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Voltage Multipliers, why not?




 
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Author Topic: Voltage Multipliers, why not?  (Read 1626 times)
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IN3IEX
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« on: March 01, 2013, 04:08:13 AM »

If you need many voltages simultaneously from a common insulation transformer, voltage multipliers are a good solution. Capacitors with high capacitance are now common and multipliers work well.
Never use half wave rectifier, the DC current in the transformer must be avoided at any cost.
Only use multipliers (with capacive input) or full wave rectifiers and or multipliers.
See the following examples.

http://www.ing.unitn.it/~fontana/Comparing%20Half.pdf

The last one I used for my transmitter, providing 300V, 600V and 1200V.  900V are available and not used.

see how small the board is:
http://amfone.net/Amforum/index.php?action=dlattach;topic=30021.0;attach=30262;image

Giorgio
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« Reply #1 on: March 01, 2013, 10:37:33 AM »

Thanks for sharing.

Will the 1N4007 continue to take the surge currents during turn on?

I would recommend something on the order of 1N5408's diodes for anything from 300V dc and up.

I didn't see any surge resistors between the transformer secondaries and the rectifiers.

Phil - AC0OB

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IN3IEX
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« Reply #2 on: March 02, 2013, 04:20:24 AM »

Yes. The 1A diode is ok. 3A diodes are preferred for most applications.
I have indeed observed less surge current with multipliers if compared to similar bridge rectifier circuits. I never used surge limiting resistor with these circuits.
Please note that the low kohm resistor in the schematics are the loads used for the simulations. They are not part of the circuits.
Try these circuits. You can also squeeze the maximum power from your transformer, even from a single vout that you can choose at Any time.
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VE3LYX
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« Reply #3 on: March 02, 2013, 08:24:49 AM »

I use miltipliers often. Sometimes I pop a 10 ohm heavy wattage resistor in where the choke would be for a cap imput filter. Seems to work. Last one was so quiet I though the set was broken!
I use them for my homebrew ad power the rx and the low power tx stuff from the transformer and use a multiplier for the PA final voltage.
Don VE3LYX
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Don VE3LYX<br />Eng, DE & petite Francais
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« Reply #4 on: March 02, 2013, 02:43:55 PM »

Multipliers have worked well since tubes and even used in commercial gear. At such a low cost I use the 3A 1N5408 for just about everything.

A 250W carrier output AM rig using 4D32's for RF and audio has been on the drawing board for a few years due to lack of time but the B+ stages will all be direct line driven multipliers which are safe as long as you pay attention to details. The 1N5408 is impervious to direct line spikes but if you really want bulletproof the 6A10 is not much larger or costly. The filaments will be transformer driven to eliminate the surge and unequal division even with same current tubes that is all too common due to production tolerances.

The goal is a compact and reduced weight rig that will give a respectable signal without requiring an amp or at least a table rack cabinet plus not require a lot of HV and filter caps to get there; the 4D32 works very well at 700-750V based on typical US line voltages.

Another choice is 2-3 814's that do very well at around 1000V if a 240-250V line is available but efficiency on 10 may be down.

Carl
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Patrick J. / KD5OEI
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« Reply #5 on: March 02, 2013, 09:53:54 PM »

That is an excellent analysis.

Here is a comparison between the full wave "4x8" voltage doubling power supply and the "economy" power supply showing that a doubler can approach the performance of a bridge and is constrained mostly by I2R loss in the transformer. Those could be improved by using a transformer with the lowest DCR in the secondary.

http://www.bunkerofdoom.com/lit/4x8/index.htm
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