JPS6160559B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a discharge lamp lighting device.

Generally, high frequency lighting using a high frequency conversion circuit is known as a discharge lamp lighting device. It is known that high-frequency lighting has better luminous efficiency of the lamp than low-frequency lighting such as commercial frequency, and lighting using high-frequency waves with a constant amplitude has the highest efficiency.

In order to obtain a high frequency wave with a constant amplitude, there is a lighting circuit that obtains a high frequency wave with a substantially constant amplitude by converting each interphase voltage of a three-phase power supply into a high frequency signal and composing each high frequency output in series. Figure 1 shows the relationship between three-phase power supplies, Figure 2 (a) shows a lighting device using a high-frequency conversion circuit with three-phase input, and (b) shows the voltage waveforms of each phase input and output V _put . show.

A problem with a lighting device using a high-frequency conversion circuit that receives a three-phase power source as input is how to synchronize the switching within the three high-frequency conversion circuits.

That is, in order to make the amplitude of the high frequency output substantially constant, which is a feature of this lighting device, it is necessary to make the operation of the switching transistors the same in the three high frequency conversion circuits.

It is generally known that there are two types of synchronization methods: self-excitation type and separately excitation type. in this case,
In the self-excited type, the switching transistors of the other two high-frequency conversion circuits operate in accordance with the self-excited oscillation of one high-frequency conversion circuit.

In addition, in the separately excited type, in addition to the three high-frequency conversion circuits mentioned above, one high-frequency conversion circuit is added (this high-frequency conversion circuit is called a synchronous circuit), and the switches of the three high-frequency conversion circuits are adjusted according to the self-oscillation. This method operates a switching transistor.

In the self-excited type, a synchronization circuit is not required and the lighting device can be made smaller and lighter, but the vibration waveform of one high-frequency conversion circuit is used as the synchronization signal. That is, it is composed of one self-excited high frequency conversion circuit and two separately excited high frequency conversion circuits.

The vibration waveform serving as the synchronization signal is pulsating at a commercial frequency.

Therefore, there is no problem with the self-excited high frequency conversion circuit, but the vibration waveform of the other two high frequency conversion circuits is
Since it is delayed by 2/3π, the synchronization signal does not have an appropriate value. That is, when these high frequency conversion circuits operate near the peak value of the commercial power supply, the drive signal required for switching the transistors becomes large. However, in this case, since the self-excited high frequency conversion circuit is shifted by 2/3π, the amplitude of the vibration waveform is small, and therefore the drive signal is also small. Due to this, there are many cases where switching is not performed properly in two separately excited high frequency conversion circuits.

For the above reasons, currently, lighting devices using a high frequency conversion circuit that inputs a three-phase power supply are of a separately excited type in which one high frequency conversion circuit is added to the outside and this circuit is used as a synchronous circuit.

However, this separately excited type lighting device also has the following drawbacks.

FIG. 3 shows an example of a conventional circuit.

As mentioned above, the synchronization method is separately excited, and three push-pull type inverters 2, 3, and 4 are used for synchronization.
In addition to the high frequency conversion circuit composed of , a high frequency conversion circuit using a DC power supply (also composed of a push-pull type inverter) is added as a synchronization circuit 5, and this output waveform is input to each high frequency conversion circuit as a synchronization signal. are doing.

The problem here is that since this synchronization circuit is a high frequency conversion circuit using a DC power supply, the output waveform, that is, the synchronization signal waveform, is a high frequency wave with a constant amplitude. That is, the three high frequency conversion circuits are constantly supplied with the same synchronizing signal, in other words, the transistor drive current.

However, the vibration waveform of each high-frequency conversion circuit is pulsating at the commercial frequency, and the collector current of the transistor is also pulsating (FIG. 4).

Therefore, in the section A in Figure 4, the collector current flows sufficiently for the drive current (base current) of the transistor, but if the same base current is supplied in the section B, where the collector current is small, the base current flows excessively. This increases the phenomenon of overdrive. In other words, the supply of a constant base current in response to changes in the collector current causes overdrive.

A more detailed explanation is as follows.

When using a transistor as a high-speed switching element, driving is an important point. There are optimal driving conditions for driving a certain transistor, and the factors include collector current I _C , base current I _B , and DC current amplification factor h _FE .
The relational expression based on these becomes I _B =I _C ×K/h _FE . Now k is called the overdrive factor,
Usually set at 1.5-2.

According to this relational expression, when a certain collector current flows during transistor operation, h _FE is determined by that collector current, and I _B determined thereby is theoretically the optimum drive current. In that case, if the actual drive current is much larger than the theoretical optimum current, the transistor will experience a phenomenon called overdrive.
It is widely known that it causes unstable vibrations.
This becomes a major problem as the switching time becomes longer, resulting in greater switching loss, heat generation, and even destruction of the transistor.

Based on the above background, in conventional circuits, the same drive signal is given from the synchronous circuit to each high frequency conversion circuit, so
Depending on the magnitude of the input voltage for each phase, the transistor may overdrive, resulting in unstable vibration.
A major drawback was that it lacked reliability as a lighting device.

The present invention was proposed in order to eliminate the above-mentioned drawbacks, and by superimposing the output of the synchronous circuit with a voltage obtained by rectifying the vibration waveform on the primary side of the oscillation transformer of each high frequency conversion circuit and smoothing the high frequency component. An object of the present invention is to provide a discharge lamp lighting device that supplies optimal driving conditions to the switching transistors of each high-frequency conversion circuit, eliminates the problem of overdrive, reduces loss in the lighting circuit, and improves reliability.

Next, the present invention will be explained with reference to examples.

FIG. 5 shows an embodiment of the invention. The discharge lamp lighting device of the present invention includes a three-phase power supply 1, high-frequency conversion circuits 2, 3, and 4 each inputting three phase voltages between each phase of the three-phase power supply 1, and the output primary side of each conversion circuit is transformed. Conversion circuits 5, 6, and 7 rectify and smooth the vibration waveform and superimpose it on the DC power supply voltage for startup and the synchronization signal of the high frequency conversion circuits 2, 3, and 4, and the outputs of the high frequency conversion circuits 2, 3, and 4. Synchronize the conversion of the current limiting element 8, the discharge lamp 9 connected via the current limiting element 8, and the high frequency conversion circuits 2, 3, 4 between the terminals where the insulated secondary windings are connected in series. It is composed of a synchronous circuit 10. Further, 21 of the modulation circuit 5 is a primary voltage feedback winding provided in the oscillation transformer 18, and its output side is connected to the bases of the transistors 24 and 25 via a rectifying and smoothing circuit, and to the transistor 24 via the DC power supply 26. ，
It is connected to 25 emitters. The same applies to the other modulation circuits 6 and 7.

Note that although the internal configurations of the high frequency conversion circuits 3 and 4 and the modulation circuits 6 and 7 are omitted in the figure, the high frequency conversion circuit 2 and the modulation circuit 5 are
It has the same configuration as .

Next, the operation of the device of the present invention will be explained.

The high frequency conversion circuits 2, 3, and 4 receive each phase voltage of a three-phase power source as input, and the conversion synchronization is obtained by a synchronization circuit 10.

Since the synchronous circuit 10 constitutes a push-pull type inverter when the DC power supplies 11 and 12 are turned on, the switching transistors 13 and 14
is alternately turned on and off at high frequency, and a voltage waveform υ ₁ as shown in FIG. 6 is obtained across the capacitor 16. Now, this waveform is the oscillation transformer 1
7's secondary winding, and the windings E-ro, H-ani,
Hohe obtains the same waveform shown in FIG. 6, which is input to the high frequency conversion circuits 2, 3, and 4 to synchronize the on and off states of each transistor pair. That is, the output voltage of the synchronous circuit 10 is the voltage _υD in FIG. At that time, each high frequency conversion circuit 2, 3,
At both ends of the 4 oscillation transformers 18, 19, 20,
As shown in FIG. 7, a high frequency oscillating voltage υ ₂ whose envelope is the commercial frequency is obtained. These high frequency conversion circuits 2, 3,
When feedback windings 21, 22, and 23 are added on the same core as the primary windings of the oscillation transformers 18, 19, and 20 of No. 4, the primary windings of the high frequency conversion circuits 2, 3, and 4 are connected to both ends of the windings. Obtain a high frequency voltage waveform similar to the waveform at both ends of the winding.

When this high frequency voltage waveform is input to the rectifier circuit,
The output is as shown in FIG. Further, when high frequency components of this waveform are attenuated by a low-pass filter, a waveform as shown in FIG. 9 is obtained.

The reason why the voltage shown in FIG. 9 has a minimum value υ _nio , which is the voltage at υ _B in FIG. 5, is to ensure that starting is performed by adding a DC power source. Due to this voltage, when the input voltage is high in each high frequency conversion circuit 2, 3, 4, the 9th
The voltage shown in the figure is also high, and a large base current flows to the switching transistor driven by this voltage. Conversely, when the input voltage is low, the voltage shown in FIG. 9 is also low, so the base current to the switching transistor also decreases, eliminating the problem of excessive base current flowing and overdrive.

By the above operation, each high frequency conversion circuit 2,
The high frequency vibrations as shown in FIG. 7 generated at both ends of the oscillation transformers 18, 19, 20 of 3 and 4 are induced into the secondary windings, and this output waveform is transmitted to each high frequency conversion circuit 2,
3 and 4, the phase is shifted by 2/3π. By combining these outputs in series, a high frequency with a substantially constant amplitude is obtained, and the discharge lamp 9 is stably lit via the current limiting element 8.

As described above, the present invention does not supply a base current of a constant amplitude as in the conventional example in a high frequency conversion circuit that receives a three-phase power supply as an input, but follows the input voltage of each high frequency conversion circuit. By adding a bias circuit that can change the base current, when the input voltage is large, a large amount of base current flows, and when the input voltage is small, the base current can be narrowed down, making it possible to control the switching of each high frequency conversion circuit. The transistor can be operated under optimal driving conditions without being overdriven.

As a result, it is possible to reduce power loss in the transistor, generate no heat, perform stable high-frequency oscillation, and obtain high reliability as a lighting circuit.

[Brief explanation of the drawing]

Fig. 1 shows the relationship between three-phase power supplies, Fig. 2 A shows a lighting device using a high-frequency conversion circuit with three-phase input, B shows voltage waveforms, Fig. 3 shows the conventional device, and Fig. 4 shows the voltage υ ₁ ,
Waveform of υ ₁ ′, Figure 5 shows the device of the present invention, Figures 6 to 9
The figure shows the waveforms of each part. 1... AC power supply, 2, 3, 4... High frequency conversion circuit, 5, 6, 7... Modulation circuit, 8... Current limiting element, 9... Discharge lamp, 10... Synchronous circuit, 11, 1
2...DC power supply, 13, 14...transistor,
16... Capacitor, 17... Oscillation transformer, 1
8, 19, 20...Oscillation transformer, 21, 22,
23...Return winding.

Claims (1)

[Claims] 1 Inputs a 3-phase power supply and 3 phase voltages between each phase of the 3-phase power supply, performs full-wave rectification of each phase-to-phase voltage, and generates a high-frequency voltage by alternating switching operations of a pair of transistors connected to the rectified output. occur 3
In a discharge lamp lighting device that connects the output ends of a set of high-frequency conversion circuits in series to obtain a substantially constant high-frequency output voltage and lights a discharge lamp with the high-frequency output voltage, the high-frequency conversion circuit is used as a bias power supply circuit for the transistor. A feedback winding for driving a transistor is provided in each oscillation transformer, and the output of a circuit that rectifies and smoothes the output of the feedback winding is applied as a bias voltage to the base of the transistor, thereby increasing the base current of the transistor. , A discharge lamp lighting device characterized in that the voltage varies depending on the input voltage of each phase of the three-phase power supply.