Ali/eBay LLC switchmode PSUs to supply Class D or E Transmitter HT

[VK3HN]

Hi there,

I've noticed a bunch of what are being called 'LLC Soft Power Modules' on Ali and eBay.  LLC refers to a pair of inductors and a capacitor that establish resonance at the switching frequency.  The switching waveform is sine rather than square and FET switching losses are reduced, which allows the switching frequency to be increased, transformer sizes to be reduced.  Here is an article introducing LLC from 2017:

https://www.electronicdesign.com/power-management/article/21805811/llc-resonant-converters-raise-the-powerefficiency-bar

The LLC SMPS modules mostly offer dual polarity outputs in the 35 to 100volt range, and are rated continuous 300W up to 2kW.  I have found one that offers a single +80v only.  All offer 12v supplementary supplies, which I wouldn't use. I believe these PSUs are from high power class D stereo amps.   I am interested in whether anyone has thought of trying one as an HT supply for a solid state transmitter in the order of 2 to 500 watts carrier power.    The advantages are the very small size and weight, and not having to build up the linear HT supply, rectifier, filter bank, fusing, soft starter, etc. 

Here is a typical description, in partial Chinglish:

"This product adopts the LLC resonant half-bridge topology, with high conversion efficiency, low interference, fast dynamic response, stable output voltage, etc., as well as integrated overcurrent, overvoltage, overtemperature, output short circuit protection, the best collocation of high-end power amplifier products. It can be used for 200-800W power amplifier power supply. The continuous power at 25℃ temperature is 500W, and the peak power can reach 1200W."

If you want to check them out, just search eBay for  'LLC Soft Power Module' or 'LLC switch mode power supply'. 

What could go wrong?  Well, the regulation could be rubbish, certainly nowhere near as clean as is required for an AM transmitter.  This seems to be the onbious problem.   Reliability may also be a problem.  Also, it appears that the new breed of LLC Controller ICs run at much higher frequencies, 35kHz to 1MHz, so this might be an un-supressable shack noise source, even with no transmitter load present.

The 500W modules are around $US50 so it might be worth getting one and testing it out. Interested in people's reactions.

73 Paul VK3HN.

[K9MB]

It is a very clever idea and is great to generate a lot of DC power with very light weight at high efficiency, but I am not sure how it can be applied as an improvement to linear supplies based on cheap and available control tramsformers in the 80-120vac range at 1-3kva.
Once you get that nice DC, also, in a class E transmitter with pwm modulation, you have to use a triangle wave and comparator circuit to generate a pwm signal running at 100-160khz and then integrate that bunch of fatter and thinner chops into a quasi-linear voltage to apply to the drain bus on a class E transmitter.
The DC to drive the pwm is the easiest part of the design.
How can this amazing featherweight circuit beat that old  iron linear supply?

[M0VRF]

Size, weight, cost, efficiency etc etc.

This is the only place I've ever seen linear supplies mentioned!

[K9MB]

Size, weight, cost, efficiency etc etc.

This is the only place I've ever seen linear supplies mentioned!

Please explain what you mean. Every single class E transmitter I have seen uses a linear supply to supply voltage for the modulator. They are universally fairly large power transformers that are about 100-120vac secondary voltage and that winding is hooked to a bridge rectifier and then to a large output capacitor of 30-60,000uF.
That supply is the source for the pwm or class H modulators that Steve has on his site.
I bought a 2kva 120vac transformer with a double 230vac primary for $70 delivered. Weighs about 40lbs, but who cares, since it keeps my 4 ft rack from tipping over, being on the bottom.
Using a switching circuit coupled to a resonant LCL filter is sexy and super light and gives something similar to my 120vac 40 lb iron transformer, but it probably also needs filtering to prevent rfi. The pwm is enough of a challenge in that respect, though.
However, I am asking a serious question. What practical advantage does this very light sexy circuit give to an amateur building a class E transmitter over a simple linear supply like Steve has used in all his designs, as well as many others?

[VK3HN]

Michael K9MB's question is fair enough, what's to be gained by breaking with the homebrew Class E tradition of a big beefy linear power supply? I've built three such transmitters to date, all in the 100 to 250 watt power range, all PWM, and they all use 500VA toroidal mains transformers with a 100VAC secondary, rectifier and filter bank, etc.  I'd not considered using a SMPS until recently. 

I *could* build another linear PSU, but I'm interested in simplifying the construction process, and a decent quality SMPS offers the following advantages:
- it can be purchased as a fully tested unit, saving the non-trivial time and effort to DIY yet another linear supply
- it is smaller by a factor of at least 3x and possibly much more
- it weighs under a kilogram, not 6 to 10kg like my linear supplies do
- it is 90% efficient, meaning it wastes far less heat
- it is novel, I want to see if it will work, in the spirit of experimentation.

SMPS have replaced linear supplies and transformers in almost all products these days, including the latest class D high power audio amplifiers.  We should try them, once they become accessible, affordable, are safe for experimenters, and meet our preformance requirements. 

On the point of saving DIY effort, I don't mind buying a module to incorporate into in a transmitter project if it isn't interesting.  A PWM or RF switching deck is a challenge. A linear power supply is not.  I am happy to buy commercial outboard audio gear to use between my microphone and my modulator line input, I don't feel the need to homebrew that gear.  Same with my transmitter's power supply. 

Anyway, that's just me.  Each of us build for different reasons and have different expectations about what we get from our efforts..  each to their own.
 
Still interested in hearing if anyone thinks these LLC soft switching SMPS would be too noisy for a high quality solid state AM transmitter. 

- Paul VK3HN. 

   

[M0VRF]

No one except folk on here it seems use linear power supplies. I guess it's an 'american' thing (everything has to be MASSIVE) + the love of old (valve) technology.

I 'm really not sure as most of the rest of the world has been using SMPSUs for ages.

One of the many advantages is that you can carry the transmitter rather than having to hire a truck to move it!

You can series them for more V or parallel them for more I.

   

[K9MB]

No one except folk on here it seems use linear power supplies. I guess it's an 'american' thing (everything has to be MASSIVE) + the love of old (valve) technology.

I 'm really not sure as most of the rest of the world has been using SMPSUs for ages.

One of the many advantages is that you can carry the transmitter rather than having to hire a truck to move it!

You can series them for more V or parallel them for more I.

   

Regarding the love for old valve (tube) technology, guilty as charged. 😉
On the subject of switch mode power supplies, I have a ton of them about running computers and nearly every other electronic device.
I have been a design engineer for 44 years and I have never automatically latched on to the latest thing, using bcd rotary switches instead of microprocessor driven LCDs, for example because customers found them easier to use and they were much more reliable in the -40C to +40C environments where my portable equipment was used to monitor wildlife behavior.
SMPS are more susceptible to lightning and other spikes which iron transformers are inherently resistant to. I actually owned an old UPS that had a linear supply driving a bipolar transistor inverter. Weighed about 60 lbs and I got rid of it because UPS are cheap and effectively shield my computers from static spikes from power surges.
The 40 lb 2kva transformer I just bought fir my Class E rig was surplus from old machine control equipment. There is a great abundance of these old transformers that are in pristine condition and available for 20% of their MSRP, and I will not be needing a crew of men to hoist it 8 inches from the floor on to the base of my rack, so it makes no sense to go with a new technology that uses a resonant circuit running at 1 mHz to produce a sine wave and then somehow rectify it to produce the DC needed to power my switch mode pwm circuit.  I wonder about how much harmonic energy is produced by that 1mHz quasi-sine wave, by the way?
It seems like a case where a great deal of added complexity may complicate, rather than simplify a design. We all worship at the shrine of Rube Goldberg for humor and as a perfect negative example while being victims of Murphy’s Law, the demon who haunts us every day we try to make something work. Occam’s Razor? 😉

Edit: Rereading my post, I came across too dogmatic on this new technology. If the criteria is very light weight and also a +- supply for driving a large class D audio amp, it offers a very compact package that can be a part of a very compact self contained desktop design. My own focus on a 4 ft rack design of a Class E rig caused me to violate my own principle of choosing the best product for a particular application in this case. Given the space, the linear supply is the best choice for me, but I can see very compelling reasons for choosing one of these modules for a compact light weight design. Apologies for my myopic take. 73, Mike

[WBear2GCR]

No one except folk on here it seems use linear power supplies. I guess it's an 'american' thing (everything has to be MASSIVE) + the love of old (valve) technology.

I 'm really not sure as most of the rest of the world has been using SMPSUs for ages.

One of the many advantages is that you can carry the transmitter rather than having to hire a truck to move it!

You can series them for more V or parallel them for more I.

   

Two issues on that?

SMPS seem to want to have a fairly stable range of current draw, and maybe don't like to be "banged"?

Noise. Gotta not have harmonics seeping out or onto the supply lines?

Cooling fan noise...

And, I suspect there is a practical limit on boosting voltage by series connection??

                        _-_-bear

[K9MB]

No one except folk on here it seems use linear power supplies. I guess it's an 'american' thing (everything has to be MASSIVE) + the love of old (valve) technology.

I 'm really not sure as most of the rest of the world has been using SMPSUs for ages.

One of the many advantages is that you can carry the transmitter rather than having to hire a truck to move it!

You can series them for more V or parallel them for more I.

   

Two issues on that?

SMPS seem to want to have a fairly stable range of current draw, and maybe don't like to be "banged"?

Noise. Gotta not have harmonics seeping out or onto the supply lines?

Cooling fan noise...

And, I suspect there is a practical limit on boosting voltage by series connection??

                        _-_-bear

Good points. I used to build low noise front ends for vhf and UHF receivers and the noise floor in oscillators used in tue first mixers were critical. For this reason, I never used digital synthesized signals for that front end, but a low noise crystal oscillator. The noise floor, then- set the limits of the nise floor for the first mixer and the first LNA had to have not only a very low noise figure, but also sufficient gain to make the first mixer noise added to not degrade overall performance.

Today, everything you buy has a switcher in it for almost every application, so that we are sitting in a noisy hell for anyone trying to hear any signals that are low in amplitude and already buried in the ambient noise at a given frequency, plus the man made noise.

Switch mode power supplies can be shielded, to lower the output, but it never really goes away, just gets weaker.

The irony may be that a PWM modulator is itself a Switch mode power generator that chops and amplifies a triangle wave into pulses of different time duration so that when they are integrated into a quasi linear audio signal by the low pass filter and then that signal feeds voltage in series with a digitally switched Class E Transmitter that generates square waves that are integrated into sine waves by the output network.

The fact that the universe is very loud out there at low HF makes that less of a problem, but again, it is about how far down the wideband noise is suppressed in the modulated output and whether it meets FCC specifications.

The question of whether the initial SMPS adds significantly to all that noise generation is a question of scientific inquiry, alongwith whether it has any significant effect on the ability of an amateur to build and operate all this noisy switching in effective communication himself and how much it all adds to the difficulty of others to live in this increasing level of EMI noise.
Good engineering along with necessary shielding and decoupling might render it pf little concern, but the problem is real and must not be ignored.

[steve_qix]

I use commercial (and CHEAP) SMPSs in most of my class E transmitter for powering up the RF drivers.  So far, they are fairly quiet.  One of them required some big perm. 5000 cores to get rid of any residual RF hash, but I was able to get rid it.

As far as use as the high voltage supply (which would need to be around 130V to 135V DC), if such a supply were available at attractive prices, I would definitely use it !!  However, there are considerations that must be taken into account.

The supply will have to be chosen based on PEAK current draw, and not average.  Consider a transmitter with a carrier power of 45V @ 10A.  Ok, 450 watts.  The PWM modulator is very efficient, but it's not 100% efficient, so figure 95%.  So, the supply needs to provide about 475 watts.  Let's call it 500 watts.  135V @ 3.7A (in rough numbers).  The PEAK current the supply will need to deliver can be figured by assuming the modulator is operating at a 100% duty cycle, and is therefore supplying the full power supply voltage to the RF amplifier.  That will be 30A.

So, the supply will need be a 135V 30A (minimum) power supply.  Keep in mind, this is for a 450 watt power input to the RF amplifier transmitter using a pulse width modulator.

It may very well be doable and practical.

I have designed and built one transmitter (450W) that indeed uses an SMPS design power supply / modulator.  There is no power transformer, and the modulator / power supply is very light (I think the whole thing weighs around 10 pounds).  It is experimental, and is somewhat complex, but it does work quite well, and I've had it for about 12 years, and use the transmitter all the time.

[Opcom]

I tend to use what's on hand or inexpensive.

[K9MB]

I have been casually looking at what is available in SMPS that could power a fairly powerful Class E or Class D rig with a PWM.

Here are two possibilities from EBAY:
2kva
110volts dc
18 amps peak.
This could power a 50volt at about 8 amps carrier (400 watts input) and hit 120% on peaks- nearly- (2.2 x 50 = 110volts) - (2.2 x 8 = 17.6 Amps- peak)
Cost $199.00
Dimensions 280mm x 140mm x 65mm
(11 inches x 5.5 inches x 2.5 inches
https://www.ebay.com/itm/184852519998?var=692631066655&_trkparms=amclksrc%3DITM%26aid%3D777008%26algo%3DPERSONAL.TOPIC%26ao%3D1%26asc%3D20201018205123%26meid%3D424ba3afd4e0442aba2a903dc04e99d1%26pid%3D101286%26rk%3D1%26rkt%3D1%26mehot%3Dnone%26itm%3D692631066655%26pmt%3D1%26noa%3D1%26pg%3D2380057%26algv%3DWatchlistVariantWithMLR&_trksid=p2380057.c101286.m47999&_trkparms=pageci%3A0353328d-cbf6-11ec-97b2-4a70a5e1d663%7Cparentrq%3A911963c51800ab85bba23d67fffec864%7Ciid%3A8




3kva
110volts DC at 27 Amps

This could power a 50 volt at 10 amps carrier (600 watts)
You could push to 120% positive easily.
$504.00 USD
Domensions: 11 x 6 x 2.75 inches
https://www.ebay.com/itm/254917069864?_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3Dfe1ab91157fa456ab098e5f1e69b5895%26pid%3D100675%26rk%3D1%26rkt%3D15%26sd%3D254917069864%26itm%3D254917069864%26pmt%3D1%26noa%3D1%26pg%3D2380057%26brand%3DUnbranded&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A0353328d-cbf6-11ec-97b2-4a70a5e1d663%7Cparentrq%3A911963c51800ab85bba23d67fffec864%7Ciid%3A14


As expected. These SMPS are very small and light, but very expensive compared to surplus control transformers available in the USA  in linear supplies.
Headroom on linear supplies for short time much bigger.
Only downside is weight and dimensions.  (7.75 x 6.5 x 7.0 for 3kva iron
Transformers in linear supply much quieter also.
Newest not best unless it is going up to space shuttle or Mars…😉

2kva - 120 @ 16 amps $55. 38 lbs
3kva - 120 @ 25 amps $75   48 lbs

[steve_qix]

You could use the 110VDC 18A supply for a 500 watt carrier input transmitter if:

You use a large filter capacitor at the output of the power supply.  The supply won't be able to charge it up all at once - it would require low value resistor in series with the capacitor until the capacitor reaches the power supply voltage.  At that point a relay would short out the resistor.

The big capacitor will average out the peaks.  

Let's say you want to run 40v @ 12.5A at carrier (12 MOSFETs - 500W input).  You will be able to modulate, at most, 175% positive with the 110V DC supply.  The peak current at full positive modulation will be 34.375A, however, most of the current will come from that nice, big capacitor and not from the power supply itself.  The average current pulled from the supply will increase somewhat, since the average power is increased by the average power in the sidebands.

That is one way to use a reasonably priced commercial SMPS power supply to power a class E transmitter that can run a reasonable amount of power.

[w9jsw]

Only on AMFone is 500W considered "a reasonable amount of power" ... 

[K9MB]

Only on AMFone is 500W considered "a reasonable amount of power" ... 

😂😂😂 That is very true, but Steve is getting a lot of peak power for a minute or two, if he resists the temptation to go “old buzzard” on transmissions and you will need $1000 worth of Computer Grade Caps that will fill a chassis and it will be necessary to turn on the supply an hour before you go on the air to store the 10 coulombs needed….😉😂😂😂.

Steve, you just made my and “your” point that a 2kva 120volt control transformer that can be purchased delivered for $70 is “lighter” and more compact than the $200 2kva 110vdc SMPS…. I say, your idea because that is what you have recommended since I started followimg the old Class E Forum in 2008…

Who knows? That 3kva $500 model might be $150 in a few years and it can source some serious power. For now, my luddite iron linear power supplies rule in the big class E transmitters. 😉

This is pretty fun and it reminds me of those guys building 813 x2 linears powered by two microwave transformers. Those transformers are hot potatoes and VOX is preferred…😉

[steve_qix]

Amazingly enough, the average power required from the power supply for a PWM class E transmitter does not increase all that much under heavy modulation.  I monitor the total current pulled from the supply.   With 100% sine wave modulation, the average power increases about 50%.  If the capacitors did not supply the peak power, the transformer(s), rectifiers and other components would be subject to the peak requirements, and would overheat and/or fail, considering the peak current at 200% positive modulation is 3x the average.

For a 500 watt carrier transmitter, I would probably use 48,000 uF of capacitance.  For a 1kW (carrier) transmitter, I typically use 64,000 uF.  I usually use 4 16,000 uF caps in parallel for such a supply, and they are (or were) not that expensive.  I have a lot of them around here.

Maybe next time I build a transmitter from scratch, I will use a commercial SMPS.  Overall, it would likely be less expensive and be a WHOLE lot lighter in weight !

I do have one off-line modulator/power supply that I use in my 400 watt transmitter.  The modulator and power supply - complete - weighs 11 pounds because there is no power transformer at all.  Just cores, and they don't weigh all that much !!  The design is a bit complex, and it took me a while to come up with it, but the thing works very well and I use it pretty much every day.  At this point, that modulator/power supply is about 15 years old and has never had any issues whatsoever.  So, that is another way to go.

Schematic is here:

[steve_qix]

The schematic,  above, does not include the required PWM generator or overload shutdown/efficiency meter board.  These are described in detail on the class E web site.

[K9MB]

Thanks, Steve.
You are right, there is a big difference between peak and average power.
I was having a bit of fun with it.
Actually, the capacitor bank is a constant, as you point out. I have 2-22,000uF caps plus two more 12,000uF caps in parallel for 66,000uF in my supply.

The transformers are indeed heavy. The 3kva I have weighs 48 lbs. As an old buzzard raised on Iron transformers, there is a natural mistrust of these 12lb wonders, but I have a dozen smaller SMPS in my shack running a lot of stuff, plus I have a 20k solar energy system with twin 10k inverters grid tied to reverse the process we are discussing…

I think the transformerless idea has merit and I keep wondering why it never caught on.
Looking at your circuit, I am wondering why you used a bridge rectifier in it, rather than a full wave CT circuit with the common-ground from power line serving as a center tapped secondary? I am probably missing something.?

In about 2009, on the old forum, I suggested just skipping transformers all together and incorporating the pwm into a circuit that ties directly to the power grid.
All US power comes to our houses as a 240 volt pair and a neutral that is at power line ground. Essentially, the pole pig, or equivalent has a center tapped secondary with 120 each side of the center tap.
Why not just put in spike suppressors and feed a full wave rectifier, followed by our 66,000uF capacitor bank?
Why should we pay for a SMPS module to rectify, power a high frequency oscillator and transformer and then rectify it again after it is chopped to 110volts when we can have 170vdc with no extra weight or expense, or very little.
Also, since we are talking about potentially more than 100amps capacity, why would we even need 60,000uF? A single 12,000uF might well serve. I have some 12,000uF @450volts I picked up a few years ago that might serve.
I realize that power surges will need to be accounted for, but these SMPS are looking at the same difficulties, so why pay them?
Also, since the full wave rectifier uses a grounded common that comes in with the service, no need to float tue supply-right?
This is a real question, not a joke. How about it, Steve- comments?