JP5834596B2 - High voltage inverter device - Google Patents

Description

  The present invention relates to switching regulators, inverters, etc. used for high voltage power supply devices that supply high voltage to various devices such as image processing equipment, lighting equipment such as fluorescent lamps, air purifiers, discharge equipment, backlights for liquid crystal TVs, etc. The present invention relates to a high voltage inverter device.

A high voltage inverter device such as a switching regulator is used to supply a high voltage to various devices such as a discharge tube for a large plasma display and a plasma generator.
Generally, an output power value of about several watts is often used, but a plasma generator or the like is a high voltage inverter device having an AC output with an output voltage of several tens KV and a power value of several tens of W or more. Is used.

  In general switching regulators (DC-DC converters), a DC voltage is switched by a switching element intermittently applied to a primary side excitation winding of a voltage conversion transformer, and is generated in a secondary side output winding. A direct current voltage is output by rectifying and smoothing the alternating current. In order to maintain the output voltage at a constant voltage, for example, as seen in Patent Document 1, the output voltage is detected to generate a feedback voltage, thereby the ratio of the on time and off time of the switching element (duty ratio). Pulse width modulation (PWM) control is performed to control the above.

  When the output voltage drops, the ON width of the switching pulse is widened to compensate for the output power shortage. Conversely, when the output voltage rises, the ON width is narrowed to limit the excess output power. The voltage is controlled to be constant.

  In addition, the inverter device, as described above, intermittently applies a DC voltage to the primary excitation winding of the voltage conversion transformer by switching with a switching element, and generates an AC voltage on the secondary output winding. Is output to the load as it is. In this case, for example, as can be seen in Japanese Patent Application Laid-Open No. H10-228707, there is a type in which an output current is detected instead of an output voltage and the voltage is replaced with a voltage to perform PWM control on the switching element.

JP 2009-11144 A International Publication No. 2007/060941 Pamphlet

When the output voltage is a DC switching regulator, as described in Patent Document 1, it is possible to detect the output voltage and perform PWM control of a switching pulse for ON / OFF control of the switching element. Further, since there is a holding time due to an electrolytic capacitor of the output smoothing circuit, control responsiveness does not become a problem.

However, since the output of the inverter device is alternating current, it is difficult to control the peak value (peak voltage value) to be constant regardless of whether it is full wave or half wave.
The reason is that the peak time is one point, there is a control delay, the higher the frequency at which the output voltage waveform is repeated, the more the influence of the delay becomes, and the peak voltage drops. Too much or too high.

Therefore, when the output is alternating current, the switching frequency is as high as several tens of KHz, and the output peak voltage is as high as several tens of KV, in addition to the above-described control responsiveness problem, the output voltage detection means There is also a problem with the pressure resistance of the parts. Therefore, in such a high voltage inverter device, it is general that the output voltage value is uncontrolled only by controlling the input supply voltage to be constant.
As described in Patent Document 2 described above, some output current is detected instead of the output voltage value, and negative feedback is performed to perform PWM control on the switching element. The crest value is not monitored and cannot be controlled.

  The present invention has been made in view of such a situation, and in a high-voltage inverter device in which the output is alternating current and the peak voltage is tens of KV, the peak voltage is controlled to be constant. For the purpose.

The present invention switches a DC voltage or an input voltage in which a pulsating current is superimposed on a DC component, causes an exciting current to flow through the exciting winding of the resonant transformer, and outputs an AC high voltage from the output winding of the resonant transformer. In order to achieve the above object in the inverter device,
The voltage generated between the terminals of the switching element for switching the exciting current or between both ends of the exciting winding is used as a monitor voltage, and from the point when the half wave of the monitor voltage is completed in the OFF period of the switching element , An output voltage control circuit that generates a control signal for controlling when to turn on the switching element according to the peak value of the monitor voltage until just before the resonance voltage appears, and the control signal is input A switching pulse by a rectangular wave pulse signal having a constant frequency is output with a pulse width modulation so as to change a ratio of a period during which the switching element is turned on in response to the control signal, and the switching element is turned on / off. A PWM control circuit for controlling is provided.

The output voltage control circuit is
A first comparison circuit that compares the monitor voltage with a reference potential and outputs a binary voltage signal that is high only during a period in which a half wave of the monitor voltage is generated;
A circuit that inputs the monitor voltage through a series circuit of a diode and a resistor, integrates it by a parallel circuit of a capacitor and a resistor, and forms a voltage signal having a triangular waveform or a waveform similar thereto,
The binary voltage signal and the voltage signal having a triangular waveform or similar waveform are compared with a reference voltage, and when at least one of the two voltage signals is higher than the reference voltage, the output is set to a low level. When both are lower than the reference voltage, the output is set to the high level and the output is output as the control signal.

  The high voltage inverter device according to the present invention is generated between the terminals of the switching element or both ends of the exciting winding of the resonant transformer even if the output voltage is an alternating current and the peak voltage is a high voltage such as a few dozen KV. Using the voltage as the monitor voltage, PWM control of a switching pulse with a constant frequency according to the fluctuation of the peak value, and controlling the ratio of the period during which the switching element is turned on makes the peak value voltage of the output voltage substantially constant. Can be controlled.

It is a circuit diagram which shows one Example of the high voltage inverter apparatus by this invention. It is a wave form diagram for demonstrating control operation of the high voltage inverter apparatus shown in FIG. It is a circuit diagram which shows the other Example of the high voltage inverter apparatus by this invention. It is a circuit diagram which shows the further another Example of the high voltage inverter apparatus by this invention.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 1 is a circuit diagram showing an embodiment of a high voltage inverter device according to the present invention.
The high voltage inverter device includes input terminals 1a and 1b and output terminals 2a and 2b, a resonant transformer 3, a switching element 4, a PWM control circuit 5, an output voltage control circuit 10, and the like.

  In this high voltage inverter device, the DC voltage supplied from the input terminals 1a and 1b or the input voltage Vin in which the pulsating current is superimposed on the DC component is switched by the switching element 4 to excite the winding NP on the primary side of the resonant transformer 3. Pass an exciting current intermittently. Then, an AC high voltage of several tens KV is output from the output winding NS on the secondary side of the resonant transformer 3, and the high output voltage Vout is output from the output terminals 2a and 2b to a load (not shown). To do. The input voltage Vin is preferably a safety extra low voltage (SELV: within DC 60V, or a voltage whose peak value does not exceed 42.4V).

  One end of the excitation winding NP of the resonant transformer 3 is connected to the positive input terminal 1a, and the other end is connected to the negative input terminal 1b through the FET between the drain and source of the switching element 4. One end of the output winding NS is connected to the output terminal 2a, the other end is connected to the output terminal 2b, and also connected to the input terminal 1b on the negative electrode side and the source side of the switching element 4 to conduct electricity. It is connected to a frame ground GND such as a body casing, chassis or frame. It is desirable for safety that the frame ground GND is grounded.

  The PWM control circuit 5 is made as an IC (integrated circuit) including an oscillation circuit. The PWM control circuit 5 operates by the input voltage Vin supplied from the input terminals 1a and 1b, applies a switching pulse Sp to the gate of the switching element 4 via the resistor R2, and turns the switching element 4 on and off. . As a result, a current is intermittently passed through the excitation winding NP of the resonant transformer 3 and an AC high voltage is generated in the output winding NS. The switching pulse Sp is also a pulse width control signal by a rectangular wave pulse, and controls the ratio (duty) of the ON period and the OFF period of the switching element 4.

  Further, between the point a on the positive side of the input power source and the point b on the positive side (drain) side of the switching element 4, a parallel circuit of the capacitor C1 and one end connected to the point a and the resistor R1 and the anode are connected to the point b. The snubber circuit 6 is configured by connecting the diode D1 connected in series. This snubber circuit 6 is provided for resetting the resonant transformer 3 and for suppressing the voltage of the switching element 4.

  The output voltage control circuit 10 determines the voltage at the connection point b between the exciting winding NP of the resonant transformer 3 and the positive electrode (drain) side of the switching element 4, in this case, the voltage Vnp between the terminals of the switching element 4 (between the drain and source). As a monitor voltage, a first comparison circuit (zero cross detection circuit) 11 using an operational amplifier for comparing the monitor voltage Vnp and a reference potential Vr (in this example, 0 potential) is provided.

  In the first comparison circuit, the output voltage signal V2 is set to the high level “H” only when the monitor voltage Vnp is at a higher potential, and the output voltage signal V2 is set to the low level “L” during the other periods. . Further, a diode D2 having an anode connected to the connection point b and a resistor R3 having one end connected to the cathode thereof are connected in series, and a charging capacitor is connected between the point c at the other end of the resistor R3 and the frame ground GND. A triangular wave forming circuit including a parallel circuit of C2 and a discharging resistor R4 is connected.

Further, a second comparison circuit 12 using an operational amplifier having one normal input terminal (+) and two inverting input terminals (−) is provided, and a direct current is connected between the normal input terminal and the frame ground GND. The power supply 13 is connected and the positive reference voltage V4 is input to the normal rotation input terminal. Further, a voltage signal V3 having a triangular waveform or similar waveform generated at point c is applied to one inverting input terminal , and a voltage signal V2 (zero-cross rectangular wave) output from the first comparison circuit 11 is applied to the other inverting input terminal. Signal).

When at least one of the voltage signals V2 and V3 input to the two inverting input terminals is higher than the reference voltage V4 input to the normal input terminal, the second comparison circuit 12 sets the output signal to the low level “L”. When both of the voltage signals V2 and V3 inputted to the two inverting input terminals become lower than the reference voltage V4 inputted to the normal input terminal, the output signal is set to the high level “H”.
The output signal of the second comparison circuit 12 is input to the feedback input terminal FB of the PWM control circuit 5 as the control signal Vf.

  The PWM control circuit 5 generates a rectangular wave pulse signal having a constant frequency (constant period) by a built-in oscillation circuit, and inputs the inversion timing from the low level “L” to the high level “H” to the feedback input terminal FB. The control signal Vf is controlled so as to coincide with the inversion timing from the low level “L” to the high level “H”. The controlled rectangular wave pulse signal is output as the switching pulse Sp and applied to the gate of the switching element 4 through the resistor R2.

The operation of the output voltage control circuit 10 will be described in detail with reference to the waveform diagram of FIG.
In the period when the switching pulse Sp shown in FIG. 2B is at the high level “H”, the gate-source voltage Vgs of the switching element 4 becomes a predetermined voltage and the switching element 4 is turned on. Excitation current flows through the excitation winding NP, and energy is stored in the resonance transformer 3. Since the monitor voltage Vnp at the connection point b in FIG. 1 is the same as the drain-source voltage Vds of the switching element 4, this period is almost 0V.

  When the switching pulse Sp becomes low level “L”, the gate-source voltage Vgs of the switching element 4 becomes 0 V, and the switching element 4 is turned off, so that the exciting current of the exciting winding NP of the resonant transformer 3 Shut off. Thus, the output voltage Vout due to voltage resonance is output from the secondary output winding NS by the energy stored in the resonant transformer 3. This output voltage Vout is an alternating high voltage of Vout = Qe · Vin, and Qe is a value indicating the sharpness of resonance.

  Therefore, the output voltage Vout is proportional to the input voltage Vin and the sharpness of resonance Qe. If Qe is increased, sufficient boosting can be achieved without increasing the winding ratio and an AC high voltage of several tens of KV is output. be able to. Here, the resonance sharpness Qe will be described. The characteristic of the resonance current with respect to the frequency is the frequency at which the resonance current becomes the maximum value at the resonance frequency fo, and the resonance current becomes 1 / √2 of the maximum value at the frequencies before and after that. Is a dimensionless number represented by Qe = fo / Δf.

  During the period when the switching element 4 is off, a connection point b between the excitation winding NP of the resonant transformer 3 and the positive electrode (drain) side of the switching element 4 in FIG. A monitor voltage Vnp having a half-wave waveform substantially similar to the output voltage Vout is generated. The monitor voltage Vnp is Vnp = Vout / n, where the turns ratio of the excitation winding NP and the output winding NS of the resonant transformer 3 is 1: n.

The first comparison circuit 11 detects the intersection between the monitor voltage Vnp and the reference potential Vr = 0V, and detects the completion of the half wave of the monitor voltage Vnp. Then, the output period of the resonant transformer 3 is completed until the next resonant voltage due to the transient phenomenon indicated by the broken line appears. Therefore, the switching pulse Sp is raised from the low level “L” to the high level “H” within the period D shown in FIG. 2B, and the switching element 4 is turned on. That is, the switching pulse Sp is PWM-controlled so that the switching element 4 is turned on within a period D from when the half-wave monitor voltage Vnp becomes 0 V until immediately before the next resonance voltage appears.

  At the point c in FIG. 1, the half-wave monitor voltage Vnp appearing at the connection point b is input through a diode D2 and a resistor R3, and is integrated by a triangular wave forming circuit comprising a parallel circuit of a charging capacitor C2 and a discharging resistor R4. A voltage signal V3 having a triangular wave shape or a waveform similar to that shown in FIG. In this circuit, the charging time constant is small and the discharging time constant is large, and the magnitude of the voltage signal V3 changes according to the peak value of the monitor voltage Vnp. This voltage signal V3 and a rectangular wave voltage signal (zero cross signal) V2 which is the output of the first comparison circuit 11 are input to two inverting input terminals (−) of the second comparison circuit 12, respectively.

  Then, the second comparison circuit 12 compares the voltage signals V2 and V3 shown in (c) of FIG. 2 with a reference voltage V4 that determines the time until the second harmonic appears, and at least the voltage signals V2 and V3 are compared. When one is higher than the reference voltage V4, the output control signal Vf is set to the low level “L”, and when both the voltage signals V2 and V3 are lower than the reference voltage V4, the output control signal Vf is set to the high level “H”. To. Therefore, the control signal Vf output from the second comparison circuit 12 is as shown in FIG.

The broken line in (c) of FIG. 2 shows the case where the peak value E of the monitor voltage Vnp shown in (a) increases, and the voltage signal V3 becomes lower than the reference voltage V4 immediately before the next resonance voltage due to a transient phenomenon occurs. The waveform of the voltage signal V3 is shown. Accordingly, the reference voltage V4 is set so that the voltage signal V3 becomes lower than the reference voltage V4 immediately before the next resonance voltage appears even when the voltage signal V3 having a triangular wave shape or a waveform similar to that is the largest.

  The control signal Vf output from the second comparison circuit 12 is input to the feedback input terminal FB of the PWM control circuit 5, whereby the PWM control circuit 5 causes the switching pulse Sp to change from the low level “L” to the high level “H”. Is controlled so as to coincide with the rising timing from the low level “L” to the high level “H” of the control signal Vf input to the feedback input terminal FB.

That is, the period in which the switching pulse Sp is at the high level “H”, that is, the period in which the switching element 4 is on, is controlled within the period indicated by D in FIG. 2 according to the magnitude of the peak value E of the monitor voltage Vnp ( PWM control) and output voltage Vout generated corresponding to monitor voltage Vnp
The crest value Eout is controlled to be substantially constant.

  Specifically, when the peak value E of the monitor voltage Vnp increases, the period during which the switching pulse Sp is at the high level “H” (switching element 4 is on) is shortened, and the time for storing energy in the resonant transformer 3 is shortened. Then, control is performed to lower the peak value Eout (Eout = n · E) of the output voltage Vout. On the other hand, when the peak value E of the monitor voltage Vnp is lowered, the period during which the switching pulse Sp is at the high level “H” (switching element 4 is on) is lengthened, and the time for storing energy in the resonant transformer 3 is lengthened. Control is performed to increase the peak value Eout of the output voltage Vout.

The frequency of the switching pulse Sp, that is, the switching frequency of the switching element 4 (the reciprocal is the period) is fixed, and the ON period of the switching element 4, that is, the excitation time ratio of the resonant transformer 3 is varied.
In this embodiment, the voltage between the terminals of the switching element 4 (the voltage between the point b and the frame ground GND) is the monitor voltage Vnp, but the voltage generated between both ends of the excitation winding NP of the resonant transformer 3 (the connection point a and The voltage between the connection points b) may be the monitor voltage.

[Other Examples]
Next, another embodiment of the high voltage inverter device according to the present invention will be described with reference to FIGS.
The high-voltage inverter device shown in FIG. 3 is different from the high-voltage inverter device described with reference to FIG. 1 only in that the resonant transformer 3 'is composed of two resonant transformers T1 and T2 having the same configuration and the same characteristics. Different.

The high voltage inverter device shown in FIG. 4 is the high voltage inverter described with reference to FIG. 1 only in that the resonant transformer 3 ″ is constituted by three resonant transformers T1, T2, T3 having the same configuration and the same characteristics. Different from the device.
Therefore, in these drawings, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Since the output voltage control circuit 10 has the same configuration as the circuit shown in FIG. 1, the output voltage control circuit 10 is simply shown as one block here.

In the high voltage inverter device shown in FIG. 3, the exciting windings NP1 and NP2 of the resonant transformers T1 and T2 constituting the resonant transformer 3 'are a point on the positive side of the input power source and a point b on the positive side of the switching element 4 by the FET. Connected in parallel.
The output windings NS1 and NS2 of the resonant transformers T1 and T2 are connected in series, and the ends of the output windings NS1 and NS2 that are not connected are connected to the output terminals 2a and 2b, respectively.

The high voltage inverter device of this embodiment excites the exciting windings NP1 and NP2 of two resonant transformers T1 and T2 having the same characteristics with separate cores having completely different magnetic paths constituting the resonant transformer 3 '. On the output side, the output voltages of the output windings NS1 and NS2 are added or multiplied. Therefore, no magnetization is generated in the plurality of exciting windings, and the number of turns of the output winding can be increased, so that a high output voltage Vout having a high boosting ratio can be obtained continuously, stably and safely. be able to.

It is desirable that the time axes of the output voltage waveforms of the output windings NS1 and NS2 of the resonant transformers T1 and T2 are synchronized. Therefore, the switching element 4 is preferably arranged so that the wiring distance between the drain terminal of the switching element 4 and the negative electrode side terminals of the excitation windings NP1 and NP2 is equal.
In the case of this embodiment, when the turns ratio of the exciting winding and the output winding of each resonant transformer T1, T2 is 1: n, the voltage Vnp generated at the point b is Vnp = Vout / 2n. Further, the peak value Eout of the output voltage Vout with respect to the peak value E of the monitor voltage Vnp is Eout = 2n · E.

In the high-voltage inverter device shown in FIG. 4, the resonant transformer 3 ″ is configured by three resonant transformers T1, T2, and T3 having the same configuration and the same characteristics.
The excitation windings NP1, NP2, and NP3 of the three resonant transformers T1, T2, and T3 are connected in parallel between the point a on the positive side of the input power supply and the point b on the positive side of the switching element 4. ing. The output windings NS1, NS2, NS3 of the resonant transformers T1, T2, T3 are all connected in series, and the ends of the output windings NS1, NS3 that are not connected to the output terminals 2a, 2b, respectively. Connected.

  In the high voltage inverter device of this embodiment, the exciting windings NP1, NP2, NP3 of the three resonant transformers T1, T2, T3 having the same characteristics with different cores constituting the resonant transformer 3 ″ having completely different magnetic paths. The output voltages of the output windings NS1, NS2, NS3 are added or multiplied on the output side, so that a higher high voltage output and a larger output voltage Vout can be stably and safely supplied. .

Also in this case, it is desirable that the time axes of the output voltage waveforms of the output windings NS1, NS2, NS3 of the resonant transformers T1, T2, T3 are synchronized. Therefore, the switching element 4 is preferably arranged so that the wiring distance between the drain terminal of the switching element 4 and the negative terminal of each excitation winding NP1, NP2, NP3 is equal.
In the case of this embodiment, if the turns ratio of the exciting winding and the output winding of each resonant transformer T1, T2, T3 is 1: n, the voltage Vnp generated at point b is relative to the output voltage Vout. Vnp = Vout / 3n. Further, the peak value Eout of the output voltage Vout with respect to the peak value E of the monitor voltage Vnp is Eout = 3n · E.

A resonant transformer that generates a high voltage may be composed of four or more resonant transformers having the same characteristics. Further, the excitation windings of the plurality of resonance transformers may be connected in series, or may be connected in combination of parallel and series. Each output winding may be connected in parallel, or may be connected in combination of series and parallel.
The preferred embodiments of the high-voltage inverter device according to the present invention have been described above. However, the present invention is not limited to these, and various modifications can be made.

  The present invention can be used for various high voltage generators such as switching regulators, inverters, high voltage power supplies, and discharge power supplies.

1a, 1b: input terminals 2a, 2b: output terminals 3, 3 ', 3 ": resonant transformer 4: switching element 5: PWM control circuit 6: snubber circuit
10: Output voltage control circuit 11: First comparison circuit 12: Second comparison circuit 13: DC power supply T1, T2, T3: Individual resonant transformers NP, NP1, NP2, NP3 having the same characteristics: Excitation winding
NS, NS1, NS2, NS3: Output winding
C1, C2: Capacitors R1, R2, R3, R4: Resistance
D1, D2: Diode GND: Frame ground

Claims (5)

In a high voltage inverter device that switches an input voltage in which a pulsating current is superimposed on a direct current or a direct current component, causes an exciting current to flow in the exciting winding of the resonant transformer, and outputs an alternating high voltage from the output winding of the resonant transformer,
The voltage generated across the terminals or between the excitation winding of the switching element for switching the exciting current to the monitor voltage, the completion of the half-wave of the monitor voltage in the OFF period of the switching element, following by transient An output voltage control circuit that generates a control signal for controlling the timing to turn on the switching element according to the peak value of the monitor voltage until just before the resonance voltage appears.
The control signal is input, and a switching pulse by a rectangular wave pulse signal having a constant frequency is output by pulse width modulation so as to change a ratio of a period during which the switching element is turned on corresponding to the control signal , A high voltage inverter device comprising a PWM control circuit for controlling on / off of the switching element. The high voltage inverter device according to claim 1,
The output voltage control circuit is
A first comparison circuit that compares the monitor voltage with a reference potential and outputs a binary voltage signal that is at a high level only during a period in which a half wave of the monitor voltage is generated;
The monitor voltage is input through a series circuit of a diode and a resistor, integrated by a parallel circuit of a capacitor and a resistor, and a circuit for forming a voltage signal having a triangular waveform or a waveform similar thereto,
The binary voltage signal and the voltage signal having a triangular waveform or similar waveform are compared with a reference voltage, and when at least one of the two voltage signals is higher than the reference voltage, the output is set to a low level, and the two voltages A high-voltage inverter device comprising: a second comparison circuit that sets an output to a high level when both signals are lower than the reference voltage and outputs the output as the control signal. The reference voltage is set so that the voltage signal becomes lower than the reference voltage immediately before the next resonance voltage appears even when the voltage signal having the triangular waveform or the waveform similar to that is the largest. The high-voltage inverter device according to claim 2, wherein The high-voltage inverter device according to any one of claims 1 to 3,
The resonant transformer is constituted by a plurality of individual resonant transformers having the same characteristics, and the respective excitation windings of the plurality of resonant transformers are connected in parallel or in series to be excited simultaneously. A high voltage inverter device, wherein each output winding is connected in series or in parallel.   5. The high voltage inverter device according to claim 4, wherein time axes of output voltage waveforms of output windings of the plurality of resonant transformers are synchronized.

Images