JP3382302B2 - Discharge lamp lighting device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting apparatus for lighting a discharge lamp at a high frequency by using an output of an inverter circuit having a half-bridge structure. 2. Description of the Related Art FIG. 3 shows a conventional discharge lamp lighting device. In FIG. 3, reference numeral 1 denotes an AC / DC converter for converting an AC power supply 2 into a DC power supply. 3 is a discharge lamp and 4 is a resonance capacitor. Reference numeral 6 denotes an inverter circuit having a half-bridge configuration, which is used for a pair of switches 7 and 8, a control circuit 9 for turning on and off the pair of switches 7 and 8 alternately, and a control circuit for supplying power to the control circuit 9. It has a power supply 10, a capacitor 13, and a ballast choke 14, and is configured to turn on the discharge lamp 3 at a high frequency by the output of the inverter circuit 6. The control circuit power supply 10 includes a resistor 11, a capacitor 12, and a Zener diode 15. A current transformer 16 is connected in series to the inverter circuit 6 on the output side.
An overcurrent determination circuit 17 is provided for determining the overcurrent to the discharge lamp 3 from the voltage drop of 6 and stopping the operation of the control circuit 9. When the discharge lamp 3 enters the end-of-life Emiless state, the discharge lamp 3 The overcurrent judging circuit 17 detects an increase in the current flowing through the ballast choke 14 due to the current flowing in one direction or not flowing at all, and the control circuit 9
The operation shifts to a minute oscillation state by the action of, the output of the inverter circuit 6 is reduced, and the discharge lamp 3 is turned off. [0003] However, in the conventional case,
The overcurrent judging circuit 17 erroneously judges that the discharge lamp 3 is in an emiless state due to an overcurrent instantaneously generated due to a disturbance such as an instantaneous power failure or a detachment of the discharge lamp 3, and the discharge lamp 3 is extinguished by the operation of the control circuit 9. Sometimes. In this case, in order to turn on the discharge lamp 3 again, it is necessary to once turn off and turn on the power supply voltage, and the operation is very complicated. SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for restarting the operation of a control circuit from an initial state when an overcurrent determination circuit erroneously determines that the discharge lamp is in an emiless state and the discharge lamp is extinguished. The purpose is to prevent the disappearing state from continuing. The technical means of the present invention for solving this technical problem includes an AC / DC converter 1 for converting an AC power supply 2 into a DC power supply, and an AC / DC converter 1 for converting the AC power supply 2 into a DC power supply. A discharge lamp lighting device that includes an inverter circuit 6 of a half-bridge configuration connected to an output side, and that discharges the discharge lamp 3 at a high frequency by an output of the inverter circuit 6, wherein the inverter circuit 6 includes a pair of switches 7 and 8; A control circuit 9 for alternately turning on and off the pair of switches 7 and 8, and a control circuit power supply 10 for supplying power to the control circuit 9.
Are connected in series, and an overcurrent determination circuit 17 for determining the overcurrent to the discharge lamp 3 from the voltage drop of the current transformer 16 and stopping the operation of the control circuit 9 is provided. A voltage detection circuit 37 for detecting the voltage of the control circuit power supply 16 is provided. After the power supply voltage of the control circuit power supply 10 is lowered for a certain period of time by resetting the control circuit 9 by the voltage drop detection of the voltage detection circuit 37, the control circuit power supply The point is that a power supply voltage adjusting circuit 38 is provided to automatically reset the power supply voltage of the power supply 10 and restart the operation of the control circuit 9 from the initial state. The output voltage of the power supply transformer 16 at point A, the output voltage of the voltage detection circuit 37 at point B, the output voltage of the power supply voltage adjustment circuit 38 and the power supply voltage of the control circuit power supply 10 at point C are shown in FIG. As shown in the timing chart of FIG. The operation will be described with reference to this timing chart. The voltage generated on the secondary side of the current transformer 16 is high during the start-up process of the discharge lamp 3 and during the normal lighting of the discharge lamp 3, so that the H signal is supplied from the voltage detection circuit 37 to the power supply. It is sent to the voltage adjustment circuit 38. When the H signal is sent, the power supply voltage adjustment circuit 38 does not operate, and the power supply voltage is continuously supplied from the control power supply 10 to the control circuit 9. When the discharge lamp 3 is in the Emiless state, the current of the oscillation circuit is reduced and the state is in the minute oscillation state.
Since the voltage generated on the secondary side of the current transformer 16 is low, the L signal is sent from the voltage detection circuit 37 to the power supply voltage adjustment circuit 38. When the L signal is sent, the power supply voltage adjusting circuit 38
Acts to lower the voltage of the control power supply 10. The operation of the control circuit 9 stops, and the microresonance of the oscillation circuit stops. When the oscillation stops, the current transformer 16
Since the voltage generated on the next side disappears, the operation of lowering the power supply voltage of the control circuit 9 is stopped after a certain period of time, and the power supply voltage to the control circuit 9 is restored. As a result, the control circuit 9 restarts from the initial state. The length of the fixed time is longer than the time required for resetting the function of the control circuit 9 after the power supply of the control circuit 9 is turned off. The present invention will be described below with reference to the illustrated embodiment. In FIG. 1, a resistor 21, a diode 22, and a capacitor 23 are provided on the secondary side of a current transformer 16 having a primary side connected to a resonance circuit. The capacitor 23 is connected in series, and the voltage generated on the secondary side of the current transformer 16 is smoothed and charged in the capacitor 23. A series circuit of a resistor 24 and a resistor 25 is connected in parallel with the capacitor 23, and another series circuit of a diode 27 and a capacitor 28 is connected in parallel with another capacitor 23. A transistor 31 is connected to the connection point between the resistors 24 and 25.
And the other end of the resistor 25 is connected to the emitter of the transistor 31. A resistor 33 is connected to a connection point between the diode 27 and the capacitor 28,
The other end of 3 is connected to the collector of transistor 31. The collector of the transistor 31 is connected to the base of the transistor 32, and the transistors 31 and 3
The two emitters are connected. Transistor 32
Is connected to a resistor 35, and another end of the resistor 35 is connected to the + side of the capacitor 12 of the control circuit power supply 10. The emitter of the transistor 32 is connected to one side of the capacitor 12. The current transformer 16 is controlled by the resistors 21, 24, 25, the diode 22, and the capacitor 23.
A voltage detection circuit 37 for detecting the voltage on the secondary side of the above is configured. The diode 27 and the transistors 31 and 3
2, a power supply voltage adjusting circuit 38 for adjusting the power supply voltage of the control circuit power supply 10 is constituted by the capacitor 28 and the resistor 33. The power supply of the power supply voltage adjustment circuit 38 is obtained from the secondary side of the current transformer 16, and the power supply voltage adjustment circuit 38 keeps operating for a certain period of time even if the power supply is lost. Next, the operation will be described. Inverter circuit 6
When the switches 7 and 8 are turned on and off alternately, a current flows through the discharge lamp 3 and the resonance capacitor 4 via the ballast choke 14 and the capacitor 13. The current flowing through the ballast choke 14 flows through the resonance capacitor 4 at the time of starting, and flows through the discharge lamp 3 and the resonance capacitor 4 at the time of lighting. Discharge lamp 3
At the time of non-lighting is the same as at the time of starting, the current at this time is larger than at the time of lighting, and the temperature rise is higher. Then, an increase in the current flowing through the ballast choke 14 is detected by the overcurrent determination circuit 17, the operation shifts to a minute oscillation state by the operation of the control circuit 9, the output of the inverter circuit 6 is reduced, and the discharge lamp 3 is turned off. Let it. When the output is reduced by the control circuit 9, the voltage generated on the secondary side of the current transformer 16 decreases, and the voltage between the base and the emitter of the transistor 31 obtained by dividing the voltage of the capacitor 23 by the resistors 24 and 25. When the applied voltage decreases, the transistor 31 is turned off, the voltage of the capacitor 28 is applied between the base and the emitter of the transistor 32 via the resistor 33, the transistor 32 is turned on, and the capacitor 12 is discharged via the resistor 35 to discharge the control circuit. The power supply voltage of the power supply 10 is dropped to stop the operation of the resonance circuit. The voltage generated on the secondary side of the current transformer 16 disappears, and the voltage of the capacitor 23 drops. However, when the capacity of the capacitor 28 is increased appropriately, current continues to flow from the capacitor 28 to the base of the transistor 32 via the resistor 33 for a certain period of time. After continuing to turn on the transistor 32, the transistor 32 turns off, the power supply voltage of the control circuit power supply 10 returns, and the control circuit 9 restarts from the initial state. According to the present invention, the voltage detection circuit 37 for detecting the voltage of the current transformer 16 is provided, and the power supply voltage of the control circuit power supply 10 is kept constant by detecting the voltage drop of the voltage detection circuit 37. After resetting the control circuit 9 by reducing the time, a power supply voltage adjusting circuit 38 is provided which automatically returns the power supply voltage of the control circuit power supply 10 and restarts the operation of the control circuit 9 from the initial state. When the discharge lamp 3 is extinguished due to the erroneous determination that the discharge lamp 3 is in the emiless state by the current determination circuit 17, the control circuit 9 is automatically reset and the operation of the control circuit 9 is restarted from the initial state. This prevents the discharge lamp 3 from continuing its extinguished state.

[Brief description of the drawings] FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is a timing chart for explaining the operation. FIG. 3 is a circuit diagram showing a conventional example. [Explanation of symbols] 1 AC / DC converter 2 AC power supply 3 Discharge lamp 6. Inverter circuit 7 Switch 8 switch 9 Control circuit 10. Power supply for control circuit 16 Current transformer 17 Overcurrent judgment circuit 37 Voltage detection circuit 38 Power supply voltage adjustment circuit

Claims (1)

(57) [Claims 1] An AC / DC converter (1) for converting an AC power supply (2) to a DC power supply, and a half-bridge configuration connected to an output side of the AC / DC converter (1). Inverter circuit (6)
And a discharge lamp lighting device for lighting the discharge lamp (3) at high frequency by the output of the inverter circuit (6), wherein the inverter circuit (6) comprises a pair of switches (7),
(8) a control circuit (9) for alternately turning on and off the pair of switches (7) and (8); and the control circuit (9).
And a control circuit power supply (10) for supplying power to the inverter circuit (6).
6) are connected in series, and an overcurrent determination circuit (17) for determining the overcurrent to the discharge lamp (3) from the voltage drop of the current transformer (16) and stopping the operation of the control circuit (9) is provided. In the discharge lamp lighting device, a voltage detection circuit (37) for detecting a voltage of the current transformer (16) is provided, and a power supply voltage of the control circuit power supply (10) is detected by detecting a voltage drop of the voltage detection circuit (37). After the control circuit (9) is reset by lowering the power supply voltage for a predetermined time, the power supply voltage of the control circuit power supply (10) is automatically restored to restart the operation of the control circuit (9) from the initial state. 38), wherein the discharge lamp lighting device is provided.