JPS6237359Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a fluorescent lamp dimmer circuit.

Conventionally, in this type of circuit, as shown in FIG. 1, a fluorescent lamp 4 is connected to an AC power supply 1 via a bidirectional thyristor 2 and a ballast 3, and the gate of the thyristor 2 is connected to the gate of the thyristor 2 to turn on the thyristor 2, A gate circuit 5 for controlling off is connected. Also, fluorescent lamp 4
A glow tube 6 is connected in parallel to the thyristor 2, and by controlling the conduction angle of the thyristor 2 with a gate circuit 5, the voltage waveform applied to the fluorescent lamp 4 can be changed as shown in FIG. Dimming is in progress. However, with this circuit configuration, since no voltage is applied to the fluorescent lamp 4 while the thyristor 2 is off, there is a pause period in the lamp current, causing problems such as the fluorescent lamp 4 flickering or being difficult to start at low temperatures. It was hot. Therefore, as a countermeasure to this problem, a resistor is connected in parallel to the thyristor 2, and as shown in FIG. 3, even when the thyristor 2 is off, voltage is applied to the fluorescent lamp 4 through the resistor, eliminating the lamp current rest period. method is known. According to this method,
Although the flickering of the fluorescent lamp 4 is considerably improved, the problem of difficulty in starting at low temperatures still remains. As can be seen from Figure 3, the voltage applied to the fluorescent lamp 4 is smaller than when the thyristor 2 is fully conductive, and the current flowing through the filament of the fluorescent lamp 4 is small, so it takes time for the temperature of the filament to rise. This is because it takes

Therefore, a resistor is connected in parallel to the thyristor 2, and the gate circuit 5 is provided with temperature characteristics.
A conceivable method is to increase the conduction angle to achieve almost full conduction at low temperatures, and to decrease the conduction angle as the temperature rises to obtain the desired dimming, but this method complicates the structure of the gate circuit 5. Further, for example, when the thyristor 2 is destroyed and becomes open, a voltage is applied to the fluorescent lamp 4 via a resistor, but this voltage cannot maintain the discharge of the fluorescent lamp 4, and the fluorescent lamp 4 goes out. Then the power supply voltage becomes glow tube 6
As a result, the glow tube 6 repeatedly discharges, shorts, and opens, leaving only the ballast 3 as a load, which causes an overcurrent to flow through the resistor, causing it to overheat and, in the worst case scenario, burst into flames. It is also possible. Therefore, as a countermeasure to this problem, it is necessary to provide a protection device such as a thermal protector to the resistor, which has the disadvantage of complicating the structure and increasing the cost.

The present invention was developed in view of the above-mentioned drawbacks. It connects a positive temperature coefficient thermistor in parallel to the thyristor, prevents flickering of the fluorescent lamp, makes it easy to start even at low temperatures, and has a simple structure for controlling the fluorescent lamp. It provides optical circuits.

Next, the structure of one embodiment of the present invention will be explained based on FIG. 4.

1 is an AC power source, and a fluorescent lamp 4 is connected to this AC power source 1 via a bidirectional thyristor 2 and a ballast 3. A glow tube 6 is connected between both filaments of the fluorescent lamp 4. A gate circuit 5 for controlling on/off of the thyristor 2 is connected to the gate of the thyristor 2, and a positive temperature coefficient thermistor 7 is connected in parallel to the thyristor 2.

The operation of this dimming circuit will be explained.

First, since the impedance of the PTC thermistor 7 is low during startup, approximately the same voltage as the power supply voltage is applied through the PTC thermistor 7 even when the thyristor 2 is off, as shown in Figure 5a. Therefore, the fluorescent lamp 4 becomes very easy to light. When the fluorescent lamp 4 is turned on, the temperature of the filament rises and the fluorescent lamp 4 becomes stably discharged. Further, the positive characteristic thermistor 7 has high impedance due to self-heating due to current. For this reason,
As shown in FIG. 5b, when the thyristor 2 is turned off, the voltage applied to the fluorescent lamp 4 becomes sufficiently low.
The fluorescent light 4 is dimmed.

Further, when the thyristor 2 is destroyed and becomes open, the power supply voltage is applied to the fluorescent lamp 4 via the positive temperature coefficient thermistor 7. Therefore, when the temperature of the positive characteristic thermistor 7 is low at startup, the fluorescent lamp 4
A voltage approximately equal to the power supply voltage is applied to the fluorescent lamp 4, and the fluorescent lamp 4 is turned on. However, since all the lamp current flows through the PTC thermistor 7, the PTC thermistor 7 becomes high impedance due to self-heating. As a result, the voltage applied to the fluorescent lamp 4 decreases, making it impossible to maintain the discharge, and the fluorescent lamp 4 goes out. In addition, since the positive temperature coefficient thermistor 7 has a high impedance, the impedance of the circuit increases when the fluorescent lamp 4 is not lit, so the current is limited and the positive temperature coefficient thermistor 7 does not generate abnormal heat. . Further, when the thyristor 2 is broken as described above, the fluorescent light 4 blinks to notify that the thyristor 2 is broken.

According to the present invention, since the positive temperature coefficient thermistor is connected in parallel with the thyristor, the impedance of the positive temperature coefficient thermistor is low when the ambient temperature is low, and the state is almost the same as full conduction, making it easy to start the fluorescent lamp and after lighting it. The impedance of the positive temperature coefficient thermistor becomes high, allowing desired dimming. In addition, there is no need to provide temperature characteristics to the gate circuit, and even when the thyristor is open, the positive temperature coefficient thermistor itself limits the current, so there is no abnormal heat generation, there is no need for a protection circuit, and the configuration is simple and inexpensive. can be formed into Furthermore, when the thyristor is opened, the fluorescent light flashes, which indicates that the thyristor is damaged.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional fluorescent lamp dimmer circuit, Figures 2 and 3 are voltage waveform diagrams showing conventional dimming states, and Figure 4 is a circuit diagram of a conventional fluorescent lamp dimmer circuit. A circuit diagram showing one embodiment, and FIGS. 5a and 5b are voltage waveform diagrams showing the same dimming state as above. 1... AC power supply, 2... Thyristor, 4... Fluorescent lamp, 7... Positive characteristic thermistor.

Claims (1)

[Scope of utility model registration request] An alternating current power source, a fluorescent lamp energized by the alternating current power source, and a thyristor inserted between the alternating current power source and the fluorescent lamp to control the phase angle of the power supply voltage applied to the fluorescent lamp. A fluorescent lamp dimmer circuit comprising: a positive temperature coefficient thermistor connected in parallel to the thyristor.