Ballast circuit for fluorescent lamps. Electronic ballasts for fluorescent lamps – Repair of electronic ballast for fluorescent lamps

Fluorescent lamps cannot operate directly from a 220V network. To ignite them, you need to create a high voltage pulse, and before that, warm up their coils. For this purpose, ballasts are used. They come in two types - electromagnetic and electronic. In this article we will look at electronic ballasts for fluorescent lamps, what they are and how they work.

What does a fluorescent lamp consist of and why is ballast needed?

A fluorescent lamp is a gas-discharge light source. It consists of a tubular flask filled with mercury vapor. There are spirals along the edges of the flask. Accordingly, on each edge of the flask there is a pair of contacts - these are the leads of the spiral.

The operation of such a lamp is based on the luminescence of gases when electric current flows through it. But current will not simply flow between two metal spirals (electrodes). To do this, a discharge must occur between them; such a discharge is called a glow discharge. To do this, the spirals are first heated by passing a current through them, and then a high voltage pulse of 600 or more volts is applied between them. The heated coils begin to emit electrons and, under the influence of high voltage, a discharge is formed.

Without going into details, the description of the process is sufficient to set the task for the power source of such lamps; it must:

1. Warm up the coils;

2. Form an igniting impulse;

3. Maintain sufficient voltage and current to operate the lamp.

Interesting: Compact fluorescent lamps, which are more often called “energy saving” lamps, have a similar structure and requirements for their operation. The only difference is that their dimensions are significantly reduced due to their special shape; in fact, it is the same tubular flask, but the shape is not linear, but twisted into a spiral.

The device for powering fluorescent lamps is called a ballast (abbreviated as ballast), or popularly simply called a ballast.

There are two types of ballast:

1. Electromagnetic (EMPRA) - consists of a throttle and a starter. Its advantages are simplicity, but there are a lot of disadvantages: low efficiency, pulsations of the light flux, interference in the electrical network during its operation, low power factor, humming, stroboscopic effect. Below you see its diagram and appearance.

2. Electronic (electronic ballasts) - a modern power source for fluorescent lamps, it is a board on which a high-frequency converter is located. It is devoid of all the disadvantages listed above, due to which the lamps produce a greater luminous flux and service life.

A typical electronic ballast consists of the following components:

1. Diode bridge.

2. A high-frequency generator made on a PWM controller (in expensive models) or on an auto-generator circuit with a half-bridge (most often) converter.

3. Starting threshold element (usually a DB3 dinistor with a threshold voltage of 30V).

4. Ignition power LC circuit.

A typical diagram is shown below, let’s look at each of its nodes:

The alternating voltage is supplied to the diode bridge, where it is rectified and smoothed by a filter capacitor. Normally, a fuse and an electromagnetic interference filter are installed before the bridge. But most Chinese electronic ballasts do not have filters, and the capacity of the smoothing capacitor is lower than necessary, which causes problems with ignition and operation of the lamp.

Advice: if you are repairing electronic ballasts, read the article on our website.

After this, the voltage is supplied to the autogenerator. From the name it is clear that a self-oscillator is a circuit that independently generates oscillations. In this case, it is made on one or two transistors, depending on the power. The transistors are connected to a transformer with three windings. Typically, transistors such as MJE 13003 or MJE 13001 and the like are used, depending on the power of the lamp.

Although this element is called a transformer, it does not look familiar - it is a ferrite ring on which three windings are wound, each with several turns. Two of them are control ones, each with two turns, and one is a working one with 9 turns. The control windings create pulses to turn the transistors on and off and are connected at one end to their bases.

Since they are wound in antiphase (the beginnings of the windings are marked with dots, pay attention to the diagram), the control pulses are opposite to each other. Therefore, the transistors open one by one, because if they are opened at the same time, then they simply short-circuit the output of the diode bridge and something from it will burn out. The working winding is connected at one end to the point between the transistors, and at the other end to the working inductor and capacitor; the lamp is powered through it.

When current flows in one of the windings, an EMF of the corresponding polarity is induced in the other two, which leads to switching of the transistors. The self-oscillator is tuned to a frequency above the audio range, that is, above 20 kHz. It is this element that converts direct current into variable frequency current.

To start the generator, a dinistor is installed; it turns on the circuit after the voltage on it reaches a certain value. Usually a DB3 dinistor is installed, which opens in a voltage range of about 30V. The time after which it opens is set by the RC circuit.

Retreat:

More advanced versions of electronic ballasts are built not on a self-oscillator circuit, but on the basis of PWM controllers. They have more stable characteristics. However, in more than five years of studying electronics, I have never come across such electronic ballasts; all of them I worked with were self-generator ones.

The LC circuit was mentioned several times above. This is a choke installed in series with the spiral, and a capacitor installed in parallel with the lamp. A current first flows through this circuit, heating the coils, and then a high voltage pulse is formed on the capacitor, igniting it. The choke is made on an W-shaped ferrite core.

These elements are selected so that they resonate at the operating frequency. Since the inductor and capacitor are installed in series at this frequency, voltage resonance is observed.

When the voltages on the inductance and capacitance resonate, the voltage in idealized theoretical examples begins to rise strongly to an infinitely large value, while the current consumed is extremely small.

As a result, we have a frequency-matched generator and a resonant circuit. Due to the increase in voltage across the capacitor, the lamp ignites.

Below is another version of the circuit, as you can see - everything is basically the same.

Thanks to the high operating frequency, it is possible to achieve small dimensions of the transformer and inductor.

To consolidate the information we have covered, let’s consider a real electronic ballast board; the picture highlights the main components described above:

And this is the board from an energy-saving lamp:

Conclusion

Electronic ballast significantly improves the lamp ignition process and operates without pulsation and noise. Its circuit is not very complicated and a low-power power supply can be built on its basis. Therefore, electronic ballasts from burnt-out energy savings are an excellent source of free radio components.

Fluorescent lamps with electromagnetic ballasts are prohibited from being used in industrial and domestic premises. The fact is that they have strong pulsations, and a stroboscopic effect may appear, that is, if they are installed in a turning workshop, then at a certain speed of rotation of the spindle of the lathe and other equipment, it may seem to you that it is stationary, which can cause injury . This will not happen with electronic ballast.

A fluorescent lamp (LL) is a light source made from a sealed glass bulb, inside which an electric electrode discharge is created that flows in a gaseous environment. On its inner surface there is a phosphorus-containing layer (luminophor). Inside the lamp there is an inert gas and 1% mercury vapor. When exposed to an electric discharge, they emit visually invisible ultraviolet light, which causes the phosphor to glow.

Ballasts for fluorescent lamps

If even one fluorescent lamp breaks in a room, mercury vapor will exceed the permissible levels by 10 times. Its harmful effects persist for 1-2 months.

Application

The electrically conductive gaseous medium inside fluorescent lamps has a negative resistance, which manifests itself in the fact that as the current increases, the voltage between the electrodes decreases.

Fluorescent lamp operation diagram

Therefore, a current limiter LL1 - a ballast - is connected to the circuit, as can be seen from the figure. The device also serves to create a short-term increased voltage for igniting lamps, which is not enough in the existing network. It is also called a throttle.

The ballast also contains a small glow lamp E1 - starter. Inside it there are 2 electrodes, one of which is movable, it is made of a bimetallic plate.

In the initial state, the electrodes are open. When mains voltage is applied to the circuit by closing contact SA1 at the initial moment, no current passes through the fluorescent lamp, and a glow discharge is formed inside the starter between the electrodes. The electrodes heat up from it, and the bimetallic plate bends, closing the contact inside the starter. As a result, the current through ballast LL1 increases and heats the electrodes of the fluorescent lamp.

After the circuit closes, the discharge inside the starter E1 stops and the electrodes begin to cool. In this case, they open, and as a result of self-induction, the choke creates a significant voltage pulse that ignites the LL. At the same time, a current equal in value to the rated one begins to pass through it, which then decreases by 2 times due to the voltage drop across the inductor. This current is not enough to create a glow discharge in the starter, so its electrodes remain open while the fluorescent lamp is on. Capacitors C1 and C2 can reduce reactive loads and increase efficiency.

Electromagnetic choke

The ballast limits the flow of current. Some of the power heats up the device, which leads to energy loss. Based on loss levels, ballast for lamps can be as follows:

• D – normal;
• C – reduced;
• B – especially low.

When the ballast is connected to the network, the alternating voltage is ahead of the current in phase. Its designation always indicates the cosine of the angle of this lag, called the power factor. The smaller its value, the more reactive energy is consumed, which is an additional load. To increase the power factor to a value of 0.85, a capacitor with a capacity of 3-5 μF is connected in parallel to the network.

Any electromagnetic choke creates noise. Depending on how much it can be reduced, ballasts are produced with normal (N), reduced (P), and very low (C, A) noise levels.

The power of lamps and ballasts must be selected in accordance with each other (from 4 to 80 W), otherwise the lamp will fail prematurely. They are supplied included, but you can choose them yourself.

The classic starting device from an electromagnetic ballast and starter (EMPRA) has the following advantages:

• relative simplicity;
• high reliability;
• low price;
• no repairs are required, since even with your own hands it will cost more than buying a new unit.

In addition, it has a whole host of disadvantages:

• long startup;
• energy loss (up to 15%);
• noise during throttle operation;
• large dimensions and weight;
• unsatisfactory startup at low ambient temperatures;
• lamp blinking.

The shortcomings of chokes led to the need to create a new device. Electronic ballast is an innovative solution that improves the quality of LL operation and makes it durable. The electronic ballast circuit (electronic ballast) is a single electronic unit that forms a sequence of voltage changes for ignition.

Block diagram of starting lamps using electronic ballasts

The advantages of electronic circuits are as follows:

• launch can be instant or delayed;
• no need for a starter to start;
• due to the high frequency there is no “blinking”, and the light output is higher;
• the design is lighter and more compact;
• durability due to optimal starting and operating modes.

Externally, the electronic ballast looks as shown in the figure below.

Electronic ballasts for fluorescent lamps

The disadvantage of electronic ballasts is the high price due to the complexity of the circuit.

Running lamps

The lamp electrodes heat up, after which high voltage is applied to them through a ballast. Its frequency is 20-60 kHz, which makes it possible to eliminate flicker and increase efficiency. Depending on the scheme, the start-up can be instantaneous or smooth - with an increase in brightness to working brightness.

During a cold start, the service life of fluorescent lamps is significantly reduced.

To the process of heating the electrodes, an oscillatory circuit is added in the lamp power circuit, which enters into electrical resonance before the discharge. At the same time, the voltage increases significantly, the cathodes are heated more intensively, and as a result, ignition occurs easily. As soon as the discharge begins in the lamp, the oscillatory circuit immediately leaves resonance and the operating voltage is established.

For cheap electronic ballasts or those assembled by yourself, the principle of operation is similar to the version with a choke: the lamps are ignited by a high voltage, and the discharge is maintained by a low voltage.

Electronic ballast circuit

As with all electronic ballast circuits, voltage rectification is carried out by diodes VD4-VD7, which is then filtered by capacitor C1. The filter capacity is selected at the rate of 1 µF per 1 W of lamp power. With lower capacitor values, the glow will be dimmer.

As soon as the connection to the network occurs, capacitor C4 immediately begins to charge. When 30 V is reached, dinistor CD1 breaks through and transistor T2 opens with a voltage pulse, then a half-bridge self-oscillator consisting of transistors T1, T2 and transformer TR1 with two out-of-phase primary and one secondary windings begins to operate. The resonant frequency of the series circuit of capacitors C2, C3, inductor L1 and generator are close in value (45-50 kHz). When the voltage on capacitor C3 rises to the start value, the lamp lights up. At the same time, the generator frequency and voltage are reduced, and the inductor limits the current. Due to the high frequency, its dimensions are small.

Malfunctions and repairs

Burnt parts in the circuit are often visible. How to check electronic ballast? Most often, transistors fail. A burnt-out part can be detected visually. When making DIY repairs, it is recommended to check the transistor paired with it and the resistors located nearby. They are not always visible when they are burnt. A swollen capacitor must be replaced. If there are several burnt parts, the ballast is not repaired.

Sometimes after the electronic ballast is turned off, the lamp continues to flicker faintly. One of the reasons may be the presence of potential at the input when the zero is turned off. You need to check the circuit and make the connections yourself so that the switch is installed in phase. It is possible that charge remains on the filter capacitor. Then a resistance of 200-300 kOhm should be connected in parallel to it for discharge.

Due to power surges in the network, repairs to luminaires with electronic ballast are often necessary. If the power supply is unstable, it is better to use an electromagnetic choke.

A compact lamp (CFL) contains an electronic ballast built into the base. Repair of LLs of low price and quality is carried out for the following reasons: combustion of the filament, breakdown of transistors or a resonant capacitor. If the spiral burns out, do-it-yourself repairs will briefly extend the service life and it is better to replace the lamp. It is also impractical to repair LLs in which the phosphor layer has been burnt (blackening of the bulb in the area of ​​the electrodes). In this case, a working ballast can be used as a spare.

Burning of phosphor on a fluorescent lamp

Repair of the electronic ballast will not be required for a long time if you upgrade the CFL by installing an NTS thermistor (5-15 Ohms) in series with the resonant capacitor yourself. The part limits the starting current and protects the filaments for a long time. It is also advisable to make ventilation holes in the base.

Do-it-yourself ventilation device to remove heat from ballast

Holes are carefully drilled next to the tube for better cooling, as well as near the metal part of the base to remove heat from the ballast parts. Such repairs are only possible in dry rooms. In the middle, you can make a third row of holes with a larger diameter drill.

Repairs involving the installation of a thermistor are carried out by desoldering the conductor on the lower area with solder. Then the convex part of the base is bent from the glass bulb and the second wire is released. Afterwards the base is removed and access to the printed circuit board is provided. After the repair is completed, the base is installed in the reverse order.

Make it yourself

Tubular luminaires 1200 mm long are inexpensive and can illuminate large areas. The lamp can be made with your own hands, for example, from 2 lamps of 36 W each.

1. The body is a rectangular base made of non-combustible material. You can use a used lamp that no longer requires repair.
2. Electronic ballasts are selected according to the power of the lamps.
3. For each lamp you will need 2 G13 sockets, stranded wire and fasteners.
4. Lamp sockets are attached to the body after selecting the distance between them.
5. Electronic ballasts are installed in the zone of minimal heating from the lamps (usually closer to the center) and connected to the sockets. Each unit is produced with a connection diagram on the case.
6. The lamp is mounted on the wall or ceiling with a connection to a 220 V power supply via a switch.
7. It is advisable to use a transparent cap to protect the lamps.

Homemade lamp

Replacement. Video

This video will clearly show you how to replace the electronic ballast in a lamp.

The LL should be powered with high frequency current, for which an electronic ballast is well suited. They contain little mercury vapor; they require heating of the filaments, standardized in time and current, to reach operating mode.

Despite the fact that durable and reliable fluorescent lamps have firmly entered our lives, the improved ballast mechanism for them has not yet been appreciated by consumers. The main reason for this is the high price of electronic ballasts.

The main advantage of the ballast circuit for fluorescent lamps is the saving of energy consumed by the light source (up to 20%) and increasing its service life. By spending money on the purchase of electronic ballasts, we save on electricity and the purchase of new lamps in the future. The advantages also include quietness, soft start and ease of installation.

Using the instructions supplied with the device, the compact electronic ballast microcircuit can be installed in the lamp without any problems. By replacing the traditional inductor, starter and capacitor with it, we will allow the lamp to become more economical.

Electronic ballast circuits for fluorescent lamps look like this:

On the electronic ballast board there is:

Operating principle of the device

together with ballast can be divided into four main phases.

The current frequency drops to the rated operating frequency. During operation, low voltage capacitors are constantly charged. Feedforward control is activated, which regulates the switching frequency of the half-bridge.

The lamp power is maintained in a fairly stable position, even if voltage fluctuations occur in the network.

Conclusions:

• Using an electronic ballast circuit for fluorescent lamps eliminates strong heating of the device, so you don’t have to worry about the fire safety of the lamp.
• The device provides a uniform glow - the eyes do not get tired.
• Recently, occupational safety regulations have recommended the use of electronic ballasts in office premises in conjunction with all fluorescent lamps.

Video with an example of the operation of a fluorescent lamp from electronic ballasts

Electromagnetic or electronic ballast for fluorescent lamps is needed for the normal operation of this lighting source. The main task of the ballast is to convert direct voltage into alternating voltage. Each of them has its own pros and cons.

How does LL work with electromagnetic ballast?

Pay attention to this connection diagram. Marking LL1 is a ballast. There is a gaseous environment inside fluorescent lamps. As the current increases, the voltage between the electrodes in the lamp gradually drops and the resistance is negative. The ballast is used precisely to limit the current, and also creates an increased short-term ignition voltage for the lamps, since there is not enough of it in a regular network. This element is also called a choke.

Such a device uses a starter - a small glow discharge lamp (E1). It contains two electrodes. One of them is bimetallic (movable).

In the initial position they are open. By closing contact SA1 and applying voltage to the circuit, the current does not initially pass through the light source, but a glow discharge appears in the starter between the two electrodes. The electrodes heat up, and the bimetallic plate bends as a result, closing the contact. The current passing through the ballast increases, heating the electrodes of the fluorescent lamp.

Next, the electrodes in the starter open. A process of self-induction occurs. The choke creates a high voltage pulse, which ignites the LL. The rated current passes through it, but then it drops by half due to a decrease in the voltage across the inductor. The starter electrodes remain in the open position as long as the light is on. And capacitors C2 and C1 increase efficiency and reduce reactive loads.

Advantages of classic electromagnetic ballast:

• low cost;
• ease of use.

Disadvantages of EmPRA:

• noise of operating throttle;
• LL flicker;
• long lamp ignition;
• weight and large dimensions;
• up to 15% energy losses due to phase advance of alternating current voltage (power factor);
• poor activation in low temperature environments.

Note! The problem of energy loss can be solved by connecting (in parallel to the network) a capacitor with a capacity of 3-5 μF.

Advice! The ballast must be selected strictly in accordance with the power of the lamp. Otherwise, your light may break prematurely.

The most common causes of malfunctions of LLs with electromagnetic ballast

The following problems are identified:

How does LL with electronic ballast work?

Due to the mass of shortcomings of electromagnetic ballast, a new, more durable and technologically advanced electronic ballast was created. This is a single electronic power supply. Now it is the most common, as it does not have the disadvantages found in EMPA. In addition, it works without starters.

For example, let's take the circuit of any electronic ballast.

The incoming voltage is rectified, as usual, by diodes VD4-VD7. Next comes the filter capacitor C1. Its capacity depends on the power of the lamp. Usually they are guided by the calculation: 1 µF per 1 W of consumer power.

Next, capacitor C4 is charged and dinistor CD1 is broken through. The resulting voltage pulse activates transistor T2, after which a half-bridge self-oscillator from transformer TR1 and transistors T1 and T2 is switched on.

The lamp electrodes begin to heat up. To this is added an oscillatory circuit that enters into electrical resonance before discharging from inductor L1, generator and capacitors C2 and C3. Its frequency is about 50 kHz. As soon as capacitor C3 is charged to the starting voltage, the cathodes heat up intensely, and the LL is smoothly ignited. The inductor immediately limits the current and the generator frequency drops. The oscillatory circuit comes out of resonance, and the rated operating voltage is established.

Advantages of electronic ballasts:

• light weight and small dimensions due to high frequency;
• high light output due to increased efficiency;
• LL has no blinking;
• protection of the lamp from voltage surges;
• no noise during operation;
• durability due to optimized start-up and operation modes;
• It is possible to set the start instantaneously or with a delay.

The only downside of electronic ballasts is their high cost.

Pay attention! Cheap electronic ballast for fluorescent lamps works like electronic ballasts: a fluorescent lamp is ignited by high voltage, and combustion is maintained at low voltage.

The cause of failures of lamps with electronic ballast, as well as their repair

Yes, nothing lasts forever. They break too. But repairing electronic ballast is much more difficult than repairing electromagnetic ballast. This requires soldering skills and knowledge of radio engineering. And it also doesn’t hurt to know how to check the electronic ballast for functionality if there is no known working LL.

Remove the lamp from the fixture. Connect the terminals of the filaments, for example, with a paper clip. And connect an incandescent lamp between them. See picture below.

When power is applied, a working ballast will light the bulb.

Advice! After repairing the ballast, before connecting it to the network, it is better to connect another incandescent lamp (40 W) in series. This means that if a short circuit is detected, it will light up brightly, and the parts of the device will remain unharmed.

Most often, 5 parts fly out in electronic ballast:

1. Fuse (2-5 Ohm resistor).
2. Diode bridge.
3. Transistors. Along with them, 30 Ohm resistors can also burn out along the circuit. They fail mainly due to power surges.
4. A breakdown of the capacitor connecting the filaments is detected a little less often. Its capacity is only 4.7 nF. Cheap lamps use such film capacitors with an operating voltage of 250 - 400 V. This is very little, so it is better to replace them with capacitors of the same capacity, only with a voltage of 1.2 kV, or even 2 kV.
5. Dinistor. Often referred to as DB3 or CD1. It is impossible to check it without special equipment. Therefore, if all the elements on the board are intact, but the ballast still does not work, try installing another dinistor.

If you do not have knowledge and experience in electronics, it is better to simply replace your ballast with a new one. Now each of them is produced with instructions and a diagram on the case. After carefully reading it, you can easily connect the ballast yourself.