MR16 lamps are a type of multi-faceted reflector lamps that are widely used in commercial retail and home decorative lighting. Since they usually use halogen filaments as light sources, they have many disadvantages such as low efficiency, high heat generation and halogen capsule handling. However, current LED technology provides a halogen lamp alternative that is compatible with MR16, highly reliable and cost-effective. For example, ON Semiconductor's driver CAT4201, which can drive three LEDs in series, provides a new option for engineers designing MR16 LED lamps. The following will combine the characteristics of MR16 lamps to introduce high-efficiency MR16 LED lamp driver solutions that replace MR16 halogen lamps.
Characteristics of halogen lamps and LEDs
MR16 halogen lamps are used in creative lighting for many retail and consumer applications due to their unique size, configurability, focusing ability, aesthetics and practicality. The luminous flux of common MR16 halogen lamps ranges from 150 lumens (lm) to 800 lm, and the luminous efficacy is about 15 lm/W, or 15% luminous efficiency. Low efficiency, heat generation and halogen capsule handling issues are the disadvantages of this technology. In addition, the typical life of a halogen bulb is about 2,000 hours. It is also possible that the filament breaks due to violent vibration, causing the bulb to fail prematurely.
In comparison, LEDs are energy-saving and environmentally friendly, with very low power consumption. The general operating voltage of LEDs is 2 to 3.6 V. LEDs are a cold light-emitting technology that generates much less heat than ordinary lighting sources; LEDs are completely encapsulated in epoxy resin, and there are no loose parts in the lamp body, so they are not easy to damage. Under the appropriate current and voltage, the service life of LEDs can reach 50,000 to 100,000 hours; LEDs are made of non-toxic materials and are pollution-free. The current disadvantage of LEDs is that they are relatively expensive and it is difficult to handle the heat, so the driving power supply is a key factor in the overall life of LED lamps.
Replace inefficient MR16 halogen lamps with LED MR16 lamps
ON Semiconductor's CAT4201 is a 300 mA LED driver that can drive 3 LEDs in series, which can be used in MR-16 LED lamp designs. Because the device has been optimized, it is more perfect in terms of the number of external components and thermal performance.
• Circuit Features
The CAT4201 uses a buck topology and does not require input/output (I/O) electrical isolation. The input voltage is 12 Vac and the output power is 2.7 W. Other specifications include: output voltage is 9.1 V, rated input power is 3.4 W, rated average current is 300 mA, maximum average current is 310 mA, minimum average current is 295 mA, and typical energy efficiency is 83%. Figure 1 is an MR16 lamp circuit using CAT4201. Figure 1: MR16 lamp circuit using CAT4201 The CAT4201 is a step-down, easy-to-configure, dimmable LED driver. The device uses a 5-pin SOT-23 package; with less than 10 discrete components (most of which are surface-mount components), the entire circuit board can be small enough to fit into the lamp holder of an MR16 lamp. The VBAT, CTRL, and SW pins are rated for 40 V, so there is enough voltage to drive 12 LEDs. The RSET pin determines the output DC current; CTRL is used for dimming signal input. SW is the output pin of the internal MOSFET. • Working Principle The working principle of this application circuit is not complicated, it is a simple buck converter. In AC application, the input is rectified by a rectifier bridge. VBAT and GND are directly connected to the two terminals of the large-capacity capacitor C1, which reduces the current ripple. During the first switching phase, the internal MOSFET charges the inductor with a linearly rising current until the MOSFET is turned off; during the second phase, the MOSFET is turned off, and the current stored in the inductor will be discharged through the Schottky diode (D5) while the current decays until the next switching cycle. The output capacitor is used to reduce the current ripple in the LED. The voltage of the RSET pin is regulated at 1.2 V, so the resistor connected to RSET determines the RSET current. The RSET current is roughly proportional to the constant current output of the CAT4201. • Circuit Configuration In terms of circuit configuration, the rated voltage of VBAT is -0.3 to +40 V, so the input voltage on the rectifier bridge is safe up to 24 Vac. A large-capacity C1 is required to maintain a higher input voltage level. The large fluctuations in the rectified AC current will pull the output current to zero at double the AC line frequency, thus reducing the output current. A capacitor of 220 μF is sufficient for this design. For 12 Vac input, C1 should be rated at 25 V. MBR0520L surface mount Schottky diodes were selected for the bridge rectifier due to the need for a lower forward voltage. Output capacitor C2 is recommended to be at least 4.7 μF to reduce output ripple. A larger value of C2 will effectively suppress the output ripple while increasing the output current by a few mA. However, since its contribution to the overall efficiency is negligible and the human eye cannot perceive high frequency fluctuations, it is not necessary to use a capacitor greater than 10 μF. The value of L is recommended to be 22 μH to set the switching frequency at about 150 kHz. The LED current range is 0 to 350 mA, so an effective inductor current rating of about 800 mA is sufficient. The total continuous current flowing through the rectifier is always less than 400 mA, even when an output current of 350 mA is provided. Therefore, a continuous current rating of 0.5 A is sufficient for the rectifier. A closer look at the voltage across the freewheeling diode D5 shows that despite the 12 Vac input, voltage spikes exceeding 20 V occur. Higher input voltages (e.g., 15 V) further stress the diode and increase the risk of failure. Therefore, the rated voltage on D5 should be 30 V or 40 V. ON Semiconductor's Schottky rectifier MBR0540 can be used as D5. The RSET pin is used to configure the output current value. The RSET voltage is regulated at 1.2 V. Adding a resistor between RSET and GND determines the RSET current, which is approximately linear with the output constant voltage: Calculation shows that for 300 mA output, IRSET = 0.12 mA. The RSET resistor value should be 10 kΩ. A smaller RSET resistor may increase the output current, and a resistor of at least 8.0 kΩ is recommended for stable operation. If the input voltage is high enough (e.g., 15 Vac), RSET can be set to 8.2 kΩ, thus ensuring at least 350 mA of output current. CTRL obtains the voltage from the cathode of the LED through R2. The value of R2 is not important. Performance and Features The basic performance and features of the circuit can be understood from the waveforms shown in Figures 2 to 4 below. Its test equipment includes: Global Specialties 1506 AC Isolated Voltage Variable AC Line Power Supply; Voltech PM1000 Power Analyzer; Tektronix TDS754D Digital Phosphor Oscilloscope; Tektronix TCP202 Current Probe; Agilent 34401A Multimeter. Figure 2: Relationship between input voltage, output current and efficiency In the circuit configured according to the circuit diagram of Figure 1, Vin = 12 Vac 50Hz. Due to the AC line input, the LED current has very slight low-frequency (twice the AC frequency, 2 × 50HZ) fluctuations. Using a larger capacity C1 or a higher Vin will further smooth out the AC-related ripple current. Figure 3: LED current waveform In a circuit configured according to the circuit diagram of Figure 1, the startup and power-off transients are shown in Figure 4. Figure 4: Startup and power-off transients Compact design
The advantages of the CAT4201 driver are compact circuitry and high efficiency, making it ideal for replacing filament-based bulbs such as spotlight applications. This ultra-small design can fit into the space of a standard connector (lamp holder) for MR16-type LED spotlights, separating these temperature-sensitive components from the hot LEDs as much as possible.
Due to optimization, the design is more perfect in terms of component count and thermal performance. This design can generally use three 1 W LEDs in the mirror part, and can be adjusted to meet the requirements of lighting system designers. In the final solution, the LED current and capacitor size must be traded off to achieve the best energy efficiency, accuracy, size and component count. Figure 5: The micro LED driver board can be embedded in the lamp holder Summary This design provides the various elements required to drive a 3-LED MR-16 lamp using the CAT4201 design. The CAT4201 helps achieve a smaller size and fewer components for MR-16 compatible adapters. Reducing the capacitor and inductor values, or not using the CTRL resistor, has the potential to further reduce cost and PCB size. Using a small capacitor will result in a significant drop in the average output current and is not recommended, but is suitable for lower brightness (200 to 250 mA) applications. Selecting high-quality LEDs with a small forward voltage is important for designs that achieve higher output currents.
Keywords：MR16 LED
Reference address：Simple, Configurable LED Driver Application Design for MR16 LED Lamps
Characteristics of halogen lamps and LEDs
MR16 halogen lamps are used in creative lighting for many retail and consumer applications due to their unique size, configurability, focusing ability, aesthetics and practicality. The luminous flux of common MR16 halogen lamps ranges from 150 lumens (lm) to 800 lm, and the luminous efficacy is about 15 lm/W, or 15% luminous efficiency. Low efficiency, heat generation and halogen capsule handling issues are the disadvantages of this technology. In addition, the typical life of a halogen bulb is about 2,000 hours. It is also possible that the filament breaks due to violent vibration, causing the bulb to fail prematurely.
In comparison, LEDs are energy-saving and environmentally friendly, with very low power consumption. The general operating voltage of LEDs is 2 to 3.6 V. LEDs are a cold light-emitting technology that generates much less heat than ordinary lighting sources; LEDs are completely encapsulated in epoxy resin, and there are no loose parts in the lamp body, so they are not easy to damage. Under the appropriate current and voltage, the service life of LEDs can reach 50,000 to 100,000 hours; LEDs are made of non-toxic materials and are pollution-free. The current disadvantage of LEDs is that they are relatively expensive and it is difficult to handle the heat, so the driving power supply is a key factor in the overall life of LED lamps.
Replace inefficient MR16 halogen lamps with LED MR16 lamps
ON Semiconductor's CAT4201 is a 300 mA LED driver that can drive 3 LEDs in series, which can be used in MR-16 LED lamp designs. Because the device has been optimized, it is more perfect in terms of the number of external components and thermal performance.
• Circuit Features
The CAT4201 uses a buck topology and does not require input/output (I/O) electrical isolation. The input voltage is 12 Vac and the output power is 2.7 W. Other specifications include: output voltage is 9.1 V, rated input power is 3.4 W, rated average current is 300 mA, maximum average current is 310 mA, minimum average current is 295 mA, and typical energy efficiency is 83%. Figure 1 is an MR16 lamp circuit using CAT4201. Figure 1: MR16 lamp circuit using CAT4201 The CAT4201 is a step-down, easy-to-configure, dimmable LED driver. The device uses a 5-pin SOT-23 package; with less than 10 discrete components (most of which are surface-mount components), the entire circuit board can be small enough to fit into the lamp holder of an MR16 lamp. The VBAT, CTRL, and SW pins are rated for 40 V, so there is enough voltage to drive 12 LEDs. The RSET pin determines the output DC current; CTRL is used for dimming signal input. SW is the output pin of the internal MOSFET. • Working Principle The working principle of this application circuit is not complicated, it is a simple buck converter. In AC application, the input is rectified by a rectifier bridge. VBAT and GND are directly connected to the two terminals of the large-capacity capacitor C1, which reduces the current ripple. During the first switching phase, the internal MOSFET charges the inductor with a linearly rising current until the MOSFET is turned off; during the second phase, the MOSFET is turned off, and the current stored in the inductor will be discharged through the Schottky diode (D5) while the current decays until the next switching cycle. The output capacitor is used to reduce the current ripple in the LED. The voltage of the RSET pin is regulated at 1.2 V, so the resistor connected to RSET determines the RSET current. The RSET current is roughly proportional to the constant current output of the CAT4201. • Circuit Configuration In terms of circuit configuration, the rated voltage of VBAT is -0.3 to +40 V, so the input voltage on the rectifier bridge is safe up to 24 Vac. A large-capacity C1 is required to maintain a higher input voltage level. The large fluctuations in the rectified AC current will pull the output current to zero at double the AC line frequency, thus reducing the output current. A capacitor of 220 μF is sufficient for this design. For 12 Vac input, C1 should be rated at 25 V. MBR0520L surface mount Schottky diodes were selected for the bridge rectifier due to the need for a lower forward voltage. Output capacitor C2 is recommended to be at least 4.7 μF to reduce output ripple. A larger value of C2 will effectively suppress the output ripple while increasing the output current by a few mA. However, since its contribution to the overall efficiency is negligible and the human eye cannot perceive high frequency fluctuations, it is not necessary to use a capacitor greater than 10 μF. The value of L is recommended to be 22 μH to set the switching frequency at about 150 kHz. The LED current range is 0 to 350 mA, so an effective inductor current rating of about 800 mA is sufficient. The total continuous current flowing through the rectifier is always less than 400 mA, even when an output current of 350 mA is provided. Therefore, a continuous current rating of 0.5 A is sufficient for the rectifier. A closer look at the voltage across the freewheeling diode D5 shows that despite the 12 Vac input, voltage spikes exceeding 20 V occur. Higher input voltages (e.g., 15 V) further stress the diode and increase the risk of failure. Therefore, the rated voltage on D5 should be 30 V or 40 V. ON Semiconductor's Schottky rectifier MBR0540 can be used as D5. The RSET pin is used to configure the output current value. The RSET voltage is regulated at 1.2 V. Adding a resistor between RSET and GND determines the RSET current, which is approximately linear with the output constant voltage: Calculation shows that for 300 mA output, IRSET = 0.12 mA. The RSET resistor value should be 10 kΩ. A smaller RSET resistor may increase the output current, and a resistor of at least 8.0 kΩ is recommended for stable operation. If the input voltage is high enough (e.g., 15 Vac), RSET can be set to 8.2 kΩ, thus ensuring at least 350 mA of output current. CTRL obtains the voltage from the cathode of the LED through R2. The value of R2 is not important. Performance and Features The basic performance and features of the circuit can be understood from the waveforms shown in Figures 2 to 4 below. Its test equipment includes: Global Specialties 1506 AC Isolated Voltage Variable AC Line Power Supply; Voltech PM1000 Power Analyzer; Tektronix TDS754D Digital Phosphor Oscilloscope; Tektronix TCP202 Current Probe; Agilent 34401A Multimeter. Figure 2: Relationship between input voltage, output current and efficiency In the circuit configured according to the circuit diagram of Figure 1, Vin = 12 Vac 50Hz. Due to the AC line input, the LED current has very slight low-frequency (twice the AC frequency, 2 × 50HZ) fluctuations. Using a larger capacity C1 or a higher Vin will further smooth out the AC-related ripple current. Figure 3: LED current waveform In a circuit configured according to the circuit diagram of Figure 1, the startup and power-off transients are shown in Figure 4. Figure 4: Startup and power-off transients Compact design
The advantages of the CAT4201 driver are compact circuitry and high efficiency, making it ideal for replacing filament-based bulbs such as spotlight applications. This ultra-small design can fit into the space of a standard connector (lamp holder) for MR16-type LED spotlights, separating these temperature-sensitive components from the hot LEDs as much as possible.
Due to optimization, the design is more perfect in terms of component count and thermal performance. This design can generally use three 1 W LEDs in the mirror part, and can be adjusted to meet the requirements of lighting system designers. In the final solution, the LED current and capacitor size must be traded off to achieve the best energy efficiency, accuracy, size and component count. Figure 5: The micro LED driver board can be embedded in the lamp holder Summary This design provides the various elements required to drive a 3-LED MR-16 lamp using the CAT4201 design. The CAT4201 helps achieve a smaller size and fewer components for MR-16 compatible adapters. Reducing the capacitor and inductor values, or not using the CTRL resistor, has the potential to further reduce cost and PCB size. Using a small capacitor will result in a significant drop in the average output current and is not recommended, but is suitable for lower brightness (200 to 250 mA) applications. Selecting high-quality LEDs with a small forward voltage is important for designs that achieve higher output currents.
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