Understand the capacitance value of TVS diode

Understand the capacitance value of TVS diode

If TVS diodes are used for lightning protection in high-frequency circuits, their PN section capacitance is too large, which will cause loss of high-frequency signals. The grounding capacitance value on the signal line can be determined based on the high frequency. The capacitance formula of a capacitor can be used to calculate the capacitance generated by the capacitor at a fixed frequency, and the degree of influence of this capacitance in the circuit can be observed. The capacitance of a general semiconductor device is measured in units of P, which has little effect on frequencies below megahertz.

The junction capacitance of TVS tubes is generally divided into two types based on different manufacturing processes: high junction capacitance type, usually in the hundreds to thousands of pF, and low capacitance type, usually a few pF. For power lines, it is not necessary to consider them. For applications in data and signal circuits, low capacitance TVS should be selected to avoid signal waveform distortion or interference. Bidirectional TVS diodes are used in circuits where the polarity should be connected in reverse, similar to a voltage regulator. The difference is that the voltage regulator in the circuit is in a reverse breakdown state as the normal state, while TVS transistors are not breakdown or conductive when the circuit is normal. Generally divided into bidirectional and unidirectional. A two-way fate with positive and negative poles. Same connection method for unidirectional and voltage regulator diodes. The one with a horizontal bar is connected to the power supply end.

Under specified reverse application conditions, TVS diodes can immediately reduce their operating impedance to a very low conduction value when subjected to a high-energy instantaneous overvoltage pulse, allowing large currents to pass through and clamping the voltage to a predetermined level, effectively protecting precision components in electronic circuits from damage. The SMD TVS tube can withstand an instantaneous Pulsed power of up to kilowatts, and its clamping response time is only 1ps (10-12S). The forward surge current allowed by TVS can reach 50-200A under the conditions of T=25 ℃ and T=10ms. Bidirectional TVS tube can absorb instantaneous large Pulsed power in both positive and negative directions, and clamp the voltage to a predetermined level. Bidirectional TVS tube is suitable for AC circuits, and unidirectional TVS tube is generally used for DC circuits.