JPH031920Y2 - - Google Patents

Description

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

When lighting a discharge lamp, the filament is sometimes preheated with direct current. In addition, when dimming a discharge lamp, if the lamp current is periodically intermittent and the ratio of the time when the lamp current is flowing and the time when it is not flowing within one intermittent period is changed, It is known that dimming is possible. Conventionally, during this dimming, when the lamp current is cut off, a DC current is simultaneously applied to the filament to start preheating. However, if preheating is started immediately using direct current in this way, the discharge lamp is still activated at that point, so the voltage drop due to the direct current in the impedance inserted in the preheating circuit will be applied to both ends of the discharge lamp. When applied, a cataphoresis phenomenon could occur. When such a cataphoresis phenomenon occurs,
It will not be possible to dim the light as desired, and it will also shorten the life of the discharge lamp.

The purpose of this invention is to prevent the occurrence of cataphoresis as much as possible when controlling the light by changing the duty of the lamp current in a configuration in which the lamp is preheated by direct current.

This idea is that when the lamp current is interrupted for dimming, the filament preheating current is stopped flowing immediately after the lamp current is cut off, and the preheating current is started flowing after the required time has elapsed. Features. By the time this amount of time has elapsed,
The activation of the discharge lamp when the lamp current is cut off subsides,
Therefore, even if a voltage drop due to the impedance inserted in the preheating circuit is subsequently applied to the discharge lamp, the discharge lamp will not be activated, and the cataphoresis phenomenon will not occur.

An embodiment of this invention will be described with reference to the drawings. The figure shows an example in which a high frequency inverter is used as a lighting power source. 1 is a high frequency inverter, transistor 2
and an oscillation transistor 3. 4 is a primary coil 5, 6 of the oscillation transistor 3 is a secondary coil, 7 is a feedback coil, 8 is a DC power terminal for a high frequency inverter, 9 is a discharge lamp,
10 is a DC power terminal for preheating. A switching element, such as a transistor 11, is inserted between the DC power supply terminal 8 and the high frequency inverter 1, and when it is on, the high frequency inverter 1 operates and induces high frequency high voltage in the secondary coils 5 and 6 of the oscillation transistor 3. let 12 is transistor 1
This terminal is a terminal to which a signal to turn on and off 1, that is, a dimming signal of about 1KHz, is given to this terminal 12.
An H level input and an L level input are alternately applied to the input signal. When an H level input is applied, the transistor 11 is turned off, and when an L level input is applied, the transistor 11 is turned on. By appropriately changing the duty of one of these inputs to the other, the ratio of the lighting time to the lighting time within the flashing cycle of the discharge lamp can be adjusted as described later.

Reference numeral 13 denotes a switching element such as a transistor, which is turned on by supplying a base current from the DC power supply terminal 8 when the transistor 11 is on.
is a delay circuit composed of a capacitor 15 and a resistor 16. Then, when the transistor 13 turns from on to off, the capacitor 15 begins to be charged via the resistor 16, and when the time determined by these time constants has elapsed, a predetermined voltage is reached.
This is connected to a switching element such as a transistor 18 via a constant voltage element (Zener diode) 17.
joins the base of and turns it on. When the transistor 13 is turned on from off, the capacitor 15 is instantly discharged via the transistor 13 which has been turned on.

For the DC power terminal 10, the filament 9
A, the secondary coil 6, the filament 9B, the secondary coil 5, and the transistor 18 are connected in series. Therefore, when transistor 18 is on, a direct current flows through the series circuit and each filament is preheated. At this time, direct current from the direct current power supply terminal 10 flows through the secondary coils 5 and 6 in opposite directions. Therefore, the direction of the magnetic field generated by the current flowing through each secondary coil is also reversed, so that the iron core of the transistor 3 is not biased.

When the transistor 18 is off (at this time, the transistor 11 is on), the voltage induced in the secondary coil 6 is applied to the discharge lamp 9, and a lamp current flows. Further, if a capacitor 19 is connected between the secondary coil 5 and the discharge lamp 9 as shown in the figure, the induced voltage of the secondary coil 5 is also applied to the discharge lamp 9, and a lamp current flows.

In the above configuration, it is assumed that the transistor 11 is turned on and off at a frequency of, for example, 1 KHz by a dimming signal applied to the terminal 12. When this is turned on and off, the discharge lamp 9 repeatedly turns on and off. Therefore, by changing the duty of the H level input and the L level input of the dimming signal, the lighting time is changed, and thereby the discharge lamp 9 is dimmed.

On the other hand, when the transistor 11 is turned on,
Transistor 18 is immediately turned off. Therefore, when the discharge lamp 9 is in the lit state, no preheating current flows through the filament. Next, when the transistor 18 is turned off, the transistor 18 remains off until the delay time of the delay circuit 14 (for example, about 0.4 msec) has elapsed. Then, when the delay time has elapsed, the transistor 18 is turned on, and from this point on, a preheating DC current begins to flow through the filament. During this delay time, the activation of the discharge lamp 9 is subdued. Therefore, after this, by turning on the transistor 18, the DC current from the DC power supply terminal 10 is transmitted to both filaments 9A, 9B and both secondary coils 5,
Even if these voltage drops are applied to both ends of the discharge lamp 9 due to the voltage flowing through the discharge lamp 6, no direct current will flow into the discharge lamp 9 due to this voltage.
Therefore, the cataphoresis phenomenon also no longer occurs. Needless to say, if the delay is 1 msec or more, the direct current preheating current will not flow completely during dimming, and the cataphoresis phenomenon will no longer occur.

Note that after the discharge lamp 9 is turned off, if the preheating current is allowed to flow through the filament after the delay time has elapsed,
As the preheating current supply time is shortened accordingly,
The input current can be reduced, and the temperature rise of the transistor 3 can also be suppressed accordingly.

As detailed above, according to this invention, in a lighting device that preheats a filament with direct current,
When the lamp current is periodically intermittent and the discharge lamp is periodically flashed and dimmed, the cataphoresis phenomenon caused by activation of the discharge lamp immediately after the discharge lamp is turned off can be reliably prevented. Therefore, the dimming of the discharge lamp is ensured, and the life of the discharge lamp is not impaired.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of this invention. 1
...High frequency inverter, 8...Power terminal, 9...
Discharge lamp, 10... Power supply terminal for preheating, 12... Terminal to which a dimming signal is given, 14... Delay circuit, 15
...Switching element.

Claims (1)

[Scope of utility model registration request] a switching element that turns on a preheating circuit of a discharge lamp when the discharge lamp is turned off and turns it off when the discharge lamp is turned on;
a lighting power source that dims the discharge lamp by periodically blinking the discharge lamp and changing the ratio between the lighting time and the extinguishing time; and a lighting power source that controls the discharge lamp by the lighting power source. A discharge lamp lighting device comprising a delay circuit that turns on the switching element, which has been in the OFF state, with a delay when the state shifts from the lighting state to the extinguishing state.