JPH0266895A - Discharge lamp lightup device - Google Patents

Abstract

PURPOSE:To secure switching operation in a safe region and enhance the reliability by furnishing an inductance element between output terminals of an inverter circuit, and by allowing a phase delay current to flow in a MOSFET even when a discharge lamp is removed. CONSTITUTION:When a discharge lamp 3 inserted between output terminals of an inverter circuit 2 is removed, a phase delay drain current flows in drains of MOSFETs 4, 5 alternately. This is because an inductor L1 as an inductance element is connected parallelly with a series resonance circuit of a current limit inductor L and a capacitor C3 and this circuit takes the phase delay current. This reduces switching loss to eliminate heat emission, and switching operation can be performed in a safe region to accomplish a high reliability lightup circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a half-bridge inverter type discharge lamp lighting device.

2. Description of the Related Art Conventionally, in this type of discharge lamp lighting device, a commercial AC power source is used as a power source to light a discharge lamp via an inverter circuit.

A half-bridge inverter type discharge lamp lighting device (circuit) for this purpose is shown in FIG. first,
A discharge lamp 3 is connected to the DC power supply 1 via an inverter circuit 2. Here, the inverter circuit 2 is connected to the DC power supply 1
Two switching elements connected in series between them, specifically MOS FETs (MO3 type field effect transistors) 4 and 5, and a current limiting inductor connected between the midpoint of their connection and the discharge lamp 3. This current-limiting inductor L and the capacitor C connected in series with the filaments 3a and 3b of the discharge lamp 3 create a C series resonant circuit, and DC-cut capacitors C, C2 each connected in parallel to the MOS FET 4.5 in a bridge. It is configured as a half-bridge type. Here, the capacitor C is connected between the non-power supply side terminals of the filaments 3a and 3b of the discharge lamp 3.

Also, one of the MO5FETs 45, here, M
A switching improvement capacitor C3 is connected between the drain D and source S of the OSFET4.

In such a configuration, two MOS FET4,
5 are individually controlled in operation by a drive control circuit (not shown), and when one is off, the other is under switching control. At this time, under normal conditions when the discharge lamp 3 is attached and lit, electric power is supplied to the filaments 3a and 3b by the current flowing through the capacitor C. Due to the presence of such a capacitor C, when the filaments 3a and 3b of the discharge lamp 3 are connected to the terminals, a current that is lagging in phase with respect to the lamp current always alternately flows through the MOS FET 4.5.

Problems to be Solved by the Invention However, when the discharge lamp 3 is detached or is not attached or is in an unloaded state, as can be seen from FIG. 3, the filament 3a
, 3b are disconnected, and no output current flows. However, since the switching improvement capacitor C3 is connected between the drain D and source S of one MOSFET 4, a discharge current flows through this MOSFET 4. Also,
The other MOS FE in series with this MOS FET4
A charging current flows through T5. As a result, MOS FE
At the on/off timing of the drain D-source S voltage VDS2 of T4, each MOS FET4
．． As shown in FIG. 4, a switching wave-shaped drain current I D+ + I D2 flows through the drain D of No. 5, which increases switching loss and causes significant heat generation. In some cases, the safe operating area of the MOS FET may be exceeded.

Means for Solving the Problems A discharge lamp lighting device is provided in which two MOS FETs connected in series are switched by a drive circuit and the discharge lamp is lit by the oscillation operation of an inverter which supplies the switching output to a series resonant circuit. , the constant of the series resonant circuit is set to a value that causes a slow phase current to always flow through the MOSFET during lighting of the discharge lamp;
In a half-bridge inverter type discharge lamp lighting device in which a switching improvement capacitor or a snubber circuit is connected between the drain and source of the FET, the MOS remains connected between the output terminals of the inverter circuit even when the discharge lamp is removed.
An inductance element is connected to cause a slow phase current to flow through the FET.

Even under no-load conditions, such as when the working discharge lamp is disconnected, the presence of an inductance element between the output terminals prevents the MOS
An LC circuit is formed between the capacitor or snubber circuit connected to the FET, and a current with a lagging phase always flows through the drain of the MOS FET, just as it would during normal lighting, resulting in a switching operation with less loss. Heat generation is suppressed.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2. The same parts as those shown in FIGS. 3 and 4 are indicated using the same reference numerals. In this embodiment, an inductor L1 as an inductance element is connected between the output terminals of an inverter circuit 2, that is, in parallel to an LC series resonant circuit formed by a current limiting inductor L and a capacitor C. Here, according to such a configuration, the inductor L1 has an inductor value that allows a slow-phase drain current ■D+ + I D2 to flow through the drain of the JEJM○5FET4.5 at no load. M O
As shown in Fig. 2, the drain current of SFE T /l, 5 always has a slow phase ■D++ID11
flows alternately, resulting in less switching loss.

Therefore, unlike conventional lighting circuits, there is no heat generation, and switching operations can be performed within a safe range, resulting in a highly reliable lighting circuit.

In this embodiment, a capacitor C3 is connected to improve switching in accordance with FIG. 3, but a snubber circuit may be used instead.

Further, the drive circuit for driving the MOS FET 4.5 may be either separately excited or self-excited. In particular, self-excitation is achieved by connecting a parallel circuit of a discharge lamp and a capacitor and a series circuit of an inductor. ■
7, can be provided with a winding to obtain a feedback signal.

Effects of the Invention In the present invention, as described above, an inductance element is connected between the output terminals of the inverter circuit to cause a slow phase current to flow through the MOS FET even when the discharge lamp is removed.
Even if there is no load when the discharge lamp is disconnected, MOS FE
Switching loss can be reduced by constantly flowing a slow-phase current through T, thus ensuring switching operation in a safe range and suppressing heat generation, resulting in a highly reliable lighting circuit. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a voltage and current waveform diagram, FIG. 3 is a circuit diagram showing a conventional example, and FIG. 4 is a voltage and current waveform diagram. 2... Inverter circuit, 3... Discharge column, 4, 5...
・MOS FET, C, ... Capacitor IDZ for switching improvement

Claims (1)

[Claims] A discharge lamp lighting device that lights a discharge lamp by the oscillation operation of an inverter that switches two MOSFETs connected in series by a drive circuit and supplies the switching output to a series resonant circuit, wherein the constant of the series resonant circuit is The value is set so that a slow phase current always flows through the MOSFET during lighting of the discharge lamp, and one of the MOSFETs
In a half-bridge inverter type discharge lamp lighting device in which a switching improvement capacitor or a snubber circuit is connected between the drain and source of the T, even when the discharge lamp is removed between the output terminals of the inverter circuit, the MOSFE
A discharge lamp lighting device characterized in that an inductance element for flowing a slow phase current is connected to the T.