Detailed explanation of the transformer and rectifier part of the high voltage DC power supplyDetailed explanation of the transformer and rectifier part of the high voltage DC power supply

Ⅰ.Detailed explanation of the transformer and rectifier part of the high voltage DC power supplyDetailed explanation of the transformer and rectifier part of the high voltage DC power supply

High volatge DC power supply is that the output voltage is very high. The high output voltage puts forward special requirements in many aspects, including component withstand voltage requirements, structural design requirements, and insulation material requirements. At the same time, the circuit structure is also different from the conventional structure. Generally, for power supplies below 10KV, various traditional topologies can be directly adopted. However, for high-voltage DC power supply, some changes must be made to the circuit structure to adapt to the high-voltage output. Due to the withstand voltage limit of the power devices in the main part of the transformer, the general drive part is still the traditional switching power supply topology, and the changes in the circuit structure are mainly concentrated on the transformer and the rectifier circuit behind it. I will mainly explain the following two parts.

1. Transformer part of high voltage DC power supply

In other words, if you have mastered the basic principles, you can choose the combination of transformer and rectifier circuit according to the actual situation of a specific engineering case.

The schematic diagram of this method is shown in Figure 1. Its characteristics are that the step-up ratio of each transformer is not very high, and the voltage difference between the core and the secondary winding is not large. The advantages of this method are: suitable for high production. The insulation of the transformer winding and the core is easy to handle. The disadvantage is that each transformer provides different power, the transformer at the lowest voltage end provides the highest power, and the transformer at the highest voltage end provides the highest power. Each transformer has different requirements for ground insulation. The transformer on the highest voltage side should have the best ground insulation. Since the transformer has leakage inductance, the equivalent leakage inductance of the circuit will increase as the distance from the driver input transformer increases. In this case, even if the turns ratio is the same, the actual output voltage of the transformer will be different.

     2. Single transformer, multiple secondary cascade mode

The schematic diagram of this method is shown in Figure 2. It is characterized in that the step-up ratio of each winding of the secondary winding and the primary winding is not too high. The advantages are: suitable for high-power output. The number of transformers is small, and only one pair of magnetic cores is required. The disadvantages are that the voltage difference between the high-voltage winding and the magnetic core is very large, and the insulation is clumsy. If the secondary winding is inconsistent with the magnetic core or the primary structure, the leakage inductance will be inconsistent, and there will be differences between the windings. If the structure is consistent, all secondary sides should be designed according to the highest insulation requirements, which will greatly reduce the utilization of the transformer window.

     3、Single transformer, insulated core, multiple secondary cascade

The schematic diagram of this method is shown in Figure 3. The magnetic core is composed of multiple parts, each part of the magnetic core is characterized by being insulated with a film with excellent insulation properties, and each core segment has a secondary winding. The advantages are: suitable for higher output. The number of transformers is small, and only a pair of magnetic cores is required. The voltage difference between each secondary winding and the magnetic core is small, and the insulation of the secondary winding and the magnetic core is easy to handle. The disadvantage is that the magnetic core is segmented and the structure is complicated. The magnetic core has an air gap, and the more segments there are, the larger the equivalent air gap is, which makes it difficult to fix the magnetic core.

Ⅱ. Rectification circuit of high voltage DC power supply

1. Half-wave multiplexing voltage circuit

The half-wave multiplexed voltage circuit has two structures. One is the structure shown in Figure 5B, which is the basic and most common voltage doubler rectifier circuit. The advantages of this circuit are simple structure, low voltage stress on diodes and capacitors , and low output voltage of the transformer. The disadvantages are insufficient load capacitance , the higher the voltage doubler order, the greater the voltage drop, and the final voltage doubler order is limited. Beyond this order, the voltage will not increase, but decrease. The other is the structure shown in Figure 5B. This circuit has a stronger load capacitance, but the voltage stress on the capacitor is very high.

2. Full-wave multi-voltage circuit

The circuit structure is shown in Figure 6. This is actually an extension of the half-wave multi-voltage circuit. It can achieve both positive and negative high voltages at the same time. Of course, this is also possible if the high voltage middle end is grounded and the secondary side of the transformer is suspended. The advantage of this is that you only need a half-wave multiplier and half the order to get the same high voltage. In this way, the voltage drop and ripple will be much smaller. The disadvantage is that if one end of the high voltage grounding system is used and the secondary side of the high voltage transformer is suspended, the insulation requirements of the high voltage transformer will be very high. If the secondary side of the high voltage transformer is grounded, higher positive and negative voltages can be obtained, which is inconvenient.

3. Dual half-wave multi-voltage circuit with taps

The circuit structure is shown in Figure 7. This structure is characterized by a center tap on the secondary side of the high-voltage transformer. The advantage of this structure is that the voltage drop of the voltage doubler is much smaller than that of the half-wave multiplexed voltage method. The ripple is also much smaller. The disadvantage is that the secondary side of the transformer must be tapped, and for the same high-voltage output, the number of turns on the secondary side of the transformer will double. It has many components and is very costly.

4. There are other extended or mixed uses

For example, the tapped double half-wave can be expanded to the tapped full-wave positive and negative multi-voltage circuit to obtain high positive and negative voltages. The structure of Figure 2 can also be mixed. Figure 5B is a schematic diagram of the structure of Figure 5B. 5A. The conventional rectification method and the voltage doubler rectification method can also be mixed. In the positive and negative voltage doubler mode, the positive and negative order may also be inconsistent. In many cases, the two solutions of transformer and rectifier circuit are combined together at the same time, such as the secondary part of the transformer, and each part is output in series after full-wave voltage multiplication.

combines diodes and capacitors into charge pump mode usually cannot withstand large output power, and the output voltage rises relatively slowly. Because it is a charge pump, it generates high voltage at the expense of power, and the capacity of the pump is relatively limited.

In other words, if you have mastered the basic principles, you can choose the combination of transformer and rectifier circuit according to the actual situation of a specific engineering case.