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Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
I was given a 555 driver, I was driving it with 5volts, but this was not enough for the gate, so I used 12v 4a Nintendo Wii supply, as my ATX supply was broken. For the FET I use 19v 4a, but when I pull an arc, it shuts off, is the circuit mean't to pull this much current, I have tuned the output for higher voltage, lower current, on the flyback side.
Schematic.
I have some questions.
I want to mod the circuit for higher powers, and voltages, 45volts? I forgot what the peak voltage is of input voltage, I have 45volts DC supply I want to use, because it's my only high power supply, that won't fail when pulling alot of current. On 45vdc what MOSFET will I need?
Also, how can I stop the high voltage pulses coming back into the circuit, as this makes the MOSFET heat, I removed the TVS as I was putting to much power through the circuit, so how do I stop this without Zeners...
Also since I removed the TVS, the power was reduced greatly, flyback used to spray like 4inches, but now only 1.7~cm's So most of the power is coming back into the FET and not the flyback, thanks!
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Platinum wrote ...
Also since I removed the TVS, the power was reduced greatly, flyback used to spray like 4inches, but now only 1.7~cm's So most of the power is coming back into the FET and not the flyback, thanks!
Did you remove the fast diode too?
If not it would be the wrong way around and giving an almost direct connection to ground with just the internal drop of the diode to stop it going short. Turn it around.
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
No I didn't, I shall move it around, thanks, Alex.
I don't get that though, I removed the zener, so won't the 4007 make no contact...I though if the zener was removed, the UF4007 wouldn't do anything...
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Platinum wrote ...
No I didn't, I shall move it around, thanks, Alex.
I don't get that though, I removed the zener, so won't the 4007 make no contact...I though if the zener was removed, the UF4007 wouldn't do anything...
You mean one leg of the UF4007 is disconnected? in that case it will make no difference.
Have you tried using 50k pots for the frequency adjust? it makes a ton of difference in my experience.
If your power supply shuts of from over current then add more primary coil turns, this will make the output voltage lower but it also reduces current draw.
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
Yes I know about current and pri turns, so I'm using 20t on my flyback, I though that would be well enough...
I tried to make a PSU from a MOT earlier, but I didn't have the tools.
Sadly I do not have any more pots...
I mean the UF4007 is connected to a disconnected 440v zener, so if the zener is not connected, wouldn't the UF4007 be disconnected by looking at the schematic.
Also I want to do is power this circuit with 45v, but when I did, the 12v 4a Wii supply for driving the 555 pulls to much current for some reason and I blew a MOSFET. I have a few more FET's...So I don't mind if I eventually get it working on 45v, as I've seen someone of youtube run it off 75vDC.
I watched your 555 driver, I like this type of arc, it is very jittery, and when you stretch it out it goes purple...
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Ah in that case with one leg of the diode/zener disconnected it doesn't hurt having one end still connected, since there will be no current flowing through it.
I think 45v input will cause your MOSFET's to fail very fast since the back emf from the primary coil will be quite high. You would just have to try with it with as much primary coil turns as you can wind onto the core with 45v and just keep an eye on current draw.
I think when you blew the MOSFET on 45v the back emf caused the drain and source to brake down and took the gate with it, meaning there was a near short from the gate to ground.
Thanks, in my video I was only using 12v input but it drew around 10 amps! this was done by using about 10 primary coil turns (can't remember 100%) and two 50k pots which gave me a huge range of frequency's to choose from. The MOSFET (both the original IRF540 and replacement IRFP250) eventually died from back EMF and they got really hot, fast.
I eventually packed this circuit in and moved on to Jmartis's excellent halfbridge using the page gren made
Registered Member #3926
Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525
I will be trying a H-bridge soon, using IRF640's :(
I have a sg6105d from a ATX psu, so I'm not sure if I can make one... Not very experienced with these circuits.
Anyway I have made a few modifications to my 555 circuit.
I've added Audio/line in, on the board, not the actual 3.5mm jack, but a small two input screw wire locker thingy... but I forgot to add a cap to pin 5 to GND, ohh well....I would use my PC, but I'm afraid I will blow it..
Also I'm know using the flybacks internal primary, and the power is alot higher, but as I said, PSU pulls to much current... it's a laptop charger afterall.
I'm using 2SK2698 it gets very hot from the emf, but I can't stop it, if I use 45v input, how can I protect the gates? All I want to do is run it off 45v and have audio modulated arcs, and I will be happy. Because as you have said also when audio modulation is added, current being pulled increases ALOT. So my only supply is my 45v one, it's pretty powerful. 20A short. When I get this 555 circuit working OK, I will add some caps in the output for higher current arcs, anyway if I give up I still have my ZVS, which now works brilliantly.
If I done it right, 7.2khz is the lowest freq of the circuit I'm using with it's pots. Tried to drive ignition coil, as I'm running out of flybacks, but I can't.
Registered Member #3943
Joined: Sun Jun 12 2011, 05:24PM
Location: The Shire, UK
Posts: 552
Daedronus wrote ...
Why do you people insist on using 555 to generate PWM signals?
The duty cycle is dependent on the frequency. When you turn the frequency pot you also change the duty cycle.
A TL494 is just as cheap and you get independent control of frequency and duty cycle.
Like this:
I don't, I know the 555 driver is crap. I use an SG3525 half-bridge now when I experiment with flybacks (which is very rarely these days, too busy with life).
nice but, 1. you need zenners across the gates, in case there is a voltage spike. 2. you should place a fast diode in parallel with the gate resistors for fast turn off. 3. you also need something like a 100k ohm across the gates to make sure the gates is off when the driver is unpowered, but there is power on the mosfet side. 4. you need a capacitor in series with the flyback primary to make sure you don't walk the core into saturation.
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555 flyback fails?
