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Self triggered Boost converter

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Armagdn03

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I want to make a boost converter which uses the least ammount of parts possible, and triggers itself.

The idea is to have a "sense" or "trigger" coil within the main inductor, that way when it reaches saturation Faraday's law dictates that the voltage falls to zero on the sense coil. I would like this to trigger the switch to open causing the magnetic field in the main inductor to collapse.

Im good with physics, but have not delved too far into the world of electronics. I can use a freq gen, or 555 or any pwm chip to manually set the frequency, but I would really like to simply use a transistor or mosfet.

Does anybody have any ideas on how to get the sense coil to trigger the opening of the switch? what type of switch do you recomend?

Sorry for not giving more specifics, however I would appreciate awnsers whose concepts are applicable to other projects as well. Im sure there must be some Tesla coilers out there with similar designs,

Thanks in advance!
 

tcmtech

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For us simpler folks...
This is what a modified joule thief looks like with a third winding for a different output voltage.

Single transistor flyback oscillator and a dual Transistor version with frequency stabilization capacitor.
 

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Mr RB

Well-Known Member
Apart from that's not a boost converter?? It's a flyback SMPS. What a pain having to wind (and correctly phase) 3 tansformer windings when you could use a 20 cent off the shelf inductor?

I have a 2 transistor boost converter here as part of my "2 transistor Black regulator" project;

Official Home Page of Roman Black
 
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tcmtech

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Most Helpful Member
When a OP does not post what he is using as a power source or a load or any reference to regulation requirements.
But simply specifies something that refers to changing a voltage level, I just take whats simple and easy!
And I did meet the one or two transistor requirement!

Yes I know its not a switch mode but how many power supply designs are there on the INTERNET that are improperly labeled? Actually winding a two coil with ct on a toroid only takes me a minute or so. HF operation only needs a few turns on each side of the ct for the primary and then what ever multiplier or divider needed for the output. It may not be regulated but it will give excellent isolation and multiple isolated voltage capabilities as a trade off!
 

Mr RB

Well-Known Member
Sorry Tcmtech I didnt mean to sound like I was criticising the circuits you provided. They are simple and practical and would indeed provide a solution to the OP's request.

The point i clumsily tried to make was that the OP asked for a "boost converter". Technically boost and buck converters have 1 switch device, 1 diode and 1 standard inductor.
 

tcmtech

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Most Helpful Member
Not a problem!
I just tried to guess at what he was talking about as well.
I know people often use the wrong names while describing things so I figured that I would just take a chance and post the simplest thing that fit what I thought he was after. ;)
Unlike a few people here I am not ego driven to get the first, best, or most unnecessarily complicated design out there. I tend to take the simple approach and then build on that.
I did however copy your schematic to my tech info archive! I may be the one that uses it first! :) Thanks.
 

Armagdn03

New Member
thanks for the circuit Mr RB, this is much closer to what I was looking for. I really want max current to set the duty cycle. Reason is that because this network will be used to feed into other similar "boosting" networks, and I dont want to have to deal with tons of timer chips, I just want each section of the network to regulate its own speed based off of maximum induction with very little unnecessary conduction taking place. i wanted to do it with only one switch per section, however your 2 solution is good, looks like I only need to take care of modifying one resistor to adjust, good stuff.

And I did not add any requirements in for regulation or supply or anything of the like (should have been dc supply, like battery, or constant voltage source) because even suggestions which I cannot use might get the wheels spinning and give me new ideas. thanks alot guys.



Thanks again


Edit:

Look at this!

http://www.switches.machinedesign.com/guiEdits/Content/bdeee4/bdeee4_20.aspx

This page describes GTO's, apparently similar to an SCR, except that when powered it turns off rather than on, says mainly for low power levels, But I know that you can make SCR's out of two back to back Fets, without freewheel diodes, so id think these could be modified as well, something along these lines would be great.
 
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Space Varmint

New Member
This one works really well. Use a powerful transistor like a 2N3055. Also you need a sizable ferrite toroid. Put allot of turns. I had to cut a slot into the toroid to make it easy to add the turns. I think I put like 10 to 800 turns. You can use 10 turns on the tickler (coil) part. The feedback path. Also on the tickler, make sure you have the proper polarity on the direction of your turns. The output of a common emitter configuration is 180 degrees out of phase, so you need to invert that by winding the tickler the opposite direction of the primary. If you get confused, just see if it oscillates, and if not then reverse the leads and should start oscillating as long as everything else is right. I got 2000 volts out of it with a 6 volt supply. I use it to light an fluorescent light.
 

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Armagdn03

New Member
This one works really well. Use a powerful transistor like a 2N3055. Also you need a sizable ferrite toroid. Put allot of turns. I had to cut a slot into the toroid to make it easy to add the turns. I think I put like 10 to 800 turns. You can use 10 turns on the tickler (coil) part. The feedback path. Also on the tickler, make sure you have the proper polarity on the direction of your turns. The output of a common emitter configuration is 180 degrees out of phase, so you need to invert that by winding the tickler the opposite direction of the primary. If you get confused, just see if it oscillates, and if not then reverse the leads and should start oscillating as long as everything else is right. I got 2000 volts out of it with a 6 volt supply. I use it to light an fluorescent light.


This one is perfect!

I dont see why a person couldnt just use the primary and sense coil off of this diagram, and do away with the "secondary". In this way you could use the Collapse of the Primary with a diode to charge a cap. Anybody see any problems with this plan? Reduces the main parts to a switch a main inductor, and a sense coil and a couple capacitors, sounds simple enough
 

Space Varmint

New Member
This one is perfect!

I dont see why a person couldnt just use the primary and sense coil off of this diagram, and do away with the "secondary". In this way you could use the Collapse of the Primary with a diode to charge a cap. Anybody see any problems with this plan? Reduces the main parts to a switch a main inductor, and a sense coil and a couple capacitors, sounds simple enough
You could try it, but the circuit is merely an oscillator. I would build it first and then maybe play around with it. The thing is, is the Armstrong is a hefty oscillator. That's one thing it's good for. Now if you are looking for frequency stability or a host of other desirable characteristics needed for something like a VCO in a PLL circuit, then hang it up. Believe me, I've tried. But the Armstrong will deliver some power!

Also the secondary is where you get control over the voltage level you need. But I know what your saying. I've seen that done before. If you try it, please report back your results. It's kind of a B____ putting all those turns on it, but by cutting a slot into the toroid, well you can just imagine how much easier it is to wrap on the turns.
 
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Space Varmint

New Member
how would you go about integrating a mosfet into this last schematic? so that you have on off vs sine?
That should be easy. Just think of it as an oscillator. Hook up the appropriate pins. I would think an IGBT would be ideal for it if your wanting something like a tazier.
 

monette999

New Member



Hello I am new here my name is Bob and I am a rockie here so I am not allowed to post here.

I am interested in the this post because I like to understand the principle of a DC/DC converter which is similar to the flyback circuit.

I am not a native speaker sorry in advance for some unprecided wording.
I like to understand the physics behind!
I am refering to a serial ocillating circuit were XL=XC.
This system is runnuig in resonance I assume.
What are the physics behind.

I remember that an inductance is delaying the current by 90 degrees.
On the serial capatitive it is the opposite.

The supply is 12V DC.
Who can explain his circuit in an understandble way.
Thank you.

Here the schematic.


BR
Bob
 

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Space Varmint

New Member
It looks to me like you got an Arsmtrong type oscillator circuit for T1. The little network over top of it is a tickler coil with a step-up transformer winding. I'm sure the W1, W2 & W3 mean Windings. So that is your DC to AC converter because it oscillates. Then the output is taken at point point "E" of the step up portion of the transformer is fed through the two diodes D1 & D7 to rectify the output back to DC. This stepped up voltage is used as the supply voltage for T3. T2 looks like some sort of switch because it is controlled by an off board relay K1.
 
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monette999

New Member
Thank you
but how does the 12V DC to AC primary works?

BR
Bob

Arsmtrong type oscillator circuit for T1

Did you mean Armstrong.
 

monette999

New Member
Why Armstrong.

I have an W1(Inductance) & C11(Capacitor) in serial hocked up to 12V DC.

The base of 2N3055 turns this circuit on & of when I have a falling transition below 0.7V
and rising transition.

How does the swing in works?
BR
Bob
 
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