JPH0318791B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a vertical deflection circuit used in television receivers and the like.

Conventional Structure and Problems First, FIG. 1 shows an example of a horizontal deflection circuit and a vertical deflection circuit of a television receiver using a conventional switching power supply circuit.

In this circuit, the AC power is connected to diodes 1, 2,
Full-wave rectification is performed by 3 and 4, and smoothing is performed by a capacitor 7 to obtain a DC power source. The voltage is switched by the transistor 6 via the primary winding 9 of the transformer 8. By controlling the switching duty ratio according to fluctuations in the output voltage using the pulse width control circuit 5, a stable rectangular wave voltage is generated in the secondary winding 10, which is rectified and stabilized by the diodes 15 and 16. Obtain a DC power source. 11 is the secondary winding 10
A tertiary winding that obtains a voltage proportional to the voltage generated in
12 and 13 are rectifying and smoothing capacitors and diodes, and 14 is a variable resistor for setting the output voltage.

Transformer 20 is a flyback transformer, 36
is a horizontal deflection output transistor, 37 is a horizontal resonant capacitor, 38 is a damper diode, 39 is a horizontal deflection coil, and 40 is a DC blocking capacitor.

Reference numeral 19 denotes a block constituting a horizontal oscillation drive circuit and a vertical oscillation drive circuit. A secondary winding 22 of a flyback transformer 20 is rectified by a diode 23 to supply anode voltage for a cathode ray tube (CRT). The DC voltage rectified by the diode 24 is supplied to a vertical deflection circuit composed of transistors 27 and 29. 31 is a DC blocking capacitor, 30 is a vertical deflection coil, and the vertical deflection current flows from the resistor 32 to the ground. The voltage generated across the resistor 32 is the terminal g.
The linearity of the vertical deflection current is improved by feeding back to the 19 vertical oscillation circuits.

A circuit consisting of a constant voltage diode 33, a capacitor 34, and a resistor 35 is a protection circuit in case the capacitor 31 is short-circuited. When the capacitor 31 is short-circuited, a DC component flows in the vertical deflection current and the electron beam hits the phosphor. Without scanning, it concentrated on the tube wall of the CRT's network, causing the tube wall to become red hot and damaging the glass.
Prevent CRT from being destroyed. In other words, if the capacitor 31 is short-circuited, a voltage larger than normal is generated in the resistor 32, so the voltage that the constant voltage diode 33 conducts is set to a value that does not conduct with normal deflection current, but conducts only when the capacitor 31 is short-circuited. Set it to .

FIGS. 2 and 3 show voltage waveforms generated across the resistor 32. FIG. 2 shows the waveforms during normal operation, and FIG. 3 shows the waveforms when the capacitor 31 is short-circuited.

When the constant voltage diode 33 becomes conductive, a voltage is applied from its terminal i to stop the operation of the horizontal oscillation circuit. For this reason, flyback transformer 2
0, voltage is no longer supplied to the vertical deflection circuit, and the beam current is not concentrated on the CRT tube wall.
CRT destruction is prevented.

In such a conventional circuit, the power supply for the vertical deflection circuit is connected to the secondary winding 10 of the switching transformer 8.
Although it is possible to reduce the loss of the horizontal deflection output circuit and downsize the flyback transformer by supplying more than 100 volts, this has been difficult to achieve in the past for the following reasons. That is, it is necessary to be able to stop supplying the power supply voltage to the vertical deflection output circuit as described above when the capacitor 31 is short-circuited.
When the power supply voltage is supplied from the switching transformer 8, in order to stop the operation of the transistor 6, it is necessary to transmit the signal using an insulating transformer or an insulated photocoupler, which increases the number of parts. Moreover, the circuit becomes complicated and the price increases. Therefore, in the past, the power supply voltage for the vertical deflection circuit was supplied from a flyback transformer, and if the capacitor 31 was short-circuited, the operation of the horizontal deflection output circuit was stopped by the circuit operation described above to protect the CRT. Ta. However, in this case, since the power supply voltage for the vertical deflection circuit is supplied from the flyback transformer, it is difficult to miniaturize the flyback transformer, and the loss in the horizontal deflection output circuit is also large.

Purpose of the Invention The present invention solves the conventional problems as described above, reduces the size of the flyback transformer, reduces the loss of the horizontal deflection output circuit, and further reduces the vertical deflection output when the DC blocking capacitor is short-circuited. The object of the present invention is to provide a device that can effectively protect a circuit.

Structure of the Invention In the vertical deflection circuit of the present invention, the power supply voltage is supplied from the switching power supply circuit, and when the DC blocking capacitor connected in series with the vertical deflection coil is short-circuited, the operation of the horizontal deflection output circuit is stopped. The vertical output transistor is protected by blocking the transistor connected to the DC power supply side. Therefore, by connecting a separate transistor to the base of that transistor,
When the operation of the horizontal deflection output circuit stops, this transistor is made conductive, the vertical output transistor is cut off, and the vertical deflection current is cut off to prevent damage to the CRT.

DESCRIPTION OF THE EMBODIMENTS FIG. 4 shows a vertical deflection circuit according to an embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same numbers and their explanations will be omitted.

In this circuit, the power supply voltage for the vertical deflection output circuit is supplied from the secondary winding 10 of the switching transformer 8 via the diode 16. The base of the transistor 43 is supplied with voltage from the flyback transformer 20 through a resistor 44, and the transistor 43 is conductive under normal conditions, and the transistor 41 is non-conductive under normal conditions. Therefore,
Under normal conditions, the collector is connected to the base of 27, but this does not affect the operation of the vertical deflection output circuit.

On the other hand, if the capacitor 31 is short-circuited, the constant voltage diode 33 becomes conductive as described above.
A voltage is applied to the horizontal oscillation circuit 19 from the terminal i,
Horizontal deflection output circuit stops operating. the result,
Transistor 43 becomes non-conductive and transistor 41 becomes conductive. Then, the base of the transistor 27 is grounded, the transistor 27 becomes non-conductive, and no current flows from the transistor 27 to the vertical deflection coil 30. The conduction of the transistor 41 is maintained while the switching power supply circuit is operating, and the operation of the protection circuit is maintained.

Effects of the Invention As described above, according to the present invention, the DC power for the vertical deflection circuit can be supplied from the switching power supply circuit, the load power of the flyback transformer can be reduced, and the size of the flyback transformer can be reduced. . This allows the price to be reduced. In addition, the loss of the horizontal output transistor can be reduced, and circuit loss can also be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional switching power supply circuit and horizontal/vertical deflection circuit, FIGS. 2 and 3 are waveform diagrams for explaining the operation of the circuit in FIG. FIG. 3 is a circuit diagram of a vertical deflection circuit according to an embodiment. 6... Switching transistor, 8... Switching transformer, 20... Flyback transformer, 27, 29... Vertical deflection output transistor,
30...Vertical deflection coil, 31...DC blocking capacitor, 36...Horizontal deflection output transistor, 4
1, 43...Fourth and third transistors.

Claims (1)

[Claims] 1. The DC voltage obtained by rectifying the AC power source is stabilized by a switching power supply circuit, and the DC power source isolated from the AC power source is connected to the first and second transistors 2.
7 and 29, and the output of the vertical deflection output circuit and the vertical deflection coil 30 are coupled via a DC blocking capacitor 31 connected in series, By stopping the operation of the horizontal oscillation circuit 19 when the voltage generated across the resistor 32 connected between the vertical deflection coil 30 and the ground exceeds a predetermined value when the DC blocking capacitor 31 is short-circuited, The voltage supply from the flyback transformer 20 is stopped, and the third transistor 43 provided on the secondary side of the flyback transformer is cut off.
The fourth transistor 41 coupled to the output of the transistor 43 is made conductive, and the first transistor 27 connected to the output of the fourth transistor 41 of the vertical deflection output circuit is cut off. Vertical deflection circuit configured to stop the current flowing to the