JPH0457477A - Horizontal high voltage output circuit - Google Patents

Abstract

PURPOSE:To obtain a satisfactory regulation characteristic even to the video signal of any horizontal scanning frequency by providing a control circuit to control a first voltage regulator so as to always set voltage difference between a third direct current voltage and a second direct current voltage constant as prescribed when the beam current of a cathode ray tube is fixed by adjusting the second direct current voltage even when the various horizontal synchronizing signals of different frequencies are applied. CONSTITUTION:The control circuit of a potential drop type switching regulator 6 (the first voltage regulator) is composed of a monostable multivibrator 1, pulse driving circuit 3, horizontal synchronizing signal detection circuit 8 and switch 9. The pulse width of a pulse outputted from the monostable multivibrator 1 is decided by the time constants of a capacitor C1 and of resistors R12 and R13. The horizontal synchronizing signal detection circuit 8 detects the frequency (horizontal scanning frequency fH) of an incoming horizontal synchronizing signal, and when the horizontal scanning frequency fH is 35kHz-24kHz, the switch 9 is short-circuited. Thus, the value of voltage difference HB2-HB3 between the input and output of a series regulator 7 (second voltage regulator) can be set at a prescribed constant value 40V in a TV mode and an HDTV mode.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a horizontal high voltage output circuit. It is an object of the present invention to provide a horizontal high-voltage output circuit particularly suitable for a variable scan type display device using a CRT (cathode ray tube).

(Prior Art) In recent years, various variable scan type display devices have been developed that are capable of reproducing various video signals with different horizontal synchronizing signal frequencies (horizontal scanning frequencies).

FIG. 5 shows an example of a horizontal high voltage output circuit used in the display device.

The step-down switching regulator 6 (first voltage regulator) that converts the first DC voltage) IBI (constant power supply voltage) to the second DC voltage) IB2 is a monostable multi-type 1' breaker (hereinafter referred to as monomulti). ) 11 and a pulse drive circuit 3.

Series regulator 7 (second voltage regulator) that converts second DC voltage HB2 to third DC voltage HB3
is controlled by a high voltage output control circuit 5.

The monomulti 2, pulse drive circuit 4, horizontal output transistor Q1, damper diode D1, resonance capacitor CR, dummy deflection yoke L3, and capacitor tcs constitute a horizontal output pulse generation circuit.

In the monomulti 2 to which the horizontal synchronizing signal is input, a pulse having a pulse width determined by the time constant of the capacitance tc2 and the resistor R2 is generated, and this pulse is sent to the horizontal output transistor Q1 via the pulse drive circuit 4. and drives the horizontal output transistor Q1.

T1 is a flyback transformer, Ll is a primary winding,
L2 is a secondary winding.

D2 is a diode for rectifying and smoothing the output pulse generated in the secondary winding L2 of the flyback transformer T1 to obtain a high voltage HV.

The illustrated horizontal high voltage output circuit supplies a horizontal output pulse Vcp obtained by parallel resonance to a flyback transformer T1 to output a high voltage HV.

This horizontal high voltage output circuit is provided with a step-down switching regulator 6 and a series regulator 7 in order to obtain a stable high voltage HV.

The step-down switching regulator 6 is a monomulti 11
and the pulse drive circuit 3, and serves to keep the horizontal output pulse Vcp constant against incoming horizontal synchronizing signals of various frequencies. Let me explain how this works.

The horizontal output pulse Vcp decreases as the frequency of the horizontal synchronizing signal (horizontal scanning frequency) increases, as shown in equation (4) below. To compensate for this drop, the DC voltage HB
3, that is, it is necessary to increase the DC voltage HB2.

Therefore, in the monomulti 11, the incoming horizontal synchronization signal is used as a trigger pulse to generate a pulse having a pulse width determined by the time constant of the capacitor C1 and the resistor R1, and this pulse is amplified by the pulse drive circuit 3 for control. The signal is supplied to the step-down switching regulator 6 as a signal. Based on this control signal, the step-down switching regulator 6 increases the DC voltage HB2 to compensate for the decrease in the horizontal output pulse Vcp when the horizontal scanning frequency becomes high.

Next, the series regulator 7 is connected to the high voltage output control circuit 5.
It functions to correct a drop in the high voltage HV caused by the current regulation characteristics of the flyback transformer T1. The current regulation characteristics of the flyback transformer T1 are as shown in FIG.
By increasing the beam current IB of T, the high voltage HV
is a characteristic that decreases.

As shown in FIG. 5, the high voltage HV is divided by resistors R3 and R4, the voltage value is detected, and the series regulator 7 is controlled by the high voltage output control circuit 5.

In this way, by providing the high voltage HV correction means, especially by providing the series regulator 7, it is possible to perform excellent correction of the high voltage HV even in the case of sudden changes in bright and dark screens. It is possible to obtain stable regulation characteristics (high voltage) and to stabilize IV (high voltage).

The circuit operation of the step-down switching regulator 6 will be further explained with reference to the circuit diagram of FIG.

FIG. 8 is a specific circuit diagram of a portion of the block diagram shown in FIG.

To supply the horizontal synchronization signal to the monomulti 11, output a pulse having a constant pulse width determined by the time constant of the capacitor C1 and the resistor R1 to the point a), and send the pulse to the transistor via the decoupling capacitor CIO. Q2 inverts and amplifies the transistor Q3. The push-pull output circuit of Q4 performs impedance conversion and current amplification. Then, the output signal of the push-pull output circuit is supplied to the P-channel FETQ5 via the decoupling capacitor C1l, and the FET
I'm driving an ETQ5.

When the gate voltage of FETQ5 becomes low and the gate voltage is lower than the source voltage by the voltage of the sum of Zener diode DIO and diode DI+, FETQ
5 is in the on state, and conversely, when the gate voltage becomes higher than the source voltage, it is in the off state, and when the point d is turned on, a voltage waveform of the same phase appears. During the ON period of the FET Q5, this is supplied as a current to the capacitor CI2 and the load to which the voltage HB2 is applied via the choke coil L10. During the off period of FETQ5, the energy stored in the choke coil LIO is transferred to the flywheel diode DI.
The loop passing through 2 supplies current to the load side.

Timing charts of this circuit are shown in FIGS. 9 and 10. Figure 9 shows TV mode (IH = 15.73kHz
), and Figure 10 shows HDTV mode (jH=33
．． 75kHz+). FIG. 11 is a diagram showing the relationship between input and output voltages of the step-down switching regulator 6.

In the HDTV mode, the horizontal scanning frequency is about twice that of the TV mode, so the voltage HB2 obtained by converting the pulse shown at point d into DC is also about twice that of the TV mode.

If 5alfix (1) is added to one horizontal scanning frequency mode and 5allix (2) is added to another horizontal scanning frequency mode, and 1ON is the pulse width (high level period) of the output pulse of the step-down switching regulator 6, +H=l
/IH...(1) HB2= Cl0N/IH) 1(Bl
・From (2), IH(1) /IH(2)・+H(2) /lH(1)
・The following relational expression is obtained: IH2(1) /HB2 (2)...(3) (However, tON and HBI are constant).

Voltage 1 (B2 is proportional to the horizontal scanning frequency, so the seventh
It is shown as a straight line HB2 in the figure.

Here, the horizontal output pulse Vcp, which is the collector pulse of the horizontal output transistor Q1 in FIG. 5, is expressed by the following equation.

Vcp=HB3[(π/2)f(tH/+R)-11+
l] ++ (4) Here, the resonance period tR is IR・π CR−Ll・L3/(L]+L3)・
...(5) (However, CR (C3) High voltage) IV is HV-n ・Vcp - (6) where n is the winding ratio of flyback transformer TI
It is expressed as

In order to keep the high voltage HV constant regardless of the horizontal scanning frequency IH, the horizontal output pulse Vcp must be constant.

Therefore, equation (4) is: Vcp (1) = Vcp (2)
...It must be (7).

In order to achieve this, as shown in Figure 5, a high voltage H
V is divided by resistors R3 and R4, the voltage value is detected by a high voltage output control circuit 5, the series regulator 7 is controlled by the high voltage output control circuit 5, and the output voltage HB3 of the series regulator 7 is corrected.

From formula (4), IH3(1) □Vcp (1)/[(π/2) t
(tH(1)/lR) -11+1]...(8) IH3(2) ・Vcp (2)/[(π/2) l
(+H(2) /lR) -1) +l]... (
9) is obtained.

For example, in order for the voltage difference between the input and output of the series regulator (IH2-11B3) to be constant at a constant beam current (constant brightness of the playback screen), regardless of the horizontal scanning frequency 1H, as shown in Figure 7. It is sufficient that the slopes of the HB2 straight line and the HB3B3 straight line shown are always the same.

That is, the value of IH2(2) −IH2(1) and IH3F2
) -IH5(1) may be the same value.

When confirmed by setting the TV mode to 5allix(1) and the HDTV mode to 1allix(2), the resonance period tR is the same in the TV mode and the HDTV mode from equation (5).

From formula (3), IH(2)/IH(1)・IH2(2) /)IH2(
]) = 33.75/15.73 = 2.145 ... (10) From equation (7), vCp; vcp (1); vcp (2) - 800vlR =
Assuming 9μs, in HDTV mode, +H(2)・29.
Since it is 6 μs, from equation (9), IH3(2+・800/[(π/2) + (29,6
/9) -11+1]174■ In TV mode, IH (1) = 63.5 μs, so the formula % formula % ] Here, the voltage difference between the input and output of the series regulator 7 (
When IH2-IH3) is set to 40v in HDTV mode, IH2(2) 174+40・214■ From formula (10), 1(B2 (1) = HB2 (2) /2.145=
99.8V, that is 1 (In DTV mode, if you set IH2 (2) - IH5 (2) = 40V, in TV mode) IH2 (1) - IH5 (1) = 99.8 - 76 =
23. It was confirmed that the voltage difference between the input and output of the series regulator 7 decreases in the TV mode.

That is, as shown in FIG. 7, with the same beam current,
HD'N' signal with high horizontal scanning frequency IH (fH-33
, 75kHz) to ensure a sufficient correction range for high voltage HV.
Apply voltage to series regulator 7 to IH2-HB3
When set to 40V, NTS with low horizontal scanning frequency IH
With the C system TV double signal (IH = 15.73kHz), only IH2-HB3 = 24■ can be obtained.

Therefore, in TV mode, due to a drop in the voltage difference between the input and output of the series regulator 7, the amount of correction that can be made in the series regulator becomes insufficient, and the regulation characteristics deteriorate, making it difficult to respond to sudden changes between bright and dark screens. Therefore, the high voltage H2 cannot be sufficiently corrected.

On the other hand, if the regulation characteristics of TV mode are improved and TV MOMO-F TEHB2-HB3 = 40V, then when HDTV signal (HDTV mode) TEHB2-)
IB3=56V, resulting in excessive power loss in the series regulator.

(Problems to be Solved by the Invention) The problems to be solved by this invention are to be able to follow sudden changes in bright and dark screens, and to be stable at all times, regardless of the frequency of the horizontal synchronizing signal (horizontal scanning frequency). The problem is what measures should be taken to create a horizontal high voltage output circuit that can obtain a high voltage HV of 100% and does not cause excessive power loss in the voltage regulator.

(Means for Solving the Problems) Therefore, in order to solve the above problems, the present invention provides a first DC voltage that converts a first DC voltage into a second DC voltage according to the frequency of a supplied horizontal synchronizing signal. a second voltage regulator that converts the second DC voltage into a third DC voltage; a flyback transformer whose primary winding is supplied with the third DC voltage; and the horizontal synchronizer. a horizontal output pulse generation circuit that is supplied with a signal and supplies a horizontal output pulse to the primary winding of the flyback transformer, and a high voltage generated on the secondary winding side of the flyback transformer to be constant. In the horizontal high voltage output circuit including a high voltage output control circuit that controls a second voltage regulator, even when various horizontal synchronization signals with different frequencies are supplied, the second DC voltage can be adjusted. A control circuit is provided for controlling the first voltage regulator so that the voltage difference between the third DC voltage and the second DC voltage is always a constant predetermined voltage difference when the beam current of the cathode ray tube is constant. The present invention provides a horizontal high voltage output circuit characterized by the following features.

(Example) As mentioned above, when the beam current of the CRT is constant, the voltage difference between the input and output of the series regulator 7 (second voltage regulator) is set to a predetermined constant value, regardless of the horizontal scanning frequency IH. The above problem can be solved by keeping it at .

In the present invention, first, the slope of the HB2 line shown in FIG.
(A method will be described in which the voltage applied to the series regulator 7 is maintained at a predetermined constant value regardless of the horizontal scanning frequency IH by closely approximating the slope of the straight line B3.

In this method, the duty of the output pulse of the monomulti is changed according to the horizontal scanning frequency IH, and the output voltage 1 (B2 (second DC voltage) of the step-down switching regulator 6 (first voltage regulator) is controlled. Thus, the slope of the HB2 straight line is infinitely approximated to the HB3B3 straight line.

FIG. 1 shows a block diagram of the first embodiment. Note that the same parts as in the conventional example are given the same reference numerals.

From Figure 7, the condition that the slope of the HB2 line is equal to 1 (the slope of the B3 line is IH2(2) -IH2(1)・)IH3(2) -1
4B3 (1) ...(11).

Substituting equations (2), (8), and (9) into equation (11), (toN (2)/LH(2))−(tON(+)/+
H(1))・(Vcp/HBI) [[]/ [(π/
2) I(ttl (2)/JR) -II +I]]
[1/[(π/2) 1(tH(1)/+R)-11+
I]]]...(12) Here, if the duty of the output pulse of monomulti 1 is expressed as δ, then δ(1)・tON (1) /lH(1)
...(13) δ(2)・tON (2) /lH(2)
...(14) Equations (13) and (14) are replaced by Equation (
12), δ (1)・δ (2) −(Vcp/)IBI) I
t/ [(π/2) f (tH(2)/+R) −1
1+l] ] + (Vcp/HBI) [1/[(
π/2)1(tH(])/1-11+l]]
... (15) Here, K=δ(2) −(Vcp/HBI) [1/[(π
/2) [(IH(2)/1R)-11+I]]
...(16)a=+H(1)/1)
If l(2) ・= (17), then δ(1) ・K+ (Vcp/HBI) [1/ [(
π/2) ((ltl (1) /)R)-1++11
1 = + (Vcp/HBI) [1/[(yr /2)
(tH(2)/lR) [a-(1-2/π) (tR/
+H(2))l]]-(18) Note that tH(1) ≧
Since tH(2), a≧1.

FIG. 2 is a graph showing equation (18). a≧
1, so δ(1) is the solid line portion of the hyperbolic curve.

sal[1x(1) is TV mode, 5allix(
2) is in HDTV mode.

Let the HDTV mode be the reference mode and set it to 1 (DTVTV mode/1. At this time, in the TV mode, a=63.
5/29.6=2.145.

When a・2.145, from equation (18), δ(1)=6
(2) -0,4454, so in Tv mode it is 4
If the duty of mono-multi output pulse is reduced by 4.54%, it will be 1lB2 in TV mode and HDTV mode.
-1 (The values of B3 are the same.

In this way, step-down switching can be achieved by using a monomultiple that can change the duty of the output pulse according to the horizontal scanning frequency IH (the frequency of the supplied horizontal synchronizing signal) along the hyperbolic characteristic shown in Figure 2. regulator 6
By controlling , the slope of the 1I82 straight line can be infinitely approximated to the HB3B3 straight line. The value of IH2-)IH3 can be kept constant regardless of the horizontal scanning frequency IH. The duly of the output pulse is changed by changing the pulse width +ON of the output pulse.

Practically, there are cases where the duty of the output pulse does not need to change along the hyperbolic characteristic shown in FIG. 2 at all horizontal scanning frequencies IH. For example, both the lowest and highest frequency modes of the incoming horizontal scanning frequency IH may vary along a hyperbolic characteristic, and intermediate frequencies may have a linear approximation to the hyperbola.

In addition, in the mode where the horizontal scanning frequency IH is 35 and 1 to 24kHz+ (this section also includes HDTV mode), the change in the duty of the output pulse is a linear approximation to the hyperbolic characteristic, and the horizontal scanning frequency IH in the TV mode is 15kHz. .73k)l
Only when x, d+rty may be switched so as to be on the hyperbolic characteristic. The first one is the one that realizes this negative point switching.
This is a first embodiment shown in the figure.

A control circuit of a step-down switching regulator 6 (first voltage regulator) is composed of a monomulti 1, a pulse drive circuit 3, a horizontal synchronizing signal detection circuit 8, and a switch 9. With the time constant of the capacitor JiC1 and the resistors R11 and 1l12,
The pulse width of the output pulse of monomulti 1 is determined.

Frequency of incoming horizontal synchronization signal (horizontal scanning frequency IH)
is detected by the horizontal synchronization signal detection circuit 8, and the horizontal scanning frequency I
When H is between 35kHz and 24kHz, switch 9 is shorted. At this time, the pulse width of the output pulse of the monomulti 1 is determined by the time constant of the capacitor C1 and the resistor RI2, and the dut
A change in y results in a linear approximation to a hyperbolic characteristic.

The horizontal scanning frequency fH15,7 is detected by the horizontal synchronization signal detection circuit 8.
When 3kHz is detected, the switch 9 is opened.

At this time, the pulse width is determined by the time constant of the capacitor C1 and the resistor R11+RI2, and the duty is a value on a hyperbola.

Therefore, the value of the voltage difference HB2-HB3 between the input and output of the series regulator 7 (second voltage regulator) is
A predetermined constant value of 4flV can be set for both the HDTV mode and the HDTV mode.

Therefore, in both modes, this horizontal high voltage output circuit:
Excellent regulation characteristics can be obtained, and rapid changes between bright and dark screens can be fully followed, and a stable high voltage HV can always be obtained.

Furthermore, in both modes, excessive power loss does not occur in the series regulator 7.

In the above embodiment, the step-down switching regulator 6
The control circuit of the (first voltage regulator) is composed of a monomulti 1, a pulse drive circuit 3, a horizontal synchronizing signal detection circuit 8, and a switch 9, and the da of the output pulse of the monomulti 1 is
Although the step-down switching regulator 6 is controlled by changing ty, the control circuit is not limited to this.

Like the control circuit 1a of the second embodiment shown in FIG. 3, the frequency of the incoming horizontal synchronizing signal (horizontal scanning frequency fit) is detected, and the signal is applied to the series regulator 7 regardless of the horizontal scanning frequency fit. Any device may be used as long as it can control the step-down switching regulator 6 so that the voltage remains at a predetermined constant value.

FIG. 4 shows a third embodiment. In this embodiment, the high voltage output control circuit 5a that controls the series regulator 7 does not detect the high voltage HV but the horizontal output pulse Vcp. From equation (6), it can be seen that even if the horizontal output pulse Vcp is detected, only the high voltage HV can be controlled.

(Effects of the Invention) As described above, the horizontal high voltage output circuit of the present invention maintains the voltage difference between the input and output of the second voltage regulator at a predetermined level regardless of the frequency (horizontal scanning frequency) of the incoming horizontal synchronization signal. can be maintained at a constant value. Therefore, the horizontal high voltage output circuit of the present invention can handle video signals of any horizontal scanning frequency.
Excellent regulation characteristics can be obtained, and rapid changes between bright and dark screens can be fully followed, and a stable high voltage HV can always be obtained. Furthermore, excessive power loss does not occur in the second voltage regulator.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the first embodiment, Fig. 2 is a hyperbolic graph showing the change characteristics of duly, Fig. 3 is a block diagram of the second embodiment, Fig. 4 is a block diagram of the third embodiment, Figure 5 is a block diagram of the conventional example, Figure 6 is a diagram showing the current regulation characteristics of the flyback transformer, Figure 7 is a diagram showing the HB2 straight line and 1 (B3 straight line), and Figure 8 is the block diagram shown in Figure 5. The circuit diagram of a part of the figure, Figures 9 and 10 are
The timing chart of the circuit diagram shown in FIG. 11 is a diagram showing the relationship between input and output voltages of the step-down switching regulator. 1.2... Monostable multivibrator, 1a
...Control circuit, 3.4...Pulse drive circuit, 5...High voltage output control circuit, 6...Step-down switching regulator (first voltage regulator), 7...Series regulator (second voltage regulator), 8...Horizontal synchronization signal detection circuit, 9...Switch, CR...Resonance capacitance, Cs...Capacitance, Dl...Damper diode, L3...Dummy deflection yoke, Ql・Horizontal output transistor, T1...Flyback transformer. Patent Applicant: Victor Japan Co., Ltd. Representative: Kunio Umiki

Claims (1)

[Scope of Claims] A first voltage regulator that converts a first DC voltage into a second DC voltage according to the frequency of a supplied horizontal synchronization signal; a second voltage regulator for converting the third DC voltage to a primary winding; a flyback transformer for supplying the third DC voltage to a primary winding; and a flyback transformer for supplying the horizontal synchronization signal to convert horizontal output pulses to the A horizontal output pulse generation circuit that supplies a primary winding; and a high voltage output control circuit that controls a second voltage regulator so that the high voltage generated on the secondary winding side of the flyback transformer is constant. In the horizontal high voltage output circuit, even when various horizontal synchronizing signals with different frequencies are supplied, the voltage difference between the third DC voltage and the second DC voltage can be reduced by adjusting the second DC voltage. A horizontal high-voltage output circuit comprising: a control circuit for controlling a first voltage regulator to always maintain a constant predetermined voltage difference when the beam current of the cathode ray tube is constant.