MC7818BTG

MC7818BTG Application Field and Working Principle

Introduction

The MC7818BTG is a monolithic linear voltage regulator designed for use in positive-voltage systems requiring up to 1.5A of output current. It is part of a range of MC7800 family voltage regulators manufactured by On Semiconductor. It is designed to provide precise output voltages that are adjustable over a wide range of values relative to the Input Voltage. The basic function of the MC7818BTG is to regulate the output voltage under dynamic load conditions by its internal reference. As the load changes or the input voltage changes, it will supply the right amount of current to keep the output voltage regulated.

Application Field

The MC7818BTG is primarily used in systems using 12V or 5V nominal input voltage. It can be used in applications such as industrial, automotive and communications where low noise, low output voltage and high input voltage regulation is required. It is particularly suitable for applications with complex system architectures, where multiple voltage regulation requirements, extensive board space and stringent performance are required. Some common applications include notebook computers, monitors, test equipment, automotive audio systems, and PDA/handheld devices. The MC7818BTG can also be used in battery powered systems.

Working Principle

The MC7818BTG voltage regulator operates by working together with the internal pass device and the servo feedback loop. The series pass device mainly consists of the powering transistor and the current sensing resistor. The pass device working together of output transistors and servo loop provides a precise regulation even with load changes. The device monitors the output voltage constantly, compares it to the internal reference voltage, and makes the necessary adjustments to the current limited output current to keep the output voltage within a ±3% accuracy.

The internal reference voltage of the MC7818BTG is adjustable and is set by an external resistor divider on the adjust pin (ADJ) to a predetermined value. This is then used to compare against the Output voltage to maintain the desired output voltage across dynamic Load changes.

The MC7818BTG also includes several protection circuits to help with device stability and performance. Included is an over-voltage protection circuit that prevents the output from exceeding an unsafe level. In case of a short circuit on the output, the current limiting feature protected the device as well as the load. Additionally, the device starts up with a soft start feature to prevent output voltage overshoots. Also included is an internal thermal shut down circuit and a current limit circuit.

The MC7818BTG is available in a TO-220 package and has an efficiency up to 98%. Its features make it a great choice for high efficiency and reliability in various applications.