LED emergency lighting lamps. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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In the event of a power outage in utility or service rooms, it is advisable to maintain at least a minimum level of illumination in order to take some measures to eliminate the malfunction or leave the premises. In this case, lamps that can shine for some time after the mains voltage is turned off will help. They will require an independent power source or energy storage device, such as a large capacitor or battery. It is advisable to use LEDs as emergency lighting lamps, since they are the most economical.

In order for the lamp to shine even after a power failure, it must, of course, contain a built-in power source. In the simplest case, it can be an oxide capacitor of a relatively large capacity, capable of accumulating energy in standby mode, sufficient to maintain a small illumination of the room for several tens of seconds.

Fig. 1

A diagram of such an emergency lighting lamp is shown in Fig. 1. It can be made on the basis of a commercially available LED lamp or made independently on the basis of elements of an LED flashlight or individual LEDs (see the article "Network lamp from flashlight LEDs" in "Radio", 2013, No. 2, p. 26). In standby mode, the LEDs connected in series are powered by a source consisting of a ballast capacitor C1, a diode bridge VD1-VD4 and a smoothing capacitor C2. Capacitor C3 is storage, immediately after the mains voltage is applied, it is charged from the bridge rectifier through the VD6 diode, and when the LEDs start to shine, through the resistor R3 from the half-wave rectifier on the VD5 diode. A current stabilizer is assembled on transistors VT1, VT2, which ensures uniform discharge of the capacitor C3 and maintains a constant brightness of the LEDs in emergency mode.

In standby mode, the current through the LEDs depends mainly on the capacitance of the capacitor C1, the stabilizer current (in this case, about 1 mA) and the number of LEDs N (for example, with N \u21d 20 and the capacitance indicated on the diagram, this current is about 2 mA ). Resistor R1 limits the inrush of charging current when the lamp is turned on, and capacitor C1 is discharged through resistor R3 when it is turned off. In an emergency, when the mains voltage disappears, the LEDs are powered from the storage capacitor C20 through a current stabilizer. A constant minimum illumination is maintained for about 30 s, after which the brightness of the LEDs gradually decreases for about 3 s. You can increase the duration of emergency lighting by increasing the capacitance of capacitor CXNUMX.

Fig. 2

All parts, except for LEDs, are mounted on a printed circuit board, the drawing of which is shown in fig. 2. Resistors - C2-33, R1-4, capacitors C2, C3 - imported oxide, C1 - from a failed energy-saving compact fluorescent lamp (CFL) or imported, designed to operate at an alternating voltage of 250 ... 400 V. From 1N4007 diodes were also removed from it. Bipolar transistor - any of the KT315, KT3012 series. The mounted board is placed in a plastic case from the CFL with parts towards the base.

The small capacitance of the storage capacitor C3 does not allow for a long glow of the lamp in emergency mode. An increase in its capacity leads to a significant increase in dimensions. The way out of this situation can be the use of an ionistor - a high-capacity capacitor (up to several farads). However, the ionistor's nominal voltage, as a rule, does not exceed 5 V, so one LED or several connected in parallel can be powered from it.

Fig. 3

A diagram of such a lamp is shown in Fig. 3. In standby mode, the LEDs are powered by a diode rectifier VD1-VD4 connected to the network through a ballast capacitor C1. At the same time, a current of about 1 mA flows through the EL3-ELN-20 LEDs connected in series, and through each of the ELN-2-ELN connected in parallel - three times less. To equalize the current through them, current-limiting resistors R3-R5 are used, which, when adjusted, are selected so that the total voltage drop across them and the ELN-2-ELN LEDs does not go beyond 4,5 ... 5 V. Before this voltage, the ionistor is charged C3. For the first time after turning on the lamp in the network (until it is charged to a voltage of 3 ... 3.3 V), the ELN-2-ELN LEDs do not light.

When the mains voltage fails, the ionistor starts to discharge through these LEDs and only they shine in the lamp. The duration of the glow depends on the capacitance of the ionistor and the number of LEDs connected to it. An increase in their number requires a proportional increase in the resistance of the resistors connected in series with them, and since the discharge current of the ionistor increases, the duration of emergency lighting is reduced.

It is possible to significantly extend the glow of the lamp in emergency mode by replacing the ionistor with a small-sized Li-ion battery (or a battery of Ni-Cd batteries) from a cell phone or radio telephone. With a selection of resistors R3-R5 (with the battery disconnected), a voltage of 2 ... 4 V is installed on them and the ELN-4,1-ELN LEDs connected in series with them when using a Li-ion battery or 4,3 ... 4,4 V, if a battery of three Ni-Cd or Ni-MH batteries is used (it is up to these voltage values ​​that they are charged in standby mode). In the event of a mains voltage failure, the ELN-2-ELN LEDs are powered from the battery. Its energy reserve is enough for several hours of continuous operation. As it discharges, the voltage and current through the LEDs decrease, but due to their non-linear current-voltage characteristic, full discharge will not occur. In series with the battery, you can install a switch SA1 to turn it off, for example, when transporting the lamp.

To increase the brightness of the lamps assembled according to the scheme in Fig. 3, in emergency mode, increase the number of LEDs connected in parallel. In principle, it is possible to turn on all the LEDs of the lamp in parallel, but in this case, to ensure normal brightness in standby mode, it will be necessary to significantly increase the capacitance of the ballast capacitor C1, which will lead to an undesirable increase (up to several hundred milliamps) of the current consumed from the network. In addition, if the battery is discharged, the brightness of the lamp for the first time after switching on may be low, since a significant part of the current will go to charge the battery.

Fig. 4

A possible way out is a serial connection of several groups of LEDs connected in parallel (Fig. 4). For the manufacture of such a lamp, a printed circuit board from a lamp with 32 LEDs connected in parallel was used. On the board, they are located as follows: 4 - in the center, 17 - along the outer circumference, 11 - along the intermediate one. The latter are allocated to a group (EL12-EL22), powered by a battery in emergency mode, and the rest are divided into two groups, one of which also contains 11 LEDs (EL1-EL11), and the second - ten (EL23-EL32). These groups and the current-limiting resistor R3 are connected in series, for which the corresponding printed conductors on the board are cut, and the necessary connections are made with pieces of insulated wire.

The current consumed by this lamp is determined by the capacitance of the ballast capacitors C1, C2 and is approximately 100 mA, i.e., a current of about 9 mA flows through each LED. Capacitor C3 smooths out the ripple of the rectified voltage, making the LEDs glow more evenly. In standby mode, a voltage of about 12 V drops on the EL22-EL3 LEDs and the resistor R4,1 (it is selected during adjustment), to which the Li-ion battery G1 is charged. If a battery of three Ni-Cd or Ni-MH batteries is used, this voltage should be increased to 4,4 V. The SA1 switch performs the same function as in the previous design.

Fig. 5

All parts, except for LEDs and resistor R3, are mounted on a printed circuit board made of foil fiberglass, made according to the drawing shown in fig. 5. The mounted board and the battery are placed in a case with a diameter of 57 mm from a CFL with a power of 35 W so that the capacitors C1 and C2, previously wrapped with insulating tape, are in the basement. The switch is installed on its side wall. The appearance of the lamp is shown in fig. 6.

Fig. 6

In order for the brightness of the lamp with series-connected LEDs to remain the same in emergency mode as in standby mode, it must be supplemented with a battery-powered step-up voltage converter. A diagram of such a lamp is shown in Fig. 7. In standby mode, the EL1-ELN LEDs are powered by a current of 15 ... 20 mA from a power supply unit consisting of a ballast capacitor C1, a diode bridge VD1 - VD4 and a smoothing capacitor C2. The voltage to which the battery G1 is charged is set by selecting the resistor R3.

Rice. 7 (click to enlarge)

The voltage converter contains a microcircuit DD1, a transistor VT1, a step-up pulse transformer T1 and a rectifier based on diodes VD6-VD9. A pulse generator with a repetition rate of about 1.1 kHz is assembled on the DD30 element, and a control pulse shaper on DD1.2. Connected in parallel elements DD1.3, DD1.4 perform the functions of an inverting buffer stage. From its output, the pulses go to the gate of the switching field effect transistor VT1. When powered from the mains and the contacts of the switch SA1 are closed, the battery G1 is charged through the LEDs EL1-ELN-1 and the zener diode VD5. A positive polarity voltage (about 1.1 V) is applied to one of the inputs of the DD5 element (pin 4) through the resistor R4, and negative (about 5 V) from the zener diode VD6 through the resistor R5.

As a result, the voltage at this input is low, the generator is inhibited and the converter does not work. When the mains voltage fails, a high-level voltage is supplied to the input of the DD1.1 element from the battery G1, the generator turns on and the LEDs are supplied with supply voltage from the rectifier on diodes VD6-VD9. The trimming resistor R7 can be used to change the duration of the control pulses over a wide range, and thus the brightness of the lamp in emergency mode. The performance of the converter is maintained when the supply voltage drops to 2,8 V.

Fig. 8

Resistors R1, R2 (MLT), capacitors C1 (K73-17 or from CFL), C2 (oxide imported) and diodes VD1-VD4 (also from CFL) are placed on a double-sided printed circuit board, the drawing of which is shown in fig. 8. Mounting is mostly surface. Capacitor C2 is installed parallel to the board and glued to it with Moment glue. Four holes on the right side of the board are designed to pass the leads of the VD1-VD4 diodes (they are soldered to the printed conductors on both sides). After checking, the mounted board is wrapped with two layers of insulating tape and placed in the base of the CFL housing.

Fig. 9

The converter is assembled on a printed circuit board made according to the drawing in fig. 9. Mounting - surface. Capacitors C5-C7 and diodes VD6-VD9 - from CFL, tuning resistor R7 - SPZ-19a.

For the manufacture of transformer T1, a ballast choke from a CFL with a power of 10 W was used. It is necessary to select a choke, the design of which allows you to wind an additional winding without disassembly - 10 turns of MGTF-0,2 wire. In the transformer, it will perform the function of the primary (I) winding, and the secondary (II) will be the inductor winding.

The Li-ion cell phone battery is glued to the board on the cell-free side. Switch SA1 - sliding PD9-1 or similar imported. The appearance of the converter together with the LED board (from a power lamp with a serial connection of 21 LEDs) is shown in fig. 10.

Fig. 10

In conclusion, it should be noted that the boost converter can also be assembled on a specialized microcircuit, which, by the way, will reduce its size. A lamp with a converter can be used as a hand lamp, but in this case it is advisable to use a battery consisting of three Ni-MH batteries as a power source.

Author: I. Nechaev

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