MC7809BT

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The MC7809BT voltage regulator is an integrated negative voltage regulator with a maximum output current ranging from 1A to 3A. It has a wide range of applications and its working principle is quite straightforward. This article will discuss the MC7809BT application field and working principle to provide you a better understanding of this integrated voltage regulator.

Applications of MC7809BT

The MC7809BT is a three-terminal negative voltage regulator which is specially designed to provide a constant voltage output and maintain regulation at such voltage level. It offers many features and thus can be used in a wide variety of applications. Some of the typical applications include:

• Servers and data storage systems, which need a high-performance, reliable and efficient power supply system to provide constant voltage supply output.
• Medical devices, where the regulator ensures that the output voltage does not go above or below the necessary operating voltage.
• Automotive, where this low-power consumption regulator is used for controlling the power management of the system.

Working Principle of MC7809BT

The working principle of the MC7809BT voltage regulator is simple and easy to understand. It is an integrated negative voltage regulator with an output voltage of 12V. It works in two parts – the sensing and controlling of the output voltage.

The output voltage is sensed using a voltage divider circuit and two resistors, where the voltage at their junction is compared with a reference voltage of 2.495V. This reference voltage is set through an on board bandgap reference circuit.

The voltage divider circuit primary job is to sense the output voltage and update the regulator with the current status. The actual regulation is done by the controlling circuit which consists of a PNP transistor and two current mirrors.

The PNP transistor acts as a switching element while the two current mirrors provide current to the load as well as regulate the output voltage as per the predetermined reference voltage. When the output voltage deviates from the required level, the voltage divider sends this information to the current mirror circuit and it adjusts its output voltage until the required output voltage is reached.

Conclusion

The MC7809BT is a reliable, efficient and high-performance linear regulator with a maximum output current range of up to 3A with an output voltage of 12V. It is widely used in the fields of servers and storage systems, medical devices and automotive due to its low-power consumption features. Its principle of operation is based on the voltage divider circuit and a controlling circuit made up of a PNP transistor and two current mirrors.

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