Understanding the topology of high voltage power supply (2)-EEWORLD

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Push-Pull Topology

The characteristics of this circuit structure are: symmetrical structure, the primary side of the pulse transformer is two symmetrical coils, the two switching tubes are connected in a symmetrical relationship, and they are turned on and off alternately. The working process is similar to the Class B push-pull power amplifier in the linear amplification circuit.

Main advantages: high-frequency transformer core utilization rate is high (compared with single-ended circuit), which can reduce the size of the transformer, high power supply voltage utilization rate (compared with half-bridge circuit), large output power, both tube bases are low level, and the driving circuit is simple.

But there is a problem. In some diagrams, the transformer secondary has the same-name terminal as the positive terminal, while in some diagrams, the transformer secondary has the opposite-name terminal as the positive terminal. I don't understand this. What is the difference between these two types?

Full-bridge conversion

The characteristic of this circuit structure is that four identical switching tubes are connected into a bridge structure to drive the primary side of the pulse transformer.

　　In the figure, T1 and T4 are a pair, driven by the same set of signals, and turned on/off at the same time; T2 and T3 are another pair, driven by another set of signals, and turned on/off at the same time. The two pairs of switch tubes are turned on/off in turn, forming positive/negative alternating pulse currents in the primary coil of the transformer.

　　Main advantages: Compared with the push-pull structure, the primary winding is reduced by half and the withstand voltage of the switch tube is reduced by half.

　　Main disadvantages: a large number of switch tubes are used, and good parameter consistency is required, the driving circuit is complex, and synchronization is difficult. This circuit structure is usually used in ultra-high power switching power supply circuits above 1KW

Half-bridge converter

The circuit structure is similar to the full-bridge type, except that the two switches (T3, T4) are replaced by two large capacitors of equal value, C1 and C2.

Main advantages: It has a certain ability to resist imbalance, and the requirements for circuit symmetry are not very strict; it can adapt to a wide power range, from tens of watts to kilowatts; the voltage resistance requirements of the switch tube are low; the circuit cost is lower than that of the full-bridge circuit, etc. This circuit is often used in various DC converters with non-regulated output, such as electronic fluorescent lamp drive circuits.

The above content comes from Baidu Knows and some other websites. I would like to express my gratitude to the people and websites that provided this information. Thank you for their selfless dedication.

After understanding it, I think it is better to use a full-bridge because it is most suitable for ultra-high power switching power supplies.

What needs to be done next include the series and parallel connection methods of the transformer, the calculation of the transformer (primary and secondary turns, wire diameter, core, frame), frequency, drive circuit, and selection of the switching tube.

Reference address：Understanding the topology of high voltage power supply (2)

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