JPH05135891A - Inverter device - Google Patents

Abstract

PURPOSE:To ensure that circuit parts are protected during failures and to prevent malfunctions. CONSTITUTION:Energy accumulated in an oscillation coil Li or the like, while a switching element Q1 is on, is used to resonate a resonance circuit when the switching element Q1 is off. High frequency power obtained by the resonance of the said resonance circuit is supplied to an electric discharge lamp La. A control circuit 1 is used to allow the said switching element Q1 to be ready for operation for a certain time since the end-to-end voltage of the switching element Q1 decreases to a specified voltage. An electric current detection circuit 2 is used to detect electric currents flowing through the switching element Q1. When the said electric current reaches a current restriction level, a current restriction circuit 4 controls the control circuit 1 to forces the switching element Q1 to turn off. A level adjustment circuit 5 varies the current restriction level based on the operation of the electric discharge lamp La.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage resonance type inverter device abnormality protection method.

[0002]

2. Description of the Related Art An example of a voltage resonance type inverter device is shown in FIG. This inverter device is a so-called monolithic inverter device and is used as a discharge lamp lighting device for lighting a discharge lamp at a high frequency. In this inverter device,
An oscillation coil L ₁ and an oscillation capacitor C are provided at both ends of the DC power source E.
Via a parallel circuit of a ₁ connected bipolar transistors to Q ₁ as a switching element, current limiting choke coil in parallel circuit between the oscillation coil L ₁ and the oscillation capacitor C ₁ (hereinafter, simply referred to as a current-limiting choke) L ₂ The discharge lamp La is connected via. A diode D ₁ is connected in anti-parallel to the transistor Q ₁ in order to flow a feedback current returned from the resonance circuit to the DC power source E, and a preheating capacitor C is connected to the non-power source side of the filament of the discharge lamp La.
₂ are connected. Then, the transistor Q ₁ is turned on,
The off control is performed by the PWM control circuit 1 that generates a square wave signal.

The operation of the above-described components will be described first. Now, as shown in FIG. 8B, when the transistor Q ₁ is turned on, the path of the DC power supply E → oscillation coil L ₁ → transistor Q ₁ and the DC power supply E → discharge lamp La → current limiting choke L ₂ → transistor Q 1 _A current flows through the path ₁ and energy is accumulated in the oscillation coil L ₁ and the current limiting choke L ₂ . When the transistor Q ₁ is turned off, with energy stored in the oscillation coil L ₁ and the current limit choke L _2, oscillation coils L _1, consisting of current limiting choke L _2, the oscillation capacitor C ₁ and the discharge lamp La resonance Resonant current flows in the circuit.

Here, the period during which the output of the PWM control circuit 1 is at a low level, that is, the period during which the transistor Q ₁ is turned off is set to a fixed time determined by the resonance frequency peculiar to the resonance circuit, and The device is adapted to repeat the above-described operations. However, the above PWM
In the control circuit 1, the period during which the output is at a high level, that is, the period during which the transistor Q ₁ is turned on can be varied, and the variable control during this high level period is the output of the reference voltage generation circuit 10. It is performed by the reference voltage V _ref . Here, in the PWM control circuit 1, when the reference voltage V _ref output from the reference voltage generation circuit 10 is high,
The ON period of the transistor Q ₁ is lengthened. At this time, the energy accumulated in the oscillation coil L ₁ and the current limiting choke L ₂ increases, and the output supplied to the discharge lamp La rises. On the contrary, when the reference voltage V _ref is low, the PWM control circuit 1 shortens the ON period of the transistor Q ₁ . At this time, the output supplied to the discharge lamp La is lowered.

An example of a method of changing the reference voltage of the reference voltage generating circuit 2 after the power is turned on will be described with reference to FIG. When the power is turned on, first, the reference voltage V _ref is lowered to lower the discharge lamp L.
Preheat filament a. Then, after preheating for a certain period of time, the reference voltage V _ref is increased to start the discharge lamp La. At this time, the discharge lamp La starts discharging when the voltage applied from the resonance circuit becomes equal to or higher than the starting start voltage. After this discharge, the reference voltage V _ref is further increased to maintain the lighting state of the discharge lamp La. It should be noted that such adjustment of the reference voltage V _ref is controlled according to a timer or the like included in the reference voltage generating circuit 2.

In this inverter device, the discharge lamp L
a can be lit in two steps, that is, the full lighting state and the dimming state, and this switching is performed by the resistor R ₃ connected between the output of the reference voltage generating circuit 2 and the ground and the dimming switch SW _1. .. That is, when the dimming lighting is performed, the dimming switch SW ₁ is turned on, the resistor R ₃ is connected to the output of the reference voltage generating circuit 2, the reference voltage V _ref is lowered, and the output of the inverter device is lowered. As a result, the discharge lamp La is dimmed and turned on.

By the way, during the above-mentioned starting period, the discharge lamp L
When a is difficult to discharge, the reference voltage V_refEndlessly on
When raised, DC power supply E → preheating capacitor C₂→ current limiting
Joke L₂→ Transistor Q₁A large current flows through the
Transistor Q₁Current I flowing through_CE, Collector d
Inter-mitter voltage V_CEBecome large together, transistor Q ₁
May be damaged.

Therefore, in the above inverter device, the current flowing through the transistor Q ₁ is detected and the PWM control circuit 1 is controlled so that the current becomes equal to or less than a predetermined value. Here, the current limiting circuit 11 is provided with an emitter resistance R _E of the transistor Q ₁ , a reference voltage V _DET corresponding to a voltage required for the discharge lamp La to start discharging, and a voltage across the emitter resistance R _E. Comparison circuit CP for comparison
₆ and a transistor Q ₂ which is on / off controlled by the output of the comparison circuit CP ₆ . Here, the reference voltage V _DET is set to a value corresponding to the voltage required for the discharge lamp La to start discharging so that the discharge lamp La can be discharged even when the current is limited. Is.

In the current limiting circuit 11, when the current flowing through the transistor Q ₁ rises above the current corresponding to the voltage required for the discharge lamp La to start discharging, the PWM control circuit for the reference voltage V _ref. 1 is stopped by turning on the transistor Q ₂ and temporarily turning off the transistor Q ₁ , so that the voltage applied to the discharge lamp La becomes unnecessarily higher than the voltage required to start the discharge. To prevent this.

After the discharge lamp La lights up, the discharge lamp La
Since the impedance of La decreases extremely,
SA C₂The current flowing in the
SA C ₂Is the transistor Q₁Almost affects the current flowing through
No longer, transistor Q ₁Between collector and emitter
Voltage V_CEStabilizes at a low level. By the way, like this
Even after the discharge lamp La lights up, the discharge lamp La has reached the end of its life.
May become difficult to discharge, or may be
In the case of extinction, the impeller of the discharge lamp La
And the capacitor C₂Current flows through
Transistor Q₁The current flowing through the
Similar problems may occur.

Therefore, the above-mentioned inverter device is provided with an abnormality protection circuit for stopping the oscillation of the inverter device when the current flowing through the transistor Q ₁ becomes large during lighting. This abnormality protection circuit is the current limiting circuit 1 described above.
It is composed of a current detector and a latch circuit 12 including an emitter resistance R _{E of} 1 and a comparator CP ₆ . In this abnormality protection circuit, when the voltage across the emitter resistor R _E has reached the current limit value as described above is detected by the comparator CP _6, the latch circuit 12 at the high level output of the comparator CP ₆ when the PWM control The operation of the circuit 1 is stopped and the transistor Q ₁ is held in the off state to protect the inverter device.

If the abnormality protection circuit operates before the discharge lamp La is lit, the discharge lamp La cannot be lit. Therefore, in order to prevent this, a certain period (at least the discharge lamp La is discharged) after the power is turned on. A timer circuit 13 for disabling the operation of the latch circuit 12 is provided during the period (starting above).

[0013]

By the way, in the above-mentioned inverter device, when the resonance circuit operates unstablely, such as when the power is turned on, the collector / transistor transiently changes as shown in (a) of FIG. 9 (a).
The phenomenon that the emitter-to-emitter voltage V _CE becomes high occurs. In order to prevent such a phenomenon, as shown in FIG. 7, at both ends of the parallel circuit of the oscillation capacitor C ₁ and the oscillation coil L ₁ ,
A snubber circuit 14 composed of a diode D ₂ , a resistor R ₂ and a capacitor C ₃ for absorbing a transient voltage is connected, or as shown by a broken line B in FIG. 9B, the reference voltage V _ref rises slowly during preheating. (For example, by providing a large-capacity capacitor in the reference voltage generation circuit 10, the reference voltage V
_It is necessary to devise to make the rise of _ref moderate).
Therefore, there is a problem that the number of parts increases, which hinders downsizing and cost reduction.

Further, if the above-mentioned abnormality protection circuit is provided, that is, if a latch circuit is provided, a so-called malfunction in which the latch circuit 12 works due to lightning surge, external noise, or extinguishing of the discharge lamp La at the moment of a momentary power failure. There is a problem that causes. Therefore, it is conceivable to temporarily turn off the transistor Q ₁ only when the current of the transistor Q ₁ reaches the limit current without using the latch circuit 12. In this case, the circuit of FIG. The circuit 13 may be omitted. However, in this case, there are the following problems.

Now, for example, the discharge lamp La is at the end of its life.
When the
Register Q₁When the current flowing in reaches the limit current,
Transistor Q₁Turns off and the transistor Q₁Flow
The current that is obtained is the voltage required for starting the start
Is limited to the current limit value. However, in this case
Since the switch circuit 12 is not provided, the broken line C in FIG.
Like transistor Q ₁Current was cut off by turning off
Later, transistor Q₁Is turned on again, the inverter
The operation of restarting the device is repeated.

At this time, the current value limited by the current limiting circuit 11 is the limited current value when the discharge lamp La is started, and the limited current value is considerably large. Accordingly, in the state in which the intermittent high current and voltage is applied to continue the switching element Q _1, Thus the switching elements Q _1, an increase in the loss of the oscillator coil L ₁ or current limiting choke L ₂ There is a problem that the temperature rises and eventually leads to thermal destruction.

Therefore, in the case of the above-mentioned inverter device, a circuit such as the latch circuit 12 which completely stops the operation is required. That is, in the above-described inverter device configuration, the latch circuit 12 is always required,
Discharge lamp L during lightning surge, external noise, or momentary power failure
It is impossible to prevent malfunction due to the disappearance of a.

The present invention has been made in view of the above points, and an object of the present invention is to provide an inverter device capable of surely protecting circuit components in the event of an abnormality and causing no malfunction. is there.

[0019]

According to the present invention, in order to achieve the above object, a switching element is connected to a DC power source through at least an inductance element of a resonance circuit,
An inverter device that resonates a resonance circuit when the switching element is turned off by the energy stored in the inductance element when the switching element is turned on, and supplies a high-frequency power obtained by the resonance of the resonance circuit to a load. The switching control means for controlling the switching element to be in the ON-enabled state for a certain period from the time when the voltage across the switching element drops below a predetermined voltage, the current detection means for detecting the current flowing through the switching element, and the current detection means A current limiting means for controlling the switching control means to forcibly turn off the switching element when it is detected that the current has reached the current limiting level; and a current limiting level of the current limiting means depending on the operating condition of the load. And a level adjusting means for changing it.

[0020]

The present invention has the above-mentioned configuration,
The current flowing through the switching element can be limited at different current limit levels depending on the load operating status, and protection that matches the operating status of the load can be performed to prevent problems such as damage to circuit components during abnormal conditions. In addition, by limiting the current flowing through the switching element according to the operating condition of the load so that the circuit components can be protected, it is not necessary to completely stop the operation of the inverter device in the event of an abnormality, and malfunctions are prevented. It was designed so that it would not occur.

[0021]

【Example】

(Embodiment 1) FIGS. 1 to 4 show an embodiment of the present invention.
As shown in FIG. 1, the configuration of the main circuit of this embodiment is similar to the above-described circuit of FIG. 7, in that switching is performed at both ends of the DC power source E via a parallel circuit of an oscillation coil L ₁ and an oscillation capacitor C _1. The element Q ₁ is connected, and the discharge lamp La is connected to the parallel circuit of the oscillation coil L ₁ and the oscillation capacitor C ₁ via the current limiting choke L ₂ . And the oscillation coil L
₁ , the current limiting choke L ₂ , the oscillation capacitor C _1, and the discharge lamp La constitute a resonance circuit. In the case of this embodiment, an FET is used as the switching element Q ₁ as shown in the concrete circuit of FIG. 2, and a feedback current returned from the above resonance circuit to the DC power source E is used for this switching element Q _1. A diode D ₁ is connected in anti-parallel to flow. A preheating capacitor C ₂ is connected to the non-power source side of the filament of the discharge lamp La. By the way, in the specific circuit, the oscillation capacitor C ₁ is connected in parallel with the switching element Q ₁ , but even with such a configuration, the resonance circuit is similar to the case where the oscillation capacitor C ₁ is connected to the oscillation coil L _1. Operate.

This main circuit is similar to that described in the conventional circuit of FIG. 7 during the period when the switching element Q ₁ is on.
A current is passed through the path of DC power supply E → oscillation coil L ₁ → transistor Q _{1 and} the path of DC power supply E → discharge lamp La → current limiting choke L ₂ → transistor Q ₁ to generate oscillation coil L ₁
And to store energy in the current limiting choke L _2, in the period the switching element Q ₁ is off, with energy stored in the oscillation coil L ₁ and the current limit choke L _2, oscillation coils L _1, limiting choke L _{2. The} resonance circuit composed of the oscillation capacitor C ₁ and the discharge lamp La is resonated, and the high-frequency resonance current generated in the resonance circuit is passed through the discharge lamp La to operate the discharge lamp La at high frequency.

[0023] In detail the operation of the resonant circuit during this addition, first stored energy in the oscillator coil L ₁ and the current limit choke L _2, and on the time of the transistor Q ₁ even after the transistor Q ₁ is turned off A current flows in the same direction, whereby the oscillation capacitor C ₁ is charged to have a positive polarity on the lower side in FIG. Next, when the energy stored in the oscillation coil L ₁ and the current limiting choke L ₂ is released, a current in the opposite direction to that before flows through the resonance circuit using the charge stored in the oscillation capacitor C ₁ as a power source. At this time, the oscillation coil L ₁ and the current limiting choke L ₂ store energy having the opposite polarity to that when the transistor Q ₁ is on.

When the charge stored in the oscillating capacitor C ₁ is discharged, the energy accumulated in the oscillating coil L ₁ and the current limiting choke L ₂ in the opposite polarity causes the resonance circuit to keep the current flowing in the opposite direction. An electric current flows. At this time, the oscillation capacitor C ₁ is charged with a polarity in which the upper side in FIG. 1 is positive, and a feedback current flows through the DC power source E through the diode D ₁ .

After that, when the energy stored in the oscillation coil L ₁ and the current limiting choke L ₂ in the opposite polarity is released, the transistor Q ₁ is turned on, and the above-described operation is repeated. The control circuit 1 controls ON / OFF of the switching element Q ₁ . This control circuit 1
As shown in FIG. 2, the voltage detection circuit 21 that detects the voltage across the switching element Q _{1 and} the time when the voltage detection circuit 21 detects that the voltage across the switching element Q ₁ has dropped below a predetermined voltage. Charging circuit 2 to start charging
2 and an output circuit 23 that compares the output voltage of the charging circuit 22 with the reference voltage V _ref and controls the switching element Q ₁ to be in the ON-enabled state when the output voltage of the charging circuit 12 is equal to or lower than the reference voltage V _ref. I am doing it.

Here, the voltage detection circuit 21 is constructed by using the comparator CP ₁ , and the switching element Q
_The divided voltage obtained by dividing the drain potential of the FET which is ₁ by the resistors R ₆ and R ₇ is compared with the reference voltage V _D2 which is the forward voltage of the diode D _{2 by} the comparator CP ₁ and the switching element Q ₁ It is detected that the voltage between both ends of the device has dropped below a predetermined voltage.

The charging circuit 22 is Yes and a resistor R ₃ and capacitor C _3, the period the output of the voltage comparator circuit 21 is at a low level not charged capacitor C _3, the output of the voltage comparator circuit 21 When at the high level, the capacitor C ₃ is charged through the resistor R ₃ . Output circuit 2
3 Yes constituted by a comparator CP _2, outputs the lower period than the output voltage V _c3 reference voltage V _ref of the voltage detection circuit 21 in the comparator CP ₂ becomes high level, applying a gate voltage to the switching element Q ₁ Then, the switching element Q ₁ is turned on.

Now, in the resonant operation of the resonant circuit, the die
Aether D₁A feedback current flows to the DC power source E via
Switching element Q₁Resistor voltage across
R₆, R₇The voltage divided by is the reference voltage V_D2Drops below
It Therefore, at this time, the output of the voltage detection circuit 21 becomes high level.
It becomes a bell and the capacitor C of the charging circuit 22₃Charging is open
Be started. At this time, the capacitor C₃Voltage V across_C3Is
Reference voltage V_refLower than the comparator CP₂of
Output becomes high level and switching element Q ₁Is on
To be done. At this time, the switching element Q₁Voltage across
Resistance R₆, R₇The voltage divided by is the switching element Q₁
Turns on the reference voltage V_D2It is retained below, so
Parator CP₁The output of the
State is capacitor C₃Is the reference voltage V_refTo
Maintained until reached. Therefore, the switching element Q₁
The ON period of is determined by the time constant of the charging circuit 22.

When the voltage V _C3 across the capacitor C ₃ exceeds the reference voltage V _ref , the output of the comparator CP ₂ goes low and the switching element Q ₁ is turned off. At this time, the voltage across the switching element Q ₁ rises, and the divided voltage of the resistors R ₆ and R ₇ exceeds the reference voltage V _D2 , which is the forward voltage of the diode D ₂ , so that the output of the comparator CP ₁ is at a low level. Becomes This comparator C
Since the output of P ₁ is connected to the output of the comparator CP _{2, while} the voltage divided by the resistors R ₆ and R ₇ of the voltage across the switching element Q ₁ is equal to or higher than the reference voltage V _D2 , the switching element Q is switched. ₁ is held in the off state.

Thereafter, by repeating the same operation,
Control circuit 1 is switching element Q₁ON / OFF control of
To do. Furthermore, in the inverter device of the present embodiment,
In addition to the configuration, the following configuration is provided. That is, switchon
Element Q₁A current detection circuit 2 for detecting a current flowing through
If the detection output of the current detection circuit 2 reaches a predetermined level,
And a level determination circuit 3 for detecting
Switching element Q with 3₁The current flowing to the specified level
When the reaching is detected, the control circuit 1 is controlled to switch.
Touching element Q ₁Current limit circuit 4 that forcibly turns off
And a level determination circuit according to the lighting control state of the discharge lamp La.
3 and the level adjustment circuit 5 that changes the judgment level
There is.

In the case of this embodiment, the current detecting circuit 2 is constructed by using the resistor R ₁ . However, this resistance R ₁
Affects the voltage across the switching element Q ₁ (voltage V _Q1 ≒ R ₁ · i _Q during the on-switching element Q ₁₎
Therefore, the resistance value of the resistor R ₁ is made as small as possible, and the input voltage of the voltage detection circuit 21 when the switching element Q ₁ is turned on becomes equal to or lower than the reference voltage V _D2 (V _Q1 · R ₆ / (R ₆ + R
₇ ) <V _D2 ). In addition to the resistor R ₁ , a current transformer may be used to detect the current.

The level judgment circuit 3 is a comparator CP.₃To
The level judgment circuit 3 uses the reference voltage.
Pressure V_AAnd resistance R₁The voltage across both ends of the
Child Q ₁Output when the current flowing through reaches a specified level
Becomes low level and the output is
Become level. The current limiting circuit 4 is the same as that of the control circuit 1 described above.
Comparator CP used as output circuit 23₂When,
Comparator CP₃Resistor R provided at the output of_Four, R_Five
And a voltage dividing circuit consisting of.

Now, the level decision circuit 3 is switched on.
Element Q₁If the current flowing through the
Computer CP₃Output becomes high level, and at this time
Reference voltage V_refIs the drive voltage V_CCResistance R_Four, R_FivePartial pressure
Voltage (V_CC・ R_Four/ (R _Four+ R_Five)) That
Switching element Q₁The current flowing through the
Whenever it happens, the comparator CP₃Output is low level
And at this time the reference voltage V_refIs lowered to almost 0V
Be done.

In the comparator CP _{2 of the} output circuit 23,
When the drive voltage V _CC is _divided by the resistors R ₄ and R ₅ , that is, the reference voltage V _ref is applied, the switching element Q ₁ can be turned on for a certain period according to the operation of the control circuit 1 described above. And Then, when the reference voltage V _{ref is} almost 0 V, the output of the comparator CP ₂ becomes a low level regardless of the output voltage V _C3 of the charging circuit 12, and therefore the switching element Q ₁ is turned off and the switching element Q ₁ is overloaded. Prevent current from flowing. In this way, it is possible to limit the maximum voltage applied across the switching element Q ₁ by limiting the maximum current flowing through the switching element Q _1.

The level adjusting circuit 5 is preset from the time when the power is turned on.
The time until the end of heat is measured and the power is turned on.
From the start of the discharge lamp La to the
The comparator C of the level determination circuit 3 according to the time measurement result of
P₃Reference voltage V_AIs variable. Implementation
In the case of the example, the time from power-on to the end of preheat
The discharge lamp La starts when the power is turned on.
In order to measure the time until it is activated, the resistance R₁₆And con
Densa C_FiveConsisting of a charging circuit and the output voltage of this charging circuit.
Pressure is the voltage of the driving power supply V_CCResistance R₁₇~ R₁₉Partial pressure with
Reference voltage V_B1, V_B2Comparator CP to compare with
_Four, CP_FiveIs equipped with. And, according to each timing result
Then, the comparator CP of the level adjusting circuit 3₃Reference voltage of
V_ATo change the comparator CP_Four, CP_Fiveof
Transistor Q conducting at output₃, Q_FourAnd resistance R ₉~
R₁₃Is equipped with.

In this embodiment, the DC power source E is an AC power source.
AC is a diode bridge DB and a smoothing capacitor C₀
Is obtained by rectifying and smoothing at
Resistance R₈, Zener diode ZD₁And capacitor C
₆It is created by converting the voltage into a constant voltage by a constant voltage circuit 6 consisting of.
The power is turned on and the drive power is supplied to the level adjustment circuit 5.
Then, the capacitor C _FiveWill start charging. This and
Comparator CP_FiveInput voltage is reference voltage V _B1Less than
Therefore, the comparator CP_FiveOutput is high level,
Comparator CP _FiveInput voltage is reference voltage V_B2Below
Therefore, the comparator CP_FourOutput is low level
It In this way the comparator CP_FiveOutput is high level
Then transistor Q₃Turns on and the reference voltage V
_AIs resistance R_Ten~ R₁₂Is determined by the constant of. Where the resistance R₁₂
Has a small resistance value. Therefore, the reference voltage V_AIs a figure
It becomes low as shown in FIG. Therefore, during the preheating period
Switching element Q₁The current flowing through the
Limited. At this time, the reference voltage V_ATo the current corresponding to
Switching element Q₁Current is limited, so for example
Resonance circuit operation becomes unstable like immediately after power is turned on.
Even then, as shown in (a) of FIG.
-Emitter voltage V_CEThe phenomenon of raising the value does not occur.

When the capacitor C ₅ is charged and the input voltage of the comparator CP ₅ exceeds the reference voltage V _B1 , the output of the comparator CP ₅ becomes low level at this time. At this time, since the input voltage of the comparator CP ₄ is the reference voltage V _B2 or less, the output of the comparator CP ₄ remains at the low level. Therefore, the transistor Q ₃ is turned off, the resistor R ₁₂ is separated from both ends of the resistor R ₁₀ , and the reference voltage V _A is increased. At this point, discharge lamp L
In the starting period of a, the voltage necessary for starting the discharge lamp La is the current value applied to the discharge lamp La, and the current flowing through the switching element Q ₁ is limited. In this embodiment, the limiting current at this time is the highest level limiting value as shown in FIG.

Then, as the charging of the capacitor C ₅ progresses,
Since the input voltage of the comparator CP ₄ is the reference voltage V _B2 above, the output of the comparator CP ₄ becomes high level, the resistor R ₁₃ by turning on this time the transistor Q ₄ is connected in parallel with the resistor R _10, thereby the reference As shown in FIG. 3A, the voltage V _A is lower than that at the start. By doing so, even when the discharge lamp La becomes the end of its life and it becomes difficult to discharge, or even if the discharge lamp La goes out for any reason, the current flowing through the switching element Q ₁ during lighting is higher than during starting. Therefore, even if the inverter device is intermittent, the switching element Q ₁ , the oscillation coil L
It is possible to suppress the temperature rise of ₁ and the current limiting choke L ₂ and prevent thermal destruction. Therefore, it is not necessary to provide the inverter device with a latch circuit that completely stops the operation when an abnormality occurs, and there is no problem that a malfunction occurs due to lightning surge, external noise, or extinguishing of the discharge lamp La at the time of a momentary power failure.

When the discharge lamp La is dimmed and turned on during lighting, the reference voltage V _A is further lowered as shown in FIG.
Can be dimmed. Here, in order to perform the dimming control in this embodiment, Yes connected in parallel with the resistor R ₁₀ and a resistor R ₉ and the switch SW _2, when turning on the switch SW _2, resistor to the resistor R ₁₀ in parallel R ₉ are connected in parallel,
The reference voltage V _A can be lowered as compared with the time of lighting (all lighting).

As is clear from the above description, in this embodiment, the control circuit 1 operates the inverter device in a constant state even during preheating, starting and lighting, and performs output control for preheating, starting and lighting. This is done by limiting the current flowing through the switching element Q ₁ to a current suitable for preheating, starting and lighting. The current limiting operation also serves as an abnormal protection function.

The following table shows the relationship between the set voltage of the reference voltage V _{A and} the limited voltage across the switching element Q ₁ .

[0042]

[Table 1]

(Embodiment 2) FIG. 5 shows another embodiment of the present invention. In the case of the above-described embodiment, the reference voltage V _A is kept at the highest state for a certain period after preheating regardless of the actual starting period of the discharge lamp La, but in the case of the present embodiment, the discharge lamp La is held. When is turned on, the current flowing through the switching element Q ₁ is immediately limited to the current limit value during lighting.

Specifically, the voltage across the discharge lamp La is detected.
The lamp voltage detection circuit 7 for
The output of the circuit 7 controls the control of the level adjusting circuit 5.
There is. Here, this lamp voltage detection circuit 7 is
SA C_Ten, C₁₁, Diode D ₃And resistance R_{twenty two}, R_{twenty three}Construction
And outputs a DC voltage according to the lamp voltage.

[0045] Then, the level adjusting circuit 5 of this embodiment, Yes comparator CP ₄ be used to detect that the output voltage of the lamp voltage detection circuit 7 is reduced below a predetermined level, the comparator CP ₄ Reference voltage V
_B3 is set by resistors R ₂₀ and R ₂₁ . However, since the reference voltage V _B3 is applied after the preheating is completed, the comparator C
A transistor Q ₅ which is turned on / off by the output of P ₄ is connected in parallel with the resistor R ₂₁ .

The operation from the end of preheating, which is the feature of the present embodiment, to lighting will be described below. When the preheating is completed, the output of the comparator CP ₄ becomes low level in the same manner as in the above-described embodiment, the transistor Q ₃ is turned off, and the switching element Q ₁ is switched to a large current value determined by the resistors R ₁₀ and R _11. The action of limiting the flowing current is performed.

[0047] When the output of the comparator CP ₄ in this way becomes a low level, it transistor Q ₅ which has been turned on until turned off, the voltage V _cc of the driving power to the comparator CP ₅ with resistors R _20, R ₂₁ A reference voltage V _B3 created by voltage division is applied. Here, not operating the comparator CP ₄ at preheating is because the output of the comparator CP ₄ at no need to detect the lamp voltage to prevent malfunction as the high level.
In other words, at the time of preheating leave 0V reference voltage of the comparator CP ₄ using transistors Q _5, it is prevented from malfunctioning.

At the time of start-up, the comparator CP ₄ compares the output voltage of the lamp voltage detection circuit 6 obtained by rectifying and smoothing the voltage of the discharge lamp La from which the DC component is cut by the capacitor C ₁₀ with the reference voltage V _B3. To start. Discharge lamp La
The voltage of the discharge lamp La keeps a high value until is lit, so that the output of the comparator CP ₄ is kept at a low level. Then, when the discharge lamp La is lit, the impedance of the discharge lamp La is rapidly reduced, so that the discharge lamp L
The voltage across a decreases sharply. At this time, the output of the lamp voltage detection circuit 6 drops below the reference voltage V _B3, and the output of the comparator CP ₅ becomes high level. Therefore, the resistor R ₁₃ is connected in parallel with the resistor R ₁₀ , and the switching element Q
The current limit value of ₁ becomes low. That is, in this embodiment, the current limit value can be switched at the same time when the discharge lamp La is turned on.

[0049]

As described above, according to the present invention, a switching element is connected to a DC power source through at least an inductance element of a resonance circuit, and the resonance circuit is resonated by the energy stored in the inductance element when the switching element is turned on. An inverter device for supplying a high-frequency power obtained by the resonance of the resonance circuit to a load, wherein the switching element is controlled to be in the ON-enabled state for a certain period from the time when the voltage across the switching element drops below a predetermined voltage. Switching control means, a current detection means for detecting that the current flowing through the switching element has reached the current limit level, and the switching control when the current detection means detects that the current has reached the current limit level. Current that controls the means to force the switching element to turn off Limiting means and level adjusting means for varying the current limiting level of the current limiting means according to the operating condition of the load, so that the current flowing through the switching element at different current limiting levels depending on the operating condition of the load It can be limited and can be protected according to the operating condition of the load, so that problems such as damage to circuit components at abnormal times do not occur.
Moreover, since the current flowing through the switching element can be limited according to the operating condition of the load to protect the circuit components, it is not necessary to completely stop the operation of the inverter device at the time of an abnormality, and the problem of causing a malfunction does not occur. There is.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of the above.

FIG. 3 is an explanatory diagram showing an operation of the above.

FIG. 4 is an operation explanatory diagram of a main circuit of a specific circuit.

FIG. 5 is a circuit diagram showing a specific configuration of another embodiment.

FIG. 6 is an operation explanatory diagram of the above.

FIG. 7 is a circuit diagram showing a schematic configuration of a conventional example.

FIG. 8 is an explanatory diagram of an on / off control method for the switching element of the above.

FIG. 9 is an explanatory diagram showing operations and problems of the conventional example.

[Explanation of symbols]

1 Control Circuit 2 Current Detection Circuit 3 Level Judgment Circuit 4 Current Limit Circuit 5 Judgment Level Setting Circuit Q ₁ Switching Element La Discharge Lamp L ₁ Oscillation Capacitor L ₂ Current Limit Choke C ₁ Oscillation Capacitor E DC Power Supply

Claims (1)

[Claims] 1. A switching element is connected to a DC power source through at least an inductance element of a resonance circuit, and the energy stored in the inductance element when the switching element is turned on causes the resonance circuit to resonate when the switching element is turned off. An inverter device for supplying a load with high-frequency power obtained by the resonance of the resonance circuit, wherein the switching device controls the switching element to be in an ON-enabled state for a certain period from the time when the voltage across the switching element drops below a predetermined voltage. Control means, current detection means for detecting the current flowing through the switching element, and when the current detection means detects that the current has reached the current limit level, the switching control means is controlled to force the switching element. Current limiting means for turning off the An inverter device comprising: level adjusting means for varying the current limiting level of the means according to the operating condition of the load.