JPS623634B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode current detection device for detecting the amount of cathode current of a cathode ray tube.

Conventionally, when detecting the cathode current of a cathode ray tube in a television receiver, a negative video signal voltage is applied to the grid electrode, and the voltage generated between the terminals of an impedance element such as a resistor connected between the cathode and the ground is detected. The amount of cathode current was detected by voltage. That is, the only way to drive a cathode ray tube was to set the cathode at zero potential and apply a negative control voltage to the grid electrode to reproduce an image, in which case the cathode current could only be detected.

However, looking at current television receivers, most of them adopt a system that allows them to be driven using only positive power supply voltage, that is, a system that applies a positive voltage to the cathode. When attempting to employ a circuit in a television receiver that detects the cathode current of a cathode ray tube and corrects for changes in emission over time, there are many problems with conventional cathode current detection configurations.

The present invention provides a device that can reliably detect the amount of cathode current while applying any voltage to the cathode. The present invention will be explained below based on the illustrated embodiments. In Figure 1, 1 is an input terminal to which the cathode applied voltage is input, 2 is an output terminal to which the cathode applied voltage is output, 3 and 4 are PNP type transistors, and their bases and the collector of transistor 3 are the input terminals. These emitters are both connected to output terminal 2. Furthermore, the collector of the transistor 4 is grounded through an impedance element 5 such as a resistor, and is also connected to an output terminal 6 for outputting a cathode current amount detection voltage.

Next, the operation of this embodiment will be explained. Now, when the output terminal 2 is connected to the cathode of a cathode ray tube (not shown) and a cathode voltage is applied to the input terminal 1, the voltage between the base and emitter of the transistor 3 will be applied to the input terminal 2. A voltage higher than the voltage applied to is obtained and is supplied to the cathode. At the same time, since transistors 3 and 4 constitute a current mirror circuit, the cathode current flows into transistors 3 and 4 in half through output terminal 2. Therefore, since the base current of the transistor 4 can be almost ignored, a current half the amount of the cathode current flows into the impedance element 5. Now, if the impedance element 5 is a resistor, a voltage equal to the product of the resistance value of the resistor and the amount of current that is half the amount of cathode current is obtained at the output terminal 6. In other words, since the value of the impedance element 5 is a previously known value, the amount of cathode current can be determined from the voltage at the output terminal 6, and this voltage is used for various controls as a voltage corresponding to the amount of cathode current. can.

Furthermore, if it is desired to provide frequency selectivity to the voltage obtained at the output terminal 6, that is, the cathode current, depending on the application, this becomes possible by providing the impedance element 5 with frequency characteristics suitable for the application.

With the above configuration, it is possible to reliably detect the amount of cathode current while applying an arbitrary voltage to the cathode of the cathode ray tube, that is, using a convenient cathode ray tube drive method.

Next, for reference, an example of a circuit for applying a cathode applied voltage to the input terminal 1 shown in FIG. 1 will be described with reference to FIGS. 2 and 3.

Figure 2 shows an example of applying a DC voltage to the cathode, where 10 is a power supply terminal, 11 and 12 are resistors for determining the voltage applied to input terminal 1, 13 is a bypass capacitor, and 14 is an output terminal. .

FIG. 2 shows an example in which a voltage obtained by dividing the voltage applied to the power supply terminal 10 by resistors 11 and 12 is applied. In this case, half of the cathode current flows into the resistor 12 via the transistor 3, so
To be precise, the voltage at the output terminal 14 fluctuates somewhat, but the cathode current is at most several hundred μA, and due to the effect of the bypass capacitor 13, the fluctuation can be ignored.

Fig. 3 is an example of a circuit when a voltage with voltage fluctuations such as a video signal voltage is applied to the cathode, 15 is a power supply terminal, 16 is an input terminal for a voltage with voltage fluctuations such as a video signal voltage, and 17 is a transistor, 18
indicates a resistor, and 19 indicates an output terminal.

Also in FIG. 3, half of the cathode current flows into the output terminal 19 via the transistor 3, but since the transistor 17 and the resistor 18 constitute an emitter follower, if the resistance value of the resistor 18 is appropriately selected, Even when the current flowing through the resistor 18 is the smallest, if the current is made larger than half of the cathode current at that time, the output voltage at the output terminal 19 will be higher than the voltage applied to the input terminal 16 at the base of the transistor 17.・A voltage lower by the voltage between the emitters is always obtained, satisfying the required performance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIGS. 2 and 3 are configuration diagrams showing examples of circuits for applying voltage to the device of the present invention. 1... Input terminal for cathode applied voltage input, 2...
Output terminal for outputting cathode applied voltage, 3, 4... transistor, 5... impedance element, 6... output terminal for outputting cathode current amount detection voltage.

Claims (1)

[Claims] 1 The base and collector of the first transistor and the base of the second transistor are connected to form a cathode applied voltage input terminal, the emitters of the first and second transistors are connected to form a cathode applied voltage output terminal, and the emitters of the first and second transistors are connected to form a cathode applied voltage output terminal. 1. A cathode current detection device characterized in that the amount of cathode current is detected by the voltage generated across an impedance element connected to the collector of the transistor No. 2.