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This article was also published in Maxim Engineering Journal, Issue 61 (PDF, 1MB).
LED lighting can effectively save energy Today, lighting accounts for nearly one-fifth of the electricity used in the United States¹, and most of them still use low-efficiency (<5%) incandescent lamps. Promoting energy-efficient lighting technology will greatly save electricity, reduce carbon dioxide emissions, and reduce the need for new power plants.
For example, the U.S. Department of Energy expects to replace embedded spotlights with LEDs alone, saving 81.2 trillion watt-hours (TWh) of electricity each year, equivalent to the annual electricity consumption of 6.7 million households. In summary, the energy saved by this item alone can reduce the construction of 13 1000MW thermal power plants².
Because of its high efficiency, MR16 halogen lamps are widely used to replace incandescent lamps in commercial and domestic lighting. The power consumption range of commonly used MR16 lamps is 10W to 50W, and its luminous flux range is 150 lumens (lm) to 800lm. Therefore, the efficiency of a typical MR16 halogen lamp is about 15 lumens per watt (lm / W) or a luminous efficiency of 15%. Although the low-efficiency incandescent lamp has improved, the MR16 halogen lamp still has a lot to be improved.
Today's LED technology provides a cost-effective, MR16 compatible solid-state lighting alternative for halogen lamps. For example, the latest generation of LedEngin ™ 5W (single-chip, 4mm × 4mm package) and 10W (four-chip, 7mm × 7mm package) high-power LEDs at a current of 1000mA and a junction temperature (TJ) of + 120 ° C The effect is 45lm / W. Under actual operating conditions, this specification is equivalent to a typical luminous flux of 155lm (1000mA, TJ = + 120 ° C, 5W package) and 345lm (700mA, TJ = + 120 ° C, 10W package). These LEDs save 50% of power consumption than halogen lamps under the same brightness conditions.
In addition, the typical halogen lamp is used within 2000hrs. LedEngin expects that its LED can maintain a fairly high (90%) light intensity after long-term operation (100,000hrs, TJ = + 120 ° C). The longer service life of LEDs effectively reduces the lamp replacement rate during the product's effective period, thereby reducing maintenance and usage costs.
MR16 LED Reference Design In the MR16 LED reference design shown in Figure 1, Maxim chose LedEngin's 5W white LED (WLED) to demonstrate the MAX16820's 1000mA current drive capability. Table 1 and Table 2 list the components and electrical parameters of the detailed MR16 reference design, which uses a typical 12VAC ± 10% input Voltage in most MR16 applications.
Figure 1. A 5W MR16 LED lamp driving circuit built using the MAX16820 LED driver. The LED in the figure is a 5W WLED from LedEngin.
Table 1. 5W MR16 LED drive circuit component list DesignaTIon DescripTIon D1–D4 RecTIfier diodes
FBR130 C1, C2 100µF / 25V tantalum capacitors or one
220µF / 25V electrolyTIc capacitor C4 1µF / 25V ceramic capacitor R1 0.2Ω ± 1% sense resistor
IRC LRC-LR1206LF-01-R200-F C3 1µF / 6.3V ceramic capacitor Q1 MOSFET
FDN359BN D5 Freewheeling diode
FBR130 U1 MAX16820 L1 39µH / 1.2A buck inductor
Sumida CDRH6D38NP-390NC
Table 2. Electrical parameters of 5W MR16 LED lamp driving circuit VIN (min) 10.8VAC VIN (max) 13.2VAC VLED (min) 5V VLED (max) 3.1V ILED 1A ILED Tolerance ± 15% Open-LED Protection Yes Shorted-LED Protection Yes
The MAX16820 is designed for LED driver applications, especially LED-based MR16 designs, and is ideal for MR16 LED lamp circuits. The MAX16820 is packaged in an ultra-small, 6-pin TDFN package and operates from an input voltage of 4.5V to 28V. It can drive external cost-effective MOSFETs to provide a wide range of LED current drive capabilities. The MAX16820 operates in the automotive temperature range (–40 ° C to + 125 ° C) and can safely operate in the high-temperature environment of MR16 lamps. In addition, the MAX16820 can provide up to 25W or higher power, and its 2MHz (typical) switching frequency allows the use of small external inductors and capacitors, so that the driving circuit can be placed in MR16 lamps.
The 5W MR16 LED lamp driver shown in Figure 1 includes a rectifier bridge (D1–D4), a 100µF filter capacitor (C1 and C2), and a buck conversion circuit. The buck LED converter consists of MAX16820, buck inductor (L1), power MOSFET (Q1), freewheeling diode (D5), and current-sense resistor (R1).
5W high brightness LED (HB LED) requires 1A drive current. Buck LED driver design can provide 1A DC output current. The driver uses a hysteretic control scheme to control the current of the buck inductor and provide the 1A current required by the LED. The hysteresis control of the MAX16820 helps build simple, highly reliable drivers and has 5% LED current accuracy.
In order to ensure that the 5W HB LED provides a fixed 1A current in the entire power supply and frequency range, a filter capacitor should be connected to the DC bus to limit the voltage ripple of the DC power line. The total capacitance is at least 200µF. Tantalum or electrolytic capacitors with a nominal value of 220µF / 25V can be used to reduce costs.
To ensure sufficient output current accuracy, the maximum ΔI / ΔT of the inductor current should be less than 0.4A / µs. As shown in Figure 1, the maximum voltage drop of the inductor is VL1MAX, and the size of the inductor L1 can be calculated by the following formula:
If VAC_IN = 12V, δ = 10%, VO = 3.6V, the inductance L1 should be greater than 37µH. Therefore, here L1 selects the standard inductance of 39µH, and δ is the allowable AC input voltage fluctuation percentage, and VO is the LED forward voltage.
The design was tested using LedEngin 5W and WLED-based MR16 lamps. The device is shown in Figure 2. Figures 3 to 6 show the test waveforms for this design. The input voltage is 12VAC (nominal value) and the output current ripple is about 10%.
Figure 2. LedEngin's LED-based MR16 lamp has a unique heat sink for cooling into the air. The lamp driver circuit board based on the MAX16820 is placed behind the heat sink.
Figure 3. The input AC current tested by the first MR16 reference design platform is shown as CH1, and the output DC current is shown as CH2.
Figure 4. Details of CH2 output current ripple.
Figure 5. In the test platform, CH1 shows the voltage envelope of the MOSFET gate driver, and CH2 shows the drain-source voltage envelope.
Figure 6. CH1 shows the MOSFET gate drive waveform, and CH2 shows the drain-source voltage waveform.
As shown in Figure 4, when a 200µF DC filter capacitor is used, the voltage ripple of the DC power bus is 8.5V. The hysteresis control mode based on the MAX16820 has a good power supply regulation rate. Since the input bus voltage ripple is very small, the change of the output LED current is reduced. For the 5W MR16 LED lamp driver, the test results show that the ripple and variation of the AC input voltage will exceed 8.5V, but the output LED current is still stable at 1A.
The PCB of the MR16 lamp driver shown in Figure 7 has two layers. All components and two AC input connection pads and two DC output connection pads (labeled LED + and LED-) are placed on the top and bottom layers.
Figure 7. The connection pads LED + and LED- for the DC output can be seen on the PCB screen printing layer (top and bottom) of the 5W MR16 LED lamp driver.
In HB LED applications, if you want to maintain 90% lumen efficiency for a long time after 100khr, it is best to limit the junction temperature of 5W LedEngin LED to + 120 ° C. As a low-cost heat dissipation solution, the heat sink can dissipate the heat generated by the LED junction into the air. The heat sink of the 5W MR16 LED lamp can dissipate 5W of LED power. The PCB of the 5W MR16 LED lamp driver is mounted on the back of the heat sink.
It is worth noting that the unique heat sink design of the 5W MR16 LED lamp is different from the halogen lamp that directly radiates the heat generated by the lamp tube to the surrounding air. In the LED-based design, the heat is first conducted to the heat sink (Figure 2 Shown), and then dissipated into the air by convection. Conclusion Compared with other low-power (1W and 3W) LED solutions, the high-power, 5W MR16 LED reference design can significantly improve the brightness. Therefore, the design eliminates the need for multiple radiation sources in the 10W halogen lamp solution to meet MR16 requirements.
To obtain Maxim ’s latest MR16 driver with standard dimming method and electronic transformer working solution, please send an application to: var name = "hbled @"; var domain = "maxim-ic.com"; document.write (" "+ name + domain +" "); (English only).
references
¹Energy Information Administration, Annual Energy Outlook 2008 (Washington DC, June 2008).
²U.S. Department of Energy, Energy Savings Estimates of Light Emitting Diodes in Niche Lighting Applications (Washington DC, 2008).
Abstract: Using LEDs to replace MR16 halogen lamps can effectively reduce energy consumption and save the cost of circuit and system maintenance. This application note details the advantages of using LEDs in the current MR16 lighting system. The 5W white LED drive circuit given in this article combined with a heat sink can replace 10W halogen lamps in MR16 lighting.