Overvoltage surge detection method for communication equipment

1、 Overvoltage surge test method

For some electronic equipment with specific environment and purpose, voltage surge often occurs in the power supply (the surge referred to in this article is overvoltage surge). Overvoltage surge of communication equipment mainly takes the following forms, and the specific parameters are as follows:

In the process of power supply design, the power supply must be subject to surge test to prevent the impact of these overvoltage surges on the back-end electrical equipment. Relevant surge test requirements are: electrical equipment shall withstand five overvoltage surges, and the time interval between two overvoltage surges is 1min. Overvoltage surge detection method: firstly, the electrical equipment is powered under normal steady-state voltage, then the input voltage of the electrical equipment is increased to the surge voltage, and finally the input voltage is restored to the normal steady-state voltage. After overvoltage surge, power supply and back-end equipment shall not fail.

2、 Actual case

When the communication company uses the SV48-28-450B-48V DC conversion power supply produced by ACBEL to conduct the 2KV surge test, the input front-end circuit catches fire, which directly damages the back-end MOSFET.

According to the analysis, because the front end anti-wave circuit is 2, the DC conversion power supply KV will produce a large current impact under the high voltage impact, causing the circuit board to fire and damaging the back end MOSFET. The most direct reason should be the fault of the anti-wave circuit designed at the front end of the power supply.

3、 Circuit design

In order to protect the communication equipment using this power supply and prevent the impact of surge voltage, the anti-surge circuit is designed. The specific circuit diagram is as follows:

The circuit adopts a two-level lightning protection circuit for lightning protection and surge processing, and is an advanced DC lightning protection and surge processing circuit. Now it is necessary to meet the requirements of input terminal IEC61000 of communication customers. The input shall meet the requirements of KV, 4KV surge voltage and lightning current of 5kA and 10kA of Dadi 2000.

The working principle of this circuit is as follows: when lightning surge voltage is induced, L1 will block the sudden change of voltage, so that the first stage circuit acts first. The first stage four-stage circuit MOV (MOV1-4) pipe, two discharge tubes (FDG1, 2) amplify the current, and then a small part of energy passes through the second stage L1 inductor. The two MOV tubes (MOV5, 6) further clamp the surge voltage at the input end in order to release a small current, Prevent damage to the rear equipment and power module. The junction capacitance of the device will affect its action time. Of the three devices, TVS has the fastest response action time, followed by FDG and MOV. Because most of the MOVs are damaged, they are in short circuit. In order to prevent fire in case of short circuit, the safety tube shall be connected in series, and the explosion-proof slow melting type shall be selected to meet the impact of 8/20 microsecond current waveform. The differential mode inductor L can also form EMC differential mode filter with the subsequent capacitor, which has a good suppression effect on the interference below 1MHZ. Please note that the inductor must be a hollow coil, so it will not be saturated by large current. When it is too large, its volume is also large. L2 and L3 are two common-mode inductors, Q1 is anti-reverse connection MOSFET, and Q2 and R9 are transient impact current at startup. The circuit not only has anti-surge function at the front end of the module, but also has interference suppression and anti-reverse connection function.

4、 Test effect after changing the design circuit

Through field analysis, after using the circuit provided by us, after many practical tests, we successfully suppressed two KV surges and protected the devices of back-end equipment.