flyback inverter for fluorescent lamp 15

Posted on Feb 6, 2014

A fluorescent lamp has quite a few unique requirements to get it to start up and stay illuminated. How does this flyback converter manage to do these things I had first looked around to see if I could find a schematic for this fluorescent lamp assembly, but nothing turned up for me. However, the parts count was low enough, and circuit board large enough, that it was a fairly simple matter to trace

flyback inverter for fluorescent lamp 15
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out and sketch the inverter`s schematic in fairly short order, as shown in Figure 1. When first powered up the switching transistor is biased on by the 812 ohm resistor, energizing transformer winding W1. This in turn applies positive feedback to the transistor through winding W2, driving it into saturation. There are two mechanisms in the flyback transformer that are critical for making this inverter work: First it has a gapped core. This allows it to store a substantial amount of energy in its magnetic field which in turn gets dumped over to the fluorescent tube through the secondary winding W3 when the transistor turns off and the transformer`s magnetic field collapses. During this period the winding voltage continues to climb as the magnetic field collapses until the energy can find a place to discharge to, in this case into the fluorescent tube. The voltage is also further increased by the turns ratio of the transformer. This is the flyback  effect that creates sufficiently high enough voltage to get the fluorescent tube to strike  or ionize its gas to get it to start conducting and give off illumination, typically many hundreds of volts. As can be seen this inverter is a very simple circuit with a minimum of parts. A second mechanism in the transformer is it is designed to saturate in order to make the inverter oscillate. At the end of the transistor`s on  period the transformer reaches its maximum magnetic flux...

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