JPH0159832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high voltage generating circuit used in a television receiver, and in particular to a high voltage generating circuit for reducing the AC maximum amplitude of a pulse voltage generated across a secondary winding of a flyback transformer. The purpose is to

In television receivers, the so-called high-voltage generation circuit that generates the high voltage for the picture tube anode generally uses a multi-voltage rectifier circuit, which is configured as shown in Figure 1, for example. ing.
That is, the figure shows the case where a double voltage rectifier circuit is used, 1 is a horizontal output transistor, 2 is a damper diode, 3 is a resonant capacitor, 4 is a flyback transformer, 5, 6, 7 are capacitors 8, 9
A diode, 1, which together constitutes a double voltage rectifier circuit.
0 is an output capacitor substituted by the anode capacitance of the picture tube, and 11 is a variable resistor for taking out the picture tube focus voltage.

Since such a conventional high voltage generating circuit is already well known, a detailed explanation of its operation will be omitted, but basically it operates as follows. That is, the secondary winding 4d of the flyback transformer 4
Assuming that the pulse voltage shown in Fig. 2 is generated between both ends of Tr (with reference to the winding start end S on the low potential side), the capacitor ₈ is The capacitor 9 is charged with the polarity shown in the figure to a voltage of V ₁ +V ₂ during the scanning period Ts.
Since the _output capacitor ₁₀ is charged to a voltage with _a magnitude _of
This means that V ₀ is supplied to the anode of the picture tube.

In addition, 12 and 13 are flyback transformers 4
A diode and a capacitor are used to rectify and smooth the positive side (scanning period) portion of the negative pulse taken out from the tertiary winding 4c, and the +
A DC voltage of approximately 18V is used as a power source for each circuit within the receiver.

By the way, in the circuit shown in Fig. 1, the secondary winding 4
The voltage generated at the winding end F on the high potential side of b (second
In Figure), the level of the thin line in the figure is the AC zero level, and the peak value on the positive side is V ₁ (normally about 9KV for a 20-inch receiver). The fact that the pulse voltage generated in the secondary winding 4b has a large AC peak value means that
It means the following disadvantages: That is, first of all, 2
With respect to the AC voltage with a large peak value generated in the secondary winding 4b, the insulation voltage between the secondary winding 4b and the primary winding 4a and between the secondary winding 4b and the tertiary winding 4c becomes a problem. Corona discharge is likely to occur.
Secondly, flyback transformers are generally filled with insulating resin such as epoxy, but alternating current flows through this resin, increasing dielectric loss, increasing the amount of heat generated by the flyback transformer, and lowering the temperature. Rise.
Furthermore, the third point is related to the first point above, if the insulation between the primary and secondary is improved, the coupling between the primary and secondary becomes shallow and the leakage inductance increases, making it difficult to maintain high voltage stability. This makes high-order harmonic tuning difficult.

Therefore, the present invention has been made to eliminate the various drawbacks of the present invention, and details thereof will be explained below with reference to embodiments shown in the drawings.

FIG. 3 shows an embodiment of a high voltage generation circuit according to the present invention. Parts corresponding to those of the conventional circuit in FIG. 1 are given the same figure numbers and explanations are omitted. It is characterized by points. That is, first, an intermediate tap M is provided at the midpoint of the secondary winding 4b of the flyback transformer 4, one end of the capacitor 14 is connected to this tap, and the other end of the capacitor is connected in the direction shown in the figure. This point is connected to the winding start end S of the secondary winding 4b via the diode 15. Next, a diode 16, a capacitor 17, and a variable resistor 1 are connected between the winding end F of the secondary winding 4b and the intermediate tap M in the direction shown in the figure.
8 is connected as shown in the figure, and the focus voltage is obtained from the slider of the variable resistor 18.

Now, in the circuit shown in FIG. 3, since the intermediate tap M is provided at the midpoint position as described above,
The voltage values generated between SM and MF of the secondary winding 4b are 1/2 of those in the case of FIG. 2. Therefore,
Now, when a pulse voltage with a peak value V ₁ is generated between both ends of the secondary winding 4b during the retrace period Tr, 1/
A pulse voltage of 2V ₁ charges capacitor 14 in the circuit shown, and the voltage across the capacitor becomes 1/2V ₁ . Since this voltage between both ends is maintained over the scanning period Ts, the point M is eventually clamped to a DC potential of 1/2V ₁ when viewed from the ground point.

On the other hand, the capacitor 8 for double voltage rectification is charged by the pulse voltage across SF during the retrace period Tr, and the voltage across it is _V1 . Therefore,
During the scanning period Ts, the other capacitor 9 for double voltage rectification is charged to V ₁ +V ₂ , and the output capacitor 10 is charged to 2V ₁ +V ₂ during the retrace period Tr. This circuit is exactly the same as the conventional circuit shown in FIG.

Here, if we consider the voltage generated in the secondary winding 4b from an AC perspective, the voltage waveform at point F is 1/2V ₁ with respect to the ground point, as shown in Figure 4.
The potential at the point is taken as the AC zero level, and the peak value (positive side)
The voltage waveform at point S becomes like a solid line with 1/2V ₁ , and the voltage waveform at point S becomes like a broken line which is symmetrical to the waveform at point F with respect to the above-mentioned AC zero level. Therefore, the secondary winding 4b
It can be seen that the maximum peak value (maximum amplitude) of the AC voltage generated is 1/2V ₁ , which is 1/2 that of the conventional circuit described above.

In addition, the pulse voltage between the previous FM (fourth
The voltage obtained by rectifying and smoothing the solid line (solid line in the figure) with the diode 16 and capacitor 17 is applied, and the divided voltage is superimposed on the DC voltage across the capacitor 14 and taken out. 1st
In order to extract a focus voltage of the same magnitude as shown in the figure, a variable resistor with a withstand voltage of 1/2 is required, and the variable resistor 18 can be made smaller.

Next, FIG. 5 shows another embodiment, in which one end of a capacitor 9 for double voltage rectification is connected to the E terminal obtained by winding the F point side of the secondary winding 4b. This changes the breakdown voltage relationship of the diodes 5, 6, and 7, but its basic operation is no different from the circuit shown in FIG. Also,
Although the anode of the diode 16 for extracting the focus voltage is connected to the cathode side of the diode 5, there is no particular feature in this point. Furthermore, contrary to this embodiment, the anode of the diode 5 may be connected to the E terminal, and one end of the capacitor 9 may be connected to the F point. Therefore, as can be seen from this, the intermediate tap M does not necessarily need to be provided at the midpoint between SF or SE.

As described above, according to the high voltage generation circuit of the present invention, the maximum AC amplitude of the pulse voltage generated in the flyback transformer can be reduced, so corona discharge is less likely to occur in the flyback transformer, and flyback is prevented. Since the amount of alternating current flowing through the insulating resin in the back transformer is also reduced, the temperature rise in the fly back transformer can be suppressed. In addition, since corona discharge is less likely to occur as mentioned above, it is possible to reduce leakage inductance by tightly coupling the primary and secondary windings, and since the secondary winding is essentially divided into two, it is possible to reduce leakage inductance. There is also the advantage that the distributed capacitance of the winding as a whole is reduced, and therefore the pulse voltage generated in the secondary winding can be tuned to desired high-order harmonics. In addition, a diode 1 is connected between both ends of the variable resistor 18 for taking out the focus voltage.
A voltage obtained by rectifying and smoothing is applied to capacitor 6 and capacitor 17, and the voltage after division is applied to capacitor 1.
Since it is superimposed on the DC voltage between both ends of the 4 and taken out, in this case, a variable resistor with a withstand voltage of 1/2 is sufficient to take out the same focus voltage as shown in Fig. 1. The size of the container 18 can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional high voltage generation circuit, FIG. 2 is a diagram showing a pulse voltage waveform generated in the secondary winding of the flyback transformer, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 4 is a diagram showing a pulse voltage waveform generated in the secondary winding of the flyback transformer, and FIG. 5 is a circuit diagram showing another embodiment of the present invention. 4: flyback transformer, 5, 6, 7: diodes for double voltage rectification, 8, 9: capacitors for double voltage rectification, 14: other capacitors, 15: other diodes.

Claims (1)

[Scope of Claims] 1 Multiplier rectifier circuits 5, 6, 7, and 9 are connected to the secondary winding 4b of the flyback transformer, and a diode 1 is connected to one end of the low potential side of the secondary winding 4b.
An intermediate tap M provided between the anode side of this diode 15 and the secondary winding is connected to the cathode side of the diode 15.
In the high voltage generation circuit in which a capacitor 14 is connected between the rectifier diode 16 for rectifying the high potential side output of the secondary winding 4b, and one end connected to the rectifier diode 16,
A high voltage generation circuit comprising: a rectifying capacitor 17 whose other end is connected to the intermediate tap M; and a variable resistor 18 connected in parallel to the rectifying capacitor 17 and outputting a focus voltage.