JPH0329156B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a preheating start type fluorescent lamp lighting device used in a copying machine.

[Background Art] In general, preheat-start type fluorescent lamps used in copying machines have problems with blackening and shortened lifespan due to frequent blinking, especially when the fluorescent lamps are not turned on properly. The promotion of blackening and shortening of lifespan has become a major problem. The conventional example will be specifically explained below. Figure 1 shows the voltage when the power is turned on and when the power is turned off by the power switch SW.
As shown in Figure 3, the rise and fall of Va is a DC power supply whose rise and fall is relatively gradual (for example, AC power input through a power switch is rectified by a diode bridge and smoothed by a smoothing capacitor). This shows a fluorescent lamp lighting _device using a constant current type self-excited inverter circuit 1 driven by a DC power source (DC power supply ₎ E. An oscillation transformer OT having a primary winding _N1 , a pair of secondary windings _N2a , _N2b , and a feedback winding _N3 , a resonance capacitor _C1 , resistors _R1 , _R2 , and a current-limiting inductance _L0. is formed and each secondary line
The N _2a , N _2b outputs are connected to the filament 3a of the fluorescent lamp 2 via the current limiting and DC blocking capacitor _C0 .
3b. Filament preheating means 4
is formed by a lighting control circuit CO consisting of a CR timer circuit and a transistor _Q3 . Conventionally, this lighting control circuit CO includes a time constant circuit consisting of a resistor Rt and a capacitor Ct, as shown in FIG.
A reference voltage generation circuit consisting of voltage dividing resistors Ra and Rb,
A voltage comparison circuit CP that compares the voltage Ve across the capacitor Ct and the reference voltage Vd, and transistors Q ₄ to _{Q 7}
As shown in Fig. 5, when the power switch SW is turned on, the power supply voltage Va
Terminal b is set to "H" and terminal c is set to "L" for a certain period of time T after rising. Therefore, the transistor _Q3 is turned on for a certain period of time T from when the power is turned on, and the filament 3
After the filaments 3a and 3b are preheated by direct current, and after a certain period of time T has passed and the filaments 3a and 3b are sufficiently preheated, the inverter circuit 1 operates to supply a high voltage _V2 for lighting the fluorescent lamp 2 (the lamp of the fluorescent lamp 2). (approximately four times the voltage) is applied to turn on the fluorescent lamp 2.
However, in such a conventional example, there is a problem in that when the power is cut off during the preheating period, the fluorescent lamp 2 is turned on abnormally, resulting in blackening and shortened lifespan. That is, in normal lighting operation, the voltage comparator circuit CP of the lighting control circuit calculates the voltage across the capacitor Ct, as shown in the left part of Fig. 3.
When Ve exceeds the reference voltage Vd (when the filaments 3a and 3b have been preheated for a certain period of time T), it becomes "H", and the output circuit outputs the control signal Vc to operate the inverter circuit 1, and the fluorescent lamp 2 A lighting output (high voltage V ₂ ) is applied to the lamp for normal lighting. However, as shown on the right side of Figure 3, during the preheating period (from power on to
When the power supply is cut off after the elapse of time T′, the reference voltage Vd falls in synchronization (proportionality) with the power supply voltage Va, while the voltage Ve across the capacitor Ct rises later than that. Therefore, even though the fixed time T has not elapsed, the output of the voltage comparator circuit CP becomes "H" for a certain time _T0 and the control signal Vc is output, and the filament 3a of the fluorescent lamp 2 , 3b is not sufficiently preheated, the inverter circuit 1 operates and the fluorescent lamp 2
There was a problem in that the fluorescent lamp 2 was lit abnormally (erroneously emitted light), which adversely affected the lifespan of the fluorescent lamp 2.

[Object of the Invention] The present invention has been made in view of the above points, and its purpose is to prevent fluorescent lamps from being turned on when the power supply voltage is low. An object of the present invention is to provide a fluorescent lamp device capable of preventing the lamp from turning black and shortening its lifespan.

[Disclosure of the Invention] Embodiment FIGS. 1 and 2 show an embodiment of the present invention. In a fluorescent lamp lighting device using an inverter circuit 1 similar to the conventional example, the power supply voltage Va is set to a predetermined voltage. A voltage monitoring circuit 5 is provided to monitor whether the voltage has fallen _{below V} The voltage monitoring circuit 5 is a Zener diode.
ZD, transistors Q ₈ , Q ₉ and resistors R ₁₀ , R ₁₁ ,
_R12 , and the predetermined voltage _VX is set within a range that prevents the fluorescent lamp 2 from being turned on abnormally.

The operation of the embodiment will be specifically explained below. Now, when the power supply voltage Va is a normal working voltage that can normally light the fluorescent lamp 2, the Zener diode ZD is turned on, and the base current flows to the transistor _Q8 via the resistor _{R11 .}
is on and transistor _Q9 is off. Therefore, as in the conventional example, the voltage comparator circuit
Turn on transistor _Q6 controlled by CP output,
When off, the control signal Vc is set to “H” and “L”,
The operating period of the inverter circuit 1 is set. On the other hand, as shown in the right part of FIG. 3, when the power switch _SW is turned off and the power supply voltage Va drops below _the predetermined voltage _V Let the drop be iR ₁₁ and the base-emitter voltage of transistor Q ₈ be V _BE . When Va < V _Z + iR ₁₁ + V _BE , Zener diode ZD is turned off and transistor Q ₈ is turned off, so transistor Q ₉ is turned on. The control signal Vc is forcibly set to "L" regardless of the voltage comparator circuit CP output, and even if the power switch SW is turned off during the preheating period and the timer circuit malfunctions, the inverter circuit 1 will not operate. Filament 3
The fluorescent lamp 2 will not be turned on abnormally in a state where the preheating of the lamps a and 3b is insufficient, and it is possible to prevent the fluorescent lamp from turning black and shortening its lifespan. It goes without saying that the predetermined voltage V _X is set higher than the power source voltage V _a2 that allows light emission and lower than the normal operating voltage V _a1 .

[Effects of the Invention] As described above, the present invention includes a DC power supply whose voltage rises and falls relatively slowly when the power is turned on and when the power is turned off, and an inverter circuit that converts the DC power supply voltage into a high-frequency voltage. In a preheating start type fluorescent lamp lighting device comprising a CR timer circuit for DC preheating the filament of a fluorescent lamp, and a control circuit for switching from a preheating state to a high frequency lighting state using the output of the timer circuit, the DC voltage is A voltage monitoring circuit is provided to monitor whether the voltage is higher than the voltage that can light the lamp but lower than the normal working voltage, and when the voltage monitoring circuit detects that the voltage has fallen below the normal working voltage, the inverter circuit Since the output is stopped and the fluorescent lamp is not turned on when the DC power supply voltage is low, it is possible to prevent the fluorescent lamp from turning black and shortening its lifespan.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a configuration example of a fluorescent lamp lighting device according to the present invention, Fig. 2 is a main circuit diagram of an embodiment of the present invention, Fig. 3 is an explanatory diagram of the same operation, and Fig. 4 is a conventional one. The circuit diagram of the main part of the example, and FIG. 5 is an explanatory diagram of the same operation as above. 2 is a fluorescent lamp, 3a and 3b are filaments, 4 is a filament preheating means, and 5 is a voltage monitoring circuit.

Claims (1)

[Claims] 1. A DC power supply whose voltage rises and falls relatively slowly when the power is turned on and off, an inverter circuit that converts the DC power supply voltage into a high-frequency voltage, and a CR timer that preheats the filament of a fluorescent lamp with DC current. and a control circuit for switching from a preheating state to a high-frequency lighting state using the output of the timer circuit. A voltage monitoring circuit is installed to monitor whether the voltage has fallen below the operating voltage.
A fluorescent lamp lighting device characterized in that the inverter circuit output is stopped when the voltage monitoring circuit detects that the voltage has fallen below the normal working voltage.