TV EAST/WEST CORRECTION CIRCUIT FOR SQUARE TUBES# Technical Documentation: TDA8145 East-West Correction IC
## 1. Application Scenarios
### 1.1 Typical Use Cases
The TDA8145 is a monolithic integrated circuit specifically designed for East-West (E-W) correction in television and monitor deflection systems. Its primary function is to generate a parabolic voltage waveform that modulates the horizontal deflection current, correcting for geometric distortion (pincushion/barrel distortion) that occurs at the edges of CRT screens. This is achieved by dynamically varying the horizontal scan amplitude during the vertical sweep period.
Core Applications:
- CRT Television Sets : Corrects pincushion distortion in standard 4:3 and 16:9 aspect ratio televisions, particularly in larger screen sizes (>20 inches) where distortion is more pronounced.
- CRT Computer Monitors : Provides dynamic geometry correction for VGA, SVGA, and other analog monitor standards, ensuring straight vertical lines across the entire display area.
- Professional CRT Displays : Used in broadcast monitors, medical imaging displays, and other high-end CRT applications where precise geometry is critical.
### 1.2 Industry Applications
- Consumer Electronics : Mass-produced in TV sets from the late 1980s through the early 2000s, prior to the dominance of flat-panel technologies.
- Industrial/Medical Displays : Employed in systems where CRT longevity, color accuracy, or specific phosphor characteristics were required despite the geometric challenges.
- Legacy System Maintenance : The component remains relevant for servicing and repairing existing CRT-based equipment in various sectors.
### 1.3 Practical Advantages and Limitations
Advantages:
- High Integration : Combines a parabolic waveform generator, modulator, and output stage in a single 8-pin package (DIP-8 or SO-8), reducing external component count.
- Adjustable Correction : Provides pins for adjusting the amplitude , trapezoidal correction , and symmetry of the parabolic output, allowing fine-tuning for different CRT yoke characteristics.
- Good Linearity : Designed to generate a well-defined parabolic signal with low distortion, leading to effective correction.
- Robustness : Includes internal protection features suitable for the high-voltage, high-current environment of a deflection system.
Limitations:
- CRT-Specific Technology : Its utility is confined to CRT-based display systems. It has no application in modern LCD, OLED, or plasma displays.
- External Component Dependency : Requires carefully selected external resistors, capacitors, and a modulation coil (saturable reactor) to function correctly. Performance is highly dependent on these external parts.
- Thermal Management : The output stage can dissipate significant heat, especially in high-correction scenarios, necessitating proper heatsinking.
- Obsolescence Context : As a component designed for a largely obsolete display technology, sourcing and future design-ins are not considerations for new products.
## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
- Pitfall 1: Incorrect Modulation Coil Selection.
- *Problem*: Using a coil with incorrect inductance or saturation current leads to insufficient correction, overheating, or distorted waveform.
- *Solution*: Select the coil as specified in the manufacturer's application note. The coil must handle the horizontal deflection current and be capable of having its inductance modulated by the DC current from the TDA8145.
- Pitfall 2: Poor Parabolic Waveform Shaping.
- *Problem*: The correction waveform is not a true parabola, causing over-correction or under-correction at specific screen positions.
- *Solution*: Ensure the RC network connected to the integrator pins (typically pins 1, 2, and 8) uses stable, low-tolerance components. The time constant must be matched to the vertical
