It is well known that electronic products often encounter unexpected voltage transients and surges in use, resulting in damage to electronic products caused by semiconductor devices (including diodes, transistors, thyristors, integrated circuits, etc.) in electronic products. ) was burned or broken down. It is estimated that 75% of electronic product failures are caused by transients and surges. Voltage transients and surges are everywhere, power grids, lightning strikes, blasting, and even people walking on carpets can generate tens of thousands of volts of static induction voltage, which are invisible killers of electronic products.
The surge protector provides a simple, economical and reliable protection method for power surge protection of electronic equipment. Through surge protection components (MOV), the surge energy is quickly transmitted when lightning strikes and operates overvoltage. Earth, protect equipment from damage.
1. Parallel surge protector is connected in parallel to the power supply line
Under normal conditions, the varistor in the lightning protection module is in a high impedance state. When the grid is subjected to lightning strikes or switching operations, the surge arrester responds within nanoseconds, and the varistor is in a low-impedance state, quickly limiting the overvoltage to a very low amplitude.
When there is a continuous pulse or continuous over-voltage in the line for a long time, the performance of the varistor is degraded and the heat is heated to a certain extent to trip the hot-release mechanism to prevent fire, thereby protecting the device.
2. Series filter type surge protector is connected in series to the power supply line
Providing safe, clean power to valuable electronic equipment. In addition to huge energy, lightning waves have extremely steep voltage and current rise rates. A shunt-type surge protector can only suppress the amplitude of a lightning wave, but it cannot change its sharply rising leading edge. The series filter type power surge protector is connected in series to the power supply line. In the case of overvoltage, MOV1 and MOV2 respond within the subtle time and clamp the overvoltage. At the same time, the LC filter reduces the steep voltage of the lightning wave, the current boost rate by nearly 1000 times, and the residual voltage by 5 times. Protect sensitive user devices.
3. Install a voltage-sensitive limiting element between the phases of the power line and between the lines to limit the surge overvoltage.
This method has better protection effect on electrical equipment with high impact voltage level such as lighting, elevator, air conditioner and motor. However, for modern electronic devices with high integration and compact structure, the actual protection effect is not satisfactory.
4. Strengthen the protection effect on electronic equipment. A super-isolation transformer (also called isolation method) is connected between the power supply and the load to isolate high-frequency spike interference, and at the same time, the secondary equipotential bonding can be facilitated.
The isolation method mainly uses an isolation transformer with a shielding layer. Since common mode interference is a relatively large ground interference, it is mainly transmitted through the coupling capacitance between the transformer windings. If the shield is inserted between the primary and secondary and grounded well, the interference voltage can be shunted through the shield to reduce the interference voltage at the output. In theory, a transformer with a shield can achieve an attenuation of about 60 dB. However, the quality of the isolation often depends on the process of the shielding layer. It is best to use a 0.2 mm thick copper plate with a shield on the primary and secondary sides. Usually, the primary shielding layer is connected to the shielding layer of the secondary side through a capacitor and then to the ground of the secondary side. It is also possible to connect the primary side of the shield to the ground of the primary side, and the secondary side of the shield to the ground of the side. And the cross-sectional area of the grounding lead is also larger. It is a good method to use an isolation transformer with a shield, but it is a large volume.
This method is too simple for the function of the transformer, relatively large in size and weight, and is not easy to install. It has a poor effect on the protection of medium and low frequency spikes and surges, so the market is limited and there are not many manufacturers. Therefore, non-special occasions are generally not used.
5. Absorption method
The absorption method mainly uses a absorbing device to absorb the surge peak interference voltage. The absorbing devices have the common feature that they exhibit a high impedance below the threshold voltage, and once the threshold voltage is exceeded, the impedance drops sharply, thus suppressing the spike voltage. Such absorbing devices mainly include varistor, gas discharge tube, TVS tube, solid discharge tube and the like. Different absorbing devices have their own limitations on the suppression of spike voltage. For example, the current absorbing capability of the varistor is not large enough; the response speed of the gas amplifying tube is slow.