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InvisibletrendalM
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I must be bored...
    #5210209 - 01/22/06 12:51 PM (18 years, 3 months ago)

I built this little device:



It takes 5v DC current from a power supply and converts it to about 70v AC. It's self-oscillating and unfortunately does so at around 550kHz which is just way too high to use in any AC applications I can think of.



The transistors also get pretty damn hot within a few seconds of turning it on. It actually produces around 85 volts at first but this quickly falls to the 65-70v range as the transistors heat up. I tried changing the supply voltage to 12v and it will put out over 120v for a brief second before the transistors REALLY start to overheat and the voltage drops to 60v.

Completely useless, but I was bored and at least now I know how :smirk:


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Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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InvisibletrendalM
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Re: I must be bored... [Re: trendal]
    #5210252 - 01/22/06 12:59 PM (18 years, 3 months ago)

:lol:

Well here's why the transistors are getting so hot...they're designed for 100mA current and this thing is drawing about 400-500mA :smirk:

I'm surprised they're holding up as well as they are!


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Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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Offlinebit_slice
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Re: I must be bored... [Re: trendal]
    #5211964 - 01/22/06 08:40 PM (18 years, 3 months ago)

out of curiosity, what made you build it?

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InvisibletrendalM
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Re: I must be bored... [Re: bit_slice]
    #5212026 - 01/22/06 08:55 PM (18 years, 3 months ago)

Mostly boredom, but also just to see if I could. Now I know how, in case I ever actually need to build one :wink:

Electronics in general is a hobby of mine.


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Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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Offlinebit_slice
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Re: I must be bored... [Re: trendal]
    #5212113 - 01/22/06 09:15 PM (18 years, 3 months ago)

i go to school for electrical engineering so let me know if you ever need help with any of your electronics.  maybe i could be of assistance. :mushroom2:

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InvisibletrendalM
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Re: I must be bored... [Re: bit_slice]
    #5212128 - 01/22/06 09:20 PM (18 years, 3 months ago)

Well yeah, actually, I do have a question!

I know the second coil (with 4 turns) provides feedback to the transistors and is what turns them on/off in sequence...but just how does this process work?


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Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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InvisibleDiploidM
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Re: I must be bored... [Re: trendal]
    #5212562 - 01/22/06 11:42 PM (18 years, 3 months ago)

Weird... it's hard to make heads or tails of that thing, but it looks like the two 2T coils don't do much but add resistance (maybe a little reactance). When you power it up, Q1 and Q2 start to conduct, then as they become shorts, they bypass their own bias and shut themselves off... which immediately raises their bias and turns them on again. The frequency is a function of the inductive reactance from the windings which slows the rate of change in the transistor bias. I think. :smirk:


--------------------
Republican Values:

1) You can't get married to your spouse who is the same sex as you.
2) You can't have an abortion no matter how much you don't want a child.
3) You can't have a certain plant in your possession or you'll get locked up with a rapist and a murderer.

4) We need a smaller, less-intrusive government.

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OfflineBaby_Hitler
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Re: I must be bored... [Re: trendal]
    #5213392 - 01/23/06 07:25 AM (18 years, 3 months ago)

Could you use it to produce ultrasound?


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This space for rent

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InvisibletrendalM
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Re: I must be bored... [Re: Baby_Hitler]
    #5213910 - 01/23/06 12:10 PM (18 years, 3 months ago)

I suppose you could, yeah, but I can think of a few much better ways to do so because I have no idea how to control the frequency that this oscillates at (I doubt it can be controlled, at least not very well).


--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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Offlinebit_slice
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Re: I must be bored... [Re: trendal]
    #5214558 - 01/23/06 04:31 PM (18 years, 3 months ago)

the transistors in the schematic are Bipolar Junction Transistors or BJTs (as opposed to MOSFETs which are more commonly used these days)

it is useful to view transistors as being on or off when in reality they are either conducting current or conducting a negligible amount of current.  Also, transistors only conduct current in one direction.  current cannot flow backwards so the transistors basically direct the path of the current flow.  In combination with the transformer, the transistors help convert dc to ac. :mushroom2:

Let me know whether or not this answers your question.

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InvisibletrendalM
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Re: I must be bored... [Re: bit_slice]
    #5214637 - 01/23/06 04:55 PM (18 years, 3 months ago)

Heh no, not really...

I understand how transistors work and all that, my question is specific to how the 2nd coil provides feedback from the transformer to the transistors. From the schematic it looks (to me) like the transitors would both receive a steady voltage through R1 and the feedback coil - so they would both turn on and stay on at about the same level. That wouldn't provide any oscillation at all, would it?

Somehow the current flowing through the feedback coil is altered by the current flowing through the primary coil, and that results in only one transistor being fully on at any given time - they switch back and forth.


--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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InvisibletrendalM
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Re: I must be bored... [Re: trendal]
    #5214650 - 01/23/06 04:58 PM (18 years, 3 months ago)

After I've had dinner I'll set up my scope to show the waveform on the base of both transistors to show you what I mean by only one being fully on at a time.


--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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Offlinebarfightlard
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Re: I must be bored... [Re: trendal]
    #5214654 - 01/23/06 05:02 PM (18 years, 3 months ago)

I'm no good at electronics, but I still have a suggestion.  Next time your bored invent a device that instantly brews beer :laugh:


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"What business is it of yours what I do, read, buy, see, say, think, who I fuck, what I take into my body - as long as I do not harm another human being on this planet?" - Bill Hicks

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InvisibletrendalM
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Re: I must be bored... [Re: trendal]
    #5214665 - 01/23/06 05:05 PM (18 years, 3 months ago)



--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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InvisibleDiploidM
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Re: I must be bored... [Re: trendal]
    #5214774 - 01/23/06 05:32 PM (18 years, 3 months ago)

The two 2T coils are inductively coupling with the other primary windings. That would account for that waveform pic. The transistors see a swinging voltage with a DC bias.


--------------------
Republican Values:

1) You can't get married to your spouse who is the same sex as you.
2) You can't have an abortion no matter how much you don't want a child.
3) You can't have a certain plant in your possession or you'll get locked up with a rapist and a murderer.

4) We need a smaller, less-intrusive government.

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Offlinebit_slice
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Re: I must be bored... [Re: trendal]
    #5214803 - 01/23/06 05:43 PM (18 years, 3 months ago)

for the current to flow from the collector (C) to the emitter (E) the voltage from the base (B) to the emitter must reach the cut-in voltage. I don't know much about transformers, but the feedback must bring the voltage across B to E high enough to allow the BJT to conduct current. The +5 does NOT determine whether the transistor is on or off.

maybe this answers your question. i can't tell if i am explaining this well enough. it would help to know your background. do you go to school for this stuff?

Edited by bit_slice (01/23/06 05:45 PM)

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OfflineTheCow
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Re: I must be bored... [Re: Diploid]
    #5214815 - 01/23/06 05:47 PM (18 years, 3 months ago)

Quote:

Diploid said:
The two 2T coils are inductively coupling with the other primary windings. That would account for that waveform pic. The transistors see a swinging voltage with a DC bias.




Yea I was just gonna say something like this. Its a function of your inductors, as youve got the +5 going into the inductors.

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InvisibletrendalM
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Re: I must be bored... [Re: bit_slice]
    #5214816 - 01/23/06 05:48 PM (18 years, 3 months ago)

No I'm completely self-taught, but as I said I already know exactly how transistors work, down to the quantum theory side :wink:

My knowledge of electrical induction is a little shakey, and that's where I'm having trouble here.


--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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OfflineTheCow
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Re: I must be bored... [Re: trendal]
    #5214824 - 01/23/06 05:49 PM (18 years, 3 months ago)

Ah mutual inductance is such an enjoyable differential equation. How much quantum do you know? I personally found wave equations to get boring pretty quickly.

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InvisibletrendalM
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Re: I must be bored... [Re: TheCow]
    #5214846 - 01/23/06 05:53 PM (18 years, 3 months ago)

Yeah I'll agree on that one :wink:

I try to stay away from the nitty-gritty mathematics whenever possible, I'm more concerned with the theories themselves.


--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.

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