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 Post subject: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 4:49 am 
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In the following voltage multiplier circuit

Attachment:
Power 2.png
Power 2.png [ 4.41 KiB | Viewed 382 times ]


Do the components further on down the line need to have a higher voltage rating or can all components be the same voltage rating?


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 5:31 am 
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That zener makes no sense. Also the voltage markings on the secondary of the transformer.


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 11:28 am 
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The zener is for regulating the voltage.

The voltage markings are what was printed on the transformer.

This is part of a display I made and if the B- is not regulated the image size changes with a change in line voltage.


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 11:38 am 
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Yes, the need a higher voltage rating.

I guess the 235v and 135v windings are used in series?


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 11:48 am 
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Yes 1/2 of the 235 volt winding and 135 volt winding are indeed used in series.

The transformer has the center tap of the 3.15-0-3.15 volt and 235-0-235 volt windings connected internally which goes to a single transformer terminal that connects to ground. Initially I wanted to use the whole 235-0-235Vac winding and the 135 volt tap which would have provided -1,710Vdc unloaded, but given the transformer is sealed I could not separate the center taps and thusfore had to use a voltage doubler followed by a resistor and cap for ripple reduction and a zener to get -940Vdc. That works, but a higher B- would produce better focus and thusfore give me a sharper image.


EDIT:

LOL as drawn the circuit don't work. I made an error.

Thanks for the assistance though. I do have the correctly rated parts.


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 4:54 pm 
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The voltage ratings of parts increase as you go down the chain.

Image

https://www.physics-and-radio-electroni ... upler.html

I would give some extra margin on component voltage ratings, for example, don't run a 1N4007 at 1000V. Put 2 in series; they are cheap. With the small capacitances you show, this circuit should be OK for microamps of output without huge ripple.

Rich


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 7:18 pm 
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I've never heard of a 1.97kv zener diode. Highest rating I know of is about 200 volts.

Also, if that's a voltage quadrupler, the output would be about 765 volts no load.


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Mon 13, 2019 7:43 pm 
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I only used one zener symbol as I do not have room on the whole schematic for a string of several zeners.

I rebuilt the circuit as Rich has it drawn. I get around -1.56KV before the 100K resistor and the zeners regulate that to -1.455KV +/- the accuracy of my DMM and HV probe.

I would have liked a higher voltage, but while messing around with the circuit as initially drawn I had a point of nearly -2KV where I tried connecting the load and I have a neon lamp I connected to an isolated from the chassis bayonet lamp holder. One terminal started arcing to the metal part which is grounded to the chassis although both lamp terminals are not.

So it was good that I wound up with a lower maximum B- voltage.

I wound up using two .22uF caps in series to ground before the 100K resistor as each is only rated for 1KV. That helped reduce the image swimming which is due to ripple on the B- supply. A .1uF 1.6KV cap on the output to ground helped the ripple be further reduced. I still have a very slight bit of barely noticeable image swimming though so I may add more capacitance. Think I got room for a .22uF 2KV film cap and a .1uF 2KV film cap which should take care of the ripple. The B- varies no more than 20Vdc for a line voltage change of 10 volts. I normally use a 10 volt line change for things like this to ensure that the zener always has enough voltage being supplied to it so that it properly regulates.


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Tue 14, 2019 3:51 am 
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Location: Santa Rosa, CA
Quote:
Also, if that's a voltage quadrupler, the output would be about 765 volts no load.


235 + 135 =370 x 1.414 (the transformer is RMS) x 4 = 2092 V theoretical max.

If you increase the capacitor uF, you may get more voltage out of this quadrupler.

Rich


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Tue 14, 2019 11:55 am 
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I could, but if I did that I might have to get some pots meant to handle high voltage plus I don't have much room for more capacitors.


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 Post subject: Re: Diode and capacitor voltage ratings
PostPosted: May Tue 21, 2019 4:25 am 
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I ordered four .22uF 2KV caps and will use two to ground in parallel before the 100K resistor and two in parallel to ground after the 100K resistor.

That will give plenty of filtering and will boost the B- some. I may put one .22uF 1KV cap in parallel with the first cap and the other cap may go in parallel with the other cap coupling to the second doubler.

That would further increase B- but I cannot go over 2KV.


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