JP2000295489A - High-voltage generating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the response characteristics of high voltage stabilization and high voltage buildup characteristics at of turn on of a power source, without using an expansive electrolytic capacitor as a capacitor. SOLUTION: The input terminal of an error amplifier 3 is connected to a high voltage detecting point (b) which is the node of a high-voltage resistor 7 and a high-voltage detecting resistor 9. A fist CR parallel circuit 21, composed of a first capacitor 31 and a first resistor 41, is connected between a terminal point (c) of a high-voltage capacitor 8 and the ground, and a second CR parallel circuit 22 composed of a second capacitor 32 and a second resistor 42 is connected between the terminal point (c) and the high voltage detecting point (b). Moreover, an instantaneous voltage buildup detection circuit 500 composed of a Zener diode 26 and a reverse current cut diode 27 is connected between a rectifying and smoothing circuit 15 connected to a tertiary winding wire 4c of a flyback transformer 4 and the input terminal of the error amplifier 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention mainly relates to a cathode ray tube (C) such as a television receiver and a display monitor.
In particular, the present invention relates to a technique for improving a high-voltage rising characteristic when power is turned on, and further relates to a technique for improving a protection characteristic during abnormal operation.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram of a high-voltage generating circuit according to the prior art. The high voltage generating circuit 100 includes a high voltage output circuit 1, a flyback transformer 4, a high voltage rectifier diode 6, a high voltage resistor 7, and a high voltage capacitor 8. A flyback pulse is generated in the primary winding 4a of the flyback transformer 4 by switching of the switching element in the high-voltage output circuit 1 including a switching element, a resonance capacitor, a damper diode, and the like.
A boost flyback pulse is induced in the secondary winding 4b.
The boosted flyback pulse is rectified by the high-voltage rectifier diode 6, passed through the high-voltage resistor 7, and smoothed by the high-voltage capacitor 8 connected in parallel with the high-voltage resistor 7, so that the DC voltage is applied to the high-voltage output point a, which is the cathode of the high-voltage rectifier diode 6. Is generated. A high voltage output voltage Vh is supplied from a high voltage output terminal 14 connected to a high voltage output point a to an anode of a cathode ray tube (CRT).

[0003] A high voltage detection circuit 250 is connected to a parallel circuit of the high voltage resistor 7 and the high voltage capacitor 8. The high-voltage detection circuit 250 is connected between the high-voltage resistor 7 and the ground GND, and is connected between the high-voltage capacitor 8 and the ground GND, and the high-voltage detection resistor 9 having the connection point as the high-voltage detection point b. A high-voltage stabilizing capacitor 10 connected in parallel to the high-voltage detection resistor 9, a backflow prevention diode 11 having an anode connected to the high voltage detection point b, and a high voltage rise connected between the cathode of the backflow prevention diode 11 and the ground GND. An adjusting capacitor 12 and a discharging resistor 13 connected in parallel to the high-voltage rising adjusting capacitor 12.
And

[0004] The high voltage stabilizing circuit 300 includes an error amplifier 3 and a high voltage control circuit 2. The high-voltage detection point b in the high-voltage detection circuit 250 is connected to the non-inverting input terminal (+) of the error amplifier 3, and the reference voltage V is connected to the inverting input terminal (-).
The reference power supply 5 of ref is connected. High voltage control circuit 2
Receives the error detection voltage Vf from the error amplifier 3 and switches the switching control signal Ssw for pulse width modulation (PWM).
To the high voltage output circuit 1.

[0005] A high-voltage detection circuit 250, a high-voltage stabilization circuit 300, and a high-voltage output circuit 1 circulatingly connected to the high-voltage output point a constitute a high-voltage stabilization loop L1.

The high-voltage output voltage Vh at the high-voltage output point a is resistance-divided by the high-voltage resistor 7 and the high-voltage detection resistor 9 in the high-voltage detection circuit 250. The high-voltage detection voltage Vb at the resistance-divided high-voltage detection point b is converted to a high-voltage stabilization circuit. 300
Is applied to the non-inverting input terminal (+) of the error amplifier 3 at. In the error amplifier 3, the reference voltage Vref from the reference power supply 5 is compared with the high-voltage detection voltage Vb, and an error detection voltage Vf, which is the difference, is output to the high-voltage control circuit 2.
The high-voltage control circuit 2 outputs a switching control signal Ssw having a pulse width corresponding to the magnitude of the error detection voltage Vf to the high-voltage output circuit 1.
Output to The high-voltage output circuit 1 performs a switching operation of the switching element in an on-time corresponding to the pulse width of the input switching control signal Ssw, and outputs a flyback pulse corresponding to the switching operation.

The extraordinary high voltage detection circuit 400 includes a rectifying and smoothing circuit 15 connected to the tertiary winding 4c of the flyback transformer 4.
And an extraordinary high voltage detection resistor 16 and 17 connected thereto, and the extraordinary high voltage detection voltage Ve at the resistance dividing point e is input to the high voltage overvoltage protection circuit 2a in the high voltage control circuit 2.

Assuming that the capacitance of the high-voltage stabilizing capacitor 10 in the high-voltage detecting circuit 250 is C1 and the capacitance of the high-voltage rise adjusting capacitor 12 is C2, both capacitors 1
The combined capacitance value C12 of 0 and 12 is C12 = C1 + C2. The product R0 · C0 of the resistance value R0 of the high voltage resistor 7 and the capacitance value C0 of the high voltage capacitor 8 is the resistance value R of the high voltage detection resistor 9.
It is set equal to the product R1 · C12 of 1 and the combined capacitance value C12. R0.C0 = R1.C12 = R1. (C1 + C2) That is, the time constant .tau.0 of the CR parallel circuit of the high voltage resistor 7 and the high voltage capacitor 8, the high voltage detection resistor 9 and both capacitors 10,
12, and the time constant τ12 of the CR parallel circuit is the same, and the high-voltage output voltage V
h and the rising phase of the high-voltage detection voltage Vb at the high-voltage detection point b are made the same,
The high pressure rising characteristics are good.

[0009] The operation of the high voltage generating circuit configured as described above will be described. In the steady operation state, the high pressure detection point b
Is equal to the reference voltage Vref from the reference power supply 5, and the error amplifier 3 comparing these outputs the error detection voltage Vf corresponding to the difference to the high voltage control circuit 2. The high-voltage control circuit 2 outputs a switching control signal Ssw having a pulse width corresponding to the error detection voltage Vf at that time to the high-voltage output circuit 1. When the high-voltage output circuit 1 receives the switching control signal Ssw, the on-time for the switching element is The flyback pulse is output to the flyback transformer 4 while maintaining the original state. As a result, the high voltage output voltage Vh at the high voltage output point a is maintained at the rated high voltage Vh0 (see FIG. 8).

When the high-voltage output voltage Vh at the high-voltage output point a decreases for some reason, the high-voltage detection voltage Vb at the high-voltage detection point b also decreases correspondingly and becomes lower than the reference voltage Vref from the reference power supply 5. Then, the error detection voltage Vf from the error amplifier 3 increases to the negative side, and the high-voltage control circuit 2 outputs the switching control signal Ssw in a state where the ON time is longer to the high-voltage output circuit 1.
The high voltage output circuit 1 lengthens the ON time for the switching element, and outputs a flyback pulse having a higher peak value to the primary winding 4a of the flyback transformer 4. This flyback pulse is boosted by the flyback transformer 4 and
The high voltage output voltage Vh is smoothed by the high voltage capacitor 8 and applied to the anode of the cathode ray tube. The high-voltage output voltage Vh increases as the peak value of the flyback pulse increases. That is, as a result of the feedback control in the high-voltage stabilization loop L1, the peak value of the flyback pulse increases as the step-down amount of the high-voltage output voltage Vh increases, and the high-voltage output voltage Vh at the high-voltage output point a increases. This increase is performed until the high-voltage detection voltage Vb at the high-voltage detection point b becomes equal to the reference voltage Vref. When the voltage becomes equal, the operation stops, and the high-voltage output voltage Vh returns to the rated high-voltage Vh0.

A non-inverting input terminal (+) of the error amplifier 3 has a high-voltage rise adjusting capacitor 12 and a discharging resistor 13.
Is connected via the backflow prevention diode 11, but the capacitor 12 for adjusting the high voltage rise is fully charged in the normal operation state. Due to the presence of the backflow prevention diode 11, the charging voltage at the high-voltage rise adjusting capacitor 12 does not affect the error amplifier 3. That is, in the steady state of operation,
The high-voltage rise adjusting capacitor 12 is separated from the high-voltage stabilizing loop L1 by the backflow prevention diode 11. The high-voltage rise adjusting capacitor 12 operates only when the power is turned on.

The operation when the power is turned on will be described below. When the power of the high-voltage generating circuit is turned on, the high-voltage output voltage Vh at the high-voltage output point a rises, and accordingly, the high-voltage detection voltage Vb at the high-voltage detection point b also rises. Before turning on the power, a capacitor 1 for adjusting the high voltage rise is usually used.
2 has completely discharged. Until the high-voltage detection voltage Vb at the high-voltage detection point b reaches the reference voltage Vref, the error amplifier 3 outputs a relatively large value of the error detection voltage V
f is output to the high-voltage control circuit 2, a switching control signal Ssw having a long on-time is output from the high-voltage control circuit 2 to the high-voltage output circuit 1, and the switching element in the high-voltage output circuit 1 is operated in a state where the on-time is long. Control. As a result, the voltage at the high-voltage output point a sharply rises, and the high-voltage output voltage Vh can be obtained with good rising characteristics.

If the high-voltage rise adjusting capacitor 12 is not connected to the error amplifier 3, the rising speed of the high-voltage detection voltage Vb at the high-voltage detection point b is too fast, and the error detection voltage, which is the difference from the reference voltage Vref, is high. The value of Vf becomes too small early and the rise of the high voltage output circuit 1 is delayed. That is, the high-voltage rise adjusting capacitor 12 is connected to the error amplifier 3 in order to quickly raise the high-voltage output voltage Vh by suppressing the rising speed of the high-voltage detection voltage Vb.

The power supply in the high voltage generating circuit is turned off.
Then, the electric charge charged in the high-voltage rise adjusting capacitor 12 is transferred to the ground GND via the discharging resistor 13.
Is discharged.

As described above, in the high voltage generating circuit having the above configuration, the switching control signal Ssw is transmitted from the high voltage control circuit 2 of the high voltage stabilizing circuit 300 to output the high voltage output circuit 1
By performing the pulse width modulation (PWM), the response characteristics of the high-voltage stabilization are improved, and the high-voltage rise characteristics at the time of turning on the power are increased. Therefore, it is possible to cope with the recent high definition of the image quality. .

In the high-voltage generating circuit of FIG. 7, in order to ensure safety when the high-voltage output voltage Vh at the high-voltage output point a abnormally rises due to some trouble such as a failure of any part, An abnormally high voltage detection circuit 400 is provided. The abnormal high voltage detecting circuit 400 includes a rectifying / smoothing circuit 15 including a rectifying diode and a smoothing capacitor connected to the tertiary winding 4c of the flyback transformer 4, a point d which is an output terminal of the rectifying / smoothing circuit 15, and a ground GND. And a series circuit of abnormal high-voltage detection resistors 16 and 17 whose resistance division point e is connected to the high-voltage overvoltage protection circuit 2a in the high-voltage control circuit 2.

The pulse voltage induced in the tertiary winding 4c of the flyback transformer 4 is rectified and smoothed by the rectifying and smoothing circuit 15 to generate a DC voltage Vd at a point d. The DC voltage Vd is resistance-divided by the abnormal high-voltage detection resistors 16 and 17, and the resistance-divided abnormal high-voltage detection voltage Ve is applied to the high-voltage overvoltage protection circuit 2a. When the abnormal high voltage detection voltage Ve has reached the threshold level of the high voltage overvoltage protection circuit 2a, the high voltage overvoltage protection circuit 2a operates, and the high voltage control circuit 2 stops outputting the switching control signal Ssw to the high voltage output circuit 1. Then, the operation of the high voltage output circuit 1 is stopped to ensure safety.

[0018]

In the high voltage generating circuit configured as described above, the condition for optimizing the high voltage rising characteristics at the time of turning on the power is as follows.
And the time constant of the high-voltage capacitor 8, the combined capacitance of the high-voltage stabilizing capacitor 10 and the high-voltage rise adjusting capacitor 12, and the time constant of the high-voltage detecting resistor 9. The reason is as follows. It is a circuit part for detecting the time constant of the high voltage resistor 7 and the high voltage capacitor 8 which are the circuit parts for outputting to the cathode ray tube (CRT), and the high voltage detection voltage Vb at the high voltage detection point b for stabilizing the high voltage output voltage Vh. If the time constants of the high-voltage detecting resistor 9 and the capacitors 10 and 12 for stabilizing the high voltage and for adjusting the rising of the high voltage are different, the responsiveness of the feedback control operation for stabilizing the high voltage is deteriorated. . As such, both time constants must be equal.

The capacitance values of the high-voltage stabilizing capacitor 10 and the high-voltage rising adjusting capacitor 12 for optimizing the high-voltage rising characteristic at power-on will be calculated. For example, if the resistance value of the high-voltage resistor 7 is 400 MΩ, the capacitance value of the high-voltage capacitor 8 is 1500 pF, and the resistance value of the high-voltage detection resistor 9 is 40 kΩ, the combined capacitance value C12 of the high-voltage stabilizing capacitor 10 and the high-voltage rise adjusting capacitor 12 is Is 15 μF from the condition that the time constants are made equal. That is, 400 × 10 ⁶ × 1500 × 10 ^-12 = 40 × 10 ³ ×
From C12, C12 = 15 × 10 ^-6 . This 15 μF is shared between the high-voltage stabilizing capacitor 10 and the high-voltage rise adjusting capacitor 12.

By the way, in order to reduce the distortion of the image on the CRT in the steady operation state, the capacitance value of the high voltage stabilizing capacitor 10 is preferably set as small as possible so that the response characteristic of the high voltage stabilization becomes optimum. Several μ
F or less is preferable. Accordingly, the capacitance value of the high-voltage rise adjusting capacitor 12 is about 10 μF.
A backflow prevention diode 1 is connected between the high voltage rise adjusting capacitor 12 and the non-inverting input terminal (+) of the error amplifier 3.
In this case, the high voltage rising adjustment capacitor 12 does not operate in the normal operation state, and therefore, even if the capacitance value of the high voltage rising adjustment capacitor 12 is large, the image is not adversely affected. From such a thing,
As an actual design, for example, a high-voltage stabilizing capacitor 1
Assuming that the capacitance value of 0 is 5 μF, the capacitance value of the high-voltage rise adjusting capacitor 12 is 10 μF.

However, such a capacitance value is relatively large, and both of the capacitors 10 and 12 for stabilizing the high voltage and adjusting the rising of the high voltage have to use electrolytic capacitors. In fact, this is the case in FIG.

As described above, in the prior art high voltage generating circuit, electrolytic capacitors are used as both capacitors 10 and 12, but if electrolytic capacitors are used,
There are two problems:

One problem is that the tolerance of the capacitance value of the electrolytic capacitor is considerably large at ± 20%, which causes the high-voltage rise characteristics at the time of power-on to vary greatly. FIG. 8 shows a high-voltage rise adjusting capacitor 12.
3 shows a high-voltage rise characteristic at the time of power-on due to a change in the capacitance value of. The characteristic [a] is a high voltage rise characteristic when the capacitance value of the electrolytic capacitor 12 is the maximum allowable error (+ 20%), and the characteristic [b] is a high voltage rise characteristic when the capacitance value of the electrolytic capacitor 12 is standard (± 0%). In the characteristic [c], the capacitance value of the electrolytic capacitor 12 has a minimum allowable error (−20).
%) Shows the high voltage rising characteristics.

If the capacitance value of the electrolytic capacitor 12 is too large as shown in the characteristic [a], a phenomenon occurs in which the high-voltage output voltage Vh jumps at a high voltage rise when the power is turned on.
Therefore, when an electrolytic capacitor is used, it must be designed so that the high voltage rise time is long so that the high voltage output voltage Vh does not jump, and it is difficult to perform an optimal design.

Another problem is that a low-cost general electrolytic capacitor has a large leakage current. Both capacitors 10 and 12 for high voltage stabilization and high voltage rise adjustment
Is connected in parallel with the high-voltage detection resistor 9, and if the leakage current is large, the high-voltage output voltage Vh cannot be controlled.
As a result of abnormally increasing the high-voltage output voltage Vh, the high-voltage overvoltage protection circuit 2a in the high-voltage control circuit 2 in the high-voltage stabilization circuit 300 operates via the abnormal high-voltage detection circuit 400, and the operation of the high-voltage output circuit 1 also stops. As a result, the high voltage output may be stopped. For this reason, both capacitors 10 for high voltage stabilization and high voltage rise adjustment,
As 12, a special electrolytic capacitor having a small leakage current must be adopted, and the cost is high.

Further, the high-voltage generating circuit according to the above-mentioned prior art also has the following problem with high-voltage discharge.

A high output voltage Vh of, for example, 27 kV
In a CRT that operates with a high voltage, a high voltage discharge sometimes occurs due to dust and the like inside the CRT. There is a possibility that the high voltage output voltage Vh instantaneously abnormally rises due to large noise due to the high voltage discharge, and the high voltage overvoltage protection circuit 2a in the high voltage control circuit 2 malfunctions. If the high-voltage overvoltage protection circuit 2a malfunctions, the operation of the high-voltage output circuit 1 stops,
The image display on the CRT disappears. In order to redisplay the image, it is necessary to turn off the power once and then turn on the power again.

There are two possible causes for the abnormal rise of the high-voltage output voltage Vh due to large noise when high-voltage discharge occurs.

One cause is that the high voltage detection voltage Vb at the high voltage detection point b applied to the non-inverting input terminal (+) of the error amplifier 3 is reduced due to malfunction. In the high-pressure stabilizing loop L1, the error amplifier 3
As a result, the high-voltage output voltage Vh at the high-voltage output point a abnormally increases as a result of the feedback control acting to restore the voltage of the non-inverting input terminal (+) of the high-voltage power supply 5 to the reference voltage Vref.

Another cause is that the high voltage resistor 7 is actually 1
It is not a single resistor but a combined resistor. Among them, there are a focus adjustment volume and a grid G2 voltage adjustment volume in the electron gun, each of which is connected to each electrode of the CRT. Is fluctuated. When the equivalent resistance value of the high-voltage resistor 7 increases, the high-voltage detection voltage Vb at the high-voltage detection point b relatively decreases, and as a result, the high-voltage output voltage Vh at the high-voltage output point a
Will rise abnormally.

The high-voltage output voltage Vh caused by this high-voltage discharge
The unexpected operation of the high voltage overvoltage protection circuit 2a due to the abnormal rise of the circuit will be described with reference to FIG.

It is assumed that a high-voltage discharge has occurred at time t21. Then, noise due to high-voltage discharge enters the non-inverting input terminal (+) of the error amplifier 3, and the high-voltage detection voltage Vb applied to the non-inverting input terminal (+) falls below the reference voltage Vref. Sometimes. Then, in the high-voltage stabilization loop L1, feedback control is performed so that the high-voltage detection voltage Vb at the non-inverting input terminal (+) of the error amplifier 3 returns to the reference voltage Vref.
That is, the error detection voltage V output from the error amplifier 3
The value of f increases to the negative side, and the output of the high voltage output circuit 1 increases via the high voltage control circuit 2. As a result,
The high-voltage output voltage Vh at the high-voltage output point a abnormally rises. That is, in the normal state, when the high voltage output voltage Vh is Vh0, the high voltage output voltage Vh abnormally rises to the high voltage upper limit level Vh2 due to the high voltage discharge. That time is t22. This high-voltage upper limit level Vh2 corresponds to the threshold level of the high-voltage overvoltage protection circuit 2a in the high-voltage control circuit 2.

When the high voltage output voltage Vh at the high voltage output point a abnormally rises, the DC voltage Vd at the point d of the rectifying and smoothing circuit 15 in the abnormal high voltage detection circuit 400 also abnormally rises, and the abnormal high voltage detection voltage Ve at the resistance dividing point e becomes The threshold level of the high-voltage overvoltage protection circuit 2a in the high-voltage control circuit 2 is reached, and at time t22, the high-voltage overvoltage protection circuit 2a is operated to stop the operation of the high-voltage output circuit 1. When the operation of the high-voltage output circuit 1 stops, the voltage at the high-voltage output point a rapidly decreases and the screen disappears.

As a countermeasure to avoid stopping the high voltage output circuit 1 due to an abnormal rise of the high voltage output voltage Vh caused by such a high voltage discharge, the operation of the high voltage overvoltage protection circuit 2a in the high voltage control circuit 2 is delayed. It can be devised. However, since the high-voltage output voltage Vh continues to rise for the delayed time, there is a problem in terms of safety.

[0035]

A high voltage generating circuit according to the present invention comprises a high voltage capacitor, a first CR parallel circuit connected in series, a connection point between the high voltage capacitor and the first CR parallel circuit, and a high voltage resistor. And a second CR parallel circuit connected between the high-voltage detection points. By appropriately setting the capacitance value of the capacitor and the resistance value of the resistor in each CR parallel circuit, the high-voltage rising characteristic at the time of turning on the power of the high-voltage generating circuit is optimized.

This will be described in some detail. 1st C
If there is no resistance component in the R parallel circuit or the second CR parallel circuit, the voltage at the terminal point of the high-voltage capacitor will be too high, but if there is a resistance component, the voltage must be made sufficiently low. Becomes possible. Therefore, each of the capacitors in the first CR parallel circuit and the second CR parallel circuit may have a low withstand voltage. In addition, the presence of the resistance component can suppress the deterioration of the insulation resistance due to the leakage current of each capacitor, suppress the deterioration of the insulation resistance due to the moisture absorption of the printed circuit board, etc., and improve the high-voltage rise characteristics at power-on. Further, as conditions for optimizing the high-voltage rise characteristic at power-on, the time constant of the first CR parallel circuit and the time constant of the second CR parallel circuit with respect to the time constant of the high-voltage resistor and the high-voltage capacitor. No need to be equal. This ensures that the capacitance value of each of the above-mentioned capacitors can be made sufficiently small. Then, by appropriately determining the resistance value of the resistor and the capacitance value of the capacitor in the first CR parallel circuit, and properly determining those values also in the second CR parallel circuit, it is possible to optimize the high-voltage rising characteristic. It will be easier.

As described above, it is possible to use a capacitor having a small capacitance value as a capacitor in each CR parallel circuit, and it is not necessary to use an expensive electrolytic capacitor having a small leakage current. The high-pressure response characteristic of is also improved.

The high-voltage generating circuit according to the present invention comprises:
As an alternative to the normal high-pressure stabilization loop, ie, the feedback control by the first high-pressure stabilization loop, when the occurrence of an instantaneous boost that does not reach abnormal high pressure is detected, the instantaneous boost is transmitted to the high-pressure stabilization means. A second high-pressure stabilization loop including a boost detection means is added. This instantaneous boost detection means is cut off in the steady state operation of the high voltage generation circuit. The first high-voltage stabilization loop may malfunction due to noise due to high-voltage discharge or the like, and the high voltage may increase unexpectedly. In such a case, the increase is captured by the instantaneous pressure detection means, and the high voltage is detected. By operating the second high-pressure stabilization loop based on the above, the high pressure can be stabilized. Therefore, it is not necessary to induce a malfunction of the overvoltage protection means.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high voltage generating circuit according to a first aspect of the present invention includes a high voltage generating means for generating a high voltage having at least a high voltage capacitor and a high voltage resistor connected in parallel with the high voltage capacitor, and a high voltage generating means for detecting the high voltage. It is configured to include a detecting unit and a high-pressure stabilizing unit that controls the high-voltage generating unit to stabilize the high voltage based on the high-voltage detected by the high-voltage detecting unit. The high voltage detecting means includes: a first CR parallel circuit connected in series to the high voltage capacitor in the high voltage generating means; a connection point between the high voltage capacitor and the first CR parallel circuit; And a second CR parallel circuit connected between the high-voltage detection point of the resistor. According to this configuration, the high-voltage rise characteristics at power-on are optimized, the high-voltage response characteristics in a steady operation state are improved, and a capacitor having a small capacitance value and a small leakage current type are used. Since it is not necessary to use a capacitor, the cost can be reduced.

According to a second aspect of the present invention, in the high voltage generating circuit according to the first aspect, the high voltage generating means generates a flyback pulse by switching a current, and a flyback by the high voltage output circuit. A flyback transformer for converting a pulse into a boost flyback pulse, a high-voltage rectifier diode connected to the secondary winding of the flyback transformer, a high-voltage capacitor connected to the high-voltage rectifier diode, and a parallel connection to the high-voltage capacitor It has a high-voltage resistance. The high-voltage detection means includes a high-voltage detection resistor connected between the high-voltage resistor and ground, the first CR parallel circuit connected between the high-voltage capacitor and ground, A high-voltage detection point connecting the high-voltage detection resistor; and the second CR parallel circuit connected between a connection point between the high-voltage capacitor and the first CR parallel circuit. . According to this configuration, the same function as the first aspect is exhibited.

According to a third aspect of the present invention, there is provided a high-voltage generating circuit having at least a high-voltage capacitor and a high-voltage resistor connected in parallel with the high-voltage capacitor, and a high-voltage detecting means for detecting the high voltage. High-voltage stabilizing means for controlling the high-voltage generating means to stabilize the high voltage based on the high-voltage detecting voltage from the high-voltage detecting means; abnormal high-pressure detecting means for detecting an abnormal rise in the high voltage; And an overvoltage protection unit that controls the operation of the high-voltage generation unit to stop based on the detection of the abnormally high voltage. Further, the occurrence of an instantaneous boost that does not reach the abnormally high pressure is detected, and when this is detected, the instantaneous boost is given priority over the input to the high-pressure stabilizing means from the high-pressure detecting means. The configuration is provided with an instantaneous pressure increase detecting means for transmitting to the high pressure stabilizing means. According to this configuration, even if the original feedback control by the first high-voltage stabilization loop malfunctions due to noise due to high-voltage discharge or the like, the unexpected high-voltage rise is captured and the second high-voltage stabilization loop operates. As a result, the high voltage can be stabilized, and an unexpected malfunction of the overvoltage protection means can be prevented.

According to a fourth aspect of the present invention, there is provided the high voltage generating circuit according to the third aspect, wherein the high voltage generating means generates a flyback pulse by switching a current, and a flyback by the high voltage output circuit. A flyback transformer for converting a pulse into a boost flyback pulse, a high-voltage rectifier diode connected to the secondary winding of the flyback transformer, a high-voltage capacitor connected to the high-voltage rectifier diode, and a parallel connection to the high-voltage capacitor And a high-voltage resistance. The instantaneous boost detection means includes a Zener diode that conducts when the abnormally high pressure detection means detects an instantaneous boost level higher than the rated high voltage by the high voltage generator and lower than the high voltage upper limit level. , And a backflow prevention diode connected in series to the Zener diode. According to this configuration, the same operation as the fourth aspect is exhibited.

According to a fifth aspect of the present invention, in the high voltage generating circuit, the instantaneous boosting detecting means may be configured such that the abnormally high voltage detecting means is higher than a rated high voltage by the high voltage generating means instead of the configuration of the third aspect. When an instantaneous boosting level lower than the high-voltage upper limit level is detected, another error amplifier is provided which performs an output prior to the output of the error amplifier in the high-voltage stabilizing means. According to this configuration, the same operation as the third aspect is exhibited.

According to a sixth aspect of the present invention, there is provided a high-voltage generating circuit having at least a high-voltage capacitor and a high-voltage resistor connected in parallel with the high-voltage capacitor, and a high-voltage detecting means for detecting the high voltage. High-voltage stabilizing means for controlling the high-voltage generating means to stabilize the high voltage based on the high-voltage detecting voltage from the high-voltage detecting means; abnormal high-pressure detecting means for detecting an abnormal rise in the high voltage; Overvoltage protection means for controlling the operation of the high-voltage generation means to stop based on the detection of the abnormally high pressure, and further detects the occurrence of an instantaneous boost that does not reach the abnormally high pressure, and detects this An instantaneous boost detection means for transmitting the instantaneous boost to the high pressure stabilization means in preference to an input from the high pressure detection means to the high pressure stabilization means. The high voltage detecting means includes a first CR parallel circuit connected in series to the high voltage capacitor in the high voltage generating means, a connection point between the high voltage capacitor and the first CR parallel circuit, and a high voltage resistor in the high voltage generating means. And a second CR parallel circuit connected between the high-voltage detection point and the high-voltage detection point. This is claimed in claim 1
Corresponds to the combination of the configuration of claim 3 and the configuration of claim 3, and has the respective functions.

Hereinafter, specific embodiments of the high-voltage generating circuit according to the present invention will be described in detail with reference to the drawings. In the following embodiments, a high voltage generation circuit for driving a cathode ray tube (CRT) will be described as an example.

[First Embodiment] FIG. 1 is a circuit diagram of a high-voltage generating circuit according to a first embodiment. In FIG. 1, reference numeral 1 denotes a high-voltage output circuit, and the high-voltage output circuit 1 includes a switching element, a resonance capacitor, a damper diode, and the like. The high-voltage output circuit 1 generates a flyback pulse by switching with a switching element while flowing a DC current based on the input DC voltage + B to the primary winding 4a of the flyback transformer 4 connected to the next stage. Has become. As the high-voltage output circuit 1, any known high-voltage output circuit can be applied, and the specific configuration thereof is not directly related to the gist of the present invention, and thus the description thereof is omitted. Reference numeral 4 denotes a flyback transformer,
The secondary winding 4a is connected between output terminals of the high voltage output circuit 1. In the flyback transformer 4, a flyback pulse induced in the primary winding 4a induces a boost flyback pulse in the secondary winding 4b. An anode of a high-voltage rectifier diode 6 is connected to one end of a secondary winding 4b of the flyback transformer 4, and one end of a high-voltage resistor 7, one end of a high-voltage capacitor 8, and a high-voltage output terminal 14 are connected to its cathode. Output terminal 14
Is connected to the anode of a cathode ray tube (CRT) not shown. The boost flyback pulse induced in the secondary winding 4b of the flyback transformer 4
The high-voltage resistor 7 flows through the high-voltage resistor 7 and is smoothed by a high-voltage capacitor 8 connected in parallel with the high-voltage resistor 7, thereby generating a DC high-voltage output voltage Vh at a high-voltage output point a, which is the cathode of the high-voltage rectifier diode 6. Then, a high voltage output voltage V is applied from the high voltage output terminal 14 to the anode of the CRT.
h. The above high voltage output circuit 1, flyback transformer 4, high voltage rectifier diode 6,
A high-voltage generating circuit 100 includes the high-voltage resistor 7 and the high-voltage capacitor 8. The high voltage generation circuit 100 corresponds to a “high voltage generation unit” in the claims.

Reference numeral 200 is a high voltage detection circuit. The high-voltage detection circuit 200 is connected between the high-voltage resistor 7 in the high-voltage generation circuit 100 and the ground GND and has a connection point as a high-voltage detection point b. A first CR parallel circuit 21 connected between the terminal point c of the high voltage capacitor 8 and the ground GND; a high voltage detection point b; the high voltage capacitor 8 and the first CR;
The second C connected between the connection point c and the parallel circuit 21
An R parallel circuit 22 is provided. First CR parallel circuit 2
Reference numeral 1 denotes a high-voltage rising and high-voltage response characteristic adjusting capacitor (first capacitor) 31 connected in series between the terminal point c of the high-voltage capacitor 8 and the ground GND, and a high-voltage rising adjusting resistor connected in parallel thereto. (First resistor) 41. Second CR parallel circuit 22
Is a high voltage rising and high voltage response characteristic adjusting capacitor (second capacitor) 32 connected between the high voltage detecting point b and the terminal point c of the high voltage capacitor 8, and a high voltage rising adjusting resistor (parallel connected thereto). (Second resistor) 42. A high-voltage detection point b, which is a connection point between the high-voltage resistor 7 and the high-voltage detection resistor 9, is a node that outputs a high-voltage detection voltage Vb. This high voltage detection voltage Vb is equal to the high voltage output point a
Is divided by the high-voltage resistor 7 and the high-voltage detection resistor 9 into a high-voltage output voltage Vh. The high-voltage detection circuit 200 configured as described above corresponds to “high-voltage detection means” in claims.

The high voltage detection circuit 200 does not include the components of the high voltage detection circuit 250 in the case of the prior art. That is, both the backflow prevention diode 11 and the electrolytic capacitor 12 connected to the cathode thereof for adjusting the high voltage rise are connected to the discharge resistor 1 connected in parallel to the diode.
Neither 3 nor the high-voltage stabilizing electrolytic capacitor 10 connected to the high-voltage capacitor 8 is provided.

The high voltage stabilizing circuit 300 is the same as that of the prior art, and includes an error amplifier 3 using an operational amplifier and a high voltage control circuit 2. The non-inverting input terminal (+) of the error amplifier 3 is connected to the high-voltage detection point b of the high-voltage detection voltage Vb in the high-voltage detection circuit 200, and the inverting input terminal (-) is connected to the reference power supply 5 of the reference voltage Vref. I have. The high voltage control circuit 2 receives the error detection voltage Vf from the error amplifier 3 and outputs a switching control signal Ssw to the high voltage output circuit 1. As the high voltage control circuit 2,
There are a pulse width modulation (PWM) type in which the pulse width is varied to control the high voltage output voltage Vh, and a pulse width modulation (PWM) type in which the + B voltage input to the high voltage output circuit 1 is varied to control the high voltage output voltage Vh. is there. In any case, timing control based on the synchronization signal is performed. Hereinafter, the description will be made based on the pulse width modulation method. As the high-voltage control circuit 2, the high-voltage overvoltage protection circuit 2 a and the error amplifier 3, any known device can be applied, and the specific configuration is not directly related to the gist of the present invention, and therefore, the description is omitted. .

High voltage output point a in high voltage generation circuit 100
The high-voltage detection circuit 200 and the high-voltage stabilization circuit 300 and the high-voltage output circuit 1 in the high-voltage generation circuit 100 which form a high-voltage stabilization loop L <b> 1 are connected.

The high-voltage stabilizing circuit 300 corresponds to “high-voltage stabilizing means” in the claims.

An abnormal high-voltage detection circuit 400 for securing safety when the high-voltage output voltage Vh at the high-voltage output point a abnormally rises due to some trouble such as a failure of any part is also a conventional technology. It is configured as in the case. The abnormal high voltage detecting circuit 400 includes a rectifying / smoothing circuit 15 including a rectifying diode and a smoothing capacitor connected to the tertiary winding 4c of the flyback transformer 4, a point d which is an output terminal of the rectifying / smoothing circuit 15, and a ground GND. And a series circuit of abnormal high-voltage detection resistors 16 and 17 whose resistance division point e is connected to the high-voltage overvoltage protection circuit 2a in the high-voltage control circuit 2. That is, when the abnormal high voltage detection voltage Ve obtained by dividing the DC voltage Vd at the point d by resistance at the resistance dividing point e becomes equal to or higher than a predetermined level, the operation of the high voltage output circuit 1 is activated by operating the high voltage overvoltage protection circuit 2a. It is designed to stop. The level of the abnormal high voltage detection voltage Ve at that time corresponds to the high voltage output voltage Vh reaching the high voltage upper limit level Vh2. The abnormally high voltage detection circuit 400 corresponds to "abnormally high voltage detection means".

Next, the operation of the high voltage generating circuit of the first embodiment configured as described above will be described.

The switching of the switching element in the high voltage output circuit 1 of the high voltage generating circuit 100 generates a flyback pulse in the primary winding 4a of the flyback transformer 4 and boosts the voltage in the secondary winding 4b of the flyback transformer 4. Induce a pulse. The boost flyback pulse is rectified by the high-voltage rectifier diode 6, passed through the high-voltage resistor 7, and smoothed by the high-voltage capacitor 8 connected in parallel with the high-voltage resistor 7, thereby generating a DC high-voltage output voltage Vh at the high-voltage output point a. , From the high voltage output terminal 14 to the anode of a cathode ray tube (CRT).

The high-voltage output voltage Vh at the high-voltage output point a is resistance-divided by the high-voltage resistor 7 and the high-voltage detection resistor 9 in the high-voltage detection circuit 200. The high-voltage detection voltage Vb at the resistance-divided high-voltage detection point b is converted to a high-voltage stabilization circuit. 300
Is applied to the non-inverting input terminal (+) of the error amplifier 3 at. In the error amplifier 3, the reference voltage Vref from the reference power supply 5 is compared with the high-voltage detection voltage Vb, and an error detection voltage Vf, which is the difference, is output to the high-voltage control circuit 2.
The high-voltage control circuit 2 outputs a switching control signal Ssw having a pulse width corresponding to the magnitude of the error detection voltage Vf to the high-voltage output circuit 1.
Output to The high voltage output circuit 1 performs a switching operation of the switching element according to the pulse width of the input switching control signal Ssw, and outputs a flyback pulse corresponding to the switching operation. High voltage output voltage Vh is rated high voltage Vh0
When the value further decreases, the pulse width of the switching control signal Ssw increases, and the peak value of the flyback pulse increases. Conversely, when the high voltage output voltage Vh rises above the rated high voltage Vh0, the pulse width of the switching control signal Ssw becomes narrow, and the peak value of the flyback pulse becomes low.

By such feedback control, the high-voltage output voltage Vh at the high-voltage output point a becomes the rated high-voltage V
h0 is maintained.

When the high voltage output voltage Vh at the high voltage output point a rises to the high voltage upper limit level Vh2, the abnormal high voltage detection voltage Ve in the abnormal high voltage detection circuit 400 becomes higher than the threshold level, and the high voltage control circuit 2 of the high voltage stabilization circuit 300 The high-voltage overvoltage protection circuit 2a is operated.
Then, the high-voltage control circuit 2 stops outputting the switching control signal Ssw to the high-voltage output circuit 1, stops the operation of the high-voltage output circuit 1, and secures safety.

Next, the operation when the power is turned on will be described.

First, a description will be given of a change in the high-voltage rising characteristic according to the magnitude of the resistance value of the first resistor 41 in the first CR parallel circuit 21 with reference to FIG. FIG. 2A shows C
5 shows a change in the high voltage output voltage Vh at the high voltage output point a to the RT anode. FIG. 2B illustrates the second capacitor 32 and the first capacitor 32.
A voltage Vc at a connection point c with the capacitor 31 of FIG.

In FIGS. 2A and 2B, a first characteristic [A] indicated by a dotted line is a case where the resistance value of the first resistor 41 is small, and a second characteristic [B] indicated by a solid line. Is a case where the resistance value of the first resistor 41 is large. Before the power is turned on, the high voltage output voltage Vh at the high voltage output point a is at zero level, and the high voltage detection voltage Vb at the high voltage detection point b is also at zero level.

Assume that the power is turned on at time t0. When the power is turned on, the first capacitor 3 is connected from the secondary winding 4b of the flyback transformer 4 through the high-voltage rectifier diode 6, and further through the high-voltage resistor 7 and the second resistor 42.
1 rapidly flows into the first capacitor 31.
, That is, the voltage Vc at the point c sharply increases.
As shown in FIG. 2B, the rate of rise of the voltage Vc at the point c is the second characteristic having a large resistance value even in the case of the first characteristic [A] in which the resistance value of the first resistor 41 is small. It is almost the same in the case of [b].

In the case of the first characteristic [A] indicated by the dotted line, the time t
In FIG. 1, the voltage Vc at the point c reaches a peak,
In the case of the characteristic [b], the time t2 is slightly later.
At the peak. This time difference is not very meaningful. The charge on the first capacitor 31 is then
, And the voltage Vc at the point c gradually decreases. When the resistance value of the first resistor 41 is small (the first
Characteristic [a]), the discharge is quickly performed, and the voltage Vc at the point c is obtained.
Fall fast. Conversely, when the resistance value of the first characteristic [A] is large (second characteristic [B]), the discharge becomes slow and the voltage Vc falls slowly.

The voltage Vc at the falling point c is supplied to the non-inverting input terminal (+) of the error amplifier 3 via the second CR parallel circuit 22 including the second capacitor 32 and the second resistor 42. Applied. This is the high-voltage detection voltage Vb at the high-voltage detection point b.

As the resistance value of the first resistor 41 is smaller and the rise of the voltage Vc at the point c is faster (first characteristic [A]), the difference between the high voltage detection voltage Vb and the reference voltage Vref at the high voltage detection point b is increased. The difference, that is, the value of the error detection voltage Vf output from the error amplifier 3 increases to the minus side. At this time, the pulse width of the switching control signal Ssw output from the high voltage control circuit 2 is widened, the switching elements in the high voltage output circuit 1 are switched in a state where the on-time is long, and the high voltage output circuit 1 The peak value of the flyback pulse induced in the primary winding 4a increases, and the rising speed of the high-voltage output voltage Vh at the high-voltage output point a also increases. That is, in the case of the first characteristic [A] indicated by the dotted line in which the resistance value of the first resistor 41 is small, the high voltage output voltage Vh reaches the rated high voltage Vh0 at time t3.

Conversely, as the resistance value of the first resistor 41 increases and the rise of the voltage Vc at the point c is slower (second characteristic [b]), the high voltage detection voltage Vb and the reference voltage Vref
Is smaller on the minus side. At this time, the pulse width of the switching control signal Ssw from the high-voltage control circuit 2 becomes narrow, the switching element in the high-voltage output circuit 1 switches in a short on-time, and the peak value of the flyback pulse from the high-voltage output circuit 1 And the speed at which the high-voltage output voltage Vh increases at the high-voltage output point a also decreases. That is, in the case of the second characteristic [b] of the solid line in which the resistance value of the first resistor 41 is large, the high voltage output voltage Vh reaches the rated high voltage Vh0 at time t4.

The rising speed of the high-voltage output voltage Vh when the power is turned on can be adjusted by setting the resistance value of the first resistor 41 in the first CR parallel circuit 21. The adjustment can also be made by setting the resistance value of the second resistor 42 in the second CR parallel circuit 22.

The presence of the first resistor 41 and the second resistor 42 greatly reduces the voltage applied to the first capacitor 31 and the second capacitor 32. For example, the rated high voltage Vh0 is 27 kV, the resistance of the high voltage resistor 7 is 400 MΩ, the capacitance of the high voltage capacitor 8 is 1500 pF, the resistance of the high voltage detection resistor 9 is 40 kΩ, and the capacitance of the first capacitor 31 is 0.1 μF. The capacitance value of the second capacitor 32 is 0.2 μF, the resistance value of the first resistor 41 is 300 kΩ, and the resistance value of the second resistor 42 is 100 kΩ.
Ω.

Here, the first resistor 41 and the second resistor 42
The first resistance 4
Assume that the first and second resistors 42 are not present. The first capacitor 31 and the second capacitor 32 are regarded as parallel capacitors. The combined capacitance value of the parallel capacitors becomes 0.3 μF by addition. On the other hand, the capacitance value of the high-voltage capacitor 8 is 1500 pF
(= 0.0015 μF), and the ratio with 0.3 μF is:
1: 200. According to the general formula V = Q / C of the capacitor, the voltage applied to the 0.3 μF parallel capacitor is about 135 V because the voltage between both ends is inversely proportional to the capacitance value.

However, in the high-voltage generating circuit according to the first embodiment, the first resistor 41 is connected in parallel to the first capacitor 31, and the second resistor 42 is connected in parallel to the second capacitor 32. . The resistance value of the first resistor 41 is 300 k
Ω, the resistance value of the second resistor 42 is 100 kΩ,
Its partial pressure ratio is 1: 3. When the voltage of 27 kV is divided by the high-voltage resistance 7 of 400 MΩ and the high-voltage detection resistor 9 of 40 kΩ, the high-voltage detection voltage Vb at the high-voltage detection point b is about 2.7.
V. When this is divided at a division ratio of 1: 3, the voltage Vc at the point c is about 2V. That is, the first resistor 41
And the voltage V at point c assuming that there is no second resistor 42
While c becomes 135V, when the first resistor 41 and the second resistor 42 are provided, the voltage becomes only 2V. Note that this is a value in a steady operation state. According to the experiment, the maximum value Vc1 of the transient voltage applied to the point c when the power was turned on was about 10V. The characteristic in FIG. 2 shows this state. In the steady state of operation,
In both the first characteristic [a] and the second characteristic [b], the voltage Vc2 at the point c is about 2V.

As described above, it is possible to use low withstand voltage capacitors as the first capacitor 31 and the second capacitor 32. That is, it is not necessary to use an expensive electrolytic capacitor, and the cost can be reduced.

Further, the first resistor 41 and the second resistor 4
By adding 2, the deterioration of the insulation resistance due to the leakage current of the first capacitor 31 and the second capacitor 32 is suppressed, and the deterioration of the insulation resistance due to moisture absorption of the printed circuit board is suppressed. Therefore, it is possible to reduce the influence of the deterioration of the insulation resistance on the startup characteristics at power-on. That is, the reliability is improved.

In the case of the above example, a high-voltage resistor 7 of 400 MΩ
And the time constant τ1 of the 1500 pF high-voltage capacitor 8 is as follows: τ1 = 400 × 10 ⁶ × 1500 × 10 ^-12 = 6 × 10
It is ^-1 . The time constant τ2 of the first CR parallel circuit 21 including the first resistor 41 of 300 kΩ and the first capacitor 31 of 0.1 μF is as follows: τ2 = 300 × 10 ³ × 0.1 × 10 ^-6 = 3 × 10 ^-2 . The time constant τ3 of the second CR parallel circuit 22 including the second resistor 42 of 100 kΩ and the second capacitor 32 of 0.2 μF is as follows: τ3 = 100 × 10 ³ × 0.2 × 10 ^-6 = 2 × 10 ^-2 .

As can be seen from this example, the conditions for optimizing the rising characteristics at power-on are not necessarily the time constant τ1 of the high-voltage resistor 7 and the high-voltage capacitor 8 and the first constant.
Need not be equal to the time constant .tau.2 of the first capacitor 31. Similarly, it is not necessary to make the time constant τ1 of the high-voltage resistor 7 and the high-voltage capacitor 8 equal to the time constant τ3 of the second resistor 42 and the second capacitor 32.

The time constant τ2 of the first CR parallel circuit 21 is 5% of the time constant τ1 of the high voltage resistor 7 and the high voltage capacitor 8, and the time constant τ3 of the second CR parallel circuit 22 is the time constant τ1
Of about 3.3%.

The above can be said as follows. Time constant τ1 of high-voltage resistor 7 and high-voltage capacitor 8
When the time constants .tau.2 and .tau.3 of the first CR parallel circuit 21 and the second CR parallel circuit 22 can be made sufficiently small as compared with the above, the high voltage rising and high voltage response characteristic adjusting capacitors 31 and 32 are used to adjust the high voltage rising. Assuming that the resistors 41 and 42 are connected in parallel, the capacitance values of the high-voltage rise and high-voltage response characteristic adjusting capacitors 31 and 32 are, for example, 0.1 μF or 0.2 μF as in the above example.
That is, it is enough to be small enough. The value of 0.1 μF or 0.2 μF is much smaller than the value of 5 μF of the high-voltage stabilizing capacitor 10 and 10 μF of the rise adjusting capacitor 12 in the conventional technology, which is a very small value of several percent. That is, it is not necessary to use an electrolytic capacitor as both the first capacitor 31 and the second capacitor 32.

As described with reference to FIG. 2, when the resistance value of the first resistor 41 is reduced, the high voltage rise time is shortened. Conversely, when the resistance value of the first resistor 41 is increased, , The high pressure rise time is longer.

Apart from the above, when the resistance value of the second resistor 42 is reduced, the high voltage rise time becomes longer,
Conversely, when the resistance value of the second resistor 42 is increased, the high voltage rise time becomes shorter.

Therefore, by appropriately combining the resistance value of the first resistor 41 and the resistance value of the second resistor 42, it is possible to optimally adjust the high-voltage rising characteristic according to various conditions. It is.

Note that a high-voltage generation circuit that does not have the abnormal high-voltage detection circuit 400 is also included in the embodiment of the present invention.

[Second Embodiment] FIG. 3 is a circuit diagram of a high voltage generating circuit according to a second embodiment of the present invention. Since the same reference numerals as those in FIG. 1 for the first embodiment indicate the same components in FIG. 3 for the second embodiment,
Here, detailed description is omitted. The configuration of the second embodiment is different from that of the first embodiment as follows.

The point is that an instantaneous boost detection circuit 500 for detecting occurrence of an instantaneous boost due to a high-voltage discharge inside the CRT is provided. This instantaneous boost detection circuit 500 has the configuration shown in FIG.
As shown in the figure, a backflow prevention diode 27 having an anode connected to a point d which is an output terminal of the rectifying and smoothing circuit 15 in the abnormally high voltage detection circuit 400, and the backflow prevention diode 2
And a Zener diode 26 having a cathode connected to the cathode of the reference numeral 7 and an anode connected to the non-inverting input terminal (+) of the error amplifier 3.

The Zener voltage VZD in the Zener diode 26 is set so as not to conduct in the steady state of the high voltage generating circuit. The backflow prevention diode 27 is for preventing a current from flowing from the high voltage detection point b to the point d. The instantaneous boost detection circuit 500 detects the occurrence of an instantaneous boost due to a high-voltage discharge in the CRT that does not reach an abnormally high level at which the high-voltage overvoltage protection circuit 2a operates. Circuit 20
From 0, the DC voltage Vd at the point d of the rectifying / smoothing circuit 15 which is the instantaneous boost is input to the error amplifier 3 in preference to the input of the high voltage detection voltage Vb to the error amplifier 3 of the high voltage stabilization circuit 300. ing. This instantaneous boost detection circuit 500 corresponds to “instantaneous boost detection means” in the claims. Further, the abnormally high voltage detecting circuit 400 corresponds to “abnormally high voltage detecting means”.

This instantaneous boost detection circuit 500 is for preventing the high-voltage overvoltage protection circuit 2a in the high-voltage control circuit 2 from operating due to the instantaneous boost due to the high-voltage discharge. In the second embodiment,
The high voltage overvoltage protection circuit 2a corresponds to "overvoltage protection means" in the claims.

In the second embodiment, the high-voltage detection circuit 200, the high-voltage stabilization circuit 300, and the high-voltage output circuit 1 in the high-voltage generation circuit 100, which are circulated to the high-voltage output point a in the high-voltage generation circuit 100, Form a first high-pressure stabilization loop L1. Further, the abnormally high voltage detection circuit 400, the instantaneous voltage increase detection circuit 500, the high voltage stabilization circuit 300, and the high voltage output circuit 1 in the high voltage generation circuit 100 form a second high voltage stabilization loop L2.

Next, the operation when a high-voltage discharge occurs inside the CRT will be described with reference to the waveform diagram of FIG.

At time t11, a high-voltage discharge occurs inside the CRT, noise due to the high-voltage discharge enters the non-inverting input terminal (+) of the error amplifier 3, and the first high-voltage stabilization loop L1
It is assumed that the high-voltage detection voltage Vb applied to the non-inverting input terminal (+) drops below the reference voltage Vref.
Then, the feedback control operates so that the high-voltage detection voltage Vb is raised and returned to the reference voltage Vref.
That is, the error detection voltage V output from the error amplifier 3
The value of f becomes negative, and the output of the high voltage output circuit 1 is increased via the high voltage control circuit 2. As a result, the high voltage output voltage Vh at the high voltage output point a starts to increase. That is, in the steady operation state, when the high-voltage output voltage Vh is the rated high-voltage Vho, the high-voltage output voltage Vh rises to the instantaneous boost level Vh1 at time t12 due to noise due to the high-voltage discharge. The instantaneous boost level Vh1 is a high-voltage upper limit level Vh that is the level of the high-voltage output voltage Vh when the high-voltage overvoltage protection circuit 2a is operated.
2, it is located between the rated high voltage Vh0 and the high voltage upper limit level Vh2. The instantaneous boosting level Vh1 at the high voltage output point a at time t12 corresponds to the conduction voltage in the instantaneous boosting detection circuit 500, that is, the Zener voltage VZD of the Zener diode 26. More specifically, a voltage obtained by adding the forward voltage VF of the backflow prevention diode 27 to the DC voltage Vd at the point d at the time t12 exceeds the Zener voltage VZD.

That is, as the high-voltage output voltage Vh at the high-voltage output point a increases, the DC voltage Vd at the point d of the rectifying and smoothing circuit 15 also increases, and this DC voltage Vd becomes (VZD-VF).
At time t12 when the Zener diode 26 which has been cut off with respect to the error amplifier 3 until then is reached.
Becomes conductive. As a result, the rising DC voltage Vd at the point d is reduced by the backflow prevention diode 27 and the Zener diode 26.
Is applied to the non-inverting input terminal (+) of the error amplifier 3. At this time, the voltage applied to the non-inverting input terminal (+) by the turned-on instantaneous boost detection circuit 500 is set to Vg. That is, prior to the high voltage detection voltage Vb applied to the non-inverting input terminal (+) in the first high voltage stabilization loop L1, the instantaneous boost detection voltage Vg in the second high voltage stabilization loop L2. Is applied to the non-inverting input terminal (+).

The series of operations just described are performed because the voltage at the non-inverting input terminal (+) of the error amplifier 3 has decreased due to noise due to the high voltage discharge. The voltage at the non-inverting input terminal (+) is rapidly increased by the conduction of the Zener diode 26, and when the Zener diode 26 becomes conductive, the error detection voltage Vf from the error amplifier 3 quickly recovers to the reference voltage Vref. Then, since the control of the high-voltage output circuit 1 by the high-voltage control circuit 2 is stopped, the increase in the peak value of the flyback pulse output from the high-voltage output circuit 1 stops there, and the high-voltage output voltage Vh at the high-voltage output point a instantaneously changes. It becomes stable at the boost level Vh1. This state continues from time t12 to time t13.

High-voltage output voltage Vh is instantaneously boosted level Vh
Therefore, the DC voltage Vd at point d in the rectifying / smoothing circuit 15 is also stabilized at the corresponding level, and the abnormal high voltage detection voltage Ve at the resistance dividing point e becomes the threshold level of the high voltage overvoltage protection circuit 2a in the high voltage control circuit 2. Will be stabilized at a lower level before reaching. That is, the high-voltage overvoltage protection circuit 2a does not operate due to the noise due to the high-voltage discharge, and therefore the operation of the high-voltage output circuit 1 does not stop.

The high-voltage output voltage Vh at the high-voltage output point a due to the conduction of the Zener diode 26 is temporarily stabilized at the instantaneous boosting level Vh1, but thereafter, from the time t13 to the time t14, the original first high-voltage stabilization is performed. Loop L1
, The high-voltage output voltage Vh gradually decreases to the rated high-voltage Vh0, and is stabilized at that Vh0.

As described above, the high-voltage overvoltage protection circuit 2a does not operate due to the noise caused by the high-voltage discharge.
Screen does not disappear unexpectedly.

Further, there are the following advantages. In the case of the conventional technique, when there is any trouble such as a failure of a component in the high-voltage stabilization loop L1, the high-voltage output voltage Vh at the high-voltage output point a may abnormally increase. However, in the second embodiment, in addition to the first high-pressure stabilization loop L1, the second high-pressure stabilization loop L1
2 is also provided, when the high-voltage output voltage Vh at the high-voltage output point a is abnormally increased due to some trouble such as a component failure in the first high-voltage stabilization loop L1, the second high-voltage stabilization is performed. It is possible to suppress the abnormal increase of the high-voltage output voltage Vh by the feedback control via the loop L2, to stabilize the high-voltage output voltage Vh at the instantaneous boost level Vh1, and to return to the rated high voltage Vh0.

Further, due to some trouble, the high-voltage output voltage V
When the voltage h has risen abnormally, the abnormal high voltage detection voltage Ve at the point e becomes equal to or higher than a predetermined threshold level, the high voltage overvoltage protection circuit 2a is operated, and the output from the high voltage control circuit 2 to the high voltage output circuit 1 is output. To stop the operation of the high-voltage output circuit 1 to ensure safety.

[Third Embodiment] FIG. 5 is a circuit diagram of a high voltage generating circuit according to a third embodiment of the present invention. Embodiments 1 and 2
Since the same reference numerals as those in FIGS. 1 and 3 indicate the same components in FIG. 5 of the third embodiment, detailed description thereof will be omitted here. In the third embodiment, the configuration of the instantaneous boost detection circuit 501 is the same as that of the second embodiment.
Is different.

As shown, the instantaneous boost detection circuit 501 includes two resistors 5 for dividing the DC voltage Vd from the rectifying and smoothing circuit 15 in the abnormal high voltage detection circuit 400.
1, 52, an error amplifier 53 using an operational amplifier,
A reference power supply 54 for the reference voltage Vref2 and a backflow prevention diode 55 connected to the output terminal of the error amplifier 53
And a backflow prevention diode 56 connected to the output terminal of the error amplifier 3 of the high voltage detection circuit 200. The two backflow prevention diodes 55 and 56 have their cathodes connected to each other and are input to the high voltage control circuit 2. The abnormally high voltage detection circuit 400, the instantaneous voltage increase detection circuit 501, the high voltage stabilization circuit 300, and the high voltage output circuit 1 in the high voltage generation circuit 100 form a second high voltage stabilization loop L2.

In the instantaneous boost detection circuit 501, when the voltage Vk obtained by dividing the DC voltage Vd from the rectifying and smoothing circuit 15 by the resistors 51 and 52 becomes larger than the reference voltage Vref2 of the reference power supply 54, the error amplifier 53 outputs Error detection voltage V
m increases on the positive side. However, the resistance values of the resistors 51 and 52 are set such that the error detection voltage Vm is lower than the error detection voltage Vf from the error amplifier 3 of the high voltage stabilization circuit 300 in the steady state of the high voltage generation circuit. I have. Accordingly, in the steady operation state, the backflow prevention diode 55 does not conduct, and the backflow prevention diode 56 conducts, so that the error amplifier 3 in the first high-voltage stabilization loop L1 has priority. That is,
The second high-pressure stabilization loop L2 is in a cutoff state.

As in the case of the second embodiment, when a high-voltage discharge occurs, the error detection voltage Vm from the error amplifier 53 of the instantaneous boost detection circuit 501 in the second high-voltage stabilization loop L2 is equal to the error amplifier 3 Error detection voltage V
f, the backflow prevention diode 56 becomes non-conductive, the backflow prevention diode 55 becomes conductive, and feedback control is performed based on the increased error detection voltage Vm. Then, the high-voltage output voltage Vh at the high-voltage output point a stabilizes at the instantaneous boosting level Vh1, and thereafter returns to the rated high-voltage Vh0. Therefore, Embodiment 2
The same effect as in the case of is exhibited.

[Fourth Embodiment] FIG. 6 is a circuit diagram of a high-voltage generating circuit according to a fourth embodiment of the present invention. Embodiments 1 and 2
The same reference numerals as in FIGS. 1 and 3 indicate the same components in FIG. 6 of the fourth embodiment, and therefore, detailed description will be omitted here. The fourth embodiment is different from the second and third embodiments in the form of the instantaneous boosting detection circuit 502.

The instantaneous boost detection circuit 502 has the same zener diode 26 and backflow prevention diode 27 as in the second embodiment, but the anode of the backflow prevention diode 27 is rectified by the abnormal high pressure detection circuit 400. Instead of connecting to the smoothing circuit 15, it is connected to another rectifying and smoothing circuit 61. That is, a rectifying / smoothing circuit 61 composed of a rectifying diode and a smoothing capacitor is connected to another tertiary winding 4d of the flyback transformer 4, and a reverse current preventing diode 27 is connected to an output terminal n of the rectifying / smoothing circuit 61.
Anodes are connected.

The operation of the fourth embodiment is the same as that of the second embodiment, and the effect is the same.

In the above-described second to fourth embodiments, the form of the high-voltage detection circuit 200 does not need to be the one shown in FIGS. 1, 3 and 5, and for example, FIG. May be the same as the high voltage detection circuit 250 shown in FIG. That is, any known high-voltage detection circuit 200 can be applied, and its specific configuration is not directly related to the gist of the second to fourth embodiments, and therefore, the description thereof is omitted.

In each embodiment, the first CR parallel circuit 21 and the second CR parallel circuit 2
The high-voltage generation circuit having the high-voltage detection circuit 200 provided with the first and second aspects corresponds to claims 1, 2, and 6. Further, an instantaneous boost detection circuit 50 forming a second high-pressure stabilization loop L2
The high-voltage generating circuit provided with 0, 501, 502
6 is supported.

[0103]

According to the present invention, by appropriately setting the capacitance value of the capacitor and the resistance value of the resistor in the two CR parallel circuits, the high voltage rising characteristic at the time of turning on the power of the high voltage generating circuit is optimized. However, as conditions for optimizing the high-voltage rise characteristics at power-on, the time constant of the first CR parallel circuit and the time constant of the second CR parallel circuit are different from the time constant of the high-voltage resistor and the high-voltage capacitor. Need not be equal. This ensures that the capacitance value of each of the above-mentioned capacitors can be made sufficiently small. This allows
By adding a resistor in each CR parallel circuit, the voltage applied to the capacitor in each CR parallel circuit is greatly reduced, and a capacitor with a low withstand voltage and a small capacitance value can be adopted as each capacitor. It is not necessary to use a type of electrolytic capacitor, and the cost can be made advantageous. That each C
As the capacitor of the R parallel circuit, a capacitor having a small capacity tolerance can be adopted, and the high-voltage rising characteristic at power-on can be made appropriate with little variation. in addition,
High-pressure response characteristics in a steady operation state can also be improved. In addition, the deterioration of insulation resistance due to the leakage current of the capacitors in each CR parallel circuit is suppressed, and the influence on the high voltage rise time at power-on due to the deterioration of insulation resistance due to moisture absorption of the printed circuit board can be significantly reduced, thus improving reliability. Can be higher. Further, the degree of freedom in adjusting the high voltage rise time is increased by setting the resistance value of the resistor in each CR parallel circuit.

Further, according to the present invention, even when noise due to high voltage discharge or the like occurs and the high voltage unexpectedly rises abnormally, malfunction of the high voltage overvoltage protection circuit can be prevented. An abnormal increase in high pressure due to a failure of a component or the like in the stabilization loop can be prevented, and safety can be further improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a high-voltage generation circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a high-voltage rising characteristic of the high-voltage generation circuit according to the first embodiment;

FIG. 3 is a circuit diagram of a high-voltage generation circuit according to a second embodiment of the present invention.

FIG. 4 is a waveform diagram when a high-voltage discharge occurs in the high-voltage generation circuit according to the second embodiment.

FIG. 5 is a circuit diagram of a high-voltage generation circuit according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a high-voltage generation circuit according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram of a high-voltage generation circuit according to a conventional technique.

FIG. 8 is a diagram showing a high-voltage rise characteristic of a high-voltage generation circuit according to a conventional technique.

FIG. 9 is a waveform diagram when a high-voltage discharge occurs in a high-voltage generation circuit according to the related art.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 high-voltage output circuit, 2 high-voltage control circuit, 2 a high-voltage overvoltage protection circuit, 3 error amplifier, 4 flyback transformer, 4 a primary winding, 4 b secondary winding, 4 c tertiary winding 4d: another tertiary winding, 5: reference power supply, 6: high-voltage rectifier diode, 7: high-voltage resistor, 8: high-voltage capacitor, 9 ...
High-voltage detection resistor, 10: High-voltage stabilizing capacitor, 11: Backflow prevention diode, 12: High-voltage rise adjusting capacitor, 13: Discharge resistor, 14: High-voltage output terminal, 15 ...
Rectifying smoothing circuit, 16, 17 ... abnormal high voltage detection resistor, 21 ...
First CR parallel circuit, 22... Second CR parallel circuit, 26
... Zener diode, 27 ... Backflow prevention diode, 3
DESCRIPTION OF SYMBOLS 1 ... 1st capacitor, 32 ... 2nd capacitor, 41
.. A first resistor, 42 a second resistor, 51, 52 a momentary boost detection resistor, 53 an error amplifier, 54 a reference power supply, 5
5, 56 ... backflow prevention diode, 61 ... rectification smoothing circuit,
100: High voltage generation circuit, 200: High voltage detection circuit, 300
... High voltage stabilization circuit, 400 ... Excessive high voltage detection circuit, 50
0, 501, 502... Instantaneous boost detection circuit, L1.
High pressure stabilization loop of L2 ... second high pressure stabilization loop,
a: High voltage output point, b: High voltage detection point, c: Terminal point of high voltage capacitor, d: Output point of rectifying and smoothing circuit, e: Resistance dividing point, Vh: High voltage output voltage, Vh0: Rated high voltage, Vh
1: Instantaneous boost level, Vh2: High voltage upper limit level, Vb
... High voltage detection voltage, Vc ... C point voltage, Vd ... DC voltage,
Ve: abnormal high voltage detection voltage, Vf: error detection voltage, Vm:
Error detection voltage

Claims (6)

[Claims] 1. A high voltage generating means having at least a high voltage capacitor and a high voltage resistor connected in parallel to generate a high voltage, a high voltage detecting means for detecting the high voltage, and a high voltage detecting voltage based on a high voltage detected by the high voltage detecting means. High-voltage stabilizing means for controlling so as to stabilize a high voltage generated by the high-voltage generating means, wherein the high-voltage detecting means includes a first CR parallel circuit connected in series to a high-voltage capacitor in the high-voltage generating means; A high-voltage capacitor and a second CR parallel circuit connected between a connection point of the first CR parallel circuit and a high-voltage detection point of the high-voltage resistor in the high-voltage generating means. Generator circuit. 2. A high-voltage output circuit for generating a flyback pulse by switching current, a flyback transformer for transforming a flyback pulse from the high-voltage output circuit into a boost flyback pulse, and the flyback A high-voltage rectifier diode connected to the secondary winding of the transformer, a high-voltage capacitor connected to the high-voltage rectifier diode, and a high-voltage resistor connected in parallel to the high-voltage capacitor. Connecting a high-voltage detection resistor connected between the high-voltage resistor and ground, the first CR parallel circuit connected between the high-voltage capacitor and ground, and the high-voltage resistor and high-voltage detection resistor. The second C connected between the high voltage detection point and the connection point between the high voltage capacitor and the first CR parallel circuit. High-voltage generating circuit according to claim 1 which is assumed that a parallel circuit. 3. A high voltage generating means for generating a high voltage having at least a high voltage capacitor and a high voltage resistor connected in parallel to the high voltage capacitor, a high voltage detecting means for detecting the high voltage, and a high voltage detecting voltage by the high voltage detecting means. A high-pressure stabilizing means for controlling the high pressure by the high-pressure generating means to be stabilized; an abnormal high-pressure detecting means for detecting an abnormal rise of the high pressure; and the high-pressure generating means based on the detection of the abnormal high pressure by the abnormal high-pressure detecting means. Overvoltage protection means for controlling the operation of the means to stop, further detecting the occurrence of an instantaneous boost that does not reach the abnormally high pressure, and detecting the high pressure from the high-pressure detection means when detecting this. A high-voltage generating circuit comprising: an instantaneous boost detection unit that transmits the instantaneous boost to the high-voltage stabilization unit prior to an input to the stabilization unit. 4. A high-voltage output circuit for generating a flyback pulse by switching current, a flyback transformer for transforming a flyback pulse from the high-voltage output circuit into a boost flyback pulse, and the flyback A high-voltage rectifier diode connected to the secondary winding of the transformer, a high-voltage capacitor connected to the high-voltage rectifier diode, and a high-voltage resistor connected in parallel to the high-voltage capacitor. The means includes a Zener diode that conducts when the abnormally high voltage detecting means detects an instantaneous boosting level higher than the rated high voltage by the high voltage generating means and lower than the high voltage upper limit level, and connected in series to the Zener diode. 4. A backflow prevention diode according to claim 3, further comprising: High-voltage generation circuit. 5. The method according to claim 3, wherein the instantaneous voltage increase detecting means is configured such that the abnormally high voltage detecting means is higher than a rated high voltage by the high voltage generating means and lower than a high voltage upper limit level. 4. The high-voltage generating circuit according to claim 3, further comprising another error amplifier that outputs an output prior to the output of the error amplifier in the high-voltage stabilizing means when a boost level is detected. 6. A high voltage generating means for generating a high voltage having at least a high voltage capacitor and a high voltage resistor connected in parallel to the high voltage capacitor, a high voltage detecting means for detecting the high voltage, and a high voltage detecting voltage detected by the high voltage detecting means. A high-pressure stabilizing means for controlling the high pressure by the high-pressure generating means to be stabilized; an abnormal high-pressure detecting means for detecting an abnormal rise of the high pressure; and the high-pressure generating means based on the detection of the abnormal high pressure by the abnormal high-pressure detecting means. Overvoltage protection means for controlling the operation of the means to stop, further detecting the occurrence of an instantaneous boost that does not reach the abnormally high pressure, and detecting the high pressure from the high-pressure detection means when detecting this. An instantaneous pressure increase detecting means for transmitting the instantaneous voltage increase to the high voltage stabilizing means in preference to an input to the stabilizing means; A first CR parallel circuit connected in series to the high-voltage capacitor, and a connection point between the high-voltage capacitor and the first CR parallel circuit and a high-voltage detection point of the high-voltage resistor in the high-voltage generating means. A high-voltage generating circuit, comprising: a second CR parallel circuit.