JPH10290377A - High voltage power source circuit for multi-scanning crt monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fix the ripple components of a high voltage regardless of the frequency of horizontal oscillation signals by switching the resonance capacitor and resonance coil of a fly-back transformer primary side winding corresponding to the frequency of the horizontal oscillation signals and fixing the ratio of the horizontal effective time and horizontal fly-back time of a fly-back voltage supplied to a fly-back transformer primary side. SOLUTION: FETs 1d, 1e, 2f and 2i are turned on/off by resonance switching signals F15A...65B, capacitors 1a, 1b and 1c and coils 2c and 2d are switched and capacitance CR and inductance LR as the resonance capacitor and the resonance coil are decided. For the decision of the CR and the LR, TS/TR is fixed based on the fact that the fly-back voltage B, the horizontal effective period TS and the horizontal fly-back period TR are VB=(π/2).(TS/TR).ECC+ ECC and TR=π(LR.CR)<1/2> . Thus, the size of the ripple components of the high voltage VHI is almost fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-scan type CR configured to operate at a plurality of horizontal synchronizing signal frequencies.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage power supply circuit of a T monitor, and more particularly to a circuit for keeping a ripple component of a high voltage constant regardless of its frequency.

[0002]

2. Description of the Related Art In a multi-scan CRT monitor, it is necessary to keep the luminance and horizontal size of a display image on the CRT monitor constant at the frequency of the corresponding horizontal synchronizing signal. Therefore, in the high-voltage power supply circuit of the multi-scan CRT monitor, it is necessary to maintain a constant horizontal deflection current for deflecting the electron beam of the CRT in the horizontal direction and a high voltage for the anode voltage for operating the CRT irrespective of the frequency. . For this purpose, the high-voltage power supply circuit of the multi-scan CRT monitor comprises a horizontal deflection circuit and a high-voltage generation circuit as a common circuit as in Conventional Example 1, or separate dedicated circuits as in Conventional Example 2. I was doing it.

(Conventional Example 1) FIG. 3 shows three types of conventional horizontal synchronizing signals (frequency: 15 kHz, 32 kHz, 65 kHz).
1 is a block diagram of a high-voltage power supply circuit of a multi-scan CRT monitor corresponding to FIG. In FIG. 3, reference numeral 21 denotes a voltage control unit 2.
A voltage regulator unit comprising 1a and a voltage detection unit 21b;
5 is a flyback transformer, 6 is a rectifying unit, 7 is a horizontal deflection transistor, 8 is a damper diode, 31 is a resonance capacitor, 41 is a horizontal deflection coil, and 51 is a linearity correction capacitor switching unit. The voltage regulator unit 21 is connected to one end 5a of the primary winding of the flyback transformer 5, and the other end 5b is connected to the horizontal deflection transistor 7, the resonance capacitor 31, the damper diode 8, the horizontal deflection coil 41, and the linearity correction. Capacitor switching unit 51
Are connected in parallel, and one of the parallel circuits is grounded. One end 5c of the secondary winding of the flyback transformer 5 is connected to the rectifying unit 6, and the other end 5d is grounded. A terminal 121 is a supply terminal of the DC voltage VCC1, a terminal 122 is an input terminal of the horizontal oscillation signal HOS corresponding to the frequency of the horizontal synchronization signal, terminals 123 and 124 are input terminals of the correction capacitor switching signals F32C and F15C, and a terminal 125 is not shown. This is an output terminal for a high voltage VHI serving as an anode voltage of the CRT.

Next, the operation of this circuit will be described.
The linearity correction capacitor switching section 51 switches the linearity correction capacitor in accordance with the frequency of the horizontal oscillation signal HOS, and has no direct relation to the present invention, so that the description of the operation is omitted. The DC voltage ECC1 from the voltage regulator unit 21 is supplied to one end 5a of the primary winding of the flyback transformer 5. In the voltage regulator unit 21, the DC voltage ECC1 is detected by the voltage detection unit 21b, and the voltage is controlled by the voltage control unit 21a so that the difference between the detected voltage and the reference voltage VREF1 is eliminated. The horizontal deflection transistor 7 is switched by the horizontal oscillation frequency HOS. As is well known, when the horizontal deflection transistor 7 performs a switching operation at the cycle of the horizontal oscillation signal HOS, the resonance capacitor 31 and the horizontal deflection coil 41 resonate, and the horizontal deflection coil 41 has a sawtooth horizontal deflection current I4.
1 flows to deflect the electron beam of the CRT (not shown) horizontally. Simultaneously, a flyback voltage VB of a half sine wave is generated at the collector of the horizontal deflection transistor 7 and supplied to one end 5b of the primary winding of the flyback transformer 5 to be boosted by the secondary winding. Then, it is rectified by the rectification unit 6 to become the high voltage VHI. This high voltage VHI is the CRT
It becomes the anode voltage of the CRT that operates the monitor.

[0005] Flyback voltage VB, horizontal deflection current I4
1. The horizontal retrace time TR is a DC voltage supplied to one end 5a of the primary winding of the flyback transformer 5 as ECC1, and the horizontal valid time is TS (= cycle of the horizontal oscillation signal HOS−horizontal retrace time TR). If the inductance of the horizontal deflection coil 41 is L41, the mutual inductance of the primary winding of the flyback transformer 5 is LFB (LFB is sufficiently larger than L41), and the capacitance of the resonance capacitor 31 is C31, It can be obtained by an equation. VB = (π / 2) · (TS / TR) · ECC1 + ECC1 (1) I41 = ECC1 · TS / L41 (2) TR = π (L41 · C31) ^1/2 (3) (1) to (3) From the equation, since the inductance L41 of the horizontal deflection coil 41 and the capacitance C31 of the resonance capacitor 31 are fixed, the horizontal retrace time TR is always constant regardless of the change in the frequency of the horizontal oscillation signal HOS. On the other hand, since the horizontal effective time TS changes with the change of the horizontal oscillation signal HOS, in order to keep the flyback voltage VB and the horizontal deflection current I41 constant, the DC voltage ECC1 supplied to the flyback transformer 5 (that is, the DC voltage VCC
It is necessary to change 1) according to the frequency change of the horizontal oscillation signal HOS. That is, when the frequency of the horizontal oscillation signal HOS increases, the horizontal effective time TS becomes shorter. Therefore, the DC voltage VCC1 is increased in proportion to the increase in the frequency. For example, if this frequency is 15 kHz, VC
C1 = 40V, VCC1 = 70V for 32kHz,
In the case of 65 kHz, VCC1 = 140V.

(Conventional Example 2) FIG. 5 shows three types of conventional horizontal synchronizing signals (frequency: 15 kHz, 32 kHz, 65 kHz).
And FIG. 6 is a block diagram of a horizontal deflection circuit for a multi-scan CRT monitor.
First, the high voltage power supply circuit will be described. In FIG.
61 is a voltage regulator unit, and 62 is a DC-DC converter. Terminal 151 is a supply terminal for DC voltage VCC2,
A terminal 152 is an output terminal for the high voltage VHI for the anode of the CRT. The voltage regulator 61 has a terminal 15
1 is supplied with a DC voltage VCC2.
Voltage fluctuations and ripple components of CC2 are absorbed. The DC voltage ECC2 thus obtained is converted to a DC-DC converter 6
2 to generate a high voltage VHI for the anode of the CRT. The high voltage VHI thus generated has a constant value irrespective of the frequency of the horizontal oscillation signal HOS.

Next, the horizontal deflection circuit will be described. In FIG. 6, 9 is a voltage regulator section, and 12 is a conventional example 1.
A choke coil serving as a primary winding of the flyback transformer 5, a horizontal deflection transistor 7, a damper diode 8, a resonance capacitor switching unit 11 for switching a resonance capacitor according to the frequency of the horizontal oscillation signal HOS, Reference numeral 13 denotes a horizontal deflection coil, and reference numeral 51 denotes a linearity correction capacitor switching unit that switches the linearity correction capacitor according to the frequency of the horizontal oscillation signal HOS. The voltage regulator 9 is connected to one end 12a of the choke coil 12, and the other end 12b of the horizontal deflection transistor 7, the resonance capacitor switching unit 11, the damper diode 8, the horizontal deflection coil 13 and the linearity correction capacitor switching unit 51. A series circuit is connected in parallel, and one of the parallel circuits is grounded.

The resonance capacitor switching section 11 includes the capacitor 1
1a and a switching element, for example, a series circuit of a field effect transistor (hereinafter referred to as FET) 11d, a series circuit of a capacitor 11b and an FET 11e, and a parallel circuit of a capacitor 11c. By switching the connection state of the resonance capacitor 11b, the capacitance of the resonance capacitor switching unit 11 can be switched.

A terminal 153 is a supply terminal for the DC voltage VCC3, a terminal 154 is an input terminal for the horizontal oscillation signal HOS, and terminals 155 and 156 are resonance capacitor switching signals F15A and F15.
Input terminals of 32A, terminals 157 and 158 are input terminals of correction capacitor switching signals F15C and F32C. The DC voltage VCC3 is supplied from the terminal 153 to the voltage regulator section 9.
Is supplied to the base of the horizontal deflection transistor 7, and the horizontal oscillation signal HOS is input to the resonance capacitor switching unit 11.
Receive the resonance switching signals F15A and F32A.

FIG. 7 shows the relationship between the frequency of the horizontal oscillation signal HOS and the resonance switching signals F15A and F32A. 7A shows the horizontal oscillation signal HOS, FIG. 7B shows the resonance capacitor switching signal F15A, and FIG. 7C shows the resonance capacitor switching signal F32A.

Next, the operation of this circuit will be described.
The operation of the linearity correction capacitor switching unit 51 is the same as that of the conventional example 1 and is not directly related to the present invention, so that the description of the operation is omitted.

The DC voltage ECC3 adjusted by the voltage regulator 9 so as to be constant is supplied to one end 12a of the choke coil 12. The horizontal deflection transistor 7 is switched by the horizontal oscillation signal HOS. As is well known, the horizontal deflection transistor 7 performs the switching operation of the cycle of the horizontal oscillation signal HOS, so that the resonance capacitors 11a, 11b, 11c and the horizontal deflection coil 13 resonate. The deflection current I13 flows to deflect the electron beam of the CRT (not shown) horizontally.

As described in the first conventional example, the horizontal deflection current I13 is T for the cycle of the horizontal oscillation signal HOS, TR for the horizontal retrace time, ECC3 for the DC voltage supplied to the choke coil 12, and the horizontal deflection coil IOS. Assuming that the inductance of L13 is L13 and the capacitance of the resonance capacitor switching unit 11 is C11, I13 = ECC3 · (T-TR) / L13. Where TR = π (L13 · C11) ^1/2
It is. Here, the FET1 of the resonance capacitor switching unit 11
1d and 11e are resonance capacitor switching signals F15A and F3
In response to 2A, as shown in (D) and (E) of FIG.
Since the capacitor is turned off, the resonance capacitance C11 is as follows, assuming that the capacitances of the capacitors 11a, 11b, and 11c are C11a, C11b, and C11c, respectively. (1) When the horizontal oscillation signal HOS is 15 kHz C11 = C11a + C11b + C11c (2) When the horizontal oscillation signal HOS is 32 kHz C11 = C11b + C11c (3) When the horizontal oscillation signal HOS is 65 kHz C11 = C11c Therefore, for example, C11a = 18, 000 pF, C11
b = 6,200 pF, C11c = 3,300 pF,
And the frequency of the horizontal synchronizing signal is 15 k
40V in the case of Hz, 80V, 65 in the case of 32kHz
If the frequency is 160 V in the case of kHz, the horizontal deflection current I13
Becomes constant regardless of the frequency of the horizontal oscillation signal HOS.

[0014]

However, such prior arts have the following disadvantages, respectively. (1) In the method of Conventional Example 1, as described above, when the frequency of the horizontal oscillation signal HOS increases, the DC voltage VCC1 is increased in proportion to the increase, so that the flyback voltage VB
Becomes a substantially constant value, and a substantially smooth high voltage VHI including a ripple component is generated. FIG. 4 shows the flyback voltage VB and the high voltage VH at each horizontal oscillation signal HOS.
FIG. 4 is a diagram schematically illustrating the magnitude of a ripple component VR of I.
(A) and (B) show the flyback voltage VB15 and the ripple component VR15 when the frequency is 15 kHz,
(C) and (D) show the flyback voltage VB32 and the ripple component VR32 when the frequency is 32 kHz.
(E) and (F) show the flyback voltage VB65 and the ripple component VR65 when the frequency is 65 kHz.

As is well known, the high voltage VHI is obtained by rectifying the pulse-shaped high voltage obtained by boosting the flyback voltage VB by the flyback transformer 5 by charging and discharging the capacitor of the rectifier 6. The ripple component is determined by the ratio between the horizontal effective time TS and the horizontal flyback time TR. When the frequency of the horizontal oscillation signal HOS increases, the horizontal effective time TS decreases in proportion to the horizontal effective time TS. On the other hand, in this circuit, the horizontal retrace time TR is constant.
The relationship among the ripple components VR15, VR32, and VR65 at kHz, 32 kHz and 65 kHz is VR15>VR32> VR65, and the magnitude of the ripple component fluctuates depending on the frequency. This fluctuation is a distortion of the image displayed on the CRT monitor. And cause size fluctuations.

(2) In the method of the second conventional example, a high-frequency pulse-like high voltage is boosted by a switching circuit inside a DC-DC converter, and then smoothed.
Have gained. Therefore, the high voltage VHI does not have a ripple component corresponding to the frequency of the horizontal oscillation signal HOS, but has a ripple component due to the switching frequency of the switching circuit in the DC-DC converter. Since this ripple component is asynchronous with the frequency of the horizontal oscillation signal HOS, noise tends to appear on the display screen of the CRT monitor. In particular, in the case of a multi-scan CRT monitor, the frequency of a specific horizontal oscillation signal HOS and the frequency of this ripple component interfere with each other, and beat noise may be generated in a displayed image. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a high voltage power supply circuit of a multi-scan CRT monitor in which a ripple component of a high voltage for a CRT anode can be constant regardless of the frequency of a horizontal oscillation signal HOS. The purpose is to:

[0017]

SUMMARY OF THE INVENTION The present invention provides a C
The ripple component of the high voltage for the anode of the RT depends on the ratio between the horizontal effective time and the horizontal retrace time, and is made in accordance with the frequency of the horizontal oscillation signal HOS. The ratio of the horizontal retrace time to the horizontal effective time of the flyback voltage supplied to the primary side of the flyback transformer by switching the capacitance of the resonance capacitor of the primary winding and the inductance of the resonance coil is determined by the frequency of the horizontal oscillation signal HOS. Is kept substantially constant even if the value changes.

Here, in addition to the resonance capacitance,
The reason for switching the resonance inductance at the same time is as follows. Even switching only the resonance capacitance,
Although it is possible to maintain the ratio between the horizontal effective time and the horizontal retrace time to a constant value, in this method, the inductance of the resonance circuit is only the mutual inductance of the primary winding of the flyback transformer, and Since the mutual inductance is large, the impedance increases when the resonance frequency increases, and the current in the resonance circuit decreases. Therefore, when the resonance frequency is high and the load current of the high-voltage output increases, the flyback voltage increases. This is because the waveform is distorted, the load fluctuation becomes large, and the variable range of the high-voltage output voltage becomes narrow.

On the other hand, by switching both the resonance capacitance and the resonance inductance, the impedance of the resonance coil of the resonance circuit can be maintained at a substantially constant value even when the frequency changes, and the impedance of the resonance coil can be maintained. Can be smaller than switching only the capacitance of the resonance capacitor, so that sufficient current flows in the resonance circuit, so that even when the resonance frequency is high and the load current is large, the flyback voltage waveform is not distorted,
This is because load fluctuation is small and the variable range can be widened.

In the high-voltage power supply circuit of the multi-scan CRT monitor according to the present invention, a DC voltage is supplied to one end of a primary winding of a flyback transformer, and a horizontal deflection transistor, a resonance capacitor, a resonance coil and A resonance circuit with a damper diode connected in parallel is connected, this horizontal deflection transistor is switched by a horizontal oscillation signal, a flyback voltage is generated by a resonance capacitor and a resonance coil, and a flyback transformer secondary winding is generated. In a high-voltage power supply circuit of a CRT monitor that generates an anode voltage of a CRT by rectifying a high voltage to be applied, a ratio between a horizontal effective time and a horizontal retrace time is constant regardless of a frequency of a horizontal oscillation signal. A resonant capacitor that determines the capacitance as a resonant capacitor according to the frequency of this horizontal oscillation signal It is characterized in that it has a replacement unit, and a resonant coil switching unit which determines the inductance of the resonant coil.

The resonance capacitor switching section of the present invention comprises a parallel circuit including a first capacitor, a series circuit of a second capacitor and a first switching element, and a parallel circuit of a series circuit of a third capacitor and a second switching element. According to the frequency of the oscillation signal, the connection state of the first, second, and third capacitors is switched by appropriately turning on / off the first and second switching elements to determine the capacitance as a resonance capacitor. It is a feature.

Further, the resonance coil switching section of the present invention includes a parallel circuit including a series circuit of a second coil, a first correction capacitor, a third switching element, and a series circuit of a second correction capacitor and a fourth switching element. The first coil is connected in series, and the third and fourth coils are set according to the frequency of the horizontal oscillation signal.
The connection state of the first and second resonance coils is switched by appropriately turning on / off the switching element, and the inductance as the resonance coil is determined.

Further, when the frequency of the horizontal synchronizing signal changes, the high voltage power supply circuit of the multi-scan CRT monitor according to the present invention supplies a voltage to one end of the primary winding of the flyback transformer for a predetermined time. And a current limiter for reducing a DC voltage to be applied.

[0024]

FIG. 1 shows three types of horizontal synchronizing signals (having a frequency of 15 kHz and 32 kHz) showing an embodiment of the present invention.
FIG. 3 is a block diagram of a high-voltage power supply circuit of a multi-scan CRT monitor capable of supporting (z, 65 kHz). In the present invention, the horizontal deflection circuit and the high voltage generation circuit are created as separate dedicated circuits. Further, since the same horizontal deflection circuit as that of the conventional example 2 is used, the description is omitted.

In FIG. 1, 1 is a resonance capacitor switching unit for determining a resonance capacitance, 2 is a resonance coil switching unit for determining a resonance inductance, 5 is a flyback transformer, and 4 is a primary winding of the flyback transformer 5. , A voltage regulator for limiting the supply voltage ECC to the flyback transformer 5, and a rectifier 6. A voltage regulator unit 4 is connected to one end 5a of a primary winding of the flyback transformer 5, and a horizontal deflection transistor 7, a resonance capacitor switching unit 1, a damper diode 8, a resonance coil switching is connected to the other end 5b. The units 2 are connected in parallel, and one of the parallel circuits is grounded. The rectifier 6 is connected to the secondary winding 5c of the flyback transformer 5, and the other end 5d is provided.
Is grounded. The output of the rectifier 6 is connected to the voltage detector 4b.

The resonance capacitor switching unit 1 includes a series circuit of a capacitor 1c as a first capacitor, a capacitor 1a as a second capacitor, and a first switching element, for example, a field effect transistor (hereinafter referred to as FET) 1d, A parallel circuit comprising a series circuit of a capacitor 1b as a capacitor and an FET 1e as a second switching element.
By appropriately turning on / off 1d and 1e, the capacitor 1
The connection state of a, 1b, and 1c is switched to determine the capacitance as a resonance capacitor.

The resonance coil switching unit 2 includes a coil 2d as a second coil and a capacitor 2e as a first correction capacitor.
And a series circuit of a third switching element FET2f,
A parallel circuit comprising a series circuit of a capacitor 2h as a second correction capacitor and an FET 2i as a fourth switching element, and a series circuit of a coil 2c as a first coil;
Depending on the frequency of the horizontal oscillation signal HOS, the FETs 2f, 2i
Is turned on / off as appropriate to switch the connection state of the coils 2c and 2d to determine the inductance as the resonance coil.

In the resonance coil switching unit 2, the FET 2f
2b and a diode 2 connected between the drain of the flyback and one end 5b of the primary winding of the flyback transformer 5.
a series circuit is a protection circuit for preventing the destruction of the FET 2f,
The series circuit of the resistor 2k and the diode 2j connected between the drain of the FET 2i and one end 5b of the primary winding of the flyback transformer 5 is a protection circuit for the FET 2i.

The resistor 2m and the capacitor 2n connected to the gate of the FET 2f are a first off-delay circuit for delaying the off-time of the FET 2f, and the resistor 2p and the capacitor 2q connected to the gate of the FET 2i are
2D is a second off-delay circuit that delays the off-time of 2i.

In the voltage limiter 3, the resistors 3b and 3c and the transistor 3d connected in series between the terminal 101 and the ground determine the bias voltage of the FET 3e according to the signal input from the terminal 102 via the resistor 3a. First
The bias circuit, FET3e, has a drain connected to the terminal 101 and a source connected to the transistor 3g via the resistor 3f.
And a gate connected to a connection point of the resistors 3b and 3c, and a second bias circuit for setting the bias of the transistor 3g by the bias of the first bias circuit. The collector of the transistor 3g is connected to the terminal 101, and supplies a DC voltage limited according to the bias voltage of the second bias circuit from the emitter to the voltage regulator unit 4.
To supply.

The voltage regulator 4 comprising the voltage controller 4a and the voltage detector 4b receives the DC voltage supplied from the voltage limiter 3 and detects the output voltage VHI of the rectifier 6 with the voltage detector 4b. In the control unit 4a, the reference voltage VREF
In response to the change in the load current of the high voltage VHI, the flyback voltage VB is dynamically changed to perform the stabilization control of the high voltage VHI. Terminal 101
Is an input terminal of a DC voltage VCC, a terminal 102 is an input terminal of a high voltage limit signal HVC that becomes "1" for a certain time every time the frequency of the horizontal oscillation signal HOS changes, a terminal 103 is an input terminal of the horizontal oscillation signal HOS, and a terminal. 104 and 105 are input terminals of a first resonance switching signal F15A for switching a resonance capacitor and a second resonance switching signal F32A, and terminals 106 and 107 are inputs of a third resonance switching signal F32B and a fourth switching signal F65B for switching a resonance coil. A terminal 108 is an output terminal of a high-voltage output voltage VHI serving as an anode voltage of the CRT.
09 and 110 are negative power supply voltage input terminals.

Referring to FIG. 1, the operation of switching the resonance capacitor and the resonance coil will be described first. FIG. 2 shows the resonance switching signal. 2A shows a horizontal oscillation signal HOS, FIG. 2B shows a first resonance switching signal F15A for switching a resonance capacitor, FIG. 2C shows a second resonance switching signal F32A for switching a resonance capacitor, and FIG. The third resonance switching signal F32B for switching the resonance coil, (E) is a fourth resonance switching signal F65B for switching the resonance coil. Since these resonance switching signals are signals as shown in FIG. 2,
By the change of the horizontal oscillation signal HOS, the FETs 1d, 1e,
Since 2f and 2i are turned on / off as shown in FIGS. 2F, 2G, 2H and 2I, the capacitance of the capacitor 1c is C15, the capacitance of the capacitor 1a is C11, and the capacitance of the capacitor 1b. To C13,
Assuming that the inductance of the coil 2c is L23, the inductance of the coil 2d is L24, and the mutual inductance of the primary winding of the flyback transformer 5 is LFB, the capacitance CR of the resonance capacitor and the inductance LR of the resonance coil are as follows. .

(1) When horizontal oscillation signal HOS is 15 kHz Resonance capacitance CR = C11 + C13 + C15 Resonance inductance LR = LFB (2) When horizontal oscillation signal HOS is 32 kHz Resonance capacitance CR = C13 + C15 Resonance inductance LR = L23 + L24 (3) Horizontal oscillation When signal HOS is 65 kHz Resonance capacitance CR = C15 Resonance inductance LR = L23

The flyback voltage VB, which is the basis of the high voltage VHI for the anode of the CRT, and the horizontal flyback period TR
Is obtained by the following equation as described in the conventional example 1. VB = (π / 2) · (TS / TR) · ECC + ECC TR = π (LR · CR) ^1/2 Therefore, for example, C11 = 7,200 pF, C13 =
3,300 pF, C15 = 1,600 pF, L23 = 4
By setting 50 μH and L24 = 950 μH, the flyback voltage VB, the horizontal effective time TS and the horizontal flyback time TR
Is constant regardless of the frequency of the horizontal oscillation frequency HOS.

Next, the operation of the protection circuit will be described. First, protection during a transition period when the frequency of the horizontal oscillation signal HOS changes will be described. This protection is needed for the following reasons: A high-voltage power supply V
A high frequency current of about 2 to 3 A flows due to the load current of the HI, but as shown in FIG. 2, the FET 2f or the FET 2i is turned off, and either the coil 2d or the coil 2c or the coil 2d ,
It is necessary to turn off both 2c. This FET 2f, 2
When turning off i, the current flowing through the coils 2c and 2d is cut off. As is well known, an induced voltage generated in the coils 2d and 2c is applied to the drains of the FETs 2f and 2i during a transition period when the FETs 2f and 2i are turned off.

As is well known, the induced voltage e generated during the off transition period of the FETs 2f and 2i is obtained by the following equation. e = −L (di / dt) L: Inductance of coil di: Change amount of current flowing in coil dt: Change time of current flowing in coil Therefore, make sure that this induced voltage e does not exceed the withstand voltage of FETs 2f and 2i. It must be as small as possible.

In this circuit, the voltage limiter 3 is used to reduce the DC voltage VCC to a constant voltage for a certain period of time during the transition period of frequency switching to reduce the current flowing through the resonance coil. The induced voltage e is reduced by lengthening the off-time in the second off-delay circuit.
Next, the operation will be described.

As shown in FIG. 2 (J), the high voltage limit signal HV
C is a signal that becomes logic “1” for a certain period of time when the horizontal oscillation signal HOS changes, and the voltage is limited by the high-voltage control signal HVC. As is well known, this type of voltage limiter is
When the high voltage limit signal HVC is “0”, the transistor 3
Since d is off and the collector current does not flow through the transistor 3d, the gate voltage of the source follower FET 3e is almost the same as the DC voltage VCC, and the source voltage is also almost the same as the DC voltage VCC. In addition, the base voltage of the transistor 3g, which is an emitter follower, is also substantially the same as the DC voltage VCC.
Is supplied with the DC voltage VCC input to the terminal 101 as it is.

On the other hand, during the off transition period, the high voltage control signal HV
Since C becomes “1” and the transistor 3d is turned on, F
Since the bias voltage of the gate of the ET 3e is divided by the resistors 3b and 3c, when the resistors 3b and 3c have the same resistance value, the source voltage of the FET 3e becomes 1/2 of the normal voltage, and therefore the emitter of the transistor 3g is also reduced. Normal voltage 1
/ 2 voltage, and the voltage regulator unit 4 also supplies a normal 1
/ 2 voltage is supplied. The voltage regulator unit 4 detects the voltage of the high voltage VHI and controls the DC voltage ECC so that there is no difference from the reference voltage VREF.
When the input voltage of the voltage regulator unit 4 is reduced to half of the normal voltage, as a result, the terminal 5 of the flyback transformer 5
The DC voltage ECC supplied to “a” also becomes の of the normal value.

Therefore, during the off transition period, the coils 2c, 2d
Of the current flowing through the DC voltage ECC is reduced to about て compared to the case where the DC voltage ECC is completely “zero” V. Further, by selecting the values of the resistors and capacitors of the first and second off-delay circuits respectively added to the gates of the FETs 2f and 2i and determining the time constant, the off time dt is quadrupled, and the induced voltage is increased. e is finally reduced to about 1/8.

Next, protection in the case where the frequency of the horizontal oscillation signal HOS decreases and both of the FETs 2f and 2i are turned off (steady state) will be described. This protection is needed for the following reasons: This is capacitor 2h and FET
Parallel resonance occurs in the series circuit of the output capacitance of 2i and the series circuit of the inductance of the coil 2d, the capacitor 2e, and the output capacitance of the FET 2f, and a voltage larger than the flyback voltage applied to the coil 2c is generated at the drain of the FET, This voltage exceeds the withstand voltage of the FETs 2f and 2i, and
This is because the ETs 2f and 2i may be damaged. In this circuit, the voltage generated by the parallel resonance is connected to the resistor 2b.
A voltage equal to or higher than the flyback voltage is applied to the FETs 2f and 2i by allowing the current to flow to the one end 5b of the primary winding of the flyback transformer 5 in the series circuit of the diode 2a and the resistor 2k and the diode 2j. Has been prevented.

[0042]

According to the present invention, as described above,
A resonance capacitor switching unit for determining a capacitance of a resonance capacitor for determining a flyback voltage and a resonance coil switching unit for determining an inductance of a resonance coil in accordance with a frequency of a horizontal oscillation signal corresponding to a horizontal synchronization signal; Since the ratio of the horizontal retrace time to the horizontal effective time of the flyback voltage supplied to the primary winding of the flyback transformer is kept substantially constant even when the frequency of the horizontal oscillation signal HOS changes, the horizontal Oscillation signal HOS
Irrespective of the frequency, the magnitude of the ripple component of the high voltage VHI, which is the anode voltage of the CRT, can be made substantially the same, so that even if the frequency of the horizontal oscillation signal changes, the display image on the CRT monitor becomes distorted or the size changes. Will not happen. Further, since the ripple component is synchronized with the frequency of the horizontal oscillation signal HOS, no beat noise is generated in the displayed image (claims 1, 2, and 3).

Further, according to the present invention, the DC voltage supplied to the flyback transformer for a certain period of time at the time of the frequency change is reduced to half of the normal voltage by using the voltage limiter, and an off-delay circuit is added to the switching element. Since the induced voltage is reduced to about 1/8 as a whole by reducing the off time of the switching element to 1/4, during the transition period in which the inductance of the resonance coil is switched in accordance with the frequency of the horizontal oscillation signal HOS. The voltage induced by the coil when the switching element is turned off can be reduced, and the destruction of the switching element can be prevented. In addition, since the DC voltage supplied to the flyback transformer is reduced to ２ and the high voltage VHI is also reduced to １ ／, the high voltage VHI is completely set to “zero” V during the switching transition period of the switching element. Compared with the case, the charge amount of the CRT anode when returning the high voltage VHI to the normal voltage after the end of the switching transition period can be reduced to about 、, and the static electricity induced on the CRT monitor screen is reduced to １ ／. Since it is reduced, it is possible to reduce the discomfort felt by the operator (claim 4).

[Brief description of the drawings]

FIG. 1 is a block diagram of a high-voltage power supply circuit of a multi-scan CRT monitor that can support three types of horizontal synchronization signals according to an embodiment of the present invention.

FIG. 2 is a timing chart illustrating operations of a resonance capacitor switching unit and a resonance coil switching unit according to the present invention.

FIG. 3 is a block diagram of a conventional high-voltage power supply circuit of a multi-scan CRT monitor that can support three types of horizontal synchronization signals.

FIG. 4 is a diagram schematically showing the frequency of each horizontal synchronization signal and the magnitude of a flyback voltage VB and a ripple component VR of a high voltage VHI at that time in the circuit of FIG. 3;

FIG. 5 is a block diagram of another conventional high voltage power supply circuit of a multi-scan CRT monitor corresponding to three types of horizontal synchronization signals.

6 is a block diagram of a horizontal deflection circuit used simultaneously with the conventional example of FIG.

FIG. 7 is a timing chart for explaining the operation of the resonance capacitor switching section of the horizontal deflection circuit of the conventional example of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resonant capacitor switching part 2 Resonant coil switching part 3 Voltage limiting part 4 Voltage regulator part 5 Flyback transformer 6 Rectification part 7 Horizontal deflection transistor 8 Damper diode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 3/18 H04N 3/18 Z 3/23 3/23

Claims (4)

[Claims] A DC voltage is supplied to one end of a primary winding of a flyback transformer, and a resonance circuit having a horizontal deflection transistor, a resonance capacitor, a resonance coil, and a damper diode connected in parallel is connected to the other end. The horizontal deflection transistor is switched by the horizontal oscillation signal, the flyback voltage is generated by the resonance capacitor and the resonance coil, and the high voltage generated in the secondary winding of the flyback transformer is rectified to thereby rectify the anode voltage of the CRT. In a high-voltage power supply circuit of a CRT monitor, a resonance capacitor is used in accordance with the frequency of the horizontal oscillation signal so that the ratio between the horizontal effective time and the horizontal retrace time is constant regardless of the frequency of the horizontal oscillation signal. Capacitor switching section that determines the capacitance of the capacitor and the inductance of the resonant coil Multi scanning CR characterized by having a that resonant coil switching unit
High voltage power supply circuit for T monitor. 2. The resonance capacitor switching section includes a parallel circuit including a first capacitor, a series circuit of a second capacitor and a first switching element, and a parallel circuit of a series circuit of a third capacitor and a second switching element. The connection state of the first, second, and third capacitors is switched by appropriately turning on / off the first and second switching elements according to the frequency to determine the capacitance as a resonance capacitor. A high-voltage power supply circuit for a multi-scan CRT monitor according to claim 1. 3. The resonance coil switching section includes a first coil in a parallel circuit including a series circuit of a second coil, a first correction capacitor, a third switching element, and a series circuit of a second correction capacitor and a fourth switching element. Are connected in series, and the connection state of the first and second resonance coils is switched by appropriately turning on and off the third and fourth switching elements according to the frequency of the horizontal oscillation signal to determine the inductance as the resonance coil. 2. The high-voltage power supply circuit for a multi-scan CRT monitor according to claim 1, wherein 4. When the frequency of the horizontal oscillation signal changes,
2. A high voltage power supply for a multi-scan CRT monitor according to claim 1, further comprising a voltage limiter for reducing a DC voltage supplied to one end of a primary winding of the flyback transformer for a predetermined time. circuit.