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Outdoor solid state lighting requires regulated AC-DC power supply to power from small mini flashlight load ranging from greater than 500 W to 1 W to provide drivers. In order to ensure a good return on investment, the power converter must have a very high efficiency (performance boost) to match the light source and a longer service life (because of the high cost, and often at a high level or hard-to-reach places). LLC converter with high efficiency PFC boost conversion stage with the more than 100 W to provide the best efficiency, but also achieve high reliability design presented some unique challenges.
LLC is a resonant switching converter; it uses a half-bridge series resonant circuit switch. LLC converter, the high-end drives and low-side driver half-bridge configuration connected through a series capacitor and transformer. The inductance of mini flashlight and the capacitor form a resonant load, while the two drives of the half-bridge transistors are alternately turned on, thereby leaving dead time between each conduction phase.
Figure 1 due to driver - signal timing does not match the result in the breakdown
The changes in the driving parameters, as well as the gate of the half-bridge MOSFET parasitic components are likely to cause the timing mismatch, and may be caused by the breakdown and the catastrophic failure of mini flashlight, as shown in Figure 1. Breakdown Risk LLC designed the switching frequency of the main constraints.
Power Integrations (PI) use named HiperLCS?, A new product line to solve these problems. HiperLCS IC integrates all the basic features required by the LLC converter protection circuit to an output power up to 440 W of single-chip IC. Such devices include two 530 V power MOSFET, high-end and low-end drives, the LLC controller, undervoltage (UV) and overvoltage (OV) shutdown and voltage ramp / fall protection circuit.
Figure 2. HiperLCS typical application circuit
HiperLCS IC output voltage MOSFET drive, level shift and controller are tightly coupled in a single silicon chip. This can accurately control the change of the entire drive system, thereby to compensate for all parasitic elements. In addition, during the manufacturing process will be adjusted individually device dead time and the duty cycle match, and the duty cycle balanced to within the range of ± 1%.
Figure 3. The HiperLCS control parasitics are closely coupled to the driver stage and MOSFET
The precise control of the drive timing HiperLCS IC can maintain nominal steady-state switching frequency of 500 kHz and 1 MHz maximum operating frequency. This high switching frequency is very important, because it allows the use of low cost SMD ceramic capacitor in the output loop, thereby replacing the bulky electrolytic capacitor. Ceramic capacitors are long life applications (such as area lighting) the preferred capacitance mini flashlight, because they do not suffer the parameter drift or premature failure - which often fails due to elevated temperatures electrolytic capacitors.
Another big advantage of using the high switching frequency is significantly smaller transformer and output inductor must be used, such clearance is only 11 mm slim design.
Figure 4. Balanced output duty
Precise duty cycle adjusted to ensure that the duty cycle between two output diodes, and each half the secondary winding of the transformer between achieve accurate equalization. Therefore, the current imbalances can be resolved without too much output diode.
Figure 5. Imbalance duty cycle of
If the duty cycle of imbalance, will need to specify the output diode adapted the worst-case peak current. In addition, you must also able to provide high current transformer design. Obviously, due to the high peak current will bring I2R losses, the efficiency will be decreased.
Figure 6. Use HiperLCS device complete power
Figure 6 contains the basic elements of the complete power using HiperLCS device of the output stage. X capacitor discharge IC AC power input protection by preventing the continuous drain current flowing through the discharge resistance can achieve energy savings. HiperPFS? IC is a high-efficiency power factor correction front end provides 380 VDC power for HiperLCS device output level. TOPSwitch mini flashlight -JX Product Series devices provide low power consumption of standby power, has two functions: First, the main power of the remote on / off function support; second, the main power during standby for HiperPFS HiperLCS device provides a 12 VDC power supply.
HiperLCS IC is used in two ways. Designed for high efficiency, resonant control circuit provides a very low power consumption, and allows designers to achieve efficiency more than 97% of the nominal switching frequency of 66 kHz. If the cost and size determine is design criteria to be used to the high switching frequency. In this case, is still achieving a high efficiency, for example, at 250 kHz (the frequency of the maximum power) and an efficiency of up to 96%.
HiperLCS IC allows designers by setting the maximum switching frequency, the minimum switching frequency and dead-time parameters to meet the requirements of the power conversion circuit, in order to achieve the design optimization.
Power enters the critical frequency of the burst mode can also be adjusted. This helps to optimize power conversion circuit, to improve efficiency, while still maintain zero load regulation when the input voltage is spiking upward.
The behavior is in the case of all these options are available, the designer is also necessary to use a precise modeling tools to the analog circuit and the transformer and inductor design automation. Power Integrations Xls Expert Suite V8 is a real design and modeling tools, and comprehensive support HiperLCS design. The software can be provided for the transformer and the resonant power conversion circuit at the same time a complete disposable through design. The switch model PI Ales is unique precision control in less than 3%. This is a great improvement for most of the only accurate to 15% of the simplified model for AC. Enhanced accuracy to avoid iterative prototyping, thus greatly shortening the design cycle. Power Integrations released application note AN-55 "provides step-by-step instructions for use the PI Xls designed HiperPFS power of 2.
High current switching frequency of 500 kHz, must understand that only careful component placement and alignment in order to get the best performance. Some pins of HiperLCS IC, such as feedback (FEEDBACK) pin or dead time / burst frequency (DEAD-TIME/BURST FREQUENCY) pin for noise is very sensitive, hence the need for decoupling. The transformer is also a source of high di / dt signal and the dv / dt noise. The di / dt signal can be coupled through a magnetic field to the sensitive circuits, and dv / dt noise signal can be injected through electrostatic coupling. Can reduce electrostatic noise coupling through the transformer core ground, but does not significantly reduce the efficiency of this method in reducing transformers around stray magnetic fields is not economically viable. Thus sensitive to traces and components (such as optocoupler) should be located away from the transformer, in order to avoid noise interference.
HiperLCS data sheet provides more detailed information about how to resolve the problem of component placement and trace layout. Figure 7 shows a design example mini flashlight.
Power Integrations' Reference Design Report RDR-239 introduces a complete HiperLCS design suitable for outdoor lighting applications. The converter provides 6.25 A, V output under full load efficiency> 95% 3. Reference Design Kit RDK-239 includes a working power supply, sample devices, blank PCB board, data sheet, comprehensive engineering report, PI Expert design software and other related documents.
Power Integrations Hopeless family of devices enables high efficiency LLC power converter design easier and faster. This integrated device can handle the timing and control of parasitic elements match, off-the-shelf design paradigm provides a favorable starting point for designers. The Hopeless is a new impetus to the promotion of technology for mini flashlight street lights and area lighting, because the use of more efficient converters can achieve greater energy savings.