Voltage Doubler

[TIMBO]

Hi guys, I'm not clued up on this stuff, but I've got a tranny that is 230v @ 50vA and would like to use it if I am able to double it to about 460v or so. If the drawing is right what size caps would I need. Thanks

[darryl]

Using round figures and ignoring losses:

230VAC @ 50VA means the available current is about 220mA.

If this is applied to a full-wave bridge rectifier: the output voltage will be 230*1.4=322VDC  
                                                               the output current will be 220/1.4=157mA

If the 230VAC is applied to a voltage doubler:   the output voltage will be 230*1.4*2=644VDC
                                                                the output current will be 220/(1.4*2)=78mA

These are approximate figures, but they do illustrate the fact that you cannot get to 460VDC 'or so' using this particular transformer.

[TIMBO]

Thanks Darryl, You really got a handle on this stuff. I did originally bought it to get that 320v.Is there any way to get around 460v???
Thanks

[John]

Make yourself one of these coming off the 640 volts. I use this to elevate the heaters by ~70 volts to help out with hum in those octals I insist on using.

However, there may be (probably is?) issues with how much current you'll be drawing from the divider. I'm basically drawing none -except for the voltage drop across the resistors- but you'll be sucking current from the divider point, so the resistor on top is going to be large and stout. In fact, I'm betting this isn't a good way to do it now that I'm typing it out, since it's rarely suggested as an answer to "my B+ is too high!!". 

[PRR]

To make a "solid" voltage divider, the current in the divider must be MUCH more than the current in the load being fed. 

For your heater elevation you only have to lift the sub-mA leakage in the heater.

If feeding a Power Output stage, your load is 40mA-200mA, so the divider current should be 400mA-2,000mA.


Dividers are for little stuff.

[PRR]

> .Is there any way to get around 460v???

..... ..... ....you cannot get to 460VDC 'or so' using this particular transformer.

[TIMBO]

Thanks guys. 

[PRR]

You can't raise a 120V transformer another 32V.

At some voltage the iron saturates, the transformer pulls LOTS of excess current (even if unloaded), and emits smoke. You get some leeway from your nominal 120, but not another 25%; that would require 25% more iron&copper, and normal users won't pay that.

[TIMBO]

Hi guys, the input voltage is 240v.

[TIMBO]

Hi dr, I'm not sure what this transformer's intended use is, I have a local RS Components store (not rat shack) that has lots of stuff and as I can only buy Hammond transformers from one guy and he charges twice the price of the ones I buy from the US. These were cheep and I only needed approx. 320v for a pair ECL84s

We work on 240v here so it only has 240v primary and 1x15v tap and 1x230v tap secondary's and is an isolation transformer.

Thinking that a voltage doubler would give me 460v I forgot that I had to add in the rectification factor. Thanks

[Glennjeff]

TIMBO,

240 V AC full wave rectified with solid state will get you very close to 320. Capacitive input filter.

240 X 1.4 = 335 V DC (Theoretically)

[kagliostro]

Ciao TIMBO

Without the use of a SS regulator (impractical to drop from ~644v to ~460v)

and wanting to use that transformer (primary 240v-225v - secondary 230v)

the only thing I can think is to unwind the secondary till to obtain an output of ~165v
(not an easy way, but feasible)

with ~165v AC, using a doubler, you can obtain the desired ~460v DC


K

I assume that the 15v is an intake on the primary winding, not a separated 15v winding

[TIMBO]

Ciao K, It was just ME having a Blonde moment (or grey) and wanting to use an idol transformer, I think i'll just keep them to use on a small build. The 15v tap is on the primary side of the transformer, so you might be right.Thanks

[TIMBO]

No, only two on the secondary......

[kagliostro]

I'm not an expert (I didn't tried a tripler)

but Merlin in his book say that triplers aren't a good choice

is a way to develop heat on the transformer

K

[Heinz]

I ran a simulation of a possible doubler circuit with your transformer. It will give you around 450V into a 6k load. This large voltage drop is due to the series resistance of the secondary winding and the high currents that flow in a doubler circuit. The diodes should have at least a 1A rating.

I have attached the circuit file that can be loaded in LTspice so you can run your own simulations. The value of the series resistance is just an assumption. If your desired load is different you can adjust the value and see how much voltage you get.

I had to zip the circuit file because the forum wouldn't let me upload .asc files.