Self-excited switching power supply circuit design with isolation function

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

description:

The non-isolated switching power supply forms a power device in common with the power supply circuit, and the "ground" of the input rectification power supply device has a commercial power, which poses a potential hazard to users and maintenance. At the same time, due to the increasing use of CMOS integrated circuits and digital processing integrated circuits, if such overvoltage-sensitive devices are used, the same reference point cannot be used with the commercial power supply. Even with ordinary equipment, with the expansion of functions, audio and video or digital signal interfaces with various specifications, the signal ground must be isolated from the mains.

Generally speaking, the parallel type switching power supply means that the switching tube and the load circuit are connected in parallel, and are currently used in a boost type non-isolated switching power supply. The I/O isolated switching power supply referred to herein is also referred to as a pulse transformer coupled switching power supply. The input power source controls the energy storage of the primary coil of the pulse transformer through the switch tube, and the energy release is performed through the secondary of the pulse transformer. By changing the turns ratio of the pulse transformer, various pulse voltages can be obtained, and after rectification and filtering, the voltage is supplied to the load by DC. Obviously, the input and output terminals of the switching power supply transmit energy through the magnetic coupling of the pulse transformer. The insulation between the pulse transformer windings completely isolates the primary side from the secondary side, and the insulation resistance and the electric strength can be very high. . At present, almost all of the power-supply devices from the mains use such switching power supplies, replacing the power frequency transformers and energy-consuming regulators that have been used for many years.

The switching power supply coupled by the pulse transformer is divided into self-excited and excited according to its excitation mode. The self-excited pulse transformer-coupled switching power supply is composed of a switching tube mainly composed of a pulse converter, which converts the direct current into a pulse wave and is sent to the load circuit through the pulse transformer coupling; the excitation mode uses the switch tube as an independent switch, and the pulse transformer The energy storage winding is connected in series to the power supply circuit, and the switch tube is controlled by the widened pulse of the independent pulse driver output. The switching transformer-coupled switching power supply can be divided into a forward type and a flyback type according to the way in which it supplies energy to the load. The switching power supply coupled by the forward pulse transformer supplies energy to the load when the switch tube is turned on; the flyback mode is the electric-magnetic-electrical conversion mode, and the energy storage of the pulse transformer is provided to the load during the cutoff period of the switch tube. energy.

The accessories are part of the design circuit, detailed circuit analysis and more information can be found in the PDF document!