The inverter circuit shown is designed to drive a 7-W, four-pin compact fluorescent lamp (CFL) from a 12-V dc power supply. The main features of this inverter circuit include direct-drive capability, preheat for improved startup, high efficiency, and a simple and economical configuration. While the inclusion of a preheating circuit helps to prevent end-blackening of the bulb, the direct-drive arrangement ensures trouble-free startup in all conditions.
The circuit finds application in solar-powered lighting, internal automobile lighting, and emergency lighting systems. The inverter is a direct-drive push-pull oscillator. The SG3524 PWM integrated circuit (U1) drives the inverter. Capacitor C4 and resistor R3 are chosen to set the oscillator frequency at around 26 kHz. MOSFETs Q1 and Q2 (IRFZ44) are used as power devices, improving the efficiency of the inverter.
Transistor Q3 along with the resistor R8, relay RL1, capacitor C9, and zener diode DZ5 form the preheating circuit. Diode D1 and a fuse have been included in the circuit to provide reverse-polarity protection.
This circuit has been built and tested using a 12-V dc input. This configuration results in a light output of 370 lumens using a 7-W, four-pin CFL. The measured circuit efficiency is around 85% at a switching frequency of 26 kHz.
The winding details for the two inductors and the transformer are given in the table.
See associated figure.