RU2402108C1 - Light-emitting diode radiation source for transport control systems - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: in a light-emitting diode radiation source having at least one or more semiconductor light emitters, monochromatic radiation emitters in the UV or optical region, a light emitter holder with connection leads, a radiator and a casing lens, in accordance with the invention, the semiconductor light emitters and monochromatic radiation emitters in the UV or optical region are coated with a luminophor. The wavelength of the radiation emitters coated with luminophor lies in the 450-455 nm range, and its chromaticity coordinates lie in the range X=(0.310, 0.315, 0.360, 0.360)±0.001, Y=(0.330, 0.310, 0.370, 0.350)±0.01.

EFFECT: invention enables design of a light-emitting diode radiation source which combines all advantages of light-emitting diode devices on one hand, and its parametres weakly depend on ambient temperature on the other hand.

9 cl, 10 dwg, 1 tbl

Description

The invention relates to light emitting means, mainly for railway control systems, such as a traffic light, and can be used in information display systems.

The main advantages of semiconductor LED radiation sources over other light sources were:

reliability - at the moment, LEDs of various designs have a service life of up to 50,000 hours or more, incandescent and fluorescent lamps have a service life of not more than 10,000 hours;

the light output of LEDs currently exceeds 120 lm / W and is constantly growing, while the light output of incandescent and fluorescent lamps is in the range of 10-100 lm / W.

The use of incandescent lamps with light filters is not effective, because the filter cuts out a rather narrow emission spectrum from a wide spectrum of radiation from incandescent lamps, from ultraviolet to infrared, which makes up 1.4-50% of the light power of an incandescent lamp, depending on the spectral range. The spectrum of the white LED light source is much narrower and the relative light power obtained after the filter is 10-60%.

The experience of using semiconductor LED radiation sources in various information display systems has confirmed the above advantages of such sources over traditional incandescent lamps. At the same time, the fundamental physical properties of semiconductor LED radiation sources reduce the efficiency of their use, especially in systems and devices of light-signal equipment.

The experience of using semiconductor LED radiation sources in various information display systems has confirmed the above advantages of such sources over traditional incandescent lamps. At the same time, the fundamental physical properties of semiconductor LED radiation sources reduce the efficiency of their use, especially in systems and devices of light-signal equipment.

From the dependences of the radiation intensity, direct voltage drop, wavelength (color coordinates) of the radiation on the ambient temperature, and hence on the PN transition temperature, it is evident that in order to satisfy the requirements of systems with unchanged ergonomics, it is necessary to stabilize the PN transition temperature in some temperature range, regardless of the ambient temperature. On the other hand, the use of semiconductor emitters, weakly dependent on physical parameters on changes in external temperature, can also solve the problem of changing chromaticity coordinates and changing light intensity in a certain temperature range.

The existing method of heat removal from the P-N junction area consists in natural convection using radiators and heat pipes.

The calculation of thermal resistances for the emitter crystal was carried out using the equivalent method proposed by the authors of [1].

The remaining thermal resistances were calculated on the basis of known data on the thermal conductivity of the layers and the geometry of the emitter, where the basic heat transfer equation is as follows:

,

,

where Q is the power dissipation, W;

k is the thermal conductivity, W / cm · K;

A is the area of the radiator, cm ² ;

T is the temperature, K.

As can be seen from (1), the main quantity that determines the outflow of heat from the crystal of the emitter to the air is the area of the radiator. The thermal resistance to air of any radiator with an area of 1 cm ² with free convection is ≈ 200 K / W. Thus, for efficient heat removal from the crystal, the area of the radiator should be at least 100 cm ² . However, when the ambient temperature changes, according to (1), the PN transition temperature changes by the magnitude of the temperature change, which clearly shows that the existing method of heat removal is effective only at a constant ambient temperature, which imposes significant restrictions on the use of LED emitting devices using in its design, a similar method of heat removal.

The task set by the authors in the creation of the present invention is to create an LED emitting device, the operational capabilities of which, on the one hand, combine all the above advantages of such devices, and on the other hand, weakly depend on the ambient temperature, i.e. creating an analogue of an incandescent lamp with all the advantages of semiconductor light emitters Table.

The possibility of creating such devices, according to the authors of [2], is due to the use of the electric method of heat transfer from the P-N transition to the radiator by using the Peltier effect. Among the known LED devices using a similar effect, the LED device according to RF patent No. 2170995 may be mentioned. The specified device, selected as a prototype, containing one or more semiconductor light emitters with connecting leads, a substrate, a lens, and equipped with one or several Peltier thermocouples connected in series and one or more radiators. Light emitters are connected in series in a circuit of thermocouples and are placed in the region of heat absorption by thermocouples, and radiators are placed in the region of heat generation by thermocouples. The design of the known device allows to increase its power dissipation, while maintaining the proportionality of the input-output parameters, in particular, the light intensity of the radiation of the LED device from direct current through the LED, with the possibility of varying the viewing angle and spatial radiation pattern.

The disadvantages of the known device include the fact that the heat generated by the semiconductor crystal of the LED radiation source, which is connected in series with the Peltier element, is always much greater than the heat removed by the Peltier element. At reasonable currents through the Peltier element, the direct voltage on the crystal of the emitting elements of the LED, while the Peltier elements are connected in parallel, is much greater than on the Peltier element. Therefore, the current through the Peltier element increases to values at which the Joule heat begins to prevail over the Peltier effect, as a result of which the LED overheats and its color parameters change. Secondly, at subzero ambient temperatures, the Peltier element begins to work more efficiently and the pn junction temperature drops sharply, which is unacceptable in devices for visual display of information due to changes in their color characteristics.

The technical result of the invention is the creation of an LED radiation source, the operational capabilities of which, on the one hand, combine all the above advantages of such devices, and on the other hand, are weakly dependent on ambient temperature, i.e. creating an analogue of an incandescent lamp with all the advantages of semiconductor light emitters (Table). It compares an incandescent lamp and an LED radiation source. The incandescent lamp has a wide spectrum from the near ultraviolet to the infrared region of the spectrum, the spectrum is continuous, so when applying filters, you can get any color: blue, red, green, etc. An ambient temperature of -55C ° to + 65C ° does not affect the color of the radiation and the luminous intensity. However, the life of any incandescent lamp does not exceed 1000 hours.

An LED light emitter, unlike an incandescent lamp, has a service life of at least 50,000 hours. However, the following physical properties of semiconductor emitters have different effects on their applications. Semiconductor emitters have a narrow emission spectrum, and also have all the necessary wavelengths for use in traffic lights. On the one hand, it is good and the use of filters is not necessary, but, on the other hand, (see the column Temperature Shift in the Table) at positive and negative temperatures, the wavelength (or color coordinate) moves away from what is allowed; example for yellow from the same table, 0.11nm / C ° X65C ° = 7.15 nm; 592.5 nm + 7.15 nm = 599.65 nm, which is beyond the scope of the traffic light permitted by technical conditions. The light intensity also behaves (see figure 2), where with increasing temperature it falls for yellow twice.

Earlier, we proposed the use of Peltier elements to stabilize the temperature of the pn junction; the disadvantages of this method are described in this patent above. Therefore, we propose to use the smallest temperature shift of the radiation wavelength, which for the blue color of the LED source is 0.03 nm / ° C, then 0.03 X65 = 1.95 nm, which fits perfectly for any color. To obtain any color, it is necessary to cover the blue emitter with a phosphor and get a white color, and then put the standard filter. We got a white emitter with a shorter spectrum, which is also a plus for us, with a small temperature shift along the wavelength and with a long life.

To achieve the technical result in an LED radiation source containing at least one or more semiconductor light emitters, single-color ultraviolet or optical radiation, a holder of light emitters, with connecting leads, a radiator and a coating lens, according to the invention, semiconductor light emitters, single color ultraviolet or optical radiation is coated with a phosphor, while the wavelength of the emitters of light coated with a phosphor lies in the range 405-455 nm, and its chromaticity coordinates lie in the range X = (0.310, 0.315, 0.360, 0.360) ± 0.001, Y = (0.330, 0.310, 0.370, 0.350) ± 0.01, while the LED source radiation can be made in the form of a T-shaped figure, with dimensions: 4 ± 0.5 mm - the long side, and 3 ± 0.5 mm - the short side, the phosphor is made by Stokesovsky based on garnets and silicates, the radiator area is ≥100 cm ² , the volume between the coating lens and the light emitters is filled with a transparent or scattering, sealing elastic compound with a refractive index of ≥1.3, the coating lens and made with a wall thickness of ≥1 mm. To obtain the desired chromaticity coordinates, in the yellow range, the cover lens is made in the form of a cut filter.

The invention is illustrated by drawings, where

figure 1 - LED radiation source with a phosphor;

figure 2 is a graph of light intensity versus ambient temperature;

figure 3 - circuit diagram of the claimed design;

figure 4 - emission spectrum of a white LED source;

figure 5 - emission spectra of a LED source located in a traffic light with a red filter;

6 - emission spectra of a LED source located in a traffic light with a green filter;

Fig.7 - emission spectra of an LED source located in a traffic light with a yellow filter;

Fig. 8 is the chromaticity coordinates of the obtained yellow color of the radiation of an LED radiation source for transport control systems (T LED = 6500K). Dotted line - railway standard;

Fig.9 - radiator LED source for dwarf traffic lights;

figure 10 - radiator of the LED source for the main traffic lights.

The LED radiation source consists of a semiconductor light emitter 1 of a single color ultraviolet or optical radiation coated with a phosphor, a holder of light emitters 2 with connecting leads 3, a radiator 4, a coating lens 5. The wavelength of the emitters of the light coated with a phosphor lies in the range 405-455 nm , and its chromaticity coordinates lie in the range X = (0.310, 0.315, 0.360, 0.360) ± 0.001, Y = (0.330, 0.310, 0.370, 0.350) ± 0.01, which allows for the placement of an LED source in a railway traffic light with standard filters by uchat desired chromaticity coordinates of a traffic light.

The semiconductor light emitter 1 is made in the form of a T-shaped figure, where several semiconductor crystals are combined into a block, for example, four crystals form the upper crossbar, with dimensions: 4 ± 0.5 mm, and two crystals form the base, with dimensions 3 ± 0, 5 mm, which allows to obtain a narrow radiation pattern in the horizontal direction and a sufficient diagram in the vertical direction for visualization at a close distance of about 10 m. The block is placed on the holder of the light emitters 2 in the focal length plane of the light filters ora, made in the form of Fresnel lenses.

The phosphor is used by Stokes on the basis of garnets and silicates to obtain the desired color coordinates of the LED emitter.

The minimum surface area of the radiator 4 for dwarf traffic lights is ≥100 cm ² , which provides the necessary heat sink. In this case, the holder of the light emitter is parallel to the connecting terminals. For the main traffic lights, the holder of the light emitter is perpendicular to the connection terminals.

The volume between the coating lens 5 and the light emitters 1 is filled with a transparent or scattering, sealing elastic compound 6 and has a refractive index of ≥1.3. Coating lens 5 is made with a wall thickness of ≥1 mm to reduce light absorption in it.

The device operates as follows. The supply voltage on the LED source ranges from 9 V to 12 V. According to this option, with a supply voltage of 7.0 V, the current passing through the LED source is 0.35 A. The characteristics of the remaining parameters are as follows: limiting resistance 7 (R1, R2, R3) 17.5 Ohms, 8 Schottky diodes (D1, D2), 9 Schottky diodes (D3, D4), current 1.05 A.

When an alternating positive electric voltage is applied to terminals 3 (VCC), which provides direct electric current through Schottky diodes 8 (D1 and D2) and light emitters 1, the latter begin to emit light. When a negative voltage is applied, current will flow through the Schottky diodes 9 (D3 and D4) and the light emitters will also emit light. Thus, both half-waves of alternating voltage work. The presence of polymer compound 6 provides a reduction in radiation power loss. The required radiation pattern is provided by filters - Fresnel lens traffic lights. In addition, the polymer compound provides moisture resistance to the emitter crystals.

The described design of the light-emitting diode radiation source provides its high technical characteristics, allowing to provide a powerful narrowly directed radiation. The proposed LED can find wide industrial application in the production of semiconductor light emitting devices, mainly for railway control systems.

Literature

[1] Zakharov A.L., Asvadurova E.I. Calculation of thermal parameters of semiconductor devices: Equivalent method. - M .: Radio and communications, 1983. - 184 p.

[2] Abramov V.S. and others. Patent for the invention No. 2170995 from 08/31/2000, LED device.

Table Device type Appliance color White Blue Yellow Green Red LED lamp Wavelength λ _max nm typ 455 475 592 525 631 Temperature LED dvig nm / ° C 0,03 0,03 0.11 0,03 0.09 Area borders 0.310 0.108 0.617 0.241 0.735 with filter 0.310 0.144 0.561 0,022 0.703 X 0.450 0,207 0.545 0.206 0.704 0.450 0.180 0.604 0,300 0.725 Y 0.335 0,090 0.383 0.746 0.265 0,306 0,030 0.439 0.420 0.297 0.390 0.129 0.427 0.376 0.290 0.420 0.164 0.383 0.490 0.267 Luminous intensity I _v , cd. 2500-10000 200-1600 4350-21750 2600-7800 2100-19000 Incandescent lamp Spectrum Continuous from 470 nm to near infrared Temperature LED dvig nm / ° C Absent Area borders with 0.310 0.108 0.617 0.241 0.735 filter 0.310 0.144 0.561 0,022 0.703 X 0.450 0,207 0.545 0.206 0.704 0.450 0.180 0.604 0,300 0.725 Y 0.335 0,090 0.383 0.746 0.265 0,306 0,030 0.439 0.420 0.297 0.390 0.129 0.427 0.376 0.290 0.420 0.164 0.383 0.490 0.267 Luminous intensity I _v , cd. 2500 200 4350 2600 2100

Claims (7)

1. An LED radiation source for transport control systems, comprising at least one or more semiconductor light emitters, single-color radiation, a light emitter holder, with connecting leads, a radiator, a coating lens, characterized in that the single-color ultraviolet semiconductor light emitters or the optical range is covered with a phosphor, while the wavelength of the emitters of light coated with a phosphor lies in the ultraviolet or optical range, namely, 405-455 nm, and its chromaticity coordinates lie in the range X = (0.310, 0.315, 0.360, 0.360) ± 0.001, Y = (0.330, 0.310, 0.370, 0.350) ± 0.01. 2. The device according to claim 1, characterized in that the LED radiation source is made in the form of a T-shaped figure with dimensions 4 ± 0.5 mm — the long side, and 3 ± 0.5 mm — the short side.
3 The device according to claim 1, characterized in that the phosphor is used by Stokes on the basis of garnets and silicates. 4. The device according to claim 1, characterized in that the radiator area is ≥100 cm ² . 5. The device according to claim 1, characterized in that the volume between the coating lens and the light emitters is filled with a transparent or scattering sealing elastic compound. 6. The device according to claim 5, characterized in that the sealing compound has a refractive index of ≥1.3. 7. The device according to claim 1, characterized in that the coating lens is made with a wall thickness of ≤1 mm 8. The device according to claim 1, characterized in that the coating lens is made in the form of a cut filter to obtain the desired color coordinates in the yellow range.

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