JPH034489A - Lighting circuit for discharge lamp - Google Patents

Abstract

PURPOSE:To lower a discharge lamp voltage between terminals so as to prevent deterioration of the discharge lamp caused by ion impact by providing an inductive variable reactance means and a reactance control means, and raising resonance frequency during preheating to above the frequency of normal lighting. CONSTITUTION:In a discharge lamp TB provided with filaments F1, F2 a tap is provided to the primary coil L of a drive transformer, and the discharge lamp is connected to the (b) side of the tap during preheating after actuation and is switched to the (a) side of the tap during normal lighting after preheating. Switching of the tap is carried out by actuation of a relay with a relay driving current supplied from a timer circuit. In this case, a resonance frequency bigger than the resonance frequency of normal lighting is obtained by switching of the tap on the first or second side of the drive transformer. Thus, voltage lowering that occurs during preheating between both terminals of a resonance coil L is big so that the voltage of the discharge lamp TB which is applied between terminals is decreased. Damage of the discharge lamp by ion impact is thereby prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a lighting circuit for a discharge lamp configured to perform appropriate lighting without biasing the discharge lamp by controlling the frequency of self-help oscillation. It is related to.

[Problems to be Solved by the Invention] Therefore, in view of the above-mentioned points, an object of the present invention is to obtain a predetermined preheating current during the preheating period, and at the same time suppress the rise in the voltage between the terminals of the discharge lamp to ensure proper lighting. An object of the present invention is to provide a lighting circuit for a discharge lamp that makes it possible.

[Prior Art] In the conventional lighting circuit for a discharge lamp having a self-supporting half bridge, the oscillation frequency during the preheating period is not appropriate, so the voltage drop in the resonant coil is not large enough. As a result, an inconvenience occurred in that the voltage between the terminals of the discharge lamp increased more than necessary. In other words, even during the period when a preheating current is flowing through the filament of the discharge lamp (for example, 0.8 seconds), a voltage of, for example, 200 V or more is applied between both filaments, which can cause deterioration of the discharge lamp due to ion bombardment. There was a drawback.

[Means for Solving the Problems] The present invention provides a lighting circuit for a discharge lamp in which the frequency during normal lighting is determined by a resonance coil and a capacitor, in which an inductive variable reactance means is connected in series with the resonance coil. and reactance control means for setting the reactance of the variable reactance means to a large value during the preheating period, and during the preheating period, the resonance frequency is increased from the frequency during normal lighting to lower the voltage between the terminals of the discharge lamp. It is something.

The present invention also provides a lighting circuit for a discharge lamp in which the frequency during normal lighting is determined by a resonant coil and a capacitor, in which a first winding connected in series with the resonant coil and a capacitor normally A second winding during lighting, a pair of oscillation sustaining circuits connected to each of the second windings, and a winding control means for setting the number of turns of the two windings to a small value during a preheating period. During the preheating period, the voltage between the terminals of the discharge lamp may be lowered by increasing the resonant frequency from the frequency during normal lighting.

[Function] In the present invention, by switching the tap on the primary side or secondary side of the drive transformer, a resonance frequency higher than the resonance frequency during normal lighting is obtained. Thus, during the preheating period, the voltage drop occurring between both terminals of the resonant coil becomes large, so that the voltage between the terminals of the discharge lamp decreases, thereby making it possible to prevent damage to the discharge lamp due to ion bombardment.

[Example] Hereinafter, the present invention will be explained in detail based on Examples.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In this figure, TB is a discharge lamp, and F and F are filaments. In this embodiment, a tap is provided in the primary winding L3 of the drive transformer, and during the preheating period after startup
(approximately 0.8 seconds), it is connected to the tap b side, and then during normal lighting, it is switched to the tap a side. This tap switching is performed by activating a relay using a relay drive current supplied from a timer circuit (not shown).

Next, the operation of this embodiment will be explained.

As mentioned above, during the preheating period (approximately 0.8 seconds), the tap b side of the primary winding is selected in advance.

First, when the power supply voltage is applied between the A and B terminals, the resistor R2
The capacitor CI is charged via the diac S
FET2 is turned on when the SS threshold is exceeded. Then, the charge stored in capacitor C1 is transferred to diode D.
, and at the same time each coil L2. L3
．． Push-pull oscillation starts due to the inductive action of L4.

At this time, the primary winding L3 of the drive transformer has tap b
Since the side is selected, magnetic saturation occurs and oscillation occurs at the first resonant frequency f+ (for example, 80 ktlz).

In other words, this first resonant frequency f is the primary winding,
The second resonant frequency tz (
For example, it is larger than 45kl(z) (f+>
f2).

Therefore, the burden ratio of the power supply voltage on the coils L1 and L3 becomes larger than that during normal lighting, and as a result,
The voltage between the terminals of the discharge lamp will be lower than the voltage during normal lighting. This can prevent deterioration of the discharge lamp due to ion bombardment.

After the predetermined preheating period has elapsed, the drive transformer 1
Since the tap of the next winding is switched to the a side, the magnetic saturation in the same winding is eliminated and the resonant frequency drops to fz (for example, 45 kHz). In this way, the voltage between the terminals of the discharge lamp also increases, and the normal lighting state is maintained.

FIG. 2 is a circuit diagram showing another embodiment to which the present invention is applied. In this embodiment, unlike the embodiment shown in FIG. 1, the taps of the two secondary windings L2 and L4 are switched.

In the embodiment shown in FIG. 2, during the preheating period (e.g.
．． 8 seconds), select the tap b side and set the first resonance frequency ft.
(e.g. 80 ktlz). Next, after a predetermined preheating period has elapsed, the tap is switched to the a side, and normal lighting is performed at the resonance frequency tz (for example, 45 kHz).

The reason why the resonant frequency is higher on the tap b side than on the tap a side is that a low voltage closer to the threshold voltage of FETI and FET2 occurs at tap b, and therefore 0N10FF of the FET is performed faster. It is from.

[Effects of the Invention] As explained above, according to the present invention, the resonant frequency during the preheating period can be made higher than the resonant frequency during normal lighting, so the voltage between the terminals of the discharge lamp can be lowered and the voltage caused by ion bombardment can be reduced. Deterioration can be prevented.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are circuit diagrams each showing an embodiment of the present invention.

Claims (1)

[Scope of Claims] 1) In a lighting circuit for a discharge lamp in which the frequency during normal lighting is determined by a resonance coil and a capacitor, an inductive variable reactance means connected in series with the resonance coil, and during a preheating period. and reactance control means for setting the reactance of the variable reactance means to a large value, and during the preheating period, the resonant frequency is raised from the frequency during normal lighting to lower the voltage between the terminals of the discharge lamp. Lighting circuit for discharge lamps. 2) In a discharge lamp lighting circuit in which the frequency during normal lighting is determined by a resonance coil and a capacitor, a first winding connected in series with the resonance coil and inductively coupled to the first winding. a pair of second windings connected to each other, a pair of oscillation sustaining circuits connected to each of the second windings, and a winding control means for setting the number of turns of the second winding to a small value during a preheating period. A lighting circuit for a discharge lamp, characterized in that during a preheating period, the resonant frequency is increased from the frequency during normal lighting to lower the voltage between terminals of the discharge lamp.