Lightning protection surge power supply

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Design of switching power supply circuit for lightning protection

0 preface

With the development of the urban economy, the damage caused by the intrusion of lightning and lightning waves has greatly increased. Lightning rods on general buildings can only prevent direct lightning strikes, while the inductive lightning and pulse voltage generated by powerful electromagnetic fields can sneak into indoors to endanger the use of televisions, telephones and electronic instruments. Especially for solar control instruments, due to the special situation of solar installation location, the stability of its use is the focus of the majority of developers. Instantaneous high-voltage lightning surges and signal system surges are important causes of poor instrument stability. The main sources of signal system surge voltage are induced lightning, electromagnetic interference (EMI), radio interference and static interference. Metal objects (such as telephone lines) are affected by these interfering signals, which can cause errors in the data being transmitted, affecting the accuracy of transmission and the transmission rate. How to design lightning protection circuits has become a key issue in instrument development.

1 lightning surge analysis

The most common electronic equipment hazards are not caused by direct lightning strikes, but by current surges induced in power and communication lines when lightning strikes occur. On the one hand, due to the highly integrated internal structure of the electronic device (VLSI chip), the level of withstand voltage and overcurrent resistance of the device is reduced, and the withstand capability of lightning (including inductive lightning and operating overvoltage surge) is reduced. The signal source path is increased, and the system is more susceptible to lightning wave intrusion than before. Surge voltage can be broken into the computer equipment from the power line or signal line. We discuss these two aspects separately:

1) Power surge

Power surges are not only caused by lightning strikes. Power surges occur when power systems experience short-circuit faults and heavy loads. The power grid stretches for thousands of miles. The probability of lightning strikes or line surges is high. When a lightning strike occurs a few hundred kilometers away from you, the lightning surge is transmitted through the light speed of the power grid. After being attenuated by the substation, there may still be thousands of volts when it reaches your computer. This high voltage is very short, only tens to hundreds. Microseconds, or not enough to burn a computer, but it is very harmful to the semiconductor components inside the computer, just as the noise of the old sound is bigger than the new one because the internal components are damaged, as these damages deepen, the computer It is also getting more and more unstable, or it may cause the loss of your important data. The United States GE company measured the low voltage distribution line (110V) of ordinary households, restaurants, apartments, etc. in the 10 000 hours (about one year and two months), the number of surge voltages that exceeded the original working voltage more than doubled to 800. For the rest of the time, there are more than 300 times in excess of 1000V. Such surge voltages are entirely possible to damage electronic equipment at one time.

2) Signal system surge

The main sources of signal system surge voltage are induced lightning, electromagnetic interference, radio interference and static interference. Metal objects (such as telephone lines) are affected by these interfering signals, which can cause errors in the data being transmitted, affecting the accuracy of transmission and the transmission rate. Eliminating these interferences will improve the transmission of the network.

Based on the above technical defects and conditions, this paper designs a single-phase parallel anti-lightning surge switching power supply circuit based on varistor and ceramic gas discharge tube.

2 Design of lightning protection surge circuit

This paper designs a single-phase parallel anti-lightning surge circuit based on varistor and ceramic gas discharge tube, and applies it to the switching power supply of the instrument. The whole circuit includes a lightning protection circuit and a switching power supply circuit. The lightning protection circuit adopts three varistor and one ceramic gas discharge tube to form a composite symmetrical circuit, which is common mode and differential touch protection. The power supply circuit of the lightning protection meter is combined with the classic switching power supply circuit, and the varistor is connected in parallel to prolong the service life, and is separated from the switching power supply circuit after the varistor short-circuit failure, and does not cause fire.

In order to achieve the above objectives, the design scheme is to apply a single-phase parallel anti-lightning surge circuit of a varistor and a ceramic gas discharge tube to the power supply of the meter. It is mainly divided into lightning protection circuit part and switching power supply circuit part. The circuit is simple, adopts compound symmetrical circuit, common mode and differential touch protection, and can be connected without L or N end. The varistor RV1 is placed in parallel with the power supply L and N at the front end of the chip rectifying module, mainly for clamping the voltage between the L and N lines. The varistor RV0 and RV2 are connected in series with the ceramic gas discharge tube FD1 and grounded, and RV0 is connected in series with the FD1. The main reason is to inductive lightning surge current on the L-line. RV2 and FD1 are mainly connected in series. The energy on the 24V reference potential of the signal port is bleed. After RV0 and RV2 are short-circuited, FD1 can separate it from the power circuit. Will cause fire. A wire wound resistor is connected in series on the RV1 front-end line. When the RV1 short-circuit fails, the wire-wound resistor can function as a fuse to disconnect the short-circuit circuit. The varistor is a voltage-clamp type protection device, and its clamp voltage point. That is, the selection of varistor parameters is relatively important (selecting a higher varistor voltage, safer and more durable flow, and a lower failure rate); selecting the external dimensions and package form according to the requirements of the current capacity, 561k is used in this circuit. The -10D varistor is connected in series with a ceramic gas discharge tube to extend service life and ensure safety. The flow capacity of the ceramic gas discharge tube is selected according to the required flow capacity, and the circuit adopts 3RM470L-7.5-L, and the flow rate is 5000A. Wirewound resistor R1 acts as a current limiting voltage divider; the chip rectification module is the front end rectification of the switching power supply circuit, C1 is a high voltage filter capacitor, Y1 is a decoupling capacitor, and the resistor R2 and the capacitor C2 and VD2 constitute the absorption of the switching power supply chip MOS tube. Clamp circuit, protection chip, switching power supply chip adopts TNY27 series of PI company, TR1 is high frequency transformer, VD3, C3 constitute secondary filter of high frequency transformer, U2, VD4, R3, R4, R5 form feedback circuit of switching power supply circuit The secondary output voltage of the transformer can be stabilized at the design value. This lightning protection anti-surge circuit has achieved good results in practical use.

3 Conclusion

The single-parallel lightning protection circuit based on varistor and ceramic gas discharge tube has been gradually favored by designers in the development of solar control instruments in recent years. The circuit designed in this paper is rigorous and fully conforms to the national standard GB/T 17626. 5 test criteria. In actual use, the space of the PCB board can be vacated to provide developers with a free-designing stage.