JPH08251433A - Horizontal deflection exciting circuit - Google Patents

Abstract

PURPOSE: To provide a horizontal deflection exciting circuit in which power loss is reduced and the circuit is simplified. CONSTITUTION: An N-channel FET 17 is switched depending on an exciting pulse Vd and its drain voltage Vdr is a square wave whose level is nearly between -En and zero. The square wave Vdr is transformed into a square wave Vb at a tap (b) of an auto-transformer 18, an output is fed to a base of an output transistor(TR) 3, and a base current Ib is supplied at a high level of the square wave Vb. The level of the drain current Idr flowing to the FET 17 is smaller than the base current Ib. A base current Ib0 at a time T1 when the conduction of the output TR 3 is started is decreased as Ib0/n depending on a winding ratio (n) of the auto-transformer 18. Since the current flowing to the FET 17 is reduced to 1/n, the power loss in the FET is reduced by the reduction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a horizontal deflection output transistor excitation circuit in a device using a picture tube.

[0002]

2. Description of the Related Art First, FIG. 3 shows an example of a conventional horizontal output circuit and its excitation circuit. In FIG. 3, reference numeral 1 is an exciting transistor which performs a horizontal exciting action by receiving an exciting pulse Vd from a preceding stage (not shown), such as a horizontal oscillation circuit. Less than,
2 is a horizontal excitation transformer, 3 is a horizontal output transistor, 4
Is a damper diode, 5 is a return resonance capacitor, 6 is a horizontal deflection coil, 7 is an S-shaped correction capacitor, and 8 is a horizontal output choke or transformer. With such a circuit, the excitation transistor 1 is firstly driven according to the excitation pulse Vd.
Performs an on / off operation, but with this, a square wave pulse such as Vcd is generated at its collector terminal. That is, when the excitation transistor 1 is on, the voltage Vcd
Has bottomed to zero and is a high level square wave when off.

This square wave Vcd is transformed by the excitation transformer 2 into a waveform Vb of the same polarity, which is added to the base of the output transistor 3. Then, the output transistor 3 is turned on during the high level period when the excitation transistor 1 is off. Further, even if these waveforms Vcd and Vb change from high level to zero, the output transistor 3 does not immediately turn off. During the accumulation time tst peculiar to the output transistor 3, the reverse base current Ib2 flows out from its base toward the transformer 2, while the output transistor 3 continues to conduct.

Next, when the accumulation time tst ends, the output transistor 3 is turned off. By repeating such a cycle, a sawtooth wave current Iy having a horizontal period flows through the horizontal deflection coil 6 according to a well-known principle, and the electron beam of the picture tube is horizontally deflected.

Although the reference numeral 8 is drawn as a choke coil for supplying electric power from the power source Eb to the circuit,
It is often practiced to provide a secondary winding on this to form a transformer. At the same time, a collector pulse Vc is generated in the collector of the output transistor 3, which is transformed to supply necessary pulses to various parts in the receiver including high voltage rectification for the cathode of the picture tube. The resistors 9 and 10 provided on the primary side and the secondary side of the excitation transformer 2 are inserted for limiting and stabilizing the base current of the output transistor 3, and may be omitted depending on design conditions. It is possible.

Next, FIG. 4 is a waveform diagram showing the operating state of each part in FIG. First, FIG. 4 (A) shows the excitation pulse Vd introduced from the previous stage, and the excitation transistor 1 is made conductive during this high level period and a short time thereafter, and its collector is shown in FIG. 4 (B). A square wave Vcd is produced. When the high level period ton of the square wave Vcd is entered, the base of the next output transistor 3 also becomes high level at the same time, so that the base current Ib starts to flow from this point as shown in FIG. 4C. As is well known, the base current Ib flows in the negative direction only during the accumulation time tst after the high level period ton of the square wave Vcd ends, and then, until the square wave Vcd next becomes high level. It becomes zero. Then, the output transistor 3 receives the base current I
Conduction takes place during the period ton during which the positive current of b flows and the accumulation time tst, and when this ends, a pulse Vc of a half-sine wave as shown in FIG.

This pulse Vc has a half cycle length and a time t.
When the value tries to fall below zero after the passage of r, the damper diode 4 is automatically turned on and the pulse Vc disappears. Then, from this point in time, a ramp current due to the damper current Id and the collector current Ic shown in FIG.
As a result, the deflection coil current Iy as shown in FIG.
Flows for horizontal deflection.

Next, FIG. 5 is a circuit diagram showing another conventional example. Here, 3 to 8 have the same functions as the same numbered parts in FIG. 3 described above, and a repetitive description will be omitted. 11
Is an exciting transistor, and unlike the case shown in FIG. 3, the emitter is not grounded but is connected to the negative DC power supply -En, and the excitation pulse Vd from the preceding stage is generated between the base and this DC power supply -En. Added in between. Furthermore, 12
Is a flywheel coil, and 13 and 14 are current limiting resistors.

FIG. 6 is a waveform diagram showing the operating state of each part in FIG. First, as shown in FIG.
The excitation pulse Vd from the previous stage is applied to the base of the excitation transistor 11, but this low level value is different from FIG.
It is En. Then, as shown in FIG. 6B, the collector voltage of the excitation transistor 11 is bottomed to the voltage -En during the high level period of the excitation pulse Vd and shortly thereafter, and the collector-emitter is brought into conduction. Since the collector-emitter of the excitation transistor 11 is in the off state while the waveform Vcd is at the high level, the current I flowing through the flywheel coil 12 is thereby generated.
As shown in FIG. 6C, L has a waveform in which the increase and decrease is linearly repeated according to the square wave Vcd.

On the other hand, when the exciting transistor 11 is turned on, a current is drawn from the base of the output transistor 3 to the negative power source -En, which continues for the accumulation time tst. After the storage time tst, no current flows through the base of the output transistor 3 while the exciting transistor 11 is conducting. However, when the exciting transistor 11 is turned off, the current that has been flowing through the flywheel coil 12 toward the collector of the exciting transistor 11 then flows to the base of the output transistor 3 as it is. Therefore, the base current Ib of the output transistor 3 is as shown in FIG. 6 (D), which has the same waveform as that of the prior art example shown in FIG. 3 (C). Therefore, the collector current waveform I of the output transistor 3
c and the deflection coil current Iy are the same as those in the circuit shown in FIG. 3, and similarly perform the horizontal deflection action.

[0011]

The circuit shown in FIG. 3 which is the conventional circuit described above does not cause much problems at a horizontal frequency of about 15.73 kHz which is used for ordinary television broadcasting. However, in the case of a so-called high-definition display having a horizontal frequency higher than this, the length of the storage time tst becomes a problem, and measures must be taken to make it as short as possible.

That is, as the horizontal frequency increases and the repetition period of the base current waveform Ib decreases, the ratio of the accumulation time tst during the off period of the output transistor 3 increases,
Finally, as shown in FIG. 7, the base current Ib may flow out before the collector pulse Vc reaches zero, and the collector loss may rapidly increase. In order to avoid this, the amount of the base reverse current Ib2 is increased as much as possible, and the accumulation time tst
It is known that the value of must be reduced.
Further, in this case, generally, the falling period required for the collector current Ic to turn off is shortened, which is also an important condition for reducing loss when the horizontal frequency is high.

However, in the circuit shown in FIG. 3, since it is necessary to consider the insulation between the primary and secondary windings of the excitation transformer 2, the leakage inductance here becomes large and a sufficient reverse base current Ib2 flows. However, the accumulation time tst tends to be long, and there is a problem when the horizontal frequency is high. In the case of FIG. 5, which is another conventional example, when the reverse base current Ib2 is caused to flow, there is no intervention of leakage inductance, which is advantageous when the horizontal frequency becomes high. However, in this case, some problems newly arise with respect to the negative power supply -En.

One is that the value of the negative power supply -En is limited due to the problem of reverse breakdown voltage between the emitter and base of the output transistor 3. That is, this reverse breakdown voltage is usually
Since it has only about 5 V, -En must be set to a small value in accordance with it. However, this -En is often produced by a transformer of a switching power supply in the receiver, and even if a negative power supply is produced by rectifying the one-turn winding of this transformer, the negative voltage may become larger than -5V. Many. In this case, the voltage must be lowered to -En by a dedicated regulator, but of course the power loss in this part will increase.

Further, in the case of a small machine which requires only a small base current, it is necessary to adjust the value of the base current with the resistors 13 and 14. However, if this resistance value is large, power loss will occur here as well. I will end up. Further, in a large machine, when the required reverse base current Ib2 is large, the load current of the power source, -En, becomes a large current. Then, the current of the rectifier diode for rectifying the voltage of the switching transformer windings to obtain -En also increases.
Since the loss of this rectifier diode has almost no relation to the rectified voltage and increases with the current, from the viewpoint of loss, it is better to make a power supply with a higher voltage and a smaller current as long as the diode withstand voltage allows, rather than such a low voltage and large current. convenient.

The same applies to the excitation transistor 11, and when used in a large current condition, the collector
Since the voltage between the emitters is almost constant, this also causes an increase in power. In both FIGS. 3 and 5, the excitation transistor is drawn as a bipolar type, but even if this is an FET, the essential operation principle is the same except that the condition of the input excitation pulse Vd is changed. Also in this case, the resistance between the drain and the source at the time of turning on has a specific value. Therefore, when the value of −En is small in the circuit shown in FIG. 5 and a large current is required to flow, the loss increases. Easy to connect to.

Further, when the reverse base current Ib2 is caused to flow depending on the output transistor 3, a small inductance may be inserted in series with the base to increase the accumulation time tst but shorten the collector current Ic drop time. Yes, there are times when this is more convenient when designing. For this purpose, a small inductance may be inserted in series with the resistor 10 of FIG. 3 or the resistor 13 of FIG. For example, the choke coil 15 in FIG. 8 corresponds to this. Where 1
Reference numeral 6 is a resistor for suppressing unnecessary vibration. However, in the case of FIG. 8 as well, the number of circuit points is increased as compared with the case of FIG. 5 after all, and the problem of FIG. 5 described above is not improved as it is.

[0018]

In order to solve the above-mentioned problems of the prior art, the present invention provides a horizontal deflection coil for deflecting an electron beam of a picture tube and a switching operation of a horizontal deflection cycle, thereby A horizontal output transistor for generating a sawtooth wave current in the horizontal deflection coil, an autotransformer having one end grounded and an intermediate tap connected to the base terminal of the horizontal output transistor, and another horizontal end connected to the other end of the autotransformer. An excitation switch element that performs an on / off operation in a deflection cycle; and a direct current power source that is connected between the excitation switch element and ground and has a polarity that draws a reverse base current of the horizontal output transistor. A characteristic horizontal deflection excitation circuit is provided.

[0019]

EXAMPLE A horizontal deflection excitation circuit of the present invention will be described below.
Description will be given with reference to the accompanying drawings. First, an embodiment of the present invention will be described with reference to FIG. In addition, in FIG.
The same parts as those in FIG. 5 are designated by the same reference numerals and detailed description thereof will be omitted. That is, the reference numerals 3 to 8 function as a horizontal deflection output circuit, and the sawtooth wave current Iy having a horizontal deflection period is supplied to the horizontal deflection coil 4 as in FIGS.
There is no change in generating the pulse Vc at the same time.

Here, 17 is an n-type FE for horizontal excitation.
T (excitation switch element) corresponds to the excitation transistors 1 and 11 in FIG. 3 or FIG. In FIG. 1, this portion is drawn with a FET, but it can be formed with a bipolar transistor as shown in FIGS. 3 and 5. Further, reference numeral 18 is an excitation autotransformer, whose intermediate tap b is connected to the base of the output transistor 3. When the hot end is a and the cold end is c, the winding ratio between bc and ac is 1: n. 19 and 20 are current limiting resistors.

The operation of the circuit shown in FIG. 1 will be described with reference to FIG. First, here in FIG. 2A, the excitation pulse Vd from the previous stage applied between the gate and source of the n-type FET 17
, And the drain and source are electrically connected at this high level portion. If the value of the negative power source applied to the source is -En, the drain voltage Vdr at that time is as shown in FIG.
It is a square wave with an amplitude between -En and zero. This square wave Vdr is transformed into the tap b point on the next autotransformer 18, and becomes a square wave Vb as shown in FIG.
It is added to the base of the output transistor 3. Then, at the high level portion of this square wave Vb, the output transistor 3
There is conduction between the base and emitter of.

At this time, as shown in FIG. 2D, the base current Ib flows in the high level portion of the square wave Vb.
However, even if the high level of the square wave Vb ends, the base current Ib does not immediately become zero, but it turns to the negative direction once and becomes zero after the accumulation time tst peculiar to the transistor has passed, and during this period. Continuing the conduction between the collector and the emitter of the output transistor 3 is exactly the same as the case described above with reference to FIG. Therefore, although not described again in FIG. 2 below, a sinusoidal half-wave pulse Vc is similarly generated in the collector of the transistor 3 and a sawtooth current Iy flows in the deflection coil 6 to perform a normal horizontal deflection operation. Will be done.

At this time, the drain current Idr flowing through the FET 17 is determined in the direction as shown in FIG.
As shown in (E). That is, the waveform is similar to that of the base current Ib shown in FIG. 2D, but its amplitude is small. For example, as shown in the figure, the base current Ib0 of the output transistor 3 at the start time T1 of conduction becomes small according to Ib0 / n and the winding ratio n. Further, since the FET 17 is turned off after this time T1,
Naturally, the value of this portion of the drain current Idr becomes zero.

As described above, in the circuit shown in FIG.
Compared with the conventional circuit of FIG. 5, an exciting transistor or F
Since the current flowing through ET is reduced to 1 / n, the power loss in the transistor or FET is reduced accordingly. In addition, the current supplied from the negative power supply -En is as shown in FIG.
Since it is the average value of the drain current Idr of (E), this is also 1 / n of the case of FIG. 5, and the loss of the power supply rectifying diode and the voltage stabilizing regulator (not shown) is reduced.

Further, in the circuit shown in FIG. 1 according to the present invention,
Since the value of the optimum negative power supply voltage -En can be freely set by the turns ratio n of the autotransformer 18, this can be shared with the power supplies of other circuits in the receiver, and the configuration is simplified. Furthermore, the resistors 19 and 20 need only have a minimum resistance value necessary for stabilizing the base current Ib, and there is no need to unnecessarily increase the resistance value, and power consumption can be reduced by this amount. .

On the other hand, compared with FIG. 3 which is another example, when the reverse base current Ib2 is passed from the output transistor 3, the equivalent leakage inductance between a and b of the transformer 18 is an autotransformer, so that it is extremely high. Few. Therefore, the leakage inductance rarely inhibits the reverse base current Ib2, and as described above,
The accumulation time tst can be shortened sufficiently. In addition, this slightly existing leakage inductance component can be set to a value suitable for shortening the fall time of the collector current Ic of the output transistor 3 as described above with reference to FIG. The number can be reduced and the circuit becomes simpler than that shown in FIG.

[0027]

As described in detail above, the horizontal deflection excitation circuit according to the present invention shortens the storage time of the horizontal output transistor, and the power supply voltage supplied to the excitation circuit is reversed between the emitter and base of the output transistor. Since it can be increased regardless of the breakdown voltage, power loss can be reduced. Further, there is a practically excellent effect that the circuit can be simplified.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a horizontal deflection excitation circuit of the present invention.

FIG. 2 is a waveform diagram showing an operating state of each unit in FIG.

FIG. 3 is a circuit diagram showing an example of a conventional horizontal deflection excitation circuit.

FIG. 4 is a waveform diagram showing an operating state of each unit in FIG.

FIG. 5 is a circuit diagram showing another example of a conventional horizontal deflection excitation circuit.

FIG. 6 is a waveform diagram showing an operating state of each unit in FIG.

FIG. 7 is a waveform diagram showing an operating state of each unit in FIG.

FIG. 8 is a circuit diagram showing still another example of a conventional horizontal deflection excitation circuit.

[Explanation of symbols]

 3 Horizontal Output Transistor 6 Horizontal Deflection Coil 17 n-type FET (Excitation Switch Element) 18 Autotransformer-En Negative DC Power Supply Ib Base Current

Claims (1)

[Claims] 1. A horizontal deflection coil for deflecting an electron beam of a picture tube, a horizontal output transistor for generating a sawtooth current in the horizontal deflection coil by performing a switching operation of a horizontal deflection cycle, and one end of which is grounded. An autotransformer having an intermediate tap connected to the base terminal of the horizontal output transistor, an excitation switch element connected to the other end of the autotransformer to turn on and off in a horizontal deflection cycle, the excitation switch element and ground. And a direct current power supply having a polarity so as to draw a reverse base current of the horizontal output transistor, the horizontal deflection excitation circuit.