WO2009051350A1

WO2009051350A1 - Planar light-source pulse-type driving circuit using a current source

Info

Publication number: WO2009051350A1
Application number: PCT/KR2008/005495
Authority: WO
Inventors: Joung-Hu Park; Jongbok Baek; In-Kyu Lee; Bo Hyung Cho
Original assignee: Samhwa Yang Heng Co., Ltd.
Priority date: 2007-10-19
Filing date: 2008-09-17
Publication date: 2009-04-23
Also published as: KR100895095B1; KR20090040077A

Abstract

A planar light-source driving circuit may include: a voltage source applying a DC voltage; an inductor supplying current depending on the DC voltage applied by the voltage source; a transformer having a primary side connected to the inductor and a secondary side connected to a planar light source, the transformer applying a pulse voltage to the planar light source using the current supplied from the inductor; and first and second switches respectively connected between both ends of the primary side of the transformer and a ground, the first and second switches controlling the current supplied to the transformer by on/off switching operations.

Description

[DESCRIPTION]

[Invention Title]

PLANAR LIGHT-SOURCE PULSE-TYPE DRIVING CIRCUIT USING A CURRENT SOURCE

[Technical Field]

The present invention relates to a planar light-source pulse-type driving circuit using a current source. More particularly, it relates to a planar light-source driving circuit, wherein current is supplied to a transformer using an inductor connected to a DC voltage source as a current source, and the current supplied to the transformer is controlled in accordance with on/off switching operations of switches respectively connected to both ends of a primary side of the transformer, so that a pulse- type voltage is generated at a secondary side of the transformer to drive a planar light source.

[Background Art]

Recently, studies on light source systems have been actively conducted in the display and illumination markets. The high-quality light emitting technique, price-reduction technique and high-efficiency technique for saving power consumption of these light source systems are achieved by a new planar light source that is planar (2-dimensional) itself, completely unlike the conventional method of converting light emitted from a linear (1-dimensional) or point (non-dimensional) light source into planar light. Fig. 1 is an example showing an operation of the aforementioned planar light source and a photograph showing a front discharge state of the planar light source.

However, such a light source requires new pulse-type driving waveforms having a considerably shorter width than a switching period. Fig. 2 is a graph exemplarily showing the aforementioned pulse-type driving waveforms. As shown in Fig. 2, the voltage T_x applied to a primary side of a transformer is shown as a pulse type depending on on/off of a gating signal S. The planar light-source is connected to a secondary side of the transformer, and is driven by lamp voltage and current V_larap and ii_amp of a bidirectional pulse type induced to the secondary side of the transformer. The pulse-type driving waveforms shown in Fig. 2 are required to drive the planar light source. Therefore, a driving circuit that generates the pulse-type driving waveforms is also required.

Fig. 3 is a circuit diagram showing the configuration of a Royer circuit that is an example of a driving circuit for a light source. The Royer circuit is a driving circuit used in driving of a cold cathode fluorescent lamp (CCFL). Referring to Fig. 3, the Royer circuit includes a converter circuit 1 and a resonant circuit 2. The converter circuit 1 applies a voltage to the resonant circuit 2 by controlling the duty ratio of a DC voltage generated from a voltage source V_Dc to be 50%. Current is inputted to the resonant circuit 2 through an inductor L_f by the applied vo11age .

In the resonant circuit 2, two transistors Qi and Q2 allow magnetizing inductance of a primary winding Wi of a transformer T_x and a capacitor C_r to be resonated using a push-pull circuit that alternately operates every half period. A sine-wave voltage is induced to a secondary winding W₂ of the transformer T_x by the resonance. A CCFL 3 is connected to both ends of the secondary winding W₂ of the transformer T_x to be driven by the voltage supplied from the transformer T_x. In Fig. 3, a tertiary winding W3 is a drive circuit that supplies base current to the two transistors Qi and Q₂.

However, in the aforementioned Royer circuit, the voltage applied to the lamp has the shape of a sine wave formed by LC resonance. Therefore, the voltage is not suitable for a planar light source, which is driven by a pulse-type driving voltage.

Fig. 4 is a circuit diagram showing the configuration of a class E inverter circuit as another example of the driving circuit for a light source. The class E inverter circuit is also a driving circuit used in driving of a CCFL. In the class E inverter circuit, the input side is driven as a current source due to a large inductance of an input terminal inductor L₃, and current of a specific frequency flows into the load side depending on on/off operations of a switch S_a. The frequency and amplitude of the current are determined by capacitors C_a and C_b and LC resonance of a resonant inductor L_b, and a driving voltage is finally applied to a CCFL 3 by a transformer T_x.

However, in the class E inverter circuit, the voltage applied to the lamp has the shape of a sine wave formed by the LC resonance, like the aforementioned Royer circuit. Therefore, the voltage is not suitable for a planar light source driven by a pulse-type driving voltage.

Since the technology for driving a planar light source itself is still in the process of development, most planar light-source driving circuits that have been developed up to now have low light efficiency as compared with high power consumption and are not empirically verified. Further, the conventional planar light-source driving circuit which allows a planar light source to emit light using a pulse voltage source has disadvantages in that the circuit is complicated and discharge characteristics are unstable. [Disclosure] [Technical Problem]

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a planar light-source driving circuit, wherein an inductor is connected to an input terminal to be used as a current source, so that a pulse-type inverter having an extremely small duty ratio can be implemented, and power consumption and light efficiency can be improved. [Technical Solution]

In accordance with an aspect of the present invention, there is provided a planar light-source driving circuit, including: a voltage source applying a DC voltage; an inductor supplying current depending on the DC voltage applied by the voltage source; a transformer having a primary side connected to the inductor and a secondary side connected to a planar light source, the transformer applying a pulse voltage to the planar light source using the current supplied from the inductor; and first and second switches respectively connected between both ends of the primary side of the transformer and a ground, the first and second switches controlling the current supplied to the transformer by on/off switching operations.

In accordance with another aspect of the present invention, there is provided a planar light-source driving circuit, including: a voltage source applying a DC voltage! first and second inductors supplying current depending on the DC voltage applied by the voltage source! a transformer having a primary winding having both ends respectively connected to the first and second inductors and a secondary winding having both ends connected to a planar light source, the transformer applying a pulse voltage to the planar light source! and first and second switches respectively connected between both ends of the primary winding of the transformer and a ground, the first and second switches controlling the current supplied from the first and second inductors to the transformer by on/off switching operations.

In accordance with still another aspect of the present invention, there is provided a planar light-source driving circuit, including: a voltage source applying a DC voltage! a transformer having a primary winding and a secondary winding having both ends connected to a planar light source, the transformer applying a pulse voltage to the planar light source! a capacitor charged or discharged with a predetermined voltage, the capacitor being connected to one end of the primary winding of the transformer to supply current to the transformer! an inductor connected to the other end of the primary winding of the transformer to supply current to the transformer depending on the DC voltage applied by the voltage source! and a switch connected between the other end of the primary winding of the transformer and a ground, the switch controlling the current applied to the transformer by on/off switching operations. [Advantageous Effects]

When using a planar light-source driving circuit according to an embodiment of the present invention, an inductor is connected to an input terminal to be used as a pulse current source, and a pulse voltage is generated by current supplied from the inductor, so that a planar light source can be effectively driven with a simple circuit configuration. Further, components used to configure the circuit are simplified, so that the size and cost of the circuit can be minimized. [Description of Drawings]

The above and other features of the present invention will be described in detail with reference to certain example embodiments thereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein:

Fig. 1 is a photograph showing a full discharge state of a planar light-source during glow discharge!

Fig. 2 is a graph showing lamp voltage and current for driving a planar light source;

Fig. 3 is circuit diagram of a conventional driving circuit of a light source;

Fig. 4 is circuit diagram of another conventional driving circuit of a light source;

Fig. 5 is a circuit diagram of a planar light-source driving circuit according to a first embodiment of the present invention;

Fig. 6 is a circuit diagram of a planar light-source driving circuit according to another embodiment of the present invention;

Fig. 7 is a timing diagram illustrating an operation of the planar light-source driving circuit according to the first embodiment of the present invention;

Fig. 8 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 1 according to the first embodiment of the present invention;

Fig. 9 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 2 according to the first embodiment of the present invention;

Fig. 10 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 3 according to the first embodiment of the present invention;

Fig. 11 is a circuit diagram of a planar light-source driving circuit according to a second embodiment of the present invention;

Fig. 12 is a circuit diagram of a planar light-source driving circuit according to another embodiment of the present invention;

Fig. 13 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 1 according to the second embodiment of the present invention;

Fig. 14 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 2 according to the second embodiment of the present invention;

Fig. 15 is a circuit diagram of a planar light-source driving circuit according to a third embodiment of the present invention;

Fig. 16 is a circuit diagram of a planar light-source driving circuit according to another embodiment of the present invention;

Fig. 17 is a timing diagram illustrating an operation of the planar light-source driving circuit according to the third embodiment of the present invention;

Fig. 18 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 1 according to the third embodiment of the present invention; and

Fig. 19 is a circuit diagram of an equivalent circuit of the planar light-source driving circuit in Mode 2 according to the third embodiment of the present invention. [Mode for Invention] Hereinafter, example embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1

Fig. 5 is a circuit diagram of a planar light-source driving circuit according to a first embodiment of the present invention. Referring to Fig. 5, the planar light-source driving circuit according to the first embodiment of the present invention includes a voltage source V_0C, an inductor L, a transformer T_x, and two switches Si and S2.

The inductor L is connected to the voltage source V_DC generating a DC voltage and operates as a current source applying current to the transformer T_x depending on the voltage applied by the voltage source V_DC.

The transformer T_x is a device that receives current supplied from the inductor L and applies a driving voltage to a planar light source. In the first embodiment shown in Fig. 5, the transformer T_x has primary and secondary windings Wi and W₂ positioned at a primary side thereof and a tertiary winding W₃ positioned at a secondary side thereof. One end of the primary winding Wi and the other end of the secondary winding W₂ are connected to each other to form an autotransformer , and the rest of the ends, which are not connected to each other, are connected to a ground through switches. The tertiary winding W₃ is connected to both power terminals of a planar light source 10 to supply a driving voltage to the planar light source 10. That is, the voltage applied to both ends of the primary or secondary winding Wi or W₂ of the transformer T_x is induced to both ends of the tertiary winding W₃ in proportion to a turn ratio [(primary : tertiary) or (secondary : tertiary)], and the induced voltage is applied as a driving voltage to the planar light source 10. The first and second switches Si and S₂ allow a pulse voltage to be induced to the secondary side of the transformer T_x by controlling current supplied to the primary side of the transformer T_x. The first switch Si is connected between the other end of the primary winding Wi of the transformer T_x and the ground, and the second switch S₂ is connected between one end of the secondary winding W₂ of the transformer T_x and the ground. The first and second switches Si and S2 periodically perform on/off switching operations.

The planar light-source driving circuit according to the first embodiment of the present invention may further include diodes that allow the respective switches to be soft-switched. Fig. 6 is a circuit diagram of a planar light-source driving circuit in which diodes are connected in parallel with the respective switches according to another embodiment of the present invention. Referring to Fig. 6, first and second diodes di and d₂ are connected in parallel with the respective switches Si and S₂ so that each of the switches Si and S₂ is soft-switched without loss in its conduction state. The first diode di has an anode electrode connected to the ground and a cathode electrode connected to the other end of the primary winding Wi of the transformer T_x. The second diode d₂ has a cathode electrode connected to the one end of the secondary winding W₂ of the transformer T_x and an anode electrode connected to the ground.

The operation of the planar light-source driving circuit, configured as described above, according to the first embodiment of the present invention will be described with reference to Figs. 7 to 10. Fig. 7 is a timing diagram illustrating an operation of the planar light-source driving circuit according to the first embodiment of the present invention. In respective waveforms of the timing diagrams described in this specification, resonance by a parasitic component is neglected. Referring to Fig. 7, the planar light-source driving circuit according to the first embodiment of the present invention is driven in four modes periodically circulating in accordance with on/off operations of the first and second switches S₁ and S2. Figs. 8 to 10 are circuit diagrams of equivalent circuits of the planar light-source driving circuit in respective modes according to the first embodiment of the present invention.

Mode 1: Referring to Fig. 8, Mode 1, in which the first switch Si is off and the second switch S2 is on, will be described. If the first switch Si is off, energy stored in the inductor L flows into the transformer T_x while current u flowing through the inductor L flows through the second switch S?. While the current flows through the secondary winding W₂ of the transformer T_x, current is induced to the tertiary winding W₃ of the transformer T_x in accordance with the turn ratio of the transformer T_x. A high lamp voltage Vi_amp is induced by the induced current, and a negative voltage is applied to the inductor L at the primary side. At this time, the planar light source 10 emits light by the current I_LAMP and voltage Vi_amp induced to the tertiary winding W₃. In Mode 1, as time elapses, the current u flowing through the inductor L, which is a constant current source, is almost constant or decreases gradually. Generally, Mode 2 may start by allowing the first switch Si to be closed before the current ϊι decreases, or Mode 2 may start together with soft switching by allowing the first switch Si to be closed just after or before the current reaches zero.

Mode 2: Referring to Fig. 9, Mode 2, in which the first and second switches Si and S₂ are on, will be described. If the first and second switches Si and S₂ are on, the current Ϊ_L is freewheeled through the first and second switches Si and S₂. At this time, the voltage applied to each of the windings Wi, W₂ and W₃ of the transformer T_x becomes zero, and all the voltage of the DC voltage source V₀C is applied to the inductor L so that the amplitude of the current -_L flowing through the inductor increases.

Accordingly, energy stored in the inductor increases. In Mode 2, current is not induced to the tertiary winding W3 of the transformer T_x, which is connected to the planar light source 10. Therefore, the planar light source 10 does not emit light.

Mode 3: Referring to Fig. 10, Mode 3, in which the second switch S₂ is off and the first switch Si is on, will be described. In Mode 3, energy stored in the inductor L flows into the transformer T_x while current flows through the first switch Si, so that the planar light source emits light. The operation in Mode 3 can be readily understood by those skilled in the art because it is the same as Mode 1, except that the direction of the current iijup applied to the planar light source 10 and the sign of the voltage Vi_amp are opposite to those in Mode 1. Therefore, detailed description will be omitted.

Through Modes 1 and 3, the planar light-source driving circuit can be driven bidirectional Iy by alternately applying voltages with opposite polarities to the planar light source 10. When the planar light-source driving circuit is driven bidirectional Iy, the lifetime of the planar light source 10 can be extended. In Mode 3, as time elapses, the current Ϊ_L flowing through the inductor decreases gradually, and Mode 4 starts together with soft switching by allowing the second switch S₂ to be closed just after or before the current Ϊ_L reaches zero.

Mode 4: Mode 4 is a mode in which energy is stored in the inductor L in the state that the first and second switches Si and S₂ are all on. Since the operation of the planar light-source driving circuit in Mode 4 is identical to that in Mode 2, it can be readily understood by those skilled in the art with reference to Mode 2. Therefore, detailed description will be omitted. Mode 1 is repeated after Mode 4.

In an embodiment of the present invention, Modes 2 and 4 that are modes in which the planar light source dose not emit light are maintained for a longer period of time than Modes 1 and 3 that are modes in which the planar light source emits light. Duty ratio of the voltage applied to the planar light source can be controlled by adjusting time for which each of the modes is maintained. For example, when the maintenance time of Modes 2 and 4 is much longer than that of Modes 1 and 3, a pulse-type voltage having an extremely small duty ratio is generated, and therefore, the planar light source can be effectively driven effectively.

Embodiment 2

Fig. 11 is a circuit diagram of a planar light-source driving circuit according to a second embodiment of the present invention. Referring to Fig. 11, the planar light-source driving circuit according to the second embodiment of the present invention includes a voltage source V_DC, two inductors Li and L₂, a transformer T_x, and two switches Si and S2.

The first and second inductors Li and L₂ are connected to the voltage source V_DC generating a DC voltage and operate as a current source which applies current to the transformer T_x depending on the voltage applied by the voltage source V_DC. When comparing with the aforementioned first embodiment, in the second embodiment, two inductors are used in place of a transformer having a center tap, so that a planar light source is driven bidirectional Iy. The transformer T_x is a device that receives current supplied from the first and second inductors Li and L₂ and applies a driving voltage to a planar light source. In the second embodiment shown in Fig. 11, the transformer T_x includes a primary winding Wi and a secondary winding W₂. One and the other ends of the primary winding W₁ are connected the first and second inductors Li and L₂, respectively, and the secondary winding W₂ is connected to both power terminals of a planar light source 10 to supply a driving voltage to the planar light source 10.

The first and second switches Si and S₂ allow a pulse voltage to be induced to a secondary side of the transformer T_x by controlling current supplied to a primary side of the transformer T_x. The first switch Si is connected between the other end of the primary winding Wi of the transformer T_x and a ground, and the second switch S₂ is connected between one end of the secondary winding W₂ of the transformer T_x and the ground. The first and second switches Si and S₂ periodically perform on/off switching operations.

Like the planar light-source driving circuit according the aforementioned first embodiment, the planar light-source driving circuit according to the second embodiment of the present invention may further include diodes that allow the respective switches to be soft-switched. Fig. 12 is a circuit diagram of a planar light-source driving circuit in which first and second diodes di and d₂ are connected in parallel with the respective switches Si and S₂ according to another embodiment of the present invention. The connection and operation of the respective diodes have been described above in conjunction with the first embodiment. Therefore, detailed description will be omitted.

In an embodiment of the present invention, a capacitor may be connected in series to the primary side of the transformer T_x of the planar light-source driving circuit according to the second embodiment of the present invention so as to prevent the transformer T_x from being saturated.

The driving mode and operation of the planar light-source driving circuit, configured as described above, according to the second embodiment of the present invention are identical to those of the first embodiment described with reference to Fig. 7. Therefore, detailed description will be omitted. Referring to Figs. 7 and 11, currents i_Li and iu that respectively flow through the first and second inductors Li and L₂ increase or decrease to be equal to the current Ϊ_L of the inductor shown in Fig. 6.

Figs. 13 and 14 are circuit diagrams of equivalent circuits of the planar light-source driving circuit in Modes 1 and 2 according to the second embodiment of the present invention, respectively. The equivalent circuits in the respective modes are similar to those of the planar light-source driving circuit according to the first embodiment of the present invention. However, the direction of current flowing through the primary winding Wi is changed using the first and second inductors Li and L2 respectively connected to both ends of the primary winding Wi in place of one inductor connected to the primary side of the transformer T_x using a center tap.

Mode 1: Referring to Fig. 13, Mode 1, in which the first switch Si is off and the second switch S2 is on, will be described. Since the second switch S₂ is on, current is freewheeled from the DC voltage source V_DC via the first and second inductors Li and L₂ and the second switch S2. At this time, while the current i_Li passing through the first inductor Li is passing through the primary winding Wi of the transformer T_x, a voltage is induced to the secondary winding W₂, so that the planar light source 10 emits light.

Mode 2: Referring to Fig. 14, Mode 2, in which the first and second switches Si and S₂ are on, will be described. In Mode 2, the currents in and i_L2 passing through the first and second inductors Li and L₂ are freewheeled through the first and second switches Si and S₂, respectively. Therefore, since current does not flow at the primary side of the transformer T_x, the planar light source 10 does not emit light.

Mode 3: The equivalent circuit in Mode 3 is identical to that in Mode 1 described with reference to Fig. 13 except for the direction of current. Since the first switch Si is on and the second switch S2 is off, the current

Ii2 passing through the second inductor L2 passes through the primary winding Wi of the transformer T_x. Therefore, a voltage is induced to the secondary side of the transformer T_x. Since the direction of the current at the primary winding Wi is opposite to that of the current in Mode 1, the voltage applied to the planar light source 10 is a negative voltage.

Mode 4: In Mode 4, since the first and second switches Si and S₂ are on like those in Mode 2 described with reference to Fig. 14, current does not flow through the primary winding Wi of the transformer T_x. Mode 1 is repeated after Mode 4.

In an embodiment of the present invention, Modes 2 and 4 that are modes in which the planar light source dose not emit light are maintained for a longer period of time than Modes 1 and 3 that are modes in which the planar light source emits light. Therefore, the planar light source can be driven effectively by a pulse-type voltage having an extremely small duty ratio.

As described above, the planar light-source driving circuit according to the second embodiment of the present invention can be driven bidirectional Iy, not by using a transformer with a structure in which an inductor is connected to a center tap of the transformer but by using a transformer with a structure in which two inductors are respectively connected to both ends of a primary side of the transformer.

Embodiment 3

Fig. 15 is a circuit diagram of a planar light-source driving circuit according to a third embodiment of the present invention. Referring to Fig. 15, the planar light-source driving circuit according to the third embodiment of the present invention includes an inductor L, a capacitor C, a transformer T_x, and a switch S. Unlike the first and second embodiments of the present invention, a planar light source 10 is driven using unidirectional driving waveforms .

The inductor L is connected to the voltage source V_DC generating a DC voltage and operates as a current source applying current to the transformer T_x depending on the voltage applied by the voltage source V_DC

The transformer T_x is a device that receives current supplied from the inductor L and applies a driving voltage to the planar light source 10. In the third embodiment shown in Fig. 15, the transformer T_x includes a primary winding W₁ and a secondary winding W₂. The primary winding Wi has one end connected to the capacitor C and the other end connected to the inductor L, and the secondary winding W2 is connected to both power terminal ends of the planar light source 10 to supply a driving voltage to the planar light source 10.

The capacitor C serves as a DC voltage source applying a voltage to the primary winding Wi of the transformer T_x, and is connected between the one end of the primary winding Wi of the transformer T_x and a ground to be charged or discharged with a predetermined voltage.

The switch S periodically performs on/off switching operations so that a pulse voltage is induced to the secondary winding W2 of the transformer T_x by controlling current supplied to the primary winding Wi of the transformer T_x. The switch S is connected between the other end of the primary winding W_x of the transformer T_x, which is connected to the inductor L, and the ground.

The planar light-source driving circuit according to the third embodiment of the present invention may further include a diode that allows the switch S to be soft-switched, like those of the first and second embodiments of the present invention. Fig. 16 is a circuit diagram of a planar light-source driving circuit in which a diode d is connected in parallel with the switch S according to another embodiment of the present invention.

The operation of the planar light-source driving circuit, configured as described above, according to the third embodiment of the present invention will be described with reference to Figs. 17 to 19. Fig. 17 is a timing diagram illustrating an operation of the planar light-source driving circuit according to the third embodiment of the present invention. Referring to Fig. 17, the planar light-source driving circuit according to the third embodiment of the present invention is driven in two modes periodically circulating in accordance with on/off operations of the switch S. Figs. 18 and 19 are circuit diagrams of equivalent circuits of the planar light-source driving circuit in respective modes according to the third embodiment of the present invention.

Mode 1: Referring to Fig. 18, Mode 1, in which the switch S is on, will be described. Since the switch S is on, a voltage of the DC voltage source V_DC is applied to the inductor L so that current increases. If the inductance of the inductor is very large, the amplitude of the current Ϊ_L is maintained almost constant. The capacitor C is charged with a predetermined voltage V_c, and therefore, a reverse voltage is applied to the primary winding Wi of the transformer T_x so that current ic discharged from the capacitor C passes through the primary winding Wi. However, since the amplitude of the voltage V_c is relatively small, the planar light source 10 does not emit light in Mode 1. The current i_on which amounts to the sum of the current i_L passing through the inductor L and the discharge current i_c of the capacitor C is freewheeled through the switch S. At this time, the switch is turned off, and Mode 2 begins.

Mode 2: Referring to Fig. 19, Mode 2, in which the switch S is off, will be described. If the switch S is off, a driving voltage Vi_amp is induced to the planar light source 10 connected to the secondary winding W₂ while the inductor current ii. flows through the primary winding Wi of the transformer T_x. Therefore, the planar light source 10 emits light in Mode 2. If the inductance of the inductor L is small, the amplitude of the current i_L decreases gradually. At this time, the inductor current i_L is charged into the capacitor C by passing through the primary winding W₁, and the switch S is turned on just before or after the inductor current i_L reaches zero.

Therefore, Mode 1 starts again.

In an embodiment of the present invention, Mode 1 in which the planar light source does not emit light is maintained for a longer period of time than Mode 2 in which the planar light source emits light, so that the planar light source can be driven effectively by a pulse-type voltage having an extremely small duty ratio.

As described above, when using a planar light-source driving circuit according to embodiments of the present invention, an inductor is connected to an input terminal to be used as a pulse current source, and a pulse voltage is generated by current supplied from the inductor, so that a planar light source can be driven effectively with a simple circuit configuration. Further, components used to configure the circuit are simplified, so that the size and cost of the circuit can be minimized.

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the accompanying claims and their equivalents. [Industrial Applicability] The present invention relates to a planar light-source pulse-type driving circuit using a current source. More particularly, it relates to a planar light-source driving circuit, wherein current is supplied to a transformer using an inductor connected to a DC voltage source as a current source, and the current supplied to the transformer is controlled in accordance with on/off switching operations of switches respectively connected to both ends of a primary side of the transformer, so that a pulse- type voltage is generated at a secondary side of the transformer to drive a planar light source.

Claims

[CLAIMS] [Claim 1]

A planar light-source driving circuit, comprising: a voltage source applying a DC voltage; an inductor supplying current depending on the DC voltage applied by the voltage source; a transformer having a primary side connected to the inductor and a secondary side connected to a planar light source, the transformer applying a pulse voltage to the planar light source using the current supplied from the inductor; and first and second switches respectively connected between both ends of the primary side of the transformer and a ground, the first and second switches controlling the current supplied to the transformer by on/off switching operations.

[Claim 2]

The planar light-source driving circuit as set forth in claim 1, wherein: the transformer has primary and secondary windings positioned at the primary side thereof; and the primary winding has one end connected to the inductor and the other end connected to the first switch, and the secondary winding has one end connected to the second switch and the other end connected to the one end of the primary winding, thereby forming an autotransformer .

[Claim 3]

A planar light-source driving circuit, comprising: a voltage source applying a DC voltage; first and second inductors supplying current depending on the DC voltage applied by the voltage source; a transformer having a primary winding having both ends respectively connected to the first and second inductors and a secondary winding having both ends connected to a planar light source, the transformer applying a pulse voltage to the planar light source; and first and second switches respectively connected between both ends of the primary winding of the transformer and a ground, the first and second switches controlling the current supplied from the first and second inductors to the transformer by on/off switching operations.

[Claim 4]

The planar light-source driving circuit as set forth in claim 3, further comprising a capacitor connected in series to the primary winding of the transformer to prevent saturation of the transformer.

[Claim 5]

The planar light-source driving circuit as set forth in claim 1 or 3, wherein: the planar light-source is driven in four modes periodically circulating in accordance with on/off operations of the first and second switches; and the four modes includes: Mode 1 in which the first switch is off and the second switch is on; Mode 2 in which the first and second switches are on; Mode 3 in which the second switch is off and the first switch is on, and Mode 4 in which the first and second switches are on.

[Claim 6]

The planar light-source driving circuit as set forth in claim 5, wherein Mode 2 is maintained for a longer period of time than Mode 1, and Mode 4 is maintained for a longer period of time than Mode 3.

[Claim 7]

The planar light-source driving circuit as set forth in claim 1 or 3, further comprising: a first diode connected in parallel with the first switch to allow the first switch to be soft-switched; and a second diode connected in parallel with the second switch to allow the second switch to be soft-switched.

[Claim 8]

The planar light-source driving circuit as set forth in claim 7, wherein each of the first and second diodes has a cathode electrode connected to the transformer and an anode electrode connected to the ground.

[Claim 9]

A planar light-source driving circuit, comprising: a voltage source applying a DC voltage; a transformer having a primary winding and a secondary winding, both ends of the secondary winding being connected to a planar light source so as to apply a pulse voltage to the planar light source; a capacitor charged or discharged with a predetermined voltage, the capacitor being connected to one end of the primary winding of the transformer so as to supply current to the transformer; an inductor connected to the other end of the primary winding of the transformer so as to supply current to the transformer depending on the DC voltage applied by the voltage source; and a switch connected between the other end of the primary winding of the transformer and a ground, the switch controlling the current applied to the transformer by on/off switching operations.

[Claim 10]

The planar light-source driving circuit as set forth in claim 9, wherein: the planar light-source driving circuit is driven in two modes periodically circulating in accordance with on/off operations of the switch; and the two modes include: Mode 1 in which the switch is on; and Mode 2 in which the switch is off.

[Claim 11]

The planar light-source driving circuit as set forth in claim 10, wherein Mode 1 is maintained for a longer period of time than Mode 2.

[Claim 12]

The planar light-source driving circuit as set forth in claim 9, further comprising a diode connected in parallel with the switch to allow the switch to be soft-switched.

[Claim 13]

The planar light-source driving circuit as set forth in claim 12, wherein the diode has a cathode electrode connected to the other end of the primary winding of the transformer and an anode electrode connected to the ground.