Dual power supply

[SounDuke]

Does anyone has schematics for a dual power supply (I have a 3 state switch and I would like to have both battery supply power and DC 9v transformer supply).

Since Core has 2 power pins I have some problems in its realization  ??? Could you help me?

[moebius]

Hmm..

DC transformer and batteries? Good! You can leave -/ground/Vs connected all the time for both supplies and only switch between +/off/+.

Both power supplies being pure DC you could also bypass diode rectifier on the core. (and if I remember right, your using AA cells: this is also preferable as diode voltage drops of the rectifier are kind of your enemy in this use. (And as batteries discharge, it's the voltage that drops))

Bye, Moebius

[SounDuke]

Thanks Moebius

So you suggest to leave out the diode rectifier.. With 6 AAs cells it is not giving problems, I haven't tested what happens when battery discharges (hey 5 hours running and still it doesn't want to stop!) Which kind of problems could I experience with the rectifier installed when the battery discharge? Why it is better to leave out the rectifier? It improves stability of voltage as the batteries wear out?

[moebius]

Uhhuh,

I THINK diode rectifier drops overall voltage by two silicon diode voltage drops, 2 x 0,7v.

And normal AA cell batteries discharge to 1,2v voltage level from the nominal 1,5 volts..

So, basicly the voltage regulator "sees" might drop below the level it needs to do its job, before the batteries are really empty.

Bye, Moebius

[SounDuke]

yeah you're right, AAs get low to 1,2V. So I should connect batteries directly to 2200mF cap to bypass the rectifier (I do not want to desolder the rectifier since the core is in place in the case) right?

[SounDuke]

Double posting :D

oops I mean can I connect batteries (obviously taking care of the polarity) directly to the 330 cap or it's better if I connect them to 2 output pins of rectifier?

[moebius]

Both ways are fine, really. So use the way that you find more convenient.

Bye, M

[Davo]

This calls to mind a similar question.  Jameco #230535CC is a 25-watt triple output supply for about $24: more or less perfect for a Midibox synth.  Since it's regulated, I removed the voltage regulator.  I then noticed the voltage drop and decided to omit the rectifier.  After all, it's not like I'll be constantly messing with the inside once I get it up and running.  Then I noticed that big capacitor.  Do I really need that 2200uF there now that filtering is taken care of by the regulated power supply?  It's not a big problem now, but when I get to work on my SID machine, considerable useful space will be saved by omitting these eight caps.

[Screaming_Rabbit]

This calls to mind a similar question.  Jameco #230535CC is a 25-watt triple output supply for about $24: more or less perfect for a Midibox synth.  Since it's regulated, I removed the voltage regulator.  I then noticed the voltage drop and decided to omit the rectifier.  After all, it's not like I'll be constantly messing with the inside once I get it up and running.  Then I noticed that big capacitor.  Do I really need that 2200uF there now that filtering is taken care of by the regulated power supply?  It's not a big problem now, but when I get to work on my SID machine, considerable useful space will be saved by omitting these eight caps.

... see this one: http://69.56.171.55/~midibox/forum/index.php?topic=4294.0

Greets, Roger