1. Field of the Invention
The invention relates to a technique field of an electric light source circuit device, and more particularly to a constant current type light emitting diode (LED) driving device. Therefore, when the brightness of the LED is linearly regulated by a tri-electrode AC switch (TRIAC) at the same time, impulses and noise generated during the conversion of the voltage source are reduced such that the LED may not generate twinkling, and the efficacy of the whole circuit device can be improved.
2. Description of the Related Art
After light emitting diodes (LED) leads the illumination markets due to its features of low power consumption and high efficacy, controlling the illumination brightness, working efficiency or service life of LED lamps become a goal studied by each company. Currently, the driving device of the LED lamp usually adopts a circuit design architecture having constant current to allow LEDs cascading a transistor and a sensing resistor such that before a TRIAC switches the conduction angle of an input voltage to regulate its brightness, the sensing resistor examines the driving current of the LED to form a voltage drop, and the voltage drop is compared with the input voltage through a comparator to output high level voltage or low level voltage to the transistor such that the transistor is properly conducted or discontinued to regulate the duty cycle of a pulse width modulation (PWM) signal, to control driving voltage magnitude, thereby influencing driving current magnitude and the illumination brightness of LEDs.
However, according to current/voltage (I/V) character curve, the LED is not a linear component. In another word, ratio value of voltages to current is not direct proportion. Therefore, the foregoing dimming method may cause incorrect dimming effect due to inconsistent change between the driving voltage and the driving current. Further, the illumination brightness of the LED controlled by utilizing the duty cycle of the PWM signal may have problem of electromagnetic interference (EMI) while switching frequencies. Consequently, to meet the safety requirement, related lamps must add safety components to decrease the practicability.