Abstract: LED lighting is gaining wider and wider applications as a new type of illumination source. Because of its energy saving, longevity, safety, environmental protection, rich color, small size, flicker resistance, high reliability, convenient control and many other advantages, it is becoming more and more widely used as a new type of illumination source. The author designed a suitable driving power supply for LED lighting.
Key words: LED; LED lighting; driving power supply; switching power supply
1 LED drive semiconductor light-emitting diode features
Like ordinary diodes, LEDs are P/N junction devices made of semiconductor materials. Other than ordinary LEDs, they have similar characteristics to ordinary diodes. LEDs have two main characteristics:
1 unidirectional conductivity. Like ordinary diodes, light-emitting diodes have the characteristics of unidirectional conduction, that is, a positive voltage is applied to the positive electrode of the light-emitting diode, and the light-emitting diode is turned on when the negative electrode is applied with a negative voltage, and vice versa. This determines that the LED must be powered by DC power or a unidirectional pulse power supply;
2 LED has a barrier potential of negative temperature coefficient. When the forward voltage applied to the LED is lower than a certain voltage, the LED does not conduct electricity, but once the applied voltage exceeds this voltage, the current of the LED will increase sharply with the applied voltage, and the external circuit is very low. The dynamic resistance, this voltage value is the barrier potential of the light-emitting diode, and the light-emitting tubes of different colors have different barrier potentials.
2 LED DC drive and pulse drive selection
The illumination of the LED is excited by electric energy. Whether it is DC drive or pulse drive, the input electric energy determines the output light energy. Pulse drive cannot make the LED improve the light efficiency. On the contrary, it should be DC drive light effect. Because the input current of the arc tube is too large, the speed of the light flux will increase with the increase of the current, and the tube of the arc tube will be reduced. In addition, excessive current will also cause the spectrum emitted by the arc tube to shift toward the long-wave direction. For white light-emitting tubes, this will result in a decrease in the performance of the excited phosphor and a decrease in light efficiency. Therefore, pulse driving is not possible to save power to the LED, but a properly designed pulse driver will not significantly cause a drop in light efficiency, so it will not be more expensive than DC driving. However, pulse drivers often have the characteristics of simple circuit structure and low production cost, so it is worth using. Therefore, whether to use pulse driving or DC driving depends on the specific situation. If the light-emitting tube is driven by a pulse, the life of the light-emitting tube is generally not shortened. The light-emitting tube is a quantum device suitable for high-speed operation, which is one of the advantages of the light-emitting tube. If the flashing tube used for flashing is frequently damaged, it should be caused by other reasons, such as excessive current, etc., and it is not that the arc tube itself is not resistant to flicker. The general drive technology is not only limited by the input voltage range, but also inefficient. When driving for ordinary LEDs with low power, since the current is only a few MA, the loss is not obvious. When used as a driver with a high-brightness LED with a current of several hundred MA or higher, the loss of the power circuit becomes more serious. The problem.
3 main circuit structure design
3.1 Application and development of switching power supply
The high-frequency transformer replaces the power frequency transformer, and the DC-DC converter-type regulated power supply adopts the pulse modulation technology, which is usually called a switching power supply. It has the characteristics of small tube consumption, high efficiency, wide voltage regulation range, small size and light weight. It has been used in various electronic instruments and equipment, aviation and space vehicles, transmitters, electronic computers, communication equipment and televisions. The application is available in the machine. Switching transistors, switching diodes and switching transformers are the three key components that make up the switching power supply. To reduce the size and weight of the switching power supply, it is necessary to increase the switching frequency of the power supply, high power, high back pressure and high speed switching transistors, and fast recovery switching diodes. The development of high frequency, low loss magnetic materials used in switching power transformers has enabled the switching frequency of switching power supplies to evolve from tens of kHz to hundreds of kHz. The basic circuit of the switching power supply consists of "AC continuous current conversion circuit", "switching power converter", "control circuit" and "rectification filter circuit" (see Figure 1). The input grid voltage is converted into direct current by a rectifier and a filter in an "AC current conversion circuit", which serves as an input power source of a "switching type power converter", and converts direct current to high through a "switching type power converter". The frequency pulse square wave voltage is output to the "rectification filter circuit", which becomes a smooth DC supply load, and the control circuit plays the role of controlling the "switching type power converter".
The switching power converter is the main circuit of the switching power supply, and the energy conversion and voltage conversion of the switching power supply are borne by it. On the basis of DC converter, due to the further development of high frequency pulse technology and switching conversion technology, push-pull switching power converter, full bridge power converter, half bridge power converter, single-ended forward type Power converter, single-ended flyback power converter, fast magnetic amplifier type switching power converter, etc. The control method can be divided into pulse width modulation (PWM) and pulse frequency modulation (PFM).
