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2x 18/20w T8/T12 12v DC MOSFET Rapid start inverter

2x 18/20w T8/T12 12v DC MOSFET Rapid start inverter

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My design for an inverter that drives 2, 18/20w T8/T12s in a rapid start configuration (this one is tricky to make).
The transformer is wound in this order: Heaters <top of symbol with insulation between>, insulation, secondary, insulation, Heaters <bottom of symbol with insulation between>, insulation, primary, then feedback. An ideal size would be around 3cm x 2cm x 2cm

small-inverter.gif mosfet-invertse-fluorescent-alt.gif mosfet-invertse-fluorescent-real-rapid-start-internal.gif mosfet-invertse-fluorescent-real-rapid-start-internal-x3-8w.gif

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Album name:eclipsislamps / Various DC Ballast Diagrams
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Date added:Feb 18, 2013
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Feb 19, 2013 at 01:44 PM Author: Medved
With these transformers I usually start with the main secondary, insulation, primary (as multiple strands parallel, half of them form one primary section, second half the second section), then the feedback, then insulation and then the filament windings with gaps between them (again for insulation purposes).
Starting with only few turn winding is rather impractical, as it mess up the pattern of wires arrangement on the bobbin, so you may get into troubles with touching wires form across large section of the secondary, so risk of insulation breakdown.

And generally with MOSFETS: Because of their strong input capacitance nonlinearity (it does differ among manufacturers), the voltage across both gates does not spread evenly, so the gate going negative would become overstressed, affecting the circuit's reliability. Dedicated ~3.3..10nF film (not ceramic, as manu ceramic materials tend to be nonlinear as well) capacitors between the gate and source of each MOSFET would keep the voltage balanced well...

And even here I see the filament voltage being too high...

No more selfballasted c***


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Feb 19, 2013 at 04:45 PM Author: eclipsislamps
@Medved I know about the filament voltage problem! As of last week in fact was when I found the correct filament voltage to be 3.6v! I used to think the correct voltage was when they glow bright orange like in switch start types but thanks for the ideas on the circuit.

Keeping electrodes hot and gases ionzied.

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