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Old 2nd December 2012, 12:57 AM   #1
dmac23 is offline dmac23  United States
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Default DC Filter Choke Working Voltage Question

I am designing a power supply with a B+ that is over 1kV. I noticed that many HV designs implement the filter choke on the 0V side for safety and to avoid absurdly expensive chokes.

I have a few questions regarding this configuration:

Does it now not matter what working voltage the choke is rated for?

Using two half wave rectifiers (866a), I plan on making a full wave rectifying circuit. It would make sense that I would have to actually ground one side of the choke. Will the other side just have continuity with my CT of the power transformer?

What if I want a more complex filter stage such as a LCLC? Will the second choke be the only one that has reference to ground?

Thanks!
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Old 2nd December 2012, 01:43 AM   #2
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The reason the choke is put on the low voltage side of the line is to reduce the voltage stress between the choke and ground. If you want to make an LCLC filter, put both chokes in the low voltage side of the circuit.
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Old 6th December 2012, 01:01 PM   #3
dmac23 is offline dmac23  United States
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Thanks for the reply. I have done some reading on this and it is indeed a common practice. Do I have to worry about current and voltage ratings of chokes still if I place them on the lower side? My instinct tells me that the chokes would only see the ripple current in this configuration is that correct?
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Old 6th December 2012, 04:33 PM   #4
DF96 is offline DF96  England
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They will see exactly the same current as if they were put in the supply rail. They will see much less voltage. The grounding arrangements need to be thought about, as you will be (almost) building the PSU opside down.

I am slightly concerned at your questions. 1kV power supplies should only be built by people who really know what they are doing. Does your wife have you properly insured?
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Old 6th December 2012, 05:25 PM   #5
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Putting the inductor in the ground line transfers the isolation trouble from the inductor to the transformer, then the problem still is present.

But there is two voltages to be considered in this tread: one is the isolation from core to winding, and another is between winding ends. The last is not affected by its position in the current path: the full AC peak rectified. (1.414VAC) and affects the voltage per turn without arcing; and the core to winding. I believe is easiest to solve in a choke with only one coil, and not in the xformer with a minimum of two isolation boundaries; between coils and from each coil and core.

What do you think?
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Old 6th December 2012, 05:37 PM   #6
dmac23 is offline dmac23  United States
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Quote:
Originally Posted by DF96 View Post

I am slightly concerned at your questions. 1kV power supplies should only be built by people who really know what they are doing. Does your wife have you properly insured?
You are probably right I am an senior EE student and have been building amps for a while but havent messed with more than 800V. I am aware of some of the dangers associated with HV. I may start out at around 800V or so and increase it after I feel better about the circuit design. I really appreciate your input as well as your concern!
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Old 6th December 2012, 11:13 PM   #7
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The old ARRL manuals from 1940 to 1980 can give you some insight in what ham radio people have done with 800 to 1500 volt supplies . Clean soldering and heavy duty ground of chassis is just the start . Humidity and dust start to do fun thing with these supplies . ARRL books give you a hands on safe approach . How much current are you looking at ?
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Old 6th December 2012, 11:17 PM   #8
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Quote:
Originally Posted by DF96 View Post
They will see exactly the same current as if they were put in the supply rail. They will see much less voltage. The grounding arrangements need to be thought about, as you will be (almost) building the PSU opside down.

I am slightly concerned at your questions. 1kV power supplies should only be built by people who really know what they are doing. Does your wife have you properly insured?
Where you meaning upside down not opside ? Or more succinctly inverted as to the placement of the choke in the curcuit?
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Old 7th December 2012, 05:01 AM   #9
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To answer your question yes the second choke is the one with the ground reference the second choke will only see a small amount of ripple, the first choke may see ripple of +/- 25% of the AC peak voltage.

I have done it both ways, choke on the ground side and on the HV side, to avoid isolaton problems all the HV components can be mounted on a deck supported on standoff insulators, that way both your chokes can be running with the iron cores connected to the HV via a bleed resistor. 1 kV is medium voltage, corona effects will be small even so avoid sharp edges. It gets more interesting with the 35 and 40kV supplies that large tubes require, HV decks are common place in these supplies.

I will second the recommendation of the ARRL handbooks even the 70's and 80's vintage books have plenty of power supply build instructions. The 866A rectifier is obsolete , I know the blue purple glow is cute, and it can be replaced by string of silicon diodes, that way there is no need to worry about a heater transformer and associated isolation requirements.
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