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Mosfet oscillating but not transistor

Hannes

Oct 11, 2015
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Oct 11, 2015
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Hi all

Im new to electronics and have 3 questions

1 mosfet n type transistors oscillate without any additional resistors caps or inductors if a centre tap coil is conneted to 5vdc + drain to one end and source to the other gate to negitive of power supply why?

2 this same circuit works perfecly om p9 battery and my home made pc power supply with vairable voltage controler from 1.5 to 11.5 volt (mosfer switches on after 2.7volts) but connect it to my pc (all in one Lenovo) makes the secondary coil's led flash a few times and then mosfet stops operating completely why?

3 what would be the best way of transfering power wirelessly from usb to phone Using a secondary coil that will fit between the battery and the cover even if i have to modify the cover to do so i also would like to turn off the circuit by lifting the phone ( possibly by means of a proximity sensor) and incorparate a charging system internaly for the circuit so that it acts as a wireless powerbank as well?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
25,510
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25,510
please show us a circuit diagram. It will help us understand what you're doing.
 

Hannes

Oct 11, 2015
9
Joined
Oct 11, 2015
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Thanx for the quick reply here it is just replace the pnp transistor with mosfet n type I used 50n06 got it from a old broken ups lying around after that used tip 35c ,tip41c, tip 36c and irfz244 only got the 2 mosfets working though

I also played around with resistors on the circuit from base to collector an collector and still did not get the tip transistors to work!
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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25,510
that circuit will not work with a bjt because in the initial state the collector is more negative than the base and emitter.
 

Hannes

Oct 11, 2015
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Oct 11, 2015
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Okay thats where I reconed a resistor will defnetly be of utmost importance is there a way of doing it with say tip41c transistor?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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no. The fact that the collector is connected to ground is the killer.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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try looking up a blocking oscillator for a similar circuit that will work with a bjt.
 

Hannes

Oct 11, 2015
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Oct 11, 2015
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This is what I tried as well but not working

I even tried using 2 tip41c connected tip41c (a) base to tip41c ( b) colletor through a 470ohm resistor and tip41c (b) base to tip 41c (a) collector through a 470ohm resistor negitive to both emitters positive to centre tap and each end of the coils to the 2 collectors

Still didnt work

But as you can see on the video with exactly the same components couldnt get it to work
 

Hannes

Oct 11, 2015
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Oct 11, 2015
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Could you please give me an example of how the circuit would look like?

It seems like there is no way the example will work on youtube

Will a diode perhaps between ground and collector be the answer?
 

Hannes

Oct 11, 2015
9
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Oct 11, 2015
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images (2).png

I removed the set and rest wires and r1 and r2 then connecte +v to centre tap of 2 coils one end to reset position and other to set position still no go with tip41c transistors
 

Hannes

Oct 11, 2015
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Oct 11, 2015
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Thank you now I know why my mosfet's die off and why switching from one power supply to anouther makes them die too!

Ill start working on the charging system while they are busy with that and finalizing the circuit!

Seems ill have to get a atmel programer and software afterall!

Is there no way to drive npn or pnp bjt's to do the same because i came across a circuit using 2n2222 transistor to power led wirelessly called the modified joule thief circuit and it seems by scaling up a larger bjt with more watage resistors should do the trick not only will it be less intensive to build but safer as it uses magnetism not induction like the project above
 
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