Common mode lightning strike: (Common Mode)
The common mode of lightning discharge path (see above the green line), first consider the cross primary and secondary due to insufficient safe distance caused by the lightning flashover path or component damage are those? (transformer / optical coupler /Y-Cap) for the three components selection and design considerations are as follows:
1 transformer:
Because of the transformer across the primary and secondary components, according to the working voltage has different safety distance requirements, general mining
With the level of Class B, the first part of the part itself through the Hi-POT 3000Vac, special attention should be paid to the distance between the foot and the iron core and the number of winding tape is consistent with the insulation strength.
2 optical coupler:
The component itself needs to comply with the requirements of the safety rules, layout parts can not be avoided under the distance Trace
Insufficient question.
3 Y-Cap:
Itself is characterized by high frequency and low impedance components, when the common mode lightning test, the energy will quickly pass Y-Cap
The placement of the path, and hence the layout layout when the semiconductor component (PWM IC, TL431, OP)... GND)
Trace should avoid Y Cap lightning energy release path to avoid damage to parts

Lightning strike of differential mode: (Differential)
Lightning energy flows through the main path of the bridge rectifier L and N circuit, the main countermeasures are as follows: Varistor (MOV) or Spark Gap (lightning tube) absorption and other components to absorb and inhibit the flow of energy into the interior of the power supply.
1 Thermistor (NTC): series connected to the L or N path, will increase the impedance value of the loop, thereby reducing the current energy into the Power supply.
2.MOV (Metal Oxide Varistor): metal oxide or surge absorber, using parallel to L and N, the component itself as a high impedance component, not in the general case and loss, leakage current only slightly, when the moment of lightning into the high potential power source input and more than MOV the breakdown voltage, while suppressing voltage action, and let the instantaneous rise current flowing through the MOV itself for energy absorption, reduce the lightning energy into Power Supply.
3 Spark Gap or Gas Discharge Tube: the use of Common Choke in parallel at both ends of the same side, according to the principle of lightning protection action voltage generated by the high potential when the moment exceeds its rated at Common Choke at both ends of the inert gas can be excited, then Spark Gap will generate electric arc discharge, the surge of energy suppression don‘t let down, a large amount of energy into the Power Supply,
4 in the layout planning form copper foil jagged ends, a distance of about 1mm, when Common Choke at both ends of the pressure is too large, resulting the discharge phenomenon, energy and catharsis.
In addition to the above design should pay attention to the place, how to achieve Layout on the prevention and control of electric shock is also an important part.
Ground wire (Ground) processing, as shown in the following figure
A. the primary side of the Ground, the layout sequence of the large capacitance of Ground - Current
Sensor - Y-Cap - primary transformer auxiliary winding Vcc capacitor Ground - PWM IC peripheral
Component ground - PWM IC ground.
B. part of the two side: 1 TL431 ground to the level of the output capacitor of second.
C. the two side of the Y-cap pin connected to the two side of the transformer ground. 2 handle the high pressure part, as shown in the following figure.
A. L, N two line distance above 2.5mm and with E distance above 4mm.
The high voltage and low voltage B. copper foil copper foil safety distance of over 1.5mm.
C. one or two times the distance of more than 6mm. Note 4 PWM IC layout, PWM for IC compared with other components is relatively fragile and easy to damage the components, for example in the PWM IC in general will define each foot who can bear the maximum potential and negative voltage as shown below, so the beginning of the layout component set the important.
Vcc electrolytic capacitors and ceramic capacitors.
Pin Cs ceramic capacitors.
Pin CT ceramic capacitors.
Pin COMP ceramic capacitors.
The capacitor should be as close as possible to the IC, to prevent the transient voltage into the PWM IC (especially negative voltage). Again
On Ground processing, the first PWM IC / CS / COMP all GND together after a single point
Enter the IC GND, then connect to the Vcc electrolytic / ceramic capacitor Ground and then connect to the auxiliary winding Ground. For the example of the layout ground, an example is used to explain the layout criteria of Ground as shown below
1 Current sense resistor directly back to the ground with large capacitance.
2 from the ground of the large capacitance to the ground of the transformer to the auxiliary winding Vcc electrolytic capacitor.
3 by the auxiliary winding Vcc electrolytic capacitor and then out to the optical coupler and IC peripheral ceramic capacitors, finally received PWM IC.