Introduction to switching power supply topologies

1. Overview of three types of non-isolated DC-DC topologies 1.1Buck type converter

The buck converter topology is shown in Figure 2.2 and the buck Converter is also known as a buck-type power supply topology. When the switching tube s is on, the diode VD negative voltage is higher than the positive reverse cutoff, at which time the current is fed through the inductance L to the capacitance and load, while the inductance L stores the energy. When the switching tube s is off, the energy stored in the inductance L cannot be released immediately, and the induced current generated by the load, the diode VD form a continuous flow path, continue to power the load. The diode is therefore called a freewheeling diode. In a buck-type power supply topology, the relationship between the output and input is v_o=dv_i when the PWM duty ratio of the switching tube is d.
1.2Boost Converters

The basic topology of the boost converter is shown in Figure 2.3. Boost converters are also known as step-up power supply topologies. When the switching tube s is on, the diode positive voltage is lower than the negative voltage reverse Pianguan, the power supply and inductance to form the path, the inductance L flow through the current storage energy, the load from the capacitor to provide energy. When the switching tube s is disconnected, the diode is in the wizard, and the power supply and inductance L store the energy simultaneously to the capacitor, the load power. In a step-up converter, when the control signal duty ratio of the driving switch is D, the output and input satisfy the relationship of v_o=1/(1-d) v_i.
1.3buck-boost Converters

The basic topology of the Buck-boost converter is shown in Figure 2.4, and the Buck-boost Converter is also known as a lift-and-pressure switching power supply topology. When the switching tube s is on, the diode negative voltage is higher than the positive voltage, the power supply and inductance form the path, and the inductance L stores energy. When the switching tube s is off, the diode is guided through, and the inductor current is not immediately released with the load, the diode forms a continuous flow path. However, the load voltage is opposite the input voltage polarity at this time. In the Buck-boost converter, when the duty ratio of the control signal of the driving switch is D, the relationship between the output and the input satisfies the v_o=d/(1-d) v_i.
2. Overview of five isolated DC-to-DC topologies 2.1 Forward-excited converters

The basic topological structure of the forward converter is shown in Figure 2.5. By placing the transformer between the switching tube and the diode of the buck converter, a forward-excited topological structure can be obtained, and the isolation of the primary and secondary sides of the transformer makes the input and output isolated. The forward-time converter is widely used in 50w~400w because of its simple circuit design and economical convenience. However, due to all the coil current in the transformer when the switch is off, all disconnected, in order to ensure that the transformer core does not occur magnetic saturation phenomenon, additional winding W3 added to the function of the core reset.

When the switching tube s is on, the supply voltage is added to the primary winding W1, according to the relationship between the N1 and N2, the primary winding energy is transferred to the secondary winding w2,vd1 conduction, inductance L, capacitance C together to obtain the primary input energy. When the switching tube s is off, the remaining energy in the W1 is returned to the input of the power supply through the auxiliary winding W3, the VD1 cutoff, the secondary inductance L, the diode VD2, the load forms the continuation circulation road.
In the forward-excited converter special attention to switch s off to the next cycle switch s on the time to make the core residual energy is released, otherwise in the subsequent time, the remaining energy value continues to increase, and finally reach the core can withstand the limit value and saturation. 2.2 Flyback Converter

The basic topology of Flyback converters is shown in Figure 2.6. In the Buck-boost-type converter, the high-frequency transformer is placed in the inductor position and there is a flyback circuit. Flyback Converter design is very easy, inexpensive, often used in multi-output low-power switching power supply occasions.

When the switching tube s is on, the supply voltage is added to the primary winding W1 at both ends, according to N1, N2, the relationship between the same name, winding W2 high potential at the lower end, diode VD1 at this time does not conduction. When the switch S is off, the high potential of the winding W2 at the upper end, the diode VD1 is guided through, the load obtains energy. 2.3 Push-Pull converters

A push-pull converter has its topology as shown in Figure 2.7. The primary side switch tube S1, S2 alternating conduction, the energy in the transformer core can be stored and released normally, thus transferring energy from the original side to the secondary side.

When the switch S1 on, S2 off, the secondary-side winding diode VD1 conduction, the load to obtain energy. When the S2 conduction, S1 off, secondary side two-stage tube VD2 conduction, the load can still obtain energy. When the switch tube s1,s2 is turned off, inductance L through the diode VD1, VD2 and load formation pathway, according to shunt shunt, load current only half through each diode, but at this time the switch tube withstand voltage is 〖2v〗_i. , so in order to ensure that the voltage stress of the switch tube is not too large, push-pull converter in low-voltage high-current occasions have a certain advantage. 2.4 Half-bridge converter

The topology of the half-bridge converter is shown in Figure 2.8. A bridge arm consists of two capacitors and the other one is comprised of two power switch tubes. In the normal operation of the circuit, the primary side windings have current during the whole period of the control signal, and the utilization of the cores is improved. So the half-bridge converter has advantages over high voltage and power.

Capacitor C1 and C2 capacitance, the model is the same, the voltage on each capacitor is the v_i. When the switch S1 conduction S2 off, the diode VD1 conduction, VD2 cut-off, at this time N21 winding to the load transfer energy. When the switch S1 off, S2 conduction, the diode VD2 conduction, VD Cutoff, at this time N22 winding can transmit energy to the load, that is, the secondary winding N21 and N22 alternately release energy. 2.5 Full-bridge converters

The full-bridge converter has its topological structure as shown in Figure 2.9. The four switch tubes make up the H-bridge circuit, and the transformer original winding is connected to the load position of the bridge circuit. When the switch S1 and S4 conduction, S2 and S3 off, the primary winding high potential at the upper end. When the switch S2 and S3 conduction, S1 and S4 turn off, the primary winding high potential at the lower end. Therefore, in a cycle of the initial winding flow in the opposite direction, the transformer does not have a core saturation problem, which also makes the full-bridge converter efficiency and power density can be done very high. The secondary windings of the full-bridge converter are provided with a central tap and the output is fully-wave rectified, so it is suitable for use in high-power conditions.
3. Summary