# wireless power transmission transistor problem

#### Jason27

Joined Nov 15, 2015
32
hi all new user, doing a project with wireless transmission with a circuit i fond on the net, problem is the transistors get VERY hot in a few minutes, the only difference is that in using 5w instead of 3w resistors. any help would be appreciated

#### Bordodynov

Joined May 20, 2015
2,906
Driving experiments very bad. Emitter junction are punched. There is a gradual degradation of the transistors. Necessary protective Schottky diodes.

#### Jason27

Joined Nov 15, 2015
32
thank you very much for your help and reply Bordodynov, ill try your circuit, what wattage resistors do you recommend?
do i need to change the pickup coil at all other than 60 winds? or anything you may think i need to know as I'm only learning here.

#### Bordodynov

Joined May 20, 2015
2,906
The calculation gave 1.33 watts. I recommend at least 2 watts.
The number of turns of the coil is determined by the geometric dimensions and the desired frequency of operation. In my model of the transformer inductance of the coil is determined by the number of turns and the inductance of one turn of "Al".
Say what you design (geometry) and on what frequency you want to work. Then I can make a more accurate calculation.
2.34 watts, which dissipates much transistor is heated. Perhaps the MOS transistors are more acceptable.

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#### DickCappels

Joined Aug 21, 2008
7,698
Hey wait...something doesn't look right. In most places these things operate between 13.56 and 13.57 MHz so as to not interfere with radio services. The 2N3055 is not fast enough. any kind of high speed use. It is quite likely that the 2N3055's don't ever fully turn off. Try faster transistors.

By the way, the wattage rating on resistors tells you how many watts you can put into them. For example, a 220 ohm 3 watt resistor will dissipate the same power as a 220 ohm 25 watt resistor in a given circuit.

#### Jason27

Joined Nov 15, 2015
32
What transistors would you recommend DickCappels?
Loving the learning.

#### DickCappels

Joined Aug 21, 2008
7,698
I cannot recommend a transistor for your application because there are too many unanswered questions about the application and circuit, and in particular the transformer, which is the (no pun) core of the circuit.

The circuit, while not incorporating best practices, is known to work, and was proven by @Bordodynov. Maybe if you can tell us something about the transformer somebody can make some suggestions., or maybe better, give some advice on the transformer you don't have any more information to share about it.

#### Jason27

Joined Nov 15, 2015
32
Yes, I understand your point, the information and help you guys have given me for this project is ample and appreciate the time given, thank you

#### AnalogKid

Joined Aug 1, 2013
9,351
The only thing limiting the current through the transistors is the transformer impedance. To know that we need the inductance and frequency.

ak

#### Jason27

Joined Nov 15, 2015
32
To tell you the truth @AnalogKid I'm not very educated in electronics yet(but I'm learning) so maybe you could suggest a method for me for the wireless transmission coils! I now have the above circuit working kindly given to me from @Bordodynov and have it working a 12V Duratech 80mm computer fan with a current draw of 0.02A.but the transistors are still getting very hot still. tnx.

#### Bordodynov

Joined May 20, 2015
2,906
I added to the electronic circuit two capacitors. Efficiency has increased dramatically. Also added a bridge rectifier. I'm also more accurately simulate the output winding connection to the input. In my opinion if you take faster transistors, it is possible to increase the frequency up to 455 kHz and use one coil turns.
See

#### Jason27

Joined Nov 15, 2015
32
fantastic, thanks @Bordodynov I've already added the the bridge rectifier. ill get the caps asap. it seems to work well now that i added the schottky diodes so i can't wait to see the new results.
do you know how to make a hall effect latch(i think thats what i need) for a 2 pole motor electromagnet (pic below) i have a AST117 hall ic from a computer fan and wish to power the electromagnet. for the same project? i can find circuits but i want 12v not 9v like i can find.

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