The following is a typical specification: (1.2uS / 50uS)
- no error: 4 kV / common mode, 2kV/ 2 differential mode
Can ac restart (shutdown, short time does not work): 6kV / 12 common mode, 4kV / 2 differential mode
Higher lightning voltage, there can be no safety problems
The lightning has two modes: differential mode and common mode of lightning lightning
The peak voltage of lightning is provided, at the kV level
The input impedance is specified, or sometimes prescribed input short-circuit current
- 6 kV / 12 = 500A
The continuous lightning pulse and reset time and very short damage is relatively large:
- a very short reset time, such as: 15s or 1 minutes, making it difficult to pass the test, because the varistor and other parts have no time to bring down the temperature!
Differential mode lightning stroke Differential mode lightning stroke is high voltage between the L and N lines
Current flows from the L line from the N line
Common mode lightning stroke (1) When the switch is in the right position, the voltage is added to the L line and the earth line ("L1/PE") on the lightning generator
When the switch is in the left position, the voltage is added to the N line and the earth line (the "L2/PE" on the lightning generator)
The above two actually produce common mode and differential mode current.
Common mode lightning stroke (2) When the lightning generator is set to "L1, L2 / PE", the switch is connected to the two line at the same time. This is the only true common mode lightning test setup. If the customer simply said common mode lightning stroke refers to this setting
The system has only two lines of input, the output is suspended (not grounded), common mode lightning strikes are meaningless (very easy to pass the test, as long as the output is really suspended)
What damage will be caused by lightning strike
The high differential mode current caused by the differential mode lightning stroke can lead to the increase of the voltage of the input capacitor, and the damage of the input large electrolytic capacitor and the drain of the switch tube.
Common mode lightning strikes a very high common mode voltage. Arc discharge will produce a very high frequency current. If no arc discharge occurs, the current is relatively small, only parasitic capacitance Cparasitic * dv/dt.
When an arc discharge occurs, a very high peak current can be obtained, and the high frequency current can be coupled into the low-voltage circuit.
Lightning damage:
- very high common mode voltage can cause damage to the Y capacitor in the primary and secondary connections.
- very high differential mode voltage causes the input circuit to produce excessive voltage and excessive current, damaging the input side of the Yuan Qijian (fuse, input rectifier bridge, X capacitor, varistor, switching tube).
Ringing damage:
High frequency current can cause unsafe high voltage on the drain.
- high frequency current can cause high voltage ringing is safe, can damage like Schottky diode device
A.
Lightning current in the circuit is how to flow?
Flow direction of differential mode lightning current in circuit (CLC structure) From the above circuit diagram, most of the differential mode current through C1 and C2
- C1 and C2 voltage will rise rapidly, resulting in high drain voltage.
- to drain is not damaged in the input capacitor voltage rises, need to join the overvoltage protection line input, the input voltage is high value, stop switch, drain voltage will decrease, as the TOP series has input over-voltage protection circuit
- reduce the value of the input capacitance and reduce the cost
The loss on the RT1 is very large, the input capacitance is quite short, all the voltage drops on the RT1, the current is very large: V * I * t = Energy ---- may fail. So is the fuse. D1 can see a very high voltage rectifier diode - if damage is because the voltage is too high, the RC is very helpful (in PIN1 and PIN2, PIN3 and PIN4 indirect capacitance, does not need the capacitor) C30 will see the high voltage capacitor voltage. The lightning X specific KV level. If a resistor is connected in parallel with the C30
- protected rectifier bridge and input capacitance
- the peak current will increase through the fuse and RT1
If the fuse, fuse into larger (higher I2f), but do not use the "circuit protection fuse"
- any additional impedance will reduce the peak current,
High - resistance of the negative temperature coefficient thermistor RT1
Input common mode inductor
- input differential mode inductor
If the differential mode due to the failure of the lightning current caused by too much (for example: fuse, RT1), can be applied a differential mode inductance to reduce peak current
- note: some very easy saturation inductance, inductance current flows from its storage in a large amount of energy, and probably because of energy release caused by arc discharge to produce high pressure or burning inductance (so inductance in the wiring without discharge needle).
The current of the differential mode lightning current in the circuit (common structure) When there is no C1 in the circuit
- common mode inductor L1 to withstand higher voltage and more current
- Multi slot common mode inductance has more resistance to arc discharge
- note: some inductors will be very saturated, from the current store a lot of energy, and probably because of release of energy generated by high pressure caused by arc discharge or burned inductance.
- MOV varistor:
The diameter of the varistor is an indicator of its energy absorption
Remember - varistor is a voltage clamp, such as: pressure sensitive resistance will increase the peak current in the device on his left
- for example, a varistor is connected in parallel with the X capacitor, and the lightning current on the fuse and the RT1 will increase.
Flow direction of differential mode lightning current in circuit (capacitance equivalent inductance) Sometimes a short time peak voltage on a large electrolytic capacitor (due to the equivalent series inductance ESL of the capacitor and the pin inductance) causes damage to the drain
Solution: in the input capacitor close to the switch tube and transformer in parallel with a high frequency bypass capacitor, reducing the size of the loop will be helpful.
Common mode lightning current in the circuit of the flow - output grounding Mobile phones, routers, set-top boxes and other applications, the output of the antenna or the external connection of the power supply equipment, the need to test the above lightning strikes on the input and output
The voltage and the power input end and an output end
- note: on the left, and lightning in L and N line (L1, L2 / PE) Lightning current flows through B+ and B- copper skin
- despite the fact that the common lightning, you can also see the effect of the differential mode
Because L and N line impedance is not exactly the same (current shunt concept)
The Y capacitor connected across the first level, need to withstand high voltage (lightning voltage kV)
The isolation layer will see after high pressure:
- optical coupler (figure not, in practice there will be light)
- secondary winding and primary winding
- secondary winding and auxiliary winding from transformer
Common mode and differential mode current (L1/PE, L2/PE) If you set the lightning generator as "L1/PE" or "L2/PE", the common mode and differential mode currents are combined
- this is not an ordinary specification
It will be the common mode current flowing into the same
In addition the rapidly rising input voltage large capacitance and other differential mode current effect
Current direction - common mode lightning voltage and output In the circuit diagram is relatively poor in the current through the transformer coupling capacitor (primary and secondary coupling capacitance) and Y capacitance, current flows between the C pin capacitance and IC the connection, a stray inductance line, resulting in a voltage drop, will be displayed on the C pin voltage (common impedance coupling)
A resistor connected in series in the optical reflector (TOP-GX) The current flows through the optocoupler: stray capacitance into primary
It can be injected into a very large C pin current caused by misoperation, damaged or locked (and burst)
In the coupler is connected to the C pin is connected in series with a 300 W resistance reducing current pulse
Common mode lightning current flows to ---3 line input If lightning has been added but not through the power supply (e.g. output is not grounded), then only the Y capacitor to withstand voltage.
If L and N line impedance imbalance will produce differential mode current
The Y capacitor have KV lightning voltage level Sometimes, the ground wire of the lightning generator must be connected to the ground terminal on the AC adapter and the output common mode
It must be separated from all two test
- some power metal chassis, and some in the inside of a grounding wire, grounding wire connected with the AC terminal.
The lightning must be considered is how to enter the customer system
- for example, if the system has a metal chassis, and the metal chassis is grounded, must try to take place a lightning generator to receive
Additional tips
Repair and prevent any arc discharge. Because of the high frequency current caused by arc discharge.
The increase of spatial distance or slotted in PCB.
The event of arc discharge in the copper on the left traces, this place is very easy to arc discharge occurs again. So need to improve the place
If the varistor is easy to explode, can heat shrinkage sleeve on the varistor. The varistor is placed farther away from the fuse.
Can not put the varistor and fuse before, if it violates the safety regulations
Lightning strikes need to consider the following questions:
- where‘s the voltage distortion?
- where is the current flow? (arc discharge produces very high current)
Keep in mind that the common mode lightning strikes the effect of a differential mode
- control the low voltage foot of the IC, and think about where the common mode impedance causes the high frequency current to cause
Question?"
Remember common mode impedance noise coupling
- can reduce the peak current and impedance
- for example, common mode inductance, differential mode inductor or resistor in series in optocoupler -- but remember
These devices will live through the arc, if necessary, need to be careful
- can gripping pressure? With varistors, capacitors, or regulators
The correct connection of the pressure sensitive resistance The shorter the line, the better the parasitic inductance