JPH0546679B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a drive circuit for a hot cathode type deuterium discharge tube, and particularly for use in ultraviolet rays such as spectrophotometers that require easy lighting and a long life. The present invention relates to a drive circuit for a hot cathode type deuterium discharge tube suitable for use as a light source.

[Background of the invention]

In a hot cathode type deuterium discharge tube, electrons are emitted from the cathode due to the collision of cations.
At the same time, the cathode material itself is also emitted in an atomic state, splashes or diffuses, and adheres to the tube wall. This phenomenon in which cathode material is scattered in all directions by fine particles due to discharge is called cathode scattering effect.

The amount of cathode material scattered by the cathode splash action increases in proportion to the discharge time, increases and decreases with the discharge current, increases with the cathode fall, and varies depending on the cathode material and the type of gas.

The life of a discharge tube is often determined by this splash effect. In other words, in addition to the cathode collapsing due to this action, the luminous intensity of the discharge tube is reduced due to the blackening of the tube wall, or when the cathode material adheres to the tube wall, it adsorbs the filler gas and gradually lowers the atmospheric pressure. let These reasons limit the life of the discharge tube.

From the above, it can be said that preventing the cathode material of the discharge tube from scattering is the most important matter for realizing a long-life discharge tube.

Traditionally, two types of discharge tubes have been used, part 1
One is shown in Figure 4a and the other in Figure 4b. The only difference in this structure is whether the cathode and shield plate are shot or not.

In the discharge tube shown in FIG. 4a, it is difficult to light up during initial lighting, and a lighting failure accident may occur. The reason for this is that at the time of initial lighting, a high pulse voltage is instantaneously applied to effectively generate positive ions and emit light through the ionization phenomenon accompanying the excitation of gas molecules, but since the shield plate and cathode are shot, This is because some of the cations from the anode flow through the shield plate, and cations sufficient to cause arc discharge cannot rush into the cathode, so the discharge tube does not emit light. Note that this tendency is particularly strong in a deteriorated cathode. This is because although a coating is provided on the cathode filament to improve thermionic emission, the amount of scattering of this coating largely depends on the discharge time and the increase/decrease of the current. In other words, considering a constant current, the longer the discharge tube is used, the more the oxide coating scatters, the more the resistance of the filament increases, and the flow bypasses the filament, resulting in no light emission and lighting failure. There is.

As a countermeasure to this problem, the cathode and shield plate's shorts are removed as shown in Figure 4b. According to this lighting method, the shield plate is completely floating, so the path through which the anode current flows is limited to the cathode, and all the cations concentrate on the cathode and rush into it, making it easy to emit light and turn on the light. do. However, as mentioned above, this results in an increased amount of oxidized coating flying off the cathode. That is, the lighting method shown in FIG. 4b is easy to light up, but has the disadvantage of short life.

To summarize the above points, the discharge tube shown in FIG. 4a is difficult to light up, but has a long life. As the discharge tube deteriorates (particularly the oxidized coating applied to the cathode), the difficulty in turning on the lamp increases significantly. On the other hand, although the discharge tube shown in FIG. 4b is easy to light, it has the disadvantage of short life.

[Purpose of the invention]

An object of the present invention is to provide a drive circuit for a hot cathode type deuterium discharge tube that facilitates lighting of a deuterium discharge tube, prevents scattering or diffusion of the oxide coating on the cathode, and has a long life. be.

[Summary of the invention]

The amount of oxide coating applied to the cathode of a deuterium discharge tube determines ease of lighting and life. The degree of scattering of this oxidized coating depends on the size of cations that rush from the anode to the cathode while the deuterium discharge tube is kept lit. That is, the greater the amount of cations, the greater the scattering of the oxide coating applied on the cathode. On the other hand, even if large cations are generated from the anode at the moment of lighting, thermionic emission due to self-heating of the cathode (10V applied before lighting, 7V applied after lighting) becomes a cushion and scatters the oxide coating applied on the cathode. It's not worth it. Based on the theoretical support described above, we conducted an experiment to confirm that, as a means to eliminate the scattering of the oxide coating, we left the cathode and shield plate in an open state only at the start of lighting, and caused large cations to flow toward the cathode. This makes it easier to light up, and after lighting, that is, while the lighting is maintained, one end of the cathode and the shield plate are shunted to divert the cations to the shield plate side, reducing the number of cations heading toward the cathode, and also reducing the scattering of the oxide coating applied on the cathode. This is a deuterium discharge tube that is easy to light and has a long life.

[Embodiments of the invention]

FIG. 1 is a configuration diagram showing an embodiment of a drive circuit for a hot cathode type deuterium discharge tube according to the present invention. In the figure, a hot cathode type deuterium discharge tube is composed of an anode 1, a shield plate 2, and a cathode filament 3, and the shield plate 2 is connected to the cathode filament 3 and the ground line 10 via an inductance L. Both ends of the cathode filament 3 are connected to a heating power source 12
It is connected to the. And cathode filament 3
is constantly heated by the power supply voltage Vf, and thermionic electrons are constantly emitted from the cathode filament 3.

On the other hand, a trigger voltage Vs from a main power source 14 is applied to the anode 1 and the cathode filament 3 via a switch S1, and a current from a constant current source 16 is supplied. That is, the anode 1 is connected to the main power source 14 via a diode D2 and a switch S1, and is also connected to a constant current source 16 via a diode D1 and a resistor Rs. moreover,
At both ends of the main power supply 14, a switch S1, a resistor R1,
Capacitor C is connected. This capacitor C is charged with the trigger voltage of the main power supply 14 when the switch S1 is connected to the contact a. When the switch S1 is switched to the contact b side in response to the lighting start command, the charge charged in the capacitor C is discharged for a certain period of time via the resistor R1 and the diode D1. That is, main power supply 14, switch S1, resistor R1, capacitor C, diode D
Reference numeral 2 is configured as a high voltage pulse signal generating means for applying a high voltage pulse signal between the anode 1 and the cathode filament 3. Further, a current of 300 mA is supplied to the anode 1 and the cathode filament 3 from a constant current source 16. That is, constant current source 1
6. The resistor Rs and the diode D1 are configured as constant current supply means.

In the above configuration, switch S1 is activated before lighting starts.
While charging the capacitor C with contact a side, the cathode filament 3 is turned on by the heating power source 12.
Heat for more than 2 seconds. Thereafter, when the switch S1 is switched to the contact b side in response to the lighting start command, the charge charged in the capacitor C1 is discharged, a high voltage pulse signal is applied between the anode 1 and the cathode filament 3, and the anode 1 A trigger current flows through the shield plate 2 and the cathode filament 3. At this time, a portion of the trigger current flows from the shield plate 2 to the ground line 10 via the inductance L. When the trigger current flows through the inductance L, the voltage across the inductance L increases in accordance with the transient phenomenon of the trigger current. When the voltage across the inductance L increases, the shield plate 2 and the cathode filament 3
The voltage between the shield plate 2 and the cathode filament 3 also becomes high, which is equivalent to an electrically open state between the shield plate 2 and the cathode filament 3.

If the trigger current continues to flow in this condition,
The trigger current flows concentratedly in the cathode filament 3, and the discharge tube is in a state where it is easy to light up, similar to the case without the shield plate 2. When the discharge tube starts discharging due to the trigger current, a constant current is supplied from the constant current source 16 to the anode 1, and a steady state is established.

When the discharge tube lights up and enters a steady state, the current flowing from the anode 1 to the shield plate 2 and cathode filament 3 becomes constant, and the voltage across the inductance L also becomes low. As a result, the voltage between the shield plate 2 and the cathode filament 3 also decreases, which is equivalent to the shield plate 2 and the cathode filament 3 being electrically shorted. When the shield plate 2 and the cathode filament 3 become at the same potential, the current from the anode 1 is divided into the shield plate 2 and the cathode filament 3.

Therefore, when the discharge tube reaches a steady state,
Since the current flowing through the cathode filament 3 is reduced, scattering of the oxide coating applied to the cathode filament 3 can be prevented, and a long-life deuterium discharge tube can be realized.

As shown in Fig. 2, the hot cathode type deuterium discharge tube used in the drive circuit of the hot cathode type deuterium discharge tube configured in this way has the terminals of the shield plate 2 placed outside the discharge tube independently. and an inductance 4 may be provided between this terminal and one of the terminals of the cathode filament 3, and
As shown in FIG. 3, an inductance 4 may be provided between the shield plate 2 and the cathode filament 3 within the discharge tube.

〔Effect of the invention〕

As is clear from the above explanation, according to the drive circuit for a hot cathode type deuterium discharge tube according to the present invention, the discharge tube can be easily lit and can have a long life.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a drive circuit for a hot cathode deuterium discharge tube according to the present invention, and FIGS. 2 and 3 are diagrams showing an example of a hot cathode deuterium discharge tube used in the drive circuit. Configuration diagram showing an example, No. 4
The figure is an explanatory diagram showing an example of a conventional method for driving a hot cathode type deuterium discharge tube and its configuration. 1... Anode, 2... Shield plate, 3... Cathode filament, 4... Inductance, 5... Thyristor.

Claims (1)

[Claims] 1 An anode, a cathode connected to a heating power source, and a shield plate inserted between the anode and the cathode and connected to the ground line of the heating power source, wherein the cathode is made of an oxide or a monoatomic adhesive material. In hot cathode type deuterium discharge tubes, a high voltage pulse signal generation means applies a high voltage pulse signal for a certain period of time between the anode and cathode at the start of lighting, and a constant current means applies a constant DC current to the anode and cathode. A hot cathode type heavy loader comprising a supply means and an inductance inserted between the shield plate and the ground line to generate a voltage between the shield plate and the ground line in accordance with the high voltage pulse signal. Hydrogen discharge tube drive circuit.