# Inductive Charger I am playing with

#### AbdulFayed

Joined Aug 7, 2019
2
Hi. I have a circuit that I found online for using inductance to light an LED. I want to try it with a stronger LED though and I want to see what needs to be modified. It has been quite a few years since I worked on circuits and circuit design so I am pretty lost.

The power output that I want is 35W. 35W = I*12V would give me a current output of ~3Amps. What changes would I need in order to achieve this? If you have any pointers at all I would appreciate them to get me in the right direction . Thank you!

#### Alec_t

Joined Sep 17, 2013
12,150
Welcome to AAC!
You would probably need to swap the 2N5551 for a N-MOSFET and seriously upgrade the two coils. Even then, I think getting 35W transferred would prove difficult.

#### AbdulFayed

Joined Aug 7, 2019
2
Thank you Alec! Why the N-MOSFET? Would the transistor not be sufficient? As for the coils, yeah they for sure need to become stronger. I have been doing research on how to do that, is there specific things you think I should know? What do you think about the 555 ic? Since I am asking for a final output of 3A, wouldnt the ic not be able to survive since it has a maximum input of 10mA and output of 225mA? Every time I peel back a layer I find 10 more haha.

I am not sure this is the right circuit for what I want to do even. My end goal is to power a 35-40W LED using induction. Here is the video I got the schematic from:

#### Alec_t

Joined Sep 17, 2013
12,150
Why the N-MOSFET? Would the transistor not be sufficient?
Check the datasheet for the 2N5551! The Absolute Maximum collector current is only 600mA continuous DC. The gain of the transistor drops dramatically as current rises and is down to about 30 at a collector current of just 50mA. With your 2.7k base resistor the base current is about 4.4mA and with the transistor switched on fully the collector current wouldn't be more than ~120mA, even assuming a gain of 30. Where did you get the 10mA and 225mA figures?
A properly chosen N-MOSFET could easily provide 10A or more coil current without overloading the 555 output.
Allowing for coil coupling inefficiency I suspect you'd need a good bit more than 3A to transfer 35-40W.

#### Lo_volt

Joined Apr 3, 2014
197
Do you mean 35 mW (milli-watts)?

#### ci139

Joined Jul 11, 2016
1,696
? i likely have not tried any SEPIC converters but this one likely meets your requirements LTC3862
35W can destroy your circuit in a flash (i'm not even considering such sophisticated converter - because i simply don't have enough lab equipment to set it up correct)

#### MrAl

Joined Jun 17, 2014
8,365
There is a certain coil shape that is considered best but you'd have to look that up i dont remember the name of it offhand.
But you use two of those coils, one to transmit, one to receive.

Even better though is if you can get a "C" core transformer/inductor core. This kind of core looks like two "C" shapes which in a normal application get pressed together tightly or with a small air gap. But once pressed together, the efficiency is high, and not bad with a small air gap either which is what you would have. So you wind a coil on each half, then use one half to transmit and the other half to receive.
You could probably transfer 100 watts or even more using this technique, depending on the overall size of the C core you choose.
The reason it works so well is these cores will easily do an 100 watt converter.
The catch is they have to be matched close to each other when you are ready to charge. You can create a rectangular slot that the second half fits into so that at charge time it matches up perfectly. Possibly add a clamp or use maybe gravity and a weight to keep the two halves together.