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Old 5th April 2011, 09:34 PM   #21
vasko is offline vasko  Czech Republic
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Is it possible to make Royer covertor on 220V ?
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Old 31st July 2011, 12:38 PM   #22
vasko is offline vasko  Czech Republic
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If I make Royer on 24V, how many turns I need on primary approximatively?

For 4V is suggested 4 turns.
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Old 13th December 2012, 02:13 PM   #23
vasko is offline vasko  Czech Republic
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So Vcc = 12V. I will use pwm IC TL494 to make it regulated.

What topology to use flyback or push-pull? I can't drive more than 60W with 12V flyback, which is possible with push-pull. Right?

And when I have DTC I don't need balast for lamp?

Click the image to open in full size.
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Old 13th December 2012, 02:43 PM   #24
vasko is offline vasko  Czech Republic
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Here is schematic reuploaded.

Click the image to open in full size.
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Old 14th December 2012, 10:19 AM   #25
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Hi Vasko

Exactly what tube are you trying to "charge"? Normal fluorescent tubes do not like to be run on high voltage, low current supplies as they are intended to run with a hot filament. You can successfully operate low power tubes (4-8W) from 2.4-6V batteries or perhaps even from 1.5V using the Royer converter. The switching supply you show gives high voltage spikes that might be useful for running a neon tube (as you originally mentioned) but the transformer needs to be wound to provide 1000-5000V... not impossible, but insulation is important. The output from such a circuit you show is a "square wave" for half the cycle (transistor "on") but a spike from the flyback when turned "off". Even for neon tubes, this seems to me to be undesirable, and may lead to premature lamp blackening (electrode sputtering). If your lamp is a neon tube it may only light during the spike. I'd recommend designing a sinewave driver of the Royer class with the operating voltage required for the secondary, not relying on a pulse which may stress the dielectrics of transformers not necessarily designed for such voltages.

Cheers
John
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Old 14th December 2012, 10:58 AM   #26
FoMoCo is offline FoMoCo  United States
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Quote:
Originally Posted by vasko View Post
Here is schematic reuploaded.

Click the image to open in full size.
You need some sort of protection for that output FET. With an open load, it's going to avalanche and be destroyed. Even an avalanche rated FET will be destroyed by the ensuing high dissipation.
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Old 14th December 2012, 11:02 AM   #27
vasko is offline vasko  Czech Republic
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Quote:
Originally Posted by john_ellis View Post
Hi Vasko

Exactly what tube are you trying to "charge"? Normal fluorescent tubes do not like to be run on high voltage, low current supplies as they are intended to run with a hot filament. You can successfully operate low power tubes (4-8W) from 2.4-6V batteries or perhaps even from 1.5V using the Royer converter. The switching supply you show gives high voltage spikes that might be useful for running a neon tube (as you originally mentioned) but the transformer needs to be wound to provide 1000-5000V... not impossible, but insulation is important. The output from such a circuit you show is a "square wave" for half the cycle (transistor "on") but a spike from the flyback when turned "off". Even for neon tubes, this seems to me to be undesirable, and may lead to premature lamp blackening (electrode sputtering). If your lamp is a neon tube it may only light during the spike. I'd recommend designing a sinewave driver of the Royer class with the operating voltage required for the secondary, not relying on a pulse which may stress the dielectrics of transformers not necessarily designed for such voltages.

Cheers
John
I'll use common neon lamps with broken heating filaments.

I have secondary winding from TV HV transformer which gives 20kV I guess.

I will not use selfoscillating, I'll use either IR2153 or TL494. I'd rather use 494 for more control. So if that's the situation with flyback, Ill use push pull then.
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Old 14th December 2012, 11:04 AM   #28
vasko is offline vasko  Czech Republic
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Quote:
Originally Posted by FoMoCo View Post
You need some sort of protection for that output FET. With an open load, it's going to avalanche and be destroyed. Even an avalanche rated FET will be destroyed by the ensuing high dissipation.
Is this protection ok? (I'll stil use FET, not BJT)

Click the image to open in full size.
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Old 14th December 2012, 01:53 PM   #29
FoMoCo is offline FoMoCo  United States
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Originally Posted by vasko View Post
Is this protection ok? (I'll stil use FET, not BJT)

Click the image to open in full size.
You're on the right path. But, I can't tell you if the values are right without knowing the inductance of your coupled inductor.

The other suggestions of a Royer oscillator are much better than the flyback, though...
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Old 14th December 2012, 03:23 PM   #30
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Hi
You should take note of FoMoCo's concern about the avalanche rating of the switching transistor. The flyback energy needs to be dissipated somewhere and if it isn't in your fluorescent tube it will be in your transistor - and maybe kill it. Leakage inductance means you will need to use an RC snubber (as you show), but if you limit the primary flyback voltage with a Zener (not an ordinary diode) the output will be limited by the turns ratio of the transformer and zener voltage.

If you use a MOSFET a series gate resistor as you originally proposed is probably needed to stop parasitic oscillation in the FET. I have found that the old TTL circuit (npn driver with two NPN outputs) works well for FETS and bipolars, but does invert the drive signal.

You might be able to resonate the primary of the LOPT with a suitable capacitor and drive the FET with short pulses (<10% duty cycle) to force it into Class C and obtain a sinewave while solving the flyback issue.

Cheers
John
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