# power wireless charger from mains

I want to run a large inductor coil for wireless charging with a 12V peak, 300kHz AC signal, starting with UK Mains voltage (230Vrms 50Hz). Should I use a step-down transformer and then a frequency changer? What should I use for my frequency changer?

Eric

Produce a low voltage DC (i.e. one that is isolated from the mains AC side) and then design an oscillator that produces 300kHz and runs from the DC supply created.

If you produce a 15V DC supply and you make an oscillator with the induction coil in the collector of the power transistor you'll be able to get 24V pk-pk no problem. Life is made easier if you resonate the coil with a capacitor. You'll probably only need a few volts pk-pk if you resonate this way.

So, basically the "frequency changer" is conversion to DC then create 300kHz from scratch using an oscillator.

• SO if I got something like this: cpc.farnell.com/vigortronix/vtx-120-3803-212/… and then used a full wave regulator, I could get out 12vDC, and then I could make an oscillator circuit after that? – ERIC May 19 '15 at 19:13
• @ERIC You can use that with a bridge rectifier and smoothing capacitor for sure but if you plan on using op-amps check they are OK for greater than +/- 16V dc on the supplies. – Andy aka May 19 '15 at 19:19
• Thanks. But if I only want a 12v peak out, why do I need an op amp that goes up to 16v? – ERIC May 26 '15 at 9:36
• That transformer has two secondary windings of 12VAC each. After rectification you can get +16V and -16V so the op-amps need to be rated accordingly. Getting a peak of 12V out has nothing to do with choosing an op-amp suitable for certain power rails. – Andy aka May 26 '15 at 10:55
1. Theoritically one does not need to step down the oscillator voltage. The tansformer voltage relation is given by Vprimary/Vsecondary=Np/Ns.
2. one can design a HF aircored transformer having Nturns. select secondary turns to suit the desired voltage.
3. I had designed a 230 volts HF oscillator with series resonance circuit using IGBT.
4. circuit design may be available on NET. VTIngole
• Are you talking about NOT stepping down the 50Hz power source mentioned in the question? What is the relevance of a 230V HF oscillator to the question? – Andy aka May 19 '15 at 19:17
• 1. I meant not to step down 230 volt AC voltage..instead rectify the voltage and use HF oscillator, may be at 300 volt DC(peak voltage of 230 volt with Cap. filter).the relation given in (1) stands for the oscillator coil voltage. vtingole – vijay ingole May 21 '15 at 2:27