Abstract: A high efficiency current regulator control circuit used to adjust and accurately control current flow in a substantially resistive load such as the low resistance filament in an electron gun of an electron microscope. The efficiency is obtained by running a solid state device such as a transistor in a switching mode. The present circuit represents an advantage over previous circuits which utilized a series or shunt pass regulator which dissipates power in performing the regulation function. The present circuit utilizes a switching mode regulator which regulates by switching a fast transistor either full "on" or full "off" in response to current flow through a sensing resistor. The ratio of "on" to "off" time determines the current transfer.

Abstract: In apparatus including a cathode ray tube, electrical circuitry for preventing "burn" spots in the phosphor of the cathode ray tube. The protective apparatus includes means to measure the rate of change of deflection of the electron beam of the cathode ray tube and means to measure the brightness level of the electron beam. The absolute value of the rate of change of the deflection of the beam is divided by the brightness level of the beam to produce a signal which is compared to a reference value. If the dividend exceeds the reference value, the CRT is shut down as in the preferred embodiment by blanking the cathode ray tube beam.