A protection circuit limits the collector current of a transistor employed as a clamp-to-ground stage in the event the collector terminal of the transistor is accidentally short circuited during conduction to a low-impedance voltage source. The protection circuit includes a transistor which has its base-emitter junction coupled across the base-emitter junction of the clamping transistor and has a collector resistor chosen to provide a saturation current for the protection transistor which holds the base-emitter junction voltage at a level which limits the collector current of the clamping transistor.
One circuit, providing a feedback signal from the horizontal output transistor to the horizontal drive circuit, prevents damage to the output transistor in the event of a disruption or noise in the input signal, and also prevents "spot burn" of the CRT screen if the input signal should fail while there is still a charge on the CRT.
An excess voltage protecting circuit for use with an automatic voltage regulating circuit of the type which has a circuit breaker, fuse or the like connected in series between the automatic voltage regulating circuit and the power supply to be regulated, the excess voltage protecting circuit including means for detecting the output voltage from the voltage regulating circuit for producing a first control signal for the voltage regulating circuit and a second control signal, and a shunt circuit responsive to the second control signal which operates to trip the current breaking device when the voltage output from the voltage regulating circuit exceeds a predetermined level.
A protection circuit for preventing excessive power dissipation in an output transistor whose conduction path is connected between a power terminal and an output terminal. The protection circuit includes means for sensing the application of a turn on signal to the output transistor and the voltage at the output terminal. When the turn on signal is maintained for a period of time greater than a given period without the voltage at the output terminal reaching a predetermined value, the protection circuit decreases the turn on signal to, and the current conduction through, the output transistor.
