JPH08298191A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE: To provide a discharge lamp lighting device having a power characteristic suited for a discharge lamp characteristic by correcting a value of detecting a current flowing in a discharge lamp, relating to controlling power of the high brightness discharge lamp. CONSTITUTION: A device has a bridge inverter circuit 13 of converting DC power into low frequency power, overlapped with high frequency power of rectangular wave, supplied to a high brightness discharge lamp 15. The bridge inverter circuit 13, by fixedly maintaining a product of supply voltage and current to the high brightness discharge lamp 15, supplies fixed power. Here, a charge of a smoothing capacitor C in a current detector circuit 26 of detecting a current flowing in the bridge inverter circuit 13 is discharged thereto in a period with no current flowing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts a DC voltage into a rectangular wave high-frequency voltage by pulse width control, switches the polarity of the converted high-frequency voltage at a low frequency, and changes a high-frequency component into a rectangular wave by a low-pass filter. The present invention relates to a lighting device for a high-intensity discharge lamp that converts into an AC voltage and stably lights a high-intensity discharge lamp, and particularly to a current detection circuit in the discharge-lamp lighting device.

[0002]

2. Description of the Related Art Conventionally, a device using a magnetic leakage transformer has been generally used as a lighting device for high-intensity discharge lamps (metal halide lamps, sodium lamps, etc.), but it is compact and lightweight, and has stable lighting (flickering and flicker Recently, electronic lighting devices have begun to be used to improve the uniformity of brightness.

Electronic lighting devices generally use high frequency modulation, which is widely used for controlling ordinary inverters, to control power.

FIG. 4 is a diagram showing a constant power control device for a discharge lamp in Japanese Patent Application No. 6-078037 proposed by the present inventor.

In the constant power controller for a discharge lamp of this background art, an AC input voltage is rectified by a rectifier circuit 11, and a boost chopper circuit 12 makes an input current to the rectifier circuit similar to the input voltage. This rectified voltage is boosted and stabilized to a voltage higher than the input voltage,
The stabilized voltage is converted into a rectangular wave AC voltage that is high-frequency modulated by the bridge inverter circuit 13, the high-frequency component thereof is filtered by the low-pass filter 14, and the discharge lamp 1 that is a load is used.
5 is supplied with a low frequency rectangular wave voltage.

Next, the constant power control in the above background art will be described.

The input current of the bridge inverter circuit 13 is detected by the current transformer CT, and the current detection circuit 16 converts it into a voltage proportional to the average value of this input current. Then, the control circuit 17 controls the width of the pulse supplied to the high frequency arm in the bridge inverter circuit 13 so that the average value of the input current of the bridge inverter circuit 13 becomes constant.

Since the input voltage of the bridge inverter circuit 13 is made constant by the step-up chopper circuit 12, if the average value of the input current is constant, the product of the input power is also constant. Bridge inverter circuit 1
The power obtained by subtracting the loss in the bridge inverter circuit 13 from the input power of 3 is output from the bridge inverter circuit 13. Since the operating power of the discharge lamp 15 is almost constant, it can be considered that the loss is also constant, and therefore the constant power is supplied to the discharge lamp 15.

The current detection circuit 16 is generally a circuit as shown in FIG. 4, and the current detected by the current transformer CT is applied to the resistor R.
The voltage smoothed by 1, R2, R3 and the capacitor C and averaged is used as the control signal.

When the detected current is I and the turns ratio of the current transformer is 1: n, the voltage Vc across the capacitor C is expressed by the following equation (1). Vc = V (expTon / C.R-1) (1) Note that V = {(R1.R3) / (R1 + R2 + R3)}. (I
/ N) ・ e × p (-T / C ・ R) / {1-e × p (-T
/ C · R)} R = R3 · (R1 + R2) / (R1 + R2 + R3).

When the time constant C · R is sufficiently longer than the switching period T of high frequency, the equation (1) is as follows: Vc≈ {R1 · R3 / (R1 + R2 + R3)} · (I / n) · (Ton / T) ... (2) and the voltage Vc across the capacitor C is proportional to the product of the ratio (Ton / T) of the on-time Ton in one cycle T and the current to be detected. Since it is proportional to the average value of the input current to 13, the average current can be obtained.

[0012]

However, the equation (1),
In (2), the exciting current of the current transformer CT is ignored, and in reality, the exciting current component indicated by the diagonal lines in FIG. 5 (2) does not flow in the secondary winding of the current transformer CT. Since the current obtained by subtracting the exciting current appears, the longer the on-time Ton, the more the influence of the exciting current, and the more the detection voltage in the current detection circuit 16 decreases.

On the other hand, in the background art described above, the pulse width in the bridge inverter circuit 13 is controlled so that the value detected by the current detection circuit 16 becomes constant (the input current of the bridge inverter circuit 13 becomes constant). As the ON time Ton becomes longer, the current detection circuit 16
Since the detected voltage (voltage across the capacitor C) at 1 decreases, the input current of the bridge inverter circuit 13 increases as the duty ratio increases to compensate for the decreased detected voltage.

In the bridge inverter circuit 13, although not shown, it is only the reverse recovery period of the flywheel diode (for example, 50 ns reverse recovery period).
A very narrow current called a "beard" flows. The current during this reverse recovery period does not flow to the discharge lamp 15 that is the load, but the current corresponding to this current is 1 in the current transformer CT.
Since the current flows to the next side and the current detection circuit 16 detects the current in the reverse recovery period, the current detection circuit 16 actually detects a current larger than that flowing in the discharge lamp 15. Since the current flowing in this reverse recovery period is constant every cycle regardless of the pulse width, the wider the pulse width, the less the influence on the average value of the current detection circuit. As a result, the average value of the current detection seems to be relatively decreased as the pulse width becomes wider due to the influence of the exciting current.

By the way, in the sodium lamp, which is a kind of high-intensity discharge lamp, when the supply power is reduced (as indicated by the solid line in FIG. 6) as the inter-electrode voltage rises, the tint becomes similar, and many Even if the sodium lamp is turned on, color unevenness due to variations in the sodium lamp tends to be inconspicuous. However, when the lamp voltage is increased in the background art described above, the duty ratio is increased, the detected value of the input current is decreased as described above, and the pulse width is increased to increase the input current. Therefore, the electric power supplied to the lamp increases, and as shown by the broken line in FIG. 6, there is a problem that the color unevenness due to the variation of the sodium lamp becomes noticeable.

According to the present invention, in power control of a high-intensity discharge lamp, a detected value of a current flowing to the discharge lamp is corrected, and thereby a discharge lamp lighting device having a power characteristic suitable for the discharge lamp characteristic is supplied. It is intended.

[0017]

According to the present invention, a bridge inverter circuit converts constant voltage direct current power into high frequency modulated low frequency rectangular wave alternating current power, and duty ratio control is performed so that the input current of the bridge inverter circuit becomes constant. In a discharge lamp lighting device that supplies constant power to a load, a current transformer that detects an input current of a bridge inverter circuit, a rectifying unit that rectifies a voltage generated in a secondary winding of the current transformer, It has a capacitor for smoothing the rectified voltage, and a discharging means for discharging the electric charge charged in the capacitor when a current flows through the primary winding of the current transformer.

[0018]

According to the present invention, the electric charge of the smoothing capacitor in the current detecting circuit for detecting the current flowing in the input of the bridge inverter circuit is discharged during the period when the current is not flowing in the input of the bridge inverter circuit. The detected current value to be detected can be corrected.

[0019]

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

In this embodiment, a current detecting circuit 26 is used instead of the current detecting circuit 16 in the background art shown in FIG.

In the current detection circuit 26, the input current of the bridge inverter circuit 13 is detected by the current transformer CT, the voltage generated on the secondary side of the current transformer CT is rectified by the diode D1, and the rectified voltage is obtained. V2 is proportional to the instantaneous value of the input current of the bridge inverter circuit 13. The rectified voltage V2 is smoothed by the resistors R2 and R3 and the capacitor C, and the smoothed voltage V1 corresponds to the average value of the input current of the bridge inverter circuit 13.

Further, the rectified voltage V2 is divided by resistors R4 and R5, the base of the transistor Q1 is connected to this dividing point, the collector of the transistor Q1 is connected to the power supply Vcc via the collector resistor R6, and the resistor R7. And a collector / emitter of the transistor Q2 are connected in series with the capacitor C, and the base of the transistor Q2 is connected to the collector of the transistor Q1.

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

First, when an input current flows through the bridge inverter circuit 13, a voltage is generated on the secondary side of the current transformer CT, and the voltage rectified by the diode D1 is applied to the capacitor C via the resistor R2. , The capacitor C is charged. In this case, on the cathode side of the diode D1, a detection voltage V2 proportional to the input current of the bridge inverter circuit 13 and corresponding to its instantaneous value is generated, and at the connection point of the resistor R2 and the capacitor C, the bridge inverter circuit 13 is connected. A detection voltage V1 corresponding to the average value of the input current of 13 is generated.

Here, when the input current is flowing through the bridge inverter circuit 13, the voltage V2 is high, so that the resistance R4
The voltage at the connection point between R5 and R5 is also high, turning on the transistor Q1 and turning off the transistor Q2. In this case, since the discharge loop for the transistor Q2 is not formed, the charging of the capacitor C is continued.

On the other hand, when the input current to the bridge inverter circuit 13 disappears, the voltage V2 decreases, the voltage at the connection point between the resistors R4 and R5 also decreases, and the transistor Q1 turns off and the transistor Q2 turns on. In this case, since a discharge loop is formed via the transistor Q2 and the resistor R7, the charge charged in the capacitor C is discharged to this discharge loop, the loop to the resistor R3, and the loop to the resistors R2 and R1. That is, if the transistor Q1 determines whether or not there is an input current to the bridge inverter circuit 13 and it is determined that the input current does not flow, the transistor Q1
A new discharge loop to 2 is formed and the charge in the capacitor C is discharged via the resistor R7.

In the above operation, the following assumptions are made in order to simplify the explanation.

The charging / discharging time constant of the capacitor C is sufficiently larger than the cycle of the input current to the bridge inverter circuit 13, the voltage is considered to be direct current, and the value of the resistor R1 is the resistors R2 and R.
4 is sufficiently smaller than the value of 4, the voltage across the resistor R1 is proportional to the secondary current of the current transformer CT, the value of the resistor R4 is sufficiently larger than the value of the resistor R2, it does not affect the detected value at all. Furthermore, the voltage between the collector and the emitter when the transistor Q2 is on is zero, and the impedance when the transistor Q2 is off is infinite.
The reverse current of is zero.

Here, when the voltage across the resistor R1 is ei and the voltage across the capacitor C is Ed, the following equation holds. {(Ei-Ed) / R2} · Ton− (Ed / R3) · Ton = {(Ed / R3) + (Ed / R7)} · (T-Ton) (3) From this equation (3) , When the detection voltage Ed is obtained, Ed = ei / [1- (R2 / R7) + (R2 · T / Ton) · {(1 / R3) + (1 / R7)}] (4) .

Therefore, from the equation (4), the on time To
It can be seen that the larger the value of n, the larger the detected voltage Ed, and the correction of the power characteristic becomes possible. Further, the denominator of the equation (4) is amended as shown in the equation (5), and the correction amount can be changed by changing the value of the resistor R7. The smaller the value of the resistor R7, the more the correction amount. Grows larger. 1+ (T / Ton) * (R2 / R3) + (R2 / R7) * {(T / Ton) -1} (5) That is, in the above embodiment, the voltage applied to the discharge lamp 15 is high. This means that the ON time Ton becomes longer, in other words, the period during which the current flows in the primary winding of the current transformer CT becomes longer, so that the ON time of the transistor Q2 becomes shorter and the transistor Q2 becomes shorter. Since the amount of discharge of the capacitor C due to turning on becomes small, the current detection value becomes relatively high as the on time Ton becomes long.
As a result, the electric power supplied to the discharge lamp 15 is reduced. That is, when the voltage applied to the discharge lamp 15 increases, the power supplied to the discharge lamp 15 decreases.

On the other hand, a lower voltage applied to the discharge lamp 15 means a shorter ON time Ton, in other words, a shorter period in which current flows in the primary winding of the current transformer CT. Therefore, the on-time of the transistor Q2 becomes long, the discharge amount of the capacitor C due to the turning-on of the transistor Q2 increases, and the current detection value by the current detection circuit 26 becomes relatively lower than the true average value. Electric light 15
It works to increase the on time Ton so as to increase the power supplied to the device. That is, when the voltage applied to the discharge lamp 15 decreases, the power supplied to the discharge lamp 15 increases.

That is, in the above embodiment, as shown by the solid line in FIG. 6, the higher the voltage applied to the discharge lamp 15, the more
When the sodium lamp is used as the discharge lamp 15 because the power supply becomes small, the tint becomes the same, and even if a large number of sodium lamps are lit, the color unevenness due to the lamp variations becomes inconspicuous.

In the above embodiment, the detected current value can be corrected with a simple structure, and the voltage-power characteristics can be arbitrarily adjusted by changing the value of the resistor R7, so that the discharge lamp lighting device can be highly functionalized. .

In the above embodiment, the current transformer CT is an example of a current transformer that detects the input current of the bridge inverter circuit, and the diode D1 is an AC voltage generated in the secondary winding of the current transformer. R1 is an example of rectifying means for rectifying, R1 is for converting the input current of the inverter detected by the current transformer CT into a voltage, and capacitor C is an example of a capacitor for smoothing the rectified voltage. Is for controlling the pulse width of the bridge inverter in accordance with the detected current value of the power supplied to the lamp.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

In the embodiment shown in FIG. 2, instead of the current detection circuit 26 in the embodiment shown in FIG. 1, the longer the period in which the bridge inverter circuit 13 is not supplying power to its load (the voltage across the discharge lamp 15). Is lower), the current detection amount compensating means for increasing the reference voltage for detecting the input current of the bridge inverter circuit 13 is provided so that the power supplied to the discharge lamp 15 increases. That is, the embodiment shown in FIG. 2 is provided with current detection amount compensating means for lowering the reference value for detecting the input current of the bridge inverter circuit 13 as the duty ratio of the on-time is lower. Accordingly, the current detection amount compensating means for correcting the reference voltage for detecting the input current of the bridge inverter circuit 13 is provided.

In the embodiment shown in FIG. 2, the output voltage of the comparator CO1 is averaged by the resistors R101 and R102 and the capacitor C101.
The increase in the voltage across both ends means that the pulse width of the comparator is widened, and the average value of the output voltage of the comparator CO1 appears as the voltage across the resistor R102, and the voltage across the resistor R102 is equal to the pulse width (time ratio). ) Rises in proportion to. Therefore, when the voltage across the discharge lamp 15 increases, the output voltage of the operational amplifier OA2 decreases, the current flowing to the resistor R14 decreases, and the reference voltage e _r decreases.

As described above, when the voltage across the discharge lamp 15 rises, the reference voltage e _r drops, so the output voltage of the operational amplifier OA rises, the pulse width of the comparator CO1 narrows, and the power supplied to the discharge lamp 15 rises. Becomes smaller. In this way, the output power characteristic can be adjusted even if the reference voltage is corrected according to the pulse width (duty ratio).

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

The embodiment shown in FIG. 3 is provided with a current detection amount compensating means for changing the detected value of the input current of the bridge inverter circuit 13 to a higher value as the duty ratio of the on time is lower. Depending on the bridge inverter circuit 1
3 is provided with current detection amount compensating means for correcting the detection amount of the input current.

In the embodiment shown in FIG. 3, the resistor R1
01, R102 and the capacitor C101 convert into a voltage proportional to the pulse width (duty ratio), this circuit amplifies this voltage with the operational amplifier OA2, and a circuit for flowing a current into the capacitor C via the resistor R108 is a current detection amount. It is a compensation means. Therefore, the wider the pulse width (duty ratio), the more current flows into the capacitor C, and the decrease due to the exciting current can be compensated. Further, it is possible to make further correction, and the power characteristic in this case can be adjusted as shown by the solid line in FIG.

[0042]

According to the present invention, the electric charge of the smoothing capacitor in the current detecting circuit for detecting the current flowing in the bridge inverter circuit is discharged during the period when no current is flowing in the bridge inverter circuit. This has an effect that the detected current value to be detected can be corrected.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing a constant power control device for a discharge lamp, which is a background art.

FIG. 5 is a diagram showing a primary current waveform and a secondary current waveform of the current transformer CT in the background art.

FIG. 6 is a diagram showing a characteristic in which the color unevenness of the sodium lamp is conspicuous and a characteristic in which the sodium lamp is not conspicuous in relation to the applied voltage and the supply voltage.

[Explanation of symbols]

 12 ... Step-up chopper circuit, 13 ... Bridge inverter circuit, 15 ... Discharge lamp, 26 ... Current detection circuit, Q1, Q2 ... Transistor, C ... Capacitor.

Claims (4)

[Claims] 1. A bridge inverter circuit converts a constant voltage DC power into a high frequency modulated low frequency rectangular wave AC power and supplies a constant power to a load by controlling a duty ratio so that an input current of the bridge inverter circuit becomes constant. In the discharge lamp lighting device, a current transformer that detects an input current of the bridge inverter circuit; a rectifying unit that rectifies a voltage generated in a secondary winding of the current transformer; and a smoothed rectified voltage. A discharge lamp lighting device, comprising: a capacitor that discharges the electric charge charged in the capacitor when a current flows through the primary winding of the current transformer. 2. The discharge lamp according to claim 1, wherein the duty ratio is controlled so that the input current of the bridge inverter circuit becomes constant according to the charge amount of the capacitor, and constant power is supplied to the load. Lighting device. 3. The discharge lamp lighting device according to claim 1, further comprising a current detection amount compensating unit that corrects a reference voltage for detecting an input current of the bridge inverter circuit according to the duty ratio. . 4. The discharge lamp lighting device according to claim 1, further comprising current detection amount compensating means for correcting the detection amount of the input current of the bridge inverter circuit according to the duty ratio.