height=224 alt="Click for larger image" 
      src="30504_5lo.jpg" width=302 
      border=0> </A></DIV>
      <P>The toroid is secured using a cable tie wrapped around the core as 
      shown and spaced above the PC board using another looped cable tie placed 
      side on. This lifts the core so that it is at the same height as the 
      primary winding side.</P>
      <P>Inductor L2 is wound on a split ferrite core with a gap of 1mm. This 
      gap is necessary to prevent core saturation and also to reduce its Q. This 
      gap is set by inserting a cable tie in the hinge portion of the split 
      core. This is shown in the detail diagram for L2 in Fig.5.</P>
      <P>Wind 42 turns of 0.4mm enamelled copper wire onto each core half, so 
      that in effect, you have an 84-turn coil split between them. Insert the 
      cable tie and snap close the core. The core is secured to the PC board 
      with a daisy-chained length of cable ties around the top and through the 
      holes in the PC board. Then strip, tin and solder the two winding ends to 
      the PC board.</P>
      <H3>Installing the board</H3>
      <P>The PC board is installed into a standard 36/40W batten and mounted on 
      6mm high metal spacers. Before you can do that, you must remove the 
      original ballast and the starter components. Find a suitable position 
      within the batten for the PC board. We positioned our PC board so that 
      three of the wires from the tube mounting tombstones reached the PC board 
      terminals. The remaining wire was extended using the existing terminal 
      block.</P>
      <DIV class=wpimg style="FLOAT: right; WIDTH: 302px"><A 
      href="http://us1.webpublications.com.au/static/images/articles/i305/30504_3mg.jpg"><IMG 
      height=221 alt="Click for larger image" 
      src="30504_3lo.jpg" width=302 
      border=0> </A></DIV>
      <P>Drill holes to mount the PC board at the six mounting positions. You 
      will also need to drill a hole in the side of the batten for the dimming 
      potentiometer. The shaft on this potentiometer may need cutting down to 
      size. Also drill and file a hole for the cordgrip grommet which can be 
      positioned on the end of the batten or in the base.</P>
      <P>Cover up any slots and holes on the underside of the batten base where 
      the PC board will be located. We used Gaffer tape for this. Attach the PC 
      board using M3 screws and nuts.</P>
      <P>Make sure that the heatsinks on the PC board do not make contact with 
      the batten top cover when it is fitted otherwise the fuse will blow.</P>
      <P>Follow the diagram of Fig.7 which shows how to connect the batten 
      wiring to the PC board. Do not forget the earth wire which connects 
      between the batten case earth and the negative terminal on the PC board. 
      Secure the 12V power leads with a cordgrip grommet.</P>
      <H3>Testing</H3>
      <DIV class=wpimg style="WIDTH: 302px"><A 
      href="http://us1.webpublications.com.au/static/images/articles/i305/30504_13mg.jpg"><IMG 
      height=53 alt="Click for larger image" 
      src="30504_13lo.jpg" width=302 
      border=0> </A>
      <DIV class=wpcaption>Fig.7: here's how the PC board is wired into a 
      standard 36/40W fluorescent light batten. The starter and its holder are 
      discarded but the original tombstones and terminal block are retained. Any 
      power factor capacitor is also removed.</DIV></DIV>
      <P><B>The fluorescent inverter circuit generates high voltages which can 
      give you an electric shock. Take care when taking measurements and 
      disconnect the 12V battery before touching any part of the circuit. 
      </B></P>
      <P>With 12V applied and without the fluorescent tube installed, check that 
      there is about 334V DC between the metal tab of Q3 and ground. This 
      voltage should be within 5% of 334V, between 317V and 350V.</P>
      <P>Now disconnect 12V, insert the tube and reapply 12V. Check that the 
      tube starts within a few seconds. The circuit may make several attempts 
      before the tube lights, particularly in cold weather.</P>
      <P>As with all fluorescent lights, the tube will not reach full brightness 
      until after five minutes or so and during this time the tube may exhibit a 
      series of darker bands (striations) along its length. These will disappear 
      once the tube has warmed up fully. The bands will be more noticeable if 
      the dimming control is set to minimum brightness.</P>
      <DIV class=wpimg style="FLOAT: right; WIDTH: 302px"><A 
      href="http://us1.webpublications.com.au/static/images/articles/i305/30504_14mg.jpg"><IMG 
      height=220 alt="Click for larger image" 
      src="30504_14lo.jpg" width=302 
      border=0> </A>
      <DIV class=wpcaption>Fig.8: connect this circuit in series with the 
      inverter if you want to check the operating current. </DIV></DIV>
      <P>With the fluorescent tube driven to full brightness the current drain 
      is around 3.7A at 12V. This means that some 45W is drawn from the battery 
      and so the fluorescent tube drive will be a little less due to losses in 
      the inverter. This is similar to the standard mains fluorescent drive 
      circuitry which uses an iron-cored ballast (inductor) to limit tube 
      current.</P>
      <P>If you wish to check the tube current, use the circuit of Fig.8. This 
      is connected in series with the positive supply to the inverter PC board 
      and uses a 0.1W 5W resistor as a current shunt. The 22kW resistor and 
      100nF capacitor filter the current drawn from the battery so that the 
      multimeter will be able to read the average current.</P>
      <P>The current drawn from the battery is the voltage measured divided by 
      0.1. For 3.7A, the reading will be 370mV across the 100nF capacitor. Note 
      that this current will only be reached after the tube has been lit for a 
      few minutes. </P>
      <P>When fully dimmed, the current will be around 3A or 300mV across the 
      100nF capacitor.</P>
      <P>If the current is substantially different to these two values, check 
      the battery voltage. It should be around 12.3V or more when driving the 
      fluorescent inverter circuit. If it is below 12V, the battery will require 
      charging. Also check that the 1mm gap is present between the core halves 
      of L2. Then check the number of turns.</P>
      <DIV class=wpimg style="WIDTH: 302px"><A 
      href="http://us1.webpublications.com.au/static/images/articles/i305/30504_6mg.jpg"><IMG 
      height=66 alt="Click for larger image" 
      src="30504_6lo.jpg" width=302 
      border=0> </A>
      <DIV class=wpcaption>It's a long narrow PC board, designed to fit inside a 
      standard fluorescent batten. We haven't shown a picture of the finished 
      fluoro batten with lamp because it looks just like a... fluoro batten with 
      lamp!</DIV></DIV>
      <P>If these are correct add more turns to the inductor if the current is 
      too high and remove turns if the current is too low. Remember that it is 
      the impedance of L2 in conjunction with the drive frequency from IC3 which 
      set the overall circuit operating conditions.</P>
      <P>During operation, the heatsinks for Q1 and Q2 will run warm - and the 
      transformer core for T1 will also run warm. Q2's heatsink will also be 
      slightly warmer than that for Q1 since it is close to the heat from T1. 
      </P>
      <P>Inductors L1 and L2 will not be noticeably hotter than the ambient 
      temperature.</P>
      <DIV style="CLEAR: both"></DIV>
      <TABLE class=breakout>
        <TBODY>
        <TR>
          <TD class=breakoutCell>
            <DIV class=breakoutTitle>NOTES AND ERRATA</DIV>
            <P>40W Fluorescent Inverter, September 2002:</B> due to tolerance 
            variations within the L6574 (IC3), it is recommended that the 
            maximum current delivered to the fluorescent tube be adjusted using 
            a trimpot. The 100kW resistor connecting between pin 2 of IC3 and 
            the top of the dimming potentiometer (VR1) should be replaced with a 
            50kW trimpot and series 82kW resistor. The 1.2W resistor between the 
            source of Q4 and ground should be changed to 2.2W to allow the full 
            dimming range available from VR1.</P>
            <P>Using the current measuring setup of Fig.8, the trimpot should be 
            adjusted for the 370mV, corresponding to 3.7A when the dimming pot 
            (VR1) is turned fully clockwise. Note that this adjustment should be 
            made after the inverter has been running for some time and is fully 
            warmed up. Once adjusted, the trimpot and 82kW resistor can be 
            swapped for a single resistor that is the same value as the total 
            series combination.</P>
            <P>When testing the current (using the setup of Fig.8), it is 
            important not to have the 0.1W 5W resistor in series with the supply 
            for any appreciable length of time as the current drawn will begin 
            to increase. To prevent this, short out the 0.1W resistor (with a 
            clip lead) when not making the measurement. Remove the clip lead 
            briefly to make the current measurement.</P>
            <P>In addition, use heavy gauge wire rated at 7.5A or more to 
            connect the inverter to the 12V battery.</P>
            <P>The lower cost MTP3055E Mosfets can be substituted for the 
            STP60NE06 devices used for Q1 and Q2.</P>
            <P>The Dick Smith Electronics D-5375 ferrite core is also suitable 
            for L2 and requires 100 turns of wire (50 turns on each half) 
            instead of the 84 total shown in Fig.6.</P></TD></TR></TBODY></TABLE>
      <DIV style="CLEAR: both"></DIV>
      <TABLE class=breakout>
        <TBODY>
        <TR>
          <TD class=breakoutCell>
            <DIV class=breakoutTitle>Parts List - 12V Fluorescent Light 
            Inverter</DIV>
            <TABLE width=590 border=0>
              <TBODY>
              <TR>
                <TD>1</TD>
                <TD>36/40W fluoro batten with tube</TD>
              <TR>
              <TR>
                <TD>1</TD>
                <TD>PC board, coded 11109021 (340 x 45mm)</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>Powdered iron toroidal core, 28 x 14 x 11 (L1; Jaycar 
                  LO-1244 or equivalent)</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>Ferrite core, 32 x 30 x 30mm (L2; Jaycar LF-1290 or 
                  equivalent)</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>Ferrite toroidal core, 35 x 21 x 13mm (T1; Jaycar LO-1238 
                  or equivalent)</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>16mm 5k<FONT face=Symbol>W</FONT> linear potentiometer 
                  with knob (VR1)</TD></TR>
              <TR>
                <TD>2</TD>
                <TD>M205 fuse clips</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>M205 quick blow 5A fuse (F1)</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>2-way PC-mount screw terminal blocks (Altronics P-2101 or 
                  equivalent)</TD></TR>
              <TR>
                <TD>2</TD>
                <TD>2-way PC-mount screw terminal blocks (Altronics P-0234A or 
                  equivalent)</TD></TR>
              <TR>
                <TD>2</TD>
                <TD>Mini-U TO-220 heatsinks 25 x 30 x 12.5mm</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>150mm length of 0.8mmm tinned copper wire</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>250mm length of 1mm diameter enamelled copper wire</TD></TR>
              <TR>
                <TD>1</TD>
                <TD>15m length of 7.5A-rated (0.75mm