DE2423726A1 - CRT beam spot suppression circuit - voltage divider inserted between cathode and modulating electrode - Google Patents

Abstract

A C.R.T. receives a supply voltage from the secondary winding of a transformer and a rectifier, and the supply voltage is applied to the voltage divider, and a capacitor is connected to the rectifier and in parallel with a voltage divider part, so that the supply voltage drop fully blocks the picture tube. The capacitor is the reservoir capacitor of the supply voltage source, and is connected to frame through a diode at the voltage divider base.

Description

Circuit arrangement for focal spot suppression The invention relates to a circuit arrangement for focal spot suppression in a television picture tube according to the generic term of the claim.

With the usual circuit arrangements for focal spot suppression in the case of television picture tubes, it is generally known that, in the event of a shutdown, the potential of the Wehnelt cylinder compared to the cathode of the television picture tube so that the capacities in the high-voltage branch of the television receiver by increasing the beam current, as long as a grid is still being written by the horizontal deflection will.

Such circuits are in transistorized television reception devices are relatively unsuitable because the horizontal deflection collapses very quickly. Therefore, the television picture tube has been proposed for this television receiving apparatus to lock in case of switch-off and to keep locked until the picture tube cathode is cold and can no longer emit electrons. This is generally done a capacitor is required, the potential of which disables the television picture tube when it is switched off causes.

The object on which the invention is based is to simplify and rationalization of a circuit arrangement of the type mentioned at the beginning.

According to the invention, this object is achieved by the characterizing features of the patent claim specified features solved.

One advantage of the circuit arrangement according to the invention is in particular to see that on an expensive component while maintaining the properties the circuit can be dispensed with.

A drawing is an example of a circuit arrangement according to the invention explained in more detail.

The circuit arrangement shown consists of a television picture tube 1 constructed in which, for the sake of clarity, only the cathode 2 and the Wehnelt cylinder 4 are drawn from a voltage divider, which consists of three connected in series Resistors 4, 5, 6 is formed and an operating voltage source. The resistance 6 is designed as a potentiometer and has a tap via a further resistor 7 connected to the Wehnelt cylinder 3. By means of the resistor 6, the brightness the television picture tube 1 is set. The base point 8 of the voltage divider 4, 5, 6 is connected to ground potential via a diode 9, the cathode being connected to ground is. In the present example, the operating voltage source is a secondary winding 10 a transformer and a rectifier 11 formed, with a charging capacitor 12 is provided, from the high point of the operating voltage source to the base point 8 of the voltage divider 4, 5, 6 is connected, so the resistors 5, 6 in parallel is switched.

There is also a video amplifier transistor in the circuit shown 1) indicated, the collector of which controls the cathode of the picture tube.

The secondary winding 10 of the transformer of the operating voltage source can for example to a mains transformer or better to a line output transformer belong.

The latter option has the advantage that even if the line deflection fails the focal point suppression is guaranteed.

During the operation of the television receiver is through the secondary winding 10 and the rectifier 11 generates an operating voltage that the charging capacitor 12 on charges. The capacitor 12 also serves as a filter capacitor, the Sieve effect by the conductive diode 9 is not impaired. The diode 9 will by the positive voltage divider current through the resistors 5, 6 during operation case held conductive.

As soon as the operating voltage breaks down, be it by switching off of the television set or if the line deflection fails, diode 9 is blocked, and the negative potential of the charging capacitor 12 is at the base point 8, whereby the Wehnelt cylinder 3 of the television picture tube 1 is negative with respect to the cathode 2. As a result, the television picture tube is blocked and the flow of jet current is prevented. The blocking must be maintained as long as the cathode is able to To emit electrons, i.e. until the cathode is cold.

This measure prevents a jet current from flowing although there is no line deflection and a focal point can arise that would destroy the luminescent layer of the television picture tube.

Claims (1)

Claim Circuit arrangement for focal spot suppression in a television picture tube, whereby a voltage divider is switched on between the cathode and the Wehnelt cylinder of the picture tube is supplied with an operating voltage and is part of the voltage divider a capacitor is connected in parallel in such a way that when the operating voltage drops the television picture tube is fully blocked, characterized in that the capacitor is formed by the charging capacitor (12) of the operating voltage source, and that the charging capacitor (12) in the base point (8) of the voltage divider (4, 5, 6) via a Diode (9) is connected to ground potential.