4 Full wave rectifier output DC voltage combination

[sizo0708]

Hello everyone,
I simulated a matched full wave rectifier and measured the DC output voltage on the load with an input of -20dBm.
Results below:

After that, I tried to simulate 4 voltage multipliers and combine all the output DC voltages to a common load to achieve something resembeling this block diagram:

I expected to receive an output voltage of at least 500mV because this is the sum of the combination of all the output DC voltages, but unfortunately these are the results:

I think this is because the connections of each full wave rectifier to the load and the connections of the rectifiers to each other are wrong, because the output caps are connected in parralel instead of in series to the load ressistor but im not sure how to properly connect it.
Guidance will be much appriciated!

 

[D.A.(Tony)Stewart]

There is no correct way to combine OR diodes unless you use an AC "voltage multiple".

The diodes being nonlinear impedance rectifiers store a ratio of the peak voltage due to the load ratio. The parallel operation of wired-OR diodes has no cumulative effect and acts as an open circuit with a variable small current charge (Varicap) when the decay time is many cycles.

In the time domain, the 10x RC time constant lets you estimate the final R-value vs the initial condition R-value.

 

[BradtheRad]

Your theory of construction is interesting because you really would achieve the sum of output voltages if only you could stack all the output capacitors in series (while keeping all four circuits separated from each other in other ways).

However to build a single circuit you can cascade several Villard stages very much like your previous thread. Of course each stage subtracts one or two diode drops.

 

[BigBoss]

The problem is coming from Combining of DC Voltages.
While a branch is creating a DC Voltage, the other bransches' Diodes are lower biased. I mean a DC Voltage bring a need to drive at higher power levels to overcome this excess voltage. So, each branch effect the others. You have to find an more appropriate solution like combining DC voltages OR you should drive the circuits with higher power levels.

 

[sizo0708]

I tried to simplify the model first and combine the DC output of 2 rectifiers with the same input frequency using a method as shown in an image below which is taken from an academic paper:

At first, I jusr wanted to unsure that this type of connection of capacitors in series really builds up the DC voltage.
So here are simulation results of a single rectifier with no load, and 2 rectifiers with a common energy storage capacitor in the output:

It seems that the output voltages were almost perfectly doubled with a slight loss of about 40mV (if you can explain what causes it I will be delighted).

After that, I hooked up a load ressistor of 10Kohm and these are the results:

I will remind that the output voltage of a single rectifier with a load was 137mv.
I dont fully understand the effect of the load ressistor on the drastic change of the voltages, if someone can expain it this will help me a lot!

 

[BradtheRad]

You're exploring operation of voltage multipliers. The basic Villard multiplier consists of 2 diodes and 2 capacitors. You can add stages yet you can also arrange the diodes to yield negative output.

Therefore you can have a positive output from one Villard doubler and negative from the other Villard doubler. Together they create a bridged voltage quadrupler. It's a terrain of numerous possibilities and numerous configurations.

It just happens your supply voltage is so low it's at the threshold of operation for diode-and-capacitor pairs. It permits very low Ampere throughput. The slightest load drags down output voltage.

 

[FvM]

Any real voltage source has a nonzero output resistance respectively V/I characteristic, output voltage versus load current, drawing load current reduces output voltage. Stacking voltage sources doubles unloaded output voltage, but not necessarily loaded voltage if load current is increasing with voltage, e.g. with a load resistor.

 

[volker@muehlhaus]

It seems that the output voltages were almost perfectly doubled

I don't understand what you are trying to do.

In your testbench, you have also doubled input power by using two sources. But in real life, the available power from the antenna does not double when you use two rectifiers. What is the reason for using more than one rectifier?