JPH048171A - Discharge lamp lighting unit - Google Patents

Abstract

PURPOSE:To start an inverter circuit positively by turning a switching element OFF for a predetermined time, through a delay circuit, after throw-in of a DC power supply circuit thereby interrupting base current flow to a transistor. CONSTITUTION:At the time of starting, a current is fed to the base of a transistor 28 through a starting resistor 40 and thereby the transistor 28 is turned ON to feed power to a discharge lamp 42. Since a capacitor 34 is not charged at that time and a Zener diode 36 is blocked, a transistor 31 is sustained in OFF state and a current is fed from a DC power supply circuit 21 to the base of the transistor 28 without bypassing a diode 32 thus starting the transistor 28 positively. Upon elapse of a predetermined time, a capacitor 34 is charged to increase the voltage, and when a Zener diode 36 is turned ON the transistor 31 is turned ON.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a discharge lamp lighting device that lights a discharge lamp using high frequency waves.

(Prior art) As a conventional discharge lamp lighting device of this type, for example, a third discharge lamp lighting device is used.
The structure shown in the figure is known.

In the discharge lamp lighting device shown in FIG. 3, a discharge lamp 4, which is a load circuit including a paralast choke 3, is connected to a DC power supply circuit 1 via an inverter circuit 2. Further, in the inverter circuit 2, a parallel circuit of a resonance capacitor 5 and an inductor 6, and an emitter-collector of a transistor 7 are connected in series between the DC power supply circuit 1.

A primary winding of a drive transformer 8 that drives the transistor 7 is connected between the discharge lamp 4 and a connection point between the resonance capacitor 5, inductor 6, and transistor 7. Further, the secondary winding of the drive transformer 8 is connected between the base of the transistor 7, a capacitor 9 for driving the transistor 7, and a diode 10 connected in parallel to the capacitor 9.

Furthermore, a starting resistor 1 is connected to the base of the transistor 7.
1 is connected.

Then, the current from the DC power supply circuit 1 is transferred to the starting resistor 11.
to the base of transistor 7 to activate transistor 7. Then, the inverter circuit 2 is caused to oscillate, and a high frequency current is supplied to the discharge lamp 4 to turn it on. Further, at this time, the current induced in the secondary winding of the drive transformer 8 is positively fed back to the base of the transistor 7, and the drive capacitor 9 is kept in an on state while being charged. Then, when the base current starts flowing in the opposite direction, the transistor 7 is turned off. That is, due to the LC resonance between the inductance L of the secondary winding of the drive transformer 8 and the capacitance C of the capacitor 8, the transistor 7
The on-period of is determined. Thereafter, resonance occurs due to the electrical energy stored in the tank circuit composed of the inductor 6 and the resonance capacitor 5, and a resonant current flows through the load circuit. The load current to this load circuit flows through the secondary winding of the drive transformer 8, the drive capacitor 9, the discharge diode 10, the resistor, and the diode to keep the transistor 7 in an off state.

Then, due to the resonant load current, a positive feedback current flows through the secondary winding of the drive transformer 8 again to the transistor 7, and the transistor 7 is turned on to repeat the above-described operation and perform high-frequency oscillation.

(Problem to be Solved by the Invention) However, in the case of the conventional discharge lamp lighting device described above, when the forward voltage of the discharge diode 10 is lower than the voltage between the base and emitter of the transistor 7, the starting resistor 11
The base current supplied to the base of transistor 7 from
The problem is that the oscillation stops.

In view of the above problems, the present invention provides a discharge lamp lighting device that can ensure the activation of an inverter circuit.

[Structure of the invention]

(Means for Solving the Problems) A discharge lamp lighting device of the present invention includes a DC power supply circuit and an inverter circuit that converts the DC of the DC power supply circuit into a high frequency. , a drive transformer with one end of a secondary winding feeding back a load current to the base of the transistor, a drive capacitor connected to the base of the transistor, and a discharge diode connected in parallel to the capacitor; A switching element connected in series with this diode,
The device further includes a delay circuit that turns on the switching element with a predetermined time delay after DC power is supplied from the DC power supply circuit.

(Function) The present invention converts direct current from a direct current power supply circuit into high frequency current using an inverter circuit. The delay circuit turns off the switching element connected in series with the diode for a predetermined period of time after the DC power supply circuit is turned on, preventing the base current of the transistor from being bypassed by the diode, and ensuring the operation of the transistor. After a predetermined period of time has elapsed, the switching element is turned on and a feedback current in the opposite direction to the base current induced by the secondary winding of the drive transformer is caused to flow through the diode.

(Example) Hereinafter, an example of the discharge lamp lighting device of the present invention will be described with reference to the drawings.

In FIG. 1, 21 is a DC power supply circuit, and this DC power supply circuit 21 has a commercial AC power supply 22 connected to a rectification circuit 23 such as a diode bridge, and a smoothing capacitor 24 connected to this rectification circuit 23. There is.

Further, an inverter circuit 25 is connected to the DC power supply circuit 21, and this inverter circuit 25 is connected to the DC power supply circuit 21.
A parallel circuit of a resonance capacitor 26 and an inductor 27, and the collector-emitter of the oscillation transistor 2B are connected in series.

The connection point between the capacitor 26 and the collector of the transistor 28 is connected to the negative winding 2 of the drive transformer 29.
One end of 9M is connected. Further, one end of the secondary winding 29b of this drive transformer 29 is connected to a transistor 28.
A capacitor 30 is connected to the other end of the secondary winding 29b. This capacitor 30 has
A series circuit of a transistor 31 and a diode 32 as switching elements are connected in parallel. Furthermore, the DC power supply circuit 21 includes a resistor 33 and a capacitor 3.
A series circuit of 4 time constant circuits is connected, and the connection point of the resistor 33 and the capacitor 34 is connected to the base of the transistor 31 via the resistor 35 and the Zener diode 36. A delay circuit 37 is formed by the diode 36. Note that the time constants of the resistor 33 and the capacitor 34 may be arbitrarily set according to the delay time. On the other hand, a diode 3 is connected between the base and emitter of the transistor 28.
8 and a resistor 39 are connected in series. Also,
The positive terminal of the DC power supply circuit 21 is connected to the base of the transistor 28 via the starting resistor 40.

Furthermore, the filament 42 of the discharge lamp 42 is connected to the positive terminal of the DC power supply circuit 21 and the other end of the primary winding 29a of the drive transformer 29 via the palust choke 41! .

42b are connected to each other, and these filaments 42a
, 42b, a starting capacitor 43 is connected between them.

Next, the operation of the above embodiment will be explained.

First, in the DC power supply circuit 21 , a current from a commercial AC power supply 22 is rectified by a rectifier circuit 23 and smoothed by a capacitor 24 .

At startup, current is supplied to the base of the transistor 28 via the startup resistor 40, and the transistor 28 is supplied with current through the startup resistor 40.
is turned on, and power is supplied to the discharge lamp 42. At this time,
Capacitor 34 is not charged and Zener diode 3
6 is in a reverse blocking state, the transistor 31 remains off, and the current from the DC power supply circuit 21 is supplied to the base of the transistor 28 without being bypassed to the diode 32, thereby reliably starting the transistor 28. Thereafter, after a predetermined period of time has elapsed, the capacitor 34 is charged, the voltage increases, and the Zener diode 36 is turned on, thereby turning on the transistor 31. When power is supplied to the discharge lamp 42, a load current flows through the primary winding 29a of the drive transformer 29. As a result, a current flows through the secondary winding 29b of the drive transformer 29, a base current flows through the secondary winding 29b, the base emitter of the h-range metal 28, the capacitor 30, and the closed circuit of the secondary winding 29b. While charging the battery, it remains in the on state. Then, due to LC resonance between the inductance L of the secondary winding 29b of the drive transformer 29 and the capacitance C of the capacitor 30, the transistor 28
When the base current of is reversed, the charge accumulated in the capacitor 30 becomes a reverse bias power source for the transistor 28, which pulls out the emitter-base capacitance of the transistor 28, turning off the transistor 28. Then, the energy stored in the tank circuit composed of the inductor 27 and the resonant capacitor 26 resonates, and a resonant current flows through the load circuit, causing a positive feedback current to flow again into the secondary winding 29b of the drive transformer 29. When the current flows, a forward base current flows to the base of the transistor 28, turning on the transistor 28, and by repeating these operations, high frequency oscillation is performed. Furthermore, since the capacitor 43 and the parasto choke 41 are set to values that cause LC resonance, a high frequency resonant current flows through the electrodes 42a and 42b of the discharge lamp 42, and at the same time, a high voltage is generated across the capacitor 43, and this voltage The discharge lamp 42 is started and lit at high frequency. After the discharge lamp 42 is lit in this manner, the inverter circuit 25 continues to oscillate, and the high frequency current limited by the paralast choke 41 keeps the discharge lamp 42 lit.

According to the above embodiment, even if the voltage between the base and emitter of the transistor 28 is lower than the voltage of the diode 32, the delay circuit 37 causes the transistor 3 to remain closed for a predetermined time at startup.
1 is turned off, the inverter circuit 25 can be reliably started without the starting base current being bypassed by the diode 32.

Further, for the secondary winding 29b of the drive transformer 29, a transistor 31, a diode 32 . Since the series circuit of the resistor 39 and the diode 38 is connected in parallel, even when the transistor 28 is reverse biased, the core of the drive transformer 29 is not saturated and a feedback current can flow. Residual magnetism can be reset.

Next, another embodiment will be described with reference to FIG.

The discharge lamp lighting device shown in FIG. 2 has a thyristor 46 connected as a switching element in place of the transistor 31 and diode 32 of the discharge lamp lighting device shown in FIG. Connect the resistor, 47.

Note that the discharge lamp lighting device shown in FIG. 2 operates by turning on the thyristor 46 after a predetermined time has elapsed, similarly to the discharge lamp lighting device shown in FIG.

〔Effect of the invention〕

According to the discharge lamp lighting device of the present invention, after the DC power supply circuit is turned on, the switching element is turned off for a predetermined time by the delay circuit, and the base current flowing through the transistor is turned off, so that the inverter circuit can be reliably started. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a discharge lamp lighting device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a discharge lamp lighting device according to another embodiment of the same, and FIG. 3 is a conventional discharge lamp lighting device. FIG. Ru. 21...DC power supply circuit, 25...Inverter circuit, 28
・・Transistor, 29・Drive transformer, 29b
Secondary winding, 3o... Capacitor, 3 Transistor as switching element, 32... Diode, 3
7...Delay circuit, 46...Sirisk as a switching element.

Claims (1)

[Claims] (1) It is equipped with a DC power supply circuit and an inverter circuit that converts the DC of this DC power supply circuit into a high frequency. a drive transformer for feeding back, a drive capacitor connected to the base of the transistor, a discharge diode connected in parallel to this capacitor, a switching element connected in series to this diode, and the DC power supply. A discharge lamp lighting device comprising: a delay circuit that turns on the switching element with a predetermined time delay after DC power is applied from the circuit.