1. Field of the Invention
The present invention relates to an LED driving apparatus of a non-insulation type step down AC-DC converter able to correspond to a triac dimmer and improve a power factor.
2. Description of the Related Art
Alight emitting device (LED) is a semiconductor device for implementing light of various kinds of colors by varying materials of a compound semiconductor such as GaAs, AlGaAs, GaN, InGaInP, or the like to constitute a light emitting source. The light emitting device has a prominent single-color peak wavelength and light efficiency, facilitates miniaturization, and is also widely used in various fields, for example, in TVs, computers, general illumination devices, automobiles and the like, due to environmental-friendliness and low-power consumption characteristics and the like. A field of use therefor is gradually being widened.
In order to drive LED modules, an AC-DC converter converting an input alternating current (AC) voltage into a direct current (DC) voltage is connected to a DC-DC converter converting the converted DC voltage into a current to drive the LED module and supplying the converted voltage. For example, there may be a buck converter used when an input voltage is greater than an LED voltage, a boost converter when an input voltage has a level lower than that of an LED voltage, a buck-boost converter used in a status in which an input voltage may be varied from more than the LED voltage to a level lower thereof, or the like.
As an LED driving circuit for improving a power factor with comparatively low expenses, there may be a PFC flyback method according to the related art. However, the flyback method requires a photo coupler transferring LED current information from a primary side to a secondary side, and a transformer supplying power from a primary side to a secondary side. In this case, circuit miniaturization is difficult to implement.
Furthermore, since in a power factor correcting circuit according to the related art, a feedback band is set to be 10 to 20 Hz so as not to respond to a frequency change of 100 to 120 Hz in order to supply a predetermined amount of current, a response is relatively very slow, which becomes a factor not to facilitate to correspond to a triac dimmer. In the power factor correcting circuit according to the related art, it is general to supply power through a bleeder resistor from a voltage provided after commercial power is rectified by applying a bridge diode thereto in driving a circuit. In this case, when brightness is lowered by the triac dimmer, overall voltage is also lowered, therefore flickering may occur and a relatively long time may be taken to turn an LED device on or off or it may not light up at all. In addition, since standard components the transformer exist, developmental expenses and much time are required.