JPS6119150B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stabilized power supply horizontal output circuit using a switching regulator.

2. Description of the Related Art As a switching regulator used in a horizontal output circuit of a television receiver, the one shown in FIG. 1 is conventionally known. In FIG. 1, the transistor Q is turned on and off by a pulse synchronized with the H period (horizontal scanning period) applied from a PWM (pulse width modulator) 2. As a result, the DC voltage applied from the power supply 1 to the primary side of the output transformer T is switched, and the voltage induced on the secondary side is rectified and smoothed by the diode D and the capacitor C. This DC output voltage is applied to the load 3 including the horizontal output circuit, and a part of it is applied to the PWM
2, and the duty ratio of the output pulse is controlled according to the output voltage. This stabilizes the output voltage.

In this circuit, the current i ₁ flowing through the transistor Q has the waveform shown in FIG. 2A, and this current i ₁ generates a magnetic flux φ ₁ shown in FIG. 2C in the core of the transformer T. Also, the current i ₂ flowing through the diode D is the second
The waveform is as shown in Figure B, and this current i ₂ causes the core of the transformer T to have a magnetic flux φ ₂ as shown in Figure 2C.
occurs. These magnetic fluxes φ ₁ and φ ₂ always generate a DC component magnetic flux φ ₀ in the core of the transformer T, as shown in FIG. 2C. This magnetic flux φ ₀ reduces the magnetic permeability μ of the winding of the transistor T, which increases the current i ₁ and may lead to destruction of the transistor Q. To prevent this, it is possible to compensate for the decrease in magnetic permeability μ by increasing the core of the transformer T, but there is a problem that the transformer T becomes large.

Various methods have been used to solve this problem. For example, by providing another transformer and a switching transistor between the transformer T and the power supply 1, switching the power supply voltage once, applying its output to the transformer T, and switching it again with the transistor Q, the magnetic flux φ ₀
There is something designed to cancel this. However, this method requires two transformers, and in order to switch two transistors,
This requires two independent drive circuits including PWM, which has the disadvantage of complicating the circuit configuration.
Additionally, a circuit called a Bethssel circuit that combines a horizontal deflection circuit and a switching regulator is known, but this circuit requires large switching power and is difficult to insulate between the circuit blocks of a television receiver. There were flaws.

The present invention can eliminate the above-mentioned drawbacks, and embodiments of the present invention will be described below with reference to the drawings.

In FIG. 3, the AC voltage applied to input terminals 4a and 4b is rectified and smoothed by a diode bridge 5 and a capacitor _C1 . This rectified DC voltage E ₁ is connected to the anode of the thyristor 6, the resistor R ₁ and the capacitor C ₂ through the winding N ₁ provided in the output transformer T ₁ such as a flyback transformer.
and a sawtooth wave generating circuit 7 consisting of the following.
On the other hand, at point a in the figure, a DC output voltage _E2 stabilized by the operation described later appears, and this voltage
E ₂ is applied to the voltage setting circuit 11 consisting of a resistor R ₂ , a variable resistor R ₃ and a resistor R ₄ and to the winding N ₂ of the transformer T ₁ . The voltage E _R divided from the slider of the variable resistor R ₃ is applied to the PWM 8, and the voltage E ₂ applied to the winding N ₂ is applied to the transistor of the horizontal output circuit 9.
Switched by the on/off operation of _Q1 . The horizontal output circuit 9 includes a transistor Q ₁ , a damper diode D ₁ , a resonant capacitor C ₃ , a horizontal deflection coil 10 and an S-shaped correction capacitor C ₄ . The transistor Q ₁ is turned on and off by a pulse synchronized with a horizontal synchronizing signal obtained from the horizontal oscillator 12 via the drive transformer T ₂ .

Due to this switching, winding _N2 has a fourth
Horizontal retrace pulse e ₁ with a waveform as shown in Figure A
is obtained. In addition, since the windings N ₁ and N ₂ are wound with opposite polarities and are closely electromagnetically coupled as shown in the figure, the pulse e ₁ causes the winding N ₂ to be connected to the thyristor 6 side. A negative horizontal retrace pulse _e2 having a waveform as shown in FIG. 4B is generated. In this case, if the winding ratio of the windings N ₁ and N ₂ is N ₁ /N ₂ , the voltage during the scanning period of this pulse e ₂ will be N ₁ /N ₂ E ₂ and the voltage E ₁ as shown in the figure. They become superimposed. This pulse _e2 is applied to the anode of the thyristor 6 and is integrated by the sawtooth wave generating circuit 7, as shown in FIG.
The result is a sawtooth wave voltage e ₃ with a horizontal period as shown in . This sawtooth voltage e ₃ is superimposed on the voltage E _R at point c to become the voltage e ₄ shown in FIG. 2D. This voltage e ₄ is applied to the base of a comparison transistor Q ₂ constituting the PWM 8 and compared with the Zener voltage V _Z of a Zener diode D ₂ connected to the emitter of this transistor Q ₂ . Therefore, when the voltage e ₄ becomes lower than V _Z -V _BE (V _BE : the base-emitter voltage of the transistor Q ₂ ), the transistor Q ₂ becomes conductive. As a result, a voltage _e5 as shown in FIG. 4E is output to the collector, and this voltage _e5 drives the drive transistor _Q3 of the next stage.
becomes conductive, and the voltage shown in Figure 4F is applied to its collector.
e ₆ is output. This voltage e ₆ is applied to the gate of the thyristor 6 via the transformer T _B as a drive voltage e ₇ as shown in FIG. 4G. This voltage e ₇
is a voltage whose pulse width changes in proportion to the DC output voltage _E2 at point a.

On the other hand, a voltage _e8 as shown in FIG. 4H is applied between the anode and cathode of the thyristor 6.
For this reason, this thyristor 6 is conductive during the period _t1 when the drive voltage _e7 is applied to its gate and the voltage _e8 is at the 0 level or higher, and due to this conduction, the thyristor 6 becomes as shown in FIG. A current i ₃ shown flows. As a result, a rectangular wave voltage e ₉ having a peak value of (E ₁ +N ₁ /N ₂ E ₂ ) and a pulse width proportional to the voltage E ₂ is obtained on the cathode side of the thyristor 6, and this voltage e ₉
is integrated by an integrating circuit 13 consisting of a choke coil _L1 and a capacitor _C5 , and becomes a DC output voltage _E2 , which appears at point a. The diode _D3 is a flywheel diode, and the energy stored in the choke coil _L1 while the thyristor 6 is conducting is transferred from the moment the thyristor 6 is cut off until the next time it becomes conductive, as shown in FIG. 4J. It is emitted as a current i ₄ .

DC output voltage at point a obtained as described above
E ₂ is applied to the winding N ₂ and switched by the transistor Q ₁ as described above, and is also applied to the PWM 8 via the voltage setting circuit 11, thereby controlling the pulse width of the drive voltage e ₇ . The resulting voltage E ₂ is stabilized. In addition, the voltages induced in the secondary windings N ₃ to _{N 6} of the transformer T ₁ by the above switching are rectified and applied to the high voltage circuit of the cathode ray tube.
It is supplied to predetermined circuits such as a heater circuit and an H/AFC circuit.

Transistor Q ₁ of horizontal output circuit 9 is conductive during period t ₂ shown in FIG. Therefore _, if the conduction period _{t 1} of the thyristor ₆ shown in FIG. The magnetic flux φ ₁ generated in the winding N ₁ due to conduction and the transistor
The magnetic flux φ ₂ generated in the winding N ₂ due to the conduction of Q ₁ cancels each other out within the core of the transformer T ₁ . Therefore, the DC component magnetic flux φ in the core can be made approximately zero.
For this purpose, the circuit constants of the sawtooth wave generating circuit ₇ and the like are selected so that the pulse width of the drive voltage e7 is, for example, about 27 μsec in a steady state. Also the third
In the figure, the primary and secondary sides of the drive transformer T ₂ are separately grounded and insulated from each other as shown, and the windings N ₁ and N ₂ of the output transformer T ₁ and the other windings N ₃ - By separately grounding N ₆ and insulating each other, the primary side and secondary side (load side) of the horizontal output circuit 9 can be easily and completely insulated. Although the thyristor 6 is used in this embodiment, other switching elements that are non-conductive to reverse voltage may be used instead.

The first of the transformer T ₁ outputs the unregulated current voltage E ₁
One end (anode) of the switching element 6 is connected through the winding N _{1 of} The switching element is controlled by the output of the circuit, and the output voltage _e9 at the other end (cathode) of the switching element is smoothed to form a DC output voltage _E2 , and this DC output voltage is applied to the first output transformer. A second winding is wound with opposite polarity to the winding of
N ₂ and in addition to the PWM circuit of the rectangular wave voltage generation circuit, the pulse width of the rectangular wave voltages e ₆ and e ₇ is controlled according to the DC output voltage, and the second The voltage applied to the winding of the horizontal output circuit 9 is switched by the transistor Q ₁ of the horizontal output circuit 9, and the regulated horizontal power supply is configured so that the conduction period t ₂ of this transistor and the conduction period t ₁ of the switching element are approximately equal to each other. This relates to the output circuit.

Therefore, according to the present invention, the DC component magnetic flux in the core of the output transformer can be reduced to approximately zero.
The output transformer can be made smaller. Furthermore, no particularly large amount of power is required, and the circuit configuration becomes simple.
Furthermore, since the primary side and the secondary side of the horizontal output circuit can be easily insulated, other equipment such as a VTR can be easily connected.

[Brief explanation of the drawing]

Figure 1 is a schematic circuit diagram of a conventional switching regulator, Figure 2 is a waveform diagram of each part of Figure 1,
FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 is a waveform diagram of each part in FIG. In addition, in the symbols used in the drawings, 6 is a thyristor, 7 is a sawtooth wave generation circuit, and 8 is a sawtooth wave generating circuit.
PWM, 9 is horizontal output circuit, 13 is smoothing circuit, T ₁
is the output transformer, and N ₁ and N ₂ are the windings.

Claims (1)

[Claims] 1 The unregulated DC voltage is applied to one end of the switching element through the first winding of the output transformer, and a rectangular wave voltage generation circuit consisting of a sawtooth wave generation circuit and a PWM circuit for driving this switching element, as well as the above-mentioned The switching element is controlled by the output of the rectangular wave voltage generating circuit, the output voltage at the other end of the switching element is smoothed to form a DC output voltage, and this DC output voltage is applied to the first winding of the output transformer. In addition to adding it to the second winding wound with the opposite polarity, it is also added to the PWM circuit in the rectangular wave voltage generation circuit to control the pulse width of the rectangular wave voltage according to the DC output voltage. A stabilized power supply horizontal output configured to switch the voltage applied to the second winding by a transistor of the horizontal output circuit, and to substantially match the conduction period of this transistor and the conduction period of the switching element. circuit.