Author Topic: Transformer tap switching between series and parallel  (Read 3665 times)

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Offline Wolfram

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Re: Transformer tap switching between serial and parallel
« Reply #25 on: April 23, 2021, 10:28:31 pm »
Here's another option, as diodes are often cheaper than relays. You need twice as many as the original solution, but they only need to be rated for half the current. There are also no issues with contact sequencing.
That will work, but is overly complex. Why not just add another diode? Now the switch doesn't have to carry the huge current surge and only passes current in one direction, so it can be a transistor. The additional diode can be, Schottky, or a MOSFET and ideal diode controller IC, if low voltage loss is a requirement.


I'm used to working at voltage and power levels where I have to parallel devices to get the required ratings, and voltage levels where you don't want your relay to switch DC currents, so my solution might be a bit biased by that. Note that my proposal uses twice the number of rectifiers, but they only need half the current rating, which might in some cases be cheaper but probably not here.

Your latest solution is the best one proposed so far in the thread in my opinion, it nicely solves the "relay between capacitors at different voltage" issue that the previous one had, and it also works directly with the MOSFET based bridge rectifier as mentioned in the other thread.
« Last Edit: April 23, 2021, 10:30:08 pm by Wolfram »
 
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Offline nemail2

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Re: Transformer tap switching between serial and parallel
« Reply #26 on: April 23, 2021, 11:30:28 pm »
It's normally use as in the links below:

Thanks for the links! Unfortunately I still do not understand how this works, when there is which voltage and why - also: are the secondary windings permanently connected in series in the schematic with the center tap buggering off to between C1/C2?
Where would I have the 20000uF? I chose to have that much capacitance so i don't have pretty much any ripple even at full load so I'd like to keep those 20k uF under any operating condition...

Also: Wouldn't lead mixing the ideal bridge rectifier with the fifth diode to issues? And how would I insert another controller (besides the fact that it is very expensive) with only one diode instead of another four diodes?

I'd like to keep the ideal bridge rectifier with MOSFETs so I don't have to worry about cooling of the rectifier diodes. I once was using diodes in this design and they did heat up to more than 100 °C.

By the way, please keep it to one thread. I thought some of my posts went missing, until I realised I was looking at the other one!

sorry, usually I don't do that, I felt that the second topic was related but still different from this topic so I thought creating a second one would be better than going haywire in this one.
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Online Zero999

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Re: Transformer tap switching between serial and parallel
« Reply #27 on: April 24, 2021, 08:33:10 am »
It's normally use as in the links below:

Thanks for the links! Unfortunately I still do not understand how this works, when there is which voltage and why - also: are the secondary windings permanently connected in series in the schematic with the center tap buggering off to between C1/C2?
Yes, the idea is to connect the secondary windings together, forming a centre tap, which goes between the two capacitors.

Quote
Where would I have the 20000uF? I chose to have that much capacitance so i don't have pretty much any ripple even at full load so I'd like to keep those 20k uF under any operating condition...
That's a large capacitance. How much current does it use? A centre tapped configuration would require two capacitors in series, which can be half the voltage rating.

Quote
Also: Wouldn't lead mixing the ideal bridge rectifier with the fifth diode to issues? And how would I insert another controller (besides the fact that it is very expensive) with only one diode instead of another four diodes?
No, it wouldn't create any issues. The ideal diode controller circuit, just goes where the fifth diode is.

Quote
I'd like to keep the ideal bridge rectifier with MOSFETs so I don't have to worry about cooling of the rectifier diodes. I once was using diodes in this design and they did heat up to more than 100 °C.
100 °C might be fine. The internal junction temperature of most diodes is something like 150 °C or more. Did you consider using Schottky diodes, which would have half the voltage drop?
 
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Offline nemail2

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Re: Transformer tap switching between serial and parallel
« Reply #28 on: April 25, 2021, 11:09:49 pm »
That's a large capacitance. How much current does it use? A centre tapped configuration would require two capacitors in series, which can be half the voltage rating.
4A max. current and I wanted to eliminate ripple to an absolute minimum.

No, it wouldn't create any issues. The ideal diode controller circuit, just goes where the fifth diode is.
but I'd then have to have two of them, wouldn't I? also, the diode controller circuit has 4 MOSFETs, replacing 4 diodes, what would I do with the other thee and which of the four would I use?
Sorry for the stupid questions...

100 °C might be fine. The internal junction temperature of most diodes is something like 150 °C or more. Did you consider using Schottky diodes, which would have half the voltage drop?
Originally I was printing the enclosure of this PSU with my 3D printer (PETG), that stuff gets all wobbly when heated up to about 80°C. Currently I'm using a PS (Polystyrol) case which I'm not too confident heating up too much either.
But wait, there's more reasons: The PSU is quite of a precision device (at least in self-made amateur measures). It allows to set and hold voltages within 1mV and it usually is bang-on over 99% of the whole voltage range. You don't want heat and temperature drift in your case if you're doing stuff like this (afaik).
Also, I already tried with schottkys, their Vf rises with current and all of them heated up to around 100°C. In retrospective, I would have had to put in some massive block all in one full bridge rectifier and put some big-ass heatsink on it (+ airflow) to keep the temperature down. But I went with the ideal diode controller and never looked back (Tcase = Tambient makes me happy :-))
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Online Zero999

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Re: Transformer tap switching between serial and parallel
« Reply #29 on: April 26, 2021, 07:44:11 am »
That's a large capacitance. How much current does it use? A centre tapped configuration would require two capacitors in series, which can be half the voltage rating.
4A max. current and I wanted to eliminate ripple to an absolute minimum.
I thought it was powering a linear regulator? The minimum voltage due to the ripple just needs to be high enough to avoid the drop-out region. Huge capacitors result in a massive inrush current, which can cause other problems.
Quote
No, it wouldn't create any issues. The ideal diode controller circuit, just goes where the fifth diode is.
but I'd then have to have two of them, wouldn't I? also, the diode controller circuit has 4 MOSFETs, replacing 4 diodes, what would I do with the other thee and which of the four would I use?
Sorry for the stupid questions...
Then use an ideal diode controller designed for one MOSFET, for the fifth diode.
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100 °C might be fine. The internal junction temperature of most diodes is something like 150 °C or more. Did you consider using Schottky diodes, which would have half the voltage drop?
Originally I was printing the enclosure of this PSU with my 3D printer (PETG), that stuff gets all wobbly when heated up to about 80°C. Currently I'm using a PS (Polystyrol) case which I'm not too confident heating up too much either.
But wait, there's more reasons: The PSU is quite of a precision device (at least in self-made amateur measures). It allows to set and hold voltages within 1mV and it usually is bang-on over 99% of the whole voltage range. You don't want heat and temperature drift in your case if you're doing stuff like this (afaik).
Also, I already tried with schottkys, their Vf rises with current and all of them heated up to around 100°C. In retrospective, I would have had to put in some massive block all in one full bridge rectifier and put some big-ass heatsink on it (+ airflow) to keep the temperature down. But I went with the ideal diode controller and never looked back (Tcase = Tambient makes me happy :-))
As long as the case isn't in direct contact with the diodes, I don't see how that's an issue.

It sounds like the Shottky didoes didn't have a high enough current rating. The reason why I'm questioning the need for a low loss rectifier is, it's driving a linear regulator and all you're doing is moving the heat there. The main advantage is it will work with a lower transformer voltage, but if it's already more than high enough, it won't make any difference.
 
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Offline nemail2

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Re: Transformer tap switching between serial and parallel
« Reply #30 on: April 26, 2021, 12:24:09 pm »
I thought it was powering a linear regulator? The minimum voltage due to the ripple just needs to be high enough to avoid the drop-out region. Huge capacitors result in a massive inrush current, which can cause other problems.
I'm having a bit of a confusion/epiphany right now - does that mean, that the linear regulator would be able to "regulate out" that 50 Hz ripple as long as the input voltage doesn't go below the dropout voltage? Thinking about it, it seems very logical to me for the regulator (two BD139/TIP3055 pairs in this case) to be at least as fast as 50 Hz. That would mean, I was doing it wrong all the time, lol.
I have an equation here:
Ripple Voltage = Max Current / Capacitance [F]

If my transformer voltage is 18VAC * 1,414 (in fact it is 27V even under load, measured, don't know why), even 8V ripple (is that peak to peak?) should work ok, which would be only 5000uF of capacitance needed instead of 20000uF. Is that possible?

Then use an ideal diode controller designed for one MOSFET, for the fifth diode.
Didn't know such a thing exists, will have to search. Thanks for the hint (you don't know one, by accident?).

As long as the case isn't in direct contact with the diodes, I don't see how that's an issue.
Well like I said, general heatup within the case, temperature drift of all the precision devices, and so on made my concerns... Also, temperature was still rising, the 100°C i had reached only after a couple of minutes. I just didn't want to deal with that kind of heat on the diodes anymore.

It sounds like the Shottky didoes didn't have a high enough current rating. The reason why I'm questioning the need for a low loss rectifier is, it's driving a linear regulator and all you're doing is moving the heat there. The main advantage is it will work with a lower transformer voltage, but if it's already more than high enough, it won't make any difference.
I was using these and I just realized they weren't Schottkys, sorry for that misinformation: https://www.mouser.at/datasheet/2/427/vs-16edu06-m3-1769326.pdf
However I remember searching for diodes with lower Vf but if I recall correctly, they were all around at least 0.6V or so, when it came to currents around 4A.

But you are of course very right about "only moving the heat to the linear regulator", I wasn't looking at this from that point of view. On the upside is that I have a large heatsink plus a fan on the dual darlington pair so I have no issues of getting rid of the heat there. Also, I was thinking about lowering the transformer voltage (18VAC transformer output vs. 16VDC PSU output, which is not good) to reduce dissipation in the first place or at least raise the output voltage of the PSU, as ~16VAC transformers don't seem to be common, at least not with that kind of amperage rating. That lowers my tolerance on voltage drop on the rectifier in any case.
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Online Zero999

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Re: Transformer tap switching between serial and parallel
« Reply #31 on: April 26, 2021, 09:34:59 pm »
I thought it was powering a linear regulator? The minimum voltage due to the ripple just needs to be high enough to avoid the drop-out region. Huge capacitors result in a massive inrush current, which can cause other problems.
I'm having a bit of a confusion/epiphany right now - does that mean, that the linear regulator would be able to "regulate out" that 50 Hz ripple as long as the input voltage doesn't go below the dropout voltage? Thinking about it, it seems very logical to me for the regulator (two BD139/TIP3055 pairs in this case) to be at least as fast as 50 Hz. That would mean, I was doing it wrong all the time, lol.
I have an equation here:
Ripple Voltage = Max Current / Capacitance [F]

If my transformer voltage is 18VAC * 1,414 (in fact it is 27V even under load, measured, don't know why), even 8V ripple (is that peak to peak?) should work ok, which would be only 5000uF of capacitance needed instead of 20000uF. Is that possible?
Yes, that's the idea. A linear regulator will output the same voltage, as long as the input is high enough.
Quote
Then use an ideal diode controller designed for one MOSFET, for the fifth diode.
Didn't know such a thing exists, will have to search. Thanks for the hint (you don't know one, by accident?).
It's the most common form of ideal diode circuit. I don't have any part numbers in my head, but it's fairly easy to find.

Quote
As long as the case isn't in direct contact with the diodes, I don't see how that's an issue.
Well like I said, general heatup within the case, temperature drift of all the precision devices, and so on made my concerns... Also, temperature was still rising, the 100°C i had reached only after a couple of minutes. I just didn't want to deal with that kind of heat on the diodes anymore.

It sounds like the Shottky didoes didn't have a high enough current rating. The reason why I'm questioning the need for a low loss rectifier is, it's driving a linear regulator and all you're doing is moving the heat there. The main advantage is it will work with a lower transformer voltage, but if it's already more than high enough, it won't make any difference.
I was using these and I just realized they weren't Schottkys, sorry for that misinformation: https://www.mouser.at/datasheet/2/427/vs-16edu06-m3-1769326.pdf
However I remember searching for diodes with lower Vf but if I recall correctly, they were all around at least 0.6V or so, when it came to currents around 4A.
Schottky diodes tend to have lower voltage ratings, than silicon diodes. Generally those with a lower voltage drop, also have a lower voltage rating.

Quote
But you are of course very right about "only moving the heat to the linear regulator", I wasn't looking at this from that point of view. On the upside is that I have a large heatsink plus a fan on the dual darlington pair so I have no issues of getting rid of the heat there. Also, I was thinking about lowering the transformer voltage (18VAC transformer output vs. 16VDC PSU output, which is not good) to reduce dissipation in the first place or at least raise the output voltage of the PSU, as ~16VAC transformers don't seem to be common, at least not with that kind of amperage rating. That lowers my tolerance on voltage drop on the rectifier in any case.
Yes, lowering the transformer voltage will reduce the power dissipation, just as long as there's still sufficient voltage headroom.
 
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #32 on: May 31, 2021, 11:03:46 pm »
Hi

sorry for not coming back earlier, I had non-hobby stuff to do unfortunately, besides making a first prototype of this project.
As expected, inrush current of even "only" 10.000uF instead of 20.000uF capacitance like planned earlier doesn't make the tap switching relay sound very good when switching under full load. Also I'm getting quite some ripple so I'd like to add even more capacitance. The ripple however may as well come from the probably too low voltage transformer but I guess it is a mix of both causes.

Anyway, I came back to the idea of Zero999 and I wonder whether this (see 1st screenshot) will work as intended. I have chosen a MOSFET like suggested, for switching the taps. I don't need the current capability of two windings, but only the lower/higher voltage to lower the dissipation on the pass transistors.

Specific questions for this design are:
- first of all I don't really understand how this works and where the voltage is at and where the current is flowing in which case. understanding would be a nice bonus :)
- will I have 10.000uF or 20.000uF of capacitance?
- are the fuses placed correctly?
- will the LTC4357 (ideal diode controller) work as intended if connected exactly like this?
- should I use a RC hold up circuit like mentioned in the LTC4357 datasheet (see 2nd screenshot) and if so, which values would be to choose?
- can I really use a MOSFET for switching the taps (T1 in the screenshot)?

Thanks, your help is very appreciated!
« Last Edit: May 31, 2021, 11:05:59 pm by nemail2 »
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #33 on: June 01, 2021, 10:45:00 am »
anyone? pleeeeaazzee :D
I'll just build it up and try it out if nobody answers my questions but then I'll still have no idea whether the fuses are in the correct places...
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Offline Circlotron

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Re: Transformer tap switching between series and parallel
« Reply #34 on: June 01, 2021, 11:24:18 am »
Another method is simply parallel the two transformer secondary windings and feed it to this circuit which will function as a normal bridge rectifier for low voltage output and as a voltage doubler for high voltage output. Only needs a single N/O relay contact, so no problem with syncing multiple contacts. This circuit has in the past been widely used for switch mode power supplies that had to run on 120 or 240V.
 
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Online Zero999

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Re: Transformer tap switching between series and parallel
« Reply #35 on: June 01, 2021, 11:30:44 am »
Come on, be pateint. Most people here have other things to do that post. I don't have time to answer all the questions, at the moment. The capacitance is 10mF in both modes and T1 must be a P-channel device, with a potential divider on the gate, to ensure the gate-source voltage rating isn't exceeded.

A voltage doubler is another option, but you're back to using a relay again to switch between voltages and much larger capacitors are required, to achieve the same ripple.
 
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #36 on: June 01, 2021, 12:09:01 pm »
Another method is simply parallel the two transformer secondary windings and feed it to this circuit which will function as a normal bridge rectifier for low voltage output and as a voltage doubler for high voltage output. Only needs a single N/O relay contact, so no problem with syncing multiple contacts. This circuit has in the past been widely used for switch mode power supplies that had to run on 120 or 240V.

ty, didn't know this! however i must admit that no relay and less capacitance needed seems more attractive to me at the moment :)

Come on, be pateint. Most people here have other things to do that post. I don't have time to answer all the questions, at the moment. The capacitance is 10mF in both modes and T1 must be a P-channel device, with a potential divider on the gate, to ensure the gate-source voltage rating isn't exceeded.

A voltage doubler is another option, but you're back to using a relay again to switch between voltages and much larger capacitors are required, to achieve the same ripple.

sooorray, i knew sh*t could hit the fan if I start pushing but i juust couldn't resist :D
i'm on vacation right now so i got time to do stuff :)

i really appreciate anyone putting time into my very newbie questions, i do not take this for granted.

i'm looking forward for you having some more time to answer the other questions, if you'd like and ty in the meantime for the already answered ones.

unfortunately another question came up with your last answer xD
depletion mode or enhancment mode p-fet? also how (potential divider??) will i be able to control the p-fet from my microcontroller which has 3.3V GPIOs?

thanks again, yall!
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Online fcb

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Re: Transformer tap switching between series and parallel
« Reply #37 on: June 01, 2021, 12:21:13 pm »
Another method is simply parallel the two transformer secondary windings and feed it to this circuit which will function as a normal bridge rectifier for low voltage output and as a voltage doubler for high voltage output. Only needs a single N/O relay contact, so no problem with syncing multiple contacts. This circuit has in the past been widely used for switch mode power supplies that had to run on 120 or 240V.
This is a great circuit - but take time to understand how it works.

With the switch open, the circuit behaves 'normally' - you'll get AC*1.414 less diode drops.

With the switch closed, you'll get approx DOUBLE the voltage out.  You couldn't use this circuit as the rectifier on a 'common' mains SMPSU as you'd end up with (in UK) either the 'normal' bus voltage (340VDC) or 680VDC(!) with the switch closed.
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #38 on: June 01, 2021, 08:26:50 pm »
This is a great circuit - but take time to understand how it works.

With the switch open, the circuit behaves 'normally' - you'll get AC*1.414 less diode drops.

With the switch closed, you'll get approx DOUBLE the voltage out.  You couldn't use this circuit as the rectifier on a 'common' mains SMPSU as you'd end up with (in UK) either the 'normal' bus voltage (340VDC) or 680VDC(!) with the switch closed.

from what I have learned, I'd rather use the version with a p-fet instead of a relay and less capacitance for the same amount of ripple. nonetheless, I have learned something new and I am very grateful for that.

I have now changed some things in regards to my previous proposal:
- P-channel FET RSH070P05GZETB instead of N-channel FET for tap switching
- BC847 NPN transistor for controlling the P-channel FET from the microcontroller
- added a voltage divider for the P-channel FETs gate

V(gs) is +-20V max for this P-FET so with my voltage from the 12/24VAC rated transformer being around 33V rectified, I guess I should be good after halfing that...?
The RDS(on) of this FET is max. 15mOhms @ -10V(gs) so at 5A load it should be dissipating around 375mW which shouldn't really bother a TO-263.

Please let me know whether this would work as intended or if I have forgotten something...

Thanks!
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Online Zero999

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Re: Transformer tap switching between series and parallel
« Reply #39 on: June 01, 2021, 09:43:26 pm »
R3 was in the wrong place.
 
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #40 on: June 01, 2021, 09:52:49 pm »
R3 was in the wrong place.

Thanks, seems obvious, now that you pointed it out, stupid me  |O :-DD
My version would blow the P-FET by exceeding the V(gs) voltage.

Otherwhise this should work or are there any objections? Have you got time to look over it whether I missed something?

- placement of the fuses
- the way I connected the LTC4357? datasheet: https://www.mouser.com/datasheet/2/609/4357fd-1269235.pdf
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Re: Transformer tap switching between series and parallel
« Reply #41 on: June 01, 2021, 10:10:15 pm »
- placement of the fuses
Makes more sense to be on pins 5 & 8 on TR1.
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #42 on: June 01, 2021, 10:30:10 pm »
- placement of the fuses
Makes more sense to be on pins 5 & 8 on TR1.

hmm seems legit to me, thank you!

edit: this (screenshot attached) is how it currently looks like, in case anyone is interested. everything will be open source, like my previous project (https://github.com/mamama1/LabPSU_CA1).
It works a treat, besides the ripple due to the too low voltage transformer and the tap switching relay not sounding good (that's why I'm trying to implement the currently discussed solution).

« Last Edit: June 01, 2021, 10:34:19 pm by nemail2 »
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #43 on: June 04, 2021, 12:09:14 am »
hmm i guess I'll just grab the money, buy the parts (LTC4357 and P-channel FET) and try it out (with R3 in the right place) on a prototyping board or something...
will report back...
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #44 on: June 10, 2021, 10:10:27 pm »
Hi

ok so I have built this up using ordinary diodes for starters (see the piece of art in the attachments) and this seems to do it (you wouldn't have expected otherwhise, i guess), so thank you very much for that advice, I will most probably implement this into my circuit for tap switching :-)
Now the only thing I have left to test is the same stuff but using the ideal mosfet rectifiers instead of diodes. I have ordered one LTC4357 and I have a LT4320 in stock to play with, as well as plenty of N-FETs so I will build this up next and report back.

In the meanwhile I'd highly appreciate any hints or advices what I may have overseen or wired wrong (or not ideally) in the last corrected schematics which Zero999 posted.

Thank you all again for your support and help!
« Last Edit: June 11, 2021, 05:28:44 am by nemail2 »
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #45 on: June 11, 2021, 09:50:16 pm »
Hi

i did build this now like in the attached schematics using the ideal diode stuff (but using FQP50N06L N-FETs and one SQD50P06-15L P-FET) and I'm getting weird voltages at the output, see scope shots SDS00001 and SDS00002. Using normal diodes in the very same circuit produces the correct results -> 13V and 26V depending on whether one or two windings are being used.

With the ideal diode controller stuff, I get around 9V mean for one tap and around 24V mean for both taps. Currently there are only 2x100 uF caps for filtering but also no load at all. In the version of the circuit where I used normal diodes, I had a 1k resistor across the output and 100uF caps as well, just like here.

Can this be due to the breadboard and/or the partially long jumper wires or is there probably some other wiring issue?

Please help, thanks!

edit:
I have double-checked the datasheets of the ideal diode controllers and the wiring as well and I couldn't find any issue. So I reconnected the piece of art from the previous post again which uses ordinary rectifier diodes and measured the output with the scope, see SDS00005 and SDS00007. I measured in DC mode so we can see the absolute output voltage as well. low pk-pk output ripple in comparison to the version with the ideal diode controllers where the voltage seems to go almost to zero as if there was absolutely no capacitance??

I'm wondering whether this is a design failure on my side, maybe this solution for tap switching is not compatible with ideal diode controllers, especially with the LT4320, because of the way it works?

I'm clueless, ideas anyone?

I would really prefer to keep using the ideal diode controllers if possible, so I don't have to worry about heat dissipation and space for a bigger rectifier + heatsink. I've got a big ass heatsink + fan on the power transistors anyway so no worries dissipating the heat there instead.
« Last Edit: June 11, 2021, 11:32:55 pm by nemail2 »
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Online fcb

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Re: Transformer tap switching between series and parallel
« Reply #46 on: June 12, 2021, 11:31:18 am »
How does it behave if you increase C53 to something like 1000uF?
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #47 on: June 12, 2021, 11:37:06 am »
will try that later today. the datasheet explicitely mentions 1 to 10uF ceramic or tantal to be mandatory as close to the output pins as possible iirc. i'll try 1000uF in parallel as well as 1000uF instead of C53.

also i will try the ideal bridge rectifier alone without all the other stuff to see whether that works on its own on the breadboard. on PCB it certainly works, i'm using it in my PSU design successfully for years now...

thanks in the meanwhile, i'll report back.
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Offline nemail2

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Re: Transformer tap switching between series and parallel
« Reply #48 on: June 13, 2021, 12:08:42 am »
How does it behave if you increase C53 to something like 1000uF?

ok i tried now a few things:
- 1000uF additionally to or instead of C53 flattens out the ripple for the output voltage when the two windings are in series, but not when only one of the windings is used, obviously, as those 1000uF are disconnected, as soon as T1 opens.
- 1000uF across the output of the whole circuit (so after the T1 switch, basically on pin 7/8 of IC1), makes the ripple go away and voltages stable around 15V and 30V depending on whether T1 is open or not.

anyone got an idea why this works with the standard diodes but not with the ideal diode controllers? With the ideal diode controller it just seems like C2 isn't being used at all when only one winding is active and if both windings are used, C2 also seems to not hold much voltage which makes the overall output voltage drop appearently.

if i disconnect C1, C2, IC1, T1 and everything and only leave the ideal bridge rectifier with 1uF ceramic + 100uF electrolyte cap across the output, I get the expected 30V so the rectifier itself seems to work fine even on the breadboard.

edit:
just verified again: using a standard diode bridge rectifier instead of the ideal bridge rectifier (IC10) with mosfets makes this work, even with the one single ideal diode controller (IC1/LTC4357). as soon as I put in the ideal bridge rectifier IC10 instead of a normal diode bridge rectifier, sh*t hits the fan. no matter if IC1 is there or a standard 1N4007 diode.

even if i connect a cap of 1000uF additionally to C53, one winding alone doesn't deliver more than around 9.5V. it seems like C2 isn't charging at all. i guess the issue could be that the ideal bridge recitifier controller isn't connected at all to the center tap of the transformer and therefore somehow some current path is missing half the time or something??
« Last Edit: June 13, 2021, 01:03:25 am by nemail2 »
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Online fcb

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Re: Transformer tap switching between series and parallel
« Reply #49 on: June 13, 2021, 12:53:28 pm »
My guess is (not sure I'll explain it properly)  that there is a 'shift' in the secondary voltages w.r.t. to your system ground which is interfering with the way your ideal-bridge IC is functioning.

Can you look at the current being drawn from an ordinary bridge-rectifier and the ideal-rectifier?  Also, 'scope the actual secondaries (scope ground=output 0V), you might see a difference between the ordinaryBR and idealBR.
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