JPH01209921A - Protecting circuit for firing lamp - Google Patents

Abstract

PURPOSE:To protect a lamp against a rush current and to suppress the deterioration of a thermistor by closing a normally open contact provided in parallel with the thermistor connected in series with the lamp after a predetermined time is elapsed from the time of initiating to fire the lamp. CONSTITUTION:A fuse 16, a lamp 12 and a thermistor 18 are connected in series with an AC power source 14A. Bypass circuits 22, 23 are composed through a normally open contact 20 at the thermistor 18. The contact 20 forms a relay circuit 24 to be energized by a coil 26. When the lamp 12 is fired, a small current flows from the power source 14A by the negative resistance of the thermistor 18 to suppress the rush current of the lamp 12, and a small current also flows to the coil 26. The current increases upon rising of the temperature of the thermistor 12. When the current of the coil 26 rises at a predetermined value or more, the contact 20 is closed to short-circuit the thermistor 18, thereby supplying a predetermined current to the lamp 12. Thus, the lamp 12 is protected against the rush current, thereby preventing the thermistor 18 from consuming.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lamp lighting protection circuit that reduces inrush current at the start of lamp lighting.

[Prior art]

Generally, the filament of a lamp, for example a halogen lamp, has a proportional relationship between its temperature and its resistance value, and when it is off, the resistance value is low. 14 compared to the current value of
~15 times the current (rush current) will flow. It is well known that the filament is likely to break due to this initial large current. Note that if the lighting continues, the resistance value increases as the temperature rises, and the current value becomes stable at the rated value.

Here, in order to reduce the rush current at the start of lighting, it has been considered to connect a thermistor in series with the halogen lamp. That is, the temperature and resistance value of the thermistor are inversely proportional, and the resistance value is high at the start of lighting, so as shown in FIG. 7, not much current flows, and as a result, the rush current can be reduced. Further, as the lighting state continues and the temperature rises, the resistance value decreases, allowing the rated current to flow through the halogen lamp. This can extend the life of the halogen lamp. Currently, there is a product on the market that can achieve the above effect by simply inserting it between a light bulb and a socket (CIRTIFIED BN).
"Thermistor button (product name)" manufactured by ERGY SYSTBMS INC1 (USA). According to this, it is easy to assemble and the effect can be achieved without making any improvements to the existing device.

[Problem to be solved by the invention]

However, with this type of circuit configuration, current always flows through the thermistor (including commercially available thermistor buttons) while the halogen lamp is on, and although the life of the halogen lamp is extended, the thermistor itself may be damaged by heat. This thermistor also needs to be protected.

In consideration of the above-mentioned facts, the present invention aims to provide a lamp lighting protection circuit that can protect both the lamp and the thermistor that protects the lamp, and extend the life of the entire circuit.

[Means to solve the problem]

The lamp lighting protection circuit according to the present invention is a lamp lighting protection circuit that includes a thermistor whose resistance value decreases as the temperature rises and is connected in series with the lamp to reduce the rush current when the lamp starts lighting. The lamp includes a normally open contact connected in parallel to the thermistor, and conduction means for closing the normally open contact after a predetermined period of time has elapsed from the start of lighting the lamp.

[Effect]

When the lamp starts lighting, the temperature is low, so the resistance value of the thermistor is high. This reduces the rush current into the lamp. After the lamp is turned on, the resistance value of the thermistor decreases as the temperature rises, and the current flowing into the lamp gradually increases until it approaches the rated current.

Here, in the present invention, the normally open contact is closed by the conduction means after a predetermined period of time from the start of lighting of the lamp, and the bypass circuit is made conductive. As a result, both ends of the thermistor are short-circuited, and no current flows to the thermistor, but the current flows in a bypass manner, so that damage to the thermistor due to heat while the lamp continues to be lit can be prevented.

In this way, in the present invention, the thermistor not only protects the lamp, but also bypasses the current when the normally open contact is conductive, so the thermistor itself can also be protected, and the life of the entire circuit can be significantly extended. can.

〔Example〕

FIG. 1 shows a lamp lighting protection circuit 10 according to this embodiment. .

In this embodiment, a halogen lamp 12 is used as the lamp, and is connected to an intermediate portion of an AC power line 14.

Further, a fuse 16 and a thermistor 18 are connected in series to this AC power line 14. The thermistor 18 is an element having a property that temperature and resistance are inversely proportional, and its resistance value is high when the halogen lamp 12 is off. Therefore, when current flows through the AC power line 14 in this state, the resistance of the thermistor 18 prevents much current from flowing through the halogen lamp 12, as shown in FIG.
Inrush current can be reduced.

Both ends of the thermistor 18 are connected by bypass wires 22 and 23 via a normally open contact 20 (bypass circuit)
. This normally open contact 20 constitutes a part of a relay circuit 24, and the coil 26 which constitutes the relay circuit 24 together with the normally open contact 20 which closes this normally open contact 2.0 by magnetic force.
are arranged corresponding to the normally open contacts 20. coil 26
The two ends of the halogen lamp 12 and the thermistor 1 are connected between one input terminal 14A of the AC power line 14 and the fuse 16.
8, respectively.

Therefore, when a current flows through the AC power line 14, a portion of the current also flows to the coil 26, generating magnetic force, which allows the normally open contact 20 to be closed. In this case, the alternating current flows to the coil 26, and the thermistor 18
Since the current value is small in the initial state of lighting of the halogen lamp 120, a slight rise time is required until the current value for generating magnetic force (the relay operating current value shown in Fig. 2) is reached, and this time ( (See time t in FIGS. 2 and 3) The closing operation of the normally open contact 20 is delayed.

Here, when the normally open contact 20 is brought into a closed state, the bypass wires 22 and 23 at both ends of the thermistor 18 are brought into a conductive state,
Current will no longer flow to the thermistor 18. Note that this delay time is set after the inrush current exceeds the maximum value, and as a result, the value of the current flowing through the halogen lamp 12 has characteristics as shown by the solid line in FIG.

The operation of this embodiment will be explained below.

When a current flows from the halogen lamp 12 to the AC power line 14 when the halogen lamp 12 is turned off, the halogen lamp 12 starts lighting up, but since the temperature of the thermistor 18 is low, the resistance value of the thermistor 18 is high, and as a result, the current flows to the halogen lamp 12. The value is also small. When the halogen lamp 12 continues to be lit, the temperature of the thermistor 18 gradually increases, and the resistance value of the thermistor 18 itself gradually decreases due to the characteristics of the thermistor 18. As the resistance value decreases, the current value flowing to the halogen lamp 12 increases.

Here, in this embodiment, when a current is passed through the AC power line 14, a current also flows through the coil 26. However, in the initial state of lighting the halogen lamp, the current value flowing through the coil 26 is small, and there is no magnetic force to close the normally open contact 20. Here, when a predetermined time t has elapsed, the current value flowing to the coil 26 exceeds the relay operating current value, the normally open contact 20 is closed, and the bypass wires 22 and 23 are brought into a conductive state. When the bypass line 22.23 is made conductive, current passes through the bypass line 22.23, so the thermistor 18
Current will no longer flow to. This prevents current from constantly flowing to the thermistor 18 while the halogen lamp 120 is on, and the thermistor 18 can be protected.

Furthermore, at the start of protection of this thermistor 18 (after time 1), the maximum value of the inrush current (see Figure 6) that would occur if the thermistor 18 is not installed is exceeded, and the current flowing to the halogen lamp 12 exceeds the maximum value. The cost is not so high, and the halogen lamp 12 can also be protected as before.

In this way, in this embodiment, the inrush current to the halogen lamp 12 can be reduced, and when the inrush current generation period is exceeded, the current flowing to the thermistor 18 is also blocked. The life of the entire lamp lighting circuit can be extended.

Although, in this embodiment, an alternating current is applied to the power source, the same effect can be obtained when a direct current is applied to the power source as shown in FIG. However, in the case of a DC power supply, current easily flows to the coil 26, so the resistor 28 connected in series
and a capacitor 30 is connected in parallel to both ends of the coil 26,
It is necessary to control the current value flowing to the coil 26 using the charging time of the capacitor 30, and delay the rise time to the relay operating current, as shown in FIG. That is, as shown in FIG. 5, at the beginning of lighting the halogen lamp, the current is dispersed in both the capacitor 30 and the coil 26, and when the capacitor 30 is fully charged, the entire current flows to the coil 26, reducing the operating current of the relay. I will cross it. - In addition, in this embodiment, the relay circuit 24 is configured and applied by combining the bypass circuit conduction means and the normally open contact, but a timer is applied to the bypass circuit conduction means, and this timer interrupts the conduction of the normally open contact. You may also try to find a time to do so.

〔Effect of the invention〕

As explained above, the lamp lighting protection circuit according to the present invention has the excellent effect of protecting both the lamp and the thermistor that protects the lamp, and extending the life of the entire circuit.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the protective circuit for lighting a halogen lamp according to this embodiment, Figure 2 is a characteristic diagram of the coil current, Figure 3 is a characteristic diagram of the current flowing through the halogen lamp, and Figure 4 is a diagram of the DC power supply. Figure 5 is the characteristic diagram of the coil current in the circuit shown in Figure 4, Figure 6 is the characteristic diagram of the current flowing through the halogen lamp when the thermistor is not installed, Figure 7 is the circuit diagram when the application is applied. It is a characteristic diagram of the electric current which flows through a halogen lamp when a thermistor is attached. DESCRIPTION OF SYMBOLS 10... Lamp lighting protection circuit, 12... Halogen lamp, 18... Thermistor, 20... Normally open contact, 22.23... Bypass line, 24... Relay circuit, 26...・Coil, 30... Capacitor.

Claims (1)

[Claims] (1) A protection circuit for lamp lighting that is equipped with a thermistor whose resistance value decreases as the temperature rises and is connected in series to the lamp to reduce inrush current when the lamp starts lighting; normally open contacts connected in parallel;
A protection circuit for lighting a lamp, comprising: a conduction means for closing the normally open contact after a predetermined period of time has elapsed from the start of lighting the lamp.