This application note presents the half bridge converter for electronic lamp ballast using the L6574 and L6561. The L6574 is a high-performance ballast driver, designed using 600-V BCD offline technology, which ensures all the features needed to properly drive and control a fluorescent bulb. It is provided with built-in VCO start-up sequence circuitry, protections, and an operation amplifier for implementing a closed-loop control of the lamp current.
This document details the design of a half-bridge converter for electronic lamp ballasts, specifically focusing on the use of the L6574 ballast driver IC. It explains how the L6574 replaces older bipolar transistor solutions by providing built-in VCO start-up sequences, protections, and operational amplifiers for closed-loop control of lamp current.
The note covers the internal block description of the L6574, including preheating and ignition sections, control sections, and bootstrap sections. It also describes a demonstration application circuit that integrates a power factor correction (PFC) section with the ballast section, detailing the start-up, supply, and safety circuitry involved in the design.
| High voltage rail | up to 600 V |
|---|---|
| dv/dt immunity | + 50 V/ns |
| Driver current capability | 250 mA source and 450 mA sink |
| Switching times | 80/40 ns |
| Package types | DIP16 and SO16N |
| Typical supply voltage | 15.6 V |
The L6574 is a dedicated IC intended to drive two power MOSFETs or IGBTs in half-bridge topology to properly drive and control a fluorescent bulb.
The preheating time (Tpre) and ignition time (Tign) are set by the capacitor Cp connected to pin 1, using internal currents to charge it to specific thresholds.
During the preheating phase, the capacitor Cp is charged by a constant internal current, and the oscillation frequency is at its highest value (fmax).