JP3372594B2 - High voltage generation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage generating circuit such as a picture tube of a television receiver (TV), and more particularly, to stabilizing the high voltage output voltage. About technology. 2. Description of the Related Art FIG. 4 shows an example of a high-voltage stabilizing circuit using a saturable transformer in a high voltage generating circuit of a general TV picture tube. In the figure, 2 is a flyback transformer (hereinafter abbreviated as FBT), 9 and 1
0 is a primary winding and a secondary winding, 21 is a saturable transformer, 22 and 20 are control and controlled windings, 23 is a choke coil, 6 is a resonance capacitor,
5 is a damper diode, 4 is a horizontal output transistor, 12 is a high voltage rectifier diode, and 24 is a DC blocking capacitor. In the above high voltage stabilizing circuit, the high voltage output voltage is stabilized according to the following operating principle. Resonant capacitor 6, the damper diode 5, a pulse voltage E ₁ of the pulsating waveform is generated from the horizontal output circuit comprising a horizontal output transistor 4 and the inductance, the primary winding of FBT2 9
Supplied to [0004] FIG. 7 shows the output pulse voltage E ₁ of the waveform. The high voltage E ₂ generated on the secondary winding 10 side of the FBT ₁ is rectified by the high-voltage rectifier diode 12 and
Output to the picture tube anode and the like. The saturable transformer 21 is connected to the control winding 2.
2, the magnetic circuit formed inside the core saturates, and the inductance Lt of the controlled winding 20 increases.
Is decreasing. FIG. 5 shows the control winding current Ic and the controlled winding 20.
3 shows the relationship of the inductance Lt. When the high-voltage load on the secondary winding 10 side of the FBT 2 increases, the current I ₁ flowing into the primary winding 9 increases, so that the current I ₁ flows into the horizontal output circuit via the control winding 22 from the power supply (EB). Current Ic to be generated also increases. However, as described above, the controlled winding 20 of the saturable transformer 21
, The induced voltage E ₁ ′ (see FIG. 7) is generated in the horizontal output circuit to compensate for the input voltage drop on the primary winding 9 caused by the overload on the secondary winding 10. . FIG. 6 shows the relationship between the high voltage output current I ₂ of the FBT ₂ and the high voltage output voltage E ₂ of the high voltage stabilizing circuit. As shown by the solid line in the figure, the high-voltage output voltage E2 of the FBT ₂ is kept constant regardless of the magnitude of the load (current) on the secondary winding 10 side. More specifically, the output voltage E ₂ of the horizontal output circuit input to the primary winding 9 is kept constant. The output voltage E ₁ of the horizontal output circuit input to the primary winding 9 is E ₁ = π · Ts · EB / 2Tp + EB (1) Ts: horizontal scanning period Tp; pulse generation time of pulse voltage E ₁ expressed. Further, Tp is represented by Tp = 2π√ (L1 · Cr) / 2 (2) L1; total inductance Cr on the primary winding side of the FBT; capacitance of the resonance capacitor. The inductance of the choke coil 23 is F
Considering that much larger than the inductance Lt of BT2 of the primary winding inductance L ₁ and the control winding 20 of the saturable transformer 21, the primary winding total inductance L1 Further, L1 = L ₁ · Lt / (L ₁ + Lt) (3) By substituting the above equations (2) and (3) into the equation (1) and rearranging, E ₁ = (Ts · EB / 2) × √ ｛(1 + L ₁ / Lt) / (Cr · L ₁ ) ｝ + EB (4), and for L ₁ / Lt≫1, the above equation becomes E ₁ 〜TsｓEB / 2√ (Cr ・ Lt) (5). inductance Lt windings 20 becomes very small, inductance Lt of the output voltage E ₁ of the horizontal output circuit controlled winding 20
It increases in inverse proportion to the square root of. In the prior art described above, when the high-voltage load on the secondary winding 10 of the FBT 2 increases, the current I ₁ flowing into the primary winding 9 increases.
The current Ic flowing from the power supply (EB) to the horizontal output circuit via the control winding 22 also increases. At this time, as the current Ic increases, the inductance Lt of the controlled winding 20 of the saturable transformer 21 also decreases. Therefore, an induced voltage E ₁ ′ (see FIG. 7 ) is generated in the horizontal output circuit so as to compensate for the input voltage drop on the primary winding 9 caused by the overload on the secondary winding 10. However, the increase in the current Ic and the inductance Lt
Is not uniform, the high-voltage output voltage E
₂ is not kept constant as shown in FIG. 3, and when the high-voltage load on the secondary winding 10 side of the FBT 2 increases, the voltage becomes high (ΔE _{2 in} FIG. 6). The present invention has been made in view of the above points, and has as its object to combine an FBT that outputs a stable high-voltage output voltage regardless of an increase in the high-voltage load on the secondary winding of the FBT. To provide a high voltage generating circuit. According to the present invention, there is provided a high-voltage generating circuit in which a horizontal deflection output circuit and an FBT are integrally connected and a high-voltage output voltage is applied from the FBT to a cathode ray tube. A voltage obtained by detecting the amount of change in the high-voltage output voltage applied to the cathode-ray tube with a high-voltage detection resistor is set as a detection voltage, and a voltage at both ends of the high-voltage detection resistor when the high-voltage load current of the CRT is maximized is set as a reference voltage. by comparing the amount of change of the detected the detected voltage detection resistor in the comparison detector outputs a detection voltage corresponding thereto is higher than the reference voltage, said detection voltage FBT
With the primary side of the FBT through the low-voltage output winding of
It is input to the amplifier circuit, the synchronized detection voltage is amplified by the amplifier circuit to induce a pulse, and the pulse is input to the primary side of the pulse transformer for reverse conversion, and the output voltage of the secondary side of the pulse transformer is converted. Is superimposed on the primary side of the FBT. When the high-voltage load on the secondary winding of the FBT increases, the amount of drop in the high-voltage output voltage is compared with a reference voltage, and a detection voltage corresponding to the potential difference is generated. F
It is superimposed on the low-voltage output of the FBT in order to synchronize with the BT, and a pulse is induced by the comparison amplifier circuit, so that the pulse converted inversely by the pulse transformer becomes small, and the primary-side collector pulse of the FBT is always constant. , A stable high output voltage can be obtained. An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing an application example of the high voltage generating circuit of the embodiment. FIG. 2 shows the collector voltage of the horizontal output transistor when the high voltage load current is minimum and the pulse waveform generated on the secondary side of the pulse transformer. FIG. 3 and FIG. 3 are characteristic diagrams showing the relationship between the high-voltage load current and the high-voltage output voltage when the high-voltage generation circuit of the embodiment is used. First, the configuration of the high-voltage generation circuit of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a horizontal deflection circuit;
BT, 3 is a high voltage correction circuit, 4 is a horizontal output transistor,
5 is a damper diode, 6 is a resonance capacitor, 7 is a horizontal deflection coil, 8 is an S-shaped correction capacitor, 9 is a low voltage coil, 10 is a high voltage coil, 11 is an additional voltage generation coil, 1
2 is a high voltage rectifier diode, 13 is a bleeder resistor, 14
Is a high-voltage detection resistor, 15 is a comparison detector, 16 is an amplification circuit,
17 is a pulse transformer, and 18 is a bias voltage. The FBT 2 has a built-in bleeder resistor 13 for reducing the amount of high-voltage output voltage fluctuation, and a lower end connected to a high-voltage detection resistor 14. As shown by the dotted line in FIG. 3, the high-voltage output voltage applied to the cathode-ray tube increases and decreases according to the load current, and becomes maximum when the load current is zero, and becomes minimum when the load current is maximum. The voltage at both ends of the high-voltage detection resistor 14 varies depending on the increase or decrease of the high-voltage load current. The amount of the change is detected, and a reference voltage based on the voltage at both ends of the high-voltage detection resistor 14 when the high-voltage load current is maximum. And a comparison detector 15 that operates when the voltage is higher than the reference voltage is provided to generate a detection voltage. The detected voltage generated therefrom is superimposed on the added voltage generating coil 11 of the FBT 2 to synchronize the horizontal cycle with the collector voltage waveform of the horizontal output transistor 4 shown in FIG. The synchronized detection voltage is amplified by the amplifier circuit 16, input to the primary side of the pulse transformer 17, and inversely converted to obtain a secondary output voltage of the pulse transformer 17 shown in FIG. The AC component of the collector voltage Vopo of the horizontal output transistor 4 when the high-voltage load current is minimum in the same figure (b) is expressed by the following equation: Vopo = (π / 2) · (Ts / Tp) · Eb Where Tp is the ON period of the collector pulse at AC = 0, Ts is the OFF period of the collector pulse,
b is a bias power supply voltage. Assuming that the high-voltage output voltage variation of the FBT ₂ is ΔE ₂ and the winding ratio is N, the maximum voltage Vt ₂ of the alternating current required output voltage of the secondary side of the pulse transformer 17 is Vt ₂ = E ₂ / N ≒ Vopo−Vopmax (7) Here, Vopmax indicates the AC component of the horizontal output transistor collector voltage when the high-voltage load current is maximum. Further, the high voltage output voltage E ₂ is represented by E ₂ = N · Vop (8). Further, a composite voltage Vt ₂ ′ in which Vt ₂ is superimposed on Vop ₂ when the high-voltage correction circuit is provided is represented by Vt ₂ ′ = Vop−Vt ₂ (9). Here, assuming that N = 32 and E ₂ = 800 V, Vt ₂ = 25 V. FIG. 3 is a characteristic diagram showing a relationship between the high voltage load current and the high voltage output voltage. When the high voltage load current is maximum, Vt ₂ is 0.
V, the high-voltage output voltage E ₂ becomes the same as the product of the turns ratio N and the AC component Vop of the collector voltage of the horizontal output transistor 4, and as the high-voltage load current decreases, the secondary voltage of the pulse transformer 17 decreases. The required output voltage on the side is applied to the collector voltage of the horizontal output transistor according to the rise amount of the high voltage output voltage. When the high-voltage load current is zero, Vt ₂
Is maximum, the combined voltage Vt ₂ ′ of Vop and Vt ₂ is always constant, and E ₂ shown by the solid line in FIG. 3 is always constant, and the high voltage output voltage is stabilized. As described above, according to the present invention,
Even if the high-voltage load current increases relatively inexpensively, a stable high-voltage output voltage can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an application example of a high-voltage generation circuit according to an embodiment of the present invention. FIG. 2 shows a collector voltage waveform (S) of a horizontal output transistor.
W. ON), the output voltage waveform on the secondary side of the pulse transformer, the collector voltage waveform of the horizontal output transistor (SW.
FIG. 6 is a waveform diagram showing the state when the switch is OFF. FIG. 3 is a characteristic diagram showing a relationship between a high voltage load current and a high voltage output voltage. FIG. 4 is a circuit diagram showing an application example using a conventional saturable transformer. FIG. 5 is a characteristic diagram showing a relationship between a control winding current and a controlled winding inductance of a conventional saturable transformer. FIG. 6 is a characteristic diagram showing a relationship between a high voltage load current and a high voltage output voltage of a conventional high voltage stabilizing circuit using a saturable transformer. FIG. 7 is a waveform diagram showing an output voltage waveform of a horizontal output circuit. [Description of Signs] 1 horizontal deflection circuit 2 FBT 3 high voltage correction circuit 13 bleeder resistor 14 high voltage detection resistor 15 comparison detector 16 amplifier circuit

Claims (1)

(57) In a high-voltage generating circuit in which a horizontal deflection output circuit and a flyback transformer are integrally connected and a high-voltage output voltage is applied from the flyback transformer to a cathode ray tube, the flyback transformer The voltage detected by the high-voltage detection resistor from the amount of change in the high-voltage output voltage applied to the cathode-ray tube as a detection voltage, the voltage across the high-voltage detection resistor at the maximum high-voltage load current of the cathode-ray tube as a reference voltage, and the reference voltage and the reference voltage by comparing the amount of variation of the detected voltage detected by the pressure detection resistor in the comparison detector outputs a detection voltage corresponding thereto is higher than the reference voltage, the flyback Trang the detected voltage
Primary of the flyback transformer through the low-voltage output winding of the
Input to the amplifier circuit in synchronism with the side, the synchronized detection voltage is amplified by the amplifier circuit to induce a pulse, and the pulse is input to the primary side of the pulse transformer for reverse conversion, and the pulse transformer is converted. A high-voltage generating circuit having a configuration in which an output voltage of a secondary side is superimposed on a primary side of a flyback transformer.