JPH0634597B2 - Inverter device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inverter device that switches a DC power supply by a switching element to supply power to a load circuit.

[Background Art] FIG. 10 shows a schematic configuration of a conventional inverter device. The inverter device is configured to connect the two switching elements Q _1, Q ₂ connected in series in parallel to the DC power source E, a load circuit 1 including the load through the capacitor C ₁ in parallel one of the switching elements Q ₁ The switching elements Q ₁ and Q ₂ are alternately switched by the output from the driver circuit 2 to supply power to the load circuit 1. However, in such a conventional inverter device, even when the load circuit 1 is unloaded, there is a disadvantage that it operates, and reliability,
There is room for improvement in terms of power consumption.

Further, such an inverter device is also used for controlling lighting by using a discharge lamp as a load, and in that case, it is configured by connecting the inductance L ₁ and the capacitor C ₂ shown in FIG. 11 in series. An LC resonance series circuit A is added, and a load R composed of a discharge lamp is connected with the terminals of its capacitor C ₂ as an output terminal to supply a high voltage to the discharge lamp. However, generally, in an inverter device, the output voltage becomes high when there is no load.
The following problems have been pointed out.

High output voltage is generated under no load condition (for example,
Regarding the discharge lamp lighting device, there are restrictions on the upper limit of secondary voltage in the Electrical Appliance and Material Control Law and JIS). Also, if the load is a discharge lamp and the filament of the discharge lamp is not broken, but the discharge lamp does not light for some reason (for example, the emitter of the filament is scattered), the circuit is equivalent. As shown in FIG. 12, one end of the discharge lamp is opened, and a high output voltage is generated even in such a case.

In the no-load state, a large oscillating current flows through the switching element to increase switching loss, and the continuation of this current may cause thermal destruction of the switching element, resulting in destruction.

Therefore, in order to solve the above problems, it is conceivable to provide a circuit for detecting the no-load state in the inverter device and stop or suppress the operation of the switching element by the output signal of this detection circuit. For example, a current transformer is provided as a detection circuit in series with the load, and the secondary side output is sent to the switch control unit to stop the operation of the switching element. However, with such a configuration, the structure is complicated and the device is large, and since the method of detecting the current flowing through the load is adopted, the operation of the inverter device is also affected and the operation of the inverter device is unstable. Causes problems such as becoming a factor. Moreover, since the potential on the load side is generally different from the control potential for stopping the inverter device, an insulated current transformer is required.

Also, as another conventional example, there is JP-A-59-132597. This Japanese Patent Laid-Open No. 59-132597 discloses
Although it prevents high voltage, it is attempted to detect abnormal high voltage during lighting of the discharge lamp by providing a voltage detection circuit with a voltage-dependent resistance at the connection point between the series circuit of the discharge lamp and capacitor and the inductance. However, this conventional example does not detect a no-load state, and has a problem that it is difficult to detect a voltage change between a normal time and an abnormal time.

[Object of the Invention] The present invention has been provided in view of the above points,
It surely detects the presence or absence of load, and when there is no load, limits the output of the switching element to reduce unnecessary power consumption,
Moreover, it is an object of the present invention to provide a highly reliable inverter device that does not make the operation unstable.

DISCLOSURE OF THE INVENTION (Structure) In the present invention, two switching elements connected in series are connected in parallel to a DC power source, and a series circuit of a capacitor and a load circuit is connected in parallel with at least one of the switching elements. In an inverter device in which a capacitor is connected so as to be on one electrode side of a DC power supply, a voltage detection circuit unit that detects a voltage between the non-power supply side of the capacitor and the other electrode side of the DC power supply, By including an output control unit that limits the operation output of the switching element according to the output voltage of the voltage detection circuit unit, the voltage between the non-power supply side of the capacitor and the other electrode side of the DC power supply is controlled. The detection voltage is detected by the voltage detection circuit unit, the detected voltage is input to the output control unit, and the operation output of the switching element is limited by the output control unit according to the detected output voltage. It is characterized in that it has a so that.

Example 1 An example of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic block diagram of the inverter device of the present invention, in which the DC power source E is composed of a constant voltage power source obtained by rectifying an AC power source. The load circuit 1 includes, for example, a discharge lamp. The driver circuit 2 is for switching the two switching elements Q ₁ and Q ₂ , and the voltage detection circuit unit 3 that detects the voltage of the load circuit 1 is
The load circuit 1 is configured by a voltage dividing circuit using a resistance element having a higher impedance than the load circuit 1. The detection output of the voltage detection circuit unit 3 is sent to the output control unit 4, and the output control unit 4 controls the output of the driver circuit 2.

Next, the basic operation of the present invention will be described. When there is a load, the output of the voltage detection circuit unit 3 becomes "H level", and a signal is sent to the output control unit 4 to switch the switching element Q.
₁ and Q ₂ are continuously driven, but when there is no load, the output of the voltage detection circuit unit 3 becomes “L level” (0) and the output control unit 4
To control or stop the operation of the switching elements Q ₁ and Q ₂ . Such operation is the same when the inverter device of the present invention is configured by adding the LC series resonance circuit A.

Next, specific examples of the present invention will be described. Figure 1 shows L
It is a concrete circuit diagram at the time of comprising and adding C series resonance circuit A. The transistors Q ₁ and Q ₂ connected in series are connected in parallel to the DC power source E via the power switch SW, and the collector of the transistor Q ₁ is connected in parallel with the additional R via the capacitor C _1. Has been done. As will be described later, the capacitor C ₁ inverts the voltage supplied to the load R when the _two transistors Q ₁ and Q ₂ are alternately turned on and off, and cuts the direct current component so that the load R has an alternating current component (high frequency component). Power supply). Also, a capacitor C ₂ is connected in parallel with the load R,
Further, an inductance L ₁ is connected to a connection point between the capacitor C ₂ and the load R (an opposite side of the capacitor C ₁ ) to form an LC series resonance circuit A. Here, the two capacitors C _1, C ₂ satisfy the relationship C ₁ »C _2. Incidentally, L
The capacitor C ₂ forming the C series resonance circuit A may be a stray capacitance existing between load terminals, and when the load R is selected as a discharge lamp, the inductance L ₁ may be formed by a ballast. Good.

The terminal on the non-load side of the inductance L ₁ is the drive transformer T ₁
Is connected to the connection point of the transistors Q ₁ and Q ₂ via the primary winding n ₁ of the drive transformer T ₁ , and the secondary windings n ₂ and n ₃ of the drive transformer T ₁ are respectively connected via the resistors R ₁ and R ₂ . Transistor Q ₁ , Q ₂
Connected to each of the bases. Further, the secondary winding n _2, n ₃ of the drive transformer T ₁ is to its polarity reversed, turns on transistor Q _1, Q ₂ alternately has a configuration that is turned off, the driving transformer T ₁ and its accompanying The circuit constitutes the driver circuit 2. Load R of capacitor C ₁
A voltage divider circuit constituted by a series circuit of resistors R ₄ and R ₅ is provided between the connection point of the DC power source E and the load terminal of the DC power source E, whereby the voltage detection circuit unit 3 is constituted. Has been done. Here, the resistors R ₄ and R ₅ are selected to have a high impedance value with respect to the load R. Furthermore, the resistance R ₄
The connection point between R ₅ and R ₅ is connected to the base of the transistor Q ₅ via a resistor R _7, and the emitter of the transistor Q ₅ is commonly connected to the emitter of another transistor Q ₄ and the negative terminal side of the DC power source E is connected. It is connected to the. On the other hand, the collector of the transistor Q ₅ is connected to the positive electrode terminal side of the DC power source E via the resistor R _{6 and} to the base of the transistor Q ₄ . The collector of the transistor Q ₄ is connected to the base of the transistor Q ₂ .
The transistors R ₄ , R ₅ and their associated circuits are the output control unit 4.
It is what constitutes.

On the other hand, a resistor R ₃ and a capacitor C ₃ are connected in parallel with the DC power source E, and a connection point between the capacitor C ₃ and the resistor R ₃
A diode D ₃ is connected between the connection point of the transistors Q ₁ and Q ₂ . The diode D ₃ has its anode connected to the connection point of the resistor R ₃ and the capacitor C ₃ as shown. Further, between the base of the resistor R ₃ and the connection point of the transistor Q ₂ of the capacitor C ₃ is provided with a diac Q _3, constitute the starting circuit 6 of the inverter device. Here, the series circuit of the resistor R ₃ and the capacitor C ₃ constitutes a trigger circuit of the diac Q ₃ , and the diode D ₃ supplies the current supplied from the DC power source E to the resistor R ₃ after the diac Q ₃ breaks over. A bypass circuit is formed that leads directly to the transistor Q ₂ via. In addition,
Each of the transistors Q ₁ and Q ₂ has a feedback diode D ₁ ,
D ₂ is connected in anti-parallel.

Next, the operation will be described. FIG. 3 shows the equivalent basic circuit of FIG.

<Operation under load> In the case of load, the equivalent basic circuit can be further expressed as shown in FIG. In this case, the voltage e _1, e ₂ appearing across transistors Q _1, Q ₂ by the switching operation of the transistor Q _1, Q ₂ are each FIG. 5 (b), becomes a square wave voltage, such as shown in (c), The voltage e ₃ across the LC series resonance circuit A has its DC component cut by the capacitor C ₁ (FIG. 5 (e))
The voltage e ₃ is supplied as shown in FIG. Incidentally, FIG. 5 (a) shows the voltage E of the DC power source E. Here, since the voltage ec ₁ across the capacitor C ₁ is obtained by ec ₁ = e ₁ −e ₃ , the capacitor C ₁
The voltage ec ₁ between both ends is E / 2. Although a slight ripple is included in FIG. 5, this ripple is reduced by increasing the value of the time constant C ₁ · R of the circuit of the capacitor C ₁ and the load R. Further, the voltage e ₄ applied to the voltage detection circuit unit 3 is obtained by e ₄ = e ₀ −ec ₁ and has the waveform shown in FIG. 5 (f), e ₄ = E / 2
Is required.

Therefore, when the load R exists, the voltage detection circuit unit 3
The voltage e ₄ generated at is E / 2. This voltage is divided by the voltage dividing resistors R ₄ and R _{5 in} FIG. 1, and the divided output is sent to the output control section 4. In the output control unit 4, the transistor Q
_{Since the} transistor Q ₂ is enabled by turning on the transistor ₅ and turning off the transistor Q ₄ , the oscillating operation of the inverter circuit is continued.

<Operation under no load> Since the impedance of the capacitor C ₂ is much larger than the impedance of the capacitor C ₁ under no load, the output terminal can be regarded as open, and the equivalent basic circuit is as shown in FIG. Is written as In other words, the capacitor C ₁ and the voltage detection circuit unit 3 constitute a charging circuit, and the DC power source E is added to this charging circuit. Therefore, the capacitor C ₁ is charged up to E by the DC power source E, and the voltage e ₀ , ec ₁ , e ₄ are as shown in FIGS. 7 (a), (b), (c), and the detection voltage e ₄ in the voltage detection circuit unit 3 becomes 0 level. Therefore, the voltage division of the voltage e ₄ applied to the resistor R ₅ is sent to the output control unit 4. Then, the output control section 4, no base current of the transistor Q _5, the transistor Q ₅ is turned off. As a result, a base current flows through the transistor Q _4, and the base and emitter of the transistor Q ₂ are short-circuited. Thus, the transistor Q ₁ is turned off, and the oscillation operation of the inverter device is stopped.

Therefore, even when the LC series resonance circuit A is added, the high resonance voltage output when there is no load can be reliably suppressed, and the safety is high.

(Embodiment 2) FIG. 8 shows another embodiment, and the portions corresponding to those of the embodiment shown in FIG. The feature of this embodiment is that a diode D ₄ is provided in series with resistors R ₄ and R ₅ that constitute the voltage detection circuit unit 3. The anode of the diode D ₄ is connected to the connection point of the load R and the capacitor C _2. , The cathode is connected to the resistor R ₄ . With such a configuration, noise components such as surge voltage generated during the operation of the inverter circuit are absorbed and the operation of the inverter circuit is stabilized. Further, a smoothing capacitor C ₄ is connected in parallel to the resistor R ₅ , and the capacitor C ₄ absorbs a surge voltage and a ripple component to ensure the operation of the transistor Q ₅ .

The load R, in case of the the R 'discharge lamp, since the secondary voltage by 6, 3 and 2 of JIS C 8108, according to the present invention is equal to the unloaded state as shown in FIG. 9 e ₄
The voltage of 0 becomes zero, oscillation can be stopped, and secondary voltage does not occur, so that it can comply with JIS.

Incidentally, in the above-mentioned embodiment, the output control unit 4 merely shows the configuration in which the operation of the transistors Q ₁ and Q ₂ is stopped when there is no load, but the present invention is not limited to these. is not. For example, when there is no load, the transistors Q ₁ and Q ₂ operate intermittently, and the output voltage is below a predetermined value (for example, below the above-mentioned predetermined voltage 300 V).
It may be forcibly reduced to the above condition, that is, it is essential only that the output voltage be suppressed and the power consumption be suppressed when there is no load.

[Effects of the Invention] As described above, the present invention is such that two switching elements connected in series are connected in parallel to a DC power supply, and a series circuit of a capacitor and a load circuit is connected in parallel with at least one of the switching elements. In an inverter device in which a capacitor is connected so as to be on one electrode side of a DC power supply, a voltage detection circuit unit that detects a voltage between the non-power supply side of the capacitor and the other electrode side of the DC power supply, Since the output control unit that limits the operation output of the switching element according to the output voltage of the voltage detection circuit unit is provided, the non-power supply side of the capacitor and the other electrode side of the DC power supply are connected. Voltage is detected by the voltage detection circuit unit, the detected voltage is input to the output control unit, and the operation output of the switching element is output by the output control unit according to the detected output voltage. By restricting, since it is possible to suppress or stop the operation of the switching element according to the detected voltage in the no-load state, it is possible to prevent the switching element from being damaged due to switching loss or heat generation.
It is possible to suppress unnecessary power consumption, and moreover, since the voltage on the load circuit side is detected, a voltage corresponding to the presence or absence of a load is output, and the configuration of the output control unit can be simplified. Thus, it is possible to provide a highly reliable inverter device. Furthermore, since the voltage detection unit is a system that detects a voltage and does not adopt a current detection method that detects a load current, it has an effect of reducing the influence on the operation of the inverter circuit.

[Brief description of drawings]

1 is a specific circuit diagram of an embodiment of the present invention, FIG. 2 is a block diagram of the same as above, FIG. 3 is a basic equivalent circuit diagram of the embodiment of FIG. 2 of the same above, and FIG. FIG. 5 is an equivalent circuit diagram under load shown in the figure, FIG. 5 is a voltage waveform diagram of each part of the same,
FIG. 6 is an equivalent circuit diagram of the embodiment shown in FIG. 2 above when there is no load, and FIG. 7 is a voltage waveform diagram of each part thereof shown above.
FIG. 8 is a specific circuit diagram of another embodiment of the above, FIG. 9 is a secondary voltage test circuit diagram, FIG. 10 is a schematic circuit diagram of a conventional inverter device, and FIG. 11 is shown in FIG. Example of use,
FIG. 12 is an equivalent circuit diagram when the conventional discharge lamp is not lit. Reference numeral 1 is a load circuit, 2 is a driver circuit, 3 is a voltage detection circuit section, 4 is an output control section, E is a DC power supply, and R is a load.

Claims (1)

[Claims] 1. Two switching elements connected in series are connected in parallel to a DC power supply, and a series circuit of a capacitor and a load circuit is connected in parallel with at least one of the switching elements, and the capacitor is one electrode of the DC power supply. In the inverter device configured to be connected to the other side, a voltage detection circuit unit that detects a voltage between the non-power supply side of the capacitor and the other electrode side of the DC power supply, and an output voltage of the voltage detection circuit unit. And an output control unit that limits the operation output of the switching element according to the above.