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Registered Member #588
Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93
hi, I am a big noob at HV anyway, I have constructed a isolated drive flyback driver using the 555 timer and some MOSFETS. The flyback is being power from a 24V and gives 2mm tiny sparks, but when the power to the 555 is turned off the flyback keeps oscillating at its own frequancy giving bigger 7/10mm sparks, there are no capacitors that could be powering the 555. Or any that could cause a L/C oscillator or tank circuit. Also it keeps on blowing my 555 timers and MOSFETS Any ideas why? Thanks.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Bacon wrote ...
hi, I am a big noob at HV anyway, I have constructed a isolated drive flyback driver using the 555 timer and some MOSFETS. The flyback is being power from a 24V and gives 2mm tiny sparks, but when the power to the 555 is turned off the flyback keeps oscillating at its own frequancy giving bigger 7/10mm sparks, there are no capacitors that could be powering the 555. Or any that could cause a L/C oscillator or tank circuit. Also it keeps on blowing my 555 timers and MOSFETS Any ideas why? Thanks.
What I can think of now: how many primary turns do you have? (you should have about 10-15 turns for this supply voltage). Is the flyback's core gapped? Are you powering the 555 from a voltage regulator ("7812")? Is the supply of the 555 well filtered with capacitors? What frequency are you using? (should be around 20Khz) What mosfet are you using? (should have at least 200V rating and on-resistance no higher than about 0.5Ohms (these are just guesses)). And finally, have you tried reversing primary polarity (if you have dc flyback)? I know these are a lot of things but if any of those is wrong it can decrease performance.
Registered Member #514
Joined: Sun Feb 11 2007, 12:27AM
Location: Somewhere in Pirkanmaa, Finland
Posts: 295
There are lots of online calculators for 555s...
Two turns on the core is too little, try winding some more and see if that helps.
I really think you should buy a cheap multimeter with frequency & duty cycle measuring capability. You can get cheap ones for around 20€/$. A (good) multimeter is probably the second best thing to having a scope. If you for some reason can't get one, you can take a small speaker and use it to "probe" the output. The tone will give you a rough idea of the frequency (atleast if its less than 20kHz.)
A mosfets gate is basically a (small) capacitor, so if you don't connect it to anything it may still pick up charge and make it conduct.
Really, if you are a complete noob at electronics, I might suggest you build the single 3055 flyback driver. it has only three parts, and it should give you some semi-nice sparks. There are lots of schematics on the net for it, just google "single transistor flyback driver" or something like that.
Registered Member #588
Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93
Thanks for the circuits. I have just found out that I have blown my third 555 timer so ill buy a new one, then make the 555 and 2N3055 flyback driver circuits.
jmartis: In your circuit on the HV secondary there is a earth symbol, where is that ment to go, earth earth or household earth?
Zb: Ive found a calculator and it is giving out about 3khz oops a bit to low...
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Bacon wrote ...
Thanks for the circuits. I have just found out that I have blown my third 555 timer so ill buy a new one, then make the 555 and 2N3055 flyback driver circuits.
jmartis: In your circuit on the HV secondary there is a earth symbol, where is that ment to go, earth earth or household earth?
mains earth (or if you call it household) May I ask you one question which I'm not sure about, where you wound your primary? Is it on the exposed ferrite core (the black rectangular thing that is coming from the flyback) or around the plastic flyback case??
Registered Member #588
Joined: Sat Mar 17 2007, 11:06AM
Location: UK
Posts: 93
I have made the 555 timer circuit with the IRF630 mosfet and... Nothing, the distance I was trying to spark across was about 2mm. The supply voltage was 15 at 2A.
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Flyback problems
