Why my Flyback transformer circuit seems to work once out of 10 times ??

[khelz]

Wassup guys,

I made the circuit below, and it worked perfectly......but just once out of 10 times... I would get some sparks, and then it kinda look like it turn off and doesn't work for a while for no reason. Sometimes it works 3 times in a row, sometimes nothing. The connections seem okay, the polarity seems fine also since it already worked. So basically I just don't get a whine or a sound everytime I put my power supply on.

I'm using a new flyback (picture below) with a MJE13009 transistor. The transistor seems fine also, doesn't even need a heatsink. I don't if there is any kind of capacitor in there so it has to discharge or something. Can you guys help me with this ?

Thank you !

 

[BrownOut]

The feedback coil will have a polarity,depending on which way it was wound. Make sure that is correct, maybe even try switching the leads on it. Otherwise, try changing the number of turns in the feedback coil. The various flyback transformers are going to have different magnetic characteristics, and it will usually take some experimentation to get it right. But at least it's working somewhat, so you're on a good path already.

PS, it's usually not recommended to use a flyback such as yours for this kind of project. It might be hard to get this to work. See if you can find one that doens't have all the focus and various other functions on it. I have one like yours on my bench, and I've considered taking a hacksaw to it and see what I can come up withl

 

[Exo]

Shouldn't there also be a diode over the transistor to protect it from the reverse voltage spike when switching a coil ?

 

[tvtech]

You need flyback caps figured into your circuit. Around 7.5 to 10 NF total will do rated at 1500V a piece.

To really learn Google "flyback cap". Good luck.

Over and out.

Otherwise wait until tomorrow when I will try and explain all to you.

And EXO is correct in his post above. You need to use something like a BU508D transistor. Designed and built for Line Stages with an internal Damper Diode.

 

[crutschow]

Shouldn't there also be a diode over the transistor to protect it from the reverse voltage spike when switching a coil ?

It's the switching spike that is reflected from the primary to the secondary and generates the output voltage. If you suppress the spike, you also suppress the output voltage.

But it might be a good idea to put a zener across the transistor with voltage rating slightly below the transistor's Vce maximum, to protect it.

 

[colin55]

You need a cap as shown in this circuit:
**broken link removed**


How many volts are you using? You need 12v
The circuit needs a cap so the feedback winding can "hit against" the cap and send its waveform to the transistor.
It will never work without this cap.

 

[MrAl]

Wassup guys,

I made the circuit below, and it worked perfectly......but just once out of 10 times... I would get some sparks, and then it kinda look like it turn off and doesn't work for a while for no reason. Sometimes it works 3 times in a row, sometimes nothing. The connections seem okay, the polarity seems fine also since it already worked. So basically I just don't get a whine or a sound everytime I put my power supply on.

I'm using a new flyback (picture below) with a MJE13009 transistor. The transistor seems fine also, doesn't even need a heatsink. I don't if there is any kind of capacitor in there so it has to discharge or something. Can you guys help me with this ?

Thank you !

Hi,

You might get this to work as is by changing the values of the two resistors to increase (or decrease) the drive to the transistor base. This circuit is similar to the "Joule Thief" except it has a secondary and a way to adjust the transistor drive. In these circuits however there is usually something that loads the output so that it does not allow the transistor collector to go extremely high. You may have to play around with the resistor values to get it to work right, as the values will depend on the winding ratio between the collector winding and base drive winding.

 

[khelz]

You need a cap as shown in this circuit:
**broken link removed**


How many volts are you using? You need 12v
The circuit needs a cap so the feedback winding can "hit against" the cap and send its waveform to the transistor.
It will never work without this cap.

But these guys below, like a lot of others too don't seem to use any capacitance, and it seems to work pretty well.....

YouTube - Homemade Flyback Transformer Driver

 

[colin55]

The capacitor improves the effectiveness of the feedback winding and changes the frequency of operation of the circuit.
If the gain of the transistor is low, as it seems to be in this case, the capacitor will improve the performance of the circuit.

 

[Dr_Doggy]

HEY , I got the very same setup going, and it works great.

I would recommend using a separate pot each for R1 & R2 so you can tune your feedback loop, i found that it worked well on several different load ratios, but find the one most stable even if its not most efficient.

Don't bother with protection diode since it dampens(or maybe i just used wrong one). and you only want one high value capacitor across your supply to take off the strain.

I run mine off 12V and it draws 700mA with sufficient results, it also runs with 2 9V batteries(in parallel)
careful though transistor will get hot and circuit breaks down after a few minutes or so when running constantly. So i just put 2 in parallel, but i didn't bother heat-sinking which would probably help alot!

 

[colin55]

Adding the capacitor will reduce the current quite considerably and increase the ouput.

 

[tvtech]

Wassup guys,

I made the circuit below, and it worked perfectly......but just once out of 10 times... I would get some sparks, and then it kinda look like it turn off and doesn't work for a while for no reason. Sometimes it works 3 times in a row, sometimes nothing. The connections seem okay, the polarity seems fine also since it already worked. So basically I just don't get a whine or a sound everytime I put my power supply on.

I'm using a new flyback (picture below) with a MJE13009 transistor. The transistor seems fine also, doesn't even need a heatsink. I don't if there is any kind of capacitor in there so it has to discharge or something. Can you guys help me with this ?

Thank you !

OK. I have time now to try and help clear up exactly what you are trying to do.

You (as per the attached photo) are trying to use a Line Output transformer from a CRT TV to generate high Voltage from the Anode of the transformer.

No problem with that. TV Line Output Transformers typically run at a Line Output Transistor Collector voltage of between 90 to 140V (depending on screen size and Manufacturer). Still no problem as you are only supplying between 6 and 24V.

Now a question. What exactly is this application for?

I ask this question to try and understand and help you make your design as simple and yet as reliable as possible.

Cheers

 

[Exo]

My guess it's just to see the electricity arc.

 

[BrownOut]

YUP. Every mad scientist's lab needs one of these.

Mine uses an automotive ignition coil.

 

[tvtech]

LOL. That's funny.

Cheers.

 

[crutschow]

Every (mad scientist's) lab should have a least one Jacob's Ladder running.

 

[khelz]

I want to create a high voltage to do a biomechanical experience. I work at the University of Toronto and we are working on a new product. But I need a high voltage without a lot of power, this is why I'm using a flyback. So if I see it arcing. It will be a nice start. after I'm gonna tune the signal, if it works of course.

But I'll try the capacitor and I come back to ya.

Khelz

 

[MrAl]

Every (mad scientist's) lab should have a least one Jacob's Ladder running.

Hi there,


Ha ha, yeah we all have or had one of these in the past i guess. Mine came in the form of a home brewed bug zapper, with a TV flyback transformer and a jar with thin bus wire criss crossed in a grid pattern. When the poor bug puts one leg on each wire he doesnt even get a chance to see that last puff of smoke. It's very 'humane' though i think.

 

[tvtech]

Hi there,


Ha ha, yeah we all have or had one of these in the past i guess. Mine came in the form of a home brewed bug zapper, with a TV flyback transformer and a jar with thin bus wire criss crossed in a grid pattern. When the poor bug puts one leg on each wire he doesnt even get a chance to see that last puff of smoke. It's very 'humane' though i think.

LOL. Poor bug. Probably had no chance. The spark is bigger than his whole body

Cheers