NE555 variable frequency circuit 50kHz-1MHz

ScottWang

Joined Aug 23, 2012
6,926
An NE555 supplying 200mA at ~15V seems much better. But I need a good circuit. And I will also need to adjust the frequency.
The better is draw the current less than 1/3(200mA) because the heat, if you want to draw more than you better prepare a heatsink, if you want to drive the MOSFET then 555 no needs the big current.

Why you want to use 555, is that because it is cheaper?
Why you need a variable frequency, how about a crystal oscillator(4 or 10 Mhz) and some counters as frequency divider (CD4518, CD4013, CD4040)?

NE555 Pulse Generator and PWM adjustable circuit.
 

AlbertHall

Joined Jun 4, 2014
10,243
the transformer is an iron core type
Was this transformer a standard mains transformer - it has a laminated iron core?
If that is the case, the high frequencies you are using are likely the cause of the problem. They are designed to be efficient at 50/60Hz and at much higher frequencies the core loss will suck up all your power.
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
The better is draw the current less than 1/3(200mA) because the heat, if you want to draw more than you better prepare a heatsink, if you want to drive the MOSFET then 555 no needs the big current.

Why you want to use 555, is that because it is cheaper?
Why you need a variable frequency, how about a crystal oscillator(4 or 10 Mhz) and some counters as frequency divider (CD4518, CD4013, CD4040)?

NE555 Pulse Generator and PWM adjustable circuit.
I already have some NE555s lying around. I don't want to have to get more stuff.
 

Wendy

Joined Mar 24, 2008
22,155
OK, if I am right about your MOSFETs try bumping your power supply to 12VDC . If things cool down I nailed it
 
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MisterBill2

Joined Jan 23, 2018
6,745
In addition to raising the driver supply voltage, also try reducing the duty cycle on the gate until the indicated current drops a bit, That will indicate that much less time is spent with a saturated magnetic core.
 

Wendy

Joined Mar 24, 2008
22,155

Wendy

Joined Mar 24, 2008
22,155
Try this to see if it can reach 1Mhz
temp.png

If it works you van add a pot in line with the R1 680Ω resistor. I am a bit out of practice drawing and designing, It has been a while. The diode shown on the MOSFET is actually part of the MOSFET.

BTW, have you considered hand winding a torrid?
 
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MisterBill2

Joined Jan 23, 2018
6,745
Try this to see if it can reach 1Mhz
View attachment 161199

If it works you van add a pot in line with the R1 680Ω resistor. I am a bit out of practice drawing and designing, It has been a while. The diode shown on the MOSFET is actually part of the MOSFET.

BTW, have you considered hand winding a torrid?
Very good drawing, Wendy!
One thought about the diode across the primary is that probably it will dampen the high voltage inductive spike, which would be good, except that the whole purpose of the project is to create an arc hot enough to start a fire. So it seems like a different approach to protect the FET would be a better choice in this case only. And it still seems like driving the transformer at a resonant frequency would produce a higher secondary voltage. I don't think that I have seen any description of that transformer, by the way. So it may be that the whole lack of performance is in that part of the project. It would not be a far stretch to admit that a lot of threads wind up finding that it was a detail not mentioned at the start that was the key to an adequate solution. MOST of the participants here are not skilled mind reders, I have observed. And that includes me.
 

Wendy

Joined Mar 24, 2008
22,155
Part of the problems with my stroke is the lack of ability to remember anything in the short term. Your mentioning resonance brought to mind a Tesla coil It could take more copper wire than the op can afford but once you find the self resonance for the secondary coil the oscillator can be tuned to it.Making a small Tesla coil would be the focus of my research if I were doing this project.
One thing about a Tesla coil, no iron core, Use PVC or a pencil or soda straw to wind using small diameter Coil. A Tesla coil is basically an open air transformer with a heavy duty coil for the primary, and a hell of a step up ratio on the secondary, It uses resonance on the secondary to generate an intense electric field an generate arcs the end of the coil is connected to a BB or metal ball The other end shares a ground connection.While a PITA to wind it is actually a simple device.
 
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MisterBill2

Joined Jan 23, 2018
6,745
One thing that has been missing is the purpose of the igniting!

The previous thread about something to ignite with an arc was for lighting campfires while camping. That was a strange concept, given that for far less money a whole package of lighters could be purchased, which would also be much lighter to carry than a battery and a circuit.
 

Wendy

Joined Mar 24, 2008
22,155
I love the Piezo approach used by modern lighters.Simple yet cheap.
I have seen electric lighter advertised, I believe this is what the TS is wanting to do. Looks like a fun project which attracted me to it.
 

Wendy

Joined Mar 24, 2008
22,155
Another possibility is a hand held Taser or stunner . Historically I have paid$15 for them as a trans girl I do worry about being assaulted, they throw a heck of an arc in my experience. Loud too.
 

Wendy

Joined Mar 24, 2008
22,155
Sounds like a fuel issue, wonder if wax in the paper would act differently?The arc is so hot it needs to be defused somehow?

An interesting problem. Would charcoal act differently?
 

Thread Starter

-live wire-

Joined Dec 22, 2017
912
In addition to raising the driver supply voltage, also try reducing the duty cycle on the gate until the indicated current drops a bit, That will indicate that much less time is spent with a saturated magnetic core.
At a certain voltage, it takes a certain amount of time to build up the magnetic field, correct? And therefore, it is drawing the least current, right? But wouldn't that be pretty much independent of the off time, assuming it was significant?

Sounds like a fuel issue, wonder if wax in the paper would act differently?The arc is so hot it needs to be defused somehow?

An interesting problem. Would charcoal act differently?
Well, you know what they say. Brute force is the solution to everything. Just increase the voltage, current, and heat sinking. ;) But actually, maybe a higher voltage and 10s of watts as opposed to a few watts would be better. I'll try to test that out if I have time.
 

Wendy

Joined Mar 24, 2008
22,155
I remember when I was a teen, someone had built a Jacobs ladder It caught a paper on fire, but not before it punched a line of holes in the paper, Seems to me we need to defuse the arc somehow, which hints that maybe the electrodes need work, Maybe pencil lead for mechanical pencils? An arc welder uses low voltage with tremendous current (I think) maybe an arc from high voltage followed by a high current. I honestly don't know, at this point I am brainstorming, trying to help. I used to make thermocouples using a graphite electrode and high current similar to an arc welder. I was never an engineer but a technician.
 

MisterBill2

Joined Jan 23, 2018
6,745
It is important to know that a flame is a much better conductor than air. I don't recall about smoke being a good conductor, but a flame certainly is, especially a yellow flame.
 

Wendy

Joined Mar 24, 2008
22,155
The plasma created from arcing is also a conductor, This is the basis o an arc welder I believe. Once a conductive path is established the current delivers the power to melt steel Lead acid batteries have the capacity to deliver such current.
 

MisterBill2

Joined Jan 23, 2018
6,745
The plasma created from arcing is also a conductor, This is the basis o an arc welder I believe. Once a conductive path is established the current delivers the power to melt steel Lead acid batteries have the capacity to deliver such current.
Yes, lead-acid batteries of the automotive size can usually deliver at least 500 Amps for a short time. BUT that sort of operation does take a toll on battery life. We once delivered a system intended to deliver 100 amps at 24 volts, regulated, from a set of those cute 12 volt 7 amp-hour batteries. It was for filming crashes inside the vehicle, so the total run time was about 45 seconds. 10 seconds to wind up the film cameras 30 seconds down the track, and then at least 5 seconds of crash and bounce. The crash dummys do bounce around in a crash.
 
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