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Been using PSUD over the years so this is my first attempt at modeling a HV power supply in LT Spice.
I'm attempting to simulate the Hammond 726 (1790v) transformer via rectifier to a GM70 load(just under 100ma).
B+ is a hair under 1100vFirst question, does the coupled choke appear to be in line with 120-1790v Hammond Transformer?
Second, what would be the preferred tube rectifier for this voltage.
Seems just at the limit of a 5R4 or GZ34, maybe a damper diode?
Edits: 08/18/15 08/18/15 08/18/15Follow Ups:
I think I used wrong inductance on first sim
Hammond 726 120v-1790vct
120-895+895 transformer is 1:7.5+7.5 voltage ratio or 1:56+56 inductance ratio (rounded up for simplicity)
56*30h primary = 1680H secondary
(I learned that from Dave Slagle)
I didn't round the figures above so 1668H is closer to not rounding off.
The schematic outputs at 844volts, Hammond site says V*.45 (1790*.45=805) for Full Wave Bridge without the cap so it seems accurate to me. Sims just under 800v without the cap input.
I recommend to use chokes in the "ground" line (C3-L4-C5, and C5-L5-C6).
Commercial chokes don't like kV voltage between coil and bondage, even the choke's bondage isolated from mounting plate.
Up to 1kV I use Tungsram PV200/1000 (200mA) dual rectifiers.
In this post from nearly ten years ago, the ARRL Handbook is quoted. Note the specific statement that chokes in the ground line are avoided in radio receivers and audio amplifiers due to excess hum.
If you click on RayP's post (to which Jimmy's is a reply) you will find a more extensive discussion. Especially note Ed Sawyer's post, where he found 1000mV hum with this topology, which was reduced to 2mV when the choke was moved back to the high-voltage side.
The ARRL often get things wrong. I'd like to see an analysis of the current path and quantities involved, not just a statement in text.
"With this connection [choke in negative side], the capacitance of the transformer secondary appears in parallel with the filter chokes tending to bypass the chokes."
How much transformer capacitance (XC) are we talking about? Is it really significant at 120Hz in terms of the output impedance of the transformer winding? I'm highly skeptical of the claim here that Ed's result (1 V ripple VS 2 mV) was due to this effect.
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To do a useful analysis, you must first determine the power transformer's winding design. When I tried to explore that last night, I came up with a very complicated circuit!
In the first analysis, the capacitance between a winding and an adjacent core (which is chassis/safety grounded) will be several hundred picofarads - not a big deal at 120Hz, but enough to pass tons of diode switching noise and other HF junk. It greatly exceeds the self-capacitance of the filter choke winding.
More realistically, consider a primary winding adjacent to the core, followed by a HV winding with the center tap in its middle. Further assume the power line neutral is adjacent to the core. Then there is a capacitance from neutral to chassis ground (the core) in parallel with the house wiring which grounds the neutral line at the power entry box. Between the hot side and neutral of the primary there is a voltage source of 120v. From the hot side to the secondary is another capacitance, followed by anther voltage source of the HV half winding, to the center tap. All of this is in parallel with the filter chokes. Lots of opportunity to induce noise bypassing the choke impedance.
At that point, realizing it was both complex and dependent on the design of the specific power transformer, I went to bed. :^)
HF noise is a different problem. I was responding to the claim regarding increased ripple ("excess hum") from this topology. I don't see any reason why that would happen, and I don't think anyone should assume it's a factual statement just because it was published by the ARRL. :)
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Buy Chinese. Bury freedom.
.
Like this 850V PSU.
Output voltage significantly depends on the secondary DCR (at given output current).
Some transformer manufacturer datasheet contains output voltage at nominated current, so unloaded voltage is different, even much greater. If power transformer secondary coil is made my thicker wire (lower DCR), the voltage drop (between unloaded and loaded conditions) is smaller. This transformers are better.
You asked about the rectifier - a 5R4GYB will handle this. Also, as I always recommend, you need to look into the power supply filter from the output side to be sure its output impedance doesn't exhibit any odd behavior.
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Buy Chinese. Bury freedom.
So my plate to plate is the 1790v from the Hammond? That's 110v under the rating.
What does the DC output Voltage rating mean at input to filter?
For 800v its 87.5ma, not sure since the rated current is 175ma @ 1900v
(you need to look into the power supply filter from the output side to be sure its output impedance doesn't exhibit any odd behavior.)
Didn't I do this by modeling with the actual Tube biased thru a transformer in lieu of using a simple load symbol?
"So my plate to plate is the 1790v from the Hammond? That's 110v under the rating."
The specified maximum voltage is not breakdown. It's the upper end of the operating window. It's not unsafe to be within 110V of that parameter, as long as there are no construction or condition issues.
"What does the DC output Voltage rating mean at input to filter?
The table indicates allowable average current at various output voltages. I believe the limitation here is the rectifier's anode dissipation.
"Didn't I do this by modeling with the actual Tube biased thru a transformer in lieu of using a simple load symbol?"
No, you need to remove the 60Hz source/xfmr/rectifier and ground the input of the filter through a low value resistor, say 200-500 ohms. Then you attach an AC generator to the output of the filter through a resistor that approximates the load presented by the amplifier. This will probably be about 5K-10K ohms at this voltage level (R=E/I). I use the AC analysis tool to sweep the voltage at the filter side of the resistor. That gives me a quick look at the relative output impedance of the supply over frequency. I have found this to be much more useful than simply monitoring the startup characteristics or using a stepped load in PSUD. You should be able to find the SPICE schematics I've posted previously on this subject through a search of the archives.
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Buy Chinese. Bury freedom.
See the link below, it explains in more detail what I'm talking about.
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Buy Chinese. Bury freedom.
I have a feeling I'm missing something.Edit- Just modeled your example and got the same results as your plot.
Used Slagles little shortcut on V(B+)/I(V1)
Looks like I get the jist
Thanks!
Edits: 08/19/15
Nice, but you need to look below 10Hz to be sure you're not overlooking any undesirable behavior. What appears in your plot to be a gradual increase in PS output Z down to 10Hz is actually a resonant response. There's an even larger response at ~4Hz...
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Buy Chinese. Bury freedom.
So you just look at the filter portion of your Power supply removing the AC component.
I like Dave's little shortcut on showing in in ohms in lieu of db.
Looks like I have some work to do checking my other power supplies to see how they behave on paper.
I learn something new every week, I need to start writing this down to help me retain.....not getting any younger!
I don't usually do it this way (I'm lazy), but it's a good tool to have on hand...
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Buy Chinese. Bury freedom.
Is LT spice a lot harder to use than PSUD? I have downloaded it but haven't got around to trying it out yet. PSUD has always worked just fine, so I didn't feel the need. Now you have me curious. Do you like it better, and if so why?
I think both programs are just a tool to get you started.....
Spice is a little harder since you have to learn how to place and change devices. I am not an engineer and learned the basics in a very short time.
LTSpice will allow you to build a custom supply, PSUD will only do the customary supplies. Spice lets you know when you make a mistake and takes some of the troubleshooting away from bread boarding.
It has countless plotting options to analyze your work.
I would be glad to zip up some files for you to get started. The hardest part is finding all the support files and getting them in the right directory.
I can probably show you more in 10 minutes of simming than you'll learn in hours of reading thru help files if you have Teamviewer. I've been using it off and on for about a year now and only touched the surface.
Someone with the Asylum should hold a class in LTSpice using GoToMeeting or something similar. It would be a cool addition to the forum.
I would really appreciate the zipped files if it's not too much trouble. I should take a look at it from the sound of things.
I don't have team viewer but I will look into seeing if it available on line.
thanks
Edits: 08/19/15
and Merry Christmas.
A years worth of files collected in that time which will save you some time and frustration.
If anyone else is interested I'll send you the link to help promote future LT Spice discussions.
Edits: 08/19/15 08/19/15
Merry Christmas indeed. Thanks very much for all those files! I am sure they will be a big help in learning how to make use of this program.
Thanks!
Interested.
Infamous sockpuppet
. send me your email address
Teamviewer is available online and used for remote desktop and simple conferencing
Its free and online.
Anymeeting.com is another way to collaborate online and its free for up to 4 people at the same time.
I'll zip up the files tonight, simply put them in the same directories where your LTSpice is installed and everything will work.
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