Protection circuit for dynamic focus amplifier

摘要

The active pullup arrangement 105 coupled to the high voltage source (+ 250V) generates an operating voltage. The amplifier 106 that amplifies the dynamic focus modulated signal has a plurality of transistors Q103, Q104, Q105, Q106, which are low voltage transistors operated by an operating voltage and coupled to a Darlington pair of different configuration, for example. One low voltage transistor Q104 is coupled in series between the resistor R140 of the pull-up arrangement and the power return of the push-pull structure, eg, ground. A fault condition of the push pull structure can destroy the resistance and cause an open circuit condition. A switch (eg, diode or zener diode CR104) is coupled between one transistor of the amplifier and the power return. The switch prevents dielectric breakdown in the reverse direction of the transistor until the resistor is destroyed in the event of a fault condition. The resistor may be a fuse resistor.