Help designing power supply

[Electric-Gecko]

I am late in the planning stage of a power supply that I will build for my DIY effects pedals.  I already have most of the parts that I will need.  I have a 2x15v transformer, in which the centre-tap will be grounded.  2.1mm barrel jacks will be used as power outputs.  The voltage regulators are in the 78Lxx and 79Lxx series.  I am going to make a custom PCB to mount the small components.

Some of the power outlets are single-power, meaning that the outer pin is connected to ground.  But some of them are dual-power, meaning that one pin is positive and the other is negative, neither are ground.

Does each outlet need to have it's own regulator or pair of regulators (for the dual-supply)?  Or can the +12v outlet share a 78L12 regulator with the ±12V outlet?

What should I do for reverse polarity protection of the regulators, for when I switch off the power?  Should I have a diode in series with the input on each regulator?  Or is it really better to have a diode in parallel with each regulator?

[PRR]

> one pin is positive and the other is negative, neither are ground.

Odd. Without clarification, these need *separate* transformer windings.

[Electric-Gecko]

> one pin is positive and the other is negative, neither are ground.

Odd. Without clarification, these need *separate* transformer windings.

Yeah, that's right.  The transformer is centre-tapped, so that's not a problem.  This is what dual-power is.

[R.G.]

It's not possible to give an answer that's correct for all loads from what you've given us here.

In other words, it depends on what you're connecting to those outlets and what they need their power - and grounds - to be.

[Electric-Gecko]

I hope that this diagram clarifies my description of the outlets.


So can the ±12v outlet share a positive regulator with the +12v outlet?

Each regulator can supply up to 100mA, which is more than what I think I will need, so that part isn't an issue.

[antonis]

So can the ±12v outlet share a positive regulator with the +12v outlet?

As long as their GND is refered to the same pin (centre-tap wire), yes you can..

Of course, you have to calculate the "common" positive regulator's current for both +12V & ±12V outlets..

What should I do for reverse polarity protection of the regulators, for when I switch off the power?  Should I have a diode in series with the input on each regulator?  Or is it really better to have a diode in parallel with each regulator?

Diode in series will result on a 650mV voltage drop and will not protect your regulator from output capacitor discharging through it (if it's placed after the cap)..
Diode in (reversed) parallel by-passes those actions to your rectifiers which have a much higher reverse voltage "strenght"..

[PRR]

Only three of your six outputs connect to ground.

It appears they can NOT all come from a common supply. You may need four separate transformer windings.

> depends on what you're connecting to those outlets and what they need their power - and grounds - to be.
> depends on what you're connecting to those outlets and what they need their power - and grounds - to be.

Worth repeating.

[anotherjim]

If some of those supplies are true bipolar -  and there is only a 2 wire feed - are you relying on signal ground connection (audio jack sleeves) to provide their 0v? Workable in principle? But what about ground hum issues?

[antonis]

Maybe stereo outlets with stereo jacks for bipolar supplies should help...

As Paul said, your bipolar supplies have no GND to "refer on"...