Technical field The present invention relates to a power-saving magnetic ballast capable of controlling illumination intensity, and more particularly, to a magnetic ballast that can control the illumination intensity of a variety of lamps such as discharge lamps for street lamps, operate properly in response to various conditions such as the status of an input power source, the status of a lamp, and ambient temperature, and also save power.

Background Art

Various kinds of ballasts are used to drive lamps such as discharge lamps for street lamps. Especially, a magnetic ballast comprises a capacitor for improving a power factor while being connected parallel to an AC input power source, and a ballast part serially connected to a terminal of the AC input power source, thereby generating a high ignition voltage through the ballast to turn a lamp on.

Meanwhile, a conventional magnetic ballast has a drawback in that it cannot easily control illumination intensity in view of its characteristics. Although an electronic ballast may be used to control illumination intensity, it has a disadvantage in that upon use thereof in a street lamp requiring relatively high power, it has a shortened life span due to a problem with the reliability of semiconductor parts.

Moreover, when the magnetic ballast is used in a street lamp that is exposed to external environment, it becomes sensitive to temperature. That is, at lower temperature, the magnetic ballast cannot turn a lamp on because it requires a higher ignition voltage. Therefore, there is difficulty in using the magnetic ballast in a cold area. Furthermore, if a stable voltage cannot be provided such as in underdeveloped countries, the magnetic ballast operates unstably, resulting in decrease in the life span of the lamp.

Due to such problems, the conventional magnetic ballast has a limitation on its use and merits of the magnetic ballast cannot be fully utilized. Additionally, since the conventional magnetic ballast deteriorates the performance of public services such as a

street lamp, it becomes a cause of inconvenience of citizens and produces unnecessary expenses.

Disclosure of Invention The present invention is conceived to solve the aforementioned problems. An object of a present invention is to provide a magnetic ballast that can automatically or manually control illumination intensity, operate properly in response to various conditions such as the status of an input power source, the status of a lamp, and ambient temperature, and also save power. To achieve the object, a power-saving magnetic ballast capable of controlling illumination intensity according to the present invention comprises a variable inductor control means that is interposed between an AC input power source and a ballast part and is constructed to have a variable inductance value according to an inductor control signal; an ignition voltage generator for controlling the ballast part according to an ignition control signal and generating an ignition voltage requiring for turning on a lamp; a power source status detector for detecting the status of the AC input power source; a load status detector for detecting the status of the lamp; a controller for controlling the variable inductor control means and the ignition voltage generator according to the status detected by the power source status detector and the load status detector; and a DC voltage generator for rectifying the AC input power source to supply a constant voltage of a predetermined amplitude as a driving voltage for the variable inductor control means and the controller.

The variable inductor control means may comprise one or more inductors serially connected between the AC input power source and the ballast part; a plurality of switches for opening a circuit between the ballast part and the AC input power source or for selectively bypassing the respective inductors; and a switch driver for turning on/off the respective switches according to the inductor control signal from the controller.

The power source status detector may detect whether the voltage of the AC input power source drops down below a predetermined value. The load status detector may detect whether the lamp is out of order, or whether the lamp is turned on.

The ignition voltage generator may be constructed to determine the level of the generated ignition voltage according to a negative temperature coefficient so as to ensure proper operation at low temperature.

The magnetic ballast of each of the aforementioned aspects may further comprise a mode setting unit for enabling selection of a manual mode or an automatic mode.

In the magnetic ballast, the controller may control the variable inductor control means to have a corresponding inductance value according to the illumination intensity set by the mode setting unit.

If the mode setting unit is set to the automatic mode, the controller may automatically control the variable inductor control means according to predetermined time and illumination intensity.

Brief Description of Drawings

Fig. 1 is a block diagram of a preferred embodiment of the present invention. Fig. 2 shows the configuration of an embodiment of a variable inductor control means.

Fig. 3 shows the configurations of embodiments of a DC voltage generator and a power source status detector.

Fig. 4 shows the configuration of an embodiment of a load status detector. Fig. 5 shows the configuration of an embodiment of an ignition voltage generator.

Fig. 6 is a flowchart illustrating the overall operation of a magnetic ballast according to the present invention.

<Explanation of reference numerals for designating main components in the drawings>

11 : Ballast part 12: Variable inductor control means

13: Ignition voltage generator 14: DC voltage generator

15: Power source status detector 16: Load status detector

17: Controller 18: Lamp 19-1 : Mode setting unit 19-2 : Illumination intensity detecting means

21 : Variable inductor 22: Switch

23: Switch driver

Best Mode for Carrying out the Invention

Referring to Fig. 1, a magnetic ballast according to the present invention comprises a capacitor Cp _FC for improving a power factor while being connected parallel to an AC input power source Vi, and a ballast part 11 serially connected to a terminal of the AC input power source Vi. The magnetic ballast turns a lamp 18 on by generating a high ignition voltage on the ballast part 11 through an ignition voltage generator 13.

At this time, a variable inductor control means 12 is disposed between the AC input power source Vi and the ballast part 11. The variable inductor control means 12 has an inductance value that varies according to an inductor control signal transmitted from a controller 17.

The configuration of an embodiment of the variable inductor control means 12 will be described with reference to Fig. 2. The variable inductor control means 12 comprises an variable inductor 21 with two inductors Ll and L2 connected between the

AC input power source Vi and the ballast part 11; a plurality of switches Sl to S3 for cutting off the ballast part 11 from the AC input power source Vi to prevent an electric current from flowing or for selectively bypassing the inductors Ll and L2; and a switch driver 23 for selectively turning on or off each of the switches Sl to S3 in response to the inductor control signal of the controller 17.

The inductors Ll and L2 may be constructed of a single core and bobbin, and each of the switches Sl to S3 maybe constructed of a solid state relay (SSR) or a relay. m the embodiment shown in Fig. 2, when the operation of the ballast part 11 needs to be stopped in response to the status of the lamp 18 or the AC input power source Vi, all the switches Sl to S3 are turned off to cut off the flow of the electric current. If only the switch S2 is turned on, the inductor Ll is bypassed so that the inductance value of only the inductor L2 is valid. If only the switch Sl is turned on, both the inductors Ll and L2 are bypassed so that the total inductance value of the variable inductor control means becomes zero. If only the switch S3 is turned on, the inductance values of both the inductors Ll and L2 become valid.

Description will be made in view of the illumination intensity of the lamp 18, which

is obtained upon control of the inductance value by the variable inductor control means

12. If all the switches Sl to S3 are turned off, the illumination intensity becomes 0%.

If only the switch S3 is turned on, the illumination intensity becomes 50%. If only the switch S2 is turned on, the illumination intensity becomes 75%. If only the switch S 1 is turned on, the illumination intensity becomes 100%. Accordingly, when the inductance value of the variable inductor control means 12 is appropriately controlled, if necessary, the lamp 18 can be operated with proper illumination intensity, thereby obtaining an advantage of power saving.

Although the embodiment of Fig. 2 has been described in connection with the variable inductor 21 employing the two inductors Ll and L2, the variable inductor 21 may be constructed to include an arbitrary number of inductors and switches, if necessary.

A DC voltage generator 14 functions to rectify the voltage of the AC input power source Vi and generates a constant DC voltage source with a predetermined magnitude, and the constant DC voltage source drives each of the switches Sl to S3 and the switch driver 23 of the variable inductor control means 12 or supplies a driving voltage to the controller 17. For example, if the switches Sl to S3 are constructed of relay devices, the DC voltage source may be constructed to supply a DC voltage for driving the relay devices. If the controller 17 is constructed of a microprocessor, the DC voltage source may be constructed to supply a driving voltage (e.g., 5V) to the microprocessor.

The configuration of an embodiment of the DC voltage generator 14 will be described with reference to Fig. 3. The AC input power source Vi is applied to a rectifier 31, where the voltage is dropped down by a transformer T and the dropped voltage is then rectified by a full wave rectifier comprising four diodes D31 to D34. The rectified voltage is output as a DC voltage of a predetermined level (e.g., 5V) through a constant voltage means 32 comprising an IC7805 and a capacitor C31,

Meanwhile, a power source status detector 15 functions to detect the status of the AC input power source Vi. As one example, the power source status detector 15 may be constructed to detect whether the voltage of the AC input power source Vi is dropped below a predetermined value.

The configuration of the power source status detector 15 will be described with

reference to Fig. 3. The power source status detector 15 can comprise the rectifier 31 and a comparison means 33. Voltage distribution resistors R31 and R32 for distributing a voltage at an output terminal of the rectifier 31 are serially connected between the output terminal of the rectifier 31 and a ground. A comparator 33-1 compares a voltage applied between the resistors R31 and R32 with a reference voltage V _r efl and outputs signals of different levels according to the comparison results. At this time, if the AC input power source Vi is at a nominal voltage, V _re n can be set as a voltage that can be applied to the resistor R32. If the voltage of the AC input voltage source Vi is lower than the nominal voltage, the comparator 33-1 outputs a low level signal. If not so, the comparator 33-1 outputs a high level signal. The output signal of the comparator 33-1 is input into the controller 17 as a power source status signal, and the controller 17 adequately controls the magnetic ballast according to the power source status signal.

Accordingly, even though the AC input power source Vi heavily fluctuates, the illumination intensity of the lamp 18 can be caused to approach a predetermined regulation value. For example, as for a magnetic ballast designed for a nominal voltage of 220V, if the voltage level of the AC input power source Vi drops down to about 180V, the controller 17 controls the variable inductor control means 12 to automatically change the illumination intensity of the lamp 18 or to turn the lamp 18 off. Thus, it is possible to protect the lamp 18 against abrupt changes in voltage.

A load status detector 16 functions to detect the status of the lamp 18 such as by detecting whether the lamp 18 is out of order or the lamp 18 is currently turned on.

A specific embodiment 16-1 for detecting whether the lamp 18 is out of order will be described with reference to Fig. 4. A load resistor R _L is serially connected to the lamp 18 and a voltage applied between the lamp 18 and the load resistor R _L is input into a + input terminal of a comparator 41 via a diode D52. A capacitor C52 is connected parallel to the + input terminal of the comparator 41 to ensure the stable operation of a circuit, and a predetermined reference voltage V _re β is input into the - input terminal of the comparator 41. That is, the comparator 41 outputs signals of different levels as a lamp failure signal according to whether or not the lamp 18 is in an open state due to termination of the life thereof or occurrence of a failure therein.

Further, a specific embodiment 16-2 for detecting the lighting status of the lamp when the lamp 18 is turned on will be described. Serially connected voltage distribution resistors R41 and R42 are connected parallel to both terminals of the lamp 18 and the load resistor R _L . A voltage applied between the resistors R41 and R42 is input into a + input terminal of a comparator 42 via a diode D51. A capacitor C51 is connected parallel to the + input terminal of the comparator 42 to ensure the stable operation of a circuit, and a predetermined reference voltage V _re c is connected to a -input terminal of the comparator 42. With this circuit, the comparator 42 outputs signals of different levels as a lamp lighting status signal according to the current lighting status of the lamp 18 since the voltage applied at both terminals of the resistors R41 and R42 varies according to the lighting status of the lamp 18.

That is, the controller 17 can check the lighting status of the lamp 18 and whether the lamp 18 is out of order by referring to the lamp failure signal and the lamp lighting status signal that have been output from the load status detector 16, and the controller

17 can also adequately control the magnetic ballast according to circumstances. As one example, when the lamp failure signal indicates that the lamp 18 is out of order, the controller can stop the operation of the ignition voltage generator 13.

The ignition voltage generator 13 functions to control the ballast part 11 according to an ignition control signal transmitted from the controller 17 and thus generate an ignition voltage required for turning the lamp 18 on. At this time, the ignition voltage generator 13 can be constructed, to determine the magnitude of the ignition voltage according to a negative temperature coefficient. With the use of this embodiment, it is possible to greatly improve adaptability to ambient temperature. The configuration of a specific embodiment of the ignition voltage generator 16 (-> 13) will be described with reference to Fig. 5.

A transistor Q62 is turned off when a gate voltage of the transistor Q62, which is an ignition control signal for turning the lamp 18 on, is made to a low state by the controller 17. Then, an electric current flows through a current path defined by a resistor R61, a diode D61, a resistor R62, a resistor NTC 51 and a capacitor C62. At this time, the resistor NTC 51 and the resistor R62 are connected parallel to each other.

When an appropriate electric current is supplied to a gate of a SCR Q61 via a zener diode ZD61 according to a voltage applied to a cathode of the diode D61, the SCR Q61 becomes short and an electric current abruptly flows through a capacitor C61.

This current is generated only at a positive power source due to the diode D61, and the SCR Q61 is repeatedly switched between short and cut-off states due to resonance of the current through the capacitor C61 and the inductors L3 and L4. Therefore, this results in a large discharge voltage between both terminals of the lamp 18 as expressed by the following equation 1 :

At this time, the diodes D62 and D63 function to cancel a minimum maintenance voltage applied during the short state of the SCR Q61 at a negative power source.

The resistor NTC 51 is a component that has a negative temperature coefficient and exhibits a characteristic by which the resistance thereof increases as temperature gets lower. That is, since the resistance of the resistor NTC 51 becomes larger as ambient temperature gets lower, a gate current can be supplied more and faster in the SCR Q61. Accordingly, effective control can be achieved even at low temperature.

Meanwhile, when the controller 17 outputs an ignition control signal by which a gate terminal of the transistor Q62 is made to a high state, the transistor Q62 is turned on and an electric current is not supplied to the SCR Q61, so that the generation of the ignition voltage is stopped.

That is, if the generation of the ignition voltage should be stopped as in a case where the lamp 18 has not yet been turned on even after several attempts to turn it on or the lamp has already been turned on, the controller 17 turns on the transistor Q62 and turns off the SCR Q61 to stop the generation of the ignition voltage. The controller 17, which is a component for generally controlling the magnetic ballast of the present invention, may be preferably constructed of a microprocessor. Especially, the controller 17 controls the variable inductor control means 12 or the ignition voltage generator 13 according to the status of the AC input power source Vi detected by the power source status detector 15 or the status of the lamp 18 detected by the load status detector 16, so that the magnetic ballast can be properly operated. At this time, the operation of the controller 17 can be performed by a computer program

installed therein. It will be apparent that the computer program for determining the operation of the controller 17 maybe variously produced as required.

Further, as shown in Fig. 1, the magnetic ballast of the present invention can be constructed to cooperate with an illumination intensity detecting means 19-2 capable of detecting illumination intensity in the external environment. In this embodiment, the controller 17 receives information on illumination intensity (brightness) in the current external environment through the illumination intensity detecting means 19-2 and controls the variable inductor control means 12 and the ignition voltage generator 13 according to the received information so as to properly drive the magnetic ballast. For example, the controller may be constructed such that it tries to turn the lamp on if the illumination intensity in the external environment falls below a predetermined value in the evening, or automatically stops the generation of the ignition voltage if the illumination intensity in the external environment rises over the predetermined value in the morning. Each of the aforementioned embodiments may be constructed to operate in manual or automatic mode. To this end, as in the embodiment shown in Fig. 1, a mode setting unit 19-1 for enabling selection of a manual mode or an automatic mode may be included, and the controller 17 controls the magnetic ballast according to the setting status of the mode setting unit 19-1. The mode setting unit 19-1 can be constructed to select a level of illumination intensity when a manual mode is selected. At this time, the level of illumination intensity that can be selected by a user may be one of levels that can be generated under the control of the variable inductor control means 12. That is, in the embodiment with the two variable inductors Ll and L2 as shown in Fig. 2, it is possible to select any one of levels of illumination intensity that are 0%, 100%, 75% and 50%.

Once a level of illumination intensity is selected, the controller 17 controls the variable inductor control means 12 to have an inductance value corresponding to the selected level of illumination intensity. That is, the controller can control the variable inductor control means 12 in the embodiment shown in Fig. 2 such that all the switches Sl to S3 are turned off if a level of 0% is selected, only the switch S3 is turned on if a level of 50% is selected, and only the switch S2 is turned on if a level of 75% is selected.

It will be apparent that the mode setting unit 19-1 may be variously constructed according to requirements in its use. Meanwhile, if the mode setting unit 19-1 is set to an automatic mode, the controller

17 may be constructed to automatically control the variable inductor control means 12 according to predetermined time and illumination intensity.

An embodiment of the overall operation of the magnetic ballast according to the present invention will be described with reference to Fig. 6.

The controller 17 checks whether AC input power is normally applied, based on the status of the AC input power source Vi detected by the power source status detector 15 (S61). If the AC input power is not normally input, an inductor control signal for turning off all switches is sent to the variable inductor control means 12 to open all the inductors, thereby stopping the operation of the magnetic ballast (S67).

However, if it is determined in step S61 that the AC input power is normally input, it is checked through the load status detector 16 whether the lamp 18 is normal (S62). If it is determined in step S62 that the lamp 18 is not normal, the variable inductor control means 12 is controlled so that the value of variable inductance is zero (S63), and the ignition voltage generator 13 is controlled to generate the ignition voltage (S64). If the attempt to turn on the lamp fails in step S64, it is repeatedly tried to turn on the lamp

18 for a predetermined period of time (S65, S66). If the attempt to turn on the lamp 18 finally fails, the procedure goes to step S67 in which the variable inductor is opened to stop the operation of the magnetic ballast.

Meanwhile, if the lamp 18 is determined to be normal in step S62 or the lamp 18 is successively turned on in step S65, a current operation mode is checked (S68).

If it is determined in step S68 that a manual mode is set, in order to turn on the lamp 18 at the currently set level of illumination intensity, an inductor control signal is transmitted to the variable inductor control means 12 to have an inductance value capable of exhibiting the corresponding illumination intensity, so that the lamp 18 is controlled to be turned on with the corresponding illumination intensity (S69-1).

On the contrary, if it is determined in step S68 that an automatic mode is set, the variable inductor control means 12 is controlled so that the lamp 18 has the intensities of illumination such as 100%, 75% and 50% at predetermined periods of time (S69-2 to

S69-4). The combination of time and the illumination intensity in automatic mode may be variously set according to a computer program.

The embodiment of Fig. 6 has been described by way of example for better understanding of the overall operation of the magnetic ballast of the present invention. Details of the operation of the magnetic ballast may be variously modified if necessary.

That is, the controller 17 may variously control the variable inductor control means 12 and the ignition voltage generator 13 according to combinations and sequences prescribed by a computer program from information input from the power source status detector 15, the load status detector 16, the mode setting unit 19-1, the illumination intensity detecting means 19-2, and the like.

Further, it will be understood by those skilled in the art that the present invention is not limited to the aforementioned embodiments and various modifications and changes can be made thereto without departing from the spirit and scope of the present invention.

Industrial Applicability

As described above, since the magnetic ballast of the present invention can operate in response to the status of an AC input power source, it is possible to control illumination intensity even when the voltage of the power source heavily fluctuates. Further, it is possible to properly set an ignition voltage according to ambient temperature and the status of a lamp. Since it is possible to manually or automatically control the illumination intensity of the lamp, it may contribute to power saving.