Connecting two light bulbs. Features of parallel connection of LEDs

The output power of a single-ended ULF can be increased by parallel connecting one or more lamps to the output stage lamp. Thus, at the same supply and anode voltage, the anode current and, accordingly, the output power of the cascade increases two or more times. Example parallel connection additional lamp in the final stage of a single-ended ULF is shown in rice. 1.

Fig.1. Schematic diagram single-ended ULF on one (a) and two (b) pentodes

In the scheme under consideration ( rice. 1, a) the so-called ultralinear connection of the pentode is used, a characteristic feature of which is the connection of the cathode to the protective grid. The pentode shielding grid is connected to pin 2 of the output transformer Tpl, with the number of turns between pins 2 and 3 being approximately 43% of the number of turns between pins 1 and 3. The transformer Tpl is designed so that the total impedance primary winding(pins 1-3) was equal to the value of the load resistance determined for each lamp according to the catalog specification. So, for example, for an EL34 lamp this resistance is approximately 3 kOhm. The automatic bias voltage is generated across resistor R3, which is shunted electrolytic capacitor C2.

When connecting an additional lamp (or lamps) in parallel to the lamp of the ULF output stage, you will need to adjust the values ​​of some elements. So, for example, when connecting one additional lamp ( rice. 1, b) the resistance value of resistor R3 in the automatic bias circuit should be reduced by approximately two times compared to the previously considered circuit ( rice. 1, a), and the value of the capacitance of the shunt capacitor C2 is doubled. This is explained by the fact that when two lamps are connected in parallel, the cathode current doubles. It should be noted that the power of resistor R3 should also be doubled, that is, from 5 to 10 W. To achieve a twofold increase in output power, it will also be necessary to reduce the impedance of the primary winding of the transformer Tpl by half.

Theoretically, in a similar way, a larger number of similar lamps with almost identical parameters can be connected in parallel with the output stage lamp. Therefore, on sale you can find already selected pairs and even fours of lamps for use in parallel connection of the ULF output stage.

As in a single-cycle tube ULF, you can increase the output power of a push-pull amplifier by parallel connecting one or more tubes to the output stage lamps. At the same supply and anode voltage, the anode current and, accordingly, the output power of the cascade increases two or more times. We will explain the features of such a connection using the example of a simple push-pull power amplifier, the circuit diagram of which is shown in rice. 2.

Fig.2. Circuit diagram of a simple push-pull power amplifier

This amplifier consists of two identical channels, each of which is based on the single-ended amplifier discussed earlier. An example of parallel connection of additional lamps in the final stage of such a push-pull ULF is shown in rice. 3.

Fig.3. Schematic diagram of a simple push-pull power amplifier with parallel connection of lamps

When choosing the parameters of elements for a push-pull tube ULF with parallel connection of lamps, all the comments and recommendations mentioned earlier for a single-ended circuit are valid.

Let's do one more experiment. Let's take several identical lamps and turn them on one after another (Fig. 1.9). This connection is called serial. It should be distinguished from the previously discussed parallel connection.

Rice. 1.9. The generator powers two lamps connected in series. The diagram shows an ammeter and three voltmeters: one measures the total voltage, the other two measure the voltage across each lamp

At serial connection several sections of the circuit (say, several lamps) the current in each of them is the same.

So, let's take two 100-watt lamps, the same as those considered in the previous experiment, and connect them in series to a generator with a voltage of 100 V.

The lamps will barely glow, their glow will be incomplete. Why? Because the source voltage (100 V) will be divided equally between both lamps connected in series. Each lamp will now have a voltage of not 100, but only 50 V.

The voltage across the lamps is the same because we took two identical lamps.

If the lamps were unequal, the total voltage of 100 V would be divided between them, but not equally: for example, one lamp could have 70 V and the other 30 V.

As we will see later, a more powerful lamp receives less voltage. But the current in two series-connected even different lamps remains the same. If one of the lamps burns out (its hair breaks), both lamps will go out.

In Fig. Figure 1.9 shows how to turn on voltmeters to measure the voltage on each lamp individually.

Experience shows that the total voltage in successive sections of a circuit is always equal to the sum of the voltages in individual sections.

The lamps burned normally when the current was 1 A, but for this it was necessary to apply a voltage of 100 V to each of them. Now the voltage on each of the lamps is less than 100 V, and the current will be less than 1 A. It will not be enough to heat the lamp filament .

We will now regulate the operation of the generator: we will increase its voltage. What will happen? As the voltage increases, the current will increase.

The lamps will begin to glow brighter. When, finally, we raise the generator voltage to 200 V, a voltage of 100 V will be established on each of the lamps (half the total voltage) and the current of the lamps will increase to 1 A. And this is their condition normal operation. Both lamps will burn at full intensity and consume their normal power - 100 W. The total power supplied by the generator will be equal to 200 W (two lamps of 100 W each).

It would be possible to turn on not two lamps in series, but ten or five. In the latter case, experience would show us that the lamps will burn normally when the total voltage is increased to 500 V. In this case, the voltage at the terminals of each lamp (we assume all lamps are the same) will be 100 V. The current in the lamps will be and is now equal to 1 A .

So, we have five lamps connected in series; all lamps burn normally, each of them consumes 100 W of power, which means general power will be equal to 500 W.

In this case, the current on each of them will be the same, which simplifies control over it. But there are times when you cannot do without a parallel connection.

For example, if there is a power source, and you need to connect several LED bulbs to it, the total voltage drop across which exceeds the source voltage. In other words, the power source is not sufficient for the lamps connected in series, and they do not light up.

Then the light bulbs are connected in parallel to the circuit and a resistor is placed on each branch.

According to the laws of parallel connection, the voltage drop on each branch will be the same and equal to voltage source, and the current may vary. In this regard, calculations to determine the characteristics of resistors will be carried out separately for each branch.

Why can't you connect everything? led light bulbs to one resistor? Because production technology does not allow making LEDs with perfectly equal characteristics. LEDs have different internal resistance, and sometimes the differences in it are very strong even for identical models taken from the same batch.

A large variation in resistance leads to a variation in the current value, and this in turn leads to overheating and burnout. This means that you need to check the current on each LED or on each branch with a serial connection. After all, with a series connection the current is the same. For this purpose, separate resistors are used. With their help, the current is stabilized.

Main characteristics of circuit elements

After a little thought, it becomes clear that one branch can contain the same maximum number of LEDs as when connected in series and powered from the same source.

For example, we have a 12 volt source. You can connect 5 LEDs of 2 volts in series to it. (12 volts:2 volts:1.15≈5). 1.15 is a safety factor, since it is necessary to calculate that a resistor will also be included in the circuit.

: I=U/R, where I will be the permissible current taken from the device characteristics table. Voltage U is obtained if the voltage drop on each LED included in the series chain is subtracted from the maximum voltage of the power source (also taken from the characteristics table).

The resistor power is found from the formula:

In this case, all quantities are written in the C system. Recall that 1 A=1000 mA, 1 mA=0.001 A, 1 Ohm=0.001 kOhm, 1 W=1000 mW.

Today there is a lot online calculators, which offer to perform this operation automatically, simply by substituting known characteristics into empty cells. But it’s still useful to know the basic concepts.

The advantage of parallel connection of diodes

Parallel connection allows you to add 2 or 5 or 10 LEDs or more. The limitation is the power of the power source and the dimensions of the device in which you want to use such a connection.

The bulbs for each parallel branch are taken strictly identical so that they have the most similar values permissible current, forward and reverse voltage.

The advantage of connecting LEDs in parallel is that if one of them burns out, the entire chain will continue to work. The bulbs will glow even if more of them burn out, the main thing is that at least one branch remains intact.

As seen, parallel connection- that's pretty useful thing. You just need to be able to assemble the circuit correctly, not forgetting about all the properties of LEDs and the laws of physics.

In many circuits, parallel connections are combined with serial connections to create functional electrical devices.

Application of parallel connection of LEDs

A parallel connection circuit with two terminals allows for two-color lighting of light bulbs if two crystals are used different color. The color changes when the source poles change (change in current direction). This scheme is widely used in two-color indicators.

If two crystals of different colors are connected in parallel in one package and a pulse modulator is connected to them, then the color can be changed in a wide range. Especially many tones are generated when combining green and red LEDs.

As you can see in the diagram, each crystal has its own resistor connected. The cathode in such a connection is common, and the entire system is connected to a control device - a microcontroller.

In modern holiday garlands, a mixed type of connection is sometimes used, in which several consecutive rows are connected in parallel. This allows the garland to glow even if several LED sources will fail.

When creating lighting in a room, a parallel connection can also be used. Mixed circuits are used in the design of many indicator electrical devices and for illuminating devices.

A few installation nuances

Separately, we can talk about how the LEDs are connected to each other. Each crystal is enclosed in a housing from which leads come. The terminals are often marked “-” or “+”, which means connection to the cathode and anode of the device, respectively.

Experienced radio amateurs can even determine the polarity by eye, since the cathode terminal is slightly longer and protrudes a little more from the housing. Connecting LEDs must be carried out strictly observing polarity.

If we are talking about, then soldering is often used during the installation process. To do this, use a low-power soldering iron so as not to overheat the crystal. Soldering time should not exceed 4-5 seconds. It's better if it's 1-2 seconds. To do this, the soldering iron is heated in advance. The conclusions do not bend much. The circuit is assembled on site from a material that removes heat well.