Introduction to precautions for designing self-excited switching power supplies
1. Insulation of primary and secondary sides
It is necessary to pay attention to the insulation of the communication side and the secondary side. Each country has corresponding regulations on this issue. If the spacing (planar distance) between adjacent printed circuits on the primary and secondary sides is 3mm, and the spatial distance between adjacent components on the primary and secondary sides is 5mm, and a transformer is used for electrical insulation.
There are three components connecting the primary and secondary sides, namely transformer T1, capacitor C12, and optocoupler IC2 in the diagram, which must meet their respective safety specifications. For transformer T1, the main focus is on the insulation layer between its primary stages. C12 is used to remove noise from power lines and requires the use of AC capacitors. And it has sufficient voltage resistance, and its capacity cannot be too large. Otherwise, it will increase the leakage current.
2. There should be no short circuit hazard in the primary side components
Surge voltage absorber SAl on the primary side Rl,Cl,C2, The rectifier bridge Dl directly bears AC mains power, and if a short circuit occurs, it may cause a fire. C1 and C2 are used to reduce common mode noise and require the use of AC capacitors. And ensure that its withstand voltage is greater than times the AC mains voltage, such as choosing 400V AC withstand voltage for 220V voltage.
3. Protection measures in the circuit cannot be omitted
The fuse F1 should be used to promptly melt in the event of a short circuit in the circuit, cutting off the AC source to prevent fire. The fast melting type should be selected, while F2 is a temperature fuse that protects the switch tube Trl. It should be installed tightly against Trl.
In addition. The ICl contains an overcurrent limiting circuit that detects overcurrent through the voltage drop on R12; SA1 can absorb external overvoltage.
4. Pay attention to the safety regulations of exported products
