Inductor for fluorescent lamps: wiring diagram

Despite increased demand for LED light sources, fluorescent lamps are still at their peak. This is largely due to the relatively low cost of the lighting device and ballasts (hereinafter ballasts) necessary for its operation. Consider the functional purpose and principle of operation of the latter.

Main functions

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

• in order to create a stable discharge in a fluorescent lamp, it is necessary to preheat its electrodes and apply a start pulse to them;
• since gas-discharge type light sources have negative differential resistance, an increase in current is characteristic of them after entering the operating mode. It must be limited in order to prevent the failure of the light source.

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

Principle of operation

Let us consider the principle of operation of an electromagnetic inductor using an example of a typical connection scheme for gas-discharge type lamps.

The diagram indicates:

• EL - gas discharge lamp (luminescent) type;
• SF - starter, it is a device consisting of a flask filled with an inert gas, inside it are contacts made of bimetal. A capacitor is installed in parallel to the flask;
• LL - inductor (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.

Power of a gas discharge source (W)	Capacitor Capacitance (μF)
15	4,50
18	4,50
30	4,50
36	4,50
58	7,00

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

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

Now we proceed 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, through the circuit the choke “LL” - spiral “1” - starter “SF” - spiral “2” begins to pass current, 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 bimetallic contacts;
• the heated electrodes in the starter close, this causes a sharp increase in current strength, up to about 600 mA. Its further growth limits the inductance of the inductor;
• due to the increased current strength in the circuit, the spirals are heated (1 and 2), 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 occurs, which enters the coating from the phosphor. As a result, it glows in the visible spectrum;
• when the light source is “ignited”, its resistance decreases, respectively, the voltage at the inductor decreases (up to 110 V);
• starter contacts cool and open.

Tandem connection

The diagram below shows where two fluorescent lamps are connected in series.

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

Features of electromagnetic chokes

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

• the presence of a bulky and "noisy" throttle;
• starters, unfortunately, are not reliable;
• the presence of the gating effect (the lamp flickers with a frequency of 50 Hz) causes increased fatigue in a person, which leads to a decrease in his working capacity;
• when the starters fail, a false start appears, that is, the lamp blinks 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 significantly reduced efficiency.

Using electronic ballasts allows you to get rid of most of the above disadvantages.

Electronic control gear (electronic ballasts)

Massive electronic ballasts appeared not so long ago, about thirty years ago, now they have almost replaced electromagnetic devices. This was facilitated by numerous advantages over the classical switching circuit, we will name the main ones:

• increased light output of fluorescent lamps due to high-frequency discharge;
• lack of noise characteristic of low-frequency electromagnetic chokes;
• reduction of the gating effect has significantly expanded the scope;
• the lack of false start increases the life of luminescent sources;
• Efficiency can reach 97%;
• Compared to ballasts of electromagnetic type, power consumption is reduced by 30%;
• no need to compensate for reactive load;
• in some models of electronic devices, it is possible to control the power of the light source, this is done by adjusting the frequency in the voltage converter.

It is also worth noting: due to the lack of a bulky inductor, it became possible to reduce the size of the electronic ballast, which allowed it to be placed in the base. This significantly expands the scope, making it possible to use in lighting devices instead of sources in which a filament is used.

As an example, we give a simple electronic ballast circuit, typical of most low-cost devices.

List of items:

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

Concluding the topic of electronic ballasts, it should be noted - their significant drawback is the relatively high cost of high-quality devices. As for low-cost models, the reliability of those leaves much to be desired.

Connection without ballast

If necessary, gas-discharge light sources can be included in the power supply without electromagnetic or electronic ballast. The scheme of such inclusion is shown below.

To implement such a connection you will need:

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

This circuit loses in its parameters to the connection using an electromagnetic inductor and electronic ballasts. It is provided for your reference.