[Moved] Wireless phone charger

[martisxxl]

Hello everyone, i am making a wireless phone charger for my project, and i need a little bit of help.
I made a little circuit, which works, but there are some problems: the transistor gets really hot, like a stove. Also, i would need to make that the wireless charger would know, that phone is placed, and turn itself on (optional).
There is the schematic:

Signalas means 150khz signal got from an arduino or some kind of microcontroller.
Could you help me improve the circuit, i have already added a diode near the transistor.
Also, i would be very pleased, if you could explain how everything really works ( with a lot of detail), because as i said, i am making this for a project, and they will ask me these kind of questions. Thank you

 

[BradtheRad]

The concept of operation is a loosely coupled transformer.

You want to optimize the transfer of energy, by a combination of:

(a) changing the operating frequency, and
(b) adjusting the secondary C value so that you tune the resonant frequency to match the operating frequency.

The capacitor at the primary winding creates LC resonance. This prevents you from adjusting the frequency as desired. I believe you can omit the capacitor. This will leave only the inductive action of the coil.

 

[martisxxl]

So you say, that i should remove the capacitor from the transmitter?

 

[BradtheRad]

So you say, that i should remove the capacitor from the transmitter?

I believe you can do this, while you are experimenting at this stage.

Another thing you should probably do, is to add a diode across the primary, pointing toward the more positive end. (This prevents high V spikes and is common practice when switching a coil on and off.)

There is an optimum frequency range, which causes the flux field to build during the entire time you turn on the transistor, then collapse when you shut it off.

That is the way to induce maximum current in the secondary.

You lose efficiency if the frequency is too slow or too fast.

Operation ends up being similar to a flyback converter. I must point out, however, I have not constructed a wireless charger myself.

 

[Audioguru]

What is the size and number of turns of the primary coil? Maybe it is too small or does not have enough turns to make enough inductance.
An inductance is a high impedance at a frequency then the transistor will be cold.