Схема соединения люминесцентных ламп: Схемы подключения люминесцентных ламп: обзор популярных методов

Подключение люминесцентных ламп: 75 фото вариантов подсоединения

Люминесцентные лампы чаще всего используются в производственных условиях, в магазинах, теплицах  и на складах. Для дома их стали покупать только с появлением образцов, имеющих цоколь Е27. При всей экономичности создать оптимальный режим их эксплуатации без дополнительных устройств достаточно сложно, например, когда речь идет о параллельном подключении люминесцентных ламп. В особенностях этого процесса мы и попытаемся разобраться.

Принцип работы

Лампа представляет собой колбу, в которую закачан инертный газ аргон с парами ртути. В конструкции имеется анод и катод. Между ними возникает разряд, вследствие чего происходит загорание в момент пуска.

Разогретые пары ртути начинают излучать инфракрасное свечение, которое не доступно глазу человека. Чтобы перевести свечение в необходимый диапазон, стенки колбы покрывают специальным люминофором. Он активизируется и начинает излучать подходящий глазу свет.

Однако испарение ртутных паров требует иного напряжения, нежели имеется в обычной сети. Способы подключения люминесцентных ламп более сложные.

Дополнительно к электродам запускаются установленные дополнительно электронные и электромагнитные ПРА. Они стимулируют появление нужного скачка напряжения и гарантируют отсутствие неконтролируемого его роста в процессе работы.

Использование стартеров

Для эксплуатации ламп с электромагнитным типом ПРА требуется стартер. Он обеспечивает замыкание в цепи. В результате электроды разогреваются, и происходит зажигание. После нагрева до требуемого уровня цепь размыкается, аргоновый промежуток пробивается.

А вот дроссель в момент замыкания электродов ограничивает ток до нужного уровня, способствует генерированию импульса напряжения для пробоя, а также является важным фактором стабильности горения разряда.

Чтобы подключить лампу надо к ее входу параллельно законтачить стартер. Для этого используют только один штырь на каждой стороне колбы. К оставшимся контактам лампы присоединяется дроссель. Параллельно надо подключить и конденсатор, который компенсирует реактивную мощность и уменьшит помехи.

На фото подключения люминесцентных ламп можно увидеть схему с электромагнитным балластом. У нее существует множество недостатков:

• долгое зажигание;
• пульсирование;
• наличие шумов;
• отсутствие пуска при низких температурах.

Поэтому использование моделей с электромагнитными ПРА сейчас ограничено. Рекомендуется использовать более эффективные устройства.

Работа без стартера

Подключение люминесцентных ламп без стартера производится при помощи пускорегулирующей аппаратуры электронного типа. Поскольку такая лампа является источником освещения с отрицательным показателем сопротивления, то ЭПРА играет роль преобразователя. Высокие токи могут испортить светильник, поэтому пускорегулирующее устройство ограничивает напряжение и сохраняет его в требуемом диапазоне.

Данная схема имеет достоинства. Во-первых, лампочка не мерцает. Во-вторых, шум в процессе работы отсутствует. В-третьих, осветительный прибор остается в рабочем состоянии намного дольше. В-четвертых, ЭПРА более компактна по сравнению с дросселем.

Электронный балласт – это блок с клеммами. Внутри корпуса есть плата. Компактность прибора позволяет его применять в любых по размеру светильниках. При выборе ЭПРА можно подобрать устройство под нужное число ламп и их мощность.

Первый и второй контакты балласта надо подсоединить паре выходов лампы, а третий и четвертый – ко второй паре. Затем на вход надо подать напряжение, лампа будет функционировать.

Подключение на две лампы

Чтобы произвести подключение двух люминесцентных ламп, необходимо ко всем линейным светильникам подсоединить параллельно устройство стартера.

Контакт происходит на два штыря, каждый из которых находится на разных сторонах колбы. Остальные контакты используются для присоединения индукционного дросселя. На них будет подаваться электропитание.

Параллельное подключение конденсатора относительно контактов запитывающего действия позволяет влиять на реактивную мощность и снижать уровень помех.

Использование пускорегулирующих приспособлений позволяет эффективно эксплуатировать люминесцентные светильники в помещениях разного типа. При этом обеспечивается надежность и долговечность работы, компенсируются скачки напряжения.

Современное оборудование позволяет облегчить подключение люминесцентной лампы к выключателю, однако работы связанные с этой задачей требуют от исполнителей электротехнических навыков.

Фото подключения люминесцентных ламп

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90000 How Fluorescent Lamp Lights Work 90001 90002 The fundamental means for conversion of electrical energy into radiant energy in a fluorescent lamp relies on inelastic scattering of electrons when an incident electron collides with an atom in the gas. 90003 90002 If the (incident) free electron has enough kinetic energy, it transfers energy to the atom’s outer electron, causing that electron to temporarily jump up to a higher energy level. The collision is ‘inelastic’ because a loss of kinetic energy occurs.90003 90002 This higher energy state is unstable, and the atom will emit an ultraviolet photon as the atom’s electron reverts to a lower, more stable, energy level. 90003 90002 Most of the photons that are released from the mercury atoms have wavelengths in the ultraviolet (UV) region of the spectrum, predominantly at wavelengths of 253.7 and 185 nanometres (nm). These are not visible to the human eye, so they must be converted into visible light. This is done by making use of fluorescence. 90003 90002 Ultraviolet photons are absorbed by electrons in the atoms of the lamp’s interior fluorescent coating, causing a similar energy jump, then drop, with the emission of a further photon.The photon that is emitted from this second interaction has lower energy than the one that caused it. 90003 90002 The chemicals that make up the phosphor are chosen so that these emitted photons are at wavelengths visible to the human eye. The difference in energy between the absorbed ultra-violet photon and the emitted visible light photon goes toward heating up the 90013 phosphor coating 90014. 90003 90002 When the light is turned on, the electric power heats up the cathode enough for it to emit electrons (thermionic emission).These electrons collide with and ionize noble gas atoms inside the bulb surrounding the filament to form a plasma by the process of impact ionization. As a result of avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the fluorescent lamp. 90003 90002 The fill gas helps determine the operating electrical characteristics of the lamp but does not give off light itself. The fill gas effectively increases the distance that electrons travel through the tube, which allows an electron a greater chance of interacting with a mercury atom.90003 90002 Argon atoms, excited to a metastable state by the impact of an electron, can impart this energy to a neutral mercury atom and ionize it, described as the 90013 Penning effect 90014. 90003 90002 This has the benefit of lowering the breakdown and operating voltage of the fluorescent lamp, compared to other possible fill gases such as krypton. 90003.90000 How fluorescent lamps work 90001 How fluorescent lamps work 90002 90003 90004 90005 90006 90007 90006 90009 90010 90011 90012 90003 90004 90015 Elliott Sound Products 90016 90006 90007 90015 How Fluorescent Lamps Work 90016 90006 90009 90023 90010 90025 © 2007 Rod Elliott (ESP) 90026 90027 90028 90015 Lamps & Energy Index 90016 90031 90032 90015 Main Index 90016 90031 90027 90015 Contents 90016 90027 90015 1 Introduction 90016 90025 The article Traditional Fluorescent Tube Lamps & Their Alternatives looks at the operation of fluorescent lamps in fairly simple terms, but here we will examine the lamps, their ballasts (both ‘traditional’ magnetic and electronic types) and delve a little deeper into their inner workings.There are alternative ballast schemes used (such as the ‘lead / lag’ arrangement) and this is shown in the previous article. It’s not covered here, because this is about how they work, rather than a discussion of the way fittings are wired. 90026 90025 The way a fluorescent lamp works is very different from a simple incandescent lamp, and modern fluorescents (especially the compact fluorescent lamp, or CFL) make use of electronic ballasts to regulate the voltage across the lamp, and the current through it.When first started, it is necessary to provide a significantly higher voltage than normal to cause the internal arc to strike, and once started, the current must be limited to a safe value for the tube. 90026 90025 This article shows some of the ways these goals are achieved, starting from the basic inductive ballast that has been the mainstay of fluorescent lamp production for many years. 90026 90025 Note that the waveforms shown here are a combination of simulations and actual measurements.Where necessary, the simulated waveforms are corrected to match those measured. The reason for this approach is simple … the simulator can not represent a negative impedance load with appropriate strike voltages and other characteristics that a fluorescent tube presents. Likewise, it is very difficult (and potentially lethal) to attempt to capture all the voltages and currents that exist in real fluorescent lamp circuits. 90026 90025 While the approach taken does introduce some minor errors in the waveforms shown, these are relatively insignificant, and the end result is well within any traditional manufacturing tolerance for ballasts, lamps and other components.90026 90027 90015 2 Inductive Ballast 90016 90025 For the inductive ballast explanations, I used an old ‘compact’ fluorescent lamp, which just happens to be ideal for testing. Although it still works, light output is somewhat below what it should be, but that only changes some of the measured values ​​a little. The principles are not changed at all. 90026 90025 The lamp itself has the following characteristics … 90026 90059 90002 90003 90004 Tube Diameter 90006 90004 11.3mm (non-standard) 90006 90009 90003 90004 Length 90006 90004 533 mm (21 «) 90006 90009 90003 90004 Filament Resistance (cold) 90006 90004 12.8 Ohms 90006 90009 90003 90004 Filament Resistance (hot) 90006 90004 23 Ohms 90006 90009 90003 90004 Ballast Resistance 90006 90004 105 Ohms 90006 90009 90003 90004 Ballast Inductance 90006 90004 2.11 H 90006 90009 90003 90004 Starter 90006 90004 Conventional Neon 90006 90009 90003 90004 Starter Capacitor 90006 90004 1.2 nF 90006 90009 90010 90110 90025 The diameter of fluorescent tubes is commonly referred to as T8 (for example). This means that the diameter is 8 x 1/8 «, which is 1» (25.4 mm). Early tubes were T12 (1½ «or 38mm diameter), but these were reduced in size to T8 when the (then) ‘new’ high efficiency types were introduced. A standard 4 ‘tube (1,200mm) used to be rated at 40W, but their replacements were 36W and light output was improved. The latest incarnation is the T5 (16mm diameter), which uses a smaller pin spacing and a different tombstone fitting. They are also shorter (1,163mm) and will not fit into a standard luminaire designed for earlier tubes. 90026 90025 In the case of my test unit, the tube diameter is much smaller than normal because the lamp is designated as a compact, so it is folded to reduce the overall length.Filament resistance is mentioned because it will be referred to later in this article. The schematic is shown below, and is conventional in all respects. 90026 90025 90031 Figure 1 — Fluorescent Lamp Schematic 90026 90025 The inductor is the ballast, and is actually a far more important component that it might appear. It not only limits the maximum tube current, but is used to generate the high voltage pulses needed to start the plasma arc within the tube. The fluorescent tube tube itself has a heater at each end, a small quantity of mercury and an inert gas (usually argon).The wall of the tube is coated with phosphors that emit visible light when excited by the intense short-wave ultra-violet light emitted by the mercury arc discharge. The extra capacitor (C2) is for power factor correction — more on this later. 90026 90025 The small bulb is the starter. A bimetallic strip is sealed into a glass envelope, with (usually) neon gas inside. When power is applied, the voltage is more than enough to cause an arc in the neon starter, but nowhere near enough to start the arc in the lamp itself.The heat from the neon arc causes the bimetallic strip to bend, until it closes the contacts. The arc in the neon starter then stops, and the mains is connected through the ballast and the filaments at each end of the tube, via the starter switch. 90026 90025 Once the starter has no arc (or glow), the bimetallic strip cools, and the switch opens after about a second or so. The interruption of current through the inductor causes a voltage ‘flyback’ — a high voltage pulse that will (hopefully) start the arc in the tube.If the arc does not start the first time, the process repeats until it does. This is why standard fluorescent lamps flicker a few times when switched on. The filaments are heaters that act as cathodes (emitters of electrons), and are needed to ensure that there is enough heat to vaporise the mercury, and to get a good electron flow to energise the plasma. Once the lamp is working normally, the electron flow is enough to maintain the filaments at an acceptable operating temperature. Both filaments act as cathodes and anodes alternately, because the polarity reverses 50 (or 60) times a second.90026 90025 The plasma has an interesting characteristic … negative resistance! Once the arc starts, a higher operating current causes the resistance to fall, and less voltage appears across the tube. If this were allowed to continue, the tube would destroy itself very quickly. The ballast prevents this from happening because it introduces a series impedance to limit the current. Resistance will not work, because it is too wasteful, and provides no energy storage to generate a flyback voltage spike to re-strike the arc with each polarity reversal.90026 90025 90031 Figure 2 — Operating Waveforms 90026 90025 In Figure 2, you can see that when the tube current (green trace) is at the maximum, the voltage (red trace) across the tube is a minimum. You can see the effect just after each voltage spike. As current goes up, the voltage falls (for this tube, the minimum was ± 126V). The spike at the zero crossing point of the current waveform is generated by the ballast, and it is this that re-ignites the arc for each half-cycle of the applied mains.Figure 3 shows the voltage across the ballast — the rapid transitions correspond to the spikes applied to the lamp, and occur near the peak of the voltage, where the current is interrupted as it passes through zero. 90026 90025 90031 Figure 3 — Voltage Across & Current Through Ballast 90026 90025 The voltage waveform across the ballast is essentially the difference between the applied mains voltage and that across the tube. For 120V operation, the voltage is obviously less, but the tube still needs somewhere between 300-400V to strike (or re-strike) the arc, so the ballast has to be able to make up the difference with a flyback pulse at each zero -crossing of current.I do not have a 120V fluorescent lamp or ballast available, so I’m unable to provide full details. That fluorescent lamps even work at all with 120V is somewhat remarkable, but it’s easy to see why electronic ballasts are so popular in the US. Many ballasts for 120V countries use an auto-transformer ‘ballast’ that increases the available voltage and acts as a current limiter. 90026 90027 90015 3 System Losses 90016 90025 There are several losses in the system, with the ballast being one of the major contributors.The ballast used for my tests has a DC resistance of 105 Ohms, so wastes almost 7W. The loss is actually higher, because the steel laminations get hot very quickly, so ‘iron loss’ is considerable. This can only be reduced by using better quality steel and thinner laminations. Both will add considerably to the cost. 90026 90025 Each filament has a hot resistance of 23 Ohms, and a voltage of almost 6V is present across each filament when the lamp is operating. Remember that when running, the end of the filament that goes to the starter is disconnected (except for the very small capacitance across the starter).The voltage measured is a gradient caused by the plasma current, and each filament dissipates about 1.5W (3W total). Just in these components, the fluorescent lamp wastes 10W of the applied power as heat (7W for the ballast, 3W for the filaments). 90026 90025 While the ballast waste can be lowered with a higher quality unit, the filament loss is necessary for the lamp to function. This applies with all fluorescent lamps except specialised cold cathode types, but they require an equally specialised electronic ballast.CCFL (cold cathode fluorescent lamps) are (were) most commonly found in LCD monitors and TV sets but are now replaced by LEDs in new models. 90026 90025 There is another loss which is not seen or even paid for by the user. This loss is the result of the poor power factor of fluorescent lamps, and this is caused by the predominantly inductive load. The inductive load causes a lagging power factor, where the maximum current occurs after the maximum voltage. You can also consider it as a point where the load (the lamp and inductor) actually return some power to the supply.For the electricity supplier, this means that transformers, cables and alternators have to be capable of more current than should be the case. This becomes very costly when a great many loads have a poor power factor. 90026 90025 90031 Figure 4 — Voltage Vs. Current, Uncorrected and Corrected 90026 90025 In Figure 4, you can see that the uncorrected current waveform has visible distortion near the zero crossing point. As you can also see, the RMS current is also significantly higher than the power rating would indicate.Reactive loads have different power and VA ratings, but for a resistive (or non-reactive) load they are the same. 90026 90025 In this case, the current without C2 is 256mA, and when C2 is added it drops to 162mA. At an applied voltage of 240V, this means that … 90026 90059 90002 90003 90004 Uncompensated 90006 90004 Total Power = 38W 90006 90009 90003 90163 90004 VA = 61.4 90006 90004 Power factor = 0.62 90006 90009 90003 90004 Compensated 90006 90004 Total Power = 38W 90006 90009 90003 90163 90004 VA = 38.9 90006 90004 Power factor = 0.97 90006 90009 90010 90110 90025 Power factor can be calculated using the phase delay or by dividing actual power by VA (Volts * Amps). For phase angle, the current lags the voltage by 57.4 °, and power factor is calculated by taking the cosine of the phase angle — 0.53 in this case. The figures are different, because the current waveform is not a pure sinewave — it has distortion. Adding the capacitor shifts the phase of the distortion so the compensated current waveform gets a flat top (somewhat like an amplifier clipping).Although this does introduce harmonics into the mains system, the effects are nowhere near as bad as the uncompensated circuit as evidenced by the corrected power factor. Adding a capacitor of the correct value to a purely inductive circuit (with no waveform distortion) will give a power factor of unity — the ideal. 90026 90002 90003 90188 90189 90006 90004 Note that using the cosine of the phase angle (CosΦ) is a shortcut, and can 90192 only 90193 be used when both voltage and current are sinewaves.It does not work at all for highly distorted waveforms such as those produced by electronic loads, and will give an incorrect answer for inductive loads that include distortion (such as fluorescent lamps). You will 90192 always 90193 get the right answer if you divide real power by VA. 90006 90009 90010 90025 There are also ‘quick start’ and starterless ballasts available. These are beyond the scope of this article, which is intended to describe the basic principles rather than an in-depth coverage of every fluorescent lighting ballast available.90026 90027 90015 4 Electronic Ballasts 90016 90025 Electronic ballasts are becoming far more common, because they can be made to be more efficient than a typical magnetic ballast, and they require far less material. This makes them cheaper (to make, though not necessarily for you to buy) than fluorescent lamps using a conventional ballast. Compact fluorescent lamps (CFLs) in particular now all use an electronic ballast, and it is commonly supplied with the lamp itself. Although convenient, this is a dreadful waste of resources, because of all the electronic parts that are simply thrown away when the lamp fails.T5 tubes are now becoming the standard for fluorescent lighting, and for maximum life an electronic ballast is mandatory. 90026 90025 To some extent, the efficiency improvement over a magnetic ballast may be an illusion — at least in part. Because they are much lighter, there are real and definite savings in transportation costs, but magnetic ballasts can be made to be just as efficient as an electronic version — perhaps even more so. Be that as it may, the swing to electronic ballasts can not be stopped now, and as the price comes down usage will continue to increase.Electronic ballasts have some other advantages too, and these will be discussed later. 90026 90025 A (more or less) typical circuit diagram of an electronic ballast as used in a CFL is shown below. Those used for conventional fluorescent lamps will be very similar, but will generally use upgraded components. While the electronics in a CFL may only have to last 15,000 hours, a fixed electronic ballast will be expected to last perhaps 100,000 hours or more (over 10 years continuous operation).In reality, an electronic ballast should be able to last as long as its magnetic counterpart, so a 40 year lifespan is not as silly as it may sound. 90026 90025 90031 Figure 5 — Electronic Ballast Schematic [2] 90026 90025 The schematic in Figure 5 is a slightly simplified version of that shown in the Infineon data sheet. It is fully power factor corrected, and has protection to detect faulty (or missing) lamps. A characteristic failure mode of fluorescent tubes is ‘rectification’, where one filament (cathode) becomes significantly weaker than the other.If not detected, the DC offset will cause the switching devices to fail, rendering the ballast useless (it is highly unlikely that anyone will repair them when they break down). 90026 90025 The electronic ballast does have some real advantages over the magnetic version. Because the arc will fully extinguish in around 1ms, by using a higher frequency than the 50 or 60Hz mains, the arc will remain. It does not need to be re-struck, but simply reverses direction [1]. In addition, light output is increased by around 10% above 20kHz, so the luminous efficacy is improved.90026 90025 Until such time as all of these electronic ballasts are power factor corrected, they will cause problems with distribution. Unfortunately, in many countries there is no requirement for low power (typically less than 75W) appliances to have power factor correction, but given the proliferation of CFLs and electronic ballasts in conventional fluorescent lamps this will have to change. Since lighting is used in every household, the problems of uncorrected power factor will get out of hand if something is not done.90026 90025 Unlike a magnetic (inductor) ballast, an electronic ballast can not be power factor corrected by simply adding a capacitor. As seen in the diagram above (although it may not be immediately apparent), there is only a very small capacitor of 220nF across the output of the input bridge rectifier. The first MOSFET operates as a boost converter, and switches right through each half cycle. By doing so, the RMS current drawn from the mains is maintained in phase with the voltage, and the current waveform is approximately sinusoidal.This gives a very good power factor — better than 0.9 is possible. In order to prevent the high speed switching pulses from getting back into the mains supply, extensive filtering is needed, as indicated by the EMI (electro-magnetic interference) filter at the input. 90026 90025 A somewhat simpler scheme is used for compact fluorescent lamps (CFLs), as the circuitry is designed to be thrown away. Personally, I consider this to be wanton waste, and hope that it does not continue (or at least recycling is put in place to recover as much as possible).A reasonably typical CFL inverter is shown below … 90026 90025 90031 Figure 6 — Typical CFL Electronic Ballast Schematic 90026 90025 I say «reasonably typical» because there are wide variations in the actual circuits. There are dedicated MOSFET driver ICs available, but most of the cheap (consumer grade) CFLs will use a variation of the above. Note that the 0.47 Ohm resistor shown at the input is usually a fusible resistor, and it is used a a fuse first and foremost. Why not use a real fuse? Resistors are cheaper.Most of the parts will be selected to survive for the designated life of the lamp, so best design practices are typically ignored if a lower rated (and cheaper) part can be expected to survive for 10,000 hours or so. 90026 90025 The transformer (T1) is there to provide feedback to the transistors, and generates the base current needed to ensure reliable switching. The cycle is initiated by the DIAC — a bidirectional device that has a sharp transition from the non-conducting to conducting state.Because it shows a characteristic very similar to a negative impedance device it is a common part in light dimmers, fluorescent ballasts and even strobe lights. For more information, click here for a DIAC tutorial. 90026 90025 Please note that the circuits shown above are for information only, and must not be built as shown. Some components require very specific ratings, transformers and inductors are critical. There is nothing inherently wrong with the circuits, they just lack all the information you need to be able to construct them.This is about how these things work, not how to build them. 90026 90027 90015 5 Power Factor 90016 90025 Power factor is not well understood by most electronics enthusiasts, and this is quite understandable because there is little call for it in general electronics circuits. There are aspects of power factor that are not even understood by many engineers, who should know better. When non-sinusoidal current waveforms are created, even many engineers will do a double-take, because they may not be used to dealing with electronic loads.I shall cover both cases here, and also intend to show both passive and active power factor correction techniques. While passive PFC (power factor correction) has the appeal of simplicity, it actually works out to be more expensive because of the large inductor needed. Active PFC appears complex (and it really is if you have to design it), but once designed uses relatively cheap components. 90026 90025 The simplest case is where a load is inductive. This applies to many electrical machines, including motors, transformers and (of course) fluorescent lighting ballasts (magnetic types).When a motor or transformer is fully loaded, it appears as a resistive load, and has an excellent PF. At light loadings, the same part appears inductive, and this causes the current to lag behind the voltage. Where the load operates in this mode for the majority of its working life, it is necessary to apply correction to return the PF to as close to unity as possible. 90026 90025 The power factor of a resistive load is 90192 always 90193 unity — it is perfect. Every volt and every amp is used to generate heat.Common examples are electric heaters, toasters, kettles and incandescent light bulbs. Not all loads are resistive though so let’s look at a typical example (but simplified for ease of description and understanding). 90026 90025 An electric machine normally runs at half load, but might need the full power at start-up or to be able to handle transient loads. This could be a motor or a transformer — being two of the most common electric machines in use (a fluorescent lamp with magnetic ballast is slightly more complex).In each case, the inductive and resistive components of the load will be equal (for half power), and the voltage, current and power waveforms look like this … 90026 90025 90031 Figure 7 — Electric Machine at Half Power 90026 90025 As expected, when the resistive and inductive components are equal, there is a 45 ° phase shift, with the current lagging behind the voltage (lagging power factor). The applied voltage is 240V, the resistive portion of the load is 120 Ohms, inductive reactance is also 120 Ohms, and the power is 240W.We 90192 should 90193 draw 1A from the mains (240V x 1A = 240W), but instead draw 1.414A. The additional current has to be supplied, but is completely wasted. Well, this is not strictly true — it is returned to the supply grid. If many loads do the same thing though, then it is simply dissipated as heat in the transformers, transmission lines and power station alternators. Very few real loads are capacitive, so a capacitor is added to the circuit. 90026 90025 With a 45 ° phase shift, the power factor is 0.707, and we are drawing 1.42A from the mains instead of 1A. To restore the current so that it is in phase with the voltage, we need to add a capacitor to the circuit. A capacitor is effectively the opposite of an inductor, and (by itself) will create a leading PF — the current will occur before the voltage. By adding a capacitor of the right value to the circuit, the power factor can be restored to unity, resulting in a significant reduction in the current drawn from the mains. For this example, 13uF is almost perfect, but even 10uF will reduce the lagging phase shift to 14.2 °, and this raises the power factor to 0.96 — generally considered to be as close to perfect as ever needed. 90026 90025 The whole process is somewhat counter-intuitive. That a load may draw more current then it should is easy enough to understand, but that drawing more current again through a capacitor will reduce the mains current does not appear to make any sense. It’s all to do with the relative phase of the two currents, and it really does work. Our power system would be in dire straights if it did not.90026 90025 90031 Figure 8 — Fluorescent Light During Normal Operation 90026 90025 The somewhat simplified diagram above shows the voltage and current waveforms of a fluorescent lamp. The simplification is because simulators do not include non-linear negative resistance loads, but the basic principle (and the resulting waveforms) are not materially affected. As you can see, the current waveform is slightly distorted, and this affects the waveform after compensation is applied. In effect, the harmonics generated by the distortion are shifted in phase, so the final current waveform looks like a clipped sinewave.Power factor is very good after compensation though, at 0.98 — an excellent result. 90026 90025 Uncompensated, the current drawn is 276.5mA (giving a power factor of 0.57), and after compensation, this drops to 159.5mA. Power in the load (the lamp itself) is 29.8W, and the resistive component of the ballast (R1) dissipates 7.8W — this is wasted as heat. All wasted heat reduces overall efficiency, but this is unavoidable because real components have real losses. 90026 90025 Things get a lot worse when a non-linear (electronic) load is used.Figure 9 shows the equivalent circuit and waveforms — current is drawn only at the peak of the applied voltage. While this current is in phase with the voltage, power factor is dreadful because the current waveform is nothing like a sinewave. The abrupt current peaks have a comparatively high RMS value, but the power supplied and delivered to the load is a great deal less. 90026 90025 90031 Figure 9 — Electronic Load Power Waveforms 90026 90025 The corrected current is not shown, for the simple reason that significant additional components are needed to correct the waveform.Unlike the case where the load current is (or is close to) a sinewave, just adding a capacitor will not achieve anything useful. The current spikes are such that they can only be removed by using a filter, designed to pass the mains frequency only. As shown, the current is 296mA, but as is evident, the peak value is almost 2A. The load dissipates 28W, but the ‘apparent power’ (VA) is 71.4VA. This gives a power factor of 0.39 — very poor indeed. In case you wondered where the 1W difference between the source and load disappeared to, that is lost in the diodes.90026 90025 By adding a filter (passive PFC) consisting of an inductor and a couple of capacitors this can be improved, but the requirement for a relatively large inductance adds considerable weight and cost. One Henry is about as small as you can use for the load’s power rating, and although a larger value will work better, it will also be larger again — as well as having higher losses. For these reasons, passive PFC is not commonly used with switchmode power supplies. 90026 90025 90031 Figure 10 — Passive Power Factor Correction 90026 90025 By adding an inductor and capacitor as shown, the power factor is improved quite dramatically.The current waveform is still not very good, but is far better than the circuit with no correction at all. The RMS current is reduced from 296mA to 136mA, giving 32.6VA. Load power is 29W, so the power factor is now 0.88 which is far more respectable. As in Figure 9, the electronics are considered essentially lossless. Needless to say this is not the case, but the discussion is PFC rather than circuit losses. 90026 90025 The inductor (L1) is a relatively large component, and because of this will be comparatively expensive.In order to reduce cost and weight, an electronic PFC circuit is a better proposition, and it will also be more efficient. Lower power losses mean less wasted heat and cooler electronics. 90026 90025 90031 Figure 11 — Active Power Factor Correction Circuit 90026 90025 The scheme shown here is almost identical to that in Figure 5, but is simplified so it can be understood more easily. The incoming mains passes through the EMI filter, consisting of C1 and L1. It then goes to a bridge rectifier, but instead of a large electrolytic cap, a 220nF (C2) capacitor is all that’s needed.The output is pulsating DC, and varies from almost zero to the full peak voltage (340V for a 240V RMS supply). This then passes to a very clever switchmode boost converter — L2, Q1 and D5. This boosts whatever instantaneous voltage is present at its input to the peak voltage — in this case the simulated converter stabilised at 446V (somewhat higher than normally used). 90026 90025 The on and off times are carefully controlled to maintain a current that is proportional to the incoming AC waveform, so the duty cycle (on-off ratio) constantly varies to maintain the correct boosted voltage and proportional current.D6 is included to allow the main filter cap (C3) to charge quickly from the mains, and also provides a ‘top-up’ charge to the cap. This allows some simplification in the control circuit. 90026 90025 The output voltage of the boost converter is (usually) regulated, but the regulation does not have to be wonderful, which again simplifies the circuit to an extent. In the circuit shown in Figure 5, you see that the boost converter’s inductor (1.58mH) has a secondary winding. This is used to tell the controller IC when the correct current has been reached.The simplified circuit shown in Figure 11 does not use this — the switching period is fixed (the circuit was simulated so I could produce the current waveform shown below). While this simplified version is not quite as good as the ‘real thing’, it does work rather well — in the simulator at least. 90026 90025 90031 Figure 12 — Active Power Factor Correction Waveforms 90026 90025 As you can see, the current waveform is rather distorted, but the measured performance from the simulator is quite impressive despite its relative simplicity.With 60W in the load (the ballast and fluorescent lamp), actual mains power is 61W (diode losses as before), and with 266mA mains current, it draws 64VA. Power factor is therefore 0.94 — a very satisfactory result indeed. This is significantly better than the passive PFC scheme, and this is to be expected. All analysis that I have seen indicates that an active PFC circuit will outperform a passive circuit, both in terms of overall efficiency and power factor. The inductors are small (electrically and physically), and losses will be much lower than those in any passive PFC circuit.90026 90025 In case you were wondering, the lamp power is double that of the two previous examples because of the boost converter’s higher than desired output voltage. I was most reluctant to spend a lot of time trying to match the power levels, and my simplified version has no regulation. Getting the simulation for the switchmode converter to run happily was a challenge, and simulations take a long time to run because of the high frequency switching. 90026 90025 It is now fairly standard that the waveform distortion is quoted as THD (total harmonic distortion), which in the case of the active PFC circuit is 11.7%. Make of this what you will. 90026 90027 90015 6 Temperature 90016 90025 One thing that is fairly critical for proper operation of all mercury arc fluorescent lamps is temperature. There is a relatively narrow band above and below which the arc is diminished, resulting in lower than expected light output. When a tube is cold, there is less mercury vapour available, so the arc can not reach full strength because there are not enough mercury molecules available to maintain the discharge at the desired level.90026 90025 When the temperature is too high, the vapour pressure increases, increasing the arc’s effective impedance, and again reducing the discharge current. For most compact lamps (and probably most standard fluorescent lamps as well), the tube should be at around 40 ° C for maximum light output. At 0 ° C, light output is only 40% — a very dim lamp indeed. Higher temperatures are not as drastic, but a lamp that runs too hot will still be down by a significant amount. 90026 90025 90031 Figure 13 — Light Output vs.Temperature 90026 90025 As the temperature approaches -38.83 ° C, light output ceases altogether. This is the temperature at which mercury freezes, so there can be no mercury vapour to support the arc and emit UV radiation. In addition, as the temperature decreases, the voltage needed to strike the arc increases, and at 0 ° C the lamp will need about 40% more voltage to strike, compared to the strike voltage at normal ambient temperatures. 90026 90025 In many parts of the world, 0 ° C (or less) 90192 is 90193 a normal ambient temperature for many months of the year, so the lamp will be harder to start and will have low output until the tube heats up a little .In such climates, the tube should be enclosed to protect it from wind that may reduce the temperature and light output significantly. 90026 90313 90003 90315 Relative Light Output (RLO) [3] 90316 90009 90003 90004 90015 Ambient Temp 90016 90006 90004 90015 Open Fixture 90016 90006 90004 90015 Closed Fixture * 90016 90006 90009 90003 90004 -10 ° C 90006 90004 25% 90006 90004 50% 90006 90009 90003 90004 0 ° C 90006 90004 50% 90006 90004 80% 90006 90009 90003 90004 10 ° C 90006 90004 80% 90006 90004 100% 90006 90009 90003 90004 25 ° C 90006 90004 100% 90006 90004 98% 90006 90009 90010 Light Output vs.Ambient Temperature 90059 * Note — a closed fixture provides a + 10 ° C rise over ambient 90110 90025 Like all material on the topic, there are variances in the way the material is presented and different tube types may have substantial variations one from another. The figures are largely in agreement with the above graph, but the small note assumes that the stated temperatures are at thermal equilibrium. This may take some time to stabilise, so initial light output when the lamp is first switched on will be the same for open and closed fixtures.Since the fixture volume with respect to the lamp is not quoted, there will be large variations if the housing is larger or smaller than the (unstated) values ​​used for the table. 90026 90027 90015 References 90016 90031 90373 90374 Electronic Ballast for Fluorescent Lamps, An Undergraduate Instructional Module — Jinghai Zhou, Virginia Polytechnic Institute and State University 90375 90374 ICB1FL02G Smart Ballast Control IC for Fluorescent Lamp Ballasts, Datasheet Version 1.2, February 2006, Infineon Technologies AG 90375 90374 Cold Temperature Operation of Fluorescent Systems (Sylvania) 90375 90380 90027 90027 90383 90015 Lamps & Energy Index 90016 90031 90387 90015 Main Index 90016 90390 90003 90004 90015 Copyright Notice.90016 This article, including but not limited to all text and diagrams, is the intellectual property of Rod Elliott, and is Copyright © 2007. Reproduction or re-publication by any means whatsoever, whether electronic, mechanical or electro- mechanical, is strictly prohibited under International Copyright laws. The author (Rod Elliott) grants the reader the right to use this information for personal use only, and further allows that one (1) copy may be made for reference. Commercial use is prohibited without express written authorisation from Rod Elliott.90006 90009 90010 Page created and copyright © June 2007. 90031 .90000 Start it Up — How Fluorescent Lamps Work 90001 90002 The classic fluorescent lamp design, which has fallen mostly by the wayside, used a special starter switch mechanism to light up the tube. You can see how this system works in the diagram below. 90003 90002 When the lamp first turns on, the path of least resistance is through the bypass circuit, and across the 90005 starter switch 90006. In this circuit, the current passes through the electrodes on both ends of the tube.These electrodes are simple 90005 filaments 90006, like you would find in an incandescent light bulb. When the current runs through the bypass circuit, electricity heats up the filaments. This boils off electrons from the metal surface, sending them into the gas tube, ionizing the gas. 90003 90002 At the same time, the electrical current sets off an interesting sequence of events in the starter switch. The conventional starter switch is a small discharge bulb, containing neon or some other gas.The bulb has two electrodes positioned right next to each other. When electricity is initially passed through the bypass circuit, an 90005 electrical arc 90006 (essentially, a flow of charged particles) jumps between these electrodes to make a connection. This arc lights the bulb in the same way a larger arc lights a fluorescent bulb. 90003 90002 One of the electrodes is a 90005 bimetallic strip 90006 that bends when it is heated. The small amount of heat from the lit bulb bends the bimetallic strip so it makes contact with the other electrode.With the two electrodes touching each other, the current does not need to jump as an arc anymore. Consequently, there are no charged particles flowing through the gas, and the light goes out. Without the heat from the light, the bimetallic strip cools, bending away from the other electrode. This opens the circuit. 90003 90002 By the time this happens, the filaments have already ionized the gas in the fluorescent tube, creating an electrically conductive medium.The tube just needs a voltage kick across the electrodes to establish an electrical arc. This kick is provided by the lamp’s 90005 ballast 90006, a special sort of transformer wired into the circuit. 90003 90002 When the current flows through the bypass circuit, it establishes a 90005 magnetic field 90006 in part of the ballast. This magnetic field is maintained by the flowing current. When the starter switch is opened, the current is briefly cut off from the ballast. The magnetic field collapses, which creates a sudden jump in current — the ballast releases its stored energy.90003 90002 This 90005 surge 90006 in current helps build the initial voltage needed to establish the electrical arc through the gas. Instead of flowing through the bypass circuit and jumping across the gap in the starter switch, the electrical current flows through the tube. The free electrons collide with the atoms, knocking loose other electrons, which creates ions. The result is a 90005 plasma 90006, a gas composed largely of ions and free electrons, all moving freely.This creates a path for an electrical current. 90003 90002 The impact of flying electrons keeps the two filaments warm, so they continue to emit new electrons into the plasma. As long as there is AC current, and the filaments are not worn out, current will continue to flow through the tube. 90003 90002 The problem with this sort of lamp is it takes a few seconds for it to light up. These days, most fluorescent lamps are designed to light up almost instantly. In the next section, we’ll see how these modern designs work.90003 .90000 Stroboscopic Effect in Fluorescent Lamps 90001 90002 90003 The Stroboscopic Effect in Fluorescent lamp is a phenomenon which causes running or moving equipment to appear stationary or appear to be operating slower than they actually are. 90004 90005 90006 90006 The stroboscopic effect in the fluorescent lamp 90002 Fluorescent materials when subjected to electromagnetic radiations of a particular wavelength, get excited and in turn, gives out radiations at some other wavelength. This is the working principle behind fluorescent lamps.90005 90010 These lamps are widely used in homes as they have higher efficiency and lifetime is almost 3 times of those of filament lamps. 90005 90012 What is Stroboscopic Effect? 90013 90010 Fluorescent lamps are provided with 50Hz or 60Hz ac current supply. 90005 90010 When operating under these frequencies the lamp becomes zero (crosses zero wave) double the supply frequency. That is 100 times for 50Hz frequency and 120 times for 60Hz frequency per second. 90003 Due to the persistence of vision our eyes do not notice those flickering.90004 90005 90010 However, if the light falls on the moving parts due to illusion, they may appear to be either running slow or in reverse direction or even may appear stationary. This effect is called the «90021 90022 Stroboscopic effect 90023 90024». 90005 90012 What is the Danger? 90013 90010 The danger of the stroboscopic effect is explained below using some examples. 90005 90010 Imagine a worker in a factory observes a running machine. Say a flywheel under the illumination of fluorescent light, the flywheel may appear to be stationary or to be operating at reduced speed.This can result in accidents and is highly dangerous. 90005 90010 A sewing machine whose needle moves up and down may appear to be stationary and the operator can prick the fingers. 90005 90010 These are some examples where the stroboscopic effect in the Fluorescent lamps can prove to be dangerous. 90005 90036 90036 Effect of Stroboscopic effect 90010 Fluorescent lamps had this effect (flicker) when mostly line frequency magnetic ballasts were used. 90005 90010 Studies involving these kinds of ballasts showed a 90005 90042 90043 doubling incidence of headaches with office workers, 90044 90043 triggering migraines in people sensitive to it (about 10% of the people), 90044 90043 and impairment of performance.90044 90049 90010 Even worse, with the aging of the lamps, AC polarity dependent fluctuation could start to occur in the 20-70 Hz frequency ranges, which can induce epileptic seizures! 90005 90010 With the introduction of electronic ballasts for fluorescent lights, most of the flicker problems were almost eliminated. 90005 90012 Methods to Avoid Stroboscopic Effect 90013 90010 This pattern of illusions is 90003 not allowed in industries 90004 as this may 90003 lead to accidents 90004. This is the main reason Fluorescent lamps are not preferred in industries.90005 90010 However, this effect occurs in three-phase as well as single-phase supply. It can be avoided by some simple techniques. 90005 90010 90003 Method to Avoid Stroboscopic Effect in Three-Phase Supply 90004 90005 90010 90003 If the industry is supplied with a 90022 three-phase supply 90023 90004, adjacent lamps should be fed with a different phase so that the zero instants of the two lamps will not be the same. 90005 90010 Fluorescent lamps around rotating or moving machinery, two lamps powered by two different phases should be used.This ensures that both the lamps do not flicker due to the zero-crossing at the same time. 90005 90010 90003 Method to Avoid Stroboscopic Effect in Single-Phase Supply 90004 90005 90010 90003 If 90022 single-phase supply 90023 is only available 90004, then the connection of two adjacent lamps is made such that the two lamps are connected in parallel with the supply . 90005 90010 In one lamp connection, a capacitor or condenser is kept in series with the choke. This makes a phase shift thereby eliminating the stroboscopic effect 90005.