**3.2. Active control methods**

### *3.2.1. Linear power drivers*

Active current control uses bipolar or MOSFET transistors as regulation devices or feedback elements to regulate the current driven through the LEDs. In contrast to the polarization resistors, this solution is the next step in a complexity qualification as it uses again a resistor but now as a current sensor load that is able to modify the gate signal of the control transistor. The resistor can be of a much lower value as it will not work as a limitation but as a sensor.

A large number of ICs from many manufacturers are available in the market to implement these types of drivers. Efficiencies over 95% can be achieved with adequate designs as observed

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**a.** They do not control the temperature of LEDs. This defines their lifetime expectation.

**b.** They include components that are not as reliable as LEDs (inductors, electrolytic capaci-

**c.** They generate an electric conversion that provides a current-regulated output. In all cases,

Another driver option is to use MOSFET transistors as commutators to create a pulse-width modulation (PWM) signal that controls the energy introduced into the LED matrix. Under this concept, DC lamps can be driven with an electronic circuit that applies regulated current PWM cycles according to the LED matrix temperature or the voltage level of the source.

The control principle assures that the temperature of the LED is kept below high values to guarantee the expected lifetime in all working conditions using only a reliable hardware architecture of very few components: one low-power microcontroller, one temperature sensor, and a power MOSFET (N-type) that acts as the control actuator in the LED matrix, plug-

This control architecture can execute, if required, a smooth reduction on the active period of the LED driving signal (from a normal status of 100% active) to reduce the power consumption. This

in **Figure 4**. However, these CC drivers present the following main drawbacks:

tors, etc.) which become the weakest points of these types of lamps.

this reduces efficiency, performance, and, as mentioned, reliability.

ging or unplugging this with a PWM commutation (see **Figure 5**).

**Figure 4.** Efficiency versus load curve of commercial DC/CC switch-mode converter drivers.

*3.2.3. LED matrix temperature-feedback drivers*

The obtained efficiency is also good in case there is a constant forward DC voltage source on the range of the nominal polarization voltage of the LED because the control neglects the entire voltage drop in the semiconductor. If the voltage variation is within ±10% of the nominal LED polarization, voltage efficiency can still be above 84% on the worst case [9].

This solution can be improved using linear voltage regulators (LVRs) set as CC control elements (e.g., LM317 or NTE956) instead of transistors [10]. They use an internal voltage reference that offers a more accurate solution, but they have a minimum dropout voltage—as high as a few volts—which introduces significant energy loses (see **Figure 3**).

In general, these types of solutions, as well as the first option, have as main advantages that both include no EMIF generation as there is no current commutations (thus, no filtering is required). However, they allow a limited supply voltage range; the LED load voltage has to be lower than the supply voltage, and there are significant energy losses due to heat dissipation.

### *3.2.2. CC switch-mode converter drivers*

This is the most implemented type of solution for commercial DC LED lighting drivers. Although there are many different variations, three standardized models are widely recognized to configure CC generators for HP LEDs. Each of them is prepared for a different relationship between the supply and the LED voltage that has to be maintained independently of the variations that can suffer the supply or the load due to "Tj" changes:


**Figure 3.** Linear power LED driver configurations: (A) MOSFET and (B) linear voltage regulator.

A large number of ICs from many manufacturers are available in the market to implement these types of drivers. Efficiencies over 95% can be achieved with adequate designs as observed in **Figure 4**. However, these CC drivers present the following main drawbacks:


#### *3.2.3. LED matrix temperature-feedback drivers*

this solution is the next step in a complexity qualification as it uses again a resistor but now as a current sensor load that is able to modify the gate signal of the control transistor. The resistor

The obtained efficiency is also good in case there is a constant forward DC voltage source on the range of the nominal polarization voltage of the LED because the control neglects the entire voltage drop in the semiconductor. If the voltage variation is within ±10% of the nomi-

This solution can be improved using linear voltage regulators (LVRs) set as CC control elements (e.g., LM317 or NTE956) instead of transistors [10]. They use an internal voltage reference that offers a more accurate solution, but they have a minimum dropout voltage—as high

In general, these types of solutions, as well as the first option, have as main advantages that both include no EMIF generation as there is no current commutations (thus, no filtering is required). However, they allow a limited supply voltage range; the LED load voltage has to be lower than the supply voltage, and there are significant energy losses due to heat dissipation.

This is the most implemented type of solution for commercial DC LED lighting drivers. Although there are many different variations, three standardized models are widely recognized to configure CC generators for HP LEDs. Each of them is prepared for a different relationship between the supply and the LED voltage that has to be maintained independently of

• Buck converters: very efficient step-down topology with many implementations: synchro-

• Boost converters: step-up topology very common in battery-powered equipment. The two

• Boost-buck converters (single-winding fly-back converters): they drive power loads with both step-up and step-down requirements. This model is characteristic from stand-alone systems powered with batteries where input voltage can suffer large variations. They are

can be of a much lower value as it will not work as a limitation but as a sensor.

20 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

as a few volts—which introduces significant energy loses (see **Figure 3**).

the variations that can suffer the supply or the load due to "Tj" changes:

nous switching, average current, peak current, or hysteric control.

basic implementations are inductive boosts or charge pumps.

more flexible but less efficient than the two previous options.

**Figure 3.** Linear power LED driver configurations: (A) MOSFET and (B) linear voltage regulator.

*3.2.2. CC switch-mode converter drivers*

nal LED polarization, voltage efficiency can still be above 84% on the worst case [9].

Another driver option is to use MOSFET transistors as commutators to create a pulse-width modulation (PWM) signal that controls the energy introduced into the LED matrix. Under this concept, DC lamps can be driven with an electronic circuit that applies regulated current PWM cycles according to the LED matrix temperature or the voltage level of the source.

The control principle assures that the temperature of the LED is kept below high values to guarantee the expected lifetime in all working conditions using only a reliable hardware architecture of very few components: one low-power microcontroller, one temperature sensor, and a power MOSFET (N-type) that acts as the control actuator in the LED matrix, plugging or unplugging this with a PWM commutation (see **Figure 5**).

This control architecture can execute, if required, a smooth reduction on the active period of the LED driving signal (from a normal status of 100% active) to reduce the power consumption. This

**Figure 4.** Efficiency versus load curve of commercial DC/CC switch-mode converter drivers.

switching current regulators are needed: boost or boost-buck solutions if the voltage of the LED lamp is over the DC source voltage and buck implementations if the voltage of the

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DC LED lighting allows eliminating components that are necessary in AC/DC conversion. To compare the component effort required in solutions with AC and DC current supplies, **Figure 6** shows a block diagram of a typical lamp driver AC operated. Once it reaches the last stage of the chain (DC/DC box), all the abovementioned for LED matrix powering are applicable [9].

• Filter: It suppresses high-frequency contents of the input source. Most of the international regulations (e.g., IEC 61000-3 or IEEE STD 519-2014) order that the maximum total harmonic distortion (THD) of the voltage and current signals generated must be under certain limits. It is also a necessary part of an active power factor corrector (PFC). It may still be required in DC drivers if switched conversions are used to avoid the generation of fluctua-

• Rectifier: It is typically implemented with a bridge of diodes. It might also be useful in DC operation to allow an arbitrary connection of the positive and negative lines. However, this

• PFC circuit: It increases the ratio between the useful (W) and the total power (VA) consumed by the driver. Many drivers use switch converters (typically a boost-type circuit) but this requires an input filter to limit high-frequency THD generation. The next review of the IEC 61000-3-2 intends to raise the requirement of integrating a PCF circuit in any lamp

problem may be solved with a mechanical system that avoids a wrong connection.

matrix of emitters is significantly below (80% or less) the DC source voltage.

**3.4. Advantages of DC versus AC drivers**

These blocks are as follows:

tions in the energy source.

driver from 25 to 5 W.

**Figure 6.** Typical topology of an AC lamp driver.

**Figure 5.** LED lamp with temperature and input voltage-feedback driver implementation.

implies reducing the light emitted but also the heat generated inside the LEDs. This situation can be reached by either abnormal working operation conditions or unusually high working temperatures. This control is a negative feedback compensation mechanism of current increments due to high "Tj" while powering with constant voltage DC values. The commutation frequency must be high enough to avoid significant flickering and low enough to produce no excessive EMIF. Values between 0.5 and 1.0 KHz are suitable.

A common DC driver adapts the grid values to the specific impedance of an LED matrix, but it is possible to flip this concept and evolve this driver to be able to modify the impedance of its LED lamp to adapt it to the variable voltage of a nonsteady power source.

The LED matrix may include also a P-channel MOSFET in series with a small impedance resistor (R) placed in parallel with the first LEDs connected on each branch of our matrix. This scheme is designed to adapt the lamp to the wide range of voltage supply of batteries. For example, the circuit in **Figure 5** is prepared for the voltage supplied by a 12 VDC lead acid battery that can vary between 11 and 15 VDC. The exponential V-I relationship of a white LED makes its brightness decrease dramatically when the voltage gets below 12.3 VDC (3.1 VDC per diode), generating unsatisfactory luminance. If the control detects an input voltage below this threshold, it activates the second PWM signal that takes out the first LED of each branch of the lamp for discrete moments. In this way, the impedance of the matrix is reduced keeping the rest of the LEDs with adequate "Vf" polarization and brightness.

This sample LED luminaire design varies its consumption from 13 (at 12.6VDC) to 7.5 W (at 11 VDC). This behavior can be considered good for PV stand-alone systems as the lamp consumption is reduced at low voltage (low energy in the battery) which contributes to a safe management of the system while maintaining a good level of illumination. The energy efficiency of the proposed control scheme is, on average, 15% higher than the one obtained with a CC switch converter control powering the same LED lamp [11].

### **3.3. Control method selection**

Designers may consider that if the voltage of the LED lamp is just below that of the DC source, both linear current regulators and temperature feedback controllers are simple, highefficient, cost-effective, and very reliable solutions. If the design is well adjusted to the input voltage, efficiencies can be extremely high; otherwise, significant loses appear. In those cases, switching current regulators are needed: boost or boost-buck solutions if the voltage of the LED lamp is over the DC source voltage and buck implementations if the voltage of the matrix of emitters is significantly below (80% or less) the DC source voltage.

#### **3.4. Advantages of DC versus AC drivers**

DC LED lighting allows eliminating components that are necessary in AC/DC conversion. To compare the component effort required in solutions with AC and DC current supplies, **Figure 6** shows a block diagram of a typical lamp driver AC operated. Once it reaches the last stage of the chain (DC/DC box), all the abovementioned for LED matrix powering are applicable [9].

These blocks are as follows:

implies reducing the light emitted but also the heat generated inside the LEDs. This situation can be reached by either abnormal working operation conditions or unusually high working temperatures. This control is a negative feedback compensation mechanism of current increments due to high "Tj" while powering with constant voltage DC values. The commutation frequency must be high enough to avoid significant flickering and low enough to produce no excessive

A common DC driver adapts the grid values to the specific impedance of an LED matrix, but it is possible to flip this concept and evolve this driver to be able to modify the impedance of

The LED matrix may include also a P-channel MOSFET in series with a small impedance resistor (R) placed in parallel with the first LEDs connected on each branch of our matrix. This scheme is designed to adapt the lamp to the wide range of voltage supply of batteries. For example, the circuit in **Figure 5** is prepared for the voltage supplied by a 12 VDC lead acid battery that can vary between 11 and 15 VDC. The exponential V-I relationship of a white LED makes its brightness decrease dramatically when the voltage gets below 12.3 VDC (3.1 VDC per diode), generating unsatisfactory luminance. If the control detects an input voltage below this threshold, it activates the second PWM signal that takes out the first LED of each branch of the lamp for discrete moments. In this way, the impedance of the matrix is reduced keeping the

This sample LED luminaire design varies its consumption from 13 (at 12.6VDC) to 7.5 W (at 11 VDC). This behavior can be considered good for PV stand-alone systems as the lamp consumption is reduced at low voltage (low energy in the battery) which contributes to a safe management of the system while maintaining a good level of illumination. The energy efficiency of the proposed control scheme is, on average, 15% higher than the one obtained with a CC

Designers may consider that if the voltage of the LED lamp is just below that of the DC source, both linear current regulators and temperature feedback controllers are simple, highefficient, cost-effective, and very reliable solutions. If the design is well adjusted to the input voltage, efficiencies can be extremely high; otherwise, significant loses appear. In those cases,

its LED lamp to adapt it to the variable voltage of a nonsteady power source.

**Figure 5.** LED lamp with temperature and input voltage-feedback driver implementation.

22 Light-Emitting Diode - An Outlook On the Empirical Features and Its Recent Technological Advancements

rest of the LEDs with adequate "Vf" polarization and brightness.

switch converter control powering the same LED lamp [11].

**3.3. Control method selection**

EMIF. Values between 0.5 and 1.0 KHz are suitable.


**Figure 6.** Typical topology of an AC lamp driver.

• Electrolytic capacitor: It levels the pulsating rectified voltage signal. In DC, they can suppress voltage dips of the energy source but most lighting applications may consider acceptable to pass them and allow short flickers on the LEDs.

means less space requirements, cost reduction, and simpler installation. Between 40 and 50% of the printed circuit board (PCB) in an AC/DC, LED driver is occupied by the AC components. **Figure 7** shows a photograph of two LED drivers. On the left, we present a 42-W AC unit by Eagle Rise with PF corrected over 0.95, an efficiency between 0.89 and 0.92 (60–100% loads) and no dimming possibilities. All parts that are necessary for AC conversion are highlighted. On the right, we have a 24VDC (18–32VDC range) input LDH-45B-700 DC dimmable LED driver by Mean Well with efficiencies between 0.95 and 0.96 (30–100% loads). It has no input diode

DC Network Indoor and Outdoor LED Lighting http://dx.doi.org/10.5772/intechopen.74974 25

**Figure 8** presents, similar to **Figure 4**, the efficiency of four commercial AC/CC drivers versus their load. These curves present larger slopes and an average decrement of efficiency of 5–6%

Nowadays, the US is the country that is adapting more DC-lighting installation in a context where, according to the 2016 calculation of its Energy Information Administration (EIA), this country used 15% of all its consumed energy for lighting purposes [12]. This is a significant reduction from the 22% calculated in 2009 due to the massive installation of LED equipment and efficiency initiatives as the AC to DC residential and commercial indoor grid translations. On account of this, these two sectors figure as very significant with 7% of the total electricity

If all general purpose lighting equipment in the world were converted to LED light sources (agreeing an average 40% saving at each point), their energy consumption could be decreased by around 1000 TW h/year, reducing 200 million tons of greenhouse gas emission [7]. Any additional development that allows higher efficiencies, as the elimination of the AC losses,

On average, 80% of the energy used in modern buildings power DC loads. Low-power devices (≤50 W), like most indoor LED lamps, are responsible for 35–50% of this use, and all of them work with small power-wasting converters. LEDs and DC power distribution in buildings

As it is considerably difficult to eliminate all the AC loads and the general distribution grid, the basic consensus is to replace all the many AC/DC converters placed on each luminaire with a common centralized frontend to provide high-efficiency conversion and protection

LED matrixes may work from just 3.3 VDC. Over this voltage, many possible solutions can be implemented using different serial/parallel LED configurations. It is important to select the

has also significant relevance due to the large amount of energy involved.

**4.1. Indoor direct current indoor led lighting: trends and applications**

can notably enhance the efficiency of this significant amount of energy.

and then conduct the electric power in DC to the LED fixtures.

bridge so that polarity has to be checked before powering the equipment.

compared to their DC/CC counterparts.

consumed (approx. 279 billion kWh) [13].

*4.1.1. Development of systems*

**4. Indoor and outdoor DC-lighting experience**

The LED driver can be housed in an external case or in the device itself (which is much cheaper and significantly simplifies the luminaire configuration). Eliminating the AC/DC components

**Figure 7.** Typical topology of a common AC lamp driver compared to a DC counterpart.

**Figure 8.** Efficiency versus load curve of commercial AC/CC switch-mode converter drivers.

means less space requirements, cost reduction, and simpler installation. Between 40 and 50% of the printed circuit board (PCB) in an AC/DC, LED driver is occupied by the AC components.

**Figure 7** shows a photograph of two LED drivers. On the left, we present a 42-W AC unit by Eagle Rise with PF corrected over 0.95, an efficiency between 0.89 and 0.92 (60–100% loads) and no dimming possibilities. All parts that are necessary for AC conversion are highlighted. On the right, we have a 24VDC (18–32VDC range) input LDH-45B-700 DC dimmable LED driver by Mean Well with efficiencies between 0.95 and 0.96 (30–100% loads). It has no input diode bridge so that polarity has to be checked before powering the equipment.

**Figure 8** presents, similar to **Figure 4**, the efficiency of four commercial AC/CC drivers versus their load. These curves present larger slopes and an average decrement of efficiency of 5–6% compared to their DC/CC counterparts.
