JPS62158Y2 - - Google Patents

Description

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

As a discharge lamp lighting device, high frequency lighting using a high frequency conversion circuit is known. High frequency lighting has better luminous efficiency than low frequency lighting such as commercial frequency,
Among them, high-frequency lighting with a constant amplitude is known to be the most efficient. An example of this is a high-frequency lighting device that has a circuit configuration in which a high-frequency conversion circuit is connected to each phase of a three-phase power supply and the respective high-frequency outputs are combined in series. A circuit diagram is shown.

In Fig. 1, high-frequency conversion circuits 2, 3, and 4 receive each interphase voltage of a three-phase power supply 1 as input, and the conversion period is controlled by separately excitation to turn on/off each transistor pair of the high-frequency conversion circuit. ing. The output of each high frequency conversion circuit 2, 3, 4 is connected in series with the secondary windings of oscillation transformers 5, 6, 7, and the combined output is a high frequency output whose amplitude is approximately constant. The discharge lamp 8 is turned on via the current limiting element 9. Here, the relationship between the voltage and current of the resonant capacitor 10 of the high-frequency conversion circuit as the primary side output is as shown in Figure 2 A if there is a single high-frequency conversion circuit (for example, only 2) with the same period as the separately excited vibration. As shown, the voltage oscillates in a sinusoidal wave, and the current has a waveform whose phase leads the voltage by π/2.

However, there are actually three high frequency conversion circuits,
Also, by using each phase voltage of the three-phase power supply 1 as its input, the phase of the input voltage is 2π/3
It's one step behind. For this purpose, the high frequency conversion circuit 2
When the transistor pair 11 and 12 is turned off and transistor 12 is turned on, the primary current flows in the resonant capacitor 10 in the direction shown in FIG. 3A. This current is the same in the single high frequency conversion circuit, and this current is caused by the input voltage of the high frequency conversion circuit 2 inducing a voltage between both terminals of the primary winding, and in order to induce this voltage, the iron core The sum of the excitation current necessary to establish the magnetic flux in the secondary circuit and the equilibrium current that flows so that the current flowing in the secondary circuit generates a magnetomotive force sufficient to cancel the magnetomotive force of the secondary winding. be. Therefore, in the circuit shown in FIG. 1, the secondary currents i ₂ and i ₃ of the high frequency conversion circuits 3 and 4 flow through the secondary circuit of the high frequency conversion circuit 2 to the resonant capacitor 10 of the high frequency conversion circuit 2. Therefore, a magnetomotive force sufficient to cancel the magnetomotive force generated thereby flows into the primary circuit. That is, this is the current (i ₂
+i ₃ ), and the current flows as shown in Figure 3 (b).

Thus, the currents A and B as shown in FIG. 3 flow in the resonant capacitor 10 in opposite directions, the currents have a relationship as shown in FIG. It vibrates at a shorter period than the period, and a zero voltage period, that is, a rest period occurs. At this time, the collector current of the transistor 12 of the high frequency conversion circuit 2 and the resonance capacitor 1
The relationship between the voltage waveforms at 0 is as shown in FIG. In this way, the pause period exists not during the entire input voltage half-cycle region of the high frequency conversion circuit 2, but during the phase when the instantaneous value of the input voltage is small.

FIG. 5 shows the relationship between the input voltages of each high frequency conversion circuit. Here, u, v, and w are input voltages of the high frequency conversion circuits 2, 3, and 4 shown in FIG. 1, respectively. Fifth
In the figure, at phase t ₁ , the input voltage u of the high frequency conversion circuit 2 is at its maximum, and the voltage induced in the primary winding is also high, which means the sum of the excitation current and the balance current, i.e. The current is also large. On the other hand, in the high frequency conversion circuits 3 and 4, the input voltages v and w are half of the peak values, so the secondary current (i ₂ + i ₃ ) is small, and due to (i ₂ + i ₃ ) of the high frequency conversion circuit 2, The magnetic flux canceling current, ie, B in FIG. 3 is small. Therefore, the current flowing through the resonant capacitor is large, and the capacitor voltage is also high accordingly.
The cycle is also long. That is, during this phase, there is no rest period in the capacitor voltage waveform as shown in FIG. On the other hand, at phase _t2 in FIG. 5, the input voltage u of the high frequency conversion circuit 2 is zero, and the current A shown in FIG. 3 does not flow. On the other hand, in the high frequency conversion circuits 3 and 4, the input voltage is as large as √3/2 of the peak, and the magnetic flux cancellation current due to (i ₂ +i ₃ ) in the high frequency conversion circuit 2 is large. Therefore, the current flowing through the capacitor is small, and the period of the voltage across the capacitor is also small and there is a rest period, as shown in FIG. 4.

Therefore, in a three-phase high frequency conversion circuit, even if there is no rest period in the capacitor voltage in the phase where the instantaneous input voltage value is large, the resonance period changes and there is a rest period in the phase where the input voltage is small. In addition, in order to eliminate the pause period, if the capacitance of the resonant capacitor is increased to increase the period, the pause period will disappear during the phase where the input voltage is small, but conversely, the oscillation period of the capacitor voltage, that is, the resonance period, will decrease during the phase when the input voltage is large. When the cycle becomes larger than the period of the synchronous circuit, a problem arises in that the capacitor voltage is cut off and the transistor is destroyed due to increased collector loss and the like. In addition, if you try to prevent the reverse current of the collector current _ic , for example, you can insert a unidirectional rectifying element such as a diode in the collector of the transistor 11 in the forward direction as shown in Fig. 3, but this will prevent the reverse current from flowing. Therefore, the magnetic flux of the output transformer becomes saturated, and in order to prevent this, it is necessary to take measures such as increasing the cross-sectional area of the primary winding and core of the output transformer, which results in a large shape of the transformer, which is a major drawback. Here, how does this collector reverse current flow in the circuit? As mentioned above, this collector reverse current flows during the rest period of the capacitor voltage waveform, and the state of the transistor is as shown in Figure 3. At this time, transistor 11 is off and transistor 12 is on. Therefore, transistor 1
2 conducts from the collector to the emitter, resulting in a reverse current from the base to the collector of the transistor 11. That is, when there is a rest period, a reverse current flows between the base and collector of the transistor that is off during that period. However, normally, a reverse current is not allowed to flow between the base and collector of a transistor, and this reverse current is not guaranteed at all in the transistor specifications. Therefore, the conventional three-phase high frequency conversion circuit described above has a problem with the reliability of the transistors, in other words, the stability of the circuit operation, which is a drawback.

The present invention was proposed in view of the above points, and by connecting a push-pull type inverter to each phase of a three-phase power supply and composing each high-frequency output in series, a high frequency with a nearly constant amplitude is obtained, and the current In a discharge lamp lighting device that lights a discharge lamp connected through a limiting element, this prevents base-collector reverse current of the oscillation transistor in the push-pull type inverter during operation, improving transistor reliability and enabling stable circuit operation. An object of the present invention is to provide a discharge lamp lighting device that does the following.

The present invention will be described below with reference to the drawings showing embodiments of the present invention.

FIG. 6 shows an embodiment of the present invention, in which a rectifying element D such as a diode is connected to each transistor pair.
The feature is that they are connected in parallel in opposite directions. As a result, the current flowing to the base and collector of the transistor during the rest period of the resonant capacitor flows from the output side of the transistor to the rectifying element without entering the emitter of the transistor, and then to the input side of the transistor, that is, the collector. It turns out. Due to the action of this rectifying element, no reverse current flows to the base-collector of the transistor at all, and current flows as shown by the broken line in FIG. 6 during the rest period. (S ₁ OFF, S ₂ ON state) Since the operating states of the other circuits are exactly the same as in the conventional example, their explanation will be omitted to avoid duplication.

As described above, in the discharge lamp lighting device of the present invention, by providing a rectifying element in parallel with each transistor pair in the three-phase high frequency conversion circuit in the opposite direction,
The transistor base-collector reverse current due to the magnetic flux canceling current caused by the secondary current, which is the essence of the operation of the three-phase high-frequency conversion circuit, is blocked by flowing through the rectifying element, and the reliability of the transistor is improved. This has a great effect without impairing the original operation, that is, the ability to obtain a high frequency output with a substantially constant amplitude as the output voltage of the three-phase high frequency conversion circuit and to obtain high efficiency.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional discharge lamp lighting device, Figure 2 is a circuit diagram of a conventional discharge lamp lighting device.
5 to 5 are explanatory diagrams of its operation, and FIG. 6 is a circuit diagram showing an embodiment of the present invention. 1...Three-phase AC power supply, 2, 3, 4...High frequency conversion circuit (inverter), 5, 6, 7...Output transformer, 8...Discharge lamp, _S1 , _S2 ...Transistor,
D... Rectifying element, 9... Current limiting element.

Claims (1)

[Scope of utility model registration request] A three-phase high-frequency conversion circuit that inputs each phase-to-phase voltage of a three-phase power supply, performs full-wave rectification of the three-phase voltage, and generates a high-frequency voltage by alternating switching operations of a pair of transistors connected to the rectified output. In a discharge lamp lighting device that connects output terminals in series to obtain a substantially constant high-frequency output voltage and lights a discharge lamp with the high-frequency output voltage, a rectifying element is bypassed in the opposite direction between the collector and emitter of the transistor, and the A discharge lamp lighting device characterized by blocking a reverse current generated in the base and collector of the transistor during a phase in which the instantaneous value of the input voltage of the high frequency conversion circuit is small.