JP2005318050A - Protective circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit, capable of protecting a flyback transformer from abnormality occurrence at an earlier stage by detecting the damper current of a switching circuit, even if abnormalities occur in the flyback transformer of a high-voltage stabilization method. <P>SOLUTION: A current flowing through the damper diode of the high-voltage output switching circuit is detected for checking the abnormal stage of a switching operation. Thus, generation of rare short circuit in the flyback transformer at an earlier state even in a high-voltage stabilization operation, and the high-voltage output switching is stopped. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a CRT television and a CRT display.

In the conventional technology, an overcurrent detection circuit for detecting the power input current of the flyback transformer, a fuse, a posistor (see, for example, Patent Document 1) or the like is attached to protect the flyback transformer, or the secondary side of the flyback transformer. The flyback transformer is protected by detecting the current and voltage of the winding (see, for example, Patent Document 2).
JP 2000-324683 A JP-A-6-70452

  In the above-described method for detecting the flyback input current, the flyback transformer does not reach the detection point unless a certain degree of breakdown occurs after the occurrence of a short circuit, such as partial short-circuit between the flyback transformers and destruction of the internal diode on the secondary side. There was a problem that the destruction progress of the transformer was high.

  The method of detecting the secondary side voltage has a problem that it is difficult to detect an abnormal voltage because stable operation feedback (high voltage stabilization circuit) of the secondary side voltage is applied.

  The protection circuit according to the present invention detects an abnormality in the flyback transformer using an abnormal current flowing in a damper diode in the high voltage generation circuit in the flyback pulse OFF period in the high voltage generation circuit having a feedback circuit for keeping the high voltage stable. And detecting a current flowing in a damper diode of the switching circuit of the high voltage output, and detecting a current flowing in the damper diode of the switching circuit of the high voltage output. By detecting the abnormal state flowing through the flyback transformer, it is possible to quickly detect the occurrence of a short-circuit in the flyback transformer even during the high-pressure stabilization operation, and to suppress the progress of destruction of the flyback transformer and reliably protect it.

  According to the present invention, even if an internal abnormality of the high voltage stabilization type flyback transformer occurs, it is possible to more quickly protect against the abnormality of the flyback transformer by detecting the damper current of the switching circuit.

  In order to detect the damper current for protecting the flyback transformer and the high-voltage output element, a current detection circuit is provided in series with the damper diode to perform current-voltage conversion. When the threshold voltage is exceeded, the microcomputer stops the power supply and switches the signal. Stop the occurrence of

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a protection circuit according to Embodiment 1 of the present invention. In order to detect a damper current in a high-voltage circuit mainly composed of the high-voltage output transistor 1, the primary side of the current-voltage conversion transformer 5 is connected to the damper diode 2 in series and is generated on the secondary side of the current-voltage conversion transformer 5. The pulse is converted into a DC voltage by the rectifying diode 6 and the smoothing capacitor 7 for rectifying the pulse to be detected, and the detected voltage information is transmitted to the microcomputer.

  Next, circuit operation will be described. The internal structure of the flyback transformer 4 has the configuration shown in FIG. 1, and each layer of the secondary winding is connected in parallel with the rectifier diode, so that current flows to the diode even if the winding is disconnected between layers. Therefore, the operation is continued. In the high voltage stabilization circuit, the flyback output voltage connected to the CRT continues to control the control of the high voltage output transistor 1 so that the output becomes constant (about 30 KV) by the feedback circuit.

  For this reason, when current concentrates on the parallel diodes of the interlayer disconnection and short-circuit breakdown occurs, the divided voltage applied to the diodes and windings connected in series increases, and breakdown occurs one after another, but because of high-voltage stable operation Unless the high-voltage output is stopped, it will lead to large-scale destruction.

  At this time, the voltage of the ABL detection used as a conventional protection circuit is stabilized in proportion to the high voltage, so the detection is very slow. As the overcurrent detection protection operation of the primary supply current, a malfunction margin is secured. Therefore, since the operation is performed at a high overcurrent point, the protection circuit operation is performed in a state where the destruction of the flyback transformer 4 has progressed.

  In the protection circuit using the damper current detection according to the present invention, the L value on the secondary side changes when an interlayer short circuit occurs. Since the damper current is generated due to the resonance condition of the capacitor and the inductance, the change in inductance on the secondary side is propagated as a leakage inductance component, and a large damper current is generated in the damper diode 2 during the flyback pulse OFF period that does not flow in the normal state. To do. The current is detected by the current-voltage conversion transformer 5, converted into a DC value by the rectifier diode 6 and the smoothing capacitor 7, and transmitted to the microcomputer. The microcomputer detects a difference in voltage value from the normal state to the abnormal state, determines that it is an abnormal state, shuts off the power supply of the high voltage circuit, and stops the high voltage control pulse.

  Note that the setting of the detection voltage that is judged to be an abnormal state in the microcomputer can be freely changed, and can be diverted to a system having a different circuit constant.

  The protection circuit of the present invention has a feature that even if an internal abnormality of a high voltage stabilization type flyback occurs, the damper circuit current can be detected more quickly by detecting the damper current of the switching circuit. And useful for CRT TVs and CRT displays

The block diagram which shows the structure of the protection circuit in Embodiment 1 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High voltage output transistor 2 Damper diode 3 Resonance capacitor 4 Flyback transformer 5 Current-voltage conversion transformer 6 Rectifier diode 7 Smoothing capacitor

Claims (1)

A detection circuit for detecting an abnormality in a flyback transformer using an abnormal current flowing in a damper diode in a high voltage generation circuit during a flyback pulse OFF period in a high voltage generation circuit having a feedback circuit for stably maintaining a high voltage, and the detection circuit A protection circuit characterized by stopping oscillation of the high-voltage output circuit based on the output of.

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