Dimmable Electronic Ballast for 250W HPS Lamp in Street Lighting with Analog Dimming Interface Circuit

A dimmable electronic ballast for 250W high pressure sodium (HPS) lamp, which is used in street lighting, is designed in this paper. Normally used dimming methods for electronic ballast are introduced and compared. Dimming control method by varying switching frequency is utilized in the designed ballast. A simple method to realize closed-loop control of lamp power is adopted. The interface circuit for analog dimming control is analyzed and tested. Open-circuit, shot-circuit and hot-lamp protections are adopted. Experimental results show that the ballast can dim from 33% to 100% rated power without acoustic resonance, its efficiency is higher than 90.3% through the whole dimming range.