JPH08288087A - Electronic ballast for discharge lamp - Google Patents

Abstract

PURPOSE: To maintain lighting even in the case where an input power source is momentarily cut off during lighting by providing an input current control means for increasing the input current to a bridge invertor circuit when an input voltage detecting means detects the lowering of the input voltage. CONSTITUTION: In the case where the input voltage of an electronic ballast of a discharge lamp is momentarily cut off, when the input voltage of a bridge invertor circuit 13 is lowered than that of the normal time, the output voltage of a computing amplifier OA is lowered, and the pulse width of the output signal of a comparator CO1 is widened. Next, a control circuit 17 widens the time ratio of the bridge invertor circuit 13 in response to the output of the comparator CO1, and enlarges the input current to the bridge invertor circuit 13 till the voltage of the non-inverted input terminal of the computing amplifier OA becomes equal to the voltage of the inverted input terminal. When the input voltage of the circuit 13 is lowered, the current reference signal is raised in response to the reduction of the input voltage, and the constant power can be thereby supplied to a discharge lamp LA. Consequently, even in the case where the alternating current input voltage is momentarily cut and the input voltage of the circuit 13 is lowered, the constant power can be supplied to a high luminance discharge lamp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-intensity discharge lamp such as a metal halide lamp or a sodium lamp which is lit by an electronic ballast at a low frequency rectangular wave voltage, and an input voltage of a bridge inverter circuit constituting the electronic ballast. The present invention relates to an electronic ballast of a discharge lamp that supplies a constant power to a high-intensity discharge lamp by maintaining a constant input current, and particularly relates to maintaining lighting when an input power is interrupted.

[0002]

2. Description of the Related Art As a ballast for lighting a discharge lamp,
Although a magnetic leakage transformer is generally known, an electronic lighting device has recently begun to be used in order to reduce the size and weight and improve the stability of lighting (flickering and uniformity of brightness).

The electronic ballast for lighting a discharge lamp has components such as an inductor and a filter, and power control can be performed by using high frequency modulation widely used for controlling an ordinary inverter. , The electronic ballast as a whole being small due to their small components.

FIG. 6 is a diagram showing an example of a circuit proposed as an electronic ballast for lighting a discharge lamp.

This proposed technique is proposed in Japanese Patent Application No. 6-078037, which has been filed by the inventor of the present application, in which the rectifying circuit 11 rectifies an AC input voltage and rectifies the AC input voltage. The boosted chopper circuit 12 boosts and stabilizes the boosted voltage to a voltage that is similar to the AC input current waveform and is higher than the peak value of the input voltage, and converts the stabilized DC voltage to this DC voltage. The bridge inverter circuit 13 performs high frequency modulation and converts the rectangular wave AC voltage into a rectangular wave AC voltage, and the low pass filter 14 filters the rectangular wave AC voltage to supply a low frequency rectangular wave voltage to the discharge lamp LA as a load.

The current detection circuit 16 detects the input current of the bridge inverter circuit 13 and generates a voltage proportional to the average value of this input current so that the average value of the input current of the inverter circuit 13 becomes constant. In addition, transistors Q2, Q3, and Q that form the bridge inverter circuit 13
4, controls the pulse width of the control signal input to the gate of Q5.

Since the input voltage of the inverter circuit 13 is made constant by the boost chopper circuit 12, if the average value of the input current of the inverter circuit 13 is constant, the product of the input power is also constant, The electric power supplied to the discharge lamp LA becomes constant.

That is, since the electric power obtained by subtracting the loss in the inverter circuit 13 from the input electric power of the inverter circuit 13 is supplied to the discharge lamp LA and the operating power of the discharge lamp LA is almost constant, the loss in the inverter circuit 13 is also reduced. Since it can be regarded as constant, the discharge lamp LA is supplied with constant power. Further, there is an advantage that the configuration of the power control of the background art is simple.

[0009]

However, in the background art described above, when the input voltage to the electronic ballast for lighting the discharge lamp is momentarily cut off (the voltage is momentarily lowered and the power supply is stopped), the inverter circuit is provided. Since the input voltage to 13 decreases, the electric power to the discharge lamp LA decreases and the discharge lamp LA turns off. Further, when the discharge lamp LA is a high-intensity discharge lamp, it cannot be relighted unless the temperature decreases and the pressure decreases, but once the high-intensity discharge lamp LA is turned off, the pipe pressure of the discharge lamp LA increases. It takes a long time for the temperature to drop and the pressure to drop, and it takes a long time before relighting is possible. This relighting time differs depending on the type of the discharge lamp LA and the like, but is required to be, for example, 5 to 15 minutes.

On the other hand, a voltage drop due to a lightning strike, a disconnection of an accident system at the time of a short-circuit accident in the vicinity, or a voltage drop due to a momentary overcurrent due to the operation of a large-sized device reaches about 10 to 20 ms (a momentary interruption Occurs), the high-intensity discharge lamp LA is turned off, and there is a problem that a long re-lighting time is required as described above.

The present invention can supply constant power to the high-intensity discharge lamp even when the AC input voltage of the electronic ballast of the discharge lamp is momentarily cut off and the input voltage of the bridge inverter circuit drops. It is an object of the present invention to provide an electronic ballast for a discharge lamp, which can keep lighting even if the input power supply is momentarily cut off while the high-intensity discharge lamp is lighting.

[0012]

According to the present invention, there is provided an input voltage detecting means for detecting a decrease in input voltage of an electronic ballast of a discharge lamp, and when the input voltage detecting means detects a decrease in input voltage, An input current control means for increasing the input current to the bridge inverter circuit is provided.

[0013]

According to the present invention, the input voltage detecting means for detecting the decrease of the input voltage of the electronic ballast of the discharge lamp is provided, and when the input voltage detecting means detects the decrease of the input voltage, the input to the bridge inverter circuit Since the input current control means for increasing the current is provided, constant power can be supplied to the high-intensity discharge lamp even when the input voltage is momentarily cut off and the input voltage of the bridge inverter circuit is lowered, and therefore high-intensity discharge lamp is provided. Even if the input power supply is momentarily cut off during the lighting of the discharge lamp, the lighting can be maintained.

[0014]

1 is a circuit diagram showing a first embodiment of the present invention.

In this embodiment, a full-wave rectifier circuit 11, a boost chopper circuit 12, and a full bridge inverter circuit 13 are provided.
It has a low pass filter 14, a voltage detection circuit 15, a current detection circuit 16, a control circuit 17, an emitter follower circuit 18, and a reference voltage generation circuit 19.

The boost chopper circuit 12 includes an inductor L1 connected in series with the rectifier circuit 11, a switching semiconductor element Q1 such as a transistor or an IGBT connected across the rectifier circuit 11 and the inductor L1, and an inductor L1. Is connected in series to the switching semiconductor element Q1, the capacitor C1 connected across the diode D1, and the control circuit SC.

The full bridge circuit 13 is a MOSFET or IGB connected diagonally, that is, on one of the opposite sides.
Switching semiconductor elements Q2 and Q5 such as T, switching semiconductor elements Q3 and Q4 such as MOSFETs or IGBTs connected to the other opposing side, and diodes connected in antiparallel to these switching semiconductor elements Q2 to Q5, respectively. D2 to D5. The control circuit 17 controls these switching semiconductor elements Q2 to Q5.

The output filter circuit 14 includes an inductor L2.
And a capacitor C2, and a full bridge circuit 13
By removing the high-frequency component of the high-frequency modulated low-frequency voltage output by, the desired low-frequency rectangular voltage can be applied to the discharge lamp LA.

The voltage detection circuit 15 is a step-up chopper circuit 1
2 is a circuit that outputs a detection voltage that is proportional to the output voltage, and is configured by a series circuit of resistors R9 and R10 connected to the output terminal of the step-up chopper circuit 12, and includes resistors R9 and R10.
The detected voltage appears at the connection point with.

The current detection circuit 16 includes a current transformer CT for detecting the input current of the bridge inverter circuit 13 and a current transformer C.
Resistors R1, R2, R3, which smooth the voltage detected by T,
A circuit having a capacitor C and outputting a voltage V1 proportional to the average value of the input current of the bridge circuit 13 and a voltage V2 proportional to the instantaneous value of the input current.

The control circuit 17 includes an operational amplifier OA and a first
No. 1 comparator CO1, a second comparator CO2 for limiting the peak value of the current flowing through the discharge lamp LA, a triangular wave generation circuit 171, an oscillator OS, and a logic circuit LC.

The operational amplifier OA amplifies the error signal between the detection voltage V1 corresponding to the average value proportional to the input current of the full-bridge inverter circuit 13 and the current reference value er which is the divided value of the reference voltage Eref. First comparator CO1
It is a circuit which is given to the inverting input terminal of. As shown in FIG. 4 (1), the first comparator CO1 compares the error amplified signal with the triangular wave signal supplied to the non-inverting input terminal, and as shown in FIG. 4 (2), the triangular wave signal has an error. It is a circuit that outputs the output signal to the logic circuit LC only during a period in which the amplified signal is exceeded. The output signal of this logic circuit LC is an output pulse whose pulse width is controlled, and the full bridge inverter circuit 1
The ON / OFF time of the switching semiconductor elements Q4 and Q5 is controlled (that is, controlled by the duty ratio) so that the average value of the input current of 3 becomes equal to the reference value.

The second comparator CO2 compares the detection voltage V2 corresponding to the instantaneous value proportional to the input current of the full-bridge inverter circuit 13 with the divided voltage value of the reference voltage value Eref, and detects the instantaneous value. When the voltage V2 exceeds the divided value, the control signals i and j shown in FIG. 3 are changed to a low level to turn off the switching semiconductor element and limit the peak value of the current flowing in the discharge lamp LA to a predetermined value or less. Is.

The emitter follower circuit 18 is composed of a transistor Q and an emitter resistor R8, and the base current supplied from the reference voltage Eref increases when the input voltage of the bridge inverter circuit 13 decreases. There is.

The reference voltage generating circuit 19 has a reference voltage Eref.
And a resistor R4, R5 for dividing the reference voltage Eref and R6, R7.

FIG. 2 is a diagram showing a specific example of the control circuit SC in the boost chopper circuit 12 in the above embodiment, and is a diagram showing a circuit example for performing the duty ratio control as described above.

The control circuit SC detects the output voltage of the step-up chopper circuit 12 and outputs the detection voltage V _a to the resistor r1,
r2, resistors r3 and r4 that detect the output voltage of the rectifier circuit 11 and output the detected voltage V _b , and a reference voltage source E _r.
And the detected voltage V _a and the reference voltage value V of the reference voltage source E _r
Error amplifier OA that amplifies the difference from _r and outputs an error signal
₀ , a multiplier MP that multiplies this error signal by the detection voltage V _b of the rectified voltage detected by the resistors r3 and r4, a triangular wave oscillator TO that outputs a triangular wave, an output voltage of the multiplier MP, and a triangular wave of the triangular wave oscillator TO. Comparator CO that compares with
_{Has 0} and.

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

First, the switching semiconductor element Q1 in the boost chopper circuit 12 is controlled by the control circuit SC so that the voltage across the capacitor C1 becomes constant. In this control method, the switching semiconductor element Q1 is switched at a constant frequency, and the duty ratio of the switching semiconductor element Q1 is set to the error voltage between the instantaneous value of the input voltage and the detected value V1 of the voltage across the capacitor C1 and the reference value V _r. It is controlled accordingly.

When the switching semiconductor element Q1 is switched at a frequency significantly higher than the input frequency, it can be considered that the input voltage during one switching cycle is constant.

Assuming that the instantaneous value of the input voltage is e _i , the current variation i _ON during the ON period of the switching semiconductor element Q1 is
It looks like this: i _ON = e _i · t / L ₁ (1) Further, the current variation i _OFF during the off period of the switching semiconductor element Q1 is as follows, where the voltage across the capacitor C1 is E ₀ . i _OFF = (E ₀ −e _i ) t / L ₁ (2) Here, since the increase / decrease in the current in one switching cycle can be regarded as zero, the ON period of the switching semiconductor element Q1 is t _ON , and one cycle is T 1. Then, it becomes as follows. e _i · t _ON / L ₁ = (E ₀ −e _i ) · (T−t _ON ) / L ₁ (3) From the expression (3), the following expression (4) is obtained. t _ON = (E ₀ −e _i ) T / E ₀ (4) The switching semiconductor element Q1 satisfies the formula (4).
When the duty ratio is controlled, the input current of the boost chopper circuit 12 has a sine wave shape. Therefore, it is possible to remove harmonics that cause harmonic interference.

Here, the amplification factor of the error amplifier OA ₀ is G
1. If the amplification factor of the multiplier MP is G2, the output voltage V _c of the multiplier MP is as follows. V _c = (V _a −V _r ) V _b · GI · G2 (5) The width P _W of the output pulse of the comparator CO ₀ when the peak value of the triangular wave of the triangular wave oscillator TO is V _P is P _W = - and _{{V P (V a -V r} ) V b · GI · G2} T / V P becomes, GI · G2 = G, When _{(V a -V r) = V} x, equation (6) can get. _{P W = (V P -V x} · V b · G) T / V P ...... (6) the ratio of the rectified voltage which is the output voltage of the rectifier circuit 11 and the detected voltage V _b, and the peak value of the triangular wave Both the ratio of V _P and the voltage across the capacitor C1 are made equal, and V _x
When G≈1, the equation (6) becomes similar to the equation (4),
It can be seen that the input current of the boost chopper circuit 12 has a sine wave shape.

On the other hand, the error amplifier OA ₀ amplifies the difference between the detected value of the voltage across the capacitor C1 and the reference voltage value V _r ,
Therefore, even a slight variation in the voltage across the capacitor C1 is amplified, so that the voltage across the capacitor C1 can be maintained at a constant voltage by controlling the duty ratio (pulse width).

Next, the operation of the bridge inverter circuit 13 will be described.

FIG. 3 is a diagram showing the signal waveform of the main part in the above embodiment.

A switching semiconductor element Q connected in series to the first arm of the full-bridge inverter circuit 13.
3 and Q2 are respectively driven by mutually complementary drive signals g and h from the control circuit 17, and the switching semiconductor elements Q4 and Q5 connected in series to the second arm thereof are respectively driven by the control signals i and j. To be done.

The drive signals g and h have a frequency (for example, 50 to 300 H) determined according to the capacity and properties of the discharge lamp LA.
z). Further, the control signals i and j are frequencies determined by circuit conditions (for example, a frequency of 20 to 100 kHz), and the switching semiconductor elements Q4 and Q5 are driven at a much higher frequency than the switching semiconductor elements Q2 and Q3. It Therefore, the switching semiconductor device Q
The switching semiconductor element Q5 is repeatedly turned on and off at a high frequency while the switching element 2 is conducting, and the switching semiconductor element Q5 is switched on and off.
The switching semiconductor element Q4 is repeatedly turned on and off at a high frequency during conduction of the full bridge inverter circuit 1
A high frequency modulated low frequency voltage appears at the output terminal of 3.

The input voltage of the full-bridge inverter circuit 13 is maintained at a constant voltage by the boost chopper circuit 12, and the average value of the input current of the full-bridge inverter circuit 13 is also controlled to be constant. Electric power also becomes constant. Full bridge inverter circuit 1
Since all the electric power input to 3 is supplied to the discharge lamp LA, a constant power is supplied to the discharge lamp LA. When the triangular wave signal is obtained by a simple circuit, the output signal from the oscillator OS is obtained by charging and discharging a capacitor (not shown) with a predetermined time constant.

On the other hand, the output signal of the duty ratio control of the first comparator CO1 as shown in FIG.
Is also input to, counted, and divided into 1 / n. Therefore, the counter CN outputs a rectangular signal as shown in c and d of FIG. 3 to the logic circuit LC. This n is often set to 50 or more. In this case, the frequency of the control signals i and j of the switching semiconductor elements Q4 and Q5 is 50 compared with the frequency of the drive signals g and h of the switching semiconductor elements Q3 and Q2. More than double. Since the output signal of the oscillator OS is, for example, a high frequency pulse of 20 to 100 kHz, the control signals i and j supplied to the switching semiconductor elements Q4 and Q5 have a frequency of 20 to 100 kHz during normal operation, and the switching semiconductor element is The drive signals g and h applied to Q3 and Q2 have frequencies equal to or lower than 1/50 of the control signals i and j.

In the control circuit 17, the output signal of the duty ratio control of the first comparator CO1 as shown by b in FIG. 3 is divided into 1 / n by the counter CN,
Switch the polarity of the output voltage.

Further, the second comparator CO2 compares the detected voltage V2 proportional to the instantaneous value of the input current of the full-bridge inverter circuit 13 with the divided voltage value of the reference voltage value Eref, and detects the value corresponding to the instantaneous value. When the voltage V2 exceeds the divided voltage value, the control signals i and j shown in FIG. 3 are changed to a low level to turn off the switching semiconductor element. In this way, the peak value of the current flowing through the discharge lamp LA is limited to a predetermined value or less.

That is, in general, the terminal voltage of the discharge lamp LA immediately after lighting is as low as 10 to 20 V, and when constant voltage control is performed by the step-up chopper 12, the output current becomes large as shown in FIG. Too much, the life of the discharge lamp LA is shortened, and the current capacity of the lighting device needs to be increased, so that the lighting device becomes large. In order to prevent this, the input current of the full bridge inverter circuit 13 is limited to a predetermined value or less.

Next, the operation when the input voltage of the electronic ballast of the discharge lamp is momentarily cut off will be described.

First, when the input voltage of the bridge inverter circuit 13 is a steady value, the values of the resistors R9 and R10 are set so that the collector current of the transistor Q in the emitter follower circuit 18 becomes zero. The voltage at the inverting input terminal of the operational amplifier OA is Eref.R7 / (R
6 + R7).

Here, when the input voltage of the bridge inverter circuit 13 is lower than that in the steady state, the base potential of the transistor Q is lowered, and a current of hfe times the base current flows in the collector of the transistor Q. Resistance R7
And the voltage across the resistor R7 rises, so the inverting input voltage of the operational amplifier OA rises.

When the hfe of the transistor Q is sufficiently large and the current input to the bridge inverter circuit 13 is sufficiently larger than the base current of the transistor Q, the collector current i _c of the transistor Q is as follows (7). It is represented by a formula. i _c = Eref / R8−R10 · E / R8 (R9 + R10) −V _BE / R8 (7) In the formula (7), the bridge inverter circuit 13 is used.
R9 and R10 are determined so that i _c becomes zero when the input voltage E of E is the steady-state voltage Era.

The voltage across the resistor R7 (voltage at the inverting input terminal) er rises when the collector current i _c flows in, and becomes the voltage of the following equation (8). er = R7 (Era + R6 · _ic ) / (R6 + R7) (8) In the equation (7), if Eref and V _BE are constant,
Since the collector current i _c increases as the input voltage E of the bridge inverter circuit 13 decreases, the voltage er at the inverting input terminal of the operational amplifier OA rises in proportion to the collector current i _c from the equation (8). .

The output voltage of the operational amplifier OA changes so that the voltage at its non-inverting input terminal becomes equal to the voltage at its inverting input terminal.
The width of the output pulse of the control circuit 17 is determined by comparing it with the triangular wave output from the triangular wave generation circuit 171.

As described above, the bridge inverter circuit 1
When the input voltage of 3 drops below the steady state, the operational amplifier O
The inverting input terminal voltage of A rises, the output voltage of the operational amplifier OA falls, and the output signal of the comparator CO1 widens the pulse width. Depending on the output of the comparator, the control circuit 1
7 enlarges the duty ratio of the bridge inverter circuit 13 and increases the input current to the bridge inverter circuit 13 until the voltage of the non-inverting input terminal of the operational amplifier OA becomes equal to the inverting input terminal.

Input voltage E of the bridge inverter circuit 13
Is decreased from the steady voltage by Δei, the collector current i _c of the transistor Q is i _c = R10 · Δei / R8 (R9 + R10) from the equation (7), and the collector current i _c causes the inverting input terminal of the operational amplifier OA. When the voltage er of Δi / Era increases from the steady state, the non-inverting input terminal of the operational amplifier OA also increases by Δei / Era and the input voltage becomes almost constant.

Therefore, R8 may be determined so that the following expression (9) is established. [{R10 · Δei / R8 (R9 + R10)} · R6 / Eref] = Δei / Era ... (9) Therefore, by setting R8 = {R6 · R10 / (R9 + R10)} · (Era / Eref), the bridge inverter When the input voltage of the circuit 13 decreases, the current reference signal is increased in accordance with the decrease of the input voltage, whereby the discharge lamp LA can be supplied with substantially constant power.

In the above embodiment, since the rate of increase of the input current is controlled to be equal to the rate of decrease of the input voltage of the bridge inverter circuit 13, the constant power cannot be accurately obtained. That is, assuming that the input voltage of the bridge inverter circuit 13 in the steady state is Era and its input current is Ira, the power P when the input voltage decreases is
It is calculated by the equation (0). P = (Era−Δei) × Ira (1 + Δei / Era) (10) Therefore, P = Era · Ira−Δei ² × Ira / Era (11) and the second term of the equation (11) is an error. The error rate is (Δei / Era) ² and the input voltage is 2/3 of the steady state.
When the error drops to 11%, the error becomes 11%, but if the error is at this level, there is no problem in maintaining the lighting. Then, when the input voltage becomes 1/2 of the steady state, the power drops by 25%, but even at this level, the lighting can be maintained.

Further, the bridge inverter circuit 13 may have a normal half-bridge structure composed of a capacitor and a switching semiconductor element. In this case, both switching semiconductor elements may be switched at a high frequency and alternately switched at a low frequency to operate.

In the above embodiment, one pair of switching semiconductor elements of the full-bridge inverter circuit 13 is driven at a low frequency and the other pair of switching semiconductor elements is controlled at a high frequency. May be switched at a high frequency, and each pair of switching semiconductor elements may be switched at a low frequency to operate alternately.

Further, in the above embodiment, the reference value control means for increasing the reference value as the decrease amount of the input voltage of the electronic ballast increases is provided, but instead of this, the input of the electronic ballast is used. An input current detection value control means for decreasing the detection current value detected by the input current detection means may be provided as the amount of decrease in voltage increases.

FIG. 5 is a circuit diagram showing a second embodiment of the present invention.

This second embodiment is basically the same as the first embodiment, but is a circuit in which the input current detection value control means 20 is added to the first embodiment. That is, in the second embodiment, when the input voltage (voltage of the capacitor C1) of the bridge inverter circuit 13 drops, the current detection circuit 16
This is a circuit for lowering the current detection value by the.

The input current detection value control means 20 has a base connected to resistors R12 and R13 forming a collector resistance of the transistor Q in the emitter follower circuit 18 and a connection point between the resistors R12 and R13.
And the emitter resistance of the transistor Q7, and the collector of the transistor Q7 is connected to the connection point between the resistors R3 and R2 (the point where the voltage V1 is generated).

Next, the operation of the second embodiment will be described.

When the input voltage of the bridge inverter circuit 13 (voltage of the capacitor C1) decreases, a base current flows through the transistor Q and is amplified to be amplified by the resistors R12 and R13.
An electric current flows through, and the value of the electric current at this time is represented by the equation (7). This current produces a voltage across resistor R13, which supplies the base current of transistor Q7. A collector current multiplied by hfe flows through the collector of the transistor Q7, and the voltage across the resistor R3 is lowered. That is, when the input voltage of the bridge inverter circuit 13 (voltage of the capacitor C1) decreases, the current detection value of the current detection circuit 16 decreases.

The value of the resistor R1 is set sufficiently smaller than the values of the resistors R2 and R3, and the transistor Q
Even if the collector current of 7 flows, the voltage across the resistor R1 is not affected. The collector current of the transistor Q7 is ic
₂ , assuming that the average voltage across the resistor R1 is e, the resistor R3
The voltage e _R3 between both ends becomes e _R3 = {R3 / (R2 + R3)} · e−R2 · ic ₂ . When the voltage across the capacitor C1 is in a steady state is ics ₂ = 0, if the voltage across the capacitor C1 is set such ics ₂ begins to flow when smaller than the steady state, the voltage of the capacitor C1 the input short break When it starts to decrease, the voltage e _R3 across the resistor R3 gradually decreases.

As a result, the conduction widths of the transistors Q4 and Q5 are widened, the constant power is supplied to the load and the lighting of the discharge lamp LA is continued. That is, also in the second embodiment, constant power can be supplied to the high-intensity discharge lamp even when the AC input voltage is momentarily cut off and the input voltage of the bridge inverter circuit drops.

[0063]

According to the present invention, constant power can be supplied to the high-intensity discharge lamp even when the AC input voltage is momentarily cut off and the input voltage of the bridge inverter circuit is lowered. Even if the input power supply is momentarily cut off during lighting of the electric lamp, the lighting can be maintained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a specific example of a control circuit SC in the above embodiment.

FIG. 3 is a diagram showing a signal waveform of a main part in the above embodiment.

FIG. 4 is a diagram illustrating the operation of the above embodiment.

FIG. 5 is a circuit diagram showing a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a constant power control method for a discharge lamp in the background art.

[Explanation of symbols]

 11 ... Rectifier circuit, 12 ... Booster chopper circuit, 13 ... Bridge inverter circuit, 14 ... Low pass filter circuit, 15 ... Voltage detection circuit, 16 ... Current detection circuit, 17 ... Control circuit, 18 ... Emitter follower circuit, 19 ... Reference voltage Generating circuit, 20 ... Input current detection value control circuit, CT ... Current transformer, CO1 ... First comparator, CO2 ... Second comparator, OA ... Operational amplifier, SC ... Control circuit, LC ... Logic circuit.

Claims (2)

[Claims] 1. A high-intensity discharge lamp is lit by an electronic ballast with a low-frequency rectangular wave voltage, and the input voltage and the input current of a bridge inverter circuit constituting the electronic ballast are maintained constant, respectively In an electronic ballast of a discharge lamp for supplying constant power to a brightness discharge lamp, an input current detecting means for detecting an average value of an input current of the electronic ballast; and an average value of the input current detected by the input current detecting means. And input current control means for maintaining a constant input current of the electronic ballast according to a predetermined reference value;
Input voltage detection means for detecting the value of the input voltage of the electronic ballast; reference value control means for increasing the reference value as the amount of decrease in the value of the input voltage detected by the input voltage detection means increases. An electronic ballast for a discharge lamp, comprising: 2. A high-intensity discharge lamp is lit by an electronic ballast with a low-frequency rectangular wave voltage, and an input voltage and an input current of a bridge inverter circuit which constitutes the electronic ballast are maintained constant, thereby increasing the high voltage. In an electronic ballast of a discharge lamp for supplying constant power to a brightness discharge lamp, an input current detecting means for detecting an average value of an input current of the electronic ballast; and an average value of the input current detected by the input current detecting means. And input current control means for maintaining a constant input current of the electronic ballast according to a predetermined reference value;
An input voltage detecting means for detecting an input voltage value of the electronic ballast; a detected current value detected by the input current detecting means as the amount of decrease in the input voltage value detected by the input voltage detecting means increases. And an input current detection value control means for reducing the electric current.