Design and Implementation of Ferroresonant Transformer for LED Driver Systems

This paper presents the design and implementation of the 60-Hz ferroresonant transformer (FRT) for the light emitting diode (LED) street lamp to achieve high-frequency (HF) noise attenuation and ac-line voltage clamping. The HF transformer (HFT) used in the LED driver system for the outdoor LED street lamps cannot effectively suppress the surge current to avoid damage to the LED street lamp. However, instead of the HFT, the low-frequency transformer (LFT) can be applied to protect the LED street lamps from the surge current. The LFT has a higher turns number, which provides larger leakage inductances and parasitic capacitances that effectively suppress and shunt the surge current. With the magnetic shunt, a 60-Hz FRT is proposed to effectively regulate the ac-line voltage to not overstress the LED street lamp systems as compared with the conventional LFT. When the ac-line voltage is higher than the rated voltage, the additional magnetic flux generated from the primary-side winding flows through the magnetic shunt but not the secondary-side winding. The rated output voltage of the secondary side can be sustained to achieve ac-line voltage clamping. A prototype of the LED street lamp with a 60-Hz FRT has been designed and implemented to verify the feasibility of the HF noise attenuation and ac-line voltage clamping.