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Miniature wireless power demonstrator

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deathell

Wed Jul 21 2010, 01:25PM

Registered Member #3020 Joined: Wed Jul 21 2010, 01:01PM
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Posts: 5

Greetings Mr. Marko!
I am very very impressed with the product. I am trying to build a wireless battery-charging system as well but I cannot find proper solutions to generate high-frequency alternating current. Here I have some questions:
Could you explain the principle of the design as detailed as possible?
Is the 12V voltage source a regular DC source?
I used Cadence Orcad Capture and PSpice 16.2 to do the simulation, but failed. I ensure that the connection and components are the same with yours. What's the problem?
How much power could the system transfer?
You say that the current in the copper loop is 20A, so how much voltage is between the two sides of the copper loop(I mean the amplitude)?
What is the type of the transmitting wave? Sine wave or something else?
How to adjust the current, voltage and frequency of the transmitting wave?
I am really crazy about your design, but I am still a fresh newbie of circuit design. I hope to hear your response.

Well, I built the circuit according to Marko's final design, but it could not work.
This is my PCB board . I add a switch and a DC jack to feed the circuit with regular 12V 500mAtransformer.

I used this WIMA KFP series 6.8n capacitor.

And I used this kind of 100uH ferrite core.

I also used the G6A-234P dc12V relay and one turn copper coil.
Saddly enough, when I plugged the transformer in to the DC jack and switch the circuit on, Only the LED lit and the MOSFETs became very hot.
I measured the Vin and Vout voltage, it's just around 3.4V. I alsoo measured the voltage between pin one of the loop and ground. it's 3.4V, too. The pin two is the same.
What is wrong?

srabon

Tue Jul 27 2010, 08:58PM

Registered Member #2896 Joined: Wed Jun 02 2010, 02:50PM
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Posts: 1

@deathell

This is what happened with me also...i am trying to find my mistake...or any dis-tune..if u find out the solution plz post it...

i think ur using a rectifier to get dc 4m transformer...this may causes the prblm..im going to try a dc pwr supply...

deathell

Wed Jul 28 2010, 07:27AM

Registered Member #3020 Joined: Wed Jul 21 2010, 01:01PM
Location:
Posts: 5

I solved the problem. I used the power adapter is 12V 500mA whose power is too small to drive the circuit. I changed it to a 9V 1A transformer, it worked perfectly. What we must care about the power supply is not only it's rated voltage but also its maximum current could be supplied

BTWï¼Œ I want to use the system for cell-phone battery charging. I found when the current was large enough( around 500mA), the voltage exceeded 20V. DC-DC conversation is needed. I consider about voltage regulator, but it just wastes the superfluous voltage and keep the current unchanged, which is quite low-efficient. Is there anything(such like DC-DC convertor chip, I don't want a large bulk) could convert sperfluous voltage to current?

Mike

Wed Jul 28 2010, 03:16PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

You could use a buck converter, they have IC's you can buy or you can make one. They're pretty simple things.

deathell

Wed Jul 28 2010, 11:34PM

Registered Member #3020 Joined: Wed Jul 21 2010, 01:01PM
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Posts: 5

Is Synchronous Rectified Step-Down Converter such as MP2307 available for my application?

Mike

Thu Jul 29 2010, 12:03AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Yeah that should work, it take 5-20v input and outs 1-20v, with up to 95% efficiency. keep in mind you'll need to supply the inductor still though.
datasheet:

deathell

Thu Jul 29 2010, 05:29PM

Registered Member #3020 Joined: Wed Jul 21 2010, 01:01PM
Location:
Posts: 5

Thanks. But MP2307 could output 3A, is it too large for cell phones?
I also heard that if the inductance of the coil is smaller, the efficiency of energy transfer is low. Should I coil more turns and use smaller capacitors to incease efficency, and keep the resonant frequency unchanged?

Mike

Thu Jul 29 2010, 05:47PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

For the first question, it doesn't really matter if it can output 3A. Current is not the same as voltage, you don't have to be worried about having extra available current, because devices should only draw as much current as they need.

2nd Q: I'm not that familiar with the specifics, you might want to start a thread about converters in General Sci and get some good info.

Mike

deathell

Thu Jul 29 2010, 09:00PM

Registered Member #3020 Joined: Wed Jul 21 2010, 01:01PM
Location:
Posts: 5

But...when I built the receiving circuit just with a resonant capacitor, a bridge rectifier and a filtering capacitor and then short the filtering capacitor with a ammeter, I measured the current was 500mA and the voltage on this capacitor was 15-18V. If I build a DC-DC conversion circuit after the filtering capacitor with MP2307 and restrict the output voltage to 5V, the output current is 18*0.5/5=1.8A, isn't it? Should I be worried about the large output current? If the battery onle drains 500mA, where will the extra current go to?
Please forgive my unwisdom.

HDR

Fri Jul 30 2010, 07:36PM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

Would this be compatible with devices designed for powermat or the palm pixi wireless charger? I purchased a palm pixi charging case to salvage the charging coil, but if the existing circuit would work, then I'd prefer to use it because they can make it much smaller than I can.

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