JPH03112092A - Inverter device - Google Patents

Abstract

PURPOSE:To surely detect an abnormal current and quickly respond to it by detecting a current at a preset position of a circuit, and short-circuiting both ends of a capacitor controlling a switching element with its output. CONSTITUTION:Both ends of a capacitor C3 provided to stabilize the reference voltage Vref of the control circuit 1 of an inverter are short-circuited by the switching of a transistor Q3. The transistor Q3 is operated by the output of an abnormality detecting circuit 3 constituted of a comparator CP1. The on- period of an oscillation transistor Q1 is controlled by comparing the reference voltage Vref via a comparator CP2. An abnormal current is detected at the position where a current flows through constituting components in common, e.g., at the transistor Q1. The abnormal state can be surely detected, and it can be quickly responded to by the action of the transistor Q3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter device including a control circuit capable of controlling the on-period of a switching element.

[Technology in the United States 1 Inverter devices are used in discharge lamp lighting devices that light discharge lamps at high frequencies. This type of discharge lamp lighting device
As shown in the figure. This discharge lamp lighting device uses a so-called Bandai inverter, and a capacitor C is connected to both ends of a DC power source E.
A transistor Q having a diode D1 connected in anti-parallel is connected through a parallel circuit of I and a choke coil L, and a series circuit of a discharge lamp la and a choke fill L2 is connected in parallel to both ends of the parallel circuit. A current transformer CT inserted in series with the choke coil L2 supplies a base current to turn on the transistor Q1, and the base current of the transistor Q, which is turned on by the output of the control circuit 1, is supplied with a current transformer CT inserted in series with the choke coil L2. The transistor Q1 is turned off by the transistor Q2 connected between the emitters.

In this discharge lamp lighting device, the transistor Q1 is turned on and off by the current transformer CT and the control circuit 1.
By generating an oscillating current in a resonant circuit consisting of choke coils L, , L and capacitors C, , C, the DC power supplied from the DC power source E is converted into high-frequency power, and this high-frequency power is used to power the discharge lamp 1a. The high frequency lighting is performed by supplying the The capacitor C2 connected in parallel to the discharge lamp 1a functions as a preheating capacitor that flows a preheating current to the filament when starting the discharge lamp Na, and also functions as a preheating capacitor that flows a preheating current to the filament when the discharge lamp Na is started.
The capacitor C2 has the function of applying a starting voltage necessary for starting the starting voltage to the capacitor C2, and the impedance of the discharge lamp 1a becomes lower after the 7α lamp of the discharge lamp in, so that the current flowing to the capacitor C2 decreases.

By the way, in the above control circuit 1, (a) in FIG.
) The output voltage V of the lance CT shown in ). □ is detected, and when this output voltage VCT reaches the reference voltage V ref, the transistor Q2 is turned on as shown in (b) of FIG. In other words, by turning on the transistor Q2 with the output of the control circuit 1, as shown in FIG.
The so-called PWM (Pulse Width Modulation) control for controlling the on period of the transistor Q shown in (e) is performed.

Here, the reference voltage V that turns on the transistor Q2 is
ref is set by the divided voltage of resistor R2゜R1,
It is stabilized by the capacitor C3, and the reference voltage Vre is kept constant when the discharge lamp 1a is normally lit.In addition, in this discharge lamp lighting device, the reference voltage Vre is
The higher ref is, the longer the on period of transistor Q1 becomes.

However, in this discharge lamp lighting device, abnormalities such as temporary saturation of the choke coils L, L2, non-lighting of the discharge lamp 1a, or turning off during lighting due to causes such as an emissionless state or an abnormally low temperature state may occur. When this occurs, an overcurrent flows through the transistor Q, and if this condition is left as it is, there is a problem that the transistor Q will be damaged.

Therefore, in the discharge lamp lighting device of FIG. 9, a Zener diode Z is installed between the current transformer CT and the capacitor C3.
A series circuit of D and diode D is connected. That is, when the resonant current increases due to the above-mentioned causes, the amplitude of the voltage VCt generated on the next side of the lance CT also increases, as shown in FIG. 10(b) (a). Therefore, the output voltage V of this current transformer CT
When the amplitude of CT increases and this output voltage VCT decreases to a certain voltage or higher, which is the sum of the Zener voltage Vz of the Zener diode ZD and the forward/directional voltage VD of the diode D3 (first
It is indicated by diagonal lines in (a) of Figure 0 (b). ), the charge in the capacitor C1 is discharged through the Zener diode ZD and the diode D.

When the charge in capacitor C7 is discharged in this way,
As shown in FIG. 10(b)(d), the reference voltage Vref
As a result, the on period of the transistor Q1 becomes shorter, as shown in (c) of FIG. Therefore, transistor Q
, can be protected.

However, since this discharge lamp lighting device detects an increase in the resonant current in the negative region and lowers the reference voltage V ref, resonance occurs in the next half cycle after the increase in the collector current of the transistor Q1. An increase in current will be detected. Therefore, in response to an instantaneous sudden increase in current (for example, an overcurrent when the discharge lamp 1a repeats discharge and non-discharge, or sudden saturation of the choke coils L, L2), the fault occurs in the half The protection operation will not be performed during the cycle, which may cause a delay in the protection operation and damage the transistor Q+.

Further, in such a protection circuit, in order to speed up the protection operation when an overcurrent flows, it is necessary to quickly discharge the charge in the capacitor C5. However, the speed of discharge of this capacitor C1 depends on the internal impedance of Zener diode ZD and diode D3, and the current transformer C.
Since the output voltage of T cannot be changed much from oT, the only option is to reduce the capacitance of capacitor C5. However, when the capacitance of capacitor C is reduced in this way, the charging speed of capacitor C5 becomes too fast.
In other words, the on-period of the transistor Q1 increases too quickly, causing a phenomenon in which the resonance of the inverter is disturbed. In this case, overcurrent, overvoltage, or abnormal vibration state may occur. Note that this condition is particularly likely to occur during the starting process of the discharge lamp 1a. Therefore, when the capacitance of the capacitor C3 is reduced, it is necessary to increase the values of the resistors R2, R, so that the charging speed does not increase.

However, if you do this, noise will easily be superimposed on the reference voltage V ref determined by the resistors Rz and Rs.
The stability of the reference voltage V ref deteriorates. Therefore, in consideration of the above points, there is a limit to reducing the capacitance of the capacitor C3, and it is difficult to reduce the capacitance to, for example, 1/100 or 1/1000.

Furthermore, with the configuration of the discharge lamp lighting device described above, there is a problem in that the current transformer CT can only detect the current flowing through the choke coil L2, and cannot detect the current flowing from the choke coil L1 to the transistor Q, for example. There was also.

Therefore, in order to solve the above-mentioned problem, a discharge lamp lighting device shown in FIG. 11 has been provided. This discharge lamp lighting device has a resistor R1 connected in series with the transistor Q, and is protected by a comparator CPI that compares the voltage across this resistor R1 with a reference voltage r, and a latch circuit 2 that latches the output of the comparator CPI. This circuit has a circuit configuration, and the other configurations are almost the same as the discharge lamp lighting device of the circuit shown in FIG.

In the protection circuit section of this discharge lamp lighting device, the transistor Q
, the capacitor C4 is charged via the diode D1 with the voltage generated across the resistor R8 due to the current flowing through the capacitor C4, and the charging voltage of the capacitor C4 is compared with the reference voltage Vr by the comparator CP1. The output when the voltage rises above this level is latched by the latch circuit 2, and the output of the latch circuit 2 controls the control circuit 1 to stop the oscillation operation of the inverter. Note that capacitor C1 is provided to prevent malfunction, and a Zener diode Z is connected in parallel to capacitor C2.
D2 limits the voltage of capacitor C2, and resistor R5 is the discharge resistance of capacitor C4.

[Problem to be solved by the invention 1 However, in the protection circuit of the discharge lamp lighting device described above,
Since the latch circuit 2 is used, a capacitor C1 is required to prevent malfunction, and there is a problem that the response is delayed by the charging time of the capacitor C1. In addition, when a transient overcurrent flows and the output of comparator CP occurs,
Even if the cause of the abnormality that caused the overcurrent is eliminated, the operation of the inverter remains stopped, and there is a problem in that operations such as turning off the power are required to reset the protection circuit.

The present invention has been made in view of the above-mentioned points, and its purpose is to provide an inverter device that can eliminate response delays as much as possible, and that can reliably protect circuit components. There is a particular thing.

[Means for Solving the Problems 1] In order to achieve the above object, the present invention sets a reference voltage by the charging voltage of a capacitor, detects the current at a point where the current flowing through the component parts commonly flows, and detects the current flowing through the component parts. A protection circuit is provided to lower the reference voltage by short-circuiting both ends of the capacitor to lower the reference voltage when the current exceeds a predetermined value.

Note that in order to further improve the discharge speed of the capacitor, it is effective to charge the capacitor through an amplifier circuit.

[Function 1] As described above, in the present invention, the protection circuit detects the current at a point where the current flowing through each component commonly flows.
It is possible to reliably detect when overcurrent flows due to various abnormalities, and when this current exceeds a predetermined value,
By short-circuiting both ends of a capacitor whose reference voltage is set by the charging voltage and lowering the reference voltage so as to reduce the above current, the discharge speed of the capacitor becomes faster and the response to abnormalities becomes faster. This is what I did.

Note that if the capacitor is charged via an amplifier circuit, the reference voltage of the control circuit can be kept stable even if the capacitor has a small capacity, and the speed of discharging can be further increased.

[LOL Example 11 An embodiment of the present invention is shown in FIGS. 1 to 3.

The basic circuit configuration of this embodiment is the same as the circuit in Figure 9, and the protection circuit has vJl, transistor Q as in the circuit in Figure 1,
An abnormality in the resonant current is detected from the current flowing through the comparator CP.
A switch means SW2 is provided to short-circuit both ends of a capacitor C3 provided for stabilizing the reference voltage Vrer of the control circuit 1 in response to the output of the abnormality detection circuit 3 constituted by +.

A concrete circuit of the circuit shown in FIG. 1 is shown in FIG. In this FIG. 3, a transistor Q is used as the switch means SW2,
is used. The control circuit 1 includes a capacitor C6 charged by the control power supply Vcc via a resistor R6, and the voltage across the capacitor C5 is set to a reference voltage V ref
The on-period of the transistor Q1 is determined by comparing it with the comparator CP2, and the charging and discharging of the capacitor C3 is controlled by the conducting state of the transistors Q, Q5. That is, in this control circuit 1, charging of the capacitor C5 is started from the time when the output voltage vcT of the current lance CT becomes a positive voltage, and when the voltage across the capacitor C3 exceeds the reference voltage Vrer, When the output becomes low level, it operates to turn off the transistor Q1.

Now, if some abnormality occurs and an overcurrent flows through the transistor Q as shown in (b) of Figure 2 (b), the output of the comparator CPI becomes high level, and as a result, the transistor Q, is turned on as shown in parentheses in the same figure (b), shorting the voltage across the capacitor C3, the reference voltage V ref is lowered as shown in (d) in the same figure (b), and this Therefore, as shown in (e) of Figure 12 (b), the on period of transistor Q1 is shortened, and overcurrent is prevented from flowing into the circuit components.The normal operation is shown in Figure 12 (a). According to this embodiment, since both ends of the capacitor C1 are short-circuited by the transistor Q, the discharge speed of the capacitor C1 can be increased, and the capacitor C3, which has a relatively large capacity, can be used. However, the discharge speed can be increased even if the capacitor C5 is small, and the response delay can be reduced.Moreover, since there is no need to increase the resistors R, , R, as in the case where the at of the capacitor C5 is small, the inverter Problems such as disturbances in the oscillation operation do not occur.Furthermore, since overcurrent is detected from the current flowing through the transistor Q when an abnormality occurs, all overcurrents can be detected.Further, Since it does not use a latch circuit that stops the operation of the control circuit 1 like the circuit in Figure 11, there is no need to reset the protection circuit when a temporary overcurrent occurs. When the transistor Q3 is turned off, the capacitor C7 is slowly charged and the normal operation is automatically restored.Also, as the latch circuit is not used as mentioned above, this prevents the protection circuit from malfunctioning. In addition, there is no need for a circuit including a capacitor or the like that causes a response delay in the input of the comparator CPI, and combined with the fact that the response delay can be eliminated by the capacitor C3 mentioned above, good responsiveness can be obtained.Therefore, the protection function is degraded due to the response delay. No problem.

[Example 2] Other embodiments of the present invention are shown in FIGS. 4 to 6.

In this embodiment, the discharging speed of the capacitor C1 is further improved, and as shown in FIG. Control circuit 1 uses a so-called Miller integration circuit connected to capacitor C3.
The capacitor C5 is made to appear larger when viewed from above.

To explain this, as shown in FIG. 5, if the current in each part of the transistor Q is determined and the overall equivalent capacitance when the switch SW2 is turned from on to off is C, then Q=C-Vref=iH・at=ic-at (hf
e large)=hfe-1B-711t=hfe-C3・(Vref-VBE)V ref>
> When V ap, C#hfe-C.

In other words, with the above configuration, if a transistor with a large hfe is used as the transistor Q6, charging will occur at a sufficiently slow charging speed even if the capacitor C1 is made small, and the discharging speed when the switch means SW2 is turned off will be It can be done quickly.

Incidentally, the above-mentioned Miller integration circuit may use Turlington-configured transistors Q and I in place of the transistor Q6, as shown in FIG. 7(b).

Also, as shown in Figure 17 <6), a transistor. NPN instead of 6) transistor. 7 can also be used. However, in this case, a transistor is used to discharge the charge of the capacitor C5. , requires.

By the way, in the above explanation, a case was explained in which a one-way inverter was used, but the present invention can also be applied to inverters with other configurations, such as a half-bridge lit type inverter. FIG. 8 shows a case where the present invention is applied to an inverter having a half-bridge configuration. In this discharge lamp and alpha lamp device, a diode D is connected to both ends of a DC power supply E.

D, are transistors connected in antiparallel. 9. Q.

In addition to connecting the transistors in series. , are connected to both ends of the discharge lamp la1 choke coil and the primary winding of the drive transformer CT through a commutation capacitor C0, and the voltage induced in the secondary winding of the drive transformer CT causes the transistor to Q s t Q + .

are switched alternately to convert the DC power supplied from the DC power source E into high frequency power and supply it to the discharge lamp ea. Then, in response to the voltage induced in the secondary winding of the drive transformer CT, the control circuit 1 inverts the transistor Q in the same way as the above-mentioned single-stone inverter. This controls the on-period.

The operation of the main parts according to the present invention has the same configuration as the circuit of FIG. 6.

[Effects of the Invention] As described above, in the present invention, since the protection circuit detects the current flowing through the various components in common, it is possible to reliably detect overcurrent flowing due to various abnormalities. Also, when this current exceeds a predetermined value, by short-circuiting both ends of the capacitor whose reference voltage is set by the charging voltage, the reference voltage is lowered to reduce the current.
By increasing the discharge speed of the capacitor, the response to abnormalities can be made faster.

Note that if the capacitor is charged via an amplifier circuit, the reference voltage of the control circuit can be kept stable even if the capacitor has a small capacity, and the speed of discharging can be increased.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram of the same operation as above, FIG. 3 is a specific circuit diagram of the same as above, FIG. 4 is a circuit diagram of the main part of another embodiment, Fig. 5 is an explanatory diagram of the main parts of the above, Fig. 6 is a specific circuit diagram of the same, Figs. 7 (a) and (b) are applied circuit diagrams of the main parts of the above, and Fig. 8 is still another example. FIG. 9 is a circuit diagram of a conventional example, FIG. 10 is an explanatory diagram of the same operation as above, and FIG. #S11 is a circuit diagram of another conventional example. Q is a transistor, ia is a discharge lamp, E is a DC power supply, C
P is a comparator, C3 is a capacitor, and 1 is a control circuit.

Claims (2)

[Claims] (1) An inverter device that converts DC power supplied from a DC power source into high-frequency power by switching a switching element and supplies it to the load, and a control circuit that can control the on-period of the switching element according to the setting of the reference voltage. , the above reference voltage is set with the charging voltage of the capacitor, the current flowing through the component parts is detected at a point where the current flows in common, and when this current exceeds a predetermined value, both ends of the capacitor are short-circuited to reduce the above current. An inverter device equipped with a protection circuit that lowers the reference voltage so as to lower the reference voltage. (2) The inverter device according to claim 1, wherein the capacitor is charged via an amplifier circuit.