LCD Backlight Inverter Drive IC# Technical Documentation: FAN7317B Ballast Control IC
Manufacturer : FAIRCHILD (ON Semiconductor)
Document Version : 1.0
Date : October 26, 2023
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN7317B is a high-performance, resonant half-bridge controller IC specifically designed for electronic ballast applications . Its primary function is to drive and control Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) or Insulated-Gate Bipolar Transistors (IGBTs) in a half-bridge configuration to generate high-frequency AC power for gas discharge lamps.
* Fluorescent Lamp Ballasts : The most common application, driving T5, T8, and compact fluorescent lamps (CFLs) in both instant-start and programmed-start configurations. The IC's integrated preheat and ignition timing functions are critical for lamp longevity.
* High-Intensity Discharge (HID) Lamp Ballasts : Used in applications requiring high luminous efficacy, such as street lighting, stadium lighting, and industrial high-bay lighting. The controller manages the complex start-up sequence and steady-state operation.
* Cold Cathode Fluorescent Lamp (CCFL) Backlight Inverters : For LCD displays in monitors, televisions, and automotive dashboards, where it provides the high AC voltage needed to illuminate the CCFL tubes.
### 1.2 Industry Applications
* Commercial & Industrial Lighting : Found in office buildings, warehouses, and retail spaces utilizing fluorescent or HID lighting systems. Its reliability and protection features are key for maintenance-free operation.
* Residential Lighting : Embedded in the electronic ballasts of higher-end CFL fixtures and some dedicated downlighting systems.
* Display Technology : Integral to the inverter boards of older LCD TVs and monitors that use CCFL backlighting.
* Specialty Lighting : Used in signage, UV curing systems, and medical equipment lighting where precise lamp control is necessary.
### 1.3 Practical Advantages and Limitations
Advantages:
* Integrated Control Logic : Combines oscillator, preheat timer, dead-time control, and protection circuits in a single 8-pin package, reducing component count and board space.
* Robust Protection Features : Includes under-voltage lockout (UVLO), over-current protection (OCP) via a sense resistor, and non-latch shutdown for fault conditions, enhancing system reliability.
* Programmable Operation : Key parameters like preheat time, frequency shift, and dead time are set by external passive components (resistors, capacitors), allowing design flexibility for different lamp types and power levels.
* High Noise Immunity : Designed for the noisy electrical environment of switch-mode power supplies and ballasts.
Limitations:
* Application Specific : Optimized for resonant half-bridge ballast topologies. It is not a general-purpose PWM controller and is unsuitable for DC-DC converters or motor drives.
* Driving Capability : The gate drivers are designed for MOSFET/IGBTs typical in ballast applications (usually up to 500W). For very high-power applications, external gate drive buffers may be required.
* Legacy Technology : With the industry shift towards Light Emitting Diode (LED) lighting, this IC is primarily used in maintaining existing fluorescent/HID systems or in niche applications where gas discharge lamps are still preferred.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
* Pitfall 1: Inadequate Preheat Leading to Lamp End Blackening.
* Cause : Setting the preheat time (`t_PH`) too short or the preheat frequency incorrectly.
* Solution : Calculate `t_PH` and the
