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Flyback troubles...

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bugsingelyn

Tue Nov 13 2007, 11:48PM

Registered Member #1112 Joined: Sun Nov 11 2007, 05:07PM
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Posts: 3

I found a fairly large TV that some one was throwing out and, after hearing about someone who made a high voltage supply out of some of the parts from a TV for cheap, I took it and got to work right away. I looked around at a bunch of different websites and found a bunch of circuits for powering it, and have decided to use the simple transistor and 2 resistor circuit to test and see if it works, and eventually make a 555 timer based circuit for better performance and longer run times. So i went out to Radio Shack and got a few things to get started and hooked everything up to what i think are the right places and powered it up, and nothing happened. I tryed it with a bunch of diferent power supplies with varying voltages and amps and none seemed to do anything. I have checked it a million times and I just can't seem to get it to work, so now I am wondering if my transformer is broken. Is there a simple way to test it to see if it is broken?

cjk2

Wed Nov 14 2007, 12:08AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

First of all, welcome to the forum

A number of points in random order:

1. Take a picture of your setup, it will help us all
2. The 2n3055 circuit is VERY bad
3. Check your transistor, it may have very quickly gone bad (as it well should have being rated for about 65v)
4. Make sure your primary and secondary are in correct phase (reverse one of them and see if it works)
5. Make sure your secondary is good (you will probably need a few tens of volts to overcome the forward drop of the HV diode to check it)
6. Check the number of turns on each coil, i remember something like 5 turns for pri. 3 turns for sec.
7. If you have a scope, see if the circuit is actually oscillating

Dr. Dark Current

Wed Nov 14 2007, 01:56PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Hi bugsingelyn and welcome to 4hv

This is a circuit I recommend if you're starting with flybacks. It well outperforms the single transistor driver and is simple to build.

The transistor needs heatsink.
You can experiment with primary number of turns.
A small foil capacitor (~0.1uF at 200 or more V) across the primary winding greatly improves performance. It is possible though that your transistor will die.

bugsingelyn

Wed Nov 14 2007, 09:59PM

Registered Member #1112 Joined: Sun Nov 11 2007, 05:07PM
Location:
Posts: 3

Thanks a lot for the help. I'll head out to Radio Shack some time this week and tell you all how it goes. I just measured about .46 volts in between the thick red wire and the HV return pin. I think this is wrong

Shaun

Thu Nov 15 2007, 04:43AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Just a note-reading the HV directly with no divider may have killed your meter, thus the .46V.

And BTW if this is a hobby you decide you are interested in, the first good decision you can make is to stop gong to Radioshack! ;) I highly doubt the will have the IRF540, if they do you can be sure of 2 things. That it will be:
1. Individually packaged
2. Way overpriced
I only go there when I'm low on random components, cause they sell assortments of resistors, caps, LEDs,etc.

Any way good luck!

bugsingelyn

Fri Nov 16 2007, 03:01AM

Registered Member #1112 Joined: Sun Nov 11 2007, 05:07PM
Location:
Posts: 3

Oh haha. Well, I like to live life without regrets, so too bad. And I have noticed that Radio Shack is awfully expensive compared to places online. But my problem is on places online, they have so many choices that I don't know what to pick (for example, there are 264 choices of 555 timers that come up on DigiKey). I guess when (not IF) I start getting more into this hobby, I will start ordering online. Thanks so much for the help!

Conundrum

Sat Nov 17 2007, 08:08AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hehe.. I've accidentally toasted a DMM in a similar way, in my case this was due to using it on low amps range, in series with the ground. Unfortunately the earth connection (via my soldering iron's ESD ground pin) was not as secure as it should have been and the whole setup floated to about -12KV. Hint:- DMM's don't like this.

Changed out the controller (ICL7106) and he worked again. I still have that meter somewhere.

If you are going to buy a DMM, get an IDM65 from RS Components, those suckers are nearly impossible to destroy. Cost Â£90 9 years ago (!) and has outlasted four other meters. Needs the PCB cleaning once in a while but it works nicely.

I agree, 2N3055's suck for everything except small disk shaped flybacks like you'd find in an old B/W TV.

Ignition coils are fairly easy to drive this way though, just watch out for the reverse spikes. Best way to fix this is to put a 0.01uF capacitor across the transistor, this takes out most of the spikes without ruining the back EMF effect you want.

regards, -A
"Bother" said Pooh, as he fell into the leech tank...

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