Obtaining a "good" square wave for high frequency

[ijuset]

Hi.
First of all I'm new to electro-tech online and glad to find such an active place for electronics. Thus let me introduce myself too, I'm a 3rd year university student in Ankara/Turkey and nowadays doing summer practice.
Moving on.
...


In my project i am building a system about wireless energy transfer through induction. The algorithm is

1)Obtain a square waveforum from DC source using Timer555. (0 / 5v, 400KHz)
2)Invert (using NOR gate or opamp) the square to have high ripple (-5v / 5v) Than using logic gates (1 Buffer and 1 NOT gate) seperate those.
3)Connect those two outputs to the inputs of an H-Bridge to obtain high currents.
4)Excite the coil using the output of the H-Bridge.

It is pretty straightforward but since the square wave is not perfect, the H - Bridge inputs are both "high" for a little interval but since the working frequncy is so high, the circuit endures 2-3 Amperes of current. (shortly the second part is the main problem)

I tried using a comparator which is built by 2 LM311 opamps for obtaining 2 distinct signals but i failed.
I thought of using a PIC but i am not so good at it and passed that option.

I dont have the photos right now but have some links similar to my design.

H-Bridge: http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/figure-1.htm

Voltage Comparator: **broken link removed**

Thank you.

 

[ijuset]

I decided to move on using comparators which are built-up with 2 LM311s.
As you said, I connected two small capacitors and re-arreanged the values of voltage division in the comparator. Now the waveforms are much prettier.

Here are some photos of the outputs.

**broken link removed**
**broken link removed**

**broken link removed**

Could be improved more.
Also i need to practice taking shots of cro screen

Thanks for your concern.

 

[hv addict]

It looks like you are getting some ringing. Are you powering the h bridge via a gate drive transformer? If so try a pair of ucc37322 ucc37321 fet drivers. for the input of the transformer.

 

[ijuset]

Wireless Energy Transfer

Are you powering the h bridge via a gate drive transformer? If so try a pair of ucc37322 ucc37321 fet drivers. for the input of the transformer.

I tried BJTs instead of mosfets and some protecting zener diodes but still pnp and npn s are short circuited (i.e, the H-Bridge works in Test mode, 1-1-1-1). I built up the circuit nearly 10 times but still does not work. I came to the conclusion that the bridge will slow me down. For now i passed the bridge option.

Before the final connection to output i connected a power mosfet with a heatsink. (Gate=Input, Drain=Vcc, Source=Coil)

In the other coil (which is induced through air) i observed a pretty good voltage (around 5v, when the input is 8v) ,but the output is sinosoidal although the input is as in the pictures in the above post.
I will try to upload some photos of waveforms and circuit if there is anyone interested.

Finally
I will try to improve the power transfer by,
-Increasing the frequency
-Connecting serial capacitors to have pure resistive loads.
-Puttting some ferromagnetic in the center of each coil to decrease leakage(just thought today not really sure if it will decrease)

That is it for now, if you have other innovative ideas i would love to hear them.

Ijuset

 

[ijuset]

Wireless power transfer

Sorry, topic has little changed but i didnt want to create a new thread. Now i get a different problem.

I obtained a high current, high frequency square wave, as in the figure:
**broken link removed**

After using the coils in the picture below, the signal is wirelessly transferred from the below coil, to the upper side coil. (Through method of induction)
**broken link removed**

The scope output is as in the figure. (Yes it is a signal not noise, it is around 6V for 10V input and succesfully lights a LED). After connecting a capacitor to smooth the waveform, output is even more surprising. It is nearly pure sine wave. (I checked the ground, it has no DC offset at all, but i had given a 0v-10v square wave.)

Initial output:
**broken link removed**

After connecting parallel capacitor:
**broken link removed**


I wish i could tell my problem. I am not really sure how did that sine wave occur in the output. It has something to the harmonics but i dont realy fully understand Fourier, if it is about it or not, can smn briefly explain ?

Thanks,

Ijuset

 

[Hero999]

Connecting a capacitor in parallel has turned the secondary of the transformer into a tuned circuit that will be resonate at a frequency determined by the inductance or capacitance or a harmonic.

[latex]F_0 = \frac{1}{2\pi\sqrt{LC}[/latex]

 

[ijuset]

Connecting a capacitor in parallel has turned the secondary of the transformer into a tuned circuit that will be resonate at a frequency determined by the inductance or capacitance or a harmonic.

[latex]F_0 = \frac{1}{2\pi\sqrt{LC}[/latex]

Yes, i thought so (It was tuned, so it was purely resistive)

But why the initial output is sinosoidal-like altough the input in the primary is square?

 

[Hero999]

Because it's resonating - that's what tuned circuits do.

The square wave is exciting it - just like hitting a bell with a hammer.