JPH0311078B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device, and more particularly to a discharge lamp lighting circuit including an inverter circuit using switching elements such as transistors.

FIG. 1 shows a conventional discharge lamp lighting circuit (see US Pat. No. 4,170,747). The circuit in the figure includes two sets of transistors 4, 6 and 8, 10 connected in series to a DC power supply 2, and each transistor 4,
Diode 1 connected in parallel with 6, 8, 10
2, 14, 16, 18, an inductor 20, and a discharge lamp 22. A series circuit of discharge lamp 22 and inductor 20 is connected between the connection point of transistors 4 and 6 and the connection point of transistors 8 and 10.

In the circuit of FIG. 1, for example, voltages V4 and V8 in an inverse relationship to each other, such as 50, 60 or 400 Hz, as shown in FIG. 2a, are applied to the bases of transistors 4 and 8, or Voltages V4' and V8' having rest periods t such as are applied, respectively. Furthermore, high frequency voltages V6 and V10 or V6' and V10' with a variable duty ratio of, for example, 20 KHz are applied to transistors 6 and 10 only while transistors 8 and 4 are in a conductive state, respectively. Therefore, for example, when transistor 4 is conductive, transistor 10 is turned on and off by high frequency voltage V10 or V10'. Then, when the transistor 10 is on,
From DC power supply 2 to transistor 4 and inductor 2
0, a current flows through the discharge lamp 22 and the transistor 10, and when the transistor 10 is turned off, the current flows from the inductor 20 to the discharge lamp 22, the diode 16,
Current flows through transistor 4. Conversely, when transistor 8 is on, transistor 6 is turned on and off by high frequency voltage V6 or V6'. When the transistor 6 is on, current flows from the DC power supply 2 through the transistor 8, the discharge lamp 22, the inductor 20, and the transistor 6; when the transistor 6 is turned off, current flows from the inductor 20 through the diode 12, the transistor 8, and the discharge lamp 22. current flows. Based on the principle described above, the discharge lamp 22 is lit by flowing an alternating current having a frequency corresponding to the on/off states of the transistors 4 and 8. Note that the diodes 14 and 18 protect the transistors 4 and 8 by providing current paths when the transistors 4 and 8 change from the on state to the off state, respectively. Also, in this circuit, high frequency voltages V6 and V10 or
By varying the duty ratio, that is, the on/off ratio of V6' and V10', the current flowing through the discharge lamp 22 is varied to perform dimming and illuminance control.

Furthermore, a circuit configuration shown in FIG. 3 has been proposed as a discharge lamp lighting device that has a simplified circuit configuration by reducing the number of constituent elements of the future circuit shown in FIG. In the circuit of FIG. 3, the first DC power supply 24 and the second
A transistor 28 as a first switching element is connected in series with a DC power supply 26, and a transistor 28 is connected between the positive terminal of the first DC power supply and the negative terminal of the second DC power supply.
and a transistor 30 as a second switching element are connected in series. An inductor 36 and a discharge lamp 3 are connected between a common connection point between the DC power supplies 24 and 26 and a common connection point between the transistors 28 and 30.
8 are connected in series. Additionally, diodes 32 and 34 are connected in parallel to transistors 28 and 30, respectively, in the direction shown.

In the circuit of FIG. 3, the same variable duty ratio high frequency voltage V6 applied to the bases of transistors 6 and 10 in the circuit of FIG. 1 is applied to the bases of transistors 28 and 30, respectively.
V10 is added. After the discharge lamp is started, if the transistor 28 is on, a current flows from the DC power supply 24 through the transistor 28, the inductor 36, and the discharge lamp 38, and returns to the DC power supply 24 to maintain the discharge. When the transistor 28 is off, the inductor 36 connects the discharge lamp 38, the power supply 26, and the diode 3.
Current flows back through inductor 36 through 4 to maintain the discharge. Similarly, when transistor 30 is on, current flows from DC power supply 26 through discharge lamp 38, inductor 36, and transistor 30 back to DC power supply 26 to maintain the discharge, and when transistor 30 is off, is inductor 3
6 to diode 32, DC power supply 24, discharge lamp 3
Current flows back through inductor 36 through 8 to maintain the discharge. The dimming of the discharge lamp uses high frequency voltage V6,
Perform this by changing the duty ratio of V10.

By the way, the conventional circuit shown in Fig. 1 or the
In the proposed circuit shown in the figure, as is clear from FIG. V6 and V10 are voltages that repeatedly change in level only when the base voltages V8 and V4 of transistors 8 and 4, respectively, are at a high level. However, especially when the discharge lamp serving as a load is a high-pressure discharge lamp, the starting voltage of the high-pressure discharge lamp is high, and a high-voltage pulse is often used as the starting voltage. Therefore, each transistor 4, 6, 8, 10
The control circuit (not shown) may malfunction, causing the transistors 4 and 6 connected in series to
Alternatively, 8 and 10 may be turned on at the same time. This simultaneous on phenomenon is caused by the fact that the base voltage applied to the transistors 4 and 8 is, for example, the second
This may occur even when V4' and V8' shown in FIG. b have a pause period t. When such a simultaneous ON state occurs, the DC power supply 2 becomes short-circuited, causing a large current to flow through each transistor, causing the transistor to be destroyed.

In view of the above-mentioned problems, an object of the present invention is to provide a discharge lamp lighting device based on the concept of inserting an inductor between transistors connected in series.
The object of this invention is to prevent a power supply short-circuit condition caused by simultaneous turning on of each transistor and the accompanying destruction of the transistors.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 4 shows a circuit of a discharge lamp lighting device according to an embodiment of the present invention. In the circuit of the same figure, the first
The DC power supply 40 and the second DC power supply 42 are connected in series, and the first DC power supply 40 and the second DC power supply 42 are connected in series.
A transistor 50 as a switching element, a first inductor 46, and a discharge lamp 44 are connected in series. A second inductor 48 and a transistor 52 as a second switching element are connected in series between the connection point between the first inductor 46 and the discharge lamp 44 and the negative terminal of the second DC power supply 42. There is. The connection point between the first transistor 50 and the first inductor 46 and the second DC power supply 42
A first diode 54 is connected between the negative terminal of the second inductor 48 and the second transistor 52, and a second diode 54 is connected between the connection point of the second inductor 48 and the second transistor 52 and the positive terminal of the first DC power supply 40. 56 are connected.

In the circuit of FIG. 4, transistors 50 and 52 are each supplied with a variable duty ratio high frequency voltage V6 applied to the bases of transistors 6 and 10 in the circuit of FIG.
V10 is added. After starting the discharge lamp, if the transistor 50 is on, current flows from the DC power supply 40 through the transistor 50, the inductor 46, and the discharge lamp 44 to maintain discharge. transistor 5
When 0 is off, the discharge lamp 44 from the inductor 46,
A current flows through the DC power supply 42 and the diode 54 to maintain the discharge. Similarly, transistor 52
is on, the discharge lamp 44 from the DC power supply 42,
Current flows through inductor 48 and transistor 52 to maintain the discharge. When transistor 52 is off, inductor 48 leads to diode 56;
A current flows through the DC power supply 40 and the discharge lamp 44 to maintain the discharge.

If the transistors 50 and 52 are turned on at the same time, the transistors 50 and 52 will be connected in series to the series power supplies 40 and 42 via the two inductors 46 and 48, and the current flowing through both transistors will be limited. The transistor is protected.

Note that each transistor in each of the above-described embodiments can be replaced with a switching element such as an SCR or a GTO. The first and second DC power sources 40 and 42 may be obtained from an AC power source through a voltage doubler rectifier circuit, or may be obtained through separate transformers or windings and rectifier circuits, and may also be obtained from a center tap. The center tap of the transformer shown in FIG.

As described above, according to the present invention, short-circuiting of the power supply and destruction of each switching transistor can be accurately prevented by adding one inductor, and since there is no element in parallel with the switching transistor, the capacitance in parallel with the switching element can be reduced. Turn-on loss is reduced. That is, generally, a snubber circuit (for example, circuit 39 shown only for transistor 28 in FIG. 3) is provided in parallel with the switching element for the purpose of protecting the switching element from power supply noise such as surge voltage. In the conventional example, an excessive current flows from the capacitor of the snubber circuit when the transistor 30 is turned on, but according to the present invention, for example, for the transistor 52, the current flowing from the snubber circuit connected in parallel with the transistor 50 to the transistor 52 is reduced. Since the current is limited by the inductor 48, the switching loss of the transistor 52 is reduced. The same applies to the transistor 50.

[Brief explanation of the drawing]

Figure 1 is an electric circuit diagram showing the configuration of a conventional discharge lamp device, Figure 2 is a waveform diagram to explain the operation of the discharge lamp lighting device, and Figure 3 is a diagram of a conventional discharge lamp lighting device. FIG. 4 is an electric circuit diagram showing the structure of a discharge lamp lighting device according to an embodiment of the present invention. 2, 24, 26, 40, 42...DC power supply,
4, 6, 8, 10, 28, 30, 50, 52...
Transistor, 12, 14, 16, 18, 32,
34, 54, 56...Diode, 20, 36,
46, 48...Inductor, 22, 38, 44...
...discharge lamp.

Claims (1)

[Claims] 1. A first DC power supply, a second DC power supply whose positive terminal is connected to the negative terminal of the first DC power supply, and a common connection point between the positive terminal of the first DC power supply and the first and second DC power supplies. a first switching element connected in series between the first inductor and the discharge lamp; connected in series between the first inductor and the discharge lamp and a negative terminal of the second DC power supply; the second
an inductor and a second switching element, the first switching element and the first inductor in a direction that causes current to flow from the first inductor through the discharge lamp and the second DC power supply when the first switching element is off; and a first unidirectional current-carrying element connected between the connection point of and a second unidirectional current-carrying element connected between the connection point between the second switching element and the second inductor and the positive terminal of the first DC power supply in the direction in which current flows through the discharge lamp. A discharge lamp lighting device characterized by: