I am confused on using MOSFETS in a voltage doubler circuit

Thread Starter

Wasswa

Joined Feb 23, 2021
9
I am using MOSFETs and comparators to lower the forward bias voltage drop of standard diodes to less than 0.7v in a voltage doubler circuit to increase its efficiency in low powered electronics.
I understand the N and P enhancement MOSFETs i am using to TURN ON gate voltage has to be greater Than or equal to the threshold voltage. NMOSFET gate voltage has to be more positive. For P MOSFET gate voltage has to more gate. My Camaparators each have +_12 v swing voltage.

In reference to the circuit below in multisim. The voltage doubler circuit simulated work for only one cycle with the PMOSFET when I run it.

The NMOSFET cycle operating in the positive flow of AC voltage is producing millivolts output reading which is wrong. I understand it about 6.7v which should be close to my RMS input voltage. Both combined circuits in positive and negative AC rail should produce almost doubled output on Capacitor C3.

What I'm I not understanding. I'm using the MOSFETs or connecting the MOSFETs the right way in the first place? I understand the source is the same as the Anode of a standard diode. Similarly, The drain operates as the Cathode.
1614546065655.png1614544357705.png1614546065655.png
 

michael8

Joined Jan 11, 2015
176
looking at Q3 N-mosfet I see that the opamp drives the gate positive to turn it on when the source side is higher than the output side (right side). In the other case current will flow back via the internal mosfet diode so there's no total diode effect.

q3.png

Try swapping the source/drain of the mosfet so that the diode doesn't allow reverse current to flow. When on the mosfet will allow current in either direction so you can use it "backwards". When off the internal diode will still allow current to flow forward but with a diode drop.
 
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LowQCab

Joined Nov 6, 2012
1,082
What problem are you trying to solve ????

Is this a Signal-Level problem?,
or are you trying to make a low-loss/low-heat Power-Supply Rectifier-Bridge?,
or are you trying to boost a too-low Power-Supply-Output up to a more desirable Voltage ?????

All the Details matter.
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Thread Starter

Wasswa

Joined Feb 23, 2021
9
I am trying to make active voltage doubler that produces a desirable voltage output from a too low power-supply-Output roughly AC in millivolts.

The active voltage doubler is working as a low power AC/DC converter that converts AC millivolts of a low-power-supply Output to a desired DC Output for use.
 

Thread Starter

Wasswa

Joined Feb 23, 2021
9
looking at Q3 N-mosfet I see that the opamp drives the gate positive to turn it on when the source side is higher than the output side (right side). In the other case current will flow back via the internal mosfet diode so there's no total diode effect.

View attachment 231692

Try swapping the source/drain of the mosfet so that the diode doesn't allow reverse current to flow. When on the mosfet will allow current in either direction so you can use it "backwards". When off the internal diode will still allow current to flow forward but with a diode drop.
Have tried swamping the source/drain of the mosfet but the voltage is still nowhere close to my initial 7.07v input RMS voltage. Its in millivolts. Can you please share a schematic if that's okay
1614596995517.png
 

michael8

Joined Jan 11, 2015
176
Swapping the mosfet direction is correct. It might help to get a simple case working first. Try a half wave rectifier rather than a voltage doubler -- half the parts and you can ground one side of the power input.

Then try the mosfet with the gate connected to it's source. This turns it into an expensive diode. This should work.

Now work on getting/generating the correct gate signal. Anytime you turn on the mosfet it will conduct in both directions so it's
important that it only be turned on at the right time.

Then you can work on the third problem -- powering your gate driving circuit...
 

LowQCab

Joined Nov 6, 2012
1,082
Wasswa

You need to fill in the Blanks on this whole arrangement.

First you state that you are working with "low-power" Electronics ........
What is "low-power" ???
Your Schematic shows 10V p-p AC power @ 50-hz,
OK, Fine, HOW MUCH CURRENT do you have available,
AND, how much Current -X- Voltage, DC-Power do you need ?????

Where did you get the -"12-Volts of Output-Swing"- for your Comparitors ????
How much Current-Capacity does that ~12-V-plus Power-Supply have ??

The specifications for the Pumping-Capacitors is critical to the operation of
a Voltage-Doubler-Circuit, especially if it must supply substantial Current.
Also, the AC-Input Voltage must be Rectified to DC, and stored in Bulk-Capacitors
before being switched, at very high Frequency,
and then Rectified, and Filtered again,
to create a reasonably efficient Voltage-Doubler.

"""I am trying to make active voltage doubler that produces a desirable voltage output from a too low power-supply-Output roughly AC in millivolts.

The active voltage doubler is working as a low power AC/DC converter that converts AC millivolts of a low-power-supply Output to a desired DC Output for use. """


These two sentences make no sense, and do not provide any useful information ........
How much is "desirable Voltage", and at how much Current ???

From a too low Power-Supply-Output, roughly AC in MILLIVOLTS ?????
I only see ~7-Volts-AC being supplied, at an un-known Current-Capacity,
and there "might be" ~12-Volts-DC powering the Comparitors ????
I have no idea where that might have come from.

A simple Switched-Capacitor Voltage-Doubler will give you almost ~20-Volts, un-regulated,
which may sag down to ~14-Volts, or less, with a Heavy Current Load,
and that Power is provided only as long as the Input Current can keep-up with the demands.

Stop talking in terms of -"Voltage"- for a minute .......
You can't get more Watts-Out, than the amount of Watts you have available at the Input.
So, how many Watts are available at the Input ?,
and, how many Watts do you need at a higher Voltage ?

Does that Higher-Voltage need to be in the form of a "Split-Supply",
such as, Plus & Minus 10-Volts ?, and if so, at how much Current ?

An EXACT description of the Supply-Capacity, and, your needed Output-Capacity,
measured in Volts-X-Amps,
is needed before any discussion on how to accomplish this goal can even be contemplated.
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MisterBill2

Joined Jan 23, 2018
9,235
If the input is in millivolts then how will you power all of those comparators? Active devices need power to function and that will not be coming from the millivolts from the source. The only way this concept can work is if it is a measurement system not intended to deliver any power. If the signal is an alternating voltage then a good choice to increase the voltage is a transformer. But even a transformer will not increase the POWER, but only the voltage.

So the impression that I get is that the TS wants one of those circuits that only function as desired in that kingdom of Utopia. (For those not familiar with that place, there are a lot of writings on the topic available.)
 

michael8

Joined Jan 11, 2015
176
You could start with something like this:

hw1.png

There is a diode drop across the n-mosfet. The correct gate signal can remove the diode drop...
 

SvanS

Joined May 1, 2020
1
What is the output impedance of your source?
If I were you, I'd stick in an audio/mains transformer and get a meaningful signal first.
 

MisterBill2

Joined Jan 23, 2018
9,235
I have seen articles about small systems that operate on very small amounts of power and actually do something useful. But in every case the task done is very specific and the description of the source of power obtained is quitespecific as well. And every one of those articles give a whole lot more description than what is given in this thread.
Using any sort of active device will add a power requirement for voltages exceeding millivolts, and that includes the the capacitor switching system. And further, all of post #7 is correct, and summarized says that you can never get out more than you start with.
 
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Thread Starter

Wasswa

Joined Feb 23, 2021
9
If the input is in millivolts then how will you power all of those comparators? Active devices need power to function and that will not be coming from the millivolts from the source. The only way this concept can work is if it is a measurement system not intended to deliver any power. If the signal is an alternating voltage then a good choice to increase the voltage is a transformer. But even a transformer will not increase the POWER, but only the voltage.

The goal is to build an AC-DC converter for Microscale energy harvesters that could typically generate low voltage (130 mV – 500 mV) and low power (30 mW-100 mW) as my homework.

From reading papers below
https://ieeexplore.ieee.org/document/5654594
https://ieeexplore.ieee.org/document/7438036
Designing an "active voltage doubler", Negative Voltage Converter(NVC) with active diode or voltage multiplier to rectify the alternating AC from the micro-scale energy harvester are one approach I could use to solve the problem.

"If the signal is an alternating voltage then a good choice to increase the voltage is a transformer. But even a transformer will not increase the POWER, but only the voltage."

Sticking in a transfer makes my circuit big there size is key in my case.
Assuming Alternating input is 130mV. If I can rectify or turn this input in millivolts to DC at the moment i am clearly struggling with I can easily add on the DC-DC boost convert and voltage regulator to fully Design the complete AC DC converter schematic for the micro-scale energy harvester.

This why I am here because my active voltage schematic isn't working and isn't going to work has clearly pointed out by many experts on the platform. It's been 3 weeks. I still can seem to get this part of my micro-scale energy AC-DC converter work.
# anniel747 and LowQCab
#michael8
#MisterBill2
 

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Thread Starter

Wasswa

Joined Feb 23, 2021
9
I have seen articles about small systems that operate on very small amounts of power and actually do something useful. But in every case the task done is very specific and the description of the source of power obtained is quitespecific as well. And every one of tose articles give a whole lot more description than what is given in this thread.
Using any sort of active device will add a power requirement for voltages exceeding millivolts, and tghat includes the the capacitor switching system. And further, all of post #7 is correct, and summarized says that you can never get out more than you start with.
Designing an "active voltage doubler", Negative Voltage Converter(NVC) with active diode or voltage multiplier to rectify the alternating AC from the micro-scale energy harvester are one approach I could use to solve the problem.

"If the signal is an alternating voltage then a good choice to increase the voltage is a transformer as A. But even a transformer will not increase the POWER, but only the voltage."

Sticking in a transformer as SvanS mentioned makes my circuit big. Size of the entire circuit is key in my case. This either "active voltage doubler", Negative Voltage Converter(NVC) with active diode or voltage multiplier approaches are considered to rectify the alternating AC from the micro-scale energy harvester
Assuming Alternating input is 130mV. If I can rectify or turn this input in millivolts to DC at the moment i am clearly struggling with I can easily add on the DC-DC boost convert and voltage regulator to fully Design the complete AC DC converter schematic for the micro-scale energy harvester.

This why I am here because my active voltage schematic isn't working and isn't going to work has clearly pointed out by many experts on the platform. It's been 3 weeks. I still cannot seem to get this part of my micro-scale energy AC-DC converter work with resources and papers i have looked. A working schematic or approach for just this section would come in handy now.
 

Papabravo

Joined Feb 24, 2006
16,773
Designing an "active voltage doubler", Negative Voltage Converter(NVC) with active diode or voltage multiplier to rectify the alternating AC from the micro-scale energy harvester are one approach I could use to solve the problem.

"If the signal is an alternating voltage then a good choice to increase the voltage is a transformer as A. But even a transformer will not increase the POWER, but only the voltage."

Sticking in a transformer as SvanS mentioned makes my circuit big. Size of the entire circuit is key in my case. This either "active voltage doubler", Negative Voltage Converter(NVC) with active diode or voltage multiplier approaches are considered to rectify the alternating AC from the micro-scale energy harvester
Assuming Alternating input is 130mV. If I can rectify or turn this input in millivolts to DC at the moment i am clearly struggling with I can easily add on the DC-DC boost convert and voltage regulator to fully Design the complete AC DC converter schematic for the micro-scale energy harvester.

This why I am here because my active voltage schematic isn't working and isn't going to work has clearly pointed out by many experts on the platform. It's been 3 weeks. I still cannot seem to get this part of my micro-scale energy AC-DC converter work with resources and papers i have looked. A working schematic or approach for just this section would come in handy now.
You might just have to accept the reality that your wishes may not come to fruition. Maybe we're all just not smart enough to figure out how to help you, or maybe there is no help for you. The reason for this just might be the lack of useful purpose.

EDIT: The guys that write the papers are smart enough to get their PhD's and tenured professorships, but they don't actually need to write about things that actually work. Come to think of it, I don't think I have ever seen a "real" part number on any schematic in any technical journal.

Maybe one of the authors will help you, but I wouldn't hold out great hopes.
 
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MisterBill2

Joined Jan 23, 2018
9,235
Passively stacking half wave diodes, like some of those high voltage stack multipliers may work. It would be worth thinking about and possibly simulating to see if the numbers allow it to be useful.
The size constraint and the actual voltage information are new requirements that we did not have any clue about previously. We still have no hint as to the impedance of the voltage source, nor of the frequency of the voltage.
And since we know nothing at all about the use of whatever higher voltage would be produced it is not possible to know what sort of energy content is actually needed.
AND the fact that you are not aware of how small transformers can be does not mean that they are not available, only that they are not used very often because they are not as cheap as other components.
 

MisterBill2

Joined Jan 23, 2018
9,235
There is a lot of amazing technology found in the kingdom of Utopia, and we do see these discoveries periodically. The downside is that many of them use that mineral, unobtainium, which is quite hard to procure in useful quantities and purity levels.
Even worse, the folks keeping this website in line seem to have a definite prejudice against many of the over-unity power generation schemes originating there.
Now as for the TS project using an unknown voltage generation method, and housed in a key-fob package, there are some piezo-electric generators already used in products. So it may be that the challenge is mostly finding a distributor of those products who would sell development quantities of the product.
 

Danko

Joined Nov 22, 2017
1,133
I am trying to make active voltage doubler that produces a desirable voltage output from a too low power-supply-Output roughly AC in millivolts.
The active voltage doubler is working as a low power AC/DC converter that converts AC millivolts of a low-power-supply Output to a desired DC Output for use.
Simple AC current chopper and voltage doubler converts 40 mV AC to 20000 mV DC:
1615174169173.png
 

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MisterBill2

Joined Jan 23, 2018
9,235
The problem with using active devices is that almost all of the active device circuits require a power source. And the challenge in working with diodes is that they almost allhave a forward voltage drop while conducting. And to get up from that 100 millivolts that I think I saw mentioned once, it will take more than a voltage doubler. and almost without exception, switching mode supplies require a fairly low supply impedance.
And so far we have NO information as to anything about the voltage source.
Without more information the best you can hope for is a lucky guess at a possible solution. And a lot of unrelated guesses as well.
 
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