# Inductive coupling - wireless charging

#### rui_alm

Joined Dec 8, 2017
2
Hi, im doing this Wireless Power transfer project and I need some help. Im trying to charge a phone using inductive coupling. The problem im facing is generating the AC square wave with enough power to acutally induce something. I've come up with a MOSFET that makes a square wave with 19V peak (0V-19V) and a push pull to sink and source current. On the simulation it works fine, as the square wave actually loses it's DC component when it's induced on the second coil. Both coils are 30uH.
I tried this circuit but the push pull output on open-circuit, was really low (around 1V peak) with distortion.
My question is: can you actually use a square wave with DC component to induce voltage on another coil? Because I'm trying to avoid generating a real AC wave since I've tried that without sucess

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#### Janis59

Joined Aug 21, 2017
1,482
Meander form means ONLY that actually You have deal with 1/7 of 7th harmonic + 1/5 of 5th harmonic + 1/3 of third harmonic. Nothing else more sophisticated. And knowing that any decent construction use a resonance in receiving coil, then You simply shall loss the harmonics but still have a basic 1 "harmonic" if I may so call the basic signal. As the form factor of meander in the terms of sinusoide is 1,11, it means You shall loss (more exact will not harvest) the 11% of radiated power. I think it is good contract between clearly simpler schematics and rather small surplus losses.

#### AlbertHall

Joined Jun 4, 2014
12,157
When you are doing this with real coils, note that they need to be very close to each other, at most a few millimetres.

#### Danko

Joined Nov 22, 2017
1,444
My question is: can you actually use a square wave with DC component to induce voltage on another coil? Because I'm trying to avoid generating a real AC wave since I've tried that without sucess
Try this circuit. Here is square collector current in transistors.
Select value of capacitor C4 for maximal efficiency.

EDIT:
Janis in post #2 calculated: "You shall loss (more exact will not harvest) the 11% of radiated power." It means that 11% of radiated energy creates wide spectrum of EMI, which affects on various electronic devices. This is very bad.
In circuit above in resonant tank L2,C1 we have 300kHz sine with amplitude 31V (peak-peak) at power supply voltage 5V. Transistors operate in ON/OFF mode with minimal losses.

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