JPS5918638Y2 - Discharge lamp lighting circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a lighting circuit for a discharge lamp, and more particularly to a lighting circuit in a discharge lamp power source that can control the lighting current to adjust the brightness of the discharge lamp.

FIG. 1 shows a lighting circuit for a conventional discharge lamp.
Problems in conventional lighting circuits will be explained with reference to the drawings.

In FIG. 1, reference numeral 2 denotes a discharge lamp, whose anode is connected to a voltage source Vt via a lighting current control circuit 4 and a resistor, and whose cathode is connected to the secondary side of a trigger coil 6. It is grounded through.

The lighting current control circuit 4 includes a variable resistor 8 for current control, and by adjusting the resistance value of the variable resistor 8, the discharge current flowing through the discharge lamp 2 can be controlled, thereby adjusting the brightness of the discharge lamp. can do.

A series circuit of a lighting switch 10 and a capacitor 12 is connected to the primary side of the trigger coil 6, and the capacitor 12 is connected between a voltage source □ and ground.

In addition, a capacitor 14 is connected between the voltage source 8 and the ground, and the voltage source side terminal of this capacitor 14 is
It is connected to the anode side of the discharge lamp 2.

In such a conventional lighting circuit, the lighting switch 1
0, the charge in the capacitor 12 charged by the voltage source VH is discharged through the switch 10 and the primary side of the trigger coil 6, and as a result, a voltage is induced on the secondary side of the trigger coil 6. Ru.

Therefore, capacitor 14 charged by voltage source V6
The charged charges are transiently discharged through the discharge lamp 2, and as a result, a large current flows through the discharge lamp 2, and the discharge lamp 2 is turned on.

By lighting the discharge lamp 2, the internal resistance of the discharge lamp 2 decreases, a discharge current is supplied from the voltage source VL, a stable state is reached, and the discharge lamp can be maintained in the lighting state. Become.

In such a lighting circuit, the discharge current can be controlled by adjusting the resistance value of the variable resistor 8.
If the brightness of the discharge lamp 2 can be adjusted and the variable resistor 8 is set so as to set the discharge current to a small value and dim the brightness of the discharge lamp 2, the above-mentioned discharge lamp At the time of lighting, there was a risk that the discharge lamp would not reach a stable state and would turn off after being turned on temporarily.

That is, when the lighting switch 10 is turned on, a transient current is supplied to the discharge lamp 2 to temporarily light it, but if the discharge current supplied from the voltage source VL via the lighting current control circuit 4 is small, Because the internal resistance of the discharge lamp 2 has not decreased to a value sufficiently small with respect to the discharge current to maintain the discharge state, a stable state may be reached and the lamp may go out.

This invention was made in view of the above-mentioned circumstances, and according to this invention, it is possible to provide a lighting circuit for a discharge lamp that can flow the maximum discharge current during lighting.

An embodiment of the discharge lamp lighting circuit of this invention will be described below with reference to the drawings.

In Figure 2, 2 is a discharge lamp, 6 is a trigger coil, and 10
12 and 14 represent a lighting switch, and 12 and 14 represent a capacitor, and their connection relationship is substantially the same as that of the conventional lighting circuit as shown in the figure, so a detailed explanation thereof will be omitted.

The lighting current control circuit in FIG.
transistors 16, 18, resistor 20 and variable resistor 22
Further, to this circuit is added a lighting stabilization circuit consisting of a relay 24, a normally open contact 26 of this relay 24, a Zener diode 28 and a resistor 30.32.

That is, the first transistor 1 is connected to the anode of the discharge lamp 2.
The emitter of 6 is connected, and this collector is connected to the voltage source Vt,
It is connected to the.

The base of the first transistor 16 is connected to the emitter of the second transistor 18 via a resistor 20, the collector of this transistor is connected to a voltage source 1, and the base is connected to a variable voltage source for controlling the discharge current. It is likewise connected to the voltage source vL via the resistor 22.

By adjusting the variable resistor 22, the base voltage of the second transistor 18 changes, and therefore the base voltage of the first transistor 16 changes, thereby changing the internal resistance of this first transistor 16, which causes this transistor to change. It is possible to control the discharge current flowing through.

A normally open contact 26 of a relay 24 is connected in parallel to the variable resistor 22 for controlling the discharge current, and a resistor 30 and a relay 24 are connected in series circuit on the secondary side of the discharge lamp 2 and the trigger coil 6. series circuit is connected.

A resistor 32 is inserted between the relay contact 26 and the resistor 30, and a Zener diode 28 is connected in parallel to the relay 24.

The series circuit of the resistor 30 and Zener diode 28 is a constant voltage circuit for driving the relay 24, and the relay contact 26 short-circuits the variable resistor 26 when the discharge lamp is turned on to maximize the base voltage of the second transistor 18. This is provided to minimize the internal resistance of the first transistor 16.

The lighting circuit according to one embodiment of this invention is configured as described above and operates as follows.

Before the lighting switch 10 is closed, the discharge lamp 2
is in a non-lit state, and its internal resistance is at its maximum.

Therefore, the power supply voltage (18) is applied to a constant voltage circuit consisting of a resistor 30 and a Zener diode 28, and a voltage regulated by this constant voltage circuit is applied to the relay 24.

As a result, the relay 24 is activated and its normally open contact 26 is maintained in a closed state, the current control variable resistor 22 is shorted, and the internal resistance of the first transistor 16 is minimized.
A state can be maintained in which the maximum discharge current can be provided from the voltage source (1).

When the lighting switch 10 is closed, the capacitor 14
is discharged through the discharge lamp 2, and the discharge lamp 2
internal resistance begins to decrease, and the maximum discharge current begins to be supplied from the voltage source (1).

After this initial lighting state continues, that is, usually 3 to 4
After about a minute has passed, the unstable discharge state at the initial stage of lighting will reach a stable state in which the internal resistance of the discharge lamp has become sufficiently small.

When the discharge state of the discharge lamp becomes stable and reaches steady lighting,
Since the internal resistance becomes sufficiently small, the voltage between the terminals of the discharge lamp decreases.

As a result, the voltage applied to the relay 24 decreases,
Relay 24 is deactivated and its relay contacts 26 are opened.

Therefore, the second transistor 18
Since a voltage is applied from the voltage source V+ to the base of the second transistor 18, the base voltage changes according to the set value of the variable resistor 22, and as the second transistor 18 changes from the saturated state to the activated state. reach.

As a result, the internal resistance of the first transistor 16 changes in the direction of increasing, and the discharge current flowing through this transistor 16 decreases.

At this time, the discharge lamp 2 has already reached a steady lighting state, so it does not turn off even when the discharge current decreases, and its brightness can remain in a dark state.

As described above, according to the discharge lamp lighting circuit of this invention, the maximum discharge current is supplied from the voltage source to the discharge lamp from the initial stage of discharge of the discharge lamp until reaching the steady lighting time, and the discharge current starts when the discharge lamp is steadily lit. Since the discharge lamp is controlled to a predetermined value, it is possible to eliminate the possibility that the discharge lamp will go out at the initial stage of discharge, and when the discharge is stable, it is possible to turn on the lamp at a preset brightness.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional discharge lamp lighting circuit, and Figure 2 is a circuit diagram of a conventional discharge lamp lighting circuit.
FIG. 1 is a circuit diagram showing an embodiment of a discharge lamp lighting circuit of the present invention.

Claims (1)

[Scope of utility model registration request] A transistor is connected in series between a power source and a discharge lamp, and the internal resistance of the transistor is controlled by a variable resistor that adjusts a control voltage applied to the base of the transistor.
In a discharge lamp circuit in which the brightness of a discharge lamp can be adjusted by controlling a discharge current, a relay that operates at a voltage higher than the steady lighting voltage of the discharge lamp and deenergizes when the voltage reaches the discharge lamp is connected to the discharge lamp. A discharge lamp lighting circuit connected between electrodes, the relay contact being connected in parallel to the variable resistor, and short-circuiting the variable resistor at the beginning of discharge of the discharge lamp.