Capacitors for high voltage X-ray power supplies

      The X-ray tube is an important part of the X-ray machine, and the electromagnetic waves it produces through radiation are called "X-rays". The generation of X-rays requires that electrons released from a hot cathode are accelerated to high speeds by high voltage, and then collide with a metal anode (usually made of tungsten).

      The collision process usually requires 180-480 volts AC as input voltage, which is then converted and stepped up to very high voltages of 10 kV and 120 kV DC for output. Figure 1 is a schematic diagram of the power supply required to power the X-ray tube. 

1.The primary side of the X-ray power supply is used to handle high voltage:

Figure 1. Two sides of the power supply required for an X-ray machine

      If the design of the X-ray power supply is not correct, serious consequences may occur - from deteriorating image quality to releasing excessive radiation that is harmful to the patient. Therefore, X-ray power supplies must be carefully designed.      

Designing an X-ray power supply that can reliably handle high voltages

      X-ray power supplies need to provide very high voltages in a small package, and the common design uses an LLC resonant converter topology to build a smooth and reliable power supply with a special application of capacitors.

       Whether it is used in X-ray machines or other applications such as electric vehicles (EVs) or defense power supplies, resonant converters have one characteristic in common - they have a "resonant cavity". A "resonant cavity" usually contains a large number of capacitors connected in parallel, which work together to create a desired resonant frequency when current is passed through them.

More specifically, as shown in Figure 1 above, the primary side of the X-ray power supply is used to handle high voltages and handles rectification from AC to DC and boosting from DC to DC. These functions require capacitors to provide special functions to ensure the safe delivery of power.

2. Capacitors for high voltage X-ray power supplies:

1) DC bus capacitors and matching filter capacitors 

       - limit voltage fluctuations to provide a more stable DC voltage

2) Decoupling and bypass capacitors

       - remove unnecessary AC noise trying to pass through the system.

3) Buffer absorption capacitors 

      - depending on the selected switching elements and diodes, it is necessary to suppress the high-frequency noise generated by the switch to convert AC to DC and boost high-voltage DC to very high-voltage DC.

4) Safety capacitors 

       - For the AC voltage in the input rectification stage, safety capacitors are likely to be needed to avoid the risk of surges, transient voltages, and provide anti-electromagnetic interference (EMI).

5) Other EMI filter capacitors 

       - In addition to safety capacitors, other EMI filter capacitors are also needed throughout the circuit board.