Protecting High Voltage Power Supplies

When high-voltage power supplies (HVPSs) are exposed to extreme operating environments beyond their ratings, their useful life may shorten. While these HVPSs have internal protection mechanisms, there are certain applications where supplemental external protection circuitry or special mounting procedures are recommended to achieve maximum performance and ensure longevity in such extreme environments.

The type of supplemental protection circuitry needed may vary depending on the anticipated faults the power supply may encounter. For example, faults such as arcing between supplies of opposite polarity, a higher voltage HVPS arcing to a lower voltage high-voltage power supplies, plasma discharge through an HVPS, high-speed current spikes, or opposite-polarity voltage spikes may require supplemental protection circuitry to ensure satisfactory operation of the high-voltage power supplies.

In addition to supplemental protection circuitry, there are also recommended mounting and electrical connection procedures that, when applied, can maximize the reliability of the HVPS. These procedures are classified into two categories: those applicable to both single and multiple HVPS systems, and those applicable only to multiple high-voltage power supplies systems. High-speed, high-energy pulse-application safeguards are covered in a separate section in this application note due to the unique nature of the problems encountered in those applications.

In a multiple-voltage power-supply system using multiple high-voltage power supplies (HVPSs), reliable operation can be achieved as long as no faults occur. However, for long-term reliability and performance, it is recommended to add supplemental protection circuitry to each supply to protect against normal fault conditions.

Since each HVPS is fully short-circuit protected, the interactions that need to be considered by the designer are between HVPSs of different polarities or significantly different voltages.

Protecting an HVPS from a supply of different polarity If two supplies of different polarities arc to each other, each HVPS will try to supply its rated current. If the supplies have different current limits, such as supplies with different power ratings but equal magnitude voltages, the supply with lower current capability may be forced to sink or source current beyond its capability. This can over-stress the lesser current capable supply and potentially cause damage. However, by using a simple reverse-biased diode on the output of the HVPS to ground, the high-voltage power supply can be protected from damage that may otherwise occur from exposure to an opposite polarity, higher current supply.