[Garbz]

Ok forgive me if this is plainly obvious but I am still sick so not working at 100% and yet not willing to let my DIY obsession rest for a week

My new DAC output stage need +/-30V and I am trying to pull that without having to buy a new transformer. So Since the current transformer has 2x 15VAC secondaries I was thinking voltage doubler. Then I was thinking about the various ground referenced, floating input, and other voltage multiplier designs and got confused. So here I drew up a rough schematic to see if someone can confirm that I will or will not end up launching capacitors into the sky or cooking my xformer.

There it is. The 1st and 3rd section and the 2nd and 4th section are linked to run off the same winding. All regulators are positive regulators and ground is referenced from after each. What I am hoping is that when I hook both grounds together I will not end up frying something.

One of the things I am worried about is the top part uses full wave rectifier bridges, whereas the voltage doublers use halfwave rectifiers. Although the output is still full wave the coils will still be rectified differently in each case.

 

[Garbz]

Dakiller pointed out to me that there is a diode drop difference between the ground reference on the top regulator and the bottom one. I propose this replacement:

 

[tangent]

I don't immediately see that your plan won't work.

What should be simpler, though, is cascading regulators. I don't see why you can't modify the Jung regs for 30V, assuming this is the Jung 2000 design. You just have to use op-amps rated for a 30V supply. Then you run the secondary regulators from the Jung regs, giving a common ground system for everything.

EDIT: Should have mentioned that you still need the cap multiplier before the first set of regs, if you wish to avoid getting a new trafo.

The only problem I see with this is that there's a greater voltage drop across the second set of regulators. If you can afford that, this should be simpler, and have better performance.

 

[Crowbar]

Use a proper full wave doubler for 120 Hz ripple instead of 60 Hz.

 

[Garbz]

Sorry tangent I should have mentioned earlier. The top half of the supply is already existing and already powering my DAC. I am adding an output stage which needs a much higher voltage and I am trying to do this without any modification to the powersupply, and preferably without spending $30 on a second transformer.

The diodes in paint were added to keep the ground at the same potential, but what if it is not? Diodes drift, and one set is a bridge the other a discrete diode, will a large current flow between the grounds?

Crowbar I saw that but had trouble understanding it. The website mentioned being unable to connect something together which I did not understand. Will this still behave if connected as above in place of the voltage doubler? I could not get my simulator working. It keeps complaining about transient response step to low :S

 

[Crowbar]

What simulator? Upload your schematic and I'll try it in mine later.

 

[Garbz]

Schematic as above. Just replace all the regulators with LM317s for sim purposes. 4700uf or 6800uf caps will do for Cf.

I am using multisim. Nothing against it, I simlpy have not yet figured it out fully.

 

[DaKi][er]

The Charge-Sharing Double-Voltage Bridge

Alredy gave this circuit to garbz, though I thought I'd better answer the thread as well