JPH03117373A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To simplify the circuitry by detecting overcurrent by means of a current detecting resistor connected between a partial smoothing circuit having high power factor for rectifying and smoothing AC voltage and a bypass capacitor arranged on the input side of an inverter. CONSTITUTION:AC voltage is rectified 1 into a DC voltage which is then smoothed through a partial smoothing circuit 2 having high power factor and ted to an inverter circuit 10 which produces an AC voltage for lighting a discharge lamp 18. The inverter circuit 10 comprises a transformer 15, a switching transistor Tr 11 and a protective diode 13 connected in reverse, and a bypass capacitor 9 is connected on the input side. A load current detecting resistor 8 is connected between the smoothing circuit 2 and the bypass capacitor 9. When abnormal overcurrent flows and the voltage across a resistor 8 exceeds a predetermined level, a Zener diode 23 is turned ON by the voltage of a capacitor 22 and a transistor Tr 25 is also turned ON while the transistor Tr 11 stops oscillation thus stopping the operation of the inverter circuit 10. By such arrangement, overload can be detected positively through a simple circuit having no insulating transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an inverter circuit equipped with a one-wheel or half-bridge type inverter circuit provided with a safety circuit that operates to reduce or stop the output in the event of a load abnormality. This invention relates to an electric light lighting device.

Conventional technology Conventionally, in a discharge lamp lighting device equipped with an inverter circuit equipped with a safety circuit to protect itself in the event of a load abnormality,
The main way to detect load abnormalities is to detect the lamp voltage Vt. In particular, in isolated type inverters, the signal of the lamp voltage VL detected on the secondary side is sent to the primary side while being isolated. It is something that exists.

Problems to be Solved by the Invention In an insulated type inverter, there is a problem in that the signal of the lamp voltage ■L detected on the secondary side must be sent to the primary side while being insulated, making the circuit complicated.

Furthermore, in a single-stone type or half-bridge type inverter circuit, there is a problem in that the DC input current has many AC components, making it difficult to detect the input current using a simple method.

Means for Solving the Problems: An inverter circuit equipped with a safety circuit that operates to reduce or stop output in the event of an abnormality, and an inverter circuit provided on the input side of the inverter circuit to reduce reactive current generated due to oscillation of the inverter circuit. In a discharge lamp lighting device comprising a bypass capacitor and a high power factor partial smoothing circuit that supplies DC voltage to the inverter, current detection means for detecting an input current is disposed between the smoothing circuit and the bypass capacitor. The safety circuit is operated according to the output level of the current detection means.

When the operating load is abnormal, the human power increases, but by disposing the current detection means between the smoothing circuit and the bus capacitor, the input current can be easily detected using only DC current. Since the detection position is on the primary side, no insulation is required, and the circuit can be easily constructed.

Example An embodiment of the present invention will be described based on FIG.

First, a rectifier circuit 1 is provided, and a partial smoothing circuit 2 as a high power factor smoothing circuit is connected to the rectifier circuit 1.

This partial smoothing circuit 2 includes two smoothing capacitors 4 and 5 with a forward-directed diode 3 interposed between them, a diode 6 connected in antiparallel to the diode 3 and the capacitor 4, and the It consists of a diode 3 and a diode 7 connected antiparallel to the capacitor 5.

Next, a bypass capacitor 9 is connected to the partial smoothing circuit 2 with a detection resistor 8 interposed therebetween as a current detection means, and an inverter circuit 10 is connected downstream of the bypass capacitor 9.

The second inverter circuit 1o is of a single-stone type and includes an oscillation transistor 11 and an inverter transformer 12.

A protection diode 13 is connected to the oscillation transistor 11 with reverse polarity, and a drive signal terminal 14 connected to a drive circuit (not shown) is connected to the base. , and a capacitor 16 are connected. Furthermore, the inverter
A lamp 18 as a load and a resonant capacitor 19 are connected to the secondary winding 17 of the transformer 12.

Therefore, the inverter circuit 10 includes a safety circuit 2o.
is provided. The input side of this safety circuit 2o is connected to both poles of the detection resistor 8. That is, a resistor 21 and a capacitor 22 forming an integrating circuit are connected in series to the detection resistor 8, and a Zener diode 23 and a resistor 24 are connected to the middle point of the connection between the resistor 21 and the capacitor 22. The base of control transistor 25 is connected. The emitter of this control transistor 25 is connected to the partial smoothing circuit 2 side, and the collector is connected to the base of the oscillation transistor 11.

In such a configuration, the rectifier circuit 19 partial smoothing circuit 2
The inverter circuit 10 is operated by the direct current supplied from the inverter circuit 10 to drive the lamp 18, and the reactive current generated at this time is bypassed by the bypass capacitor 9. Since all of the input current passes through the detection resistor 8, a voltage corresponding to the input terminal value is generated across the detection resistor 8. Although the voltage across the detection resistor 8 changes due to load fluctuations, charges are stored in the capacitor 22 based on the voltage, and a voltage proportional to the voltage across the detection resistor 8 is generated in the capacitor 22. When the voltage of this capacitor 22 exceeds the Zener voltage, the Zener diode 23 becomes conductive and turns on the control transistor 25 via the resistor 24.
do. As a result, the base voltage of the oscillation transistor 11 decreases, and the oscillation operation of the inverter circuit 10 is stopped.

Therefore, if the number of input terminals increases due to a load abnormality or the like, the safety circuit 20 operates to stop the oscillation operation of the inverter circuit 10. Of course, depending on the circuit configuration, the output may be reduced or the lamp 18 may be blinked without stopping the oscillation of the inverter circuit 1o when the load is abnormal.

Since the operation of the safety circuit 20 is performed based on the increase in the voltage across the detection resistor 8, its position is on the primary side, and there is no need to take insulation treatment or the like into consideration. Therefore, the circuit is simple. Further, at this position, a detection output can be obtained only by direct current input current, so a reliable detection operation is possible.

Next, as shown in FIG. 2, connecting an inductance element 26 having an L component of a predetermined value in series with the detection resistor 8 is effective in reducing the alternating current at the detection position. Insertion of such an inductance element 26
Even if it is connected in parallel with the detection resistor 8 as shown in the figure, it is equally effective in reducing the alternating current component.

Further, in the case shown in FIG. 4, an inductance element 26 is connected in series with a diode 28 and a smoothing capacitor 29 constituting a smoothing circuit 27, and a midpoint between the inductance element 26 and the diode 28 is connected to the oscillation transistor 11. The collector is connected to the collector by a diode 30. In this case as well, the alternating current component at the detection resistor 8 can be reduced as described above.

Effects of the Invention As described above, the present invention includes an inverter circuit equipped with a safety circuit that operates to reduce or stop output in the event of an abnormality;
In a discharge lamp lighting device comprising a bypass capacitor provided on the input side of the inverter circuit and bypassing a reactive current generated due to oscillation of the inverter circuit, and a high power factor partial smoothing circuit supplying a DC voltage to the inverter. , a current detection means for detecting the input current is disposed between the smoothing circuit and the bypass capacitor, and the safety circuit is operated according to the output level of the current detection means, so that when there is an abnormality in the load, Although the input power increases, since the current detection means is placed between the smoothing circuit and the bypass capacitor, the input current can be easily detected using only DC current, and the detection position is Since it is on the primary side, there is no need for insulation, and the circuit can be easily constructed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a variation thereof, in which an inductance element is connected in series to a detection resistor, and Fig. 3 is a circuit diagram showing an inductance element connected in parallel to a detection resistor. FIG. 4 is a circuit diagram showing a modification in which an inductance element is connected to a smoothing circuit. 2... Smoothing circuit, 8... Current detection means, 9... Bypass capacitor, 10... Inverter circuit, 18...
・・Load, 20・Safety circuit, 27・Smoothing circuit ratio

Claims (1)

[Claims] An inverter circuit equipped with a safety circuit that operates to reduce or stop output in the event of an abnormality, a bypass capacitor provided on the input side of the inverter circuit to bypass reactive current generated due to oscillation of the inverter circuit, and the inverter. In a discharge lamp lighting device comprising a high power factor partial smoothing circuit that supplies a DC voltage to a discharge lamp, a current detection means for detecting an input current is disposed between the smoothing circuit and the bypass capacitor, and the current detection means A discharge lamp lighting device characterized in that the safety circuit is operated according to the output level of the discharge lamp.