If you are looking for a "varilight" (dimmer) for resistive loads allowing light bulb filament, you will find an infinity. If however you are looking for a drive neon tubes (no filament) you'll be hard pressed to find one: does the searching, we propose to build.
Drives (in English "dimmer") or "varilights (dimmers), you probably know them well: they lower the supply voltage to light the filament of the bulb power to a minimum. Such a filament bulb is actually a strength and drive so far proposed to allow only vary the voltage applied across a resistive load, ie concerned only with incandescent bulbs. But how to adjust the brightness of the fluorescent tubes, neon, more and more popular and so good for lighting fixtures or other household? They contain no filament, therefore are not resistive loads and a classic controller can not order them.
Well, today the L6574 integrated circuit controls the brightness of neon light as if it were an ordinary bulb filament!
Good timing, because one hand, fluorescent tubes are effective, economical in terms of energy and life and now available in warm lights and colored (see Figure 7) and, secondly, no one has so far wanted to deprive themselves of the opportunity to modulate the light intensity.
How does a neon tube 
To light a fluorescent tube neon (the classic 36 W one meter in length for example), you must add two crucial elements, as shown in Figures 1 and 2: the engine and starter. tube (or bulb or envelope) is a true tube glass whose inner surface is lined with a phosphor substance giving it a light color and different qualities. In the tube are two electrodes supplied from outside. The reactor is a solenoid (from the outside it looks like a transformer similar to those powering the spotlights 12 V) consists of a coil of insulated copper wire and sized according to the power of the tube (18 W, 36 W , 60 W and so on).
The starter is a small cylinder with two electrodes to promote the ignition of the tube: in fact, the voltage of 230 V is not sufficient to initiate cold discharge in the gas (the gas used is generally rare neon, precisely) in his glass bulb filled with inert gas (usually argon) is a normally open bimetallic parallel with a capacitor of 5.6 nF , which is fed from the neon tube, between the open terminals of the bimetal arcing occurs (see Figure 3). The heat closes the contact of the bimetal which, being in series with the filaments of the tubes, causes the heating and ionization of the gas across the contact of the bimetal, now closed, the discharge ceases, and therefore the bimetal cooled and the contact opens again; This opening combined with the reactor, which has stored energy, produces a self-induction which is manifested by a high voltage discharge, which promotes an upcoming ionizing discharge in the gas and then igniting the tube .
Another way to light a neon tube is to provide a high voltage of a thousand volts (from a transformer, of course) and is heated filaments and tubes can be supplied very long. This is the method set out Tesla in the 1900s (see Figure 6). Note: If you live near a power plant or if the high voltage cables pass over your home, you can light a neon tube simply by holding it by hand, without having to feed it.
Another way to light the neon tubes to feed them back with an alternating current high frequency fixed. In this case, instead of the starter is mounted a PTC.
tubes and fed perform better and save us the tedious flashing at 50 Hz that you do not fail to deplore (what happens with the tubes at the end of life), but more importantly, with this method, n did not need Nor reactor.
Note: this can be experienced through the tube in close proximity to transmitting antennas (transmitter or repeater radio / television or radio tower or a mobile phone base station). But do not stay too long in these latitudes and especially never look the invisible beam emerging from a transmitting antenna UHF Directive, the risk of retinal damage are high ... well, do not have this experience, we believe his word and run away these unhealthy places!
Figure 1: The reactor is mounted in series with the neon tubes (or fluorescent bulbs) to stabilize and limit the current drawn. Sometimes the entire ignition system is installed in the foundation of the bulb, which makes it quite bulky.
Figure 2: The starter is the device that allows the ignition of the fluorescent lamp. Inside the small glass bulb are two normally open bimetal and a capacitor.
Figure 3: When we fed the neon tube, the contacts close and a voltage spike occurs. 
Figure 4: At the end of this preheating, the contacts open and the twinkling starts. 
Figure 5: Sequence of ignition of a fluorescent tube. The light is produced by an electric discharge passing through the tube filled with gas. These tubes can be bent according to the most diverse fantasies, it does no harm to the operation ... to the great satisfaction of designers and other pub companies (see Figure 7). 
Figure 6: The Serbian-American scientist Nikola Tesla was born in Smiljan in Croatia in 1857 and died in New York in 1943. His most famous invention, the Tesla coil, a transformer is capable of producing electric currents and voltages at very high frequencies. 
Figure 7: Most advertising illuminations come from fluorescent tubes whose efficacy is much higher, energy consumption and much lower life much longer than incandescent bulbs 
Note on the discharge At ambient pressure, the tube current remains very low and it is due to some ions still present in the gas. When the pressure in the tube is small enough (less than 10 mm Hg or 10 mm Hg), the current increases and generates ionizing discharge light filiform connecting the two electrodes. In air, this release has some brightness, but in the presence of other gases it gives different colors: for example, with neon, the color is red with the argon blue-green it is. If we further reduced the pressure, light pervades the entire volume of the tube (glow discharge). The tubes illuminated signs operate on this principle, with different gases depending on the color desired. The luminescence of the tube is due to specific ray emitted by the cathode. These rays do not create only the luminescence of the glass, but also other substances. Eg gypsum (plaster which gives the rock when it is heated to high temperature) emits a reddish glow, zinc sulfide glow green. A small amount of mercury which characterizes the neon lights are used in tanning devices or sterilizers.
The wiring diagram Unlike the old systems at a fixed frequency in which the starter is replaced by a PTC, the L6574 integrated circuit consists of an intelligent controller that we can adjust the brightness of a fluorescent tube using only resistors and capacitors. During all these phases: - preheating of the filaments,
- priming tube, - control the frequency of initiation, - control the frequency of maintenance,
the circuit is powered directly by the sector through a bridge rectifier SR1 (electrical diagram of Figure 9) which rectifies the mains voltage before C13 does not smooth the rectified voltage.
At power up, the circuit is powered by the voltage available at the end of C13 (320 VDC) to Dropping through the two resistors R8 and R9 (which can-shouldered by the zener DZ1-feeding pin 12 with a voltage of 15 V). This is possible since the L6574 consumes very little.
When the circuit is in steady state, through C8, it takes a portion of this square wave on pin 14 for the limit then amplitude DZ1 and apply through DS1 to pin 12 of IC1.
Thus, the function of R8-R9 is solely to supply the voltage to the circuit at power up. The center of the whole system is located inside VCO integrated circuit (see Figure 8) : Its frequency is controlled by the oscillator and modified according to the various phases of starting and ignition of the tube néon.Tout control is based on time and fixed internal reference voltage and, in specific sequences, all phases of startup and control MOSFETs are controlled. See them in detail.
When, during ignition, the supply voltage exceeds the threshold of 15.6 V, with the internal zener connected to pin 12 (see Figure 8), the preheating phase begins, it is to feed both filaments of the tube by means of MOSFET MFT1 MFT2 with a signal- HF (about 60 kHz) determined by the values of C4 and R4-R5-R6. After a delay caused by the value of C3 (about 1.5 s), the operating frequency down to the resonant frequency determined by the circuit consisting of Z1 and C15-C16 (38 kHz). For about 150 ms, the voltage increases across the neon tube, causing the boot. The current control and therefore the brightness is achieved by varying the frequency of the internal VCO. The power stage consists of two MOSFETs connected in a half bridge provides the necessary energy in the form of square wave amplitude equal to the peak line voltage (320 V), the floor consisting of Z1, C14, C15, C16 ... and of course the tube. With internal sequences
predetermined, the L6574 provides a voltage across C7 trigger adequate to control MFT1 which, since its source is not grounded, requires a gate voltage greater than the supply voltage . This tension is precisely provided by C7.
To control the output power, it uses the internal operational amplifier, which corresponds to pins 7-6-5 (see Figure 8). It controls the brightness of the tube by comparing the current flowing through the power stage current-voltage converted through R20-R21, and a reference voltage present on pin 2.
Potentiometer R4 is used to modify the course of an internal comparator connected to the VCO. Thus, by changing the frequency, it also changes brightness.
Note: when turned off, the tube behaves like an open circuit when the gas is ionized, however, a current runs through it (it depends on the characteristics of the tube) With the diode DS2 and resistor R15, the VCO changes the frequency so that it never falls below a certain value determined by the resistor R15.
To avoid that by adjusting the potentiometer R4 at minimum brightness, the tube starts to flash, we connected in parallel with the capacitor C14 two resistors R24-R25, providing a minimum current, and ensuring a bright uniform even when adjusting the potentiometer is at minimum.
Figure 8: Block diagram and pin internal top view of the IC L6574.
Figure 9: Diagram of the drive for neon tubes.
Figure 10a: Diagram of location of the drive components for neon tubes. With this device you can adjust the brightness of each room according to your desires and at the same time you save energy and increase the life of your fluorescent tubes. Power MOSFET pinout STP9NK50Z. 
Figure 10b-1: Drawing to scale 1, double-sided PCB with plated through holes of the plate of drive for neon tubes, solder side. 
Figure 10b-2: Drawing scale 1, the PCB double sided plated through holes of the plate to drive Neon side components. 
Figure 11: Photograph of a prototype of the plate of drive for neon tubes. Look at the two MOSFETs in the top middle, their sole apparent metal-keyed provides a benchmark and those that you find are likely to present a somewhat different, the shoe is completely covered with insulating plastic, as shown in Figure 10a. 
Iist R1 ......... R2 390 k ......... 10 k R3 ......... 10 k
R4 ......... 4,7 k potentiomètre lin. R5 ......... 100
R6 ......... 82 k R7 ......... 10 k R8 ......... 120 k 1/2 W R9 ......... 120 k 1/2 W R10 ........ 10
R11 ........ 47 R12 ........ 22 R13 ........ 22
R14 ........ 100 k
R15 ........ 100 k
R16 ........ 10 k
R17 ........ 1 k
R18 ........ 6,8 k
R19 ........ 6,8 k
R20 ........ 1,2
R21 ........ 1,2
R22 ........ 820 k
R23 ........ 3,9 k
R24 ........ 100 k 1 W
R25 ........ 100 k 1 W
R26 ........ 560 k
R27 ........ 10 2 W
C1 ......... 10 μF électrolytique
C2 ......... 100 nF polyester
......... C3 1 uF polyester
C4 ......... 470 pF ceramic
C5 ......... 100 nF polyester
......... C6 C7 470 nF polyester
......... C8 100 nF polyester
......... 680 pF 2000 V ceramic C9
......... 8.2 nF polyester
C10 ........ 330 nF polyester
C11 ........ C12 4.7 nF polyester
........ 100 nF 400 V polyester
C13 ........ 22 uF 450 V electrolytic
C14 ........ 100 nF 400 V polyester
C15 ........ 2000 V 4.7 nF ceramic C16
........ 2000 V 4.7 nF ceramic C17
........ 10 nF 1000 V ceramic
Z1 ......... self VK1449
Z2 ......... self VK900
DS1 ........ 1N4150
DS2 ........ 1N4150
DS3 ........ 1N4150
DZ1 ........ 15 V zener
RS1 ........ Bridge rectifier 600 V 1 A
IC1 ........ L6574
MFT1 ....... MOSFET STP9NK50Z
MFT2 ....... MOSFET STP9NK50Z
F1 ......... Fine-delayed 400 mA
Note: All resistors are 1 / 4 W, unless otherwise specified.
The safety circuit
The resistors R18-R1-R2-R3 act on pin 8 of integrated circuit IC1 (L6574) by turning off when there is no neon tube, so that the current through the MOSFET output transistor reaches values too large to destroy the transistors.
Off and on again it resets the circuit normal operation.
LED DS3, resistors R17-R19 and capacitor C10 act on pin 9 of integrated circuit IC1 (L6574) by forming a network of protection against high input voltage produced by the neon tube in the phase preheating or if you use very old tubes.
The practical
When you have completed the double-sided PCB with 11b-1 and 2 shows a scale drawing or you your copies, press and solder all three at once pins and the support of the integrated circuit.
Check out these first welds (or short-circuit between tracks or pads or cold solder joints) and assemble all other ingredients starting with the lowest and ending with the most voluminous.
Mount resistors (resistors hold the two big "sugar" to one or two millimeters of the surface), and the zener diodes (attention to the orientation of their rings mark-polarizing), polyester and ceramic capacitors and the electrolytic (note the polarity), the toroidal coil Z2 bridge RS1 (note the polarity), the fuse F1, the two MOSFETs (standing without heatsink, attention orientation of their soles metal: up to the plate), the big self Z1 and finally the three terminals at both poles.
When all this is over and that the welds were tested, get the plate in its plastic case, with two tapping screws (see Figure 14): the control is set to front and impose its button command, the son goes out also by the tube face. From rear lot the 230 V mains protected by a pass-son rubber. You can now insert the chip into the socket (note: Landmark-keyed U to C1).
course, you may prefer to install the plate under the hood of the original neon tube, in which case, you will not have to install assembly in plastic, but be careful that no track circuit comes into contact with a metal piece located in the cap (or cover itself).
As the potentiometer, nothing prevents the remote and have you do in this case his son pass through the conduit plastic electrical installation standard.
Figure 12: Diagram of a connection neon tube. The electrodes of the tube are fed from outside with the reactor connected in series with the choke tube and mounted in parallel. Without these two elements the tube does not light.
Figure 13: If you use our system to adjust the brightness of the fluorescent tube, you do not need a reactor or choke, so after being removed, connect the electrodes of the tube the two terminals with two poles of the plate EN1638.
Figure 14: Possible installation in the plastic housing nonspecific. You'll need to drill (without any difficulty, especially with wood drill tip) on a small side for the potentiometer shaft and son from the neon tube and the other for entering the cord . The plate is fixed to the bottom of the box with 2 self tapping screws. 
trials After eventually installed the deck in its plastic case, try the circuit to be certain of having committed any error. Get a neon tube 18 or 36 W (these are the most common and least expensive). Be careful, the voltage of 230 V can be deadly!
And peaks at 320 V even more. For this setting, you can take an "old" Ceiling neon tube, so as to benefit both carriers support the tube.
Delete the reactor and the choke, as shown in Figures 12 and 13 (you no longer need): disconnect itself every son and realize with the remaining elements (brackets and tubes) and plate circuit of the EN1638 Figure 13. Connect the power cord into a 230 V and the fluorescent tube lights up gradually when you turn the knob. You can unplug the power cord and remove the test circuit. But again, attention to the mains voltage 230 V which is preserved longer in the capacitors! It'll only make the new electrical installation of the ceiling tube neon: you can now order it gradually.
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