Electronic and electromagnetic choke for fluorescent lamps

There are times in life when a low-voltage power source for fluorescent lamps . Such a lamp can be powered by a rechargeable battery while camping or in the country, and can also easily find its use in the garage and at home; it can even start a burnt-out fluorescent lamp.

Main functions

It is not possible to connect fluorescent light sources directly to the electrical network. There are the following reasons for this:

• to create a persistent discharge in a fluorescent lamp, it is necessary to preheat its electrodes and apply a starting pulse to them;
• Since gas-discharge light sources have a negative differential resistance, they are characterized by an increase in current strength after entering the operating mode. It must be limited to prevent the light source from failing.

Based on the reasons described above, it is necessary to use ballasts.

Electromagnetic type ballasts

Principle of operation

Let's consider the principle of operation of an electromagnetic choke using the example of a typical connection diagram for gas-discharge lamps.

Typical connection diagram

The diagram shows:

• EL – gas-discharge (fluorescent) type lamp;
• SF is a starter, it is a device consisting of a flask filled with an inert gas, inside it there are bimetal contacts. A capacitor is installed parallel to the flask;
• LL – choke (electromagnetic);
• lamp spirals (1 and 2);
• C – capacitor (compensates for reactive power), its capacity depends on the power of the lamp, the correspondence table is shown below.

There are devices in the circuits of which there is no compensating capacitor; this is unacceptable, since reactive load leads to the following negative consequences:

• there is an increase in power consumption, which leads to increased energy consumption;
• The service life of the equipment is significantly reduced.

Now let's move directly to the principle of operation of the above typical scheme. Conventionally, it can be divided into the following stages:

• when connected to the mains, a current begins to flow through the circuit inductor “LL” – spiral “1” – starter “SF” – spiral “2”, the strength of which is from 40 to 50 mA;
• under the influence of this process, an inert gas is ionized in the starter flask, which leads to an increase in current strength and heating of the bimetallic contacts;
• the heated electrodes in the starter close, this causes a sharp increase in current, up to approximately 600 mA. Its further growth limits the inductance of the inductor;
• due to the increased current in the circuit, the spirals (1 and 2) are heated, as a result of which electrons are emitted by them, the gas mixture is heated, which leads to a discharge;
• Under the influence of the discharge, ultraviolet radiation appears, which hits the phosphor coating. As a result, it glows in the visible spectrum;
• when the light source “lights up”, its resistance decreases, and accordingly, the voltage at the inductor decreases (up to 110 V);
• The starter contacts cool down and open.

Tandem connection

Below is a diagram where two fluorescent type lamps are connected in series.

Tandem connection diagram

The operating principle of the presented circuit does not differ from a standard connection, the only difference is in the parameters of the starters. For a two-lamp connection, starters are used whose “breakdown” voltage is 110 V (type S2), for a single-lamp connection - 220 V (type S10).

Starters S10 and S2 for 220 and 110 V respectively

Converter for fluorescent lamp - assembly

To demonstrate the functionality of the circuit, it was assembled on a breadboard. The circuit is powered from the breadboard power supply - 5V. The transformer is removed from the power supply and turned on in reverse, i.e. a winding with a large number of turns goes to the contacts of the fluorescent lamp. The transistor heats up during operation, it is advisable to install it on at least a small radiator. After an hour of working with the radiator, it became simply warm.

Our very first test lamp was an 8 W lamp. The glow is quite bright, its brightness is slightly different from turning it on in the standard way.

The second 18 W lamp came on, but very dimly. The power that this voltage converter produces for such a fluorescent lamp is clearly not enough.

In general, given the simplicity of this circuit, it can be safely recommended for assembly. If necessary, the circuit can be powered from 12 V , but in this case 5 V stabilizer is required to power the microcircuit.
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Features of electromagnetic type chokes

Speaking about the features of electromagnetic ballasts, it should be noted that the only advantages of these devices are their relatively low price, simple operation and simple installation. The classical connection scheme has much more disadvantages :

• the presence of a bulky and “noisy” throttle;
• starters, unfortunately, are not reliable;
• the presence of a strobe effect (the lamp flickers at a frequency of 50 Hz) causes increased fatigue in a person, which leads to a decrease in his performance;
• when the starters fail, a false start occurs, that is, the lamp flashes several times before “lighting up”, this reduces the working life of the light source;
• approximately 25% of the power is spent on electromagnetic ballast, resulting in a significant reduction in efficiency.

The use of electronic ballasts allows you to get rid of most of the disadvantages listed above.

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Electronic ballast (EPG)

Electronic ballasts appeared en masse not so long ago, about thirty years ago, and now they have practically replaced electromagnetic devices. This was facilitated by numerous advantages over the classical switching circuit; we will name the main ones:

• increasing the luminous efficiency of fluorescent lamps due to high-frequency discharge;
• absence of noise characteristic of low-frequency electromagnetic chokes;
• reducing the gating effect significantly expanded the scope of application;
• the absence of a false start increases the service life of luminescent sources;
• Efficiency can reach 97%;
• compared to electromagnetic type ballasts, energy consumption is reduced by 30%;
• there is no need to compensate for reactive load;
• Some models of electronic devices provide control of the power of the lighting source; this is done by adjusting the frequency in the voltage converter.

EPLA appearance and internal structure
It is also worth noting: due to the absence of a bulky inductor, it became possible to reduce the size of the electronic ballast, which made it possible to place it in the base. This significantly expands the scope of application, making it possible to use it in lighting devices instead of sources that use a filament.

Electronic ballast located in the base

As an example, let's take a simple electronic ballast circuit, typical of most inexpensive devices.

Diagram of a typical electronic ballast

List of elements:

• resistor ratings: R1 and R2 -15 Ohm, R3 and R4 – 2.2 Ohm, R5 – 620 kOhm, R6 – 1.6 Mohm;
• capacitors used: C1 – 47 nF 400 V, C2 – 6800 pF 1200 V, C3 – 2200 pF, C4 – 22 nF, C5 – 4.7 µF 350 V;
• diodes: VD1-VD7 – 1N400;
• transistors: T1 and T2 – 13003;
• diode triac VS – DB3.

Concluding the topic of electronic ballasts, it is necessary to note that their significant drawback is the relatively high cost of high-quality devices. As for inexpensive models, their reliability leaves much to be desired.

Energy-saving lamp from a low-voltage power source - diagram

The voltage converter for a fluorescent lamp conventionally consists of three parts.

• Master generator of rectangular pulses on the K155LA3 or K555LA3 (you can take any other analogue). Our generator is assembled on K555LA3.
• Field effect transistor IFRZ44N , controlled by a generator, the load of which includes the transformer winding
• Step-up transformer

The rectangular pulse generator on the K155LA3 microcircuit is controlled using a construction resistor R1. T1 KT315 transistor with an LED is connected to the output of the generator , which will visually help control the frequency and operation of the generator.

At different frequencies, the operating modes of the transistor and transformer will change, and the fluorescent lamp will glow with different brightness. Using a construction resistor, it is necessary to select the frequency at which there will be an optimal balance between the current flowing through transistor T2 and the brightness of the fluorescent lamp. The frequency will be approximately 70 - 120 Hz .

Connection without ballast

If necessary, gas-discharge light sources can be connected to the power supply without electromagnetic or electronic ballast. The diagram of such a connection is shown below.

Throttleless connection method

To implement such a connection you will need:

• fluorescent lamp - 40 W and incandescent lamp - 60 W (the latter will work as a ballast resistance);
• two capacitors 0.47 uF 400 V (play the role of a multiplier);
• diode bridge KTs404A or similar, you can use four diodes designed for a current of at least 1 A and a reverse pulse voltage of 600 V.

This circuit is inferior in its parameters to connection using an electromagnetic choke and electronic ballasts. It is provided for informational purposes only.

A simple voltage converter for powering a fluorescent lamp

The technical literature describes many voltage converter circuits for powering fluorescent lamps, but for most of them it is necessary to make a transformer yourself. The author offers his own version of the converter using as a transformer a television TBC (output line transformer - “line transformer”) type TVS-110LA from a black-and-white TV with a slight modification.

TVS-110LA

The converter ensures operation of a fluorescent lamp from a 12 V power source. It provides ignition and combustion of fluorescent lamps with a power of 6 to 40 W. A special feature of the device is that it can work with a fluorescent lamp whose filaments are broken (burnt out).

The electrical circuit diagram of the converter is shown in Figure . As can be seen from the diagram, the basis of the device is a classic multivibrator. TVS-110LA with minor modifications was used as the converter transformer. The mounting aluminum plate in the transformer is removed and instead of this plate a strip of fiberglass is installed, in which two holes must be drilled for the studs.

Voltage converter circuit for powering a fluorescent lamp

There is no need to disassemble the TBC, except to remove the high-voltage winding, but this is not necessary. Then the ferrite rod, together with the installed strip, must be wrapped in thick paper and wound 16 turns into two PEV-2 wires with a diameter of 0.8 mm - these will be windings I and II, which must be connected in series in phase, i.e. connecting the end of the first winding to the beginning of the second. The remaining TBC windings are used unchanged. The number of turns of TVS-110LA windings, in accordance with [1], is:

• high-voltage winding: 1200 turns of PEV-2 wire with a diameter of 0.1 mm;
• winding III (pins 4-9) contains 960 turns, of which winding 4-5 contains 80 turns of PEV-2 wire with a diameter of 0.41 mm, the rest - PEV-2 with a diameter of 0.23 mm;
• winding IV (terminals 1-3) - 96 turns PEV-2 0.23 mm.

To power the fluorescent lamp, two series-connected windings III and IV are used.

If there is a need to increase the output voltage, then to do this you should reduce the number of turns of windings I and II, but leave at least 10 turns. Transistors VT1, VT2 must be installed on radiators with S=50 cm2. Instead of the KT808A transistor, you can use KT805 transistors with any letter indices.

The converter can be powered from a TP7-12 battery (12 V, 7 Ah).

In conclusion, we note the following:

• as experiments show, the high-voltage winding (V) is also suitable for powering a fluorescent lamp;
• If the high-voltage winding in the transformer is faulty, then it is better to remove it.

Literature

1. Kuznets L.M., Sokolov V.S. Television receiver units. Ref. - M.: Radio and Communications, 1987.
2. Brezhnev KM and others. Transistors for equipment of wide application. Ref. — M.: Radio and communications. 1981.

Author: Svyatoslav Babyn, village Kelmentsi, Chernivtsi region.

Source: Radioamator No. 2, 2015