BB135,115

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Varicaps - or variable capacitance diodes, or varactors - have a wide range of applications and working principles. The BB135 and BB115 Varicap diodes are arguably two of the most commonly used components within this category. In this article, we will discuss their applications and explore the principles behind their operation.

Understanding Varicaps

Varicaps are composed of two junctions, two terminals, and two layers made from a semiconductor material. They act like a capacitor, injecting electrical energy into circuits. When voltage is applied to the diode, the junctions - known as the depletion layer - allow electrons to flow between the two layers, creating a field of capacitance. By altering the voltage applied to the diode, the size of the depletion layer can be controlled, thus allowing a variable capacitance.

The BB135 and BB115 Varicap Diodes

The BB135 and BB115 Varicap diodes are ruggedly constructed, high-performance devices commonly used in high-frequency and sharp-tuning applications. They feature a low-leakage-current capability and good isolation characteristics, making them perfect for use in such applications. The BB135 is capable of handling a reverse-voltage rating of up to 35 V, while the BB115 can be rated for up to 15 V reverse-voltage performance.

The BB135 and BB115 diodes feature a broad capacitance range from 4 pF to 75 pF and are designed for use in either low- or high-frequency applications. They also offer excellent linearity, which makes them well suited for use in applications where modulation or tuning is required. Additionally, these devices are available in different package sizes, allowing for a greater degree of flexibility for the user.

Applications of Varicaps

Varicaps have a wide range of applications, including interference suppression, signal modulation, signal mixing, and frequency control. They are commonly used in oscillators, frequency multipliers, and frequency dividers, as well as in voltage-controlled oscillators and switched-diode filters. In addition, they are used in analog-to-digital and digital-to-analog conversion. Furthermore, they are often employed in several varieties of VHF, UHF, and microwave circuits.

Working Principle of Varicaps

The capacitance of the varicap is proportional to the voltage applied to it. As the applied voltage decreases, the capacitance increases. Conversely, as the voltage increases, the capacitance decreases. This principle of operation relies on the properties of the semiconductor material of which the device is made. The semiconductor has a negative potential barrier, which when exposed to an electric field due to the applied voltage, breaks down and allows electrons to move between the two layers.

As mentioned previously, the capacitance of the varicap is determined by the depletion layer, which is further determined by the applied voltage. When a higher voltage is applied, the depletion layer increases, thus decreasing the capacitance. Conversely, when a lower voltage is applied, the depletion layer decreases, resulting in a higher capacitance.

Conclusion

Varicaps (or variable capacitance diodes) are useful components with a wide range of applications. The BB135 and BB115 devices are the two most popular components in this category, offering excellent linearity and a broad capacitance range of up to 75 pF. The working principle of varicaps relies heavily on the properties of the semiconductor material of which they are made. When voltage is applied to the device, the negative potential barrier breaks down, allowing electrons to move between the two layers and resulting in a change in capacitance. Varicaps are commonly used for interference suppression, signal modulation, signal mixing, and frequency control.

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