Voltage multiplier

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What on earth am I doing wrong? I am having problems with this phantom power circuit. Voltage regulator is working. I can turn right down to next to nothing. I copied this schematic and assembled it to the best of my ability. The voltage multiplier is not working on either of the 3 outputs. I am getting approximately 18, 18 and 36 where I should be seeing maximum of 36, 36 and 48Volts.
Any help would be greatly appreciated.
 
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Just at a very quick look are you using a centre tapped transformer with the ground (centre) correctly connected ?

The transformer needs to be 30-0-30. Are you sure yours isn't 15-0-15 :)
That might account for the results you are getting.

1. What is the DC voltage across C5 and also across C7... that will tell all.
2. Does the midpoint of those caps go to the centre tap of the transformer.

Edit... a 30-0-30 transformer should give around 45 volts across C5 and the same across C7 at light loading. So that's 90 volts DC across the bridge.
 
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It is my understanding that this circuit will double my voltages. My transformer does not have center tap and I am beginning to wonder if I have it wired incorrectly. It does not go to ground at all. Each of the two transformer leads is connected to a pair of diodes, then it is branched to another pair of diodes.
 
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It is my understanding that this circuit will double my voltages. My transformer does not have center tap and I am beginning to wonder if I have it wired incorrectly. It does not go to ground at all. Each of the two transformer leads is connected to a pair of diodes, then it is branched to another pair of diodes.

If you trace the charge/discharge current it seems that the voltage divides itself across the caps C1-C4-C3-C2 in some proportion, depending on the cap value. This would be a nice circuit for a sim and looking at the actual value of the voltage on the caps versus time.

jd
 
You need to make sure that you have the connection going to ground. If you don't it won't work.

When using a center tap transformer you have full wave rectifer circuit, with noncenter tap it's a half wave rectifer and will have more humat less load current.

Good luck

BZ
 
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It's a very confusing diagram.
The version shown with the transformer as shown (center tapped) is OK.

To use a single winding you connect... hope I get this right looking at this :)... you use only Diode D1 and D3. D2 and D4 are not used. The 0v transformer winding must go to the junction of C5 and C7 as shown.
That configuration give the peak AC voltage of the transformer as a DC voltage after the rectifiers. So 30 v ac gives 30*root 2 which is 42 volts. This applies only for very light current draw from the rails... this configuration is no good for supplying large currents.
So you should measure around 42 volts across C5 and the same across C7.

So far so good...

The voltage multiplier looks weird... so I will describe how it "should look"... which is not to say that the circuit as drawn doesn't work.

C2 is OK as long as it goes to the AC winding that is not used as "ground"... so just as shown.

D8 is OK as shown.

D6 is OK as shown.

C3 and C4 are OK. These are in series with resistors across simply to allow use of 50 volt parts. The resistors equalise the voltage across each and can be any high value as long as both are the same.

D5, D7 and C1 are not needed.

The ground line is correct as long as it too goes to the 0V connection of the transformer.

Hope I've got that right ;)
 
This is an ugly diagram. Four-way junctions. Sideways gnds.

You need to pay attention to the ground routing.

There is no voltage doubler as it is commonly thought of, just a full-wave bridge rectifier and a full-wave centre-tapped dual polarity rectifier both clagged onto the same CT txfrmr, which is why you need to think about where the ground return currents go, and keep them local to their own parts of the circuit before bringing all the grounds together.

I haven't seen this done before, it's probably OK, but in some ways I'd feel more comfortable if there were actually 2 tx's. It definitely won't work if you haven't got a centre tap on the tx.

w
 
I would be impressed if I could understand how this circuit would give me +/- 18V and 48VDC with my 30-0 transformer. Do you know the answer?

Oh, explanation. The transformer has 2 sections of 30vac, which, ignoring loading considerations, produces 2 sections of 30 x 1.414VDC. ~42 Volts. The bridge rectifier stacks them 42+42=84V (over gnd, which is where you connect the negative output. The CT full-wave rectifier stacks them -42, 0, +42 since you connect the CT to gnd. The regulators ensure the voltages are reduced to that required.

Note that LM317 is good for ~37V across it so with ~85V being supplied you don't have much room to regulate (85-37=48!!!) and you probably need to have a zener in there to lose a few volts before the reg.

w
 
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I had to look long and hard at the diagram... because my first thought was "voltage doubler"... where ?
But there is... it's just not obvious. You see what you want to see... a centre tapped tranny and "conventional" rectifier... but if you draw it out as I describe in post #9 using a single winding on a transformer the doubler is there, using two diodes of the bridge (D6 and D8.

As to using a 25-0-25 Well that will give reduced rails.
I say it should work with the single winding.
It's just very badly drawn with no explanation. The grounds have to be correct as shown.
 
Thanks so much for your time. I am having quite a bit of trouble with this. I have no formal education and very little experience. I have INA217 going into DRV134 running into my recording interface. Currently powered by a heathkit +/-15V it sounds great. I think I need an OPA134 in there somewhere. I copied this schematic and buttoned all these parts into perforated board hoping to get +/-18v as well as phantom power for my condenser mic. I don't think I have all four diodes connected. I have two diodes on each transformer secondary going to the circuit. I was about to attatch transformer secondaries to two diodes and to the common ground.
 
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You need to look at and get each part working one at a time. It will work :)

If you are buiding on stripboard why not start again, and just get the diodes and supplies correct before fitting any other parts.

You can also make the "doubler" just by "taking" parts together to prove it works...

I'll draw that part out and post it here :)
 
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This is the classic doubler arrangement and is "formed" by the diodes in the bridge D8 and D6.
It's just not obvious when you first see it.

Edit... that should read on the diagram "Vout is equal to nearly 2*Vac peak.

So 30 Vac gives (30*root 2) x 2 which is 84 volts approx.
 

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Ok. I have the diodes all tied up as in schematic. It is kind of unclear to me where to connect the two secondaries of transformer. I kind of inclined to connect them to diodes but almost appears that one lead goes to diodes and the other goes to ground. I kind of think that it doesn't make sense because ground is dc and trans secondary is still ac.
 
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One end of the single winding or the center tap of the tranny becomes what we call "ground" or zero volts. It's just a known point of reference... it's only AC or DC when you measure something relative to that chosen point.

If you are struggling, why not just hard wire the doubler part up to the tranny to prove to yourself it works... one component at a time as in my drawing above.
 
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