JPS6035320Y2 - Horizontal output circuit of television receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for obtaining a DC voltage lower than the operating power supply of the horizontal output circuit in a television receiver by using a flyback transformer of the horizontal output circuit.

In Europe, Australia, etc., the commercial AC N source voltage is 200 to 240V, so television receivers that use such AC power have recently become very high voltage resistant (2500V).
Since horizontal output transistors have been realized (on the order of p-, V), and the design of the power supply circuit and flyback transformer is facilitated, the operating power source of the horizontal output circuit is obtained by directly rectifying the AC power source. It is desirable to use a DC voltage of 200-240V.

However, within a television receiver, there are circuits that require an operating voltage lower than this, such as a tuner, video circuit, and audio circuit that require 18V, and a color output circuit that requires about 170V.

Therefore, the DC voltage, which is lower than the operating power supply of the horizontal output circuit such as 18V or 170V, is taken out from the flyback transformer.

That is, FIG. 1 shows a conventional horizontal output circuit configured in this manner, where 1 is a horizontal drive circuit, 2 is a horizontal output transistor, 3 is a damper diode, 4 is a resonant capacitor, and 5 is a horizontal output circuit.
is a horizontal deflection coil, 6 is a figure-8 correction capacitor, 1 is a flyback transformer, 8 is its primary winding, 9 is a current limiting resistor, 10 is a secondary winding for high voltage of the transformer 1, 11
1 is a high voltage rectifier circuit, 12 is a low voltage of the transformer 7 (i.e. 1
8V and 170V), and the 170V DC voltage has a peak value according to the turns ratio between terminals a and b of the primary winding 8 and terminals d and f of the tertiary winding 12. The positive polarity flyback pulse of diode 13 and capacitor 14
The DC voltage of 18V is obtained by rectifying and smoothing the voltage at the positive potential of the negative flyback pulse mouth with a peak value corresponding to the winding ratio between the terminals a and b and the terminals L and G of the tertiary winding 12. This is obtained by rectifying and smoothing the portion using a diode 15 and a capacitor 16.

Note that C in the figure is a positive pulse taken out from the terminal e of the tertiary winding 12, and this is used as a blanking pulse.

In this conventional example, 18V is obtained by smoothing the positive potential portion corresponding to the scanning period Ts of the negative pulse, so there is little ripple in the horizontal period, and the secondary winding 10
It is also less susceptible to the influence of the picture tube anode current 1b flowing through the
Although it is relatively stable, since the voltage of 170V is obtained by smoothing the retrace period Tr of the positive pulse, there are many ripples in the horizontal period and it is easily influenced by the beam current, making it extremely unstable.

For this reason, it is possible to obtain 170V by smoothing the positive potential part of the negative pulse in the same way as 18V, but in that case, since the voltage is as high as 170V, the number of turns required to take out the negative pulse is much larger than the number of turns between terminals d and f, which not only hinders the miniaturization and cost reduction of flyback transformers, but also increases the coupling between the primary and secondary due to the increase in the number of turns of the tertiary winding 12. This also means that it becomes difficult to design high-frequency tuning of the secondary winding 10 because the leakage inductance increases.

Therefore, the present invention is designed to eliminate the drawbacks mentioned above, and the details thereof will be explained below.

2 and 3 show different embodiments of the horizontal output circuit of the present invention, and in each circuit, corresponding parts to those in FIG. The following points apply.

That is, an intermediate tap C is provided on the primary winding B of the flyback transformer 1, and a DC power supply (+220V) is applied to this tap C via a current limiting resistor 9.
A switching diode 17, a charging/discharging capacitor 18, and its discharging resistor 19 are connected between the low potential side terminal b' of this primary winding 8 either directly as shown (in the case of FIG. 2) or via the resistor 9. (in the case of Fig. 3) and connect it to the connection point J.
At this time, the number of turns between the high potential side terminal a' of the primary winding 8 and the intermediate tap C is made to be equal to the number of turns between the terminals at and b in Fig. 1. , the number of turns between the intermediate tap C and the low potential side terminal b' is such that a negative polarity flyback pulse as shown in FIG. 4 appears at the low potential side terminal b'. This is determined by considering the turns ratio.

Figure 5 is an equivalent circuit diagram for explaining the operation of the circuit in Figure 2. In the figure, figure number 20 represents the impedance of a load circuit (for example, a color output circuit) to which 170 V DC is supplied, and other is exactly the same as in Fig. 2.

In FIG. 5, during the horizontal retrace period Tr, as shown in FIG. 4, the potential of terminal b' is lower than +220V, so the switching diode 17 is turned on, and its conducting current flows in the loop shown by the solid line, charging and discharging capacitor 18 is charged, and the voltage between its terminals is 50
Therefore, the potential difference between one point and the ground is approximately 170V.

Next, during the scanning period Ts, the switching diode 17 is turned off because the potential of the terminal b' is higher than 220V, so the charging/discharging capacitor 18 attempts to further charge from the +220V DC power supply in the loop shown by the broken line in the figure. However, on the other hand, the charge stored in the capacitor 18 is discharged in a loop indicated by a dashed line in the figure.

Therefore, if the value of the discharging resistor 19 is appropriately selected in consideration of the value of the load impedance 20 so that this discharging current (dotted chain line) is equal to or slightly larger than the charging current indicated by the broken line, it is possible to The change in the inter-voltage voltage during the scanning period S is very small as shown by the broken line in FIG. 4, and therefore a substantially constant DC voltage (170V) can be obtained from one point.

It will be easily understood that the operation of the circuit shown in FIG. 3 is the same as that of the circuit shown in FIG.

For reference, an example of the specific specifications of the circuit in Figure 2 is as follows: Number of turns between aI and 0: ts5T', Number of turns between C and b' =
The capacitance value of the 5T capacitor 18 = 4.7 μF, the value of the resistor 19 = 2.2Ω, and the value of the resistor 20 = 8.5Ω, and when we conducted an experiment with this specification, we found that
It can be seen that the difference in output voltage at one point when the picture tube anode current is QmA and 1.2rrIA is about IV, and the fluctuation is extremely small.

By the way, in the conventional method shown in Figure 1, the number of turns between d and f was about 1000, and the same variation in the anode current as above was about 20V, which was difficult in practice. .

Also, in the method of smoothing the negative polarity pulse of the tertiary winding, the variation with respect to the anode current is slightly smaller than that in Figure 1, but in that case, the number of turns required for the tertiary winding is approximately 145. Ding and very many.

As detailed above, according to the present invention, it is possible to obtain a DC voltage slightly lower than the operating power supply of the horizontal output circuit by simply increasing the number of windings of the primary winding of the flyback transformer.
At this time, since the positive potential portion of the negative pulse generated in the primary winding is used, an extremely stable voltage is generated that is almost unaffected by the beam current flowing through the high voltage secondary winding. In addition, it does not hinder the miniaturization and cost reduction of the flyback transformer due to the increase in the number of turns of the tertiary winding, and also does not make the design of harmonic tuning of the secondary winding complicated.
It is suitable for implementation in a horizontal output circuit of a television receiver.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional horizontal output circuit, Figs. 2 and 3 are circuit diagrams showing different embodiments of the horizontal output circuit of the present invention, and Fig. 4 is a waveform diagram for explaining its operation. ,
FIG. 5 is an equivalent circuit diagram for explaining the circuit of FIG. 2. 1...Horizontal output transistor, 7...
Flyback transformer, 8...Primary winding, 17
...Switching diode, 18...
・Charge/discharge capacitor, 19... Discharge resistor.

Claims (1)

[Scope of utility model registration request] An intermediate tap is provided in the primary winding of the flyback transformer whose high potential side terminal is connected to the output electrode of the horizontal output transistor, and the intermediate tap is connected to a DC power supply, and the negative polarity pulse of the primary winding is connected to the DC power source. A cathode of a switching diode is connected to the low potential side terminal to be obtained, a charging/discharging capacitor and a discharging resistor of the capacitor are connected in parallel between the anode of the diode and the intermediate tap, and the connection between the parallel circuit and the anode is A horizontal output circuit for a television receiver, characterized in that a DC voltage lower than that of the DC power source is obtained from a connection point.