Self-excited Switching Voltage Regulator
Typical circuit of self-excited switching regulated power supply: This is a switching power supply composed of intermittent oscillator circuits, and is one of the basic power supplies widely used at present.
When connected to the power supply in R1 to the switching tube VT1 to provide start-up current, so that VT1 began to conduct, its collector current Ic in L1 in the linear growth in L2 induced so that the base of VT1 is extremely positive, extremely negative positive feedback voltage emitter, so that VT1 saturated very quickly. At the same time, the induction voltage to C1 charging, with the C1 charging voltage increases, VT1 base potential gradually become lower, resulting in VT1 out of the saturation region, Ic began to decrease in L2 inducted so that the base of VT1 is extremely negative, emitting a very positive voltage, so that the VT1 quickly cut off, then the diode VD1 conduction, the high-frequency transformer T primary winding in the energy storage released to the load. In the VT1 cut-off, L2, there is no inductive voltage, DC power supply input voltage by R1 to C1 reverse charging, gradually increase the VT1 base potential, so that it re-conductivity, once again flipped to reach saturation, the circuit is so repeated oscillation down. Here is like a single-ended flyback switching power supply, by the secondary winding of the transformer T to the load output the required voltage.
Self-excited switching power supply in the switching tube plays a dual role of switching and oscillation, but also eliminates the control circuit. Circuit because the load is located in the secondary transformer and work in the flyback state, with the advantages of input and output isolation. This circuit is not only suitable for high-power power supplies, but also for low-power power supplies.
Single-ended Flyback Switching Power Supplies
Typical circuit of single-ended forward switching power supply: this circuit is similar to the single-ended flyback circuit in form, but the working situation is different. When the switching tube VT1 conductive, VD2 also conductive, then the power grid to the load to transmit energy, filter inductor L stored energy; when the switching tube VT1 cut-off, inductor L through the continuity of the diode VD3 continue to release energy to the load.
There is also a clamp coil with diode VD2 in the circuit, which limits the maximum voltage of switching tube VT1 to between twice the supply voltage. In order to satisfy the core reset condition, i.e., the flux build-up and reset times should be equal, so the duty cycle of the pulses in the circuit cannot be greater than 50%. Since this circuit transmits energy to the load through the transformer when the switching tube VT1 is on, it has a large output power range of 50-200W. The transformer used in the circuit has a complex structure and a large size, and it is for this reason that the practical application of this circuit is less.
