Description BIPOLAR PULSE GENERATOR

Technical Field

[1] The present invention relates to a bipolar pulse generator, and more particularly to a bipolar pulse generator capable of generating a bipolar pulse, in which pulse widths of a positive pulse and a negative pulse are symmetrical, in order to smoothly turn on a carbon nanotube (CNT) lamp. Background Art

[2] A hybrid ballast for driving a triode CNT lamp generally includes a bipolar pulse generation circuit for generating a bipolar pulse.

[3] In order to generate the bipolar pulse, a phase-shift type full-bridge circuit which can achieve zero voltage switching is widely used.

[4] However, if a phase-shift type full-bridge driving integrated circuit (IC) which is currently available commercially is operated with a very small pulse width (several microseconds) having a low duty cycle (less than 5%) in order to drive a CNT lamp, a probability that a positive pulse and a negative pulse are not symmetrical is high.

[5] When the phase-shift type full-bridge driving IC which is currently available commercially generates the bipolar pulse, the pulse widths of the positive pulse and the negative pulse are unlikely to be accurately symmetrical. In a serious case, a difference between the pulse widths of the positive pulse and the negative pulse may be 1 microseconds.

[6] The bipolar pulse for turning on the triode CNT lamp requires a pulse width of 3 microseconds or less. However, the difference between the pulse widths of the positive pulse and the negative pulse of the phase-shift type full-bridge driving IC is 33% or more and thus a serious problem may occur. If the size of the CNT lamp is increased, a capacitive load between a gate and a cathode is increased and ripple of a high DC voltage is increased. Thus, light efficiency deteriorates. Disclosure of Invention

Technical Problem

[7] 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 bipolar pulse generator capable of generating a bipolar pulse, in which pulse widths of a positive pulse and a negative pulse are symmetrical, in order to smoothly turn on a carbon nanotube (CNT) lamp. Technical Solution

[8] In accordance with the present invention, the above and other objects can be accomplished by the provision of a bipolar pulse generator including: a driving power

supply source which outputs a driving voltage for generating a bipolar pulse; an inverter which alternately generates positive and negative pulses, of which the pulse widths are symmetrical, using the driving voltage and outputs a rectangular wave bipolar pulse; and a resonance circuit which converts the rectangular wave bipolar pulse into a sinusoidal wave bipolar pulse and increases the level of the bipolar pulse.

[9] The inverter may include a full-bridge portion including a first half-bridge circuit including two FETs Ql and Q2 and a second half -bridge circuit including two FETs Q3 and Q4; a first half -bridge driving portion which outputs two signals for driving the two FETs configuring the first half -bridge circuit, the two signals each having a dead time; an operational frequency determining portion which outputs a frequency determination signal for determining an operational frequency of the first half-bridge driving portion; a phase delay portion which receives the frequency determination signal, delays a phase of the frequency determination signal, outputs the frequency determination signal having the delayed phase; and a second half -bridge driving portion which has an operational frequency determined by the signal output from the phase delay portion and outputs two signals for driving the two FETs configuring the second half-bridge circuit, the two signals each having a dead time.

[10] The bipolar pulse generator may further include a second bipolar pulse generator connected to the bipolar pulse generator, the second bipolar pulse generator may include a second inverter which receives the driving voltage for generating the bipolar pulse from the driving power supply source, alternately generates positive and negative pulses, of which the pulse widths are symmetrical, using the driving voltage, and outputs a rectangular wave bipolar pulse; and a second resonance circuit which converts the rectangular wave bipolar pulse into a sinusoidal wave bipolar pulse and increases the level of the bipolar pulse, and the second inverter may include a second full-bridge portion including a third half-bridge circuit including two FETs Ql and Q2 and a fourth half -bridge circuit including two FETs Q3 and Q4; a third half-bridge driving portion which outputs two signals for driving the two FETs configuring the third half -bridge circuit, the two signals each having a dead time; an inter- generator phase delay portion which delays the frequency determination signal output from the operational frequency determining portion and outputs a frequency determination signal for determining an operational frequency of the third half -bridge driving portion; a second phase delay portion which receives the output signal of the inter- generator phase delay portion, delays a phase of the output signal, and outputs a signal having the delayed phase; and a fourth half -bridge driving portion which has an operational frequency determined by the signal output from the second phase delay portion and outputs two signals for driving the two FETs configuring the fourth half- bridge circuit, the two signals each having a dead time.

Brief Description of the Drawings

[11] FIG. 1 is a block diagram showing a bipolar pulse generator according to an embodiment of the present invention;

[12] FIG. 2 is a circuit diagram showing in detail the bipolar pulse generator according to the embodiment of the present invention;

[13] FIG. 3 is an output waveform diagram of the bipolar pulse generator according to the embodiment of the present invention; and

[14] FIG. 4 is a circuit diagram showing in detail a combination of two bipolar pulse generators according to the embodiment of the present invention. Best Mode for Carrying Out the Invention

[15] Hereinafter, a bipolar pulse generator according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[16] FIG. 1 is a block diagram showing a bipolar pulse generator according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing in detail the bipolar pulse generator according to the embodiment of the present invention.

[17] As shown in FIG. 1, the bipolar pulse generator according to the present invention includes a driving power supply source 10 which outputs a driving voltage for generating a bipolar pulse, an inverter 20 which outputs a rectangular wave bipolar pulse using the driving voltage output from the driving power supply source 10, and a resonance circuit 30 which converts the rectangular wave bipolar pulse output from the inverter 20 into a sinusoidal wave bipolar pulse and increases the level of the bipolar pulse. The sinusoidal wave bipolar pulse output from the resonance circuit 30 is input to a gate terminal and a cathode terminal of a CNT lamp to drive the CNT lamp.

[18] The driving voltage output from the driving power supply source 10 is an input voltage for generating the bipolar pulse. The driving power supply source 10 generates and outputs a DC voltage to the inverter 20. The inverter 20 generates and outputs the rectangular wave bipolar pulse using the DC voltage.

[19] The inverter 20 alternately generates positive and negative pulses, of which pulse widths are symmetrical, using the driving voltage and outputs the rectangular wave bipolar pulse. That is, the inverter 20 receives the driving voltage and outputs the rectangular wave bipolar pulse having a constant frequency and pulse width. The rectangular wave pulse is generated and output such that the pulse widths of the positive pulse and the negative pulse of the bipolar pulse are symmetrical.

[20] As shown in FIG. 2, the inverter 20 which generates and outputs the bipolar pulse, in which the pulse widths of the positive pulse and the negative pulse are symmetrical, includes a full-bridge portion 21 including four FETs, a first half-bridge driving portion 22 which outputs signals for driving two FETs among the four FETs

configuring the full-bridge portion 21, an operational frequency determining portion 23 which outputs a frequency determination signal for determining an operational frequency of the first half -bridge driving portion 22, a second half-bridge driving portion 25 which outputs signals for driving the other two FETs of the four FETs, and a phase delay portion 24 which delays the phase of the signal determination signal and outputs the signal determination signal having the delayed phase as a signal determination signal for determining an operational frequency of the second half -bridge driving portion 25.

[21] The full-bridge portion 21 is formed by connecting a first half -bridge circuit and a second half-bridge circuit. The first half -bridge circuit includes a first FET Ql and a second FET Q2 and the second half-bridge circuit includes a third FET Q3 and a fourth FET Q4 as shown in FIG. 2.

[22] The first FET Ql and the second FET Q2 configuring the first half-bridge circuit are driven by the first half bridge driving portion 22. Accordingly, the first half -bridge driving portion 22 alternately outputs two signals for driving the two FETs (the first FET Ql and the second FET Q2).

[23] The first half-bridge driving portion 22 outputs two signals each having a dead time.

That is, as shown in FIG. 3, the first half-bridge driving portion 22 (denoted by Ul in FIG. 3) alternately outputs the output signals HVG and LVG each having the dead time.

[24] The operation of the first half-bridge driving portion 22 is performed by the frequency determination signal output from the operational frequency determining portion 23. That is, the operational frequency determining portion 23 outputs the frequency determination signal for determining the operational frequency of the first half-bridge driving portion 22 and controls the operation of the first half-bridge driving portion 22.

[25] The phase of the frequency determination signal output from the operational frequency determination portion 23 is delayed by the phase delay portion 24, and the frequency determination signal having the delayed phase is sent to the second half- bridge driving portion 25 to determine the operational frequency of the second half- bridge driving portion 25. That is, the phase delay portion 24 receives the frequency determination signal, delays the phase of the frequency determination signal by a predetermined time, outputs the frequency determination signal having the delayed phase, and controls the operational frequency of the second half -bridge driving portion 25.

[26] The operational frequency of the second half -bridge driving portion 25 is determined by the signal output from the phase delay portion 24. The second half-bridge driving portion 25 alternately outputs two signals for driving the two FETs (the third FET Q3 and the fourth FET Q4) configuring the second half-bridge circuit according to the op-

erational frequency.

[27] The second half -bridge driving portion 25 outputs two signals each having a dead time. That is, as shown in FIG. 3, the second half-bridge driving portion 25 (denoted by U2 in FIG. 3) alternately outputs the output signals HVG and LVG each having the dead time.

[28] The phases of the two signals output from the second half -bridge driving portion 25 are delayed from the phases of the two signals output from the first half-bridge driving portion 22, as shown in FIG. 3. This is because the driving time of the second half- bridge driving portion 25 is delayed from the driving time of the first half-bridge driving portion 22 by the phase delay portion 24.

[29] As described above, the two signals each having the dead time are output from the first half -bridge driving portion 22, the two signals each having the dead time are output from the second half-bridge driving portion 25, and the phases of the signals output from the second half-bridge driving portion 25 is delayed from those of the signals from the first half-bridge driving portion 22, as shown in FIG. 3.

[30] The four signals (HVG and LVG of Ul and HVG and LVG of U2 in FIG. 2) drive the four FETs configuring the full-bridge portion 21. Then, the rectangular wave bipolar pulse shown in FIG. 3 is input to the resonance circuit 30.

[31] A process of outputting the bipolar pulse will be briefly described.

[32] First, if only the output signal HVG of Ul and the output signal LVG of U2 are at a high level " 1", the first FET Ql and the fourth FET Q4 become a short circuit and the third FET Q3 and the second FET Q2 become an open circuit. The positive pulse of the driving voltage of the driving power supply source 10 is input to the resonance circuit 30. The positive pulse is maintained until the third FET Q3 is driven and switched.

[33] In contrast, if only the output signal LVG of Ul and the output signal HVG of U2 are at a high level " 1", the second FET Q2 and the third FET Q3 become a short circuit and the first FET Ql and the fourth FET Q4 become an open circuit. The negative pulse of the driving voltage of the driving power supply source 10 is input to the resonance circuit 30. The negative pulse is maintained until the fourth FET Q4 is driven and switched.

[34] As described above, in the present invention, the four FETs are driven with a phase shift using the two half -bridge driving portions 22 and 25. In the present invention, the half-bridge driving portion 22 can be driven in connection with the driving portion 25 through a terminal Rf and the half-bridge driving portion 25 can be driven in connection with the driving portion 22 through a terminal Cf, as shown in FIG. 2.

[35] Due to such a characteristic, the operational frequency is determined using a resistor

Rl and a capacitor Cl configuring the operational frequency determining portion 23

shown in FIG. 2, an input signal Rf of Ul (the first half-bridge driving portion 22) is sent to the phase delay portion 24, which delays the signal by the predetermined time using a resistor R2 and a capacitor C2. The delayed signal is input to the terminal Cf of U2 (the second half -bridge driving portion 25) to drive U2.

[36] When Ul and U2 are driven using the above-described method, it is possible to generate the rectangular wave bipolar pulse of which the pulse widths of the positive pulse and the negative pulse are symmetrical.

[37] Now, the operation of the bipolar pulse generator shown in FIG. 2 will be briefly described. First, the four FETs Ql, Q2, Q3 and Q4 configure the full-bridge portion, the driving voltage for generating the bipolar pulse is applied to the full-bridge portion, the operational frequency of Ul is determined by the resistor Rl and the capacitor Cl configuring the operational frequency determining portion connected to the terminals Rf and Cf of Ul, the signal of the terminal Rf of Ul is delayed by the predetermined time using the resistor R2 and the capacitor C2 configuring the phase delay portion, and the delayed signal is applied to the terminal Cf of U2 to operate U2.

[38] Accordingly, the signals HVG and LVG of Ul respectively drive the FETs Ql and

Q2 and the signals HVG and LVG of U2 respectively drive the FETs Q3 and Q4 such that the full-bridge portion is driven with the phase shift to generate the rectangular wave bipolar pulse.

[39] The resonance circuit may receive the rectangular wave bipolar pulse and generate the sinusoidal wave bipolar pulse using resonance between a leakage inductor of an output transformer Tl and a capacitive load (capacitor) between the gate and cathode of the CNT lamp. The capacitor C3 of the resonance circuit is a DC blocking capacitor, which prevents magnetic flux from being accumulated in the output transformer Tl to saturate the output transformer Tl due to non-symmetry of the pulse widths of the positive pulse and the negative pulse.

[40] The bipolar pulse generator may be connected to another bipolar pulse generator in parallel such that the CNT lamp is division-driven. The number of bipolar pulse generators connected in parallel may be at least two. Hereinafter, a case where two bipolar pulse generators are connected in parallel will be described with reference to FIG. 4.

[41] FIG. 4 shows a case where the bipolar pulse generator shown in FIG. 2 and another bipolar pulse generator (also called a second bipolar pulse generator) are connected in parallel.

[42] As shown in FIG. 4, the second bipolar pulse generator includes a second inverter 20' which receives a driving voltage for generating a bipolar pulse from the driving power supply source 10, alternately generates positive and negative pulses, of which pulse widths are symmetrical, using the driving voltage, and outputs a rectangular wave

bipolar pulse, and a second resonance circuit 30 which converts the rectangular wave bipolar pulse into a sinusoidal wave bipolar pulse and increases the level of the bipolar pulse.

[43] Similar to the inverter 20 shown in FIG. 2, the second inverter 20' includes a second full-bridge portion 21 including a third half-bridge circuit including two FETs QI l and Q 12 and a fourth half-bridge circuit including two FETs Q13 and Q 14.

[44] The second bipolar pulse generator further includes a third half-bridge driving portion 22' which outputs two signals, each having a dead time, for driving the two FETs QI l and Q 12 configuring the third half-bride circuit and a fourth half-bridge driving portion 25' which outputs two signals, each having a dead time, for driving the two FETs Q 13 and Q 14 configuring the fourth half-bridge circuit.

[45] The operational frequency of the third half-bridge driving portion 22' is not determined by the signal of the operational frequency determining portion 23 shown in FIG. 2. That is, as shown in FIG. 4, an inter-generator phase delay portion 23' delays the frequency determination signal output from the operational frequency determining portion 23 and outputs a frequency determination signal for determining the operational frequency of the third half bridge driving portion 22'.

[46] A second phase delay portion 24' shown in FIG. 4 receives the output signal of the inter-generator phase delay portion 23' and delays the phase of the output signal, and outputs the signal having the delayed phase, thereby controlling an operational frequency of the fourth half-bridge driving portion 25'.

[47] When a plurality of bipolar pulse generators are connected, the CNT lamp can be division-driven in order to increase light efficiency of the CNT lamp. In order to division-drive the CNT lamp, the circuit shown in FIG. 4 is employed.

[48] The operation of a bipolar pulse generator 1 shown in FIG. 4 (bipolar pulse generator located at the upper side of FIG. 4) is equal to that of the bipolar pulse generator shown in FIG. 2. In a bipolar pulse generator 2 shown in FIG. 4 (bipolar pulse generator located at the lower side of FIG. 4), the signal of the terminal Rf of Ul of the bipolar pulse generator 1 is delayed by a predetermined time using the phase delay portion 23', the delayed signal is input to Ul 1 of the bipolar pulse generator 2 to drive UI l, and the signal of the terminal Rf of Ul 1 is input to a terminal Cf of U 12 through the second phase delay portion 24' to drive U 12.

[49] The FETs Ql, Q2, Q3 and Q4 are driven by Ul and U2 to drive the bipolar pulse generator 1 and the FETs QI l, Ql 2, Q13 and Q 14 are driven by Ul 1 and U 12 to drive the bipolar pulse generator 2. When the positive pulse of the bipolar pulse generator 2 is located at the center of the positive pulse and the negative pulse of the bipolar pulse generator 1 by the above-described method, it is possible to output a bipolar pulse for two-division driving, in which the positive pulse and the negative pulse of the bipolar

pulse generator 1 and the positive pulse and the negative pulse of the bipolar pulse generator 2 respectively have a phase difference of 90°. If necessary, the CNT lamp can be driven by a plural-division driving method.

Industrial Applicability [50] According to a bipolar pulse generator of the present invention, since positive and negative pulses of which pulse widths are symmetrical are generated, it is possible to smoothly turn on a CNT lamp. In addition, since a rectangular wave bipolar pulse is converted into a sinusoidal wave bipolar pulse using a resonance circuit, it is possible to increase light efficiency of the CNT lamp. [51] It is possible to output a bipolar pulse for division-driving the CNT by connecting a plurality of bipolar pulse generators in parallel and delaying only the phases of the pulses output from the bipolar pulse generators.