💬 The Harvester: ultimate power supply for the Raybeacon DK

[NeverDie]

And here is Version 2, which uses an Arduino UNO to and a load switch to measure an E-PEAS solar module that's charging a 100uF capacitor using a solar keychain solar cell. This time I did use a prototype board.

It's too soon to evaluate, but it seems as though it's off to a good start....

Edit: nope. I'll have to migrate the Arduino design to dead-bug, because the voltage is only very slowly crawling up. Maybe that's just how it is with this the E-PEAS, or else maybe mounting leakage (the higher the voltage the higher the leakage) is what's causing the drag.

Edit2: confirmed. These measurements were taken at 1 minute intervals, under varying cloud conditions, and it's clearly not able to hold on to the charge the E-PEAS has accumulated on the 100uF ceramic cap:

734, raw = 652, volts = 3.267
735, raw = 689, volts = 3.453
736, raw = 371, volts = 1.859
737, raw = 399, volts = 1.999
738, raw = 445, volts = 2.230
739, raw = 556, volts = 2.786
740, raw = 616, volts = 3.087
741, raw = 671, volts = 3.362
742, raw = 371, volts = 1.859
743, raw = 444, volts = 2.225
744, raw = 510, volts = 2.556

[NeverDie]

I punted on the Arduino and hooked up the E-Peas AEM10941 module to the deadbug op-amp for measurement, as the dead-bug op-amp appears to work flawlessly. The results were: the AEM10941 does build up to a voltage of about 4.135v max when under fairly bright lighting, and then all that disappears and it reverts to starting to charge up again from a voltage of about 1.8v, and it cycles over and over like that. Kinda weird, but that unexpected result may explain the above 1 minute interval readings: probably (?) it wasn't current leakage but instead this kind of cycling that explains the measurements.

Edit: Unfortunately, the AEM10941 breakout board can't seem to rise above 0.352 volts when tested with the same solar cell and same dead-bug op amp assembly under the same 1 flux light source, so I'm afraid I have to label it a FAIL for use in boosting, just by itself, from that particular low light scenario. Given its datasheet, I'm rather disappointed. I did clean the board and my soldered connections pretty thoroughly with IPA, but perhaps there are other leakages inherent in that board, or perhaps the chip itself has limitations that maybe aren't apparent from its datasheet.

Which raises an interesting question: are some types of PCB's less prone than others when it comes to leakage currents? It might make a difference in what kind I order from a PCB fabhouse if some types are better than others. Anyone know?

I didn't test whether the AEM10941 might have some other beneficial use if that barrier is somehow passed, or assisted in being passed, but for now I'm moving on to test some other chips and see how they perform under these conditions to see whether they perform any better and without needing help.

---

Edit: BQ25504 has no problem charging under the 1 lux light, under the same conditions, even from a starting voltage of zero volts.

Edit2: Well, not quite. Despite a promising start, the BQ25504 peaked at 0.812v and couldn't seem to pull itself above that. It was able to charge up further than the AEM10941, but it hit a ceiling nonetheless. So this time I gave it some bright light to bring its supercap voltage up to 0.814v, and now the voltage appears to be climbing again, al beit slowly. Assuming it is able to continue on its own from this point forward, then my theory is that internally there is a schmitt trigger which is causing this effect: as the voltage slowly rises, the current drain increases up to a peak and then declines again as the voltage continues to rise. At least that is how TI describes typical schmitt trigger behavior in Figure 1 of TI's application report entitled "Understanding Schmitt Triggers": http://www.ti.com/lit/an/scea046/scea046.pdf

Vertical axis is current and horizontal access is voltage.
So, if that peak current drain is greater than the current generated by the solar cell at the 1 lux light level, it simply can't push past it to the other side.

Both chips seem rather pathetic if, as seems to be the case, a solar cell alone and without assistance can charge up a capacitor to its open circuit voltage of somewhere around 2.7v but they can't. To be fair, there could be other factors in play, though, like the PCB material type, the dialectric the manufacturer used to impregnate the FR4 to make the PCB, how much humidity had gotten into the FR4 (resulting in extra leakages), component choices as well as layout. That was my earlier hunch, but that hunch may get upended and replaced with the schmitt trigger theory if the BQ25504 continues its upward charge. We shall soon see.

Meanwhile, somewhere I have laying around a BQ25570 on a chinese breakout board, and it might (?) possibly avoid this problem that the other two seem to share....

Edit3: Nope. The BQ25504 simply got stuck again, this time at 0.851v. According to the datasheet, it's still in cold-start mode until the voltage on VSTOR reaches at least 1.6v (or possibly higher), and that matches what I recall about the BQ25504 from earlier experimentation with it: it performs pretty terribly while in cold-start mode.

Punt!

Unfortunately, BQ25570 also remains in cold start mode up to the same 1.6v+ as the BQ25504, so I'm losing optimism that it might be any better... And like the BQ25504, the BQ25570 also requires typically 15uw to get its mojo on, and at 88na of current that just isn't going to happen.
So, there's no rush to test the BQ25570. If the datasheet is right, it's almost certainly another FAIL. :( Judging from the datasheet, the BQ25570 is largely just the BQ25504 mashed together with a buck converter. And the BQ25505 looks about the same as the BQ25504, except with a little bit less quiescent current.

What a disappointment! I would have thought that TI had the in-house talent to do a lot better than this.

[NeverDie]

Well, doing a little back of the envelope calculations: if a silver zinc 8mah SR416 primary battery, which is just 4.8mm in diameter and 1.6mm thick, were used to continuously drive a 35na TLV5110 timer, then assuming all 8mah could be extracted and ignoring self discharge, it would last for 26 years. Then consider that a properly designed energy harvesting circuit could relieve the battery from needing to run whenever there is adequate harvested energy available, and the expected lifespan of the system would probably be even longer.

The only purpose of the timer would be to pulse accumulated energy into an off-the-shelf energy harvester, probably none of which can handle extreme low energy accumulation. One maybe can't know what the optimal duty cycle should be, but one could make educated guesses, and perhaps a more refined circuit could even self adapt to some degree.

Anyhow, I'd rather not go that route, but as an exploratory tool, it would be fun to make these harvesters work in "scotopic" darkness and yet still accomplish something useful with whatever energy they can somehow squeeze out of it, all while remaining tiny. :sunglasses:

[Mishka]

Hi @NeverDie, thanks a lot for doing the experiments!

Basically, the circuit needs to remain inert until enough charge builds up and a trigger gets tripped. And, it needs not to bootlooop even though it ramps up using just very little current. A tall order, I know. Not sure if the right kind of circuit exists, but that's what I'm in the hunt for.

Yeah, this is would be very interesting to achieve indeed. Looks like the water bucket from aquapark. Unfortunately, have no practical ideas at the moment. Maybe a FET + BJT combo where the FET generates spike of the current which activates the BJT which then drains the input capacitor? The idea here is to utilize the inrush current from the FET before it will be stabilized. A comparator may have higher quiescent current, or may not.

8mv was as low as I could take it, but I suspect even then there may have been some slight amount of light getting at it. The room was very dark...

8 mv is fair enough. So it seems all about the structure of the amorphous cell. Interesting!

Should I start a separate thread for this, or continue it here? It seems that your project is completed, and although this is all relevant, maybe it would be better to split it off? @Mishka Since you're the OP, what's your preference? Continue as is, or fork your thread and continue in a separate thread? I'm enjoying the collaboration, and hope you feel the same. I'm fine with either choice.

Although the discussion went beyond the original project, the topic is very interesting. While most of existing harvesters are aimed at low-voltage sources, it seems that we're trying to address the unique property of a-Si cells to have high-voltage bias in the extremely low light. This is not only enjoying, but might also have (and I hope will do) some practical extension. Of course, if there is a better place for the discussion - it's completely okay to move it, I'll be glad to follow-up there.

Regarding the project, it wasn't finished yet. I'm currently waiting for newest PCBs - they're still based on SPV1050, fully configurable, the components selection is for the boost. Appropriate solar panels are also on the way.

BTW, I had a chance to try the SPV1050 (buck) and nRF52833 with a single one SolarBit I have, no battery attached. In the direct sunlight it works without any issue, even with 1 mA red LED blinking 50% of time. This is definitely not the best setup, so the mentioned PCBs and panels should make it more useful and especially for a cloudy day. Also, for the version 2.0 I'm considering to replace the harvester IC with the AEM1094. I also have somewhat different idea about form-factor, but that's for another topic.

And here is Version 2, which uses an Arduino UNO

Perhaps the right thing would be to charge the capacitor first, and only after that connect it to the Arduino. The Arduino has to read the ADC often so it should be possible to determine highest voltage before it decays.

Unfortunately, the AEM10941 breakout board can't seem to rise above 0.352 volts when tested with the same solar cell and same dead-bug op amp assembly under the same 1 flux light source, so I'm afraid I have to label it a FAIL for use in boosting, just by itself, from that particular low light scenario.
...
Despite a promising start, the BQ25504 peaked at 0.812v and couldn't seem to pull itself above that.

From my (perhaps not too careful) review I did earlier in this thread the AEM10941 requires 3 µW input, and the BQ25504 requires 15 µW. Either of those are far beyond the 3V*80nA condition.

Unfortunately, by most of manufacturers a nanoamp source seem usually considered as zero current.

if a silver zinc 8mah SR416 primary battery, which is just 4.8mm in diameter and 1.6mm thick, were used to continuously drive a 35na TLV5110 timer, then assuming all 8mah could be extracted and ignoring self discharge, it would last for 26 years.

Hmm... taking in account those 80 nA collected in 10 seconds will be wasted in one millisecond, and then the next 9.999+10 seconds it will wait for another portion, it sounds like bargaining 35 nA for 40 nA. Well, fair enough! :face_with_cowboy_hat:

[NeverDie]

@Mishka said in 💬 The Harvester: ultimate power supply for the Raybeacon DK:

Hmm... taking in account those 80 nA collected in 10 seconds will be wasted in one millisecond, and then the next 9.999+10 seconds it will wait for another portion, it sounds like bargaining 35 nA for 40 nA. Well, fair enough!

TI makes a range of different TLP5xxx chips, and Adafruit makes convenient breakout boards for at least two of the different models. I even used one in an earlier leak detection project: https://www.openhardware.io/view/534/Extremely-Simple-Arduino-Pro-Mini-LoRa-Water-Leak-Detector

What I haven't yet tested (and haven't read nor heard) is whether ia TPL5xxx can self excite and start-up normally if powered from the very slowly rising voltage created by a tiny solar cell in weak lighting.

[NeverDie]

I stumbled across this: http://www.prc68.com/I/JouleThief.shtml
which is a fascinating goldmine of information about blocking oscillators and their use in just about every cheap solar circuit you've ever seen or heard of, including some that maybe you haven't. Be that as it may, for tiny panels in ultra low light (1 lux and below), I'm pretty sure they'll need to be spoon fed, just like these commercial chips we've been examining.

As for a proper DIY trigger circuit, about 5 years ago David Pilling made some very interesting posts regarding the use of PUTs (programmable unijunction transistors): https://www.davidpilling.com/wiki/index.php/PUT
and on his wiki he built some solar harvesters around that. What I really like and appreciate about his work is that he published ltspice models of his circuits, so it's very easy to download them and run the simulations. Earlier today I emailed David Pilling to see if he'd like to join the discussion here. A lot of technological progress in ultra low power has happened over the last 5 years, and so I think maybe he would be interested and perhaps he'd want to upgrade his circuitry to take advantage of the much lower-voltage/lower-energy components commonly available now that simply didn't exist back then.

@Mishka said in 💬 The Harvester: ultimate power supply for the Raybeacon DK:

Hmm... taking in account those 80 nA collected in 10 seconds will be wasted in one millisecond, and then the next 9.999+10 seconds it will wait for another portion, it sounds like bargaining 35 nA for 40 nA. Well, fair enough!

What I forgot to mention in the post directly above was that the tlp5xxx chips can be resistor programmed for much longer cycles than 10 seonds. e.g. the TLP5110 can be set anywhere from 100ms delay all the way up to a 2 hour delay. So, that's a very pliable range for collecting tiny amounts of solar on a cap, which can then be fed into a harvester as a unified kick. The 10 seconds you're referring to just an arbitrary number that I had picked and which just happened to work in the earlier circuit. The time delay could be set much less or much greater than 10 seconds. It's whatever you choose.

I think I'll try a tpl5xxxx timed collector and then pipe the accumulated current into the LTC3508 circuit through an ultra low leakage load switch. Since the LTC3801 needs only 20mv, it should be easy to collect at least that voltage level, even in very dark conditions, using the solar keychain solar cell (amorphous silicon): https://www.openhardware.io/view/732/Extreme-Energy-Harvester So, while the hunt is on for something better and more elegant as a trigger than the crudity of just how much time has passed, this is a brute force approach whose virtue is that it's pretty much guaranteed to work provided that leakage currents are tightly controlled to extremely low levels Fortunately, because of ohm's law, ultra low voltage is likely to make ultra low leakage easier to achieve during the accumulation phase. :grin: What will be interesting is: 1. how big a cap is needed and 2. how long the cycle time needs to be, because boosting extremely low voltages still needs to meet the minimal power requirements (i.e. a lot of current). Unfortunately, nowhere that I can find in the LTC3108 datasheet does it specify the minimum input power to operate. Just the 20mv minimum voltage. Therefore, I'm guessing the minimum power is probably rather high, since companies often hide their bad news by simply not reporting it in the datasheet. Anyhow, I'll just have to derive the minimum power as best I can through experimentation. :face_with_rolling_eyes:

The main downside to the TPL5xxx is that it reads the resistor values exactly once during the startup phase, and then never again. Although that has the benefit of limiting forever after the amount of current the TPL5xxx needs to operate, it also means that you can't easily change the periodicity anytime after the TPL5xxx starts up: even if you change the resistors after it gets going, it never reads them again. Thinking ahead, it might (?) be possible to hack around that limitation by changing the resistor values and then power cycling the TPL5xxx so that it reads the new values and incorporates them. The tradeoff for that result though is the extra circuitry needed to accomplish that. It would be much easier if (?) one of the TPL5xxx variants had a reset pin, so perhaps I'll look soon into whether or not any of them have that feature....

[NeverDie]

I put David Johnson's 3na oscillator circuit:
http://www.discovercircuits.com/DJ-Circuits/3na-osc.htm
into LTSpice and ran the simulation, and it looks promising:

It also runs just fine at 2v. Fairly easy to get a shorter or longer cycle by tweaking the resistor values and/or capacitor values.

The voltage swing is even better than I was expecting: it drops all the way down to around 30 or 40mv. :yum:

Of course, it would be nice if it could run at even lower voltages than 2v. Seems like that should be possible. Anyone have suggestions for which transistors to try for that?

The simulation shows that there's a very nice current pulse of about 4.2ma through Q2 during the very brief discharge phase, so I'm guessing that could drive a buffer transistor to turn on hard, which in turn could, in theory, drive a meaningful load without disturbing the underlying timer circuit. :sunglasses: If that's the architecture, though, there may need to be a separate, isolated capacitor to drive the load that charges up in parallel with the capacitors in this oscillator circuit--unless perhaps there's some way to recycle/reuse the current that gets dumped and otherwise wasted during each discharge.

Or, quite possibly, it could be used to drive a flyback type circuit, in which case I possibly wouldn't need a commercial boost chip at all and could instead do all the boosting with a homemade DIY circuit made out of discrete components. :heart_eyes: That's the promise of what this type of low-level control could grant.

Edit: I posted the LTSpice circuit simulation file for David Johnson's 3 nano-ampere circuit here:
https://github.com/rabbithat/3nanoAmpOscillator

Edit2: I anticipate a potential problem though: the 3na oscillator has very high input impedance. PV cells are modeled as having a shunt resistance, and unless that shunt resistance is exceptionally high, then most of the generated solar cell current won't be entering into the oscillator but will instead be lost as wasted current through the shunt resistor. I'm hoping that doesn't preclude the oscillator from working, but it might if that reduced current translates into reduced voltage at the inputs to the oscillator. The best case scenario would be that the oscillator simply has a much longer cycle time with the PV cell as compared to a battery. In any case, shunt resistance doesn't seem especially easy to measure, so one strategy would be to just build the circuit and see how it works with the target PV cell rather than fuss too much over constructing an accurate equivalent circuit to plug into the simulator.

Edit3: Good news. Using the method published in IEEE to calculate PV shunt resistance (https://ieeexplore.ieee.org/document/1483817), I calculate the shunt resistance on the keychain solar cell to be 30,681,818 ohms. So, more than likely the oscillator will work when hooked up to it. This also finally explains why these solar cells perform so well at even ultra low lighting conditions.

This thread seems to have petered out, so I guess that's the end of it. It was nice while it lasted. :-)

[Mishka]

Dear @NeverDie, you've done tremendous amount of work! The topic is extremely interesting, but I admit I can't keep up the pace, especially when discussion dived so deep and requires fair amount of research and simulation. Let's just keep it floating and open for everyone (I really hope David might kick it up). I personally try to follow up your recent posts a bit later, sorry :-(

P.S. Asked a colleague about it and he's like: "Nano... what?!" :)

[NeverDie]

@Mishka I recently had some convivial email exchanges with David Pilling after I reached out to him. He seemed interested in this thread, or maybe he was just being polite. Regarding his previous efforts, he mentioned that he was eventually able to run his PUT oscillator at 200 nanoamps.

[NeverDie]

@Mishka I've got good news, and I've got bad news. The bad news is that according to the LTSpice circuit simulator, the Dave Johnson circuit, as given, is nowhere near 3na of power consumption. It's much higher than that. Here's what it shows as the current passing through the R10 resistor in the figure below:

The good news is that by increasing the resistance and capacitance, I've confirmed it's possible to run the oscillator at 1 lux on the keychain solar cell:

If measured at the output pin of transistor Q2, it produces a 2 volt pulse every couple of seconds:

I'm pretty confident it will run at even lower lux, al beit producing a lower voltage, but I'm not yet setup to test at less than 1 lux yet.
Here is an approximation of the modified circuit and its current consumption:

As you can see, both the average and the instantaneous current consumption are less than for TI's TLV5110 chip.

And yes, I've confirmed through testing that it can self-start at 1 lux even if it had been pitch black prior! In that case it starts a pulse train at lower magnitude but higher frequency and gradually works it's way up to the 2 volt magnitude at the 0.5 Hz frequency, which at 1 lux is where it settles.

:smile: :smile: :smile: :smile: :smile:

[Mishka]

@NeverDie Oh, nice! You may eventually turn it out into a PWM/PFM charger.

[NeverDie]

@Mishka The circuit is more stable and consistent than the 3v simulation would suggest. I'm now totally sold on the value of simulation, but it's a bit problematic when a solar cell/panel is involved because for an accurate simulation you need to find an accurate "equivalent circuit" to use in place of the cell/panel, and for accuracy that means a 5 element circuit: two diode, shunt resistor, series resistor, and a current source. However, figuring out the correct values for those parts requires a lot of measurements to get the desired accuracy and is a project in itself.

That said, I'm optimistic that there are some less mainstream transistors that will allow the circuit to run at lower voltage.

[NeverDie]

Here's a courtesy heads-up.

I just now stumbled across a circuit:

published here:
https://www.edn.com/solar-powered-motor-runs-on-10-na/
that allegedly can operate on as little as 10na while collecting energy, which it then uses to power a small pager motor once a threshold voltage is reached.

It also has the virtue of utilizing inexpensive jelly bean parts and not relying on gigaohm resistors, which in the Dave Johnson circuit turned out to be so large that I lack the means to verify their specs through measurement after they are delivered.

This other guy instantiated the circuit as a PCB, and he made the gerber for it available as a free download: https://hackaday.io/project/159691-electron-bucket-extreme-power-management-module

If it turns out to be true that the circuit can both collect the current and trigger at a threshhold voltage all with just 10na of overhead, then on its face it sounds better than the David Johnson circuit turned out to be and possibly also better than many/most/(all?) of the commercial chips that we've reviewed on this thread if paired with an appropriate amorphous solar panel.

Edit:
But wait! There's more. There appears to exist an equivalent single chip voltage detector that also consumes a mere 10na of current: https://www.akm.com/content/dam/documents/products/power-management/power-ic-for-energy-harvesting/ap4405aen/ap4405aen-en-datasheet.pdf
It's itty bitty, so it's probably a great fit for your uber-compact design.

"But I want more!" I can hear you say. "I want a total step-up solution! And I want one that doesn't use a transformer!" Well, of course you do. Who wouldn't? Apparently, a 0.2v transformerless step-up solution does exist as well. I'm just not sure where. They developed it for a customer who wanted to harvest energy from... bacteria. Actually, the official term is "microbial fuel cell." The chip is the AP4470, and thankfully it can also be powered by solar, without bacteria.
https://solutions.akm.com/us/en/applications/energy-harvesting/
But can we buy it? Or is it just another inaccessible research project? I don't yet know. Can you read Japanese? The trail of bread crumbs written in English seems to run cold after the above link, but there's more about it that's written in Japanese. Argh.

[Mishka]

@NeverDie This. Is. Stunning!!!

I must admit that I were stuck with a CMOS driven circuit, but there are BJT circuits with amazing level of practicality. The decision to employ a LED is simply brilliant. I don't know shall we put it into a SPICE, perhaps to facilitate selection of real components, but taking in account the Hackaday project it should simply fall into place. Going to examine the project. It's definitely worth implementing it, thank you very much for finding the project!

The AP4470 looks very interesting too. With reported 7µA current consumption when boosting starting from 0.2V, and fixed high to low output voltage from 2.6V to 3.55V, it looks like a strong competitor to the AEM10941. I'd still stick to the latter though, not only because of availability (including documentation), but the e-peas product also has very appealing buck-boost configuration.

I'm also thinking about even more modular design of the boards (details will follow later), so having two harvesting circuits targeting different scenarios is the right way to go.

Thanks again for your interest!

[NeverDie]

Here's another one: https://patents.google.com/patent/US20170133938
He claims the startup power is just 100nW. For contrast, TI says their BQ255xx chip requires 15 uW. i.e. an entire order of magnitude more. Sounds too good to be true, doesn't it? Which leads me to wonder: just how well are patents vetted before they're granted? Might it still be granted even if the author never made a a circuit that performed anywhere near as well as the patent claims? Is anyone even checking?

By the way, on a different topic, this might interest you: https://www.mouser.com/ProductDetail/426-DFR0579 It's a $12.90, 30mmx30mm, fully assembled breakout for the SPV1050, configured as a boost converter.

[Mishka]

@NeverDie said in 💬 The Harvester: ultimate power supply for the Raybeacon DK:

Here's another one: https://patents.google.com/patent/US20170133938
He claims the startup power is just 100nW. For contrast, TI says their BQ255xx chip requires 15 uW. i.e. an entire order of magnitude more. Sounds too good to be true, doesn't it?

What's interesting about the circuit is that it uses the self-resonant converter together with a MOSFET (HEMT is recommended) which is closed at low voltage. There, the 1:1 transformer is used to bump the gate voltage and thus fully open the MOSFET when it reaches the threshold value Vth (the paper notices it at 120 mV, but for the a-Si cell it might be at 2.6V). The more it opened - the more voltage at the gate. This results in discharge of the input capacitor to the load until the gate capacitor voltage + the second inductor voltage won't drop below Vth. The input capacitor cut-off voltage could be configured to 1.8V so it will charge faster on the next cycle.

The patent mentions 0.1V x 1µA = 1nW startup power. Upon charge of the input capacitor, the leakage current will be at about tens on nanoamps. Perhaps rest of the harvester circuit consumes something too. Obviously, when it's going to discharge the inductors will cut some efficiency, but it's worth it anyway.

Looks interesting!

Which leads me to wonder: just how well are patents vetted before they're granted? Might it still be granted even if the author never made a a circuit that performed anywhere near as well as the patent claims? Is anyone even checking?

Well, a patent is just an exclusive right to the invention, and AFAIK there is no practical consideration neither verification of the patent subject. All that's checked is the invention wasn't patented before.

By the way, on a different topic, this might interest you: https://www.mouser.com/ProductDetail/426-DFR0579 It's a $12.90, 30mmx30mm, fully assembled breakout for the SPV1050, configured as a boost converter.

Yeah, it's nice! Thanks for the link! I think we here will be able to offer something interesting too: both boost & buck-boost combo board with USB and LDO, 25 mm diameter. Now in trendy corona-shaped profile from the OSHPark :-)

Unfortunately, can't assemble them due to the quarantine :-(

[NeverDie]

@Mishka said in 💬 The Harvester: ultimate power supply for the Raybeacon DK:

(HEMT is recommended

Wait. He reccommended a PHEMT for part 315 and an E-PHEMT for part 445:

The self-starting oscillator 445 utilizes a transistor. In one embodiment, the transistor is an E-PHEMT (Enhancement Mode Pseudomorphic High Electron Mobility Transistor) transistor, as the switching device to form a resonant step-up oscillator using a coupled inductor (the left and right inductors, ratio 1:1, 1 mH) and a resistor and capacitor in parallel at transistor's gate. The self-starting oscillator 445 is in series with the inductors. The transistor is normally off at zero gate voltage which would be the case with the two solar cells in complete darkness. The transistor's threshold voltage is very low and has a value greater than 110 millivolts.

[0065]

The E-PHEMT transistor 445 can be described as having the combined characteristics of a FET (Field Effect Transistor) and BJT (Bipolar Junction Transistor) and is used primarily for high-speed RF amplifiers in cell phones or other communication gear, but it is also an excellent candidate for low voltage self-starting oscillators like the oscillator 445.

I'm confused. Aren't 315 and 445 simply different aliases for the same physical component? 315 at a higher abstraction layer and 445 at the detailed layer? Except... isn't an E-PHEMT different from a PHEMT? So, they aren't aliases for the same part after all? Or, maybe they are the same, but 315 refers to a different potential embodiment than 445? Or... do HEMT, PHEMT, and E-PHEMT all mean the same thing?

By the way, I mispoke in my earlier post. 100nW is actually two orders of magnitude lower than TI's 15uW cold start minimum for TI's flagship energy harvester. If the patented circuit now under discussion here really does perform as well as it claims, then that makes it all the more impressive.

If it needs 100nw of continuous power, then it's of little use to me. If, instead, it can draw the needed power from harvested energy stored on a capacitor--and then collapse after the cap power runs out--then, cool! That I could use.

If only there were a proper LTSpice simulation of the circuit already available....

Unfortunately, can't assemble them due to the quarantine 😞

You mean their automated assembly is off-line, or that you can't source all the parts you need due to the quarantine, and so you can't DIY the soldering even if you wanted to?

BTW, I like your PCB homage to the caronavirus. Subtle, yet amusing!

[Mishka]

@NeverDie said in 💬 The Harvester: ultimate power supply for the Raybeacon DK:

I'm confused. Aren't 315 and 445 simply different aliases for the same physical component? 315 at a higher abstraction layer and 445 at the detailed layer? Except... isn't an E-PHEMT different from a PHEMT? So, they aren't aliases for the same part after all? Or, maybe they are the same, but 315 refers to a different potential embodiment than 445? Or... do HEMT, PHEMT, and E-PHEMT all mean the same thing?

I see the components are numbered through all the figures in the form XYY where X is the figure number, and YY is the component number. Such, 115, 315, and 415 are referring to the energy harvesting circuit. The circuit contains x20 resonant DC-DC converter, and x45 do reference the transistor or crystal oscillator.

An enhancement mode transistor (N-channel MOSFET or an E-HEMT) is required because it has to be closed at zero bias.

By the way, I mispoke in my earlier post. 100nW is actually two orders of magnitude lower than TI's 15uW cold start minimum for TI's flagship energy harvester. If the patented circuit now under discussion here really does perform as well as it claims, then that makes it all the more impressive.

Oh, my, it's 100 times different, rght. I'm still not used to the numbers and feel that if we take a couple more steps, we will go to the quantum level :laughing:
:hole: :walking:

Unfortunately, can't assemble them due to the quarantine 😞

You mean their automated assembly is off-line, or that you can't source all the parts you need due to the quarantine, and so you can't DIY the soldering even if you wanted to?

Just can't get to the soldering station, it's closed in the office with some other components until May.

BTW, I like your PCB homage to the caronavirus. Subtle, yet amusing!

All credits go to OSHPark which didn't bother to remove the panel tabs :-D

[NeverDie]

@Mishka said in 💬 The Harvester: ultimate power supply for the Raybeacon DK:

I'm still not used to the numbers and feel that if we take a couple more steps, we will go to the quantum level

LOL. In that case, strap yourself in Dorothy, because Kansas is about to go bye-bye: here's a voltage detector which claims to have a quiescent current of less than 6 pico-amps!
! https://www.bristol.ac.uk/media-library/sites/engineering/research/eem-group/zero-standby/UB20M_Datasheet_Rev.1.5.pdf
The only thing which appears to tarnish that claim is that it has a leakage current of 100 pico-amps. Even so, though, I'm not aware of anything else that even comes close to that. If it does what it claims to do, then I'm imagining we could harvest energy from even a very dark environment and yet still be net positive on harvested energy (without the control hardware consuming all of it and then some). :-)

Unfortunately, their UB20X chip doesn't seem to be stocked anywhere. I sent an email to the company yesterday to inquire about how to buy it, but so far I haven't heard anything back yet. I hope they're still in business.

[Mishka]

@NeverDie Well :-)

What can I say? Only that the PDF is here. They seem achieved this ridiculous leakage with careful transistor selection. Very nice!