## Overview of the LM2445 The **LM2445** is a monolithic high-voltage CRT (Cathode Ray Tube) driver circuit designed specifically for use in high-resolution color monitors. It belongs to a class of integrated circuits known as **RGB CRT Drivers**, which amplify low-level video signals to the high voltages required to drive the cathodes of a picture tube. --- ### 1. Key Technical Specifications The following table summarizes the primary electrical characteristics of the LM2445: | Parameter | Value | | :--- | :--- | | **Supply Voltage ($V_{CC}$)** | +60V to +90V | | **Bandwidth (-3dB)** | 10 MHz | | **Rise/Fall Time** | 35 ns (typical) | | **Output Swing** | 40 $V_{pp}$ to 50 $V_{pp}$ | | **Number of Channels** | 3 (Red, Green, Blue) | | **Package Type** | TO-220 (Molded Plastic) | --- ### 2. Functional Description The LM2445 operates as a triple-channel amplifier. Each channel is independent but shares a common power supply and ground. #### Internal Architecture - **Input Stage:** Receives low-voltage video signals (usually from a video preamplifier). - **Gain Stage:** Provides a fixed gain (typically around -14 to -20) to boost the signal. - **Output Stage:** A high-voltage emitter-follower or similar structure capable of driving the capacitive load of the CRT cathodes. #### Circuit Features * **High Voltage Operation:** Capable of handling up to 90V, which is necessary for managing the "cutoff" and "drive" levels of a CRT. * **Thermal Protection:** Often includes internal circuitry to prevent damage from overheating during high-frequency operation. * **Simplified Design:** By integrating three channels into one chip, it reduces the component count compared to discrete transistor designs. --- ### 3. Pin Configuration (Typical TO-220 9-Lead) | Pin No. | Function | Description | | :---: | :--- | :--- | | 1 | $V_{IN}$ (Red) | Video input for the Red channel | | 2 | Ground | Common system ground | | 3 | $V_{IN}$ (Green) | Video input for the Green channel | | 4 | $V_{CC}$ | High voltage supply (+80V typically) | | 5 | $V_{IN}$ (Blue) | Video input for the Blue channel | | 6 | $V_{OUT}$ (Blue) | Amplified output for the Blue cathode | | 7 | NC / Case | No connection or heat sink contact | | 8 | $V_{OUT}$ (Green) | Amplified output for the Green cathode | | 9 | $V_{OUT}$ (Red) | Amplified output for the Red cathode | --- ### 4. Application Considerations When designing or repairing a circuit with the LM2445, keep the following in mind: 1. **Heat Dissipation:** Because it operates at high voltages and high frequencies, the LM2445 generates significant heat. It **must** be mounted to a substantial heat sink. 2. **Power Supply Decoupling:** Use high-quality capacitors (e.g., 0.1µF ceramic and 10µF electrolytic) close to the $V_{CC}$ pin to filter out noise. 3. **Arc Protection:** CRTs are prone to internal arcing. Spark gaps or limiting resistors (around 100$\Omega$ to 330$\Omega$) are usually placed between the IC output and the CRT socket to prevent the IC from being destroyed by high-voltage transients.