LEDs, tapes and their power from ET AC
Probably, I will not be mistaken if I say that more than 90% of the inhabitants of Russia know what LED strips are, to the question “can transformers from“ halogen ”be used to power LED strips?” they will answer “no, it is impossible!”. The most common explanation will be trivial "an electronic transformer is an alternating current, and LEDs need a constant current." That’s exactly what they say in stores, just such a leitmotif the vast majority of “professional” articles on this topic have, which, in general, have taught people to spend significantly more money.
Whether this is always justified and how LEDs actually behave in the most common LED tapes when powered by alternating current, we will try to find out during the presentation of reading this article.
I’ll make a reservation right away that for the designation “LED” I will continue to use a naturally occurring and completely natural abbreviation of LEDs and I will not intentionally use the English technical abbreviation LED (Light Emitting Diode) for this concept. In our current country, the lack of any proper technical training of managers and salespeople in stores has already led to litter and the appearance of such unnatural for a technical language, foolish for hearing and terrible in writing the letters "ice", "led'y", "ice", or as I recently saw in a running line - "LED LEDs." Not only is “oil - oil”, I just don’t want to echo and produce this “tongue-and-seek” ...
The ideological source for writing the study was a long-standing desire to refute unfounded and categorical allegations about the inadmissibility of supplying diabetes with alternating current. In general, the controversy of this statement is certainly striking to any specialist (as well as to a "non-specialist"), who understands that an LED, although it emits light, is primarily a DIODE. And this means that it will still radiate under the influence of alternating voltage, but only in its half-cycle.
1) Will the ET “start up” when the load is connected in the form of semiconductor diodes;
2) If the ET starts, will the pulse “alternating” electrical effect exceed the allowable parameters of the individual LEDs in the tapes. If it does exceed, then how long the diabetes will last under such conditions;
3) What is the economic efficiency of using ET in lighting designs on LED strips.
I needed to illuminate the space in the drawers and cabinets of the tables of my workshop. After equipping the kitchen, I had at my disposal 1.2 meters of a single-color LED tape with a total power of about 17 W (Aztech 14 W / meter) and one electronic transformer from the halogen - EAC 12V 20-60 W, the most common and cheapest, bought for 74 rubles in July 2014 To start, to start the ET, I loaded it with an ordinary 20 W halogen lamp and then connected all 1.2 meters of tape in parallel (Fig. 1). As expected, the tape lit up. In this case, the glow of the tape was uniform, of medium brightness, without any flicker visible to the eye, which is not surprising, because the output meander ET is modulated in amplitude to a subtle eye with a frequency of 100 Hz. During the experiment, turning off the lamp in such a circuit immediately led to the cessation of the illumination of the LED tape, which indicated the impossibility of starting ET on one half-wave of voltage. Then I broke the tape into two sections and turned them on in parallel (Fig. 2), which, according to the plan, was to ensure the operation of the output stage of the ET on both half-periods. At the same time, in order to exclude the bias of currents in the opposite direction and the overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. Then I broke the tape into two sections and turned them on in parallel (Fig. 2), which, according to the plan, was to ensure the operation of the output stage of the ET on both half-periods. At the same time, in order to exclude the bias of currents in the opposite direction and the overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. Then I broke the tape into two sections and turned them on in parallel (Fig. 2), which, according to the plan, was to ensure the operation of the output stage of the ET on both half-periods. At the same time, in order to exclude the bias of currents in the opposite direction and the overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. in order to exclude the bias of currents in the opposite direction and overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. in order to exclude the bias of currents in the opposite direction and overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not.
So, the answer to the first question - whether ET will start when replacing halogen lamps with an LED is positive. Yes, it will start! If you provide cross-parallel inclusion of tapes as in Figure 2.
Move on. Now we are trying to find the answer to the second question of our study. But now we are not having enough experiments, we need knowledge from the Fuel and Energy Center (Theory of Electro-Radio Circuits and Elements), which ultimately allows us to suggest: is it possible to supply LED tapes for a long time in this mode without serious damage to their durability, if at all to talk about damage?
Let's start with the SD tape device. The tape consists of parallel working sections (Fig. 3) of three emitters (indicated in the diagram - E) which are three separate LEDs under a common phosphor layer. Each diode (in the diagram - D) of the emitter is connected in series in triads with diodes from other emitters and a resistor that sets the calculated operating point of the diodes (see Fig. 4).
The resistor in the triad is selected in such a way that, when powered from 12 V and the calculated operating point of the diode, Upr = 3.3 V, Ipr = 14 mA, an excess voltage of about 2 volts was suppressed on it.
Rummaging around the manufacturers of SMD LEDs, it is easy to find the electrical parameters of the LEDs used:
To complete the study, I additionally took the current-voltage characteristic (CVC) of the working section of the tape (Fig. 5), and by simple recalculation I got the CVC for a separate LED (Fig. 6).
Fig. 5 Fig. 6
The I – V characteristics shown in the figures do not require additional explanations. I will only add that at a voltage of less than 2.35 V on a separate LED, its glow is completely absent, which corresponds to a supply voltage of the working section of about 7 V., and a supply voltage of 15.5 Volts on the tape is completely safe, because current through a separate LED does not exceed normal operational 30 mA.
However, all these numerical expressions of the operating parameters are relevant only for direct current. We are going to test the diode when exposed to alternating voltage, i.e. surge voltage in different directions. However, with such a supply, the maximum permissible values of currents and voltages on the diode can be several times, or even tens of times greater than the limits for direct current (this is well known and doubting managers can give lectures on fuel and energy centers) - it all depends on the duration and frequency of exposure. But the trouble is: the output voltage of the ET has a rather complex shape, which does not allow mathematically reliable description of it within the framework of this article, and the TTX for LEDs is not equipped with a section of absolute values for pulsed operation modes. Although there, however, there is one parameter (Ipr imp), but for what pulse duration it is relevant - it is not clear
Therefore, to study the degree of influence of alternating voltage of ET on LEDs, we will start from the postulate that any long-term pulsed current can be brought to such a value of direct current at which the work performed by the LED under the influence of pulsed current will be identical to work with constant current.
How do we evaluate the LED work? Yes, very simple. The LED under the action of the current flowing through it does the work of releasing light energy and heat. And we can very easily measure and compare these two parameters for both types of current, which means to determine how much the output voltage of the ET loads the LED compared to the standard 12 V stabilizer.
To assess the light energy emitted by a separate working section of the LED tape, I took the dependence of the illumination on the supply voltage. Illumination was measured at a distance of 10 cm from the emitters (Fig. 7).
Fig. 7
Thus, at this stage, everything is ready for us in order to get an answer to the second and third questions of our study.
First, we examine the output voltage of our ET:
Fig . 8
I must say right away that it is impossible to use a household electronic tester-ampervoltmeter to measure the voltage amplitude of this form. It is designed to measure strictly harmonic oscillations, and in our case it will lie very strongly, because we are dealing with an alternating pulse voltage modulated in amplitude by a current of twice the industrial frequency. The modulation frequency is 100 Hz, the filling frequency: 10 KHz is a bi-directional meander, the signal amplitude is Uа = 18 Volts. The oscilloscope did not record individual emissions with an amplitude of more than 18 V. Since the filling is meander, the effective voltage value will completely obey the law of the modulating signal, and therefore in our case Udeist = Uа / √2 = 18 / 1.41 = 12.7V. That is why the passport on the ET indicates that the output voltage is ~ 12V.
Looking at the diagrams and comparing them with the performance characteristics and current-voltage characteristics, it becomes clear that under the action of direct current on the LED, we are unlikely to go beyond the limits of permissible parameters. The claimed maximum direct pulse current for a single LED of 60 mA is achievable only at Upr> 3.9 V, i.e. with a voltage of more than 20 V on the tape (see volt-ampere characteristics), but we still do not reach such values. On the other hand, it is easily seen that the duration of the voltage exposure above the mentioned and perfectly safe 15.5 V (at which the current through the LED is not more than 30 mA) is no more than 8% of the total power supply time from the considered ET. I think riding it is dangerous for diabetes. OK. Remember. Check later.
Now let's figure out if we will go beyond the limits of the permissible reverse voltage even when the reverse half-cycle of the voltage is applied. In this case, the resistance R in the triad can be neglected, Uа (18V) will be evenly distributed over the LED in the triad, and the amplitude value of the voltage across the diode will be 6 V, which is more than the declared 5V. But, the duration of the excess will again not exceed 8% of the total operating time of the LED, and the second thing that confused me very much is that the permissible reverse voltage in all datasheets is very suspiciously the same for different series of LEDs. It is always 5V. OK. Let us remember this and begin to summarize the first results.
So, theoretically, with a direct half-time, we should not exceed the direct currents for LEDs, and with a reverse half-time, exceeding the declared permissible reverse voltage is small, both in terms of exposure duration and in absolute value.
Well, now it's time to test our findings in practice. Let's practically appreciate the light and heat output. If the light and heat generated by the tape do not exceed those emitted when powered by a standard power source for LED tapes, then our positive theoretical conclusion will be confirmed.
Having fed the tape from the ET, we counter-measure the light output of a single working section of the tape from three emitters and compare the values with the characteristic in Fig. 7. The light meter fixes the values at the level of 970-990 lux, which corresponds to the power supply of the tape from a voltage source slightly below 10 V !!! The heating of the tape turned out to be negligible and after 1 hour of operation did not exceed 35 degrees Celsius, at an ambient temperature of 25 ° C. Under similar conditions, but when supplied with direct current Upr = 12V, the tape was heated to 49 ° C, and the created illumination was about 2000 Lux. These results clearly indicate that, despite all the marketing admonitions, the semiconductor, when powered by ET, works in an underloaded mode and it is hardly necessary to expect its imminent death. By the way, looking at Fig. 9, and having measured the area of the figures of light blue and brick colors, you can understand why it is the LEDs that glow as if they are powered by 10V. The fact is that the light blue figure characterizes the conditions under which the LED tape does useful work (remember that this happens when Upit> 7 Volts). A light brown figure minus light blue is the condition under which the LED tape is idle - it does not work! The ratio of their areas is just 10 to 8. Everything converges, however, hehe.
Fig. 9
And nevertheless, against the background of a positive answer, the second question of our study, the thought of albeit insignificant, but still exceeding the permissible reverse voltage, did not give me rest. In short, I decided on a hard one: I connected the tape to a direct current source and gradually increasing the reverse voltage, I began to expect when the milliammeter would fix an electrical breakdown. Bringing the reverse voltage on a separate LED to almost 20 Volts, I still did not achieve a breakdown. The reverse current did not exceed 15 μA. Leaving this whole thing for almost a day, I was convinced that nothing had happened to the emitters, and apparently from the short pulsed effects of 6V versus 5V and nothing else should happen in the foreseeable future.
It is possible to use ET from halogens to power LED strips and it seems that this will not affect the durability of the LED strips and light sources at all. Rather, it will even be the opposite, but they will serve longer. Probably. So far it turns out that way. Forget only about counter-parallel inclusion and equality of shoulders.
Now the main question is not that - is it possible? The question is - Is it worth it?
The answer is the following - if you are planning to install a lighting system with novi, then you probably shouldn't . So the low cost of ET will be blocked by buying more or more power LEDs, because at 10 V the light flux created by the LED tape is two times less than what we have at 12V (see Fig. 7)
Power supply from the ET is justified in cases when:
Thanks.
Vink01
Whether this is always justified and how LEDs actually behave in the most common LED tapes when powered by alternating current, we will try to find out during the presentation of reading this article.
I’ll make a reservation right away that for the designation “LED” I will continue to use a naturally occurring and completely natural abbreviation of LEDs and I will not intentionally use the English technical abbreviation LED (Light Emitting Diode) for this concept. In our current country, the lack of any proper technical training of managers and salespeople in stores has already led to litter and the appearance of such unnatural for a technical language, foolish for hearing and terrible in writing the letters "ice", "led'y", "ice", or as I recently saw in a running line - "LED LEDs." Not only is “oil - oil”, I just don’t want to echo and produce this “tongue-and-seek” ...
The ideological source for writing the study was a long-standing desire to refute unfounded and categorical allegations about the inadmissibility of supplying diabetes with alternating current. In general, the controversy of this statement is certainly striking to any specialist (as well as to a "non-specialist"), who understands that an LED, although it emits light, is primarily a DIODE. And this means that it will still radiate under the influence of alternating voltage, but only in its half-cycle.
In fact, we will need to consistently answer three questions :
1) Will the ET “start up” when the load is connected in the form of semiconductor diodes;
2) If the ET starts, will the pulse “alternating” electrical effect exceed the allowable parameters of the individual LEDs in the tapes. If it does exceed, then how long the diabetes will last under such conditions;
3) What is the economic efficiency of using ET in lighting designs on LED strips.
So, six months ago, I just turned up a case convenient for experiments.
I needed to illuminate the space in the drawers and cabinets of the tables of my workshop. After equipping the kitchen, I had at my disposal 1.2 meters of a single-color LED tape with a total power of about 17 W (Aztech 14 W / meter) and one electronic transformer from the halogen - EAC 12V 20-60 W, the most common and cheapest, bought for 74 rubles in July 2014 To start, to start the ET, I loaded it with an ordinary 20 W halogen lamp and then connected all 1.2 meters of tape in parallel (Fig. 1). As expected, the tape lit up. In this case, the glow of the tape was uniform, of medium brightness, without any flicker visible to the eye, which is not surprising, because the output meander ET is modulated in amplitude to a subtle eye with a frequency of 100 Hz. During the experiment, turning off the lamp in such a circuit immediately led to the cessation of the illumination of the LED tape, which indicated the impossibility of starting ET on one half-wave of voltage. Then I broke the tape into two sections and turned them on in parallel (Fig. 2), which, according to the plan, was to ensure the operation of the output stage of the ET on both half-periods. At the same time, in order to exclude the bias of currents in the opposite direction and the overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. Then I broke the tape into two sections and turned them on in parallel (Fig. 2), which, according to the plan, was to ensure the operation of the output stage of the ET on both half-periods. At the same time, in order to exclude the bias of currents in the opposite direction and the overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. Then I broke the tape into two sections and turned them on in parallel (Fig. 2), which, according to the plan, was to ensure the operation of the output stage of the ET on both half-periods. At the same time, in order to exclude the bias of currents in the opposite direction and the overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. in order to exclude the bias of currents in the opposite direction and overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not. in order to exclude the bias of currents in the opposite direction and overheating of the output winding of the ET from the appearance of a constant component, I ensured that the number of LEDs in both load arms was equal (8 W). Immediately after connecting according to such a scheme (Fig. 2), the transformer successfully entered the generation mode, and both LED strips lit evenly and were left for 1 hour, during which neither they nor the ET itself were completely heated, which indicated rather normal electrical modes than not.
So, the answer to the first question - whether ET will start when replacing halogen lamps with an LED is positive. Yes, it will start! If you provide cross-parallel inclusion of tapes as in Figure 2.
And looking ahead ...
Looking ahead, I’ll say that as a further experiment showed, an ET with a passport minimum starting power of 20 W, successfully started even at 10 W of the total LED load (5 W in each arm).
Move on. Now we are trying to find the answer to the second question of our study. But now we are not having enough experiments, we need knowledge from the Fuel and Energy Center (Theory of Electro-Radio Circuits and Elements), which ultimately allows us to suggest: is it possible to supply LED tapes for a long time in this mode without serious damage to their durability, if at all to talk about damage?
Let's start with the SD tape device. The tape consists of parallel working sections (Fig. 3) of three emitters (indicated in the diagram - E) which are three separate LEDs under a common phosphor layer. Each diode (in the diagram - D) of the emitter is connected in series in triads with diodes from other emitters and a resistor that sets the calculated operating point of the diodes (see Fig. 4).
The resistor in the triad is selected in such a way that, when powered from 12 V and the calculated operating point of the diode, Upr = 3.3 V, Ipr = 14 mA, an excess voltage of about 2 volts was suppressed on it.
By the way, interesting ...
This arrangement of the triad is reliable and practical, because in the event of a failure of a single LED in the triad, none of the emitters will completely turn off, but will continue to burn, albeit with a third less brightness. You can of course create a triad based on a single emitter (and such tapes are found on sale). In them, the working section determining its cutting will be a fragment with a single emitter and a resistor, but in this case, failure of a single LED in the triad will lead to a loss of luminescence by the whole emitter, which will be immediately noticeable in any lamp.
Rummaging around the manufacturers of SMD LEDs, it is easy to find the electrical parameters of the LEDs used:
To complete the study, I additionally took the current-voltage characteristic (CVC) of the working section of the tape (Fig. 5), and by simple recalculation I got the CVC for a separate LED (Fig. 6).
I hope you...
I hope you have no doubt that this could be done physically, and the results would be the same.
Fig. 5 Fig. 6
The I – V characteristics shown in the figures do not require additional explanations. I will only add that at a voltage of less than 2.35 V on a separate LED, its glow is completely absent, which corresponds to a supply voltage of the working section of about 7 V., and a supply voltage of 15.5 Volts on the tape is completely safe, because current through a separate LED does not exceed normal operational 30 mA.
However, all these numerical expressions of the operating parameters are relevant only for direct current. We are going to test the diode when exposed to alternating voltage, i.e. surge voltage in different directions. However, with such a supply, the maximum permissible values of currents and voltages on the diode can be several times, or even tens of times greater than the limits for direct current (this is well known and doubting managers can give lectures on fuel and energy centers) - it all depends on the duration and frequency of exposure. But the trouble is: the output voltage of the ET has a rather complex shape, which does not allow mathematically reliable description of it within the framework of this article, and the TTX for LEDs is not equipped with a section of absolute values for pulsed operation modes. Although there, however, there is one parameter (Ipr imp), but for what pulse duration it is relevant - it is not clear
The thing is ....
The thing is that the pn junction of the semiconductor when working from alternating (pulsed) current works with a variable load. The current periods that cause the LED to heat up and work due to the emission of light waves are replaced by rest pauses (at which the current does not flow through the junction) and in which the semiconductor cools. And the question here is not so much in the absolute value of the current through the semiconductor, but how much will the semiconductor have enough time to cool so much during the currentless pause that it would compensate for the heating that occurred during the current period. Those. prevent thermal breakdown.
Here, I want to recall the “physics” of semiconductor failure. This will allow us to understand the essence of the ongoing processes. She, a physicist, is generally known, but still in her own words: the durability of any device is determined by its fault tolerance. Failures of diodes during normal operation occur in the event of thermal or electrical breakdown.
Electrical breakdown usually occurs when the permissible reverse voltage (Ureb) is exceeded. In this case, the diode loses the property of one-sided conductivity and begins to conduct in both directions. In most cases, an electrical breakdown is reversible and the instrument is restored to normal operation.
But thermal breakdown, on the contrary, is irreversible and occurs when there is an excess current of the direct (less often the reverse, which occurred after the electrical breakdown) direction and entails a destructive change in the semiconductor crystal as a result of strong local overheating of the pn junction, unable to let a large number of charged particles pass through it .
The bottom line here is that until conditions are created for the occurrence of thermal breakdown - the semiconductor is working. I repeat, in general, it doesn’t matter what absolute value the current flowing through it has. He can be very big! The main thing is that our diode does not have time to overheat. In the passport for any diode, two maximum permissible parameters are indicated: Maximum forward current Ipr mzx and Maximum reverse voltage U arr max, for prolonged exposure to direct current, which under standard operating conditions are guaranteed to lead to neither electric nor thermal breakdown.
Here, I want to recall the “physics” of semiconductor failure. This will allow us to understand the essence of the ongoing processes. She, a physicist, is generally known, but still in her own words: the durability of any device is determined by its fault tolerance. Failures of diodes during normal operation occur in the event of thermal or electrical breakdown.
Electrical breakdown usually occurs when the permissible reverse voltage (Ureb) is exceeded. In this case, the diode loses the property of one-sided conductivity and begins to conduct in both directions. In most cases, an electrical breakdown is reversible and the instrument is restored to normal operation.
But thermal breakdown, on the contrary, is irreversible and occurs when there is an excess current of the direct (less often the reverse, which occurred after the electrical breakdown) direction and entails a destructive change in the semiconductor crystal as a result of strong local overheating of the pn junction, unable to let a large number of charged particles pass through it .
The bottom line here is that until conditions are created for the occurrence of thermal breakdown - the semiconductor is working. I repeat, in general, it doesn’t matter what absolute value the current flowing through it has. He can be very big! The main thing is that our diode does not have time to overheat. In the passport for any diode, two maximum permissible parameters are indicated: Maximum forward current Ipr mzx and Maximum reverse voltage U arr max, for prolonged exposure to direct current, which under standard operating conditions are guaranteed to lead to neither electric nor thermal breakdown.
Therefore, to study the degree of influence of alternating voltage of ET on LEDs, we will start from the postulate that any long-term pulsed current can be brought to such a value of direct current at which the work performed by the LED under the influence of pulsed current will be identical to work with constant current.
How do we evaluate the LED work? Yes, very simple. The LED under the action of the current flowing through it does the work of releasing light energy and heat. And we can very easily measure and compare these two parameters for both types of current, which means to determine how much the output voltage of the ET loads the LED compared to the standard 12 V stabilizer.
To assess the light energy emitted by a separate working section of the LED tape, I took the dependence of the illumination on the supply voltage. Illumination was measured at a distance of 10 cm from the emitters (Fig. 7).
Fig. 7
Thus, at this stage, everything is ready for us in order to get an answer to the second and third questions of our study.
Let's get started.
First, we examine the output voltage of our ET:
Fig . 8
I must say right away that it is impossible to use a household electronic tester-ampervoltmeter to measure the voltage amplitude of this form. It is designed to measure strictly harmonic oscillations, and in our case it will lie very strongly, because we are dealing with an alternating pulse voltage modulated in amplitude by a current of twice the industrial frequency. The modulation frequency is 100 Hz, the filling frequency: 10 KHz is a bi-directional meander, the signal amplitude is Uа = 18 Volts. The oscilloscope did not record individual emissions with an amplitude of more than 18 V. Since the filling is meander, the effective voltage value will completely obey the law of the modulating signal, and therefore in our case Udeist = Uа / √2 = 18 / 1.41 = 12.7V. That is why the passport on the ET indicates that the output voltage is ~ 12V.
Looking at the diagrams and comparing them with the performance characteristics and current-voltage characteristics, it becomes clear that under the action of direct current on the LED, we are unlikely to go beyond the limits of permissible parameters. The claimed maximum direct pulse current for a single LED of 60 mA is achievable only at Upr> 3.9 V, i.e. with a voltage of more than 20 V on the tape (see volt-ampere characteristics), but we still do not reach such values. On the other hand, it is easily seen that the duration of the voltage exposure above the mentioned and perfectly safe 15.5 V (at which the current through the LED is not more than 30 mA) is no more than 8% of the total power supply time from the considered ET. I think riding it is dangerous for diabetes. OK. Remember. Check later.
Now let's figure out if we will go beyond the limits of the permissible reverse voltage even when the reverse half-cycle of the voltage is applied. In this case, the resistance R in the triad can be neglected, Uа (18V) will be evenly distributed over the LED in the triad, and the amplitude value of the voltage across the diode will be 6 V, which is more than the declared 5V. But, the duration of the excess will again not exceed 8% of the total operating time of the LED, and the second thing that confused me very much is that the permissible reverse voltage in all datasheets is very suspiciously the same for different series of LEDs. It is always 5V. OK. Let us remember this and begin to summarize the first results.
So, theoretically, with a direct half-time, we should not exceed the direct currents for LEDs, and with a reverse half-time, exceeding the declared permissible reverse voltage is small, both in terms of exposure duration and in absolute value.
Well, now it's time to test our findings in practice. Let's practically appreciate the light and heat output. If the light and heat generated by the tape do not exceed those emitted when powered by a standard power source for LED tapes, then our positive theoretical conclusion will be confirmed.
Having fed the tape from the ET, we counter-measure the light output of a single working section of the tape from three emitters and compare the values with the characteristic in Fig. 7. The light meter fixes the values at the level of 970-990 lux, which corresponds to the power supply of the tape from a voltage source slightly below 10 V !!! The heating of the tape turned out to be negligible and after 1 hour of operation did not exceed 35 degrees Celsius, at an ambient temperature of 25 ° C. Under similar conditions, but when supplied with direct current Upr = 12V, the tape was heated to 49 ° C, and the created illumination was about 2000 Lux. These results clearly indicate that, despite all the marketing admonitions, the semiconductor, when powered by ET, works in an underloaded mode and it is hardly necessary to expect its imminent death. By the way, looking at Fig. 9, and having measured the area of the figures of light blue and brick colors, you can understand why it is the LEDs that glow as if they are powered by 10V. The fact is that the light blue figure characterizes the conditions under which the LED tape does useful work (remember that this happens when Upit> 7 Volts). A light brown figure minus light blue is the condition under which the LED tape is idle - it does not work! The ratio of their areas is just 10 to 8. Everything converges, however, hehe.
Fig. 9
And nevertheless, against the background of a positive answer, the second question of our study, the thought of albeit insignificant, but still exceeding the permissible reverse voltage, did not give me rest. In short, I decided on a hard one: I connected the tape to a direct current source and gradually increasing the reverse voltage, I began to expect when the milliammeter would fix an electrical breakdown. Bringing the reverse voltage on a separate LED to almost 20 Volts, I still did not achieve a breakdown. The reverse current did not exceed 15 μA. Leaving this whole thing for almost a day, I was convinced that nothing had happened to the emitters, and apparently from the short pulsed effects of 6V versus 5V and nothing else should happen in the foreseeable future.
Of course, I must admit ....
Of course, I admit that this is perhaps the most controversial moment in my research, but the practical result is the experience more valuable than mathematical calculations. After all, experience is a reflection of the essence, and theory is just an attempt to calculate this essence in the brain.
Conclusions and answer to the third question
It is possible to use ET from halogens to power LED strips and it seems that this will not affect the durability of the LED strips and light sources at all. Rather, it will even be the opposite, but they will serve longer. Probably. So far it turns out that way. Forget only about counter-parallel inclusion and equality of shoulders.
Now the main question is not that - is it possible? The question is - Is it worth it?
The answer is the following - if you are planning to install a lighting system with novi, then you probably shouldn't . So the low cost of ET will be blocked by buying more or more power LEDs, because at 10 V the light flux created by the LED tape is two times less than what we have at 12V (see Fig. 7)
Power supply from the ET is justified in cases when:
- - you already have a working halogen lighting solution, and you would like to install LEDs without additional costs for PSUs and extra wires. I, for example, have done so in the kitchen;
- - you still have unused ETs (of which more and more will be released now), and the requirements for the planned lighting power are not large;
- - when you have matured the decision to replace the halogen lamps with LED ones, and you cannot make changes to the wiring for some reason.
Thanks.
Vink01