Boost converter

[0001] 1. Field of the Invention

[0002] The invention generally relates to a boost converter, and more particularly, to a boost converter utilizing coupled coils.

[0003] 2. Description of the Prior Art

[0004] A boost converter is a periodically switching converter commonly used for boosting voltage and adjusting power factor in circuits. FIG. 1 is a circuit diagram of a conventional boost converter 100. The boost converter 100 includes a voltage source 110, an inductor 120, a power switch component 130, a diode 140, a capacitor 150, and a load 160. A gate terminal G of the power switch component 130 is controlled by a pulse width modulation (PWM) signal. Furthermore, a turn-on time for the power switch component 130 in a period is controlled by modulating a duty cycle of the PWM signal. When the power switch component 130 is turned on, the voltage source 110, the inductor 120, and the power switch component 130 form a closed loop, and thus current I₁ flowing through the closed loop drives the inductor 120 to store energy until the power switch component 130 is turned off. When the power switch component 130 is turned off, the inductor 120 is in an energy releasing state, and thus current I₂ from the inductor 120 flows to the load 160 through the diode 140. In other words, when the power switch component 130 is turned off, the inductor 120 continuously releases its stored energy. As the current I₂ charges the capacitor 150, the released energy is gradually stored in the capacitor 150 and the load 160, thus achieving the goal of voltage boost. As known to those skilled in the art, the relationship between an input voltage Vi and an average value of an output voltage Vo is as follows:
Vo/Vin=1/(1−D)  equation (1).

[0005] Due to excessive current and switching loss, the power switch component 130 suffers from a great deal of dissipated heat, thus degrading effectiveness and bringing the extra burden of needing to incorporate a heat dissipation mechanism. As a result, a relatively expensive power switch component capable of sustaining high stress and having low switching loss is needed herein. However, if power loss from the power switch component 130 can be distributed, the heat dissipation mechanism can be simplified or avoided, thus utilizing restricted space for circuits more efficiently. As shown in FIG. 2, another conventional boost converter 200 includes two boost conversion units 201 and 202. Currents from an alternating current (AC) voltage source 210 flow through the boost conversion units 201 and 202, and thus are rectified by rectifiers 220 respectively to form a direct current (DC) voltage. The remaining parts, including inductors 230, power switch components 240, diodes 250, capacitors 260, control circuits 270 for controlling an on/off status of the boost conversion units 201 and 202, and resistors 280, are identical to those in the boost converter 100 shown in FIG. 1. Outputs of the two boost conversion units 201 and 202 are both connected to two ends of a load 290, which means the boost conversion units 201 and 202 are connected in a parallel style. The boost conversion units 201 and 202 utilize a same control circuit as their control circuits 270 respectively. In other words, the power switch components 240 of the boost conversion units 201 and 202 are controlled by the same control signal. Therefore, the two power switch components 240 are both turned on or turned off simultaneously, and thus the two inductors 230 store or release energy simultaneously. Because of the parallel connection style, currents in the whole circuits are evenly distributed to the two boost conversion units 201 and 202, and thus heat dissipation is evenly distributed to the two power switch components 240 in FIG. 2, which differs from the situation in the boost converter 100 shown in FIG. 1.

[0006] One aim of the present invention is to provide a boost converter. According to an embodiment of the present invention, a boost converter is disclosed. The boost converter comprises a first boost conversion unit and a second boost conversion unit. The first boost conversion unit comprises: a first coil, having a first end coupled to a first voltage level; a first switch component, coupled between a second end of the first coil and a second voltage level, for selectively connecting the second end of the first coil to the second voltage level; a second switch component, wherein the first switch component and the second switch component are not turned on simultaneously; and a capacitor, having a first end coupled to the second switch component and a second end coupled to the second voltage level; wherein the second switch component is coupled between the second end of the first coil and the first end of the capacitor for selectively connecting the second end of the first coil to the first end of the capacitor. The second boost conversion unit comprises: a second coil, having a first end coupled to the first voltage level; a third switch component, coupled between a second end of the second coil and the second voltage level, for selectively connecting the second end of the second coil to the second voltage level; and a fourth switch component, coupled between the second end of the second coil and the first end of the capacitor, for selectively connecting the second end of the second coil to the first end of the capacitor; wherein the third switch component and the fourth switch component are not turned on simultaneously. The first coil and the second coil are coupled to each other. When the first switch component is turned on, the fourth switch component is turned on simultaneously, and when the third switch component is turned on, the second switch component is turned on simultaneously.

[0007] According to another embodiment of the present invention, a boost conversion method is disclosed. The boost conversion method comprises: storing energy into a first coil of a first boost conversion unit in a first time period, wherein a voltage of the first coil is coupled to a second coil of a second boost conversion unit, and a cross voltage across the second coil is further coupled to a capacitor; and stopping storing energy into the first coil of the first boost conversion unit in a second time period, wherein a cross voltage across the first coil is coupled to the capacitor, and the cross voltage across the second coil is prohibited from being coupled to the capacitor.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

[0020] Please refer to FIG. 3. FIG. 3 is a circuit diagram of a boost converter 300 according to an embodiment of the present invention. In this embodiment, the boost converter 300 includes a voltage source 310, two conjugate coils 320 and 330, two power switch components 340 and 350, two switch components 360 and 370, and a filter 380. The voltage source 310 includes a first voltage level point and a second voltage level point, which can be a positive voltage output point and a negative voltage output point respectively in this embodiment. The negative voltage output point can also be regarded as a ground point. The two conjugate coils 320 and 330 are coils winding around the same core. Materials of the core can be air, or iron materials, where the iron materials can enhance mutual induction between the two conjugate coils 320 and 330. In this embodiment, the two conjugate coils 320 and 330 can be coils 320 and 330, for example. First coil ends of the coil 320 and the coil 330 are both connected to the first voltage level point of the voltage source 310, while second coil ends thereof are connected to the power switch component 340 and the power switch component 350 respectively. In this embodiment, the power switch component 340 or 350 can be, but is not limited to, an N-channel metal oxide semiconductor (NMOS) transistor, i.e. an N-channel metal oxide semiconductor field effect transistor (MOSFET), or a junction field effect transistor (JFET). The power switch component 340 or 350 can also be implemented using a P-channel MOS (PMOS) transistor, i.e. a P-channel MOSFET. In this embodiment, the power switch component 340 is an NMOS transistor, where a first end of the power switch component 340 is connected to the coil 320, and a second end is connected to the second voltage level point of the voltage source 310. Similarly, a first end of the power switch component 350 is connected to the coil 330, and a second end is connected to the second voltage level point of the voltage source 310. Moreover, gate terminals of the power switch component 340 and the power switch component 350 are respectively connected to first and second control signals V_G1 and V_G2. The first control signal V_G1 and second control signal V_G2 respectively control whether the power switch component 340 and the power switch component 350 are turned on or turned off. In this embodiment, the two switch components 360 and 370 are implemented by diodes 360 and 370. A first end of the diode 360 is connected to a second coil end of the coil 320. Similarly, a first end of the diode 370 is connected to a second coil end of the coil 330. Moreover, second ends of the diode 360 and the diode 370 are connected to each other. It should be noted that the switch components 360 and 370 are not limited to be implemented by the diodes 360 and 370. Therefore, other active switch components or passive switch components, for example, switch components formed by MOS transistors, can be utilized instead. In this embodiment, the filter 380 can be a capacitor 380, where a first end of the filter 380 is connected to the switch components 360 and 370, and a second end of the filter 380 is connected to the second voltage level point of the voltage source 310. In other embodiments, the filter 380 can also be a filter formed by a combination of inductor(s) and capacitor(s).

[0021] Please refer to FIG. 3 again. The boost converter 300 includes a DC voltage source 310, a first boost conversion unit, and a second boost conversion unit. The first boost conversion unit includes the coil 320, the power switch component 340, the diode 360, and the capacitor 380. The second boost conversion unit includes the coil 330, the power switch component 350, the diode 370, and the capacitor 380. Please note that the capacitor 380 is common to the first and the second boost conversion units. The coil 320 and the coil 330 are conjugate coils coupled to each other. With internal magnetizing inductance in a transformer, the coils 320 and 330 form inductive energy storing components, thus achieving the effects of mutual coupling and induction using a transformer architecture.

[0022] First, the first coil end of the coil 320, which is coupled to the DC voltage source 310, is defined as a positive end, and the second coil end of the coil 320, which is coupled to the power switch component 340, is defined as a negative end. It should be noted that the first coil end of the coil 320 and the second coil end of the coil 330 correspond to the same polarity, and the second coil end of the coil 320 and the first coil end of the coil 330 correspond to the same polarity. In other words, when current flows through the coil 320 in a direction from the DC voltage source 310 to the power switch component 340, a positive voltage is established at the first coil end of the coil 3201; otherwise, a negative voltage is established at the first coil end of the coil 320. V_G1 is the control signal of the power switch component 340, and V_G2 is the control signal of the power switch component 350. In this embodiment, it is feasible that the power switch components 340 and 350 are not turned on at the same time. Moreover, frequencies of the control signal V_G1 and the control signal V_G2 are adjustable, which means that the power switch components 340 and 350 are controlled in a frequency-variable style. It should be noted that the power switch components 340 and 350 can be, but are not limited to, NMOS transistors in this embodiment. However, the power switch components 340 and 350 can be implemented by JFETs or PMOS transistors in other embodiments of the present invention. Please refer to FIG. 4. FIG. 4 is a timing diagram corresponding to the embodiment shown in FIG. 3 where the power switch components 340 and 350 are implemented by NMOS transistors. Between time points t₀ and t₁, the power switch component 340 is turned on, the power switch component 350 is turned off, and the diode 360 is reversely biased. An equivalent circuit diagram of the first boost conversion unit is shown in FIG. 5(a). Meanwhile, a voltage V_LN1 across the two coil ends of the coil 320 is a positive voltage equal to a voltage provided by the DC voltage source 310, and a current I_LN1 flowing through the coil 320 increases linearly. At the same time, the coil 330 induces a voltage V_LN2 thereon by effects of coupling with the coil 320, thus forcing the diode 370 in the second boost conversion unit to be forwardly biased. An equivalent circuit diagram of the second boost conversion unit is shown in FIG. 5(b). Meanwhile, energy stored by the coil 330 is released to a load 390. Between time points t₁ and t₂, the power switch components 340 and 350 are both turned off, and the coil 320 in the first boost conversion unit starts releasing its stored energy, thus forcing the diode 360 to be forwardly biased, i.e. be turned on, and then transferring energy to the load 390 via the turned-on diode 360. Meanwhile, the voltage V_LN1 across the two coil ends of the coil 320 reverses its polarity from positive to negative, and the current I_LN1 decreases linearly. An equivalent circuit diagram of the first boost conversion unit is shown in FIG. 6(a). Moreover, the voltage V_LN2 on the coil 330 in the second boost conversion unit reverses its polarity from negative to positive by the effects of mutual inductive coupling. The diode 370 is thus reversely biased, so current flowing through the coil 330 drops to 0 in a very short period of time. An equivalent circuit diagram of the second boost conversion unit is shown in FIG. 6(b).

[0023] Between time points t₂ and t₃, the power switch component 350 is turned on, the power switch component 340 is turned off, and the diode 370 is reversely biased. An equivalent circuit diagram of the second boost conversion unit is shown in FIG. 7(b). Meanwhile, the coil 330 is in an energy storing state, the voltage V_LN2 across the two coil ends of the coil 330 is positive, and thus a current I_LN2 flowing through the coil 330 increases linearly. Moreover, the coil 320 induces a voltage V_LN1 thereon by the effects of coupling with the coil 330, thus forcing the diode 360 in the first boost conversion unit to be forwardly biased. An equivalent circuit diagram of the first boost conversion unit is shown in FIG. 7(a). Meanwhile, energy stored by the coil 320 is released to the load 390, and current flowing through the coil 320 decreases gradually. Afterwards, between time points t₃ and t₄, the power switch components 340 and 350 are both turned off, and the coil 330 in the second boost conversion unit starts releasing its stored energy, thus forcing the diode 370 to be forwardly biased, i.e. be turned on. As a result, the load 390 acquires energy released from the coil 330. Meanwhile, the voltage V_LN2 across the two coil ends of the coil 330 reverses its polarity from positive to negative, and the current I_LN2 decreases linearly. An equivalent circuit diagram of the second boost conversion unit is shown in FIG. 8(b). Moreover, the voltage V_LN1 on the coil 320 in the first boost conversion unit reverses its polarity from negative to positive by the effects of mutual inductive coupling. The diode 360 is thus reversely biased, so current flowing through the coil 320 drops to 0 in a very short period of time. An equivalent circuit diagram of the first boost conversion unit is shown in FIG. 8(a).

[0024] Afterwards, the first boost conversion unit and the second boost conversion unit operate repeatedly in the same process as mentioned above. Due to coupling of the coils 320 and 330, the second boost conversion unit releases energy while the first boost conversion unit stores energy in a period of time. Thus, the load 390 acquires energy in the same period of time. Then, when the first boost conversion unit completes storing energy and transits from an energy storing state to an energy releasing state, the load 390 acquires energy from the first boost conversion unit, and energy stored in the first boost conversion unit is gradually transferred to the load 390. Meanwhile, the second boost conversion unit is temporarily idle. Afterwards, in a similar way, the first boost conversion unit releases energy while the second boost conversion unit stores energy in another period of time due to coupling of the coils 320 and 330. Thus, the load 390 acquires energy in the same period of time. Then, when the second boost conversion unit completes storing energy and transits from an energy storing state to an energy releasing state, the load 390 acquires energy from the second boost conversion unit, and energy stored in the second boost conversion unit is gradually transferred to the load 390. Meanwhile, the first boost conversion unit is temporarily idle.

[0025] In conclusion, the present invention discloses that two boost conversion units are connected in a parallel style. Due to coupling of the coils, when one of the two boost conversion units stores energy, the other can still provide a load with energy. Moreover, the two boost conversion units are controlled by different control signals. Periods of the control signals are adjustable, and thus the two boost conversion units are controlled in a frequency-variable style. Therefore, a switching frequency of the two boost conversion units as a whole can be enhanced by connecting the two boost conversion units in a parallel style. If the two control signals, controlling the two boost conversion units, have frequencies of f₁ and f₂ respectively, the switching frequency as a whole can be enhanced to be f₁+f₂. Furthermore, the two boost conversion units operate alternately, thereby adjusting switching loss and averaging output power of components. As the switching frequency increases, the coil inductance, as well as the capacitance required in the two boost conversion units can be reduced correspondingly, thus substantially enhancing responses of the two boost conversion units as a whole. In addition to the above embodiments, the present invention can also utilize a multi-parallel style to connect more than two boost conversion units. In other words, an embodiment having three or more boost conversion units connected in a parallel style still falls in the scope of the present invention.

[0026] Although the present invention has been described with reference to preferred embodiments, those skilled in the art can easily ascertain its essential characteristics and, without departing from the spirit and scope thereof, can make numerous modifications, alterations, and equivalents of the invention to adapt it to various usages and conditions. Such modifications, alterations, and equivalents are intended to be encompassed in the scope of the present invention.

[0027] Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.