JP2860068B2 - Chopper type high voltage generation control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chopper type high voltage generation control circuit for generating a secondary high voltage of a flyback transformer which is stable regardless of a change in the frequency of a horizontal drive signal.

[0002]

2. Description of the Related Art In a high-voltage generating circuit for supplying a high voltage to the anode of a picture tube of a so-called multi-scan type monitor, the frequency of a signal for horizontally driving a beam is caused by a change in resolution of an image signal input to the monitor. It is necessary to keep the high voltage output constant even if it changes.

As one of the high-voltage generating circuits for maintaining the high-voltage output constant, there is a chopper-type high-voltage generating control circuit. One example will be described with reference to FIG.

In FIG. 1, a power supply voltage supply section 1 intermittently switches a power supply voltage B with a pulse P output from a PWM wave generating circuit 6 to be described later, thereby generating a DC voltage corresponding to the width of the pulse P. It is supplied to the primary winding side of the flyback transformer 3 of the high voltage generator 2.

A pulse of the horizontal drive signal HD is input to the base of the transistor Q1, whereby the DC voltage supplied to the primary winding of the flyback transformer 3 is switched, and the DC voltage is switched to the secondary winding. Outputs a boosted pulsed high voltage.

The pulsed high voltage output to the secondary winding is rectified by the diode D1 and smoothed by the capacitor C1 to become a DC high voltage HV, which is supplied to the anode.

The high voltage HV output from the high voltage generator 2 is divided by resistors R1 and R2 connected in series, and a feedback voltage Vf extracted from a connection point between these resistors is supplied to an error detection circuit 4. Is entered.

[0008] The error detection circuit 4 outputs the feedback voltage V
By comparing f with the reference voltage Eb1, the difference between the actual high voltage HV level and the desired level is detected and amplified, and the error voltage Ve is output.

The sawtooth wave generating circuit 5 outputs a sawtooth wave SAW synchronized with the frequency of the input horizontal drive signal HD. The sawtooth wave generating circuit 5 includes an AGC circuit to generate a sawtooth wave having a constant amplitude regardless of a change in the frequency of the horizontal drive signal HD.

The PWM wave generator 6 compares the voltage level of the sawtooth wave SAW with the level of the error voltage Ve, and outputs a pulse P having a width corresponding to the level of the error voltage Ve.

In the above configuration, when the voltage supplied to the primary winding side of the flyback transformer 2 is constant, the high voltage generator 2 increases the high voltage HV when the frequency of the horizontal drive signal HD is low. When the frequency of the horizontal drive signal HD is high, the high voltage HV is low. The chopper-type high-voltage generation control circuit changes the voltage supplied to the primary winding side of the flyback transformer 2 in accordance with the frequency of the horizontal drive signal HD, so that the secondary drive is performed even if the frequency of the horizontal drive signal HD changes. It operates to keep the high voltage HV output from the winding side constant.

The specific operation will be described with reference to FIG. The sawtooth wave SAW is output from the sawtooth wave generation circuit 5 at a frequency synchronized with the horizontal drive signal HD, as shown in FIG.

If the frequency of the horizontal drive signal HD becomes relatively low, the voltage of the high voltage HV becomes higher than a desired level. The voltage supplied to the battery becomes lower. That is, the level of the error voltage Ve decreases. At this time, for example, as shown in FIG.
Assuming that the level of e is Ve1, the pulse P output from the PWM wave generating circuit 6 is a relatively narrow pulse as shown in FIG.

Conversely, if the frequency of the horizontal drive signal HD becomes relatively high, the voltage of the high voltage HV becomes lower than a desired level. The voltage supplied to is increased. That is, the level of the error voltage Ve increases. At this time, for example, as shown in FIG.
Assuming that the level of e is Ve2, the pulse P output from the PWM wave generating circuit 6 is a relatively wide pulse as shown in FIG.

As described above, the pulse width of the pulse P applied to the power supply unit 1 is changed according to the difference between the voltage level of the high voltage HV that changes according to the frequency of the horizontal drive signal HD and the desired level. This changes the voltage supplied to the primary winding side of the flyback transformer 2 and stabilizes the high voltage HV.

[0016]

However, the conventional chopper-type high-voltage generation control circuit has a problem in that the circuit stability cannot be maintained over the entire variable range of the horizontal drive signal.

That is, when the chopper type high voltage generation control circuit is viewed as one feedback system, the error detection circuit 4 and the P
The WM wave generation circuit 6 outputs an output signal corresponding to the input signal, and has a specific gain independent of the frequency of the horizontal drive signal HD. However, while the reference voltage EB1 input to the error detection circuit 4 is constant,
The voltage output to the power supply voltage generator 1 is the horizontal drive signal H
It changes over a wide range according to the change of the frequency of D.

That is, although the open gain of the feedback system is constant irrespective of the frequency of the horizontal drive signal HD as described above, the output of the feedback system changes with respect to a constant input. The fact that the frequency changes in a wide range according to the change in the frequency means that the feedback amount changes in accordance with the change in the frequency of the horizontal drive signal HD.

On the other hand, the stability of the feedback system can be determined from the frequency characteristics of the loop gain and the phase if the loop gain obtained as the product of the open gain and the gain of the feedback circuit is constant. The required amount of phase correction can also be optimally determined. However, when the loop gain changes, the optimal phase correction amount also changes.

Therefore, in the above-mentioned conventional chopper type high voltage generation control circuit, optimum phase compensation must be performed at the center of the frequency variable range of the horizontal drive signal HD, and the frequency of the horizontal drive signal HD is far from the center of the variable range. If
There is a problem that the system becomes unstable due to insufficient phase compensation and oscillates, and that the response of the system deteriorates due to excessive phase compensation.

As one method for solving such a problem, the AGC circuit is not provided in the saw-tooth wave generating circuit, so that the saw-tooth wave SAW is saturated when the frequency of the horizontal drive signal HD decreases, and the horizontal drive signal There is a method of reducing a change in loop gain with respect to a change in HD frequency. However, in this case, the change width of the duty of the pulse P with respect to the change of the error voltage Ve becomes narrow at a low frequency, which causes a problem that the control range of the high voltage HV becomes narrow.

The present invention has been made in view of the above circumstances, and provides a chopper-type high-voltage generation control circuit that requires a constant phase correction amount regardless of a change in a horizontal drive signal and has a wide control range for high-voltage output. The purpose is to:

[0023]

According to a first aspect of the present invention, there is provided a chopper type high voltage generation control circuit comprising a feedback voltage obtained by dividing a reference voltage and a secondary high voltage of a flyback transformer by resistance. The power supply voltage is intermittent by the pulse width modulation signal obtained by comparing the error voltage generated by comparing with the above and the sawtooth wave generated by the sawtooth wave generator in synchronization with the horizontal drive signal that drives the beam in the horizontal direction. By supplying a voltage corresponding to the pulse width to the primary side of the flyback transformer,
In the chopper type high voltage generation control circuit that generates a secondary high voltage of the flyback transformer stably irrespective of a change in the frequency of the horizontal drive signal by switching according to the horizontal drive signal, the sawtooth wave generation is performed. The unit synchronizes with the horizontal drive signal, generates a sawtooth wave whose waveform slope continuously decreases within one cycle of the horizontal drive signal, and changes the amplitude from the lowest level to the highest level of the frequency of the horizontal drive signal. It is characterized in that the output is kept almost constant regardless of the change.

According to a second aspect of the present invention, a chopper type high voltage generation control circuit compares an error voltage generated by comparing a reference voltage with a feedback voltage obtained by dividing a secondary high voltage of a flyback transformer by resistance, and a beam. The power supply voltage is intermittently switched on and off by a pulse width modulation signal obtained by comparing a sawtooth wave generated from a sawtooth wave generator in synchronization with a horizontal drive signal to be driven in the horizontal direction, so that a voltage corresponding to the pulse width is changed. A chopper that supplies the primary voltage of the flyback transformer to the primary side of the flyback transformer and performs switching in accordance with the horizontal drive signal to generate a stable secondary high voltage of the flyback transformer regardless of a change in the frequency of the horizontal drive signal. In the high-voltage generation control circuit, the saw-tooth wave generating section is synchronized with the horizontal drive signal and outputs one cycle of the horizontal drive signal. Characterized in that the CR charging waveform waveform rises exponentially, irrespective of the amplitude from the lowest level to the highest level to the change of the horizontal drive frequency and outputs maintained substantially constant at.

[0025]

According to the configuration of the first aspect, the saw-tooth wave generating unit generates a saw-tooth wave in synchronization with the horizontal drive signal, and the slope of the waveform of which is continuously reduced within one cycle of the horizontal drive signal. Since the amplitude of the output sawtooth wave from the lowest level to the highest level is kept substantially constant irrespective of the change in the frequency of the horizontal drive signal, the error voltage according to the change in the horizontal drive signal Is small when the frequency of the horizontal drive signal is low, and large when the frequency of the horizontal drive signal is high. Therefore, the loop gain of the circuit is kept constant irrespective of the change in the frequency of the horizontal drive signal.

According to the second aspect of the present invention, the sawtooth wave generating section synchronizes with the horizontal drive signal and generates a CR charging waveform whose waveform rises exponentially within one cycle of the horizontal drive signal. Output. This CR charging waveform is a sawtooth wave having a constant amplitude in which the slope of the waveform continuously decreases within one cycle of the horizontal drive signal. Further, the amplitude of the output CR charging waveform from the lowest level to the highest level is kept substantially constant irrespective of the change in the horizontal drive frequency. Therefore, similarly to claim 1, the change width of the duty of the pulse width modulation signal with respect to the change width of the error voltage according to the change of the horizontal drive signal is small when the frequency of the horizontal drive signal is low, and Is high when the frequency is high, the loop gain of the circuit is kept constant irrespective of the change in the frequency of the horizontal drive signal. Further, a sawtooth wave having a constant amplitude in which the slope of the waveform continuously decreases within one cycle can be realized by a simple CR charging circuit.

[0027]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

The configuration of the chopper type high voltage generation control circuit according to the embodiment of the present invention, except for the sawtooth wave generation circuit 5,
This is exactly the same as the conventional chopper type high voltage generation control circuit shown in FIG. Therefore, the description of the configuration other than the sawtooth wave generation circuit 5 is omitted.

The configuration of the sawtooth wave generating circuit 5 of this embodiment will be described with reference to FIG.

In FIG. 1, a capacitor C2 having one end grounded is connected to a voltage source Eb2 via a resistance between a drain and a source of a field effect transistor Q3.
Therefore, the voltage source Eb2, the transistor Q3,
The capacitor C3 forms a CR charging circuit. The drain-source resistance changes depending on the voltage applied to the gate. A saw-tooth wave output SAW is taken out from a connection point between the transistor Q3 and the capacitor C2.

The transistor Q3 and the capacitor C2
Is connected to the collector of the transistor Q2. The emitter of the transistor Q2 is grounded. The horizontal drive signal HD is input to the base of the transistor Q2. Transistor Q2 has its horizontal drive signal H
It is turned on / off by D. Therefore, when the transistor Q2 is turned on, the charge of the capacitor C2 is released, and the level of the saw-tooth wave SAW becomes zero.

Although only the configuration described above can output the sawtooth wave SAW of the CR charging waveform, it is output from the PWM wave generation circuit 6 with respect to the variation of the error voltage Ve regardless of the frequency of the horizontal drive signal HD. In order to make the duty change amount of the pulse P constant, the time constant of the CR charging circuit is changed so that the amplitude of the CR charging waveform from the lowest level to the highest level is independent of the frequency of the horizontal drive signal HD. It needs to be kept constant.

That is, the sawtooth wave SAW is expressed by SAW = Eb2 · (1−e (−t / (C2 · Rq))). Where e is the base of the natural logarithm and Rq
Is a source-drain resistance of the transistor Q3.
Therefore, if the time constant (C2 · Rq) is shortened in inverse proportion to the frequency of the horizontal drive signal HD, the amplitude from the lowest level to the highest level of the CR charging waveform is constant regardless of the frequency of the horizontal drive signal HD. Can be kept.

To change the time constant (C2 · Rq),
The capacitance of the capacitor C2 may be changed or the resistance of the resistor Rq may be changed. In this embodiment, the resistance of the resistor Rq is changed by changing the voltage applied to the gate of the transistor Q3.

To this end, the connection point of the capacitor C2 to the transistor Q3 is connected via a diode D2 to the other end of the capacitor C3, one end of which is connected to the other end of the capacitor C3. The amplitude voltage from the lowest level to the highest level of the charging voltage waveform is stored, the amplitude voltage is compared with the reference voltage Eb3 by the comparator G1, and an amplified voltage corresponding to the difference is supplied to the gate of the transistor Q3. Accordingly, if the horizontal drive signal HD is stable at a certain frequency and the amplitude voltage of the capacitor C2 (and C3) is stable at a certain level, the frequency of the horizontal drive signal HD becomes lower. When the amplitude voltage of the capacitor C2 (and C3) increases, the amplified voltage corresponding thereto is applied from the comparator G1 to the gate of the transistor Q3, the resistance Rq changes in the increasing direction, and the time constant (C2 · Rq) increases. This acts to lower the amplitude voltage of the capacitor C2 (and C3). Conversely, when the frequency of the horizontal drive signal HD increases and the amplitude voltage of the capacitor C2 (and C3) decreases, an amplified voltage corresponding thereto is output from the comparator G1 to the transistor Q3.
, The resistance Rq changes in the decreasing direction, the time constant (C2 · Rq) becomes shorter, and acts to increase the amplitude voltage of the capacitor C2. Therefore, the amplitude voltage of the capacitor C2 is returned to the original level, and the amplitude of the sawtooth wave SAW, which is the charging waveform of the capacitor C2, is maintained at a substantially constant level regardless of the frequency of the horizontal drive signal HD.

As a result, the sawtooth wave SAW is synchronized with the frequency of the horizontal drive signal HD, becomes a CR charge waveform whose waveform rises exponentially within one cycle of the horizontal drive signal HD, and has the CR charge waveform. The amplitude from the lowest level to the highest level is kept constant regardless of a change in the frequency of the horizontal drive signal HD.

FIG. 2 shows the operation of the chopper type high voltage generation control circuit of the present embodiment in which the sawtooth wave generation circuit 5 configured as described above is applied to the conventional chopper type high voltage generation control circuit shown in FIG. It will be described with reference to FIG.

The sawtooth wave SAW is output from the sawtooth wave generation circuit 5 at a frequency synchronized with the horizontal drive signal HD, as shown in FIG.

If the frequency of the horizontal drive signal HD becomes relatively low, the voltage of the high voltage HV becomes higher than a desired level. The voltage supplied to the battery becomes lower. That is, the level of the error voltage Ve decreases. At this time, for example, as shown in FIG.
Assuming that the level of e is Ve3, the pulse P output from the PWM wave generating circuit 6 is a relatively narrow pulse as shown in FIG.

Conversely, if the frequency of the horizontal drive signal HD becomes relatively high, the voltage of the high voltage HV becomes lower than a desired level. The voltage supplied to is increased. That is, the level of the error voltage Ve increases. At this time, for example, as shown in FIG.
Assuming that the level of e is Ve4, the pulse P output from the PWM wave generating circuit 6 is a relatively wide pulse as shown in FIG.

As described above, the pulse width of the pulse P applied to the power supply unit 1 is changed according to the difference between the voltage level of the high voltage HV that changes according to the frequency of the horizontal drive signal HD and the desired level. As a result, changing the voltage supplied to the primary winding side of the flyback transformer 2 to stabilize the high voltage HV is the same as the conventional one.

Next, a description will be given of an operation specific to the present embodiment, which is performed by using the sawtooth wave SAW as a CR charging waveform.

When the level of the error voltage Ve is Ve3 and the error voltage Ve changes by a small width ΔV from Ve3 due to a voltage drop due to a change in the anode current, the output from the PWM wave generation circuit 6 is output. The pulse P changes by ΔP1, as shown in FIG.

On the other hand, when the level of the error voltage Ve is Ve4, if the error voltage Ve changes from Ve4 by the same small width ΔV as that of Ve3, P
The pulse P output from the WM wave generation circuit 6 changes by ΔP2 as shown in FIG.

As described above, the change in the pulse width of the pulse P with respect to the change in the error voltage Ve having the same width, in other words, PW
The gain of the M-wave generation circuit is low when the level of the error voltage Ve is low, and high when the level of the error voltage Ve is high. This is saw wave SA
As described above, W is represented by SAW = Eb2 · (1−e (−t / (C2 · Rq))), and the slope of the sawtooth wave SAW is obtained by differentiating the above equation with time to obtain d (SAW ) / Dt = Eb2 / (C2 · Rq) · e (−t / (C2 · Rq)), so that the sawtooth wave SAW is synchronized with the frequency of the horizontal drive signal HD and the slope of the waveform is horizontal drive. Signal HD
Horizontal drive signal H continuously decreases within one cycle of
This is because a sawtooth wave having a constant amplitude is obtained regardless of the frequency of D.

That is, when the chopper type high voltage generation control circuit is viewed as a whole, the open gain of the PWM wave generation circuit 6 changes in accordance with the frequency of the horizontal drive signal HD by making the sawtooth wave SAW a CR charging waveform, Since the change in the loop gain of the feedback system according to the frequency of the horizontal drive signal HD is canceled, the loop gain of the system is kept constant.

Thus, the necessary amount of phase correction can be optimally determined regardless of the frequency of the horizontal drive signal HD.
There is no danger that the system will become unstable due to insufficient phase compensation, and the problem that the response of the system will deteriorate due to excessive phase compensation will be eliminated. Increases stability.

The optimum CR charging waveform of the sawtooth wave SAW can be selected by appropriately selecting the capacitance of the capacitor C2.

Further, in the embodiment described above, the sawtooth wave generating circuit 5 can be obtained with a simple configuration by using the sawtooth wave SAW as the CR charging waveform.
Not limited to the CR charging waveform, the waveform is synchronized with the frequency of the horizontal drive signal HD, and the slope of the waveform continuously decreases within one cycle of the horizontal drive signal HD. A sawtooth wave having a constant amplitude regardless of the frequency of the horizontal drive signal HD Then, the change in the loop gain can be canceled by the change in the frequency of the horizontal drive signal HD.

[0050]

According to the present invention, since the loop gain of the circuit is kept constant irrespective of the change in the frequency of the horizontal drive signal, the phase correction amount is independent of the change in the horizontal drive signal. And the stability of the circuit can be increased. Further, since the waveform of the sawtooth wave changes continuously, the control range of the high voltage output does not become narrow.

According to the second aspect of the present invention, since the loop gain of the circuit is kept constant irrespective of the change in the frequency of the horizontal drive signal, the phase correction amount is kept constant regardless of the change in the horizontal drive signal. And the stability of the circuit can be increased. Also, since the waveform of the sawtooth wave changes continuously,
The control range of the high voltage output does not become narrow. Further, since a sawtooth wave having a constant amplitude in which the slope of the waveform continuously decreases within one cycle can be realized by a simple CR charging circuit, a low-cost circuit configuration can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a sawtooth wave generating circuit according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the chopper type high voltage generation control circuit according to the embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional chopper type high voltage generation control circuit.

FIG. 4 is a diagram for explaining the operation of a conventional chopper type high voltage generation control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply voltage part 2 High voltage generation part 3 Flyback transformer 4 Error detection circuit 5 PWM wave generation circuit

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 3/185 H04N 3/18 H04N 3/27

Claims (2)

(57) [Claims] An error voltage generated by comparing a reference voltage with a feedback voltage obtained by dividing a secondary high voltage of a flyback transformer by a resistance, and a horizontal drive signal for driving a beam in a horizontal direction. By intermitting the power supply voltage by a pulse width modulation signal obtained by comparing the sawtooth wave generated from the sawtooth wave generation unit, a voltage corresponding to the pulse width is supplied to the primary side of the flyback transformer, A chopper-type high-voltage generation control circuit that generates a secondary high voltage of the flyback transformer that is stable regardless of a change in the frequency of the horizontal drive signal by switching according to the horizontal drive signal. The unit is synchronized with the horizontal drive signal,
A sawtooth wave whose waveform slope continuously decreases within one cycle of the horizontal drive signal is output while keeping its amplitude from the lowest level to the highest level substantially constant regardless of the change in the frequency of the horizontal drive signal. And a chopper-type high-voltage generation control circuit. 2. An error voltage generated by comparing a reference voltage with a feedback voltage obtained by dividing a secondary high voltage of a flyback transformer by resistance and a horizontal drive signal for driving a beam in a horizontal direction. By intermitting the power supply voltage by a pulse width modulation signal obtained by comparing the sawtooth wave generated from the sawtooth wave generation unit, a voltage corresponding to the pulse width is supplied to the primary side of the flyback transformer, A chopper-type high-voltage generation control circuit that generates a secondary high voltage of the flyback transformer that is stable regardless of a change in the frequency of the horizontal drive signal by switching according to the horizontal drive signal. The unit is synchronized with the horizontal drive signal,
A CR charging waveform whose waveform rises exponentially within one cycle of the horizontal drive signal is output while keeping the amplitude from the lowest level to the highest level substantially constant regardless of the change in the horizontal drive frequency. A chopper-type high-voltage generation control circuit.