JPS5825631Y2 - Power supply switching circuit in a television receiver capable of receiving television broadcast waves according to different television systems - Google Patents

Description

[Detailed explanation of the invention] There are two different types of TV receivers used in areas where two types of television broadcasting using different standard systems (hereinafter referred to as TV) are being conducted at the same time. It is desirable that the TV receiver be configured so that it can receive and listen to any TV broadcast that is broadcast according to the standard system.

In order to be able to receive the TV broadcast waves according to two different standard systems that are to be received, if the horizontal scanning period is different from each other. The TV receiver is configured so that the horizontal scanning period can be switched depending on which TV system the TV broadcast waves to be received are based on.

By the way, in general, in TV receivers, the flyback pulse obtained from the horizontal deflection circuit or the pulse obtained based on the flyback pulse is rectified and used as a high voltage power supply (H-T) for the picture tube. However, as mentioned above, TV receivers receive TV broadcast waves according to two different standard systems that have different horizontal scanning periods. TV to be received so that it is possible to
If the horizontal scanning period is configured to change depending on the broadcast wave, unless some measure is taken,
The size of the flyback pulse generated in the horizontal deflection circuit changes as the horizontal scanning period changes, and as a result, the above-mentioned flyback pulse or the high voltage power source obtained by rectifying the pulse obtained based on the flyback pulse. The DC voltage in the operating DC power supply of each part of the receiver and receiver will fluctuate, which may change the size and brightness of the reproduced image, or change the operating point of transistors and ICs in the video intermediate amplification stage and other circuits. A TV receiver that operates stably can be provided.

Therefore, a TV that can receive TV broadcast waves according to two different TV systems with different horizontal scanning periods.
Conventionally, in television receivers, the switching of the horizontal scanning period by switching the horizontal oscillation circuit and the switching of the power supply voltage element B of the horizontal deflection circuit are performed at the same time. Normally, the peak value of the flyback pulse is kept constant, but even if such measures are taken, changes in the horizontal scanning period will affect the output voltage of the DC power supply for operating various parts of the TV receiver. Conventionally, flyback pulses or pulses obtained based on flyback pulses are rectified and filtered, as shown in Figure 1, because DC voltage fluctuations occur to a non-negligible extent and change the operating status of various parts of the TV receiver. By making it possible to switch the magnitude of the pulses supplied to the DC power supply to obtain a DC voltage in accordance with the horizontal scanning period of the TV broadcast waves to be received, Also, the output voltage of the DC power supply was prevented from fluctuating.

The above-mentioned conventional problems and the problems in the conventional circuit shown in FIG. 1 will be explained in more detail as follows.

In FIG. 1, reference numeral 1 denotes a horizontal deflection output transistor, which performs a predetermined switching operation in response to a drive pulse P1 or P2 supplied from a previous excitation stage (not shown).

Further, 2 is a damper diode, 3 is a retrace resonance capacitor, 4 is a horizontal deflection coil, 5 is a horizontal linearity correction capacitor, 6 is a flyback transformer, and 7 is connected to the secondary winding 6b of the flyback transformer 6. This is a high voltage rectifier diode.

When the DC power supply element B is connected to one end of the primary winding 6a of the flyback transformer 6, the horizontal deflection output transistor 1 and the damper diode 2 perform a switching operation, and the horizontal deflection coil 4 receives a sawtooth wave current. y, and a flyback pulse Pf is applied to both ends of the retrace resonance capacitor 3.
to occur.

This flyback pulse Pf is boosted by the secondary winding 6b of the flyback transformer 6 and given to the high voltage rectifying diode 7, where it is rectified and the voltage of the picture tube anode power supply +
It is made H-T.

The flyback transformer 6 includes a tertiary winding 6C, and the base side of the negative pulse Pm generated in the tertiary winding 6C is rectified and filtered (rectified and smoothed) by a diode 8, a smoothing capacitor 9, etc. Then, it is used as a DC power supply voltage +B' for operating various parts of the TV receiver.

As mentioned above, two TVs with different horizontal scanning periods
For TV receivers that receive TV broadcast waves of different formats, regardless of which TV format the TV broadcast waves to be received comply with, even if the horizontal scanning period is switched during reception, the size of the receiving screen In order to prevent changes in the brightness of the reproduced image, the horizontal deflection current y and the picture tube anode power supply voltage H-T must be kept at constant values, regardless of changes in the horizontal scanning period. Therefore, the flyback pulse P generated in the horizontal deflection circuit is
The pulse width of f can be changed according to the switching of the horizontal scanning period (this method has many difficulties in implementation, so it is possible to change the pulse width of ), or by changing the horizontal scanning period so that a flyback pulse Pf having a constant peak value is obtained in the horizontal deflection circuit regardless of changing the horizontal scanning period. The power supply voltage element B of the horizontal deflection circuit is changed accordingly.

As described above, by changing the power supply voltage B of the horizontal deflection circuit at the same time as the horizontal scanning period is switched, it is possible to fly back a constant peak value regardless of which horizontal scanning period the horizontal deflection circuit is operating in. If the pulse Pf is generated within the horizontal deflection circuit, the horizontal deflection current Iy and the voltage of the picture tube anode power supply +H-T will be unrelated to the switching change of the horizontal scanning period, and the intended purpose will be achieved. The base side of the negative pulse Pm generated by the flyback transformer 6 in the tertiary winding 6C is rectified and filtered to provide DC voltage as a power source for operating various parts of the receiver. The output voltage of the power supply fluctuates widely as the horizontal scanning period changes, causing changes in the operating state of each part of the TV receiver.

That is, when the flyback pulse Pf generated in the horizontal deflection circuit is made to have a constant peak value regardless of the switching change of the horizontal scanning period as described above, the flyback pulse Pf is generated based on this flyback pulse Pf. The peak value V of the negative pulse Pm obtained by the tertiary winding 6C of the transformer 6
Pm also remains constant regardless of switching changes in the horizontal scanning period.
1 and the negative pulse Pm2 shown in FIG. 2, which represents the case where the horizontal scanning period is short, have the same peak value VPm. DC voltage value ■1. ■2 corresponds to the height from the AC axis O-0 to the base of the pulse for each pulse, so the AC axis OO for two pulse trains with the same pulse width and different pulse repetition periods. By moving the position of
The voltage value of the output voltage +B' of the DC power supply consisting of the diode 8 and the smoothing capacitor 9 fluctuates widely in response to the switching change of the horizontal scanning period. The operating conditions of each part of the machine change significantly, and in some cases, active elements constituting each part may be damaged or destroyed.

To prevent this from happening, a so-called DC stabilized power supply circuit could be used as the DC power supply described above, but this would complicate the configuration, increase costs, and require extra current to flow. Therefore, such a solution cannot be adopted, and normally an intermediate tap is provided on the tertiary winding 6C of the flyback transformer 6 as shown in the first diagram, and the negative voltage supplied to the diode 8 is A solution is adopted in which the peak value of the pulse Pm changes in accordance with the switching of the horizontal scanning period, so that the output voltage value of the DC power supply +B' does not change even when the horizontal scanning period is switched. has been done.

In the example shown in the first diagram, 12, 13.14 are relays 10
One end of the excitation winding of the relay 10 is connected to a DC power supply, and the other end of the excitation winding is connected to the collector of a control transistor 11. 11 emitters are grounded,
A control voltage is applied to the base from a channel selector (not shown) in response to switching changes in the horizontal scanning period.

Figure 2 a, l) As is clear from the illustration, the magnitude of the DC voltage obtained when rectifying pulse trains with the same pulse width, the same peak value VPm, and different repetition periods is The longer the period, the smaller it becomes, so the first
In the illustrated example, at the base of the control transistor 11,
Only when receiving TV broadcast waves with a longer horizontal scanning period, a positive voltage is applied from the channel selector to make the control transistor 11 conductive and to apply an operating current I to the excitation winding of the relay 10.
r is applied to the movable contacts 12 to 14 of each contact set of the relay 10.
is switched to one fixed contact side, the movable contact 12 applies a negative pulse with a high peak value to the rectifying diode 8, and the other movable contacts 13 and 14 perform horizontal oscillation frequency switching operation and switching of the 10B voltage. In addition, when receiving TV broadcast waves with a shorter horizontal scanning period, the control transistor 11 is cut off to return the relay 10 and the movable contact 12 transmits a negative pulse with a lower peak value to the rectifier diode 8. and other movable contacts 13.1
4, the horizontal oscillation frequency is switched, the 10B voltage is switched, etc., and the desired operation is performed well even when the TV receiver is receiving TV broadcast waves with a long or short horizontal scanning period. It is done like this.

However, in the conventional circuit arrangement shown in the first diagram,
The flyback transformer 6 is required to have a tertiary winding 6C with an intermediate tap, and a method for switching the taps of the tertiary winding 6C in accordance with changes in the horizontal scanning period is required. Relay 1 with a configuration that also includes a contact set
In addition to the complicated structure and high cost, the rectifier diode 8 is also used to supply current IO to the load circuit and excitation current Ir (current I of the excitation winding of IJ 0).
r) is required (the excitation current I of the relay 10
(r has a non-negligible magnitude compared to the load current Io), this also leads to high costs, and furthermore,
Since the movable contact 12 to be provided in the relay 10 described above is required to switch a relatively large current, the contact often suffers damage, which also poses a problem in terms of reliability.

When receiving TV broadcast waves of two TV systems with different horizontal scanning periods, the present invention enables switching depending on which TV system the TV broadcast waves to be received are based on. By the means, the circuit operation is always switched to match the horizontal scanning period of each TV system, and the flyback pulse from the horizontal deflection circuit,
Or, in a TV receiver in which the DC voltage obtained by rectifying and filtering the base side of the pulse obtained based on the flyback pulse is used as a DC power source for operating the rotation of each part of the TV receiver. , the emitter of a control transistor whose collector is connected to the DC power supply side that generates a DC voltage by rectifying and filtering the base side of the flyback pulse from the horizontal deflection circuit or the pulse obtained based on the flyback pulse. Connected to the load circuit side, and connected to the collector and emitter of the control transistor, an excitation winding of a relay equipped with a set of contacts for circuit switching, and has an appropriate DC resistance value as required. An impedance element is connected in parallel with the excitation winding of the relay, and when receiving TV broadcast waves according to the TV system with a longer horizontal scanning period, the control transistor is made conductive; A power source in a TV receiver capable of receiving TV broadcast waves according to a different TV system, comprising means for controlling the control transistor to be in a cut-off state when receiving TV broadcast waves according to the TV system with a shorter cycle. By providing a switching circuit, the problems of the above-mentioned conventional circuits have been satisfactorily solved.Hereinafter, the circuit diagrams showing the embodiments of each part of the present invention shown in FIGS. 3 and 4 will be described. The contents will be explained in detail with reference to the following.

FIG. 3 is a circuit diagram of an example of implementing the power supply switching circuit of the present invention using an NPN type transistor as the control transistor 11, and FIG. This is a circuit diagram of an example of implementing the power supply switching circuit of the present invention using transistors, and in each of these figures, each component corresponding to the component shown in the first diagram described above is shown. are given the same drawing numerals as those used in FIG. 1.

First, in the circuit arrangement shown in FIG. 3, the non-grounded end side of the tertiary winding 6C of the flyback transformer 6 is connected to the anode side of the diode 8, and the cathode side of the diode 8 is connected to the smoothing capacitor 9. It is connected to the collector of the control transistor 11, one end of the excitation winding 10a of the relay 10, and the resistor 15.
is connected to one end of the

The emitter of the control transistor 11 is connected to the other end of the excitation winding 10a of the relay 10 and the other end of the resistor 15, which is also connected to the output terminal 17 of the DC power supply. .

In the circuit arrangement shown in FIG. 4, one end of the tertiary winding 6C of the flyback transformer 6 is connected to the anode side of the diode 8, and the cathode side of the diode 8 is connected to the one end of the tertiary winding 6C of the flyback transformer 6. end, as well as the output terminal 17 of the DC power supply.

The other end of the smoothing capacitor 9 is connected to the other end of the tertiary winding 6C of the flyback transformer 6, and is also connected to the collector of the control transistor 16.

The emitter of the control transistor 16 is grounded,
An excitation winding 10a of the relay 10 and a resistor 15 are connected in parallel between the collector and emitter of the control transistor 16, respectively.

The base of the control transistor 11 in FIG.
The base of the control transistor 16 in the figure is connected to the control transistor 11.16 when the TV broadcast to be received by the TV receiver follows the TV system with the longer horizontal scanning period. A control voltage (a positive control voltage for the transistor 11 and a negative control voltage for the transistor 16) is supplied from the channel selector to enable each control Transistors 11 and 16 are rendered conductive when the TV receiver receives TV broadcast waves according to the TV system with the longer horizontal scanning period, and when the TV receiver receives the TV broadcast wave according to the TV system with the shorter horizontal scanning period. When receiving TV broadcast waves, the system is in a cut-off state.

When the TV receiver is receiving TV broadcast waves according to the TV system with the longer horizontal scanning period and the control transistors 11 and 16 are in a conductive state, the cathode side of the diode 8 and the ground are connected. The DC voltage that appears between the two appears between the output terminal 17 of the DC power supply and the ground as a DC output voltage with almost the same magnitude, whereas the TV receiver follows the TV system with the shorter horizontal scanning period. The control transistor 11.16 is used to receive TV broadcast waves.
When relay 10 is cut off, relay 10 is determined from the DC voltage value appearing between the cathode side of diode 8 and ground.
A DC voltage value lower by the voltage drop caused by the load current flowing in the load circuit in the parallel circuit of the excitation winding 10a and the resistor 15 appears at the output terminal 17 of the DC power supply.

As already mentioned with reference to FIG. 2, the output voltage V2 of the DC power supply when the horizontal scanning period is short is originally higher than the output voltage V1 of the DC power supply when the horizontal scanning period is long. In the power supply switching circuit of the present invention shown in FIGS. 3 and 4 above, when the horizontal scanning period is long, the DC voltage between the cathode side of the diode 8 and the ground is directly output from the DC power supply. In addition, when the horizontal scanning period is short, the DC voltage of the DC voltage value V2 appearing between the cathode side of the diode 8 and the ground appears at the output terminal 17 of the DC power supply, and the DC voltage value V2 appears at the output terminal 17 of the DC power supply. It is possible to obtain the voltage drop by a parallel circuit of the excitation winding 10a of the relay 10 and the resistor 15 so that it appears as a DC voltage of □.

When the horizontal scanning period is short, the excitation winding 10 of the relay 10
The value of the voltage drop that should be caused by the parallel rotation of a and the resistor 15 is V2 Vl, and the value of this voltage drop corresponds to the value of the load current that should be supplied to the load circuit. This can be easily obtained by setting the parallel DC resistance value of a and the resistor 15.

Note that, as a matter of course, the excitation winding 10 of the relay 10
If the product of the winding resistance value of a and the load current is the same as the required voltage drop V2-V, the resistor 15 does not need to be connected.

Here, as an example, the resistor 15 has a resistance value of 82Ω, the relay 10 has a rating of 6■, and the DC resistance value of the excitation winding 10a is 4(l). The power supply switching circuit consists of a so-called French system with 819 scanning lines (horizontal scanning period of approximately 48.8 μs),
Table 1 shows the experimental results obtained when switching to the CCIR method with 625 scanning lines (horizontal scanning period of about 64.0 μs).

As is clear from Fig. 1, in the power supply switching circuit of the present invention, it is extremely easy to create a DC power supply in which the DC output voltage value hardly changes even when the horizontal scanning period is switched. There are two configurations, so for that configuration there is an intermediate tap.

It becomes possible to use a flyback transformer 6 having a tertiary winding without a tertiary winding, and accordingly, it becomes unnecessary for the relay 10 to have a contact set for switching taps. The load current Io is such that the excitation current required for the operation of is supplied to the load circuit.
Since a portion of the diode 8 is used, the diode 8 may be rated only to allow the load current Io to flow.

It goes without saying that the movable contacts 13 and 14 are switched by the operation of the relay 10, and each set of contacts causes the operating state of the TV receiver to be adapted to the respective horizontal scanning period.

As is clear from the detailed description above, the power switching circuit of the present invention satisfactorily solves all the problems with the conventional power switching circuits mentioned above. A TV receiver with excellent performance can be provided at low cost.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example. Further, FIG. 2 is a waveform diagram for explaining the operation, and FIGS. 3 and 4 are circuit diagrams of the power supply switching circuit of the present invention. 1...Horizontal deflection output transistor, 2...
... Damper diode, 3 ... Capacitor for retrace resonance, 4 ... Horizontal deflection coil, 6 ...
・Flyback transformer, 6C...Third winding,
7... High voltage rectifier diode, 8...
Diode, 9...Smoothing capacitor, 10
...Relay, 10a... Excitation winding, 1
1.16...Control transistor, 12-14
......Movable contact, 15...Resistance, 17.
...Output terminal.

Claims (1)

[Scope of utility model registration request] When receiving television broadcast waves of two television systems with different horizontal scanning periods, switching is performed depending on which television system the television broadcast waves to be received comply with. means so that the circuit operation is always adapted to the horizontal scanning period of each television system, and the base side of the flyback pulse from the horizontal deflection circuit or the pulse obtained based on the flyback pulse is rectified. In a television receiver in which the DC voltage obtained by filtering is used as a DC power source for operating various circuits in the television receiver, the flyback pulse or flyback pulse from the horizontal deflection circuit is used. The emitter of a control transistor whose collector is connected to the DC power source side that generates a DC voltage by rectifying and filtering the base side of the pulse obtained based on the above is connected to the load circuit side, and
The collector and emitter of the control transistor,
Connect the excitation winding of a relay equipped with a set of contacts for circuit switching, and if necessary, connect an impedance element with an appropriate DC resistance value in parallel with the excitation winding of the relay, and When receiving television broadcast waves according to a television system with a longer scanning period, the control transistor is turned on; conversely, when receiving television broadcast waves according to a television system with a shorter horizontal scanning period, A power supply switching circuit in a television receiver capable of receiving television broadcast waves according to different television systems, comprising means for controlling the control transistor to be in a cut-off state.