Author Topic: Russian voltage multiplicator stacking  (Read 697 times)

Offline nix85

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Russian voltage multiplicator stacking
« on: May 30, 2020, 11:50:10 PM »
I was looking into voltage multipliers and i stumbled on this russian craziness.

/>
So they used this 3 stage multipliers from old TVs. Now, before i proceed, here is great video on basic principle of voltage multiplier i'm sure you all know well.

/>
So, what happens is simple altho it looked complicated to me at first, and i summed it up like this.

Starting with negative halfcycle, C1 charges to 12V through D1. Important notice, C1 is now charged in way that opposes the original voltage. Why doesn't current go through D3 or D5? Current simply goes through path of least resistance.

So now we got C1 charged and voltage source changes direction. Now voltage source and C1 are in same direction and through D2 they together charge C2 to 24V. Important notice, C1 does not discharge, it remains at 12V.

Then source changes direction again, now we have 12V from the source in same direction with 24V on C2 so 36V althogether will charge C3 through D3, but there is already 12V on C1 in opposite direction, so 36-12 means C3 also charges to 24V.... and so on in same manner.

Now, back to russians, they used these multipliers from old TVs and you will notice they don't have the first cap.



It's not a mistake, here is the schematic.



Also you will notice they flipped every other multiplier. This must be because there is no first cap. If there was a first cap, they would just continue the stack like this.



But since no first cap, they inverted the next one and now there are two diodes in parallel which act like a single one.



Russians claim it converts 7kV from the flyback into 35kV. Just like in the video i linked where 12V (24V peak to peak) is converted to 72V, that is, x6, this multiplier missing the first cap multiples x5, that is, 7 into 35.

My questions is why is ground terminal disconnected from V terminal and what is the use of V terminal if nothing is connected to it?

« Last Edit: May 31, 2020, 12:28:30 AM by nix85 »

Offline davekni

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Re: Russian voltage multiplicator stacking
« Reply #1 on: May 31, 2020, 03:54:03 AM »
Definitely don't ground the "V" terminal as in your last schematic.  That shorts the AC source on negative half-cycles.

I suspect the V terminal was for some low-current negative bias voltage for some CRT electrodes or whatever.  Presumably had an external capacitor, or perhaps a resistor divider before capacitor to get the correct voltage.  Most "normal" TVs have a positive focus grid bias around 2kV, usually generated within the flyback, often with a POT to adjust voltage built into the flyback package.  Sometimes two separate adjustable voltages.  Perhaps this potential is ground in the Russian TVs, with the cathode negative.

If you assume an external capacitor from V to ground, this is a +5x/-1x multiplier (relative to peak AC input voltage).
David Knierim

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #2 on: May 31, 2020, 07:09:09 AM »
I think it could power the focus, which takes a couple kV.

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #3 on: May 31, 2020, 05:54:56 PM »
Definitely don't ground the "V" terminal as in your last schematic.  That shorts the AC source on negative half-cycles.

I assume what you mean is that load would drain the negative half-cycles and thus the voltage could not build up. Dave in the vid below addresses this saying load current has to be low or very low for it to work.

But that is classical representation of the multiplier, it should work when "V" and "ground" are one, as long as load current is low.

/>
Besides, "V" terminal is not connected to anything it the russian stack, so it is as if the first diode is not there.



Quote
I suspect the V terminal was for some low-current negative bias voltage for some CRT electrodes or whatever.  Presumably had an external capacitor, or perhaps a resistor divider before capacitor to get the correct voltage.  Most "normal" TVs have a positive focus grid bias around 2kV, usually generated within the flyback, often with a POT to adjust voltage built into the flyback package.  Sometimes two separate adjustable voltages.  Perhaps this potential is ground in the Russian TVs, with the cathode negative.

If you assume an external capacitor from V to ground, this is a +5x/-1x multiplier (relative to peak AC input voltage).

Maybe.
« Last Edit: May 31, 2020, 06:54:52 PM by nix85 »

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #4 on: May 31, 2020, 07:05:04 PM »
No, if you look at the diagram on the EEVblog video you can see there's no diode between the AC terminals. If you short V and gnd, that's basically conencting a diode between the 2 AC terminals

Offline davekni

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Re: Russian voltage multiplicator stacking
« Reply #5 on: May 31, 2020, 07:32:32 PM »
Yes, as ritaismyconscience said, grounding V will short-circuit the AC input.  Doesn't matter what loading is after that.

Yes, I presume F is for focus.  I'm just guessing that the Russian TV needed some negative voltage as well.  I've seen some TVs with two separate positive focus voltages, so there are clearly different options in CRT electron gun designs.  Perhaps they bias the cathode negative, or have some other negative electrode(s).  This is just guessing.  I have no documentation suggesting how the V terminal was used.

If you added an external series capacitor to the AC input, then V could be grounded, and it would become a 6x multiplier.  However, I don't know if the first (lowest) internal capacitor could handle 2x voltage.  It normally sees only 1x voltage, half as much as the other 4 capacitors.
David Knierim

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #6 on: May 31, 2020, 07:42:19 PM »
Quote
Yes, I presume F is for focus.

I think so too.

Quote
I'm just guessing that the Russian TV needed some negative voltage as well.  I've seen some TVs with two separate positive focus voltages, so there are clearly different options in CRT electron gun designs.  Perhaps they bias the cathode negative, or have some other negative electrode(s).  This is just guessing.  I have no documentation suggesting how the V terminal was used.

If you added an external series capacitor to the AC input, then V could be grounded, and it would become a 6x multiplier.  However, I don't know if the first (lowest) internal capacitor could handle 2x voltage.  It normally sees only 1x voltage, half as much as the other 4 capacitors.

And how exactly would they tap that negative voltage, between V and the ground?
« Last Edit: June 01, 2020, 10:39:23 PM by nix85 »

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #7 on: May 31, 2020, 07:45:04 PM »
No, if you look at the diagram on the EEVblog video you can see there's no diode between the AC terminals. If you short V and gnd, that's basically conencting a diode between the 2 AC terminals

I don't understand what you mean. There is no V terminal in his diagram, which is classical VM diagram. The shortest path between AC terminals is through 1 diode and 1 cap.

« Last Edit: May 31, 2020, 07:52:46 PM by nix85 »

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #8 on: May 31, 2020, 08:20:07 PM »
if they connect capacitor between V and GND, it's basically a single diode rectifier that charges the capacitor every negative half wave.

if you short V and GND, it'll look like this:

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #9 on: May 31, 2020, 08:32:03 PM »
if they connect capacitor between V and GND, it's basically a single diode rectifier that charges the capacitor every negative half wave.

That would be like this.



Quote
if you short V and GND, it'll look like this:


I don't understand. I mean, again, there is no V terminal in classical MV depiction, ground and V are shorted by default. Can you elaborate. I don't understand what you mean at all.
« Last Edit: May 31, 2020, 08:33:54 PM by nix85 »

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #10 on: May 31, 2020, 08:40:02 PM »
Here's what happens if you conenct them:

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #11 on: May 31, 2020, 08:50:17 PM »
Here's what happens if you conenct them:


Ok, that is how russian multiplier without the first cap would look if V and ground were one. Are you saying that would be an issue?

Main point is why all of you claim it can't work if V and ground are one as in classical depiction? It doesn't seem right.
« Last Edit: May 31, 2020, 08:59:05 PM by nix85 »

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #12 on: May 31, 2020, 08:57:42 PM »
Yes, its an issue because you'll short out the power supply. Also, the other caps wont be charged because the AC voltage is shorted by the diode

On the negative cycle, the AC input is at lower voltage than ground. This means the diode would conduct and cause large current to flow through it

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #13 on: May 31, 2020, 09:00:46 PM »
Yes, its an issue because you'll short out the power supply. Also, the other caps wont be charged because the AC voltage is shorted by the diode

On the negative cycle, the AC input is at lower voltage than ground. This means the diode would conduct and cause large current to flow through it

Yes, you are right about that.
« Last Edit: May 31, 2020, 09:36:35 PM by nix85 »

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #14 on: May 31, 2020, 09:12:09 PM »
You can test your circuits using the simulator here: http://falstad.com/circuit/

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #15 on: May 31, 2020, 09:19:32 PM »
I guess u meant putting cap like this. But this is also shorting the input on the negative halfcycle. I don't understand.

« Last Edit: May 31, 2020, 09:23:59 PM by nix85 »

Offline ritaismyconscience

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Re: Russian voltage multiplicator stacking
« Reply #16 on: May 31, 2020, 09:25:26 PM »
Once the capacitor charges fully no more current flows through it

Offline nix85

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Re: Russian voltage multiplicator stacking
« Reply #17 on: May 31, 2020, 11:03:45 PM »
Here is exactly what happens.

When C1 and source charge C2 to 24V C1 is now discharged but on next (negative) halfcycle C1 is charged to 12V again. AT THE SAME TIME (in parallel) 12V from source + 24V on C2 charge C3 to 24V (36V - 12V on C1). This discharges C2 but on next (positive) halfcycle it gets charged to 24V again and at the same time 12V from source + 12V on C1 + 24V on C3 charge C4 also to 24V (48V-24V). And so on in same manner.



PS Lenz's "law" is not a law AT ALL, but no need to go into that here. :)
« Last Edit: June 03, 2020, 12:49:02 AM by nix85 »

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Re: Russian voltage multiplicator stacking
« Reply #17 on: May 31, 2020, 11:03:45 PM »

 


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