The MR16 lamp is a type of multi-faceted reflector lamp, usually with a halogen filament as a light source. They are suitable for many retail and consumer applications, with practicality and creativity through unique dimensions, configurability, concentrating power and aesthetics. However, inefficiencies, heat generation and halogen pocket handling problems often become a disadvantage of this technology. The MR16 lamp typically operates with a 12V DC or 12V AC universal electromagnetic transformer.
LEDs are an ideal alternative to halogen lamps because of their higher efficiency and no heat radiation.
This reference design can be installed in the standard connector space of the MR16 LED spotlight. It has been optimized to be even better in terms of part count and thermal performance. This design can be used with three 1W LEDs in the mirror section, and can be adjusted to meet the lighting system designer's requirements.
Figure 1: MR16 application with ZXLD1350
Figure 2 shows the system wiring diagram for the MR16 lamp solution using the ZXLD1350 and ZXSBMR16T8, and Table 1 provides a list of components.
Figure 2: System wiring diagram for the ZXLD1350 MR16 lamp solution
Table 1: List of components
The ZXLD1350 is designed for LED current drive applications up to 350mA. This monolithic NMOSFET is moderately sized to provide a cost-effective chip size with a current rating of 400mA and sufficient margin in hysteresis mode of operation (current waveform draws +/-15% from nominal current set point) . Key features of the ZXLD1350 include:
* Output current up to 380mA
* Wide input voltage range: 7V to 30V
* Internal 30V 400mA NDMOS switch
* High efficiency (above 90%)
* Switching frequency up to 1MHz
The ZXSBMR16T8 is a space-saving and thermally efficient device designed specifically to meet the critical requirements of MR16 applications. It includes a full bridge and a freewheeling diode to achieve a nominal 12V AC input operation with a low leakage 1A, 40V Schottky diode. This combination of Schottky bridges and embedded freewheeling diodes helps to increase system efficiency compared to standard silicon diodes with an integrated design. With a bypass weld in the reference design, the bridge rectifier can be omitted and the final lamp design is also suitable for pure DC operation.
Since the ZXLD1350 uses a hysteresis conversion circuit topology, the conversion efficiency depends on several factors â€“ input voltage, target current, and number of LEDs. There is also an Excel-based calculator for initial evaluation of the system and decision making.
System efficiency and LED current measurements are included in the design, and the ADJ pin remains floating to measure the current rating in the device. The ADJ pin has a high impedance input (200K) and is susceptible to leakage currents from other sources. Any current that is carried from this pin will reduce the output current. In order to avoid any electromagnetic coupling, the protective track is placed around the pins.
As can be seen from the circuit schematic in Figure 2, only a 0 ohm resistor is required, and a jumper connection can be used to achieve pure DC operation.
Since the system does not have reverse polarity protection, users should be very careful.
Figure 3 shows the circuit layout design, illustrating the advantages of space saving and compact design. The bottom layer and top layer are clearly displayed, and the efficient device layout is clearly visible.
Figure 3: Circuit Design