JPH04357771A - Focus coil driving device - Google Patents

Abstract

PURPOSE:To improve the focus performance of the entire screen by providing the focus coil driving device with low power consumption obtaining the accurate focus current. CONSTITUTION:A pulse modulation/demodulation circuit 6 compares a carrier signal generated from a carrier signal generator 7 with a signal to be modulated to output a pulse width modulation signal. A switching amplifier 1 composed of three switch circuits for the positive power source, negative power source, and a GND performs switching operation based on the pulse width demodulation signal. The current of the focus coil 2 is detected as a voltage signal by a serially connected current detection resistor 3, and an error detection amplifier 4 amplifies the difference with the focus reference signal to output the error signal. Thus, the focus current with less distortion can be obtained since the output of the switching amplifier takes three values.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coil drive circuit for a focus coil or the like of a cathode ray tube.

0002

[Prior Art] A low power consumption device that passes current through a coil switches the power supply voltage according to the output voltage.
There are power supply voltage switching type linear amplifiers that operate the amplification elements at the optimum power supply voltage, and pulse width modulation type switching amplifiers that turn switching elements on and off using pulse width modulation signals with pulse widths that correspond to the input signal level. Related devices of this type include, for example, Japanese Patent Publication No. 62-22484 and Japanese Patent Publication No. 1-32684.

0003

Generally, when driving an inductance such as a focus coil, a class B output circuit suitable for a large output amplifier is used. However, B
Even in a class output circuit, the efficiency is about 70% at maximum output, and the loss is large. On the other hand, pulse width modulation type switching amplifiers are extremely low-loss amplifiers, but have the problem of large waveform distortion. For this reason, when a pulse width modulation type switching amplifier is used as a focus coil driving device, there is a problem that deviation from the optimum focus occurs due to waveform distortion, and focus deteriorates.

[0004] An object of the present invention is to provide a highly efficient focus coil drive device that can flow a highly accurate focus current.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention uses a high-efficiency pulse width modulation type switching amplifier, and provides switching elements at the positive power source, negative power source, and GND for the focus coil. , these switching elements are switched according to the polarity of the slope of the focus coil current.

[0006]

[Operation] The switching amplifier performs amplification by switching operation, so it realizes a focus coil drive device with low power consumption.The switching amplifier output has three values: positive power supply voltage, negative power supply voltage, and GND, so the waveform of the focus coil current It is possible to suppress distortion and bring the entire screen into optimal focus.

[0007]

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 4. 1 is a block diagram showing the configuration of an electromagnetic focus circuit according to the present invention, FIG. 2 is a waveform diagram of the operation of the electromagnetic focus circuit of FIG. 1, and FIG. 3 is a circuit diagram showing details of each block of the electromagnetic focus circuit of FIG. 1. FIG. 4 is an operational waveform diagram for explaining the operation of each block of the electromagnetic focus circuit shown in FIG.

In FIG. 1, a carrier signal generator 7 outputs a carrier signal having a frequency n times that of a horizontal blanking signal (hereinafter referred to as an H.BLK signal) b. The pulse width modulation circuit 6 compares the error signal passed through the low pass filter (hereinafter referred to as LPF) 5 with the carrier signal and outputs a pulse width modulation signal. The switching amplifier 1 performs a switching operation based on a pulse width modulation signal. The switch 10 is controlled by the pulse width modulation signal c shown in FIG. 2, the switch 8 is controlled by the pulse width modulation signal d, and the switch 9 is controlled by the pulse width modulation signal e. In addition, switches 8, 9, 10 in FIG.
is in an on state when the pulse width modulation signals c, d, and e in FIG. 2 are at a high level, and is in an off state when they are at a low level.

In FIG. 2, in the first half period T1 of the horizontal cycle, the slope of the focus current g flowing through the focus coil 2 is positive, so switching is performed between the positive power source and GND. During this period, the slope of the current changes from positive to 0 as time passes, so the switches 8 and 10 are controlled so that the on period of switch 8 gradually becomes shorter and the on period of switch 10 gradually becomes longer. The waveforms of the output voltage f of the switching amplifier 1 and the first half of the focus current g can be obtained. Conversely, in the second half period T2 of the horizontal cycle, the slope of the focus current is negative, so switching is performed between the negative power supply and GND. During this period, the slope of the current changes from 0 to negative as time passes, so the switches 9 and 10 are controlled so that the on period of the switch 9 gradually becomes longer and the on period of the switch 10 gradually becomes shorter. The waveforms of the latter half of the output voltage f and focus current g of the switching amplifier 1 can be obtained. Note that during the first half period T1, the switch 9 is always off, and during the second half period T2, the switch 8 is always off. The focus current g obtained in this manner is compared with a horizontal periodic parabola wave (hereinafter referred to as H parabola wave) a, which is a focus reference signal, by a current detection resistor 3 and an error detection amplifier 4, and after passing through an LPF 5, an error signal is generated. The signal is returned to the pulse width modulation circuit 6 as a signal. This allows a focus current similar to the focus reference signal a to flow through the focus coil 2.

Next, the specific configuration and operation of the first embodiment will be explained using FIGS. 3 and 4. Assume that the desired focus current is an upwardly convex H parabolic wave. The carrier signal generation circuit 7 is a phased lock loop (hereinafter referred to as PLL).
It is abbreviated as ) 84, Exclusive-OR (hereinafter, Ex
-Abbreviated as OR. ) Consists of a gate 83, an integrator 58, a capacitor 59, and a resistor 60. PLL84 has H. A BLK signal b is input, and a carrier clock c having a frequency n times higher is output. Ex-OR gate 83
The output of the comparator 49 is input to one terminal of the , and the output of the pull 84 is input to the other terminal. A signal d for switching the polarity of the power source to be switched is obtained by passing the H parabolic wave a through the differentiating circuit 61 and the comparator 49. The signal d becomes high level in the first half period T1 of the horizontal cycle, and becomes low level in the second half period T2. This signal d and carrier clock c are compared by an Ex-OR gate 83 to obtain a signal e whose phase is inverted between the first half and the second half of the horizontal period. The signal e is passed through an integrator 58 to obtain a triangular carrier signal g biased with opposite polarities in the first half and the second half of the horizontal period. The DC component is removed by capacitor 59. Note that the resistor 60 is a bias resistor. When the carrier signal is g, a modulated signal having a horizontal periodic sawtooth waveform such as f is required in order to cause an H parabolic wave current such as o to flow through the focus coil. The carrier signal g and the modulated signal f are compared by a comparator 47, and pulse width modulated signals j, k,
Obtain the original signal h of l and m. The original signal h and the inverted signal i of the signal d are applied to the Ex-OR gate 81 to obtain a first pulse width modulation signal j whose phase is inverted with respect to the original signal h in the second half period T2. First pulse width modulation signal j and inverter 50
The switch circuit 10 is controlled by both signals of the second pulse width modulation signal k inverted by . The switch circuit 10 operates during a high level period (
It turns on during the low level period of the second pulse width modulation signal k). The switch circuit 8 on the positive power supply side is turned off when the output of the gate drive circuit 54 is at a high level, and turned on when the output is at a low level. An OR gate 5 is input to the gate drive circuit 54.
2 are connected. The OR gate 52 receives the signal i and the first pulse width modulation signal j. OR gate 52
outputs a third pulse width modulation signal l such that the switch circuit 8 repeats on and off during the first half period T1 and is always off during the second half period T2. Conversely, the switch circuit 9 on the negative power supply side is turned on when the output of the gate drive circuit 53 is at a high level, and turned off when the output is at a low level. Gate drive circuit 53
An AND gate 51 is connected to the input of the . AND
A signal i and a second pulse width modulation signal k are input to the gate 51 . The AND gate outputs a fourth pulse width modulation signal m such that the switch circuit 9 is always off during the first half period T1 and repeatedly turned on and off during the second half period T2. The pulse width modulated signals j to m obtained in this manner are applied to the switching amplifier 1 via a gate drive circuit. Therefore, the switching amplifier 1 performs switching between the positive power supply voltage and GND during the first half period T1, and switches between the positive power supply voltage and GND during the second half period T2.
Switching is performed between the negative power supply voltage and GND to obtain an output voltage waveform n. At this time, the current waveform becomes like o. The focus current o is detected as a voltage signal by the current detection resistor 3, and is input to the - input terminal of the error detection amplifier 4, which includes an operational amplifier 41 and resistors 42 and 43. At this time, the error detection amplifier 4 calculates the difference between the focus reference signal a and the current detection signal and outputs an error signal. LPF5
is for removing the sawtooth wave component having the same frequency as the carrier signal g of the error signal, and the output of the LPF 5 becomes an H sawtooth wave like f. This error signal is sent to the comparator 47 -
It returns to the input terminal to form a feedback loop. When changing the amplitude of the focus current, it is sufficient to change the amplitude of the focus reference signal a, and the amplitude of the error signal f changes. Furthermore, if the DC component of the focus current is to be changed, the DC component of the focus reference signal a may be changed, and the DC component of the error signal f will be changed.

Note that the power MOSFETs 16, 23, 3
0, 38 are switching elements, resistors 12, 19, 26,
35 is a resistor for gate protection, resistors 15, 22, 29, 37
are gate capacitance charge discharge resistors, diodes 13, 20,
27 and 34 are diodes for quickly discharging the gate capacitance charge when the power MOSFET shifts from on mode to off mode; diodes 14, 21, 2;
8, 36 are clamp diodes, diodes 17, 24
, 31, 39 are power MOSFET parasitic diodes,
The diodes 32 and 40 are diodes for preventing reverse voltage of the power MOSFET.

According to the present invention, there is provided a voltage/current conversion circuit that switches the polarity of the power supply according to the polarity of the slope of the current, converts the focus current into a voltage, and controls the focus current so that there is no difference from the focus reference signal. Because of this method, it is possible to suppress waveform distortion of the output current and obtain a highly accurate focus current proportional to the focus reference signal.

A second embodiment of the present invention will be explained using FIGS. 5 and 6. FIG. 5 is a circuit configuration diagram of the upper and lower pincushion distortion correction circuit according to the present invention, and FIG. 6 is an operation waveform diagram for explaining the operation of the upper and lower pincushion distortion correction circuit of FIG. In this embodiment, a carrier signal generator 7, a pulse width modulation circuit 6, a switching amplifier 1, a current detection resistor 3, an error detection amplifier 4,
Since the operation of the LPF 5 is the same as in the first embodiment, the explanation will be omitted.

The vertical deflection circuit 61 causes a sawtooth vertical deflection current to flow through the vertical deflection yoke 62 in synchronization with a vertical synchronization signal. The vertical deflection yoke current is detected by current detection resistor 76 and returned to vertical deflection circuit 61. The secondary coil of the vertical pincushion distortion correction transformer 63 is connected in series to the vertical deflection yoke 62. When correcting the upper and lower pincushion distortions, a current in which an H parabolic wave is superimposed on a vertical sawtooth wave like f shown in FIG. 6 is passed through the vertical deflection yoke 62. Therefore, a current that modulates the amplitude of an H parabolic wave with a vertical periodic triangular wave, such as the signal d shown in FIG. 6, is passed through the primary coil of the vertical pincushion distortion correction transformer 63. The + input terminal of the error detection amplifier 4 receives the signal d.
Add a reference signal proportional to . On the other hand, the maximum amplitude of the H parabola wave current is determined by the power supply voltage, and when the H parabola current changes in a vertical period as in the signal d, the power supply voltage of the switching amplifier is changed in a vertical period. Regulator circuits 77, 7 are connected to the power supply terminal of the switching amplifier 1.
8 is connected, and in this example, the power supply voltage is set to 6b.
, c using vertical periodic triangular waves. In addition,
In the regulator circuits 77 and 78, the resistors 70 and 71
, 65, 66 are bias resistors, transistors 73, 67
is an output element of the regulator circuit, and inductances 74 and 68 and capacitors 75 and 69 form a line filter.

According to the present invention, the same effect as the first embodiment can be obtained, and when the amplitude of the horizontal periodic current changes in the vertical period, the amplitude can be reduced by making the power supply voltage proportional to the current amplitude. Waveform distortion can also be minimized.

A third embodiment of the present invention will be described with reference to FIGS. 7 and 8. FIG. 7 is a circuit diagram showing the configuration of an electromagnetic focus circuit according to the present invention, and FIG. 8 is an operation waveform diagram for explaining the operation of the electromagnetic focus circuit of FIG. 7.

The current detection signal b detected by the current detection resistor 3 is compared with the focus reference signal a by a comparator 47. At this time, the waveform of the comparator 47 becomes d. By inputting the focus reference signal a to the differentiating circuit 61 and passing it through the comparator 49, a clock e for switching the polarity of the power source is obtained. Comparator 47 is resistor 80 and resistor 79
It has a hysteresis characteristic determined by the ratio of Therefore, the specified value Δ is the difference between the focus reference signal a and the current detection signal b.
When the value exceeds x, the output of the comparator 47 changes. In the first half period T1 of the horizontal cycle, the switch circuits 8 and 10 are operated to perform a switching operation with respect to the positive power supply and GND. At this time, if the level of the current detection signal b is higher than the focus reference signal a, the comparator 47 outputs a low level, the switch circuit 10 is turned on, and the switch circuit 8 is turned off. Therefore, the focus current increases, and the current detection signal b tends to eliminate the difference from the focus reference signal. Conversely, when the level of the current detection signal b is lower than the focus reference signal a, the output of the comparator 47 is high level, and the switch circuit 1
0 is in the off state, and the switch circuit 8 is in the on state. Therefore, the focus current remains constant and the current detection signal b
tends to eliminate the difference from the focus reference signal. On the other hand, in the second half period T2 of the horizontal cycle, switch circuits 9 and 1
0 and performs switching operation with respect to the negative power supply and GND. At this time, if the level of the current detection signal b is higher than the focus reference signal a, the comparator 47 outputs a low level, and the switch circuit 10 is turned off.
The switch circuit 9 is turned on. Therefore, the focus current decreases, and the current detection signal b tends to eliminate the difference from the focus reference signal. Conversely, when the level of the current detection signal b is lower than the focus reference signal a, the output of the comparator 47 is high level, the switch circuit 10 is turned on, and the switch circuit 9 is turned off. Therefore, the focus current maintains a constant value, and the current detection signal b tends to eliminate the difference from the focus reference signal. In this way, the pulse width modulation circuit 6 operates so that the focus reference signal a and the current detection signal b match, and the focus current becomes an H parabola wave proportional to the focus reference signal a. Further, the output voltage waveform of the switching amplifier is as shown in c.

According to the present invention, the same effects as the first embodiment can be obtained, and the circuit configuration can be simplified since the carrier signal generator, error detection amplifier, and LPF are unnecessary.

[0019]

[Effects of the Invention] According to the present invention, in a focus coil drive device, switching elements are provided for a positive power source, a negative power source, and GND to constitute a switching amplifier, and the polarity of the power source is switched according to the polarity of the slope of the current. By setting the output level of the switching amplifier to three levels, distortion of the current waveform can be suppressed and a suitable focus coil current can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment according to the invention.

FIG. 2 is an operational waveform diagram of FIG. 1.

FIG. 3 is a circuit diagram of each block in FIG. 1.

FIG. 4 is a waveform diagram for explaining the operation of FIG. 3;

FIG. 5 is a circuit diagram of a second embodiment according to the present invention.

FIG. 6 is an operation waveform diagram of the second embodiment.

FIG. 7 is a circuit diagram of a third embodiment according to the present invention.

FIG. 8 is a waveform diagram for explaining the operation of the third embodiment.

[Explanation of symbols]

1...Switching amplifier, 2... Focus coil, 3...Current detection resistor, 4...Error detection amplifier, 5...LPF, 6...Pulse width modulation circuit, 7...Carrier signal generator, 8, 9, 10...Switch circuit. 49...Comparator, 61... Differential circuit 81, 83...Ex-OR gate

Claims (5)

[Claims] Claim 1: A device comprising switching amplification means and its control means; a focus coil is connected to the output of the switching amplification means; and the output of the switching amplification means takes three values: a positive power supply voltage, a negative power supply voltage, and GND. Focus coil drive device. 2. According to claim 1, a first switching element connected between the positive power source and the focus coil, a second switching element connected between the negative power source and the focus coil, and a second switching element connected between the negative power source and the focus coil; A focus coil drive device comprising switching amplification means including a third switching element connected between GND and the focus coil, and a control means thereof. 3. According to claim 1, the switching amplification means switches the polarity of the power supply according to the direction of the gradient of the current waveform of the focus coil, the focus coil connected to the output of the switching amplification means, and the switching amplification means. A focus coil drive device provided with a control means. 4. In claim 1, the switching amplification means switches the polarity of the power supply between the first half and the second half of the scanning period, the focus coil is connected to an output of the switching amplification means, and a control means for the switching amplification means. A focus coil drive device equipped with 5. In claim 1, the focus coil and the current detection circuit are connected to the output of a pulse width modulation amplifier comprising carrier signal generation means, pulse width modulation signal generation means, switching amplification means, error detection means, and carrier component removal means. A pulse width modulation type focus coil drive device connected to a means.