Thursday, May 29, 2008

High Voltage Power Supply Selection Issues

When comparing high voltage power supplies from different manufacturers, here are a few issues to look at:

Is ripple specified in peak-to-peak or rms? For many applications, it is the peak-to-peak that matters. If the ripple is specified as rms, it is not as simple as multiplying the rms by roughly 3 to get peak-to-peak. Due to switching regulator spikes or high voltage diode issues, the ratio between peak and rms may be much higher.

Are the monitors derived from separate sources as the feedback control signals? If so, then these independent signals can be used to determine when the power supply is not working correctly. On the contrary, when the same signal is used for both voltage monitor and voltage feedback, it is possible that the power supply output is much lower than the set point, and the monitor will not know.

What is the output connector? As high voltage connectors are not standardized, the output connector might even be the deciding factor. Issues include shielded vs. unshielded, the bend radius of the wire, size and cost. Lead time of the mating connector and cable can be substantial, and in some cases it can take longer to get a cable than the power supply.

Friday, May 2, 2008

Plasma Sterilization

In still another use for high voltage, researchers have developed a plasma that operates at room temperature. The plasma is generated between a high voltage probe and the surrounding room air. One use envisioned is to sterilize medical instruments. A second use is to kill bacteria, specifically dental.

Generally, plasmas operate at high temperature, and thus are impractical to use on humans. However, these develpments appear promising.

The research paper is in Applied Physics Letters.

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