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Trouble with 555 flyback driver circuit

Agrionemys

Jan 13, 2017
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I tried doing a search to no avail, and have been searching any and all media for an answer to what must be a simple question since everyone seems to understand but me.

The circuit I am trying to build requires a power source for the 555, and a secondary source to drive the flyback primary with much more power than the timer can handle. I have built ZVS drivers, 555 drivers, 2n3055 drivers, you name it. I even have a wonderful resonant MOT setup. For the life of me, however, I don't seem to grasp how exactly the second supply is to be wired in. It seems you disconnect the primary from the 555 positive supply, and connect it to the second power source, but I have found no details on it. Where does the negative of the primary supply go? it shows ground, but I have had no success with this. It simply tries to destroy my variac at anything over 12v. From what I can tell, the positive from PS2 goes to the primary and resonant cap, to the the drain and ground, and source goes to ground and in some schematics has a couple caps and a diode on ground side, but I must be wiring it wrong because its simply not working whatsoever, If I omit a second source and limit it relative to the 555 it works, but only just barely, not reaching anywhere near the ZVS levels of power. I'm trying to build a plasma speaker using this, but I can't seem to figure it out and have found no information or anyone willing to even reply to my requests.

Can anyone here help me understand what I'm doing wrong? I'm working mainly off the schematic provided by Jozef Bogin, the "moster 555 flyback driver", but when he mentions the second supply he says to just "disconnect the primary from the 12v rail", which is exactly zero help at all.
 

Harald Kapp

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It might be a good idea to share a schematic diagram of your circuit for our understanding, think so? ;)
 

Agrionemys

Jan 13, 2017
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Wow, that was fast haha, yeah that's the scehmatic I was working off, I see you have a PS2 on there hahaha

So you literally just slap the negative to negative? Is there a reason people like to use ground symbols for that instead?

I never had occasion to use two supplies before, hehe.

I was trying to do it like this, but now I'm not even sure the two circuits can be combined in that fashion. Either way my trouble is the PS's are always drawn in like this
F0JCOBOI24M1N5C.MEDIUM.jpg
 
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Alec_t

Jul 7, 2015
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So you literally just slap the negative to negative? Is there a reason people like to use ground symbols for that instead?
Yes.
Ground symbols are for convenience and tidiness, so that you don't have to draw straggly wires snaking all over the place in the schematic.
Your drawing looks ok.
 

davenn

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So you literally just slap the negative to negative? Is there a reason people like to use ground symbols for that instead?

I never had occasion to use two supplies before, hehe.


Yes.
Ground symbols are for convenience and tidiness, so that you don't have to draw straggly wires snaking all over the place in the schematic.
Your drawing looks ok.


tho it would probably be a really good idea to keep the grounds on the left of the FET together and not connected to the ground on the right of the FET that is fed from a totally different voltage source
This would substantially lessen the chances of high voltage spikes generated by the right side circuitry from damaging components on the left side of the FET
 

Agrionemys

Jan 13, 2017
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Alright so it's essentially assumed that these are going to a negative rail as well as ground then?

My confusion also stems from the fact I could in theory power the 555 timer with a 9v, the FET I'm using (IRFP250N) might make that impossible due to it's minimum working voltage, but if using a 9v battery, I'd be using a much higher power source on the primary side, so I'm curious as to how this will affect the battery if they share a negative rail.

Edit: It seems I should brush up on my schematics reading skills.
 
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davenn

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Alright so it's essentially assumed that these are going to a negative rail as well as ground then?

no, not physically grounded ... just the negative rails of the 2 power supplies as I commented on :)

but if using a 9v battery, I'd be using a much higher power source on the primary side, so I'm curious as to how this will affect the battery if they share a negative rail.
.
it wont affect the battery .... just could have the bad spike effects on the rest of the circuit

again, see my previous post :)
 

Agrionemys

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Ahhhh that makes so much more sense, hence the need for grounding all over the place as well as grounding to separate grounds for each side. From what I understand this particular circuit generates quite a bit of EMF as well adding importance to grounding the hell out of everything. Thanks very much for your help guys, I will be sure to come back with the results :D
 

Agrionemys

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I don't suppose it would be untoward of to ask why it would have no effect on the battery though? Fell free to tell me to do more research,I understand this maybe be all common questions around here, judging by the number of "flyback" posts I see. In fact, any materials that could be suggested for their efficacy in order for me to gain a better theoretical understanding of these basics would be appreciated, I think the first project I worked on was with a disposable camera cap charger cicuit and several electrolytic caps in series. Once I started learning more safety was the obvious priority so I've done quite well but there are some chapters I missed, such as powering sectional circuits with different sources at different power levels. The whys of things sometimes elude me. I do plan on being formally educated in all this, but for now I just enjoy it so much I learn constantly on my free time. I plan on assembling a signal jammer soon, not for use but to better understand RF circuit receiving and transmission. I've obviously like many others been more attracted to the applications of the science rather than the theoretical academic portion, hehe.
 
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davenn

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Ahhhh that makes so much more sense, hence the need for grounding all over the place as well as grounding to separate grounds for each side. From what I understand this particular circuit generates quite a bit of EMF as well adding importance to grounding the hell out of everything. Thanks very much for your help guys, I will be sure to come back with the results :D

It appears you are still misunderstanding the ground symbol in this circuit
Again, they are NOT physical grounds, they are just common negative PSU points

read again what @Alec_t posted in post #5

Ground symbols are for convenience and tidiness, so that you don't have to draw straggly wires snaking all over the place in the schematic.
 

duke37

Jan 9, 2011
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I do not like lumps of ground floating in the air, in pratice they need to be connected together. I prefer a common rail, normally at the bottom of the diagram.
In the case of a delicate circuit driving a circuit which takes high current pulses or produces high voltages, then the associated ground currents should be restricted to the part of the circuit that produces them.
A piece of wire will have resistance, capacitance and inductance so practical layout is critical.
 

Agrionemys

Jan 13, 2017
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Sorry for the misunderstanding, I wasn't referring to those grounds but certin parts of the circuit that do need to be grounded due to the EMF generated by the LOPT in operation. For example its highly recommended to ground the core of the LOPT
 

Alec_t

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For actual grounding you might want to read up about "star grounds"; the idea being to have a single ground point from which connections-paths-to-ground radiate, so that heavy power currents are kept separate from small signal currents in those paths.
 

duke37

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Sorry for the misunderstanding, I wasn't referring to those grounds but certin parts of the circuit that do need to be grounded due to the EMF generated by the LOPT in operation. For example its highly recommended to ground the core of the LOPT
The core of a LOPT is made of ferrite which is insulating or of very high resistance so it will be difficult to ground it. There may be a metal clamp which can be grounded.
 

Agrionemys

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Interestingly enough I've developed the habit of using star grounding without knowing it was a technique, I had just assumed that was a usual thing, like pcb solder joints touching screws to case to ground at mains input kind of thing like you would see in a PC PSU
 

Agrionemys

Jan 13, 2017
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Well thank you all for your help, it is very much appreciated, and I apologize if any (or all) of my questions were run-of-the-mill annoyances, I didn't expect to have so much trouble finding an answer to that particular question in searches. I'm glad for that though as it seems this site is a very valuable resource for everything electronic! :)

Edit: And going back to my first post.... yeah a schematic would have been nice, I don't know why I assumed anyone would have a frame of reference to what I was talking about, sorry for my noobishness!
 

Agrionemys

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And just to update/finalize, it turns out I was dumb. The second build I did didn't have the rest of the circuit in series with the capacitor connected to DC input, mistake #1. Then, I had attempted to alter the way the negative rail off the second PSU would connect, mistake #2. The actual fixes were incredibly simple, after what you all helped me to understand. I rebuilt the circuit, put the smoothing cap first, then in series connected the rest off of that (well those, I don't have a 6800uF 18v cap, or even a 6800uF cap at all of any voltage tolerance so I used three 2200uF 18v caps in parallel) then disconnected the primary and resonant cap from the 12v rail running the 555 circuit, connected that to my rectified variac input and used a wall wart smps to run the 555 and simply connected the variac negative to the common negative and hot damn it works fantastic! Now all I need to do is find some decent components for audio input which is simple enough.

Are there any ways to decrease electrical noise from input devices? An iPod does in fact generate a ton and it makes it almost impossible to hear any audio, wondering if anyone has any tricks or insight on this?
 
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