Ultra-Quiet High Voltage Source

Abstract

High voltage power supplies, even regulated ones, are typically rather noisy (0.1-percent ripple or so), because the relative slowness of high voltage semiconductors limits the bandwidth of voltage regulators, and hence, their ac loop gain. For some applications, such as large area scanning tunnelling microscopy, it is important to have a high voltage supply with noise levels of no more than 10 -6 (for STM, that corresponds to 1 A out of 100 μm), or even less. Using a conventional regulator makes this very difficult, since the unregulated supply is likely to have a ripple of 1 percent or even worse, including significant power in high harmonics of 60 Hz, while most high voltage semiconductors are very limited in bandwidth. In this paper, a very simple, very inexpensive circuit is described, for conditioning a high voltage source to reduce supply ripple and noise from several volts p-p to microvolts, achieving a wideband supply noise level of better than -140 dB. It can be retrofitted to an existing supply with an immediate improvement in performance. © 1989 IEEE