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The device required to limit the current in gas discharge lamps and fluorescent lamps is called the ballast .


Series choke (KVG) for a compact fluorescent lamp 18 watts

A ballast is required to operate a gas discharge lamp. Otherwise, the discharge current would continue to rise due to the impact ionization required for its function until the lamp is destroyed or the fuse is triggered.

It can be built into the luminaire as a separate component or it can also be integrated into the light source (for example in the case of so-called energy - saving lamps ). In this case, the lamp can be operated directly from the mains.

Ballasts can also contain the ignition (depending on the lamp type, pulses from a few hundred volts to several kV) and starting equipment (preheating of the electrodes / filaments in fluorescent lamps) required for some lamps .

Ballasts (VG) are available in two types:

  • so-called conventional ballasts (KVG for short, conventional ballasts)
  • Electronic ballasts (abbreviation EVG)

Conventional ballasts (KVG)

Conventional ballasts are series chokes that work at mains frequency and consist of an iron core with an air gap and a copper or aluminum enamelled wire winding.

Due to the ohmic resistance of the winding (the so-called copper losses ) and the magnetic reversal and eddy current losses in the core, there are losses of around 10–20% of the nominal lamp power. Heat is generated in the throttle.

The calculation of the required inductive resistance is shown in this example .

The CCG is connected in series with the lamp and must match the lamp, since at a mains frequency of 50 or 60  Hz it limits the current of the lamp to its nominal value. In the case of lamps that require an ignition device (such as sodium vapor lamps and metal halide lamps ), the ignition circuit is also in series with the lamp.

KVG for fluorescent lamps also require a so-called starter , which switches the hot cathodes directly into the circuit when starting for preheating (see under fluorescent lamps ). Glow starters cause the characteristic flickering of fluorescent lamps when starting, fast starters do not have this disadvantage.

Conventional ballasts cause reactive current in the network due to their inductance . In some cases, luminaires are therefore equipped with a capacitor that compensates for the reactive current ( reactive current compensation ). If the capacitor is connected in parallel to the lamp, it is not required for the function. In some cases, compensation capacitors connected in series with the choke are also used in order to avoid the surge in parallel compensation when switching on. The capacitance value of such series capacitors must have a tight tolerance (e.g. 2%) in order to guarantee the nominal current of the lamp. If they fail due to a short circuit, the luminaire continues to work without interference, but is no longer reactive current compensated.

KVG are extremely reliable, they can work for decades without problems and do not have to be replaced.

The sale of KVG with energy efficiency class D has been banned in the EU since May 21, 2002, the sale of class C devices since November 21, 2005.

However, efforts have been made for a long time to reduce the losses of the series chokes, which, however, usually requires a greater mass (lower magnetic flux density, lower current density) and / or more expensive magnetic materials. Designations such as low-loss ballast (VVG) or ultra-low-loss ballast have been introduced for this purpose.

KVG for explosion-protected areas also show lower losses because their surface temperature must be limited.

Low-loss ballast (VVG) for a T8 fluorescent lamp with 18 watts of power

Due to the small variety of materials, CCG are easier to recycle than electronic ballasts.

For ballasts for fluorescent tubes, see there. Conventional ballasts for light or cold cathode tubes are stray field transformers and combine the transformation of the mains voltage into a higher voltage as well as the required current limitation. They often have an adjustment option for the current in the form of a mechanically variable magnetic shunt.

Electronic ballasts (EVG)

Electronic ballast for fluorescent lamps T8 with 36 or 58 W.
Open electronic ballast
Electronic ballast of an energy-saving lamp built into the base ; Diameter of the board 42 mm
Electrical circuit of an electronic ballast in the form of a resonance converter .

Electronic ballasts (EVG) operate the lamp at a higher frequency than the mains frequency (a few kHz up to mostly 32 to over 40 kHz) and therefore have lower losses than conventional ballasts when using less material. Electronic ballasts for fluorescent lamps also contain the starting mechanism. There are also electronic ballast types that can supply up to four fluorescent lamps. Depending on the system, electronic ballasts can also be made dimmable and remotely controllable.

With larger units, electronic ballasts have a better power factor (0.97 to 0.99) and the lamp achieves a higher degree of efficiency with them. The higher operating frequency inherent in the system means that fluorescent lamps cannot flicker in a physically perceptible manner.

With a so-called warm start (a cold start can damage the lamp cathodes ), the glow cathodes of the fluorescent lamp are preheated for a period of about 0.5–2 seconds before it is ignited. The starting and ignition processes of electronic ballasts are flicker-free in contrast to conventional ballasts (KVG) with conventional starters. The start-up process is therefore usually noticeably faster than with KVG.

Small electronic ballasts in energy-saving lamps often have no power factor correction , have negative power factors and load the network with harmonics. Permanently installed electronic ballasts, on the other hand, usually have a power factor correction and a power factor close to one.

Dimmable electronic ballast

Dimmable electronic ballasts are available in two versions:

  • analog dimmable electronic ballast
  • digital dimmable electronic ballast

Analog dimmable electronic ballasts are controlled with a control signal of 1 to 10 volts . The ECG is disconnected from the mains when the luminaire is switched off and therefore has no standby losses.

Digital dimmable electronic ballasts are a DALI - bus signal activated. The system enables up to 64 lights to be operated on one bus segment. States can be reported back. Even when the luminaire is switched off, the ECG is always connected to the mains and thus causes stand-by losses.

In both variants, the control line is also included in the supply line. Due to the reactive control power , the decrease in luminous flux is always greater than the decrease in current.

Clip-on ECG / T5 adapter

For modernizations, clip-on ECGs are offered by various providers in which existing lights can still be used. The electronic ballast is inserted between the old socket and a conventional, smaller type of lamp. With these clip-on ECGs, however, considerable problems arise due to the design (service life of the ECG, correct operation of the lamp, electromagnetic compatibility , missing test marks and approvals), so that this solution has not yet been able to establish itself on the market. This mainly applies to the operation of T8 lamps with electronic ballasts. Since 2004, individual providers have had all the necessary test marks and approvals, but these electronic ballasts interfere with the design of the luminaire and their test marks and approvals expire. Most manufacturers also deny guarantees and product liability. After retrofitting, the manufacturer of the electronic ballast is considered to be the luminaire manufacturer and must process warranty claims and product liability for the luminaire. Since providers repeatedly provided incorrect information, one should pay attention to test certificates from TÜV, VDE and the Federal Institute for Occupational Safety and Health .

Another variant of the retrofit are adapters to operate T5 lamps in T8 sockets. The advantages are savings without changing the luminaire housing, i.e. low retrofitting costs. Although there are advantages of the T5 lamp generation in the old luminaire housings, the lighting properties of the luminaires are only achieved to a limited extent. A disadvantage can be a low luminous flux and fire hazard due to the adapters heating up during operation. The power factor λ of the entire luminaire also changes with this conversion due to the lower output of a T5 lamp. The CCG or VVG contained in the luminaire is only used as a line filter, they remain in this.

The service life of the retrofit ECG is around 15 years. T5 lamps are available from every well-known supplier; the service life is around 16,000–30,000 hours instead of 6,000–8,000 hours for the T8 lamps with light color 840.

Note : For safety and EMC reasons, the use of T5 adapters in T8 luminaires is very questionable. In addition to the electrical problems, some adapter systems do not take into account the permissible total T8 lamp weight (e.g. CB Scheme ). Complete luminaires that control T5 lamps on both sides with the help of electronic ballasts can be used without hesitation if there is electromagnetic compatibility in order to take advantage of the advantages of the T5 lamp. Manufacturers of lamps and luminaires advise against using adapters in luminaires. Measurements in Switzerland do not prove useful for T5 adapters.

ECG for operation on low voltage

Lamp operated by a 12V battery
Homemade lamp with 12V ECG module (open)

There are also electronic ballasts for operation with low-voltage direct voltage (12 or 24 volts). These can be operated on a battery, which makes them suitable for use with solar systems , in vehicles, on boats or in allotments.

Often such lamps as well as mains voltage energy-saving lamps are equipped with an E27 screw base, which means that there is a high risk of confusion.

Electronic ballast for fluorescent tubes

Adjustable electronic ballast for fluorescent tubes

Ballasts for cold cathode tubes (CCFL, backlighting of LCD and fluorescent tubes for advertising) are often designed as inverters ; they generate a current-limited high voltage (500 V to a few kV) of high frequency from the battery or mains voltage and do not require a preheating function.

Electronic ballasts for cold cathode tubes often have an electronic or mechanical ( potentiometer ) dimming function.

In illuminated advertising , several fluorescent lamps are often operated in series on one ballast or power supply unit. Their maximum AC voltage is limited to 7.5 kV by VDE regulations.

Special features of EVG

The high inrush current can, depending on the design, require the number of electronic ballasts within a circuit to be limited. Due to aging electronic components, the reliability and service life do not yet reach the values ​​of a KVG. It is calculated with 50,000 hours (approx. 6 years non-stop nominal service life), which has to be taken into account in the amortization.

Critical to the operation of multiple ECG with a residual-current device as EVG due contained mains filter a reactive current derived through the protective conductor. The leakage current must be below 0.5  mA , but it is higher when the device is switched on. Therefore, when installing a new RCCB, you should ensure that it is pulse current-proof or that it triggers with a delay. For safe operation, only half the tripping current of the residual current circuit breaker should be set as the planning value: for a residual current circuit breaker with a tripping current of 30 mA, half the tripping current is 15 mA;

15 mA / 0.5 mA (per ECG) = 30 ECG.

The economic efficiency of electronic ballasts depends heavily on the annual burning hours, which should not be less than 1,500 hours.

Electronic ballasts are sensitive to a break in the neutral conductor, but they cannot cope with the resulting higher phase voltage.


  • Günter Springer: Expertise in electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
  • Alfred Hösl, Roland Ayx, Hans Werner Busch: The electrical installation in accordance with regulations, residential construction, commercial industry. 18th edition, Hüthig Verlag, Heidelberg, 2003, ISBN 3-7785-2909-9

Individual evidence

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Web links

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