With the rise in the field of solid-state lighting industry and the continuous improvement of the light-emitting diode (LED), because it has the characteristics of high efficiency, energy saving, long life, environmental protection, and has become a lighting technology options, and gradually is used in lighting. It brings attention to a key factor in Best CREE flashlight technology, which greatly reduces the energy consumption, and can achieve long-term and reliable work.
Of course, the use of Best CREE flashlight, the first thing to consider is the brightness, cost and life. LED life mainly due to its frequent start the moment the current impact various surge pulse of the outside world, as well as the current limit of normal working hours, the circuit of the author of the article describes a combination of these factors, from circuit design to avoid the impact of high-current Best CREE flashlight, and the work of the current stable within a certain range, to solve the brightness of LED flashlight attenuation, thereby effectively extending its life.
LED DC drives, so the need to add a power adapter that LED drive power between the mains and LED. Its function is to convert a commercial AC power into a DC power suitable for LED. Usually drive LED dedicated constant current source or driver chips easily limited by factors such as the volume and cost of the most economical and practical method is to use a capacitor buck-power. Use it to drive low-power LED not afraid load short, simple circuit, etc., and a circuit can drive 1 to 70 small power LED (However, the start of this power supply circuit current impact, especially frequent start, give Cree flashlight damage. course, take appropriate protection can avoid this impact).
Capacitor buck mode power supply is a typical circuit shown in Figure 1, C1 is the the buck capacitor (metalized polypropylene capacitors), R1 is a C1 to provide a discharge circuit. Capacitor C1 to provide is constant current for the entire circuit. The capacitor C2 for the electrolytic capacitor, the number of the pressure value depends on the series LED (about 1.5 times or more of their total voltage), its main role is inhibition of voltage caused by the tenderization instant mutations, thereby reducing the voltage surge on LED the impact of life. R4 bleeder resistor capacitor C2, the resistance should be appropriately increased with increasing LED number.
Note, the circuit must be based on the current size of the load to select the appropriate capacitance, rather than in accordance with the voltage and power of the load, usually the buck the capacity C of the capacitor C1 and the load current Io, the relationship can be approximated that: C = 14.5Io where C is the capacity of the unit is uF Io units A. Limiting capacitor must be non-polar capacitor, and the capacitor voltage value shall be more than 630V Cree flashlight.
Capacitor step-down power supply is a non-isolated power, power is instantly generated a lot of current, which is the so-called surge current. In addition, due to the impact of the external environment (such as lightning) grid system will invade various surge signals, some surge can cause damage to LED. LED anti-surge current and anti-reverse voltage capability than the poor, is also very important to strengthen the protection in this regard, especially some LED lights installed outdoors (such as LED street lamp). Therefore, Cree flashlight power supply to have inhibitory surge intrusion, and the ability to protect LED without being damaged. The circuit with the negative temperature coefficient thermistor to limit the current mutation, using a positive temperature coefficient thermistor automatically adjusts the current size, and so tends to a certain range of variation, the power input at the same time, and a transient voltage suppressor voltage in order to avoid overload.
(A) negative temperature coefficient thermistor protection
Negative temperature coefficient thermistor referred NTC thermistor NTC Negative Temperature Coefficient of abbreviations, the meaning of the negative temperature coefficient refers to the negative temperature coefficient of semiconductor materials or components, the most simple and effective to limit inrush current series an NTC thermostat line inputs, shown in Figure 1, R2. Because at cold start, NTC thermostat presents a high impedance, and thus the surge current can be restrained. When the heating effect of current so that the temperature of the NTC thermistor element increases, the NTC resistance sharply, the current limiting effect on the system will be smaller. Since the NTC thermostat in the hot state, the impedance is not zero, it will produce power loss, of course, and this loss is very small.
(B) The positive temperature coefficient thermostat protection
Positive temperature coefficient thermostat PTC (Positive Temperature Coefficient) is a means to increase sharply at a certain temperature resistance having a positive temperature coefficient thermostat. In order to stabilize the current in the circuit in normal operation, the circuit also uses a PTC thermostat, and R3 is shown in Figure 1. Temperature rise caused after the current through the PTC thermostat, i.e. heating element temperature rise, when the temperature exceeds the Curie point, the resistance is increased, thus limiting the current increases, then the current causes lower element temperature decreases, the resistance value decreases so that the circuit current is increased, the element temperature is increased again, again and again, so it has to keep the temperature in a specific range of functionality.
Under normal circumstances, PTC element connected in series in the circuit, the low resistance state, to ensure the normal working of the circuit; its increased impedance to limit the current to a sufficiently small when short circuit occurs or Cantu abnormal large current, self-heating of the PTC element, played over current protective effect. When the current fault is excluded, the PTC element is automatically restored to the low resistance state. Not only avoids maintenance or replacement, and also to avoid the open or closed state of the cycle may cause circuit damage sustained.
(3) Transient voltage suppressor protection
Transient voltage suppressor (Transient Voltage Suppressor), (TVS) is the regulator on the basis of development of efficient protection devices, mainly used for to fast over voltage of Cree flashlight protection circuit elements. TVS tube poles by the reverse transient high energy impact it can to speed on the order of 10-12s between the poles of high impedance into low impedance to absorb high-energy surge, voltage clamp between the poles located in a predetermined value, and to protect the components from the impact of the various surge pulse damage electronic circuits.
Over voltage of CREE flashlight protection in this regard, the circuit is in parallel with the mains input TVS, Figure 1 VD3, so you can maintain the voltage TVS Maximum range, when a voltage higher than TVS breakdown point too the pressure phenomenon can let the current flowing through the TVS, so as to protect Best Cree flashlight.
The experiments show that, the millimeter pointer to the string into the circuit, at the moment the circuit is energized, the pointer sudden deflection of the large angle of the phenomenon have been significantly improved, to effectively prevent the inrush current impact of LED. Meanwhile, the start of a period of time, the current decline, and gradually stabilized. In device selection instead of the NTC, with 1W metal film resistors or wire wound resistors can also meet the requirements; over voltage protection can choose TVS or arrestor. In circuit board design, to note, that the high-voltage input portion (i.e. the power supply input terminal to the rectifier bridge portion) should be as far away from the back of the load circuit, and in the case of the allowed distance between the wires of the high-voltage input section should ensure more than 1 mm.