Voltage multiplier

[argonrepublic]

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.

[argonrepublic]

Ooooops. Should add that the Transformer is 30VAC. I have about 36 VDC after both sets of diodes. Here is the schematic.

[Mooly]

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.

[janneman]

Originally Posted by argonrepublic

Ooooops. Should add that the Transformer is 30VAC. I have about 36 VDC after both sets of diodes. Here is the schematic.

Hmm.

Edit: deleted, was nonsense ;-)

jd

[argonrepublic]

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.

[janneman]

Originally Posted by argonrepublic

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

[argonrepublic]

A sim would be very cool. That is beyond my electronics knowledge. 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?

[BZed]

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

[Mooly]

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

[wakibaki]

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