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Old 20th February 2011, 08:49 PM   #1
vasko is offline vasko  Czech Republic
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Default Neon lamp charger

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I made this charger,used ferrit transformer,BDX34 darlington,1k resistor and 22n capacitor.

And I want to enhance it. I doesn't work below 5V, I'd like to make it on 1,5V. What should I change?

Also I'd like to make this adjustable power with pot,but in pulse with modulation fashion,not just amplitude scaling. I don't want to use IC's, want to keep it simple.

Also I used transformer that can give 40-50W on 40-50kHz, but when I start it I have impression that it pumps less than 15W as it is now.
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Old 21st February 2011, 07:01 AM   #2
Elvee is offline Elvee  Belgium
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Designing a proper converter is a bit more complicated than throwing three components around any transformer.
You need to calculate the core area, number of turns, airgap, etc.
Self-oscillating converters look simple, but they are the most challenging to design.
And a fluorescent tube is a pretty challenging load too.
You should have a look at some application notes:
http://www.diodes.com/_files/product.../zetex/an1.pdf
http://www.diodes.com/_files/product...zetex/an14.pdf
http://www.diodes.com/_files/product...zetex/an17.pdf

If you want dimming, you'll need a Royer converter associated with a PWM controller
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Old 21st February 2011, 01:49 PM   #3
vasko is offline vasko  Czech Republic
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Thanks for links and references.

I've noticed that impedance of secundar is also important for neon to light properly.

Neon lamp does practically short circuit and that affects oscillating,it just pumps spikes with no energy. All that suggests to use 555 square generator, but then voltage supply should be at least 5V which I don't like.

Also I don't like transformer squealing, don't know how to make it silent?

I definitely want to use one transistor solution,no push pull.

Here are some circuits for flash capacitator charging,they work on 1.5V.I'm confused how secundar of 350V is connected to transistor base?

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Old 23rd February 2011, 10:24 PM   #4
vasko is offline vasko  Czech Republic
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I made this Royer variation,and it works very nice,only problem it has it works just with 10V or more. How to bias it to work at least voltage possible (3V for example)?

I used BDX34 for Q1,Q2.

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Old 24th February 2011, 07:41 AM   #5
Elvee is offline Elvee  Belgium
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Using the main winding also as the feedback one is a bit borderline. But since you want to work at low voltages, this shouldn't be an obstacle.
But why do you insist on using BDX34's?
These are darlingtons, pretty unsuitable for this kind of application.
You should use Zetex superbeta transistors (ZTX849, etc), they are ideal for this kind of job. Or alternatively, a D44H11 or similar.
To make the circuit operate at low voltages, you'll also need to reduce R1 & R2; to 820ohm f.e.
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Old 24th February 2011, 10:47 AM   #6
vasko is offline vasko  Czech Republic
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I'll try reducing R1,and R2 right away.

I'm using BDX34 because I have a few unused.
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Old 24th February 2011, 10:58 AM   #7
Elvee is offline Elvee  Belgium
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In the links I gave you, there is a Royer designed for 2.4V supply. Did you try it?
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Old 24th February 2011, 01:31 PM   #8
vasko is offline vasko  Czech Republic
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Yes, but I don't like that extra winding for feedback, it's hard to control frequency and power with such design.

I made R1, R2 1k,and it's oscillating on 3V but doesn't have voltage to fire the lamp. Don't know how to solve that? I have 2 x 3 rounds on primary and approximatively 1 x 500 on secondary.


Also discovered that L1 and C1 affect oscillating allot. If I haven't need low (3V) operating voltage I'd just use CD4047 to drive transistors (MOSFET's).

Last edited by vasko; 24th February 2011 at 01:34 PM.
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Old 24th February 2011, 01:54 PM   #9
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by vasko View Post
Yes, but I don't like that extra winding for feedback, it's hard to control frequency and power with such design.
It is the opposite: having a separate winding increases flexibility


Quote:
I made R1, R2 1k,and it's oscillating on 3V but doesn't have voltage to fire the lamp. Don't know how to solve that? I have 2 x 3 rounds on primary and approximatively 1 x 500 on secondary.
Using proper transistors, you could get ~1500V peak at the output. With the BDX34's, this will fall to ~1000V, which is insufficient to trigger the tube without preheating. Did you make heating connections?

Quote:
Also discovered that L1 and C1 affect oscillating allot.
That's normal, this kind of oscillator has to be tuned.
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Old 24th February 2011, 02:05 PM   #10
vasko is offline vasko  Czech Republic
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No heating, CCFL.

If I have 2 x 3 rounds in primary, how many rounds I need for Royer feedback winding? There isn't info about that in pdf link you gave me.

For operating on 3V.
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