JP2940652B2 - AC discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC lighting device for a discharge lamp such as a metal halide lamp.

[0002]

2. Description of the Related Art In general, in order to light a discharge lamp, for example, a metal halide lamp, a lighting device usually called a ballast is required. This ballast used to be large and large in the past, but recently a small and lightweight ballast employing a semiconductor switching element has become mainstream. Therefore, MOSFE is used as a semiconductor switching element.
A method of alternating-current lighting using T or the like has been put to practical use.

FIG. 5 is a circuit diagram of a main part of a conventional AC lighting device for a discharge lamp. In the figure, reference numeral 1 denotes a high-pressure discharge lamp such as a metal halide lamp (hereinafter simply referred to as a lamp). Reference numeral 7 denotes a commercial AC power source. A first smoothing circuit 6 having a rectifying diode 61 and a smoothing capacitor 62 is connected to both terminals of the AC power source via a switch 70 to form a DC power source. A MOSFET 31 is connected to an output terminal of the DC power supply as a first switching element that opens and closes at a high frequency, and a chopper circuit 3 is configured. The output terminal of the chopper circuit 3 has a second
Is connected to the second smoothing circuit 10.
Is output to the polarity switching circuit 2. This polarity switching circuit 2 uses a MOSF as a second switching element.
The ETs 21 to 24 are connected in a full bridge type, and the low frequency output is supplied to the lamp 1 via the capacitor 11 and the starter 12. The starter 12 starts the lamp 1 when starting.
An ultra-high voltage pulse for causing dielectric breakdown between the electrodes is supplied.

In the chopper circuit 3, the MOSFET 31
Controls the opening and closing at a high frequency of about 50 KHz, and when it is off, a current flows by the energy stored in the choke coil 13 as an inductance element. Chopper circuit 3
Is controlled by a pulse signal output from the control circuit 4.
In the polarity switching circuit 2, the MOSFET 21 and the MOSF
ET24, a pair of series-connected second switching elements of MOSFET22 and MOSFET23 are alternately opened and closed at about 400 Hz by a polarity switching drive circuit (not shown). The current input to the polarity switching circuit 2 is smoothed by the choke coil 13, the capacitor 15 and the choke coil 14 in the second smoothing circuit 10 and is almost in a DC state. Supplied.

[0005] In order to control the power supplied to the lamp 1, constant power control is generally employed. The constant power control is performed by the control circuit 4
This is mainly performed by controlling the chopper circuit 3 by a negative feedback operation. As described above, since the polarity switching circuit 2 simply switches the DC output of the second smoothing circuit 10 to a square wave AC, a current signal I equivalent to the current flowing through the lamp 1 is output from the shunt resistor 45 to the voltage An equivalent voltage signal V is obtained from the voltage dividing resistors 43 and 44. The current signal I and the voltage signal V are converted into a power signal W by the multiplier 46 and input to the error amplifier 47 together with the power reference signal ST.

The error signal E output from the error amplifier 47
R is input to the PWM control IC 48, and the error signal ER
The PWM control IC 48 controls the MOSFET 3 of the chopper circuit 3 via the drive transformer 49 so that
1 controls the pulse width of the output pulse. The drive transformer 49 is for driving the control circuit 4 and the MOSFET 31 with insulation, and can be removed when insulation is not required.

[0007]

By the way, the MOSFE which is the second switching element in the polarity switching circuit 2
At T21, T24, T22, T23, and T23, all are turned off at the moment of the on / off switching by the polarity switching drive circuit for about 2 μsec. Therefore, the output voltage Va and the output current Ia of the second smoothing circuit 10 and the output voltage V of the polarity switching circuit 2
b and the output waveform of the current Ib are as shown in FIG. Here, the horizontal axis t is time, and t ₁ is MOSFET21,22,2.
This is a quiescent period in which all 3 and 24 are off. FIG.
, The output current I from the second smoothing circuit 10
a, the polarity switching output current Ib of the circuit 2, immediately after the rest period t _1, includes any frequency component rises to a step function shape. And the capacitor 15 in the second smoothing circuit 10
And the resonance frequency f = 1 / (2π
Resonance of a current having a frequency component matching (L ₁₄ C ₁₅ ) ^1/2 occurs. Here, L ₁₄ is the choke coil 1
The inductance of 4 and C ₁₅ is the capacitance of the capacitor 15. The resonance frequency depends on the inductance of the choke coil 14 and the capacitance of the capacitor 15 determined in the circuit design, but is usually a high frequency of several KHz or more.

Accordingly, a current signal I having a resonance frequency component amplified so that other high-frequency components can be ignored is input from the shunt resistor 45 to the constant power control negative feedback loop.
The negative feedback loop starts oscillating depending on the circuit element constant in the negative feedback loop determined in the circuit design.
When the oscillation occurs, the current ripple increases, so that the lamp life is deteriorated or the lamp is turned off in severe cases.

Therefore, the present invention has been made in view of such circumstances, and even if the above-described current resonance occurs, the lamp 1 is stably turned on without generating oscillation in the constant power control negative feedback loop. It is an object of the present invention to provide a lamp lighting device.

[0010]

In order to achieve the above object, the present invention provides a first smoothing circuit to which a commercial AC power supply is connected , a chopper circuit having a first switching element, an inductance L and a capacitance. With C
A second smoothing circuit that includes a polarity switching circuit having a second switching element, set to an output side of said second smoothing circuit
Current and voltage supplied to the discharge lamp
A control circuit for generating a valuable current signal and a voltage signal ,
The control circuit controls the operation of the chopper circuit to control the power supplied to the discharge lamp. In the lighting device for an AC discharge lamp, the control circuit has a cutoff characteristic with respect to a frequency equal to or higher than a resonance frequency of the second smoothing circuit. A low-pass filter provided in the control circuit.

[0011]

By providing a control circuit comprising a low pass filter having a cut-off characteristics for [action] inductance L ₁₄ and frequency above the resonance frequency f according to the capacitance C ₁₅ of the capacitor 15 of the second choke coil 14 in the smoothing circuit, Even if the current starts to resonate, a signal containing a resonance frequency component is not transmitted to the PWM control IC 48. Therefore, the negative feedback loop does not reach oscillation, and the current ripple caused by the oscillation does not increase, so that the lamp 1 is stably turned on. The resonance of the current is attenuated by a resistance component existing in the circuit.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the drawing, components having the same reference numerals as those in FIG. 5 indicate the same elements. In the figure, reference numeral 1 denotes a lamp. Reference numeral 7 denotes a commercial AC power source. A first smoothing circuit 6 having a rectifying diode 61 and a smoothing capacitor 62 is connected to both terminals of the AC power source via a switch 70 to form a DC power source. A MOSFET 31 is connected to an output terminal of the DC power supply as a first switching element that opens and closes at a high frequency, and a chopper circuit 3 is configured. A smoothing circuit 10 for removing high-frequency ripple is connected to an output terminal of the chopper circuit 3, and a DC output from the second smoothing circuit 10 is input to the polarity switching circuit 2. This polarity switching circuit 2 has MOSFETs 21 to 24 connected as a second switching element in a full-bridge type,
1 and the starter 12 are supplied to the lamp 1. The starter 12 supplies an ultra-high voltage pulse for causing a breakdown between the electrodes of the lamp 1 at the time of starting.

In the chopper circuit 3, the MOSFET 31
Controls the opening and closing at a high frequency of about 50 KHz, and when it is off, a current flows by the energy stored in the choke coil 13 as an inductance element. Chopper circuit 3
Is controlled by a pulse signal output from the control circuit 4.

In the polarity switching circuit 2, the MOSFET 2
1 and MOSFET 24, MOSFET 22 and MOSFE
A pair of second switching elements connected in series at T23 are alternately opened and closed at about 400 Hz by a polarity switching drive circuit (not shown). That is, MOSFET 21 and MO
SFET24 is on and MOSFET22 and MOSFET
When 23 is off, MOSFET 21 → lamp 1 → MO
A closed circuit of the SFET 24 is formed. Also MOSFET
21 and MOSFET 24 are off and MOSFET 22 and M
When the OSFET 23 is on, a closed circuit of the MOSFET 22 → the lamp 1 → the MOSFET 23 is formed. The current input to the polarity switching circuit 2 is smoothed by the choke coil 13, the capacitor 15, and the choke coil 14 in the second smoothing circuit 10 and is almost in a DC state. Is supplied.

The starter 12 is specifically constituted by a circuit as shown in FIG. 2 and has a pulse transformer 63 for generating a high voltage therein, and its secondary winding 631 is connected in series with the lamp 1. ing. The winding 631 functions as a current limiting element of the polarity switching circuit 2 after the lamp 1 is turned on. The capacitor 11 is for removing noise generated from the starter 12.

After the power switch 70 shown in FIG. 1 is turned on, the terminals 12a and 12a of the polarity switching circuit 2
The voltage is supplied from b. First, the capacitor 65 is charged via the resistor 64, and when the charged voltage reaches the discharge voltage of the Sidac 66, the capacitor 65 starts discharging. Then, the capacitor 69 is charged via the transformer 67 and the diode 68. Similarly, when the charging voltage of the capacitor 69 reaches the discharging voltage of the spark gap 71, discharging is started, and a high-voltage pulse is generated in the secondary winding 631 of the transformer 63.

When the breakdown of the lamp 1 is caused by the high-voltage pulse, the voltage across the lamp 1 becomes lower than before the breakdown, and becomes lower than the discharge voltage of the SIDAC 66. Therefore, after the dielectric breakdown, the starter 12 does not operate.
Then, the lamp 1 shifts from the dielectric breakdown state caused by the application of the high-voltage pulse to the stable state when a low-frequency current is supplied by the polarity switching circuit 2 that follows.

As before, the power supplied to the lamp 1 is generally controlled at a constant power. The constant power control is performed by controlling the chopper circuit 3 mainly by a negative feedback operation by the control circuit 4. As described above, since the polarity switching circuit 2 simply switches the DC output of the second smoothing circuit 10 to a square wave AC, a current signal I equivalent to the current flowing through the lamp 1 is output from the shunt resistor 45 to the voltage An equivalent voltage signal V is obtained from the voltage dividing resistors 43 and 44. The current signal and the voltage signal are converted into a power signal W by the multiplier 46 and input to the error amplifier 47 together with the power reference signal ST.

The error signal E output from the error amplifier 47
R is input to a PWM control IC 48 via a low-pass filter 80 (hereinafter, referred to as LPF) formed by a capacitor 81 and a resistor 82, and the PWM control IC 48 is connected via a drive transformer 49 so that the error signal ER becomes constant. Thus, the pulse width of the pulse output from the MOSFET 31 of the chopper circuit 3 is controlled. For example, the error signal ER
Becomes larger, the pulse width of the pulse output from the MOSFET 31 is increased (ON DUTY is increased).
Such a control method is called pulse width control (PWM), and the lamp 1 is turned on with a constant power by this method.
The drive transformer 49 is connected to the constant power control circuit 4 and the MOS
This is for driving the FET 31 with insulation.
If insulation is not required, it can be removed.

As described in the conventional example, when current resonance occurs, the resonance frequency f = 1 / (2π (Lπ) by the capacitor 15 and the choke coil 14 in the second smoothing circuit 10.
A current signal I from the shunt resistor 45 having a frequency component matching ₁₄ C ₁₅ ) ^1/2 ) is input to the constant power control negative feedback loop. However, even if the constant power negative feedback loop has an oscillation condition at its resonance frequency, the LPF 80
Signal containing a resonance frequency component by the PWM control IC
The constant power control negative feedback loop does not oscillate. Therefore, the current ripple caused by the oscillation does not increase, and the lamp 1 is stably turned on. The resonance of the current is attenuated by a resistance component existing in the circuit.

In order to confirm the effect of the present invention, the capacitance of the capacitor 15 was 1 μF, and the choke coil 14
Has an inductance of 1 mH and a resonance frequency f = 1 / (2
In the case of π (1 μ × 1 m) ^1/2 ) = 5 KHz, an LPF 80 composed of a 2200 pF capacitor 81 and a 220 KΩ resistor 82 with a cutoff frequency of ² KHz
The waveforms of the output current Ib of the polarity switching circuit 2 when and were not connected were compared. FIG. 3 is a waveform of the output current Ib of the polarity switching circuit 2 when the LPF 80 is not connected, and FIG. 4 is a waveform of the output current Ib of the polarity switching circuit 2 when the LPF 80 is connected. Here, the vertical axis i is current, and the horizontal axis t is time.

When the LPF 80 is not connected, a current ripple having an amplitude of 0.4 A and a half cycle of 200 μsec is present in the output current Ib of the polarity switching circuit 2, whereas
When 80 is connected, the current ripple having a maximum amplitude of 0.4 A is attenuated within 1 msec. Therefore lamp 1
It can be seen that stable lighting is possible.

Here, L consisting of a resistor and a capacitor
Although the PF is shown, the present invention is not particularly limited to this configuration. For example, a general constant-K filter or an induction M filter formed of a coil and a capacitor may be employed.

[0024]

As described above, in the AC discharge lamp lighting device according to the present invention, since the low-pass filter 80 is formed in the control circuit 4, the second smoothing circuit 10 is formed.
Current resonance occurs in a loop composed of the capacitor 15, the choke coil 14, and the lamp 1 inside, and the current signal I from the shunt resistor 45 having a frequency component matching the resonance frequency f of the loop is controlled by constant power. Even when the signal is input to the negative feedback loop and the constant power negative feedback loop has an oscillation condition at its resonance frequency, a signal containing a resonance frequency component does not propagate to the PWM control IC 48, and the constant power control negative feedback loop Does not oscillate. Therefore, the current ripple caused by the oscillation does not increase, so that the lamp 1 is stably provided.
Can be lit. Although the case where the constant power control is performed as the control of the power supplied to the lamp 1 has been described, it is apparent that the same effect can be obtained when the constant power control is performed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a main part of an AC lighting device for a discharge lamp according to the present invention.

FIG. 2 is an example of a specific circuit of a starter 12;

FIG. 3 shows a polarity switching circuit 2 when an LPF 80 is not connected.
3 shows a waveform of the output current Ib.

FIG. 4 shows a waveform of an output current Ib of the polarity switching circuit 2 when an LPF 80 is connected.

FIG. 5 shows a circuit diagram of a main part of a conventional AC lighting device for a discharge lamp.

6 shows output waveforms of an output voltage Va and an output current Ia of the second smoothing circuit 10, an output voltage Vb and a current Ib of the polarity switching circuit 2. FIG.

[Brief description of reference numerals]

DESCRIPTION OF SYMBOLS 1 High-pressure discharge lamp 2 Polarity switching circuit 3 Chopper circuit 4 Control circuit 6 First smoothing circuit 7 Commercial AC power supply 10 Second smoothing circuit 11 Capacitor 12 Starter 12a, 12b Terminal 13 Choke coil 14 Choke coil 15 Capacitor 21, 22 , 23, 24, 31 MOSFET 43, 44 Voltage dividing resistor 45 Shunt resistor 46 Multiplier 47 Error amplifier 48 PWM control IC 49 Drive transformer 61 Rectifier diode 62 Smoothing capacitor 63 Pulse transformer 631 Secondary winding 64 Resistance 65, 69 Capacitor 66 Sidak 67 Transformer 68 Diode 70 Switch 71 Spark gap 80 Low pass filter (LPF) 81 Capacitor 82 Resistance I Current signal V Voltage signal W Power signal ST Power reference signal ER Error signal Va Output voltage of second smoothing circuit 10 Ia Output current of second smoothing circuit 10 Vb Output voltage of polarity switching circuit 2 Ib Output current of polarity switching circuit 2 L ₁₄ Inductance of choke coil 14 C ₁₅ Capacitance of capacitor 15 t Time t ₁ rest period f resonance frequency i current

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-171596 (JP, A) JP-A-3-283393 (JP, A) JP-A-3-283394 (JP, A) JP-A-3-283394 283395 (JP, A) JP-A-3-283396 (JP, A) JP-A-4-196094 (JP, A) JP-A-3-124591 (JP, U) JP-A-3-124592 (JP, U) JP-A-3-124593 (JP, U) JP-A-3-124594 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) H05B 41/24-41/29

Claims (1)

(57) [Claims] 1. A first smoothing circuit to which a commercial AC power supply is connected , a chopper circuit having a first switching element, a second smoothing circuit having an inductance L and a capacitance C, and a second switching element. A polarity switching circuit having: a discharge switch provided on the output side of the second smoothing circuit;
Current and voltage signals equivalent to the current and voltage supplied to the
A control circuit for generating a signal, the control circuit comprising: a lighting device for an AC discharge lamp that controls power supplied to a discharge lamp by controlling an operation of the chopper circuit; An AC discharge lamp lighting device, characterized in that a low-pass filter having a cut-off characteristic with respect to a frequency higher than a frequency is provided in the control circuit.