Abstract: An improved drive for the deflection coil of a cathode ray tube. A first deflection, low-power supply means drives the deflection coil causing the electron beam to scan the face of the tube. A separate second deflection, high-power supply means drives the deflection coil causing retract of the beam. A switch means including a mono-stable multi-vibrator produces an output pulse of selected duration which controls a transistor switch connecting the second supply means to the deflection coil during the retrace cycle. A source of sync signals connected to the multi-vibrator produces the pulse input signals necessary to drive the multi-vibrator thereby controlling the timing of the transistor switch for causing retrace. The use of a separate second high power supply permits rapid retrace, improved power supply matching and minimal heat loss.

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.