JPH0343760B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device for lighting a so-called high-pressure discharge lamp that requires high voltage for starting.

FIG. 1 shows a conventional circuit. The conventional example shown in Fig. 1 utilizes the fact that the voltage Vla across the high-pressure discharge lamp (hereinafter abbreviated as discharge lamp) Lp is approximately equal to the voltage V _S of the AC power supply 1 before the lamp starts, and V _S > V la during lighting. The voltage Vla is detected and connected to the resistors Ra and Rb.
The output voltage V _O of the rectifier DB2 is V _O ≧ with respect to the Zener voltage V _Z 1 of the Zener diode Z1.
When V _Z1 , the discharge lamp Lp is interrupted to the non-lighting state, and a high voltage pulse is applied to the discharge lamp Lp to start it.
Next, when V _O <V _Z1 , the circuit determines that the discharge lamp Lp is in the lighting state, and does not apply a high voltage pulse for starting to the discharge lamp Lp. That is, this is a system in which the generation of high-voltage pulses is controlled by the magnitude of the voltage Vla across the discharge lamp Lp. To briefly explain the operation of the conventional circuit shown in FIG. 1, when the discharge lamp Lp is not lit, when the voltage V _O reaches the voltage V _Z1 or more, the voltage across the resistor R2 is V _O・R2/(R1+R2)−V _Z1 . A voltage is generated which fires the thyristor SCR.
On the other hand, the voltage V _S of the AC power source 1 is rectified by the rectifier DB1 via the transformer T, and charges the capacitor C1 via the resistor R3 and the conductive thyristor SCR. When the voltage V _C1 across this capacitor C1 reaches the response voltage V _BO of the voltage-responsive switch element SBS, this switch element SBS becomes conductive, and the charge in the capacitor C1 is transferred to the primary winding of the pulse transformer PT and the diode D.
1, the triac TRC is fired by the voltage generated on the secondary side of the pulse transformer PT, and a high voltage pulse is generated by resonance of the winding L1 and capacitor C2 and boosting of the windings L1 and L2. is generated and applied to both ends of the discharge lamp Lp. As a result, the discharge lamp Lp starts discharging and lights up. Thus, when the discharge lamp Lp is lit, in terms of effective value, V _S > Vla
At this time, if each constant is set so that V _O < V _Z1 , the thyristor will turn on after the discharge lamp Lp is turned on.
There is no ignition of the SCR and therefore no high voltage pulses are applied to the discharge lamp Lp.

However, in such conventional examples, discharge lamps
Due to some cause such as variations in Lp, changes in the characteristics of the discharge lamp Lp itself, changes in the power supply voltage, etc., the restriking voltage Vla-p included in the voltage Vla increases at both ends of the discharge lamp Lp, and this voltage Vla-p increases. When V _S <Vla-p, the thyristor SCR is turned on, causing a problem in that a high voltage is applied to the discharge lamp Lp that is being lit due to the previous operation.

The present invention was provided in view of the problems of the conventional examples, and the impedance of the discharge lamp decreases while the discharge lamp is lit. By utilizing the fact that a slow-phase current flows through the inductance element and the phase of the voltage across the discharge lamp lags behind that of the AC power supply, this phase lag is detected and the high voltage generator for starting discharge lamp is turned on. It is an object of the present invention to provide a discharge lamp lighting device that eliminates malfunctions in the device.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows an example of the basic configuration of the present invention, in which 1 is an AC power supply, 2 is a current-limiting inductance element, 3 is a logic circuit, 4 is a high voltage generator, 5 is a power synchronization signal generator, and 6 is a This is a voltage phase detection device on the discharge lamp side, and Lp is the discharge lamp. Thus, in the circuit shown in FIG. 2, the zero-crossing point detection pulse of the power supply voltage obtained as the output of the power supply synchronization signal generator 5 and the zero-crossing point detection of the voltage across the discharge lamp Lp obtained as the output of the voltage phase detection device 6. The AND circuit 3 performs an AND with the pulse, and turns the high voltage generator 4 on and off.

FIG. 3 shows a specific embodiment circuit of the present invention;
The figure is an explanatory diagram of its operation.
B indicates that the light is on. The operation of the embodiment in FIG. 3 is as follows: First, when the discharge lamp Lp shown in FIG. 4A is not lit, there is almost no phase difference between the two voltages at V _S Vla. Furthermore, when the relationship between the output voltage V _SO of the rectifier DB1 as shown in FIG. 4a and the Zener voltage V _Z2 of the Zener diode Z2 becomes V _SO <V _Z2 , the output of the transistor Tr ₂ as shown in FIG. becomes H”,
It is applied to one input terminal of the AND circuit 3. On the other hand, the relationship between the output V _O of the rectifier DB2 as shown in c in the figure and the Zener voltage V _Z1 of the Zener diode Z1 is V _O
When <V _Z1 , the transistor
The output of Tr ₁ becomes "H" and is applied to the other input terminal of the AND circuit 3. In this way the supply voltage
The vicinity of each zero crossing point of V _S and the voltage across the discharge lamp Vla is detected, and the detection output is input to an AND circuit 3 consisting of an AND gate. Therefore, when the lights are not lit, the timings of the zero crossing points of both lights are almost in the same phase, so the output of the AND circuit 3 becomes "H" as shown in e in case A in the figure. Thus, when the output of the AND circuit 3 becomes "H", the thyristor SCR is fired, and the capacitor _C1 is charged. Discharging through the transformer PT and igniting the triac TRC, a high voltage pulse is generated by the resonance of the winding L1 and capacitor C2 and boosting by the windings L1 and L2, and is applied to the discharge lamp Lp. Then the discharge lamp Lp starts. Next, while the discharge lamp Lp is lit, which is the case shown in FIG. Discharge lamp as shown in c
The zero crossing point of the voltage Vla across Lp lags behind that of the power supply voltage V _S , and there is no phase in which both the output of transistor Tr ₁ and the output of transistor Tr ₂ become "H", and the AND circuit 3 is " Since the voltage does not become H'', no high voltage pulse is generated.

The present invention detects the presence or absence of a phase difference between the voltage across the high-pressure discharge lamp with respect to the voltage of the AC power supply by detecting the zero crossing point of the voltage of the AC power supply and the zero crossing point of the voltage across the high-pressure discharge lamp. This is determined by taking a theoretical product, and the high voltage generator is activated only when the result of the theoretical product is "H", so this occurs when the power supply voltage drops while the discharge lamp is lit. Even if phenomena peculiar to high-pressure discharge lamps occur, such as an increase in re-ignition voltage, an increase in lamp voltage at the end of its life, or an increase in lamp voltage during the starting process, it will not be affected and will start even if the discharge lamp is still lit. There is no need for high voltage pulses to be applied to the discharge lamp.
This has the effect of improving operational stability and reliability.

Furthermore, since the configuration is as described above, the circuit for detecting the zero crossing point of the voltage of the AC power supply and the circuit for detecting the zero crossing point of the voltage across both ends of the high pressure discharge lamp can be configured as independent circuits, and the circuits for both can be configured as independent circuits. This has the effect of providing a high degree of freedom in design.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional example, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a specific circuit diagram of the same.
Figure 4 is an explanatory diagram of the same operation as above, where 1 is an AC power supply, 3 is an AND circuit, 4 is a high voltage generator, Lp
is a discharge lamp.

Claims (1)

[Claims] 1. A discharge lamp lighting device that lights a high-pressure discharge lamp that requires high voltage for starting from an AC power source through a current-limiting element having an inductance component, and is equipped with a high-voltage generator for starting the high-pressure discharge lamp, The presence or absence of a phase difference between the voltage across the high-pressure discharge lamp with respect to the voltage of the AC power supply is detected by detecting the zero crossing point of the voltage of the AC power supply and the zero crossing point of the voltage across the high-pressure discharge lamp, and calculating the logical product of both detection outputs. A discharge lamp lighting device characterized in that the high voltage generator is operated only when the result of the logical product is “H”.