JPS643320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a constant input current for a discharge lamp that can control the input current of the discharge lamp to be below the input current at the rated time from immediately after the discharge lamp starts to when the discharge lamp shifts to the rated lighting state. It relates to a lighting device.

In recent years, in order to meet the demand for compact, lightweight, and power-saving lighting devices, AC control elements are connected in series with the discharge lamps, even in the lighting circuits of high-pressure vapor pressure discharge lamps such as mercury lamps and high-pressure sodium lamps. A so-called phase control method, which reduces current-limiting impedance by controlling the conduction phase angle of an AC control element, has been researched and has been put into practical use in some cases. Figure 1 is a diagram showing the principle circuit, in which 1 is a commercial power supply, 2 is a current-limiting impedance element, 3 is a discharge lamp,
4 is an AC control element, and 5 is a current limiting element that compensates for the current limiting impedance element 2 when the AC control element 4 is off. Figure 2 a and b show the lamp current of discharge lamp 3.
The phase relationship between I _la and the power supply voltage V _s is shown. Figure a shows the state immediately after starting, and figure b shows the state at rated time.

Generally, immediately after starting a high-pressure discharge lamp, the lamp conductance is much larger than at the rated time, so it is necessary to appropriately delay the conduction phase θ of the AC control element 4 compared to the rated time, as shown in FIG. It is known that if such phase control is performed, the input current can be kept below the rated input current during the period until the engine reaches the rated value (hereinafter referred to as the starting period), and constant input starting is possible. There is.

One of the phase control methods is to detect and control the phase of the lamp current. This method utilizes the property that the internal conductance of a discharge lamp is large immediately after starting, and decreases as the lamp reaches its rated value, so that the phase of the lamp current is delayed immediately after starting compared to when it is rated. As mentioned above, _FIGS . 2a and 2b are comparison diagrams of the conduction phase θ of the AC control element 4 when the input current is constant immediately after starting and at the rated time, respectively. With respect to the commutation phase angle T until the current I _la commutates, the off period ΔT of the AC control element 4
Looking at the relationship between the two, it can be seen that it is necessary to increase the off-period ΔT immediately after starting (see FIG. 2 a), and to reduce the off-period ΔT as it moves to the rated value. If we follow this relationship along with the starting process, we will find something like the one shown in Figure 3. Conversely, if the phase is controlled from point ○A to point ○B, constant input starting is possible. In FIG. 3, the horizontal axis indicates the commutation phase angle T _i (deg) of the lamp current I _la , and the vertical axis indicates the off period ΔT _i of the AC control element 4.
(deg). In the figure, the ○ mark indicates immediately after starting, and the ○ mark indicates the time of rated operation. And the measurement conditions are: discharge lamp 3
Using a 400W mercury lamp, the impedance voltage of current limiting impedance 2 is 80V/3.3A, and the power supply voltage is V _s .
This is a case where the input current is 200V, the conduction phase of the triac 4 can be arbitrarily controlled by an external trigger, and the input current is 2.4A.

When the discharge lamp 3 is started under such control conditions, the following problems occur. That is, the AC control element 4
If the conduction phase θ of is fixed at point ○A and then controlled from point ○A to point ○B due to changes in the lamp condition, immediately after the commutation phase T of the lamp current I _la becomes small. Positive/negative asymmetry in the lamp current I _la waveform may occur. Therefore, a convergence condition for the conduction phase θ of the AC control element 4 is required in the above control condition (the process from point A to point B in FIG. 3). The asymmetric waveform not only causes a flickering phenomenon during the starting process, but also causes the drawback that the rated point cannot be reached. The positive and negative asymmetry of the lamp current waveform will be described below.

The control conditions in FIG. 3 do not include a convergence condition for the conduction phase (θ=T+ΔT) of the AC control element 4. This is due to the following reason. In FIG. 3, let us consider a starting process in which the engine is fixed at point ○a immediately after starting, and moves to the rated point ○○ro over time. As the vapor pressure within the lamp increases and the lamp voltage increases, the lamp current commutation phase T advances. If an unbalance occurs for each half wave before and after this, as shown in FIG. 4, it will remain asymmetric and will not converge. Figure 5 shows the cause. For example, assume that the conduction phase angle θ is stable until the (i+1) half cycle. Therefore, when the power supply voltage V _s suddenly decreases, the lamp current commutation phase T _{i +2} will be smaller than T ₀ in the figure.
decreases to T ₂ . As a result, according to the control conditions shown in Fig. 3, the off period ΔT of the AC control element 4 also becomes smaller, the conduction phase angle θ _i+2 decreases from θ ₀ to θ ₂ , and the lamp current I _la tends to flow larger. . The result (i+
3) The lamp current commutation phase T _i+3 in the half cycle is delayed, and the off period ΔT _i+3 in the (i+3)th half cycle becomes larger, which acts to throttle the lamp current I _la . In this way, the lamp current I _la is repeatedly increased and decreased every half cycle, resulting in an asymmetrical waveform. In FIG. 5, this situation is expressed by the vibrations of the conduction phase θ of the AC control element 4 and the lamp current commutation phase T.

The reason for this is that the OFF period ΔT of the AC control element 4 within a half cycle to be determined is determined by the lamp current phase T of the same half cycle, and the control conditions are strictly conventional T _i This is because the condition was −ΔT _i . Under such control conditions, the lamp current I _la of the half cycle to be controlled will excessively compensate for the change in lamp current of the immediately preceding half cycle, resulting in oscillation. If the lamp state is fixed as it is, the vibration will naturally attenuate, but
During the starting process, the lamp state changes as the lamp current commutation phase T progresses moment by moment, as shown in Figure 3.
The starting process is carried out while the waveform remains asymmetrical.

This asymmetry not only causes the flickering phenomenon during the starting process as described above, but also increases the cost because the AC control element 4 must also satisfy the current capacity in the larger half cycle of the lamp current I _la . In addition, discharge lamps such as metal halide lamps, which have a short starting time, flicker significantly and have the disadvantage that they cannot be switched to rated lighting.

The present invention has been made in view of these drawbacks, and its purpose is to change the commutation phase T of the lamp current and the off period ΔT of the AC control element in order to eliminate the asymmetry of the lamp current waveform during the starting process of the discharge lamp. The goal is to improve control conditions.

The reason for the conventional drawbacks is that the starting process is controlled based on the relationship between the commutation phase T _i of the lamp current I _la and the OFF period ΔT _i of the AC control element 4 within the same half cycle, as described above. . Therefore, in the present invention, control conditions are defined based on the relationship between the commutation phase T _i-1 and the off period ΔT _i . T _i-1 is the commutation phase of the lamp current I _la in the half cycle immediately before the off period ΔT _i of the AC control element 4 to be controlled. This control condition is shown in FIG. Now, under such control conditions, even if the conduction phase θ of the AC control element 4 enters the unbalanced state once every half cycle, there is a convergence effect to return the state to the balanced state, and an asymmetric waveform does not occur.

Before explaining the reason, let us briefly consider the mechanism by which the lamp current commutation phase T is determined.

As explained in FIG. 5, T _i is determined by θ _i-1 , that is, the conduction phase θ in the previous half cycle.

How this is determined depends on the lamp condition, but it is generally known that T _i+1 =g(θ _i ) and g(θ) is expressed as a monotonically decreasing function. During the starting process, the lamp conductance is large, so the
The absolute value of dT _i+1 /dθ _i is large.

Considering the conventional control conditions in this situation, from Fig. 4, ΔT _i = k × T _i + α... Note that α is the constant of the identification formula shown in Fig. 3 obtained from the experimental results, and the identification The equation becomes a linear function and shows its constant term.

The conduction phase angle θ _i is expressed as θ _i =T _i +ΔT _i …… from the formula θ _i =T _i +kT _i +α ……. From the formula, a situation where T _i < T _i-1 (8th
When point ○ in the figure) occurs momentarily, θ _i is a linear function due to T _i , so θ _i <θ _i-1 . The next T _i+1 is determined by the formula and is found at point ○C in Figure 8. Since T _i+1 > T _i-1, θ _i+1 > θ _i-1 from the formula, and the two points in Figure 8 are obtained from the formula, and T _i+2 can be found. Therefore, the vibration of θ can be explained from the formula and the formula.

So, what about the relationship between the control conditions T _i-1 and ΔT _i of the present invention? Figure 6 is approximated by the following equation.

As mentioned above, FIG. 6 shows the relationship between the lamp current commutation phase T and the OFF period ΔT of the AC control element 4, which was determined through experiments as a necessary condition for constant input starting.
Same as Figure 3. However, the time relationship between T and ΔT is the relationship between ΔT _i and T _i-1 according to the present invention. Further, the constants k and α in the following equation are the same as in FIG. 3 and the equation.

ΔT _i+1 =k×T _i +α... From the formula, θ _i =T _i +k×T _i-1 +α... It is clear from this that in the present invention θ _i is controlled not only by T _i but also by T _i-1 . Similarly, if the lamp current commutation phase T _i shifts to point ○ in Figure 8 in the i-th half cycle, θ _i of the present invention can be found by the formula, θ _i of the present invention = T _i +kT _{i- 1} + α, and θ _i of the conventional example becomes θ _i of the conventional example = T _i +kT _i + α from the formula. From these two equations, (θ _i of the present invention) − (θ _i of the conventional example) = k(T _i-1 − _{T i} ), and since T _i-1 > T _i , θ _i-1 > (θ i of the present invention). The relationship of _i > (θ _i of the conventional example) is obtained. Therefore, θ _i of the present invention becomes the ○ point in FIG. At this point, T _i+1 for (i+1) half cycles can be found by the formula.In other words, the variation in θ is smaller than in the conventional example.This means that the variation in θ is smaller than in the conventional example. Figure 7 clearly shows how θ converges every half cycle of the power supply.The dotted line in Figure 7 indicates θ _i in the equation. shows how T _i+1 is determined. Approximately 2~
It has the effect of converging in 3 cycles.

FIG. 9 shows a block diagram showing the operation of the circuit that realizes the present invention, and shows the lamp current commutation phase.
T _i-1 is detected during the addition count period of the first block, and the off period ΔT _i is the same number of second clocks as the addition count number of the first block, and the contents of the subtraction counter become zero from T _i onward. The period is until. FIG. 10 shows the control conditions for constant input starting realized in FIG. 9, and has a relationship between T _i-1 and ΔT _i . 9th
In the figure, the initial value no of the addition counter is the 10th
This is the second clock count number corresponding to ΔT ₀ in the figure. The operation is as follows.

When the zero cross of the power supply voltage V _s is detected, the first
The contents of the period addition counter of T ₀ in figure 0 are n ₀
to preset. Then, after T ₀ has elapsed, the addition counter adds and counts the first clock pulse and continues counting until the lamp current I _la commutates. On the other hand, the subtraction counter presets the output of the delay circuit (latch circuit) from after the zero crossing of the power supply voltage _Vs is detected until the lamp current I _la commutates. At the same time as the lamp current I _la commutates and the contents of the addition counter are input to the delay circuit, the subtraction counter starts subtracting the clock pulses of the second clock. The subtraction counter therefore subtracts the number of first clock pulses corresponding to the commutation phase angle of the lamp current I _la during the previous half cycle. Then, when the content of the subtraction counter reaches zero, a trigger pulse of the AC control element 4 is generated. According to this control method, the control gradient k of ΔT _i =k×T _i-1 +α under the constant input condition when T _i-1 > T ₀ is the period of the first clock (τ ₁ ) and the period of the second clock. (τ ₂ ).

As described above, the present invention includes a main lighting circuit in which an AC control element, a current limiting impedance element, and a discharge lamp are connected in series to a commercial power source, a compensation current limiting element connected in parallel to the AC control element, and the AC control element. A discharge lamp lighting device comprising: a control circuit that controls the conduction phase of the lamp every half cycle of the power supply in accordance with the lamp current commutation phase from the zero-crossing phase of the power supply voltage until the lamp current commutates. , in the above control circuit, the lamp current commutation phase in the current half cycle is T _i , the lamp current commutation phase immediately before the current half cycle is T _i-1 , and the conduction phase of the AC control element in the current half cycle is θ _i
By configuring the structure so that θ _i is controlled by a linear function of θ _i =T _i +kT _i-1 + α (where k and α are constants), even if the lamp current waveform is asymmetrical, Converged quickly. Therefore, it is possible to eliminate the flickering phenomenon during the discharge lamp starting process, and the current capacity of the AC control element is small, which is advantageous in terms of cost.In addition, the AC control element is not destroyed due to fluctuations in lamp current, and reliability is improved. It has the effect of improving.

[Brief explanation of drawings]

Fig. 1 is a principle circuit diagram of a discharge lamp constant input lighting device, Fig. 2 a and b are waveform diagrams of the lamp current and power supply voltage of the same discharge lamp, and a shows the state immediately after starting.
b indicates the rated state. Fig. 3 is an explanatory diagram showing the relationship between the lamp current commutation phase and the off period of the AC control element required for constant input starting, Fig. 4 is a waveform diagram of the lamp voltage and power supply voltage during the starting process, and Fig. 5 is An explanatory diagram showing the relationship between the lamp current commutation phase and the conduction phase of the AC control element when an asymmetric waveform occurs, FIG. 6 is an explanatory diagram showing the control conditions of the present invention, and FIG. 7 shows the conduction phase under the same conditions as above. An explanatory diagram showing the convergence effect, FIG. 8 is an explanatory diagram showing the relationship between the conduction phase of the AC control element and the lamp current commutation phase according to the present invention,
FIG. 9 is a block diagram showing the operation of a circuit implementing the present invention, and FIG. 10 is an explanatory diagram showing control conditions for constant input starting same as above.

Claims (1)

[Claims] 1. A main lighting circuit in which an AC control element, a current-limiting impedance element, and a discharge lamp are connected in series to a commercial power source;
The current limiting element for compensation connected in parallel to the AC control element and the conduction phase of the AC control element are set in accordance with the lamp current commutation phase from the zero cross phase of the power supply voltage until the lamp current commutates. A discharge lamp lighting device comprising a control circuit that controls each half cycle, the control circuit having a lamp current commutation phase of the current half cycle as T _i and a lamp current commutation phase immediately before the current half cycle as T i . When T _i-1 and the conduction phase of the AC control element in the current half cycle are θ _i , θ _i is controlled by a linear function of θ _i = T _i +kT _i-1 + α (where k and α are constants). A constant input lighting device for a discharge lamp, characterized in that it is configured to