V (or a bit higher) out of 220V (110V out of europ).

check this schematic;

http://www.ucapps.de/mbhp/mbhp_opl3_psu.pdf

TK uses another smaller (unipolar) transformer to also get the +5V for the core.

in short i fink your psu won't work.

cheers, marcel

[raphael]

check this schematic;

http://www.ucapps.de/mbhp/mbhp_opl3_psu.pdf

If you use this schematic, don't forget to place a fuse (100mA is more than enough here) and a two-pole switch on the primary side of the transformer!

[SuperBad]

What I was wondering was if I could replace the transformer with a 12.5 V supply and run it throught the circuitry to get both +12 and -12 out of it.  I have actually decided to try the other power supply Duggle suggested in this thread http://69.56.171.55/~midibox/forum/index.php?topic=3970.0 but I am terrible at making my own pcb's and my last attempt with stripboard worked briefly and then I released the magic smoke out of one of the capacitors :(  I am much better when I have a ready made PCB, but aren't we all.  Going to try making my own traces with solder on a piece of perfboard this weekend once I get some more caps, and a new Voltage reg.

Bobby

[illogik]

hi bobby

What I was wondering was if I could replace the transformer with a 12.5 V supply and run it throught the circuitry to get both +12 and -12 out of it.

no, because the thing about the transformer is that it actually has two transformers (2 supplies) that both have 12V; you can connect 2the 2 together (in different ways), or use em separate.

what's done here is to connect them in series so you get a 24V Voltage between the negative side of one and the positive side of the other.

when you consider the point where you connected them ground; you get +12V on the pos.pole and -12V on the negative pole.

you can do this with the right transformers and with batteries (9V for example) but not with a line of a power supply like a wall wart (but thats more bad experience then theory)

good luck, marcel

[moebius]

Hi,

You can use schematic suggested by Duggle, if you have an AC wall wart. It uses half-wave rectifying and should be ok, because OPAMPs don't need much power.

Stable bipolar voltages are important, but voltage levels don't matter that much ie. in a private conversation TK suggested that OPAMPs might even be powered from as low as +/-5 volts.

Bye, Moebius

[Stigmata]

[applaud] [smite]

Posts: 354

 

Re: Power supply question (again sorry)

« Reply #2 on: 2005-06-23 at 15:32 »

Quote

check this schematic;

http://www.ucapps.de/mbhp/mbhp_opl3_psu.pdf

If you use this schematic, don't forget to place a fuse (100mA is more than enough here) and a two-pole switch on the primary side of the transformer!

??? :-[

Do I put the fuse on the primary 12V before the rectifier??

Christoffer

[smashtv]

Do I put the fuse on the primary 12V before the rectifier??

No, on the primary (line voltage/220VAC) side of the transformer.  (and do be careful!)  :)

You want the switch here also, so transformer does not stay powered when not in use....

Best

Smash