JP3345206B2 - DC-DC conversion circuit and flat panel display using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a device using a DC voltage such as a flat panel display device such as a plasma display device or an electroluminescent display device. The present invention relates to a DC-DC conversion circuit that generates a DC voltage insulated from an input voltage by rectifying and smoothing a current flowing through a secondary coil of a transformer, and a flat panel display device using the same.

[0002]

2. Description of the Related Art Along with demands for miniaturization, weight reduction and low power consumption of OA equipment, the same demands have been made on DC-DC conversion circuits. FIG. 7 shows a conventional DC-DC conversion circuit. The primary coil 121 of the transformer 12A and the MOS transistor switch 14 are connected in series to the storage battery 10. The MOS transistor switch 14 is periodically turned on / off by a pulse train output from the control circuit 16. The power supply voltage Vcc for the control circuit 16 is higher than the voltage Vdd of the storage battery 10 in order to increase the conversion efficiency by reducing the on-resistance of the MOS transistor switch 14 and to perform high-speed switching of the MOS transistor switch 14. Is used. For example, when Vdd = 12V,
Vcc = 15V.

The alternating current induced in the secondary coil 123 of the transformer 12A is rectified by the diode 18 and
0, and the power supply voltage input terminal Vcc of the control circuit 16
Supplied to If the MOS transistor switch 14 is not turned on / off, no voltage is induced in the secondary coil 123.
A voltage is supplied to the control circuit 16 via the control circuit 16.

[0004] The AC voltage induced in the secondary coil 122 of the transformer 12A is rectified by a rectifier circuit 24A, smoothed by a smoothing circuit 26A, and output as a DC voltage Vee. M
When the OS transistor switch 14 is turned off from on, the primary coil 121
Then, a so-called flyback voltage is induced, and a high-voltage spike noise is applied to the MOS transistor switch 14 and the control circuit 16. A snubber circuit 28A is connected to the primary coil 121 to remove the spike noise. This flyback voltage causes the capacitor 28
1 is charged, and the charged charge is discharged through the resistor 282A.

FIG. 8 shows another conventional DC-DC conversion circuit. In this circuit, the output voltage Vee is supplied to the three-terminal regulator 30 using the transformer 12 having only the coil 122 on the secondary side, and the power supply voltage Vcc for the control circuit 16 is generated.

[0006]

However, in the circuit of FIG. 7, since the transformer 12A has two secondary coils, the size and weight of the transformer 12A are increased. In addition, in the circuit of FIG.
Is stepped down to the voltage Vcc, the power consumption of the three-terminal regulator 30 is large.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a DC-DC conversion circuit which can be reduced in size, weight and power consumption, and a flat panel display device using the same. .

[0008]

FIG. 1 shows the principle configuration of a DC-DC converter according to the present invention. According to the present invention, the transformer 1 having the primary coil 121 and the secondary coil 122 each having one end connected to the first DC voltage input terminal.
2, a switch element 14 connected between the other end of the primary coil 121 and the second DC voltage input terminal and turned on / off in response to a signal supplied to the control input terminal; A rectifying circuit 24 for rectifying the induced alternating current to direct current, a smoothing circuit 26 for smoothing the rectified direct current and outputting it as a DC power supply voltage, and a control circuit 16 for supplying a pulse train as the signal to the control input terminal And the primary coil 1
21 is connected between the one end and the other end of the switch 21 and absorbs energy by a flyback voltage from the secondary coil 122 to the primary coil 121 when the switch element 14 is turned off. Voltage is the first
A snubber circuit having a terminal applied to the potential of the DC voltage input terminal in a direction of increasing the absolute value; and a low-pass filter connected between the terminal of the snubber circuit 32 and a power supply voltage input terminal of the control circuit. 34.

In the present invention, when the switch element 14 is turned off, the energy due to the flyback voltage from the secondary coil 122 to the primary coil 121 is absorbed by the snubber circuit 28, and the absorbed energy is transmitted to the low-pass filter. The voltage is supplied to the power supply voltage input terminal of the control circuit 16 through the low-pass filter 34, the voltage is smoothed by the low-pass filter 34, and the spike noise of the flyback voltage is cut. The potential of the terminal of the snubber circuit 28 is a potential obtained by adding a voltage generated by the absorbed energy to the potential of the first DC voltage input terminal in a direction in which the absolute value increases. Therefore, the energy due to the flyback voltage
Is used effectively and the transformer has two power supplies for the control circuit.
There is no need to provide a secondary coil, and the DC-DC converter can be reduced in size, weight, and power consumption.

In the first embodiment of the present invention, as shown in FIG. 2, for example, the snubber circuit 28A includes a capacitor 281 having one end connected to one end of the primary coil 121,
1 has a diode 283 connected between the other end of the capacitor 281 and the other end of the capacitor 281; and a discharge element 282 connected in parallel with the capacitor 281 to discharge the electric charge stored in the capacitor 281. As described above, the direction of the diode is such that the voltage generated by the absorbed energy is applied to the potential of the first DC voltage input terminal in a direction in which the absolute value increases.

In a second embodiment of the present invention, as shown in FIG. 2, for example, a low-pass filter 34A includes a coil 341 connected between the terminal of the snubber circuit 28A and the power supply voltage input terminal of the control circuit 16, A capacitor 3 having one end connected to the power supply voltage input terminal and the other end held at a constant potential;
42. According to the second aspect, the coil 34
1 and the capacitor 342 constitute the low-pass filter 34A, so that the configuration of the DC power supply circuit 32 for the control circuit 16 is particularly simple.

In a third embodiment of the present invention, the discharge element is a resistor 282, for example, as shown in FIG. Capacitor 28
The surplus energy of the energy absorbed in 1 is
It is consumed by the resistor 282. In the fourth embodiment of the present invention, for example, as shown in FIG.
84. The direction of the Zener diode is the direction in which the flyback voltage is applied in the opposite direction.

In the fourth embodiment, since the reverse current flows through the Zener diode 284 only when the voltage between the terminals of the capacitor 281 exceeds the breakdown voltage of the Zener diode 284, the flyback voltage is higher than in the third embodiment. Energy can be used efficiently. In the fifth aspect of the present invention, as shown in FIG. 2, for example, an overcurrent protection circuit is provided which forcibly turns off the switch element 14 when the current obtained by smoothing the current flowing through the switch element 14 becomes equal to or more than a reference value. .

In a sixth aspect of the present invention, as shown in FIG. 2, for example, there is provided an overvoltage protection circuit for forcibly turning off the switch element 14 when the output voltage of the smoothing circuit 26B exceeds a reference value. In the sixth embodiment of the present invention, for example, as shown in FIG. 2, the control circuit 16 controls the output voltage V of the smoothing circuit 26B.
The duty ratio of the output pulse is controlled so that ee becomes a constant value.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 2 shows a DC-DC conversion circuit according to a first embodiment. The same components as those in FIGS. 7 and 8 are denoted by the same reference numerals.

The positive electrode of the storage battery 10 is connected to one end of a primary coil 121 of the transformer 12, and the other end of the primary coil 121 is connected to a ground line via a MOS transistor switch 14 and a resistor 151 of a current detection circuit 15. It is connected. The control circuit 16 for controlling ON / OFF of the MOS transistor switch 14 is, for example, a model MB37 manufactured by Fujitsu.
70, a circuit for generating a triangular wave Vt as shown in FIG. 3, a circuit for generating a reference voltage V0,
A comparator for comparing t with the reference voltage V0 to generate an output signal OUT as shown in FIG. 3 is incorporated. The output terminal OUT is connected to the gate of the MOS transistor switch 14 via the resistor 17, and the MOS transistor switch 14 is turned on only when the output terminal OUT is at a high level. Turn on the MOS transistor switch 14
A circuit 19 in which a resistor 191 and a capacitor 192 are connected in series is connected in parallel to the MOS transistor switch 14 in order to bypass a spike current flowing through the MOS transistor switch 14 when the MOS transistor switch 14 is turned off.

The secondary coil 122 of the transformer 12 is connected to an output terminal of the DC voltage Vee via a well-known rectifier circuit 24A and a smoothing circuit 26B. The rectifier circuit 24A
The smoothing circuit 26 </ b> B includes a coil 261, a capacitor 262, and an electrolytic capacitor 263. When the MOS transistor switch 14 transitions from on to off, the secondary coil 1
Since a spike-like flyback voltage is induced from 22 to the primary coil 121, a snubber circuit 28A is connected to the primary coil 121 to absorb this energy. The snubber circuit 28A includes a capacitor 281 and a resistor 2
82 and a diode 283, and a capacitor 281
Is connected to one end of the primary coil 121, a resistor 282 is connected in parallel with the capacitor 281,
The other end of 1 is connected to the cathode of diode 283, and the anode of diode 283 is connected to the other end of primary coil 121.

With this flyback voltage, charges are accumulated in the capacitor 281 through the diode 283, and the accumulated charges are gradually discharged through the resistor 282. In order to effectively use the energy stored in the capacitor 281, the cathode of the diode 283 is connected to the power supply voltage input terminal Vcc of the control circuit 16 via the LC low-pass filter 34A, and the snubber circuit 28A and the LC low-pass filter 34A And the auxiliary power supply circuit 3 for the control circuit 16
2A is configured.

Next, an additional circuit for the control circuit 16 will be briefly described. For example, when the output terminal of the voltage Vee is short-circuited to the ground line, the MOS transistor switch 14
Overcurrent flows in In order to detect this overcurrent, MO
The current detection circuit 15 is composed of a resistor 151 for converting a current flowing through the S transistor switch 14 into a voltage, and an integration circuit for smoothing spike noise, which includes a resistor 152 and an electrolytic capacitor 153. , And its output is supplied to an input terminal OCP of the control circuit 16. When the internal comparator detects that the input terminal OCP has become equal to or higher than the reference voltage, the control circuit 16 outputs the output terminal OCP.
The UT is forced to a low level, and the operation of the transformer 12 is stopped.

The overvoltage detecting circuit 36 is for detecting that the output voltage Vee has become an overvoltage equal to or higher than a set value, and includes resistors 361 and 362 for dividing the output voltage Vee.
And an electrolytic capacitor 363 for ignoring an overvoltage due to noise, a reference voltage generator 364, and a comparator 365 for comparing the voltage of the reference voltage generator 364 with the voltage between terminals of the electrolytic capacitor 363. The output of the comparator 365 is supplied to the input terminal OVP of the control circuit 16. When the input terminal OVP goes high, the control circuit 16 forcibly sets the output terminal OUT low and stops the operation of the transformer 12. Let it.

The feedback circuit 38 controls the control circuit 16
And resistors 381 and 382 for supplying the divided voltage of the output voltage Vee to the terminal + IN of the control circuit 16 and the input terminal −I of the control circuit 16 by dividing the reference voltage Vref generated by the control circuit 16.
It comprises resistors 383 and 384 for supplying N, and a capacitor 385 and a resistor 386 which are external circuits to the control circuit 16. The control circuit 16 calculates the difference A between the two partial pressures.
The C component is added to the divided voltage of the reference voltage Vee via the capacitor 385 and the resistor 386, and the duty ratio of the pulse from the output terminal OUT is controlled so that the output voltage Vee becomes constant.

In FIG. 2, for example, Vdd = 12 V, V
cc = 18V and Vee = 100V. Next, the operation of the DC-DC converter configured as described above will be described. At first, since the transformer 12 is not operating, the voltage Vdd of the storage battery 10 is controlled by the control circuit 1 via the resistor 282 and the coil 341.
6 is applied to the power supply voltage input terminal Vcc, and the control circuit 16 starts operating.

When the output terminal OUT of the control circuit 16 transitions to the high level and the MOS transistor switch 14 is turned on, a current flows through the primary coil 121 and the secondary coil 12
2, a voltage is induced. Output terminal OUT of control circuit 16
Transitions to the low level and the MOS transistor switch 14
Is turned off, the primary coil 12
A flyback voltage is induced to 1 and charge is stored in the capacitor 281 through the diode 283. On this occasion,
The high frequency spike noise hardly passes through the coil 341 due to the inductance of the coil 341, but is absorbed by the capacitor 342 even if it passes. The sum of the voltage Vdd of the storage battery 10 and the voltage Vr between terminals of the capacitor 281 is L
The voltage is smoothed by the C low-pass filter 34A and supplied to the voltage Vcc, and the surplus energy is consumed by the resistor 282.

The current I flowing through the MOS transistor switch 14 and the voltage V between the drain of the MOS transistor switch 14 and the ground line are as shown in FIG. [Second Embodiment] FIG. 4 shows a schematic configuration of a DC-DC converter according to a second embodiment. The same components as those in FIG. 2 are denoted by the same reference numerals.

The snubber circuit 28B uses a Zener diode 284 instead of the resistor 282 in FIG. The auxiliary power supply circuit 32B includes the snubber circuit 28B and an LC low-pass filter 34A. The preferred value of the breakdown voltage of the Zener diode 284 is the voltage V
This value is equal to dd, and is 12 V in the above example. Since a reverse current flows through the Zener diode 284 only when the voltage between the terminals of the capacitor 281 exceeds this voltage,
Energy from the flyback voltage can be used efficiently. Other points are the same as those of the first embodiment.

Third Embodiment FIG. 5 shows a schematic configuration of a DC / DC converter according to a third embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals. In this DC / DC conversion circuit, the storage battery 10, the diode 28 of the snubber circuit 28C
3. The connection directions of the diodes 241 and 242 of the rectifier circuit 24B and the electrolytic capacitor 263 of the smoothing circuit 26C are opposite to those in FIG.
Is generated. Accordingly, the LC low-pass filter 34
The output terminal of A is connected to one power supply voltage input terminal GND of the control circuit 16, the other power supply voltage input terminal Vcc of the control circuit 16 is connected to the ground line, and a pMOS transistor is used instead of the nMOS transistor switch 14 of FIG. 14A is used. 5, the circuits 15, 19 and 36 of FIG. 2 are not shown for simplicity.

As is apparent from the above configuration, this DC /
In the operation of the DC conversion circuit, the direction of the current is opposite to that in the case of FIG. Note that the snubber circuit 28C may use a Zener diode connected in the opposite direction to the case of FIG. 4 instead of the resistor 282. Fourth Embodiment FIG. 6 shows an AC-type and two-electrode type plasma display device 40 according to a fourth embodiment to which the DC / DC converter of the present invention is applied.

Conventionally, the power supply voltage VCC, for example, 5 V, and Vee, for example, 100 V, are supplied to the plasma display device 40 without using the DC / DC conversion circuit 41. Thus, the power supply voltage VCC and the voltage Vdd, for example, 12 V, are supplied to the plasma display device 40. A row driver 43 and a column driver 44 are applied to the row electrodes and the column electrodes of the display panel 42, respectively.
Is supplied. The row driver 43 includes a control circuit 45
Panel 42 based on a scanning signal and a control signal from
, A scanning drive signal is supplied line-sequentially, or one of the sustain voltages is supplied. Column driver 44
Supplies the display drive signal for one row to the column electrode of the display panel 42 every one pulse of the horizontal synchronization signal HSYNC based on the display data and the control signal from the control circuit 45, or the other of the sustain voltage. Supply potential. The control circuit 45
The above signals to the row driver 43 and the column driver 44 are represented by the display data DATA, the clock CLK, and the vertical synchronization signal VS.
It is generated based on the YNC and the horizontal synchronization signal HSYNC.

The power supply voltage VCC is supplied to the logic circuits of the row driver 43, the column driver 44 and the control circuit 45.
The column electrode drive voltage is supplied to a column driver 44 from a DC / DC conversion circuit 41 that converts a DC voltage Vdd into a DC voltage Vee. The voltage Vee is also supplied to the write voltage generation circuit 46 and one input terminal of the addition circuit 47. The write voltage generation circuit 46 generates the write voltage Vw for a predetermined period based on the control signal from the control circuit 45 using the voltage Vee, and supplies the write voltage Vw to the other input terminal of the adder circuit 47. Adder circuit 47
Are supplied to the row electrodes of the display panel 42 via the row driver 43 as the sustain voltage when Vw = 0 and the scanning voltage when Vw ≠ 0.

The plasma display device 40 having the above configuration
According to the method, the storage battery can be used, and a relatively lightweight transformer is used for the DC / DC conversion circuit 41, so that the plasma display device 40 becomes lightweight, and the DC / DC conversion circuit 41 uses a flyback voltage. Since the energy is effectively used, the usable time of the storage battery is prolonged.

The DC / DC conversion circuit of the present invention can be applied to various types of plasma display devices other than the plasma display device 40 shown in FIG. The output voltage of the DC / DC conversion circuit of the present invention is supplied between the sustain discharge electrodes of a three-electrode type plasma display device provided with address electrodes so as to be separated from and intersect with the discharge electrodes. Is also good. Also,
The present invention is naturally applicable not only to the AC type but also to a DC type plasma display device, and further to other flat panel display devices and the like.

[0032]

As described above, the direct current according to the present invention is
In the DC conversion circuit, the energy due to the flyback voltage from the secondary coil to the primary coil of the transformer when the switch element is turned off is absorbed by the snubber circuit, and the absorbed energy is passed through the low-pass filter. The voltage is supplied to a power supply voltage input terminal of the control circuit, the voltage is smoothed by the low-pass filter, the spike noise of the flyback voltage is cut, and the potential of the terminal of the snubber circuit is set to the first DC voltage input terminal. The voltage generated by the absorbed energy becomes the potential applied in the direction of increasing the absolute value to the potential of the power supply. Therefore, the energy by the flyback voltage is effectively used, and the secondary for power supply to the control circuit is provided to the transformer. It is not necessary to provide a coil, so that a DC-DC conversion circuit and a flat panel display device using the same can be reduced in size and weight. Beauty an excellent effect that power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a DC-DC conversion circuit diagram showing the principle configuration of the present invention.

FIG. 2 is a DC-DC conversion circuit diagram of the first embodiment of the present invention.

FIG. 3 is a waveform chart showing an operation of the circuit of FIG. 2;

FIG. 4 is a DC-DC conversion circuit diagram of a second embodiment of the present invention.

FIG. 5 is a DC-DC conversion circuit diagram according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a plasma display device to which the DC-DC conversion circuit of the present invention is applied.

FIG. 7 is a conventional DC-DC conversion circuit diagram.

FIG. 8 is another conventional DC-DC conversion circuit diagram.

[Explanation of symbols]

 Reference Signs List 10 Storage battery 12A, 12 Transformer 14, 14A MOS transistor switch 15 Current detection circuit 24, 24A, 24B Rectifier circuit 26, 26A, 26B, 26C Smoothing circuit 28, 28A, 28B, 28C Snubber circuit 32, 32A, 32B, 32C Power supply circuit 34, 34A Low-pass filter 36 Overvoltage detection circuit 38 Feedback circuit

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Rikuo Tanahashi 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Akira Yamamoto 1015 Ueodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited ( 56) References JP-A-5-176533 (JP, A) JP-A-5-344724 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/28 G09G 3/20

Claims (10)

(57) [Claims] 1. A transformer having a primary coil having one end connected to a first DC voltage input terminal and a secondary coil; and a transformer between the other end of the primary coil and a second DC voltage input terminal. Connected and turned on according to the signal supplied to the control input terminal.
A switch element to be turned off; a rectifier circuit for rectifying the alternating current induced in the secondary coil to convert it to a direct current; a smoothing circuit for smoothing the rectified direct current and outputting it as a DC power supply voltage; A control circuit for supplying to the control input terminal; a control circuit connected between the one end and the other end of the primary coil;
A snubber circuit having a terminal for absorbing energy generated by a flyback voltage to the next coil and applying a voltage generated by the absorbed energy to a potential of the first DC voltage input terminal in a direction of increasing an absolute value; A low-pass filter connected between the terminal of the snubber circuit and the power supply voltage input terminal of the control circuit, wherein the snubber circuit and the low-pass filter constitute a DC power supply circuit for the control circuit. DC-DC converter circuit. 2. The snubber circuit includes: a capacitor having one end connected to the one end of the primary coil; a diode connected between the other end of the primary coil and the other end of the capacitor; The DC-DC conversion circuit according to claim 1, further comprising: a discharge element connected in parallel to the capacitor for discharging electric charges stored in the capacitor. 3. The low-pass filter comprises: a coil connected between the terminal of the snubber circuit and the power supply voltage input terminal of the control circuit; one end connected to the power supply voltage input terminal; The DC-DC converter according to claim 2, further comprising: a capacitor held at a constant potential. 4. The DC-DC converter according to claim 2, wherein the discharge element is a resistor. 5. The DC-DC converter according to claim 2, wherein the discharge element is a Zener diode. 6. The overcurrent protection circuit according to claim 3, further comprising: an overcurrent protection circuit for forcibly turning off the switch element when a current obtained by smoothing a current flowing through the switch element becomes equal to or more than a reference value. DC-DC conversion circuit. 7. The DC-DC converter according to claim 3, further comprising: an overvoltage protection circuit for forcibly turning off the switch element when an output voltage of the smoothing circuit becomes higher than a reference value. circuit. 8. The DC-DC converter according to claim 3, wherein the control circuit controls a duty ratio of the output pulse so that an output voltage of the smoothing circuit becomes a constant value. 9. A flat panel display device, comprising the DC-DC conversion circuit according to claim 1, wherein an output voltage of the DC-DC conversion circuit is used as a driving voltage of the flat panel. A flat panel display device. 10. One end is connected to a first DC voltage input terminal.
A transformer having a primary coil and a secondary coil, and a transformer connected between the other end of the primary coil and a second DC voltage input terminal.
Connected in response to the signal supplied to the control input terminal.
A switch element to be turned off; and a rectifier for rectifying an alternating current induced in the secondary coil to a direct current.
Current circuit and smoothes the rectified DC, and outputs it as a DC power supply voltage.
And a control circuit for supplying a pulse train as the signal to the control input terminal.
A circuit connected between the one end and the other end of the primary coil;
From the secondary coil when the switch element is turned off.
Absorbs energy due to flyback voltage to secondary coil
Then, the voltage generated by the absorbed energy is the first direct current.
Current voltage input terminal potential in the direction of increasing absolute value.
And an overcurrent detection circuit for detecting a current flowing through the switch element.
And an overvoltage detection circuit for detecting an output voltage of the smoothing circuit , wherein the control circuit is connected to the terminal in the snubber circuit.
Power supply voltage input terminal to which the voltage output from
Output of the overcurrent detection circuit and the overvoltage detection circuit.
Controlling the operation of the transformer based on the force.
DC-DC conversion circuit.