BB178,315

Series:	--
Packaging:	Tape & Reel (TR)
Lead Free Status / RoHS Status:	--
Part Status:	Obsolete
Moisture Sensitivity Level (MSL):	--
Capacitance @ Vr, F:	2.754pF @ 28V, 1MHz
Capacitance Ratio:	15
Capacitance Ratio Condition:	C1/C28
Voltage - Peak Reverse (Max):	32V
Diode Type:	Single
Q @ Vr, F:	--
Operating Temperature:	-55°C ~ 125°C (TJ)
Mounting Type:	Surface Mount
Package / Case:	SC-79, SOD-523
Supplier Device Package:	SOD-523
Base Part Number:	BB178

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Diodes - Variable Capacitance (Varicaps, Varactors)

Variable capacitance (varicaps, varactors) diodes, such as the BB178,315, are silicon semiconductor devices used for a variety of tasks in the radio frequency (RF) electronics industry. By changing the voltage across the device, their capacitance can be varied, enabling them to act as voltage-controlled capacitors.Varicaps can be used as frequency-determining elements in oscillators, as automatic frequency control elements, and in tuning circuits. They are also commonly used in electronic power supply circuits to provide voltage regulation by providing a voltage-selective feedback loop.

Application Field

Varicaps can be used to build oscillators and as tuning elements in a variety of RF and microwave applications. They are used in Fm transmitters and receivers, narrow-band and wide-band receivers, antenna tuning, video amplifiers and transceivers, carrier-current systems, and a vast array of other communications electronics systems.Varicaps are also widely used in microwave ovens, as they can be used to tune the cavity resonant frequency of the appliance. By tuning the frequency of the resonant cavity, the cooking effect of the oven is optimized.

Working Principle

At low currents and voltages, varicaps behave like normal diodes, blocking current in a reverse-biased configuration. However, when a voltage is applied, they become highly-conductive and act as variable capacitors.This variable capacitance is due to charge movement across the PN junction of the diode, which increases as the voltage across the junction increases. This increases the electric field strength across the diode and causes electrons to be pulled out of the valence bands of the P and N materials which make up the diode.This charge redistribution creates a negative charge near the P side and a positive charge near the N side, resulting in an electric field. This electric field is what provides the capacitance of the diode, which can be controlled by adjusting the voltage across the junction.

Conclusion

Variable capacitance diodes, such as the BB178,315, are invaluable components in the RF and microwave industries. They are used in a wide range of applications, from frequency control to microwave ovens, due to their ability to be voltage-controlled capacitors. By applying a voltage across the junction of the diode, the charge across the PN junction can be manipulated, resulting in a change in capacitance.

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