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 Post subject: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Wed 23, 2022 6:18 am 
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Hello All,

ArtfromNY here on the forum was nice enough to send me a couple of 6012 thyratron tubes. They are quite lovely and are begging to be used in some kind of project.

I was wondering. Since these tubes characterized by their relatively high current capability, how feasible would it be to use a pair of these tubes to build a switch mode power supply of some kind? I was thinking a phone charger outputting 5V via a USB port. Now of course I know that this would be a ridiculous project from a practicality point of view, but I think it would be a very fun experiment if it is doable. Just for kicks. I'd love to show my fellow nerd friends an iPhone charger that runs on tubes. The funny thing is whatever I use to power the tube filaments is already much closer to being able to charge an iPhone than the actual finished circuit itself. :mrgreen: I suppose my point in this project would be to mimic the type of circuitry that makes the every day dime a dozen phone charger work. It shows what a massive leap in technology enables us to do that wasn't even practical to do before.

My idea was to configure the tubes somewhat in the fashion shown below, almost like a class AB audio amplifier with an audio transformer. Except instead of producing a sine wave, a square wave could be used to drive the output transformer. For maximum efficiency (perhaps the only efficiency here) some kind of high frequency ferrite transformer could be used. The output could be 5V to be a simple USB phone charger or alternatively the output could be something like 12V or 19V to power a laptop and perhaps with an additional regulator circuit to also put out 5V USB. I'd love for the tubes to play the role of switching devices rather than to configure them as rectifiers. I'm always fascinated by the low on resistance characteristics of mosfets, this plays tribute to do that by showing the world of difference between all electrical switching devices now and then.

The average cell phone consumes between 1.8A to 2.4A with a completely dead battery. So about 12 watts maximum. It might be tricky filtering the output enough not to kill any of the phones or USB devices it will charge and a feedback or at least voltage limiting circuit will be needed. Then of course my idea of how to lay out the circuit may not be the best and perhaps a buck converter/boost converter type circuit would be best. The biggest issue I can think of when it comes to the tubes performing the switching to drive the transformer is that these tubes don't stop conducting until the load is disconnected.

Again, yes this is stupid and over complicated. But I'm sure it will make for a funny meme.

All that said, how feasible is this really?

Below is the tube data sheet.

http://www.tubebbs.com/tubedata/sheets/049/6/6012.pdf


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Wed 23, 2022 2:55 pm 
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Where does one find the specs for how a particular battery likes to be charged?


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Wed 23, 2022 3:25 pm 
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That wouldn't really factor in as the battery being charged would be handled by the phone's own battery management and charge system. It would only be receiving the 5V as it always does. Basically we would be emulating the circuit in a cheap phone charger as shown below but with all tubes. The more I think of it the harder I realize this is. For one I'm not sure how I would switch off the thyratron tubes. Perhaps the job would be better done by one or two sharp cutoff pentodes driving the transformer. Another thing is how to rectify the low voltage high current output without the use of semiconductors. I suppose some exceptions could be made. The switching tubes could be driven by a CD4047.

This idea is partly inspired by this video where someone made an all tube 555 timer.

https://www.youtube.com/watch?v=bjAlzA4Cyys


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Wed 23, 2022 7:00 pm 
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I'm not a thyratron expert. What I do know is that they are the ancestors to SCRs. Turning on an SCR is easy, but the challenge, save in applications where the supply is AC or pulsating DC is making it turn off.

There were TV horizontal output sections that used SCRs. SONY used a special type of SCR called a gate turn-off SCR in which the gate could either turn the device on or off. One of the European TV manufacturers used a circuit with two SCRs and some passive devices in a "commutation circuit," whereby turning on one of the SCRs would pull enough current away from the other SCR (which was already conducting) to make it turn off.

These thyratrons have two grids. Perhaps, there is a way to use the shield grid to make the thyratron turn off. Or, perhaps, there is a way to use two thyratrons in a way similar to what was done in the European TVs. Since I've never played with thyratrons, I don't know whether either of these is a practical solution.


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Sat 26, 2022 2:05 am 
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If you want a simplified PS that produces 5 vdc with one or both of your thyratrons, you can simply wire them as dodes, I think. Certainly it was done with normal triode tubes.

Ground the plate and other grids, use only the cathode, pin 1 and the nearest grid, pin 3, which will be the anode of your diode. Copy a schematic for a battery eliminators that uses a tube rectifier. Two thyratron diodes can be wired in series. Or they can be wired with their cathodes on the two secondary leads and their grids tied together as the DC out to the filter.

Needs a hefty 3 amp 6.3 vac transformer to power each tube heater, or 6 amp for the two tubes ( you'll need that no mater what design you choose ) and possibly a small 6 volt transformer, the 6 VAC supply to the cathodes of your thyratron diodes. Each tube filament draws 2.6 amps. The 5 volt charger won't need 1/4 that much.

Other parts - two 47 mfd electrolytic capacitors and maybe a resistor, that's the filter, then add a voltage regulator #7805 for a steady 5 VDC, easy to build and fun to show off. You might add bigger filter caps, but we'd have to read the tube specs.

An iPhone probably will refuse to accept a charge tho, have to use a cheap phone for the demo.

https://www.radiomuseum.org/tubes/tube_6012.html

Your diodes can be wired as a full wave rectifier in place of the solid state rectifier used in this old schematic. Your resistor replaces the choke, L, in the schematic for the A battery supply. Just an example. If you want a better schematic, somebody here can draw one. Cheers.
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Last edited by westcoastjohn on Nov Sat 26, 2022 3:50 am, edited 1 time in total.

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Sat 26, 2022 3:02 am 
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I too like the idea of impractical tube circuits from some alternate, non-transistorized timeline :lol:


You can use thyratron for phase-angle control, but the input voltage must swing through zero or they lose control. Typically only used for preregulators.

More "practical" would be a flyback circuit. This is the switching power supply from an old tek 503 scope, for example

Image

Image

Note that getting it to work at 5VĀ±5% and amps of output, especially without solid state diodes, is completely silly

At the heart of it, this really is the same circuit as in a modern phone charger.

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Sat 26, 2022 8:04 am 
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Wow thank you much for the input!

Perhaps I can just drive a flyback transformer from a donor TV? Simply mimic an existing drive circuit as you posted, marko. The thyratrons could be on the rectification side producing B+. To drive the flyback a standard horizontal output tube. The filament winding should be able to put out enough juice to charge a phone! If not perhaps I can wind my own on the ferrite bar of the flyback.

What I'm curious about is, would there be a high current rectifier available for the job without having to resort to solid state technology?

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Sat 26, 2022 8:43 am 
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If its one of the old flybacks that has a wax donut on it (not plastic and drowned in epoxy) I think it would be suitable. You'd want to get rid of the existing secondary of course.

The highest current tube diodes I'm aware of were all gas diodes, for low voltage things like (automotive) battery chargers, a 'tungar' tube was typical. Don't think I've ever seen one, though. Replaced fairly early with metal rectifiers in a lot of applications.

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Sat 26, 2022 10:56 am 
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You mean like the one shown in the right side of this picture? I tried searching around for a few random CRT numbers to see what a typical filament current is and it seems the most common one I got in my quick search is 0.6A. The highest one I found was 1.35A. So indeed our own winding will have to be added and the existing filament winding discarded. However, I'm assuming the typical flyback core will not be able to produce as much power as we need no matter what kind of secondary winding we add. Am i correct on that? Keeping in mind of course we are going to need at least 5V @ 2.4A to achieve full current charging on the phone. Otherwise the phone will charge in slow mode or report problems. Perhaps finding a pretty beefy flyback will be necessary. The typical flyback is designed to drive a 6V @ 0.6A filament which is only 4 watts of power. Or do the other supplies derived from the flyback really consume that much additional power in typical operation? I would imagine for example even with the vertical supply and high voltage winding, the typical flyback core is not going to sufice to produce 12 watts. Let me know if I'm wrong on that one. I really have no idea. Maybe if we changed the frequency of the drive?


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Nov Sat 26, 2022 7:07 pm 
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Yeah, the bulk of the power goes to the EHT (10-or-20-whatever-kV for the CRT) and boost B+, if it has it. Getting rid of that and putting a thicker filament winding would deliver more current, the core itself must be good for 50W+ or something like that. (it's quite a lot of ferrite, even for 15khz). Your typical phone charger is probably running between 100-300kHz but it only has like 1/4 cubic inch of ferrite... better quality ferrite though...

try looking at some TV schematics from the era, take heed on the "DO NOT MEASURE" bits :shock:

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Fri 02, 2022 12:46 am 
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I'm looking for a flyback transformer in the classifieds but so far no one is biting. If anyone can throw some vintage flyback part numbers at me I can maybe speed up the process by looking for one on eBay. Searching "Vintage Flyback Transformer" on eBay yields surprisingly few results. I see a NOS Zenith flyback on there but I would hate to ruin a NOS part and would rather someone sell me a junk box transformer.

In the meantime I am brushing up on my Flyback Converter theory. It has been a very long time since I wanted to find out how to design one of these gizmos and how the theory applies in practicality. FINALLY I found a great video that details how to calculate the transformers, diodes, and mosfets. Anyone wanting to know more I highly recommend you watch this video. This young girl does a wonderful job of explaining it all so that even a monkey like me can understand.

https://youtu.be/Lalsahf5cGo

With this knowledge I am tempted to simply try and build this circuit using a modern ferrite transformer. However for the moment I think it would still be cool to use a flyback transformer and existing horizontal circuit. Mostly because it might help leave less room for error.

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Fri 02, 2022 1:37 am 
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You might try a push pull audio output transformer. Probably easier to find, especially since you're stepping down anyway. As long as it's good for a few kHz it should be fine. You'll want to run this circuit at as high a frequency as practical in order to have good output regulation, but the deionization time of the thyratron is likely going to limit it to audio frequencies.


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Fri 02, 2022 6:30 am 
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Bob, those Audio Xformers are indeed easy to find but they may be a bit too heavy. I'm already wondering how I will resolve the high amperage needed for all the filaments and how heavy that transformer will be. Of course worrying about the weight of such a project is already a bit ironic. If I can find the right filament tubes it will probably end up as a series string set up with perhaps the output rectifier filaments being fed from the output itself for better isolation.

I believe I've settled on instead winding my own ferrite core transformer from scratch. I found a very nice looking core on eBay and have ordered a couple. They not only seem beefy, they look period correct for the 1950's. They already kinda look like flyback cores. They also already come with bobins and are hardware mountable.

https://www.ebay.com/itm/125605076268

If needed, this will give us more flexibility if we need to try different winding schemes vs an existing pre-wound transformer. The thyratrons will be used as rectifiers on the output. This is where their high current capability is really needed. Everything on the primary side will be higher voltage lower current. Don't know what I was thinking using them as switching devices. The transformer could be driven in either push pull style or single ended style. It seems to me having a single ended configuration using a horizontal sweep tube with a separate oscillator tube would give the most stability and ease of frequency and duty cycle adjustment. All the while a push pull configuration could be easily set up in a "wig wag" type circuit but also be more unstable. Basically the circuit would be what is shown below, where the switch represents the Horz. Sweep Tube.

Mostly I will be trying to copy as much of a television as I can as I am not so great at designing circuits from scratch. The basic block diagram of the circuit would go something like this:

120VAC->Rectifier->B+.->Oscillator->Drive Tube->Transformer->Thyratron rectifiers.

The primary would not be isolated. The isolation would come from the ferrite transformer. Of course one issue is there's no easy way to full wave rectify using tubes. That would require a transformer or more tubes which I would like to avoid adding. I'm hoping half wave rectification will not add much more added instability. I'm guessing B+ would fall at around 110VDC or so? Is that too low for the tube? Oscillator could be an almost complete copy of a TV's horizontal oscillator. The drive tube could be any old loctal horizontal sweep tube. As BobWeaver pointed out, the switching frequency of the thyratrons will be an important limiting factor. I had actually not thought of this part at all. Perhaps some kind of feedback winding can be added to regulate the voltage. That last part would be really cool! One of the best parts of of switch mode PSU's is their ability to quickly self regulate. But well first things first.

I will gather some more ideas and materials.


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Sat 03, 2022 4:56 pm 
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Quote:
the core itself must be good for 50W+ or something like that. (it's quite a lot of ferrite, even for 15khz). Your typical phone charger is probably running between 100-300kHz but it only has like 1/4 cubic inch of ferrite... better quality ferrite though...


A flyback core is a LOT of ferrite... typically running more than 25 W in a TV set. A phone charger has a smaller core BECAUSE it runs over 100 KHz. The ferrite is different, not necessarily better.

Why not build the original switch-mode power supply? Use a vibrator!

Any tube-based power supply will be much larger and much less efficient than using a power mosfet. The ON state of a transistor has less than one volt drop; any kind of tube will be over 10 V.

Phone chargers put our AMPs of current; that's hard to do with any kind of tube.

Rich


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Sat 03, 2022 6:22 pm 
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If I were to try building a 5vdc @ 1.8-2.5 amps power supply using a television oscillator circuit, I'd be more inclined to use the vertical oscillator running at 60 hz. A vertical output transformer is specifically designed to step down to a low voltage/impedance at high current. The horizontal output transformer on the other hand is tailored to multiple functions and really more than what's required. Basically you could full wave rectify the output of the vertical output transformer. The vertical height control should give you some control of the rectified voltage value. You'll have to experiment to see what raw voltage you end up with coming out of the rectified circuit. I'm not sure if you can get 13 watts from a singe vertical output, but you could always make it push pull. Ideally you'll want an older style isolated vertical output transformer rather than a auto-former.


Last edited by Kevin Kuehn on Dec Thu 08, 2022 1:11 am, edited 1 time in total.

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Sat 03, 2022 7:23 pm 
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Quote:
You'll have to experiment to see what raw voltage you end up with coming out of the rectified circuit. I'm not sure if you can get 13 watts from a singe vertical output, but you could always make it push pull. Ideally you'll want an older style isolated vertical output transformer rather than a auto-former.


Find/buy an old 25W amplifier, maybe running 6V6 or EL84 output tubes. Feed it with a 5 KHz sine wave input. Rectify the output with Schottky diodes in TO-220 packages (on a heatsink). If the voltage is too high, you may need a series linear regulator. Someone smarter than me could create a feedback circuit to automatically control the input audio to get the correct output DC.

Lots of effort for nostalgia.

Rich

PS: a quick look at 6V6 datasheet says you won't get 25W out; you probably don't need that much as your goal is 12.5W DC


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Sat 03, 2022 7:55 pm 
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Rich, W3HWJ wrote:
Someone smarter than me could create a feedback circuit to automatically control the input audio to get the correct output DC.


Like a radio's AVC circuit. :wink:


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Mon 05, 2022 12:24 am 
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Kevin, that's a very interesting idea. Earlier we discussed the possibility of using audio output transformers and regular iron core power transformers in a push pull type set up. I hadn't thought of simply copying over a vertical deflection type circuit. The main attraction for me there is the abillity to control output voltage using the vertical height control as you previously mentioned. I'm just not sure how well an existing vertical output transformer would lend itself to our application. Or how much the vertical circuit itself would lend itself to being adapted to use a different transformer. When I say I don't know, I don't mean as to say that I don't think it could work. I mean, I really don't know. :lol: I think this will be my Plan B. It certainly sounds like it may be easier to design for overall so if my first choice gets too complicated for me I may end up going towards this plan.

I thought about using a vibrator but I decided against it as I'd like the circuit to be all electronic with no electromechanical components.

For the time being I think I may already be a little too enamored with the idea of using a ferrite transformer and a higher frequency. These two things just make it much closer to what is found in the modern day SMPS. I always found one of the most fascinating things about a SMPS to be it's high frequency and the advantages that come with it, mainly regarding the transformer weight and size. I'm a little disappointed that my tube rectification may be limiting the top frequency I can drive the transformer at. However if I end up running it at around 15khz and the PS makes that cool TV high voltage sound then it might even add a bit to the cool factor of the whole thing.

For those who may have not seen, I posted a thread in the Television Discussion forum requesting schematics of the most simple and run of the mill series strung sets available during the octal/miniature tube era. These are the most fitting schematics I obtained. The first one being my top choice as reference material. Thank you to bandersen.

https://www.earlytelevision.org/pdf/ge_ ... er_tv4.pdf

https://earlytelevision.org/pdf/rca_kcs ... _315-9.pdf
https://earlytelevision.org/pdf/rca_14p ... _396-3.pdf

We've determined that as is, a horizontal deflection circuit will not be suitable as a power supply. A deflection circuit has many other jobs to do besides producing power that we do not need or even want in our project. However it is great to have this as reference material as it's pretty much the only thing I can think of from the tube era which counts as a switching power supply. Rather than copying these schematics directly, they are helping me see what a tube looks like when configured as an oscillator and a high power switching device for driving a transformer. I am not so great at designing from scratch so I will have to "borrow" a lot of ideas for sure.



As the ferrite transformer I ordered will be arriving this week I will now need to start thinking of how this will actually play out.


The circuit will be divided into two main parts. The primary and secondary. The primary will be everything before the ferrite transformer and the secondary will be everything after the ferrite transformer. All isolation will be provided by the actual flyback transformer just like in a modern SMPS. This means everything on the primary side will be extra hazardous due to it not being isolated. This may also pose some interesting challenges if we need to do any kind of feedback circuitry from the secondary side for voltage control. Modern day SMPS use an optocoupler for this purpose.

There will be no filament transformer. This will be a series string set. Some searching will have to be done to find enough filament voltages to add up to the 120VAC line voltage but I'm sure it can be done. We can always end up with something where the filaments run just a tad bit under voltage or where we get rid of some of the extra voltage with a large resistor or ballast. Since isolation is important, the output rectifier tubes may have to not run off the series string but rather off their own winding on the ferrite transformer. Alternatively to make things easier I may implement a small filament transformer just for the rectification stage. Additionally, someone pointed out that working with series string type filaments will be tricky during the experimentation stage. I will initially use 6 volt filament tubes for bread boarding purposes then switch to series string tubes for the final build.

Frequency will be around 15khz. I originally wanted to run this closer to 100khz or maybe even twice that just like a modern SMPS. However someone pointed out the tube rectifiers will be the limiting factor here. The thyratron tubes I was initially intending on using need to ionize and de-ionize and may not be fast enough for the job. Does anyone know if they are even good enough for the 15khz? Or any other beefy enough high current rectifiers that can switch faster?

Output tube will be a 6DQ6. I already have a couple of these in my stash so it will be perfect. This will be the tube driving the ferrite transformer. As mentioned earlier once the final build is made this will probably be a 17DQ6 to make the filament series.

Output rectifier(s) will be thyratron tubes 6012. The maximum switching frequency of these tubes may be a limiting factor as well as their high filament current. I originally thought of using two tubes to full wave rectify the output but this being a 15khz power supply, half wave rectification will probably more than suitable. Many modern SMPS only use one rectifier at the output. This will cut down current consumption from these power hungry rectifiers. Again if anyone knows of a more efficient rectifier tube let me know.

Oscillator will be a PWM type circuit. At 15Khz(?) this oscillator will produce a square wave with varying duty cycle depending on voltage feedback from the secondary to keep the voltage well regulated. I'm not so sure what tube I will use for this in the end. Horizontal oscillators seem to always use 8CG7 but since that's not what we're building here I'm not sure if that will be the best choice. Again, your suggestions are welcome.

All of this is of course subject to change as we figure out what works.

So with that basic ground work layed out I think what I will be doing first is figuring out my transformer windings using some of the formulas I've learned but taking into account the voltage drop of a tube. At least that's what I hope I can do. For the moment I think what I'll do is drive the tube using a solid state PWM circuit. This will help me figure out if the "heart" of the circuit is operational, the output tube and transformer. Get ready to see some smoke! :lol:

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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Mon 05, 2022 3:05 am 
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From what I can tell, it looks like the only difference between a linear regulator and switching regulator is that transistors can be instantly turned fully on or off, I don't think tubes can do that??? Tubes are constantly dissipating heat, so now that I actually look into it further it doesn't seem like anything but an oscillator circuit or linear supply can be done with tubes, since switch mode power supplies take advantage of the fact that transistors can be rapidly turned fully on or off, unless there's something I'm not getting.


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 Post subject: Re: Tube Based Phone Charger/Switch Mode PSU
PostPosted: Dec Mon 05, 2022 4:32 pm 
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jethro98 wrote:
unless there's something I'm not getting.
Yes what you're not getting is that a tube can also be biased in to the cut-off(zero plate current) region, and turned on and off. It's true that in general tubes are high impedance devices while semiconductors are lower impedance, which is why tube equipment often uses impedance matching transformers when driving a low impedance load .


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