JPH08322265A - Inverter - Google Patents

Abstract

PURPOSE: To obtain an inexpensive highly reliable inverter by relieving the excessive increase of a load current by jointly using the function of an auxiliary switching element which detect the excessive rise of a DC power source voltage and the characteristics of a saturable current feedback transformer. CONSTITUTION: An inverter is provided with an inductor 2 for vibration across which a voltage is intermittently applied from a DC power source 1 through a switching transistor 4 and to which AC loads 6-8 are connected in parallel, a capacitor 3 for vibration connected in parallel with the inductor 2, a saturable current feedback transformer 5, to the primary winding of which the loads 6-8 are connected in series, and a base circuit containing the base-emitter junction of the transistor 4, a secondary winding of the transformer 5, and a capacitor 11 for base. An auxiliary switching element which operates when the voltage supplied from the power source 1 excessively rises is connected to the capacitor 11 so that the switching element can limit the forward voltage of the capacitor 11 when the switching element operates. The limitation of the forward voltage of the capacitor 11 lowers the voltage of the capacitor 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device provided with means for limiting over-output of a discharge lamp due to a rise in DC power supply voltage.

[0002]

2. Description of the Related Art A conventional device shown in FIG. 5 will be described. This device includes a DC power supply 1 and a switching transistor 4, and includes a vibration inductor 2 to which a voltage of the DC power supply 1 is intermittently applied via the switching transistor 4, and includes a switching transistor 4 and a vibration inductor 2. The vibration capacitor 3 is connected in parallel with one of them, and the AC loads 6 to 8 are connected in parallel with the vibration inductor. The loads 6 to 8 include a discharge lamp 8, a ballast inductor 6, and a preheating capacitor 7. AC load 6-8
Is provided with a saturable current feedback transformer 5 whose primary winding is connected in series with the base of the switching transistor 4.
The base circuit includes the emitter junction, the secondary winding of the saturable current feedback transformer 5, and the base capacitor 11.
While the switching transistor 4 is turned off in parallel with the base capacitor 11, the base capacitor 11
It is provided with a series circuit of a diode 12 and a resistor 13 that determines the voltage to be charged to the. A series circuit of a diode 9 and a resistor 10 for discharging the electric charge of the base capacitor 11 while the switching transistor 4 is off is provided between the base and the emitter of the switching transistor 4.

[0003]

[SUMMARY OF THE INVENTION Conventional FIG. 5 device, as shown in broken line in FIG. 2, (current of the discharge lamp 8) DC power supply 1 voltage V ₁ and the lamp current increases I _L together in conjunction Then
When the DC power supply 1 voltage V ₁ rises from V _a to V _c , the lamp current I _L increases from I _a to I _c . At the overvoltage V _c , the lamp current also becomes the overcurrent I _c . Thus, each component flowing a lamp current I _c becomes that of large high tolerance. An object of the present invention is to reduce and alleviate the burden of the above overcurrent.

[0004]

SUMMARY OF THE INVENTION In the present invention, an auxiliary switching element that operates when the DC power supply voltage rises excessively is provided. This auxiliary switching element is connected so as to limit the forward voltage (voltage having the same polarity as the base-emitter junction) of the base capacitor during its operation.

[0005]

Operation: The DC power supply voltage V _{1 in} FIG. 2 rises, and V _a to V
_When it becomes _b , the auxiliary switching element operates. Along with this, the forward voltage of the base capacitor is limited, the ON period of the switching transistor is shortened, and the increase of the lamp current _IL is also limited.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. The part numbers in FIG. 5 are used as they are for this description, and a part of the overlapping description is omitted. The apparatus shown in FIG. 1 includes a DC power supply 1 and a switching transistor 4
And a vibration inductor 2 to which a DC power supply 1 voltage is intermittently applied via a switching transistor 4, and is connected in parallel with either one of the switching transistor 4 and the vibration inductor 2 (2 in this embodiment). And a vibration capacitor 3 connected to. AC loads 6 to 8 are connected in parallel with the vibration inductor 2. AC load 6 of this embodiment
8 is a discharge lamp lighting circuit similar to FIG. A saturable current feedback transformer 5 having a primary winding connected in series with AC loads 6 to 8 is provided. A base circuit including the base-emitter junction of the switching transistor 4, the secondary winding of the saturable current feedback transformer 5, and the base capacitor 11 is provided. An auxiliary switching element 14 is provided which operates when the DC power supply 1 voltage rises excessively. The auxiliary switching element 14 of this embodiment is a Zener diode. When the auxiliary switching element 14 is operated, the base capacitor 11
Are connected so as to limit the forward voltage (voltage having the same polarity as the base-emitter junction). This limitation is intended to lower the indicated voltage of the base capacitor 11. In FIG. 1, 9 is a diode, 10 is a resistor, 12 is a diode, 13 is a resistor, and 21 is a resistor. These are the same as those in FIG. The operation of the apparatus shown in FIG. 1 will be described. A base current flows from the DC power source 1 to the switching transistor 4 via the resistor 21. The switching transistor 4 is turned on. A DC power supply 1 voltage is applied to a parallel circuit of the vibration inductor 2 and the vibration capacitor 3.
At the same time, a preheating current flows through one filament / preheating capacitor 7 of the discharge lamp 8, the other filament, the ballast inductor 6, the primary winding of the saturable current feedback transformer 5, and the switching transistor 4. The switching transistor 4 is forward biased by the current generated in the secondary winding of the saturable current feedback transformer 5. When the saturable current feedback transformer 5 is saturated, the electric charge charged in the base capacitor 11 (the resulting charging voltage has a polarity opposite to that shown in the drawing) discharges the switching transistor 4 in the direction of reverse biasing. The switching transistor 4 turns off rapidly. When the switching transistor 4 is turned off, a vibration phenomenon occurs in the series resonance circuit of the vibration inductor 6 and the vibration capacitor 7, and a high voltage is applied across the discharge lamp 8 to start it. After that, when the current flowing through the saturable current feedback transformer 5 reverses in the forward direction (leftward in the drawing), the switching transistor 4 is turned on again. After that, the above operation is repeated. The operation of the apparatus of FIG. 1 will be further described with reference to the characteristics of FIG. As indicated by the solid curve in FIG. 2, the DC power supply voltage V ₁
Is increasing from V _a to V _b , the auxiliary switching element 14 maintains the off state, and the same process as in FIG. 5 is followed,
The lamp current I _L increases. The voltage of the base capacitor 11 increases substantially in proportion to the DC power supply 1 voltage V ₁ .
Auxiliary switching the device 14 to be set to turn on the DC power supply 1 voltage V _b, the voltage V _b voltage of polarity shown in the base capacitor 11 in以高auxiliary switching element 1
The operating voltage (Zener voltage) of 4 is exceeded. Therefore, the auxiliary switching element 14 is turned on. This limits the forward voltage of the base capacitor 11 during the off period of the switching transistor 4. This limit is
It acts to shorten the ON period of the switching transistor 4 thereafter. This increases the voltage generated in the secondary winding of the saturable current feedback transformer 5 (voltage having a right polarity in the drawing) during the ON period, and acts to accelerate the magnetic saturation timing of the saturable current feedback transformer 5. This is because. When the ON period is shortened, the dimming state is set, and the lamp current _IL is suppressed. Therefore, the point of V _c · I _{L in} the apparatus of FIG. 5 is V _c · I _c ′ in the apparatus of FIG.
Will be revised downward. Another embodiment of FIG. 3 is that an auxiliary switching element (zener diode) 15 is provided across the resistor 13.
Is connected. Even with this, the forward voltage of the base capacitor 11 is limited. In another embodiment of FIG. 4, a thyristor 18 is used instead of the Zener diode 15 of FIG. In FIG. 4, the level of the reverse current of the base capacitor 11 is detected by the resistor 20, and the trigger element 19 is operated at an appropriate timing.
By turning on the thyristor 18, the forward voltage of the base capacitor 11 is limited. 16-1 in FIG.
7 is a resistor.

[0007]

According to the present invention, an auxiliary switching element for detecting an excessive rise in the DC power supply voltage is provided, and its function and the characteristics of the saturable current feedback transformer are used together to alleviate the excessive rise in the load current. is there. According to this, an inexpensive and highly reliable device can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a device of the present invention.

FIG. 2 shows its characteristics.

FIG. 3 is a circuit diagram showing another embodiment.

FIG. 4 is a circuit diagram showing another embodiment.

FIG. 5 is a circuit diagram of a conventional device.

[Explanation of symbols]

1: DC power supply, 2: vibration inductor, 3: vibration capacitor, 4: switching transistor, 5: saturable current feedback transformer, 6 to 8: AC load, 11 base capacitor, 4 ・ 15 ・ 18: Auxiliary switching element

Claims (1)

[Claims] 1. A direct current power supply, a switching transistor, and a vibration inductor to which the direct current power supply voltage is intermittently applied via the switching transistor. One of the switching transistor and the vibration inductor. A vibration capacitor connected in parallel with one side, an AC load connected in parallel with the vibration inductor, a saturable current feedback transformer having a primary winding connected in series with the AC load, A base circuit including a base-emitter junction of a switching transistor, a secondary winding of the saturable current feedback transformer, and a base capacitor is provided, and an auxiliary switching element that operates when the DC power supply voltage rises excessively is provided. When the switching element is in operation, the forward voltage (preceding Inverter device is characterized in that connected to limit the voltage) of the base-emitter junction of the same polarity.