Understand the application of transient suppression diodes in AC circuits

Understand the application of transient suppression diodes in AC circuits

The most commonly used electronic protection device is the transient suppression diode, which is also one of the overvoltage protection devices. TVS diodes are widely used for the protection of semiconductors and sensitive devices, usually used for secondary protection. It is generally used for secondary protection after ceramic gas discharge diodes, and some users directly use it for product protection.

The transient suppression diode is characterized by fast response (ps level), small size, large Pulsed power, low clamping voltage, etc. Its 10/1000 μ The s wave Pulsed power ranges from 400W to 30KW, and the pulse peak current ranges from 0.52A to 544A; The breakdown voltage ranges from 6.8V to 550V, making it convenient for various circuits with different voltages.

When selecting TVS transient suppression diodes, specific circuit conditions must be considered, generally summarized as the following:

1. Vrmax (reverse working voltage) ≥ normal working voltage;

2. Vcmax (clamp voltage) ≤ allowable safe voltage. If the power supply voltage of a conventional CMOS circuit is 3-18V and the breakdown voltage is 22V, a TVS transistor with a Vcmax of 18-22V should be selected;

3. Pp (value of transient Pulsed power)=peak pulse current Ipmax and Vcmax. Pp is greater than the transient of the protected device or circuit;

4. Surge power.

A DC regulated power supply with a transistor that amplifies the current output, and a transient voltage suppression diode is added to its regulated output to protect the instruments and equipment using the power supply. At the same time, it can absorb the peak voltage between the collector and emitter of the transistor in the circuit, protecting the transistor. Adding a TVS diode at each output end of the voltage regulator can greatly improve the reliability of the entire machine application.

Examples of AC circuit applications:

DC lines use unidirectional transient voltage suppression diodes, while AC lines must use bidirectional TVS transistors. AC is the grid voltage. The transient voltage generated here is random, and sometimes lightning strikes (transient voltage generated by lightning induction) are encountered, so it is difficult to quantitatively estimate the instantaneous Pulsed power PPR. However, the correct selection of reverse working voltage is necessary.

The general principle is to multiply the AC voltage by 1.4 times to select the reverse operating voltage of the TVS transistor. The reverse working voltage VRWM of the TVS transistor is selected based on a DC voltage of 1.1 to 1.2 times.