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Diodes - Variable Capacitance (Varicaps, Varactors)

Variable Capacitance Diodes, commonly known as Varicaps, Varactors or Diodes - Variable Capacitance, are an important and widely used class of diodes used in various applications. The most common type of Variable Capacitance Diode, the BB149A and the 135, are used for many purposes, from high frequency tuning, filtering, and more.

BB149A and 135

The BB149A and 135 are two of the most widely used diodes for variable capacitance applications. They are both capable of operating at voltages of up to 50 Volts and delivering current up to 10mA. They are both characterized by their high stability, low leakage current and low capacitance. They are also both encapsulated with epoxy, making them an ideal choice for static sensitive applications.

Application Field

The BB149A and 135 are mainly used in high frequency tuning and filtering applications. They are also widely used in TV set and microwave transceivers. The BB149A and 135 are also used for frequency dependent filters, voltage sources, and other audio frequency applications.

Working Principle

Variable Capacitance Diodes work using the principle of the tunnel diode, which is that high voltage voltage applied will cause electrons to tunnel through the junction barrier, resulting in a short circuit. This creates an electric field between the surface of the diode junction and the barrier, which allows the capacitance of the junction to be varied by varying the applied voltage.

When a certain voltage is applied, the junction’s capacitance is determined by the product of the medium’s dielectric constant and the area of the junction as well as voltage. As the voltage increases, the capacitance increases as well. This gives variable capacitance diodes their unique variable capacitance feature.

Conclusion

The BB149A and 135 are two of the most popular Varicaps Diode available on the market. Their popularity stems from their high stability, low leakage current, low capacitance, and encapsulation with epoxy. These diodes are primarily used for various applications such as high frequency tuning, filtering, and more. They also utilize the tunnel diode working principle, allowing them to have a variable capacitance that can be adjusted by varying the applied voltage.

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