JPH04137397A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To control a power source frequency at a low cost and within a wide range so as to realize light dimming by adjusting a switching period of a switching element interposed between a base and an emitter of a bipolar transistor. CONSTITUTION:A pulse wave current of a constant period from an oscillation circuit 22 flows in a primary winding of a transformer 37 and a proportional current is generated in secondary windings 12 and 13. When a current flows in a secondary winding 35, this current flows into a gate of an FET 29 via a resistor 32 for making continuity so that a base and an emitter of a transistor Tr8 have equal electric potential to each other to make the Tr8 discontinuous. When the secondary winding is not electrified, the FET 29 becomes discontinuous. Consequently, a current generated in the secondary winding 12 of a current transformer 10 flows into the base of the Tr8 via a resistor 31 to make the Tr8 continuous. On the other hand, an FET 30 as well as a Tr9 operates similarly, however, a winding direction of the secondary winding 13 is reverse to that of the secondary winding 12 so that polarity of a generated current becomes reverse. Accordingly, the bipolar transistors Tr8, Tr9 are on/off operated alternately and a switching period thereof depends on a period of an output current pulse of the oscillation circuit 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a discharge lamp lighting device capable of controlling the dimming of a discharge lamp by adjusting the frequency of a power supply.

(Prior art) Generally, in a discharge lamp lighting device using an inverter circuit,
Brightness can be adjusted by adjusting the frequency of the power supply supplied to the discharge lamp. FIG. 4 shows a conventional example of such a discharge lamp lighting device. In the same figure, 100
~200 [V].

A commercial power source 1 having a frequency of 50 to 60 [Hz] is full-wave rectified by a rectifier circuit 2, smoothed by a smoothing circuit 3, and then supplied to an inverter circuit 4.

The inverter circuit 4 has a current transformer 1o, and when current flows through the primary winding 11 of the transformer 1o,
A current proportional to this flows through the secondary winding 12. and 13
occurs in Since this current is supplied to the gates of transistors 8.9, each transistor 8.9 self-oscillates. At this time, since the secondary winding 12 is wound in the opposite direction to the secondary winding 13, each transistor 89
The currents supplied to the transistors are of opposite polarity, thereby driving each transistor 8, 9 alternately.

As a result, an alternating current voltage is generated at both ends of the discharge lamp 6, thereby lighting it up.

In addition, the core of the current transformer 10 includes a control circuit 14.
．． Or, 17 windings 15 are wound, and a variable resistor 16
or by adjusting the variable power supply 18 to control the current flowing through the control circuit 14.17, the saturation current of the secondary winding 12.13 changes, so the switching period of each transistor 8.9 can be changed. can. Therefore, the frequency of the voltage applied to both ends of the discharge lamp 6 can be controlled by the variable resistor 1 of the control circuit 14.
6° or can be adjusted by the variable power supply 18 of the control circuit 17, and conventionally this variable resistor 16. Alternatively, the brightness of the discharge lamp was controlled by adjusting the variable power supply 18.

(Problem II to be solved by the invention) However, in such a conventional discharge lamp lighting device,
The frequency is controlled by adjusting the saturation current of the current transformer 10, and there is a limit to the adjustment range of the saturation current.
It is not possible to change the frequency over a wide range. Therefore, there is a problem that the range of dimming is limited and characteristics with a desired control width cannot be obtained.

Therefore, for example, as shown in FIG. 5, it is easy to consider installing FETs 20 and 21 in place of the bipolar transistors 8 and 9 and controlling them with an oscillation circuit 22 to increase the control range. However, this method has a disadvantage in terms of cost since the FETs 20 and 21 are more expensive than the bipolar transistors 8 and 9.

The present invention was made to solve these conventional problems, and its purpose is to provide a discharge lamp lighting device that can vary the power frequency over a wide range and can be constructed at low cost. It's about doing.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention alternately turns on and off a DC voltage obtained by rectifying and smoothing a commercial power supply using a current given from a current transformer. In a discharge lamp lighting device that converts an alternating voltage of a desired frequency into an alternating current voltage of a desired frequency using an inverter circuit having a pair of bipolar transistors in an off-operation state, and supplies this to a discharge lamp to light the discharge lamp, the voltage between the base, the emitter, and the ivy of the bipolar transistor is provided. It is characterized by having a switching element provided therein, and a driving means for applying a control current to operate the switching element.

Further, the switching element provided in the high-side bipolar transistor of the pair of bipolar transistors is driven by a level shift circuit.

(Function) If configured as described above, when a switching element such as an FET interposed between the base and emitter of the bipolar transistor is turned on, the base and emitter of the bipolar transistor will be at the same potential, so that the current transformer will not No current flows into the base of the bipolar transistor. Therefore, the bipolar transistor becomes non-conductive. Also, when this switching element is turned off,
Since the current from the current transformer flows into the base of the Ibora transistor, the Ibora transistor becomes conductive.

By adjusting the switching period of the switching element, the operation of the bipolar transistor is controlled so that the output frequency of the inverter circuit becomes a desired frequency. Therefore, the frequency control width becomes significantly wider.

Further, if the high-side switching element is operated by a level shift circuit, an isolation transformer is not required, so that cost reduction and space saving can be achieved.

(Embodiment) FIG. 1 is a configuration diagram showing an embodiment of a discharge lamp lighting device to which the present invention is applied.

As shown in the figure, this discharge lamp lighting device has a power of 100 to 200
[V], 50 to 60 [Hz] A rectifier circuit 2 performs full-wave rectification of a commercial power supply 1, a smoothing circuit 3 smoothes the rectified pulsating voltage, and converts the smoothed DC voltage into an AC of a desired frequency. It has a half-bridge type inverter circuit 4 for converting into voltage, a choke coil 5 for obtaining a resonant current, and a capacitor 7, and lights a discharge lamp 6.

The inverter circuit 4 includes a pair of bipolar transistors 8
, 9 and the series connection of a resistor 23 and a capacitor 24 are connected in parallel, and a diode 25
connected via. The connection point of the transistor 8.9 is also connected to the primary winding 11 of the current transformer 10, and a current proportional to the current flowing through the secondary winding flows through the secondary winding 12.13. It looks like this.

The secondary winding 12 has one end connected to the emitter of the transistor 8 and the other end connected to the base of the transistor 8 via a resistor 31. Further, an FET 29 is provided between the base and emitter of the transistor 8, and the gate of the FET 29 is connected to the emitter of the transistor 8 via a resistor 32° and a secondary winding 35 of a transformer 37.

On the other hand, the other secondary winding 13 of the current transformer 10
is wound in the opposite direction to the secondary winding 12 described above, one end of which is connected to the emitter of the transistor 9,
The other end is connected to the base of transistor 9 via resistor 33. Furthermore, an FET 30 is disposed between the base and emitter of the transistor 9, and the gate of the FET 30 is connected to the emitter of the transistor 9 via a resistor 34 and a secondary winding 36 of a transformer 37. Here, the secondary winding 36 of the transformer 37 is wound in the opposite direction to the above-described secondary winding 35, and its -secondary winding 38 is connected to the oscillation circuit 22. Further, the base of the transistor 9 is connected to a resistor 23 via a bidirectional diode 26.
It is also connected to the connection point of the capacitor 24 and the capacitor 24.

Furthermore, a diode 27. is connected between the collector and emitter of the transistors 8 and 9 to prevent damage caused by reverse current.
28 are provided.

In such a configuration, when a pulse wave current with a constant period is output from the oscillation circuit 22, this current flows through the primary winding of the transformer 37, so that a current proportional to this current flows through the secondary winding 12. and 13. Now, when current flows through the secondary winding 32, this current passes through the resistor 32 and passes through the FET 29.
flows into the gate. As a result, the FET 29 becomes conductive, so that the base and emitter of the transistor 8 become at the same potential, and the transistor 8 becomes non-conductive.

In addition, when no current flows through the secondary winding 35, the FE
Since no current flows into the gate of T29, FET29 becomes non-conductive. Therefore, the current generated in the secondary winding 12 of the current transformer 10 flows into the base of the transistor 8 via the resistor 31, and the transistor 8 becomes conductive.

That is, when the FET 29 is on, the transistor 8 is turned off, and conversely, when the FET 29 is off, the transistor 8 is turned on.

On the other hand, FET30. Transistor 9 operates similarly, but since the winding direction of secondary winding 13 is opposite to that of secondary winding 12, the polarity of the generated current is opposite. That is,
When current flows into the gate of FET29, FET30
No current flows into the gate of FET2, on the contrary,
When no current flows into the gate of FET 9, current flows into the gate of FET 30.

Therefore, bipolar transistors 8 and 9 are alternately turned on and off.
The oscillation circuit 22 is turned off, and this switching cycle is
depends on the period of the output current pulse. Therefore, oscillation circuit 2
By adjusting the output frequency of 2, the frequency of the AC voltage output from the inverter circuit 4 can be controlled.

In this manner, in this embodiment, the base currents of the bipolar transistors 8 and 9 are controlled by the on/off operations of the FETs 29 and 30, and the transistors 8 and 9 are turned on and off. Therefore, the frequency of the voltage supplied to the discharge lamp 6 can be controlled over a wide range.

In addition, although this embodiment uses FET29.30, as shown in FIG.
, 21 is not used, so the cost is low.

FIG. 2 is a block diagram showing another embodiment of the present invention. In this example, the transformer 37 shown in FIG. 1 is not used, and the oscillation circuit 22 directly operates the FETs 29 and 30. At this time, since the emitter of transistor 8 and the emitter of transistor 9 have different potentials, a level shift circuit 41 is connected to the gate of FET 29.

FIG. 3 shows a level shift circuit 41. FIG. 3 is a diagram showing the oscillation circuit 22 in detail. However, in this figure, a discharge lamp 6 is provided as a load on two sides, and an isolation transformer 42 is used as an output transformer.

The level shift circuit 41 includes transistors 50.51, diodes 52. It consists of resistors 53, 54, etc.
Operate FET29.

The oscillation circuit 22 generates a pulse signal that switches at a predetermined period.
Output end 55. and 56, and the output pulses at both output terminals 55 and 56 have opposite polarities.

Now, when the output pulse at the output terminal 55 turns "on," this signal flows into the transistor 51 via the resistor 54 of the level shift circuit 41, making the transistor 51 conductive. As a result, current flows from the positive side of the DC power supply smoothed by the smoothing circuit 3 through the diode 52, and current flows into the base of the transistor 50 through the resistor 53.

As a result, the transistor 50 becomes conductive, so the current flowing through the diode 52 passes through the transistor 50 and flows into the gate of the FET 29.
29 is made conductive.

Further, the output pulse from the output terminal 55 of the oscillation circuit 22 is "
When the transistor 51 becomes "off", no current flows into the base of the transistor 51, so it becomes "off", and the transistor 50 also becomes "off".
Since the FET 29 is turned off, the FET 29 is also turned off. Therefore, the FET 29 operates in synchronization with the output pulse from the output terminal 55.

On the other hand, the output pulse from the output terminal 56 directly flows into the gate of the FET 30 and controls "on" and "off".
In synchronization with the output pulse from this output terminal 56, the FET 30
works.

Therefore, the FETs 29 and 30 alternately turn on and off in synchronization with the output pulses of the oscillation circuit 22, and by adjusting the period of the output pulses from the oscillation circuit 22, the output frequency of the inverter circuit 4 is controlled. can do.

In this way, the other embodiments do not require an isolation transformer to operate the FETs 29 and 30, so they can be constructed at low cost, and the level shift circuit 41 can be integrated into an IC. Therefore, the space of the inverter circuit 4 can be saved.

[Effects of the Invention] As explained above, in the present invention, the current from the current transformer flowing into the bases of a pair of bipolar transistors constituting an inverter circuit is transferred to the FET, etc. provided between the base and emitter of the bipolar transistors. It is controlled by turning on and off the switching elements. Therefore, the control range of the output frequency of the inverter circuit can be widened, and the dimming range of the discharge lamp is widened.

Further, since the switching elements such as FETs used have a small capacity, it can be constructed at low cost.

Furthermore, since the base of the bipolar transistor is supplied with current from a conventional current transformer, the stability of the switching operation is excellent and the switching loss is also small.

Furthermore, if the high-side switching element is operated by a level shift circuit, an isolation transformer is not required, resulting in lower cost and space-saving effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is an explanatory diagram showing details of the other embodiment, and FIG. , FIG. 5 is a configuration diagram showing a conventional example. 1... Commercial power supply 2... Rectifier circuit 3... Smoothing circuit 4... Inverter circuit 6... Discharge lamp 8.9... Bipolar transistor

Claims (2)

[Claims] (1) The DC voltage obtained by rectifying and smoothing the commercial power supply is converted into an AC voltage of the desired frequency using an inverter circuit that has a pair of bipolar transistors that are turned on and off alternately by the current supplied from the current transformer. , a discharge lamp lighting device for supplying this to a discharge lamp to light it, comprising: a switching element provided between the base and emitter of the bipolar transistor; and a driving means for applying a control current to operate the switching element. A discharge lamp lighting device characterized by: (2) The discharge lamp lighting device according to claim 1, wherein the switching element provided in the high-side bipolar transistor of the pair of bipolar transistors is driven by a level shift circuit.