WO2006001601A1

WO2006001601A1 - Starting circuit for electric motor

Info

Publication number: WO2006001601A1
Application number: PCT/KR2005/001489
Authority: WO
Inventors: Young Chang Cho
Original assignee: Texas Instruments Korea Limited
Priority date: 2004-06-28
Filing date: 2005-05-23
Publication date: 2006-01-05
Also published as: KR100486663B1

Abstract

Disclosed is a starting circuit used for initially driving an electric motor by temporarily supplying power to a starting coil of the electric motor and constructed in the form of an integrated circuit such that it stably operates the electric motor with power save functions. The starting circuit includes a switching unit for switching power applied to a starting coil of the electric motor from a power source; a rectifying unit including bridge diodes for full-wave rectifying AC power generated from the power source; a charging unit receiving the full-wave rectified power from the rectifying unit and restricting generation of a control signal used for controlling the switching unit during a predetermined period of time; and a control signal generating unit for receiving the full- wave rectified power from the rectifying unit and generating the control signal according to signals outputted from the charging unit in order to control the switching unit.

Description

STARTING CIRCUIT FOR ELECTRIC MOTOR Technical Field [1] The present invention relates to a starting circuit for an electric motor. More par¬ ticularly, the present invention relates to a starting circuit used for initially driving an electric motor by temporarily supplying power to a starting coil of the electric motor and embodied in the form of an integrated circuit such that it can stably operate the electric motor with power save functions. Background Art [2] In general, a starting circuit of an electric motor drives the electric motor by temporarily supplying power to a starting coil of the electric motor installed in electronic appliances, such as refrigerators and the like. Once the electric motor is driven, the starting circuit shuts off power supplied to the starting coil of the electric motor. Recently, a PTC (positive temperature coefficient) device has been extensively used as a starting circuit for a cooling apparatus. The PTC device may be made of a barium titanate ceramic and electric resistance of the PTC device is significantly increased as the temperature thereof rises. [3] As shown in FlG. 1, in a starting circuit using a PTC device 14, AC current generated from a power source 12 is applied to an electric motor 10 having a main coil and a starting coil. The PTC device 14 is connected to an end of the starting coil in series. [4] According to the starting circuit having the above-mentioned construction equipped with the PTC device 14, since the PTC device 14 has a low resistance value when the electric motor 10 is initially driven, the AC current generated from the power source 12 is applied to the starting coil. If the AC current is applied to the starting coil, the electric motor 10 is driven so that the temperature of the PTC device 14 is increased by heat due to the AC current applied to the PTC device 14. Thus, the resistance value of the PTC device 14 is also significantly increased. As a result, the AC current applied to the starting coil is shut off, and then the AC current flows only through the main coil. [5] However, since a low level current may continuously flow through the PTC device while the electric motor 10 is being operated, the starting circuit employing the PTC device causes great power consumption due to the characteristics of the PTC device. In addition, since the heated PTC device may not normally operate until it has been cooled to a predetermined temperature level, it is impossible to minutely control the temperature of the cooling appliances using the electric motor 10. [6] In order to solve the above problems of the PTC device, there has been suggested a circuit device without using the PTC device in the starting circuit. The circuit device uses charge/discharge operations of a capacitor, thereby to supply power to a motor within a short time when initially driving the motor, and shut off the power by using a switching device such as an SCR (silicon controlled rectifier) or a Triac (triode ac switch). [7] However, the above-mentioned circuit device has a tendency to cause the switching device to be shorted due to the characteristics of the semiconductor device. In addition, since a motor controlled by the switching device is an inductance load, malfunction may occur due to a counter electromotive force and an inductive power applied to the starting coil from the main coil when the motor 10 operates. In addition, the above- mentioned circuit device is unstable against instantaneous current interruption, so there are limitations to use the circuit device in practice. Disclosure of Invention Technical Problem [8] The present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a starting circuit for an electric circuit without using a PTC device, capable of obtaining op¬ erational time sufficient for starting a motor by extending charge time of a capacitor; removing limitations for a restart operation by shortening discharge time of the capacitor; stably operating against a counter electromotive force or an inductive power generated when the motor is driven; and forming a low- voltage internal circuit therein such that it can be constructed in the form of an integrated circuit (IC). Technical Solution [9] In order to accomplish the above object, there is provided a starting circuit for an electric motor, the starting circuit comprising: a switching unit for switching power applied to a starting coil of the electric motor from a power source; a rectifying unit including bridge diodes for full- wave rectifying AC power generated from the power source; a charging unit receiving the full-wave rectified power from the rectifying unit and restricting generation of a control signal used for controlling the switching unit during a predetermined period of time; and a control signal generating unit for receiving the full-wave rectified power from the rectifying unit and generating the control signal according to signals outputted from the charging unit in order to control the switching unit. [10] According to the preferred embodiment of the present invention, the switching unit includes a Triac (triode ac switch), which is a bi-directional switching device interposed between terminals in order to control the AC power inputted into the terminals, and a protecting unit connected to one end of the Triac in order to prevent the electric motor from being damaged due to a short-circuit of the Triac when over- current is applied to the Triac. [11] Alternatively, the switching unit includes an SCR (silicon controlled rectifier), which is connected to the rectifying unit including the bridge diodes for full- wave rectifying the AC power, and a protecting unit connected to one end of the SCR in order to prevent the electric motor from being damaged due to a short-circuit of the SCR when over-current is applied to the SCR. [12] The protecting unit includes a resistor, a fuse, or at least one diode having a potential barrier according to the kind of power (AC power or DC power) applied to the switching unit. [13] The charging unit includes a first resistor connected to a cathode of a fifth diode, which receives the full- wave rectified power from the rectifying unit through an anode thereof; a first capacitor connected to a first branch of an output terminal of the first resistor in order to smooth the rectified power; a capacitance diode having a cathode connected to a second branch of the output terminal of the first resistor through a second resistor used for adjusting charge time, and a zener diode connected to the cathode of the capacitance diode. [14] The control signal generating unit includes first to third transistors. The first transistor has a base connected between the second resistor and the capacitance diode of the charging unit through the zener diode and a third resistor and a collector for receiving the full- wave rectified power from the rectifying unit through a fourth resistor. The second transistor has a base connected to the collector of the first transistor and a collector for receiving the full- wave rectified power from the rectifying unit through a fifth resistor to amplify the full- wave rectified power. The third transistor has a base connected to an emitter of the second transistor, a collector for receiving the full- wave rectified power from the rectifying unit through a seventh resistor, and an emitter connected to a gate of the Triac through a diode. Advantageous Effects [15] As described above, according to the present invention, the first transistor Ql of the control signal generating section 220 can be stably maintained in a turned-off state, so that the starting circuit for the electric motor may stably operate against the inductive power or counter electromotive force generated when the electric motor is driven. [16] In addition, since the control signal generating section 220 includes the second transistor Q2, which is an amplifier transistor, it is possible to prevent the driving current for the third transistor Q3 from being continuously consumed when the starting circuit is in a waiting mode. [17] Furthermore, the zener diode ZDl is connected to the capacitance diode CDl in order to reduce charge voltage of the capacitance diode CDl. Thus, the capacitance diode CDl can be fabricated by using a semiconductor device, such as a capacitance diode. Accordingly, charge time and discharge time of the charging unit 210 can be shortened, so the time delay may be significantly reduced when operating the staring circuit and the starting circuit for the electric motor can be constructed in the form of an integrated circuit. Brief Description of the Drawings [18] FlG. 1 is a circuit diagram illustrating a structure of a conventional starting circuit for an electric motor employing a PTC device. [19] FlG. 2 is a circuit diagram illustrating a structure of a starting circuit for an electric motor according to a first embodiment of the present invention. [20] FlG. 3 is a circuit diagram illustrating a structure of a modified example of a protecting unit shown in FlG. 2. [21] FlG. 4 is a circuit diagram illustrating a structure of a starting circuit for an electric motor according to a second embodiment of the present invention. [22] FlG. 5 is a circuit diagram illustrating a structure of a modified example of a prot ecting unit shown in FlG. 4. Best Mode for Carrying Out the Invention [23] Reference will now be made in detail to the preferred embodiments of the present invention. [24] FlG. 2 is a circuit diagram illustrating a structure of a starting circuit for an electric motor according to a first embodiment of the present invention; FlG. 3 is a circuit diagram illustrating a structure of a modified example of a protecting unit shown in FlG. 2; FlG. 4 is a circuit diagram illustrating a structure of a starting circuit for an electric motor according to a second embodiment of the present invention; and FlG. 5 is a circuit diagram illustrating a structure of a modified example of a protecting unit shown in FlG. 4. [25] The starting circuit for the electric motor according to the present invention is connected to terminals Tl and T2 instead of using the PTC device as shown in FlG. 1. In FlGs. 2 and 3, the motor and a power supply are omitted for the purpose of convenience. [26] Referring to FlGs. 2 and 4, the starting circuit for the electric motor according to the present invention includes a switching unit 100 for switching AC power applied to a starting coil of the electric motor and a driving unit 200. The driving unit 200 operates using a power rectified by a rectifying unit including bridge diodes Dl to D4 for full- wave rectifying the AC power. The driving unit 200 includes a charging unit 210, which restricts generation of a control signal used for controlling the switching unit 100 during a predetermined period of time, and a control signal generating unit 220, which operates using the power rectified by the rectifying unit and generates the control signal in order to control the switching unit 100 according to the signals outputted from the charging unit 210. [27] As shown in FlG. 2, the switching unit 100 according to the first embodiment of the present invention includes a Triac (triode ac switch) 110 and a protecting unit 120. The Triac is a bi-directional switching device interposed between terminals Tl and T2 to which AC power is inputted and controls the AC power. The protecting unit 120 having a resistor R9 connected to one end of the Triac 110 prevents the electric motor from being damaged due to the short-circuit of the Triac 110 when over-current is applied to the Triac 110. As shown in FlG. 3, the protecting unit 120 can be formed of at least one diode having a potential barrier. If the protecting unit 120 is fabricated by using the resistor or the diode having the potential barrier, the protecting unit 120 not only prevents the Triac 110 from being short-circuited when over-current is applied to the Triac 110, but also stably supplies a minimum amount of power to the driving unit 200 such that the driving unit 200 can stably operate. [28] In addition, the protecting unit 120 may include a fuse. In this case, the fuse shuts off over-current when the over-current is applied to the Triac 110. [29] The driving unit 200 operates using a power rectified by a rectifying unit including bridge diodes Dl to D4 for full- wave rectifying the AC power supplied from the power source. That is, the charging unit 210 includes a first resistor Rl connected to a cathode of a fifth diode D5 in series. The fifth diode D5 receives the full-wave rectified power from the rectifying unit Dl to D4 through an anode thereof. In addition, an output terminal of the first resistor Rl is branched in such a manner that one branch of the first resistor Rl is connected to a first capacitor Cl used for smoothing the rectified power and the other branch of the first resistor Rl is connected to a second resistor R2 and a cathode of a capacitance diode CDl used for adjusting charge time of the charging unit 210. Further, a zener diode ZDl is connected to the cathode of the ca¬ pacitance diode CDl. The zener diode ZDl may reduce charge capacity of the ca¬ pacitance diode CDl, so that the capacitance diode CDl can be embodied by using a semiconductor device such as a capacitance diode, which can be constructed in the form of an integrated circuit at a low cost. [30] In addition, the control signal generating unit 220 includes first to third transistors Ql to Q3. The first transistor Ql has a base connected between the second resistor R2 and the capacitance diode CDl of the charging unit 210 through the zener diode ZDl and the third resistor R3 and a collector for receiving the full- wave rectified power from the rectifying unit Dl to D4 through a fourth resistor R4. The second transistor Q2 has a base connected to the collector of the first transistor Ql and a collector for receiving the full-wave rectified power from the rectifying unit Dl to D4 through a fifth resistor R5, and amplifies the received power. Further, the third transistor Q3 has a base connected to an emitter of the second transistor Q2, a collector for receiving the full- wave rectified power from the rectifying unit Dl to D4 through a seventh resistor R7, and an emitter connected to a gate of the Triac 110 through the fourth diode D4. [31] Hereinafter, an operation of the starting motor for the electric motor having the above-mentioned construction according to the present invention will be described. [32] First, the power source supplies AC power to terminals Tl and T2 for driving the electric motor. The AC power inputted into the terminals Tl and T2 is full- wave rectified through the rectifying unit including bridge diodes Dl to D4. Then, the full- wave rectified AC power is applied to a P terminal as shown in FIG. 2, and then, transferred to the base of the second transistor Q2 through the fourth resistor R4 of the control signal generating unit 220. Thus, both the second transistor Q2 and the third transistor Q3 having the base connected to the emitter of the second transistor Q2 are turned on. Accordingly, the third transistor Q3 applies a trigger voltage to the gate of the Triac 110 through the emitter of the third transistor Q3 and the fourth diode D4, thereby turning on the Triac 110. As the Triac 110 is turned on, power is fed into a starting coil (not shown) of the electric motor through the terminals Tl and T2, so that the electric motor is driven. [33] At the same time, the full-wave rectified power applied to the P terminal is applied to the charging unit 210 through the fifth diode D5. In addition, ripples of the full- wave rectified power applied to the charging unit 210 through the fifth diode D5 may be removed by means of the first resistor Rl and the first capacitor Cl, so that smoothing power is inputted into the second resistor R2 and the capacitance diode CDl. At this time, charge time of the charging unit 210 is determined according to the R*C time constant, which is a value of the second resistor R2 and capacitance diode CDl. Preferably, the value of the second resistor R2 is determined to adjust the charge time of the capacitance diode CDl within a range of about 0.3 to 0.8 second. Further, the zener diode ZDl connected to the capacitance diode CDl may operate in such a manner that the capacitance diode CDl is not over-charged. Accordingly, the charge voltage of the capacitance diode CDl can be lowered and the capacitance diode CDl can be embodied by using a capacitor device with a low cost. If the charge voltage of the capacitance diode CDl becomes lowered, discharge time of the charging unit 210 may be shortened and the starting circuit for the electric motor can be embodied in the form of an integrated circuit (IC). [34] If charge of the capacitance diode CDl has been completed within a capacitance range of the zener diode ZDl during the predetermined charge time determined according to the R*C time constant of the second resistor R2 and the capacitance diode CDl, the power inputted into the second resistor R2 and the capacitance diode CDl is applied to the base of the first transistor Ql of the control signal generating unit 220 through the third resistor R3. Thus, the first transistor Ql is turned on and the power of the P terminal inputted into the base of the second transistor Q2 through the fourth resistor R4 flows into the emitter of the first transistor Ql so that the second transistor Q2 is turned off. In addition, the third transistor Q3 having the base connected to the emitter of the second transistor Q2 is also turned off. Accordingly, the trigger voltage being applied to the gate of the Triac 110 through the emitter of the third transistor Q3 and the fourth diode D4 is shut off, so the Triac 110 is turned off. As the Triac 110 is turned off, the power being applied to the starting coil (not shown) of the electric motor through the terminals Tl and T2 is also shut off. [35] The first transistor Ql of the control signal generating unit 220 can be stably maintained in a turned-off state, so that the starting circuit for the electric motor according to the present invention may stably operate against the inductive power or counter electromotive force generated when the electric motor is driven. In other words, if the inductive power or counter electromotive force is applied to the starting coil of the electric motor when the electric motor is driven, the power is applied to the P terminal so that the capacitance diode CDl is charged through the second resistor R2. Then, the first transistor Ql is turned on and the second and third transistors Q2 and Q3 are turned off, thereby turning off the Triac 110. Thus, malfunction caused by the inductive power or counter electromotive force applied to the starting coil of the electric motor can be prevented. [36] In addition, the fifth resistor R5, which receives the full-wave rectified power from the rectifying unit Dl to D4, and the second transistor Q2, which receives the power through the collector thereof and the ninth resistor R9 and amplifies the power, can be omitted from the control signal generating unit 220 if the collector of the first transistor Ql is directly connected to the base of the third transistor Q3. [37] The second transistor Q2 is an amplifier transistor for preventing a driving current for the third transistor Q3 from being continuously consumed when the starting circuit is in a waiting mode. Thus, the driving current used for driving the third transistor Q3 is continuously applied to the second transistor Q2 with low current consumption without being directly applied to the third transistor Q3. When it is necessary to drive the third transistor Q3, the second transistor Q2 amplifies the driving current being applied thereto, thereby driving the third transistor Q3. Accordingly, power consumption in the waiting mode of the starting circuit may be significantly reduced. [38] An operation and a structure of a starting circuit according to the second embodiment of the present invention shown in FlGs. 4 and 5 are substantially similar to those of the starting circuit according to the first embodiment of the present invention shown in FlGs. 2 and 3, except that the structure of the switching unit 100. That is, as shown in FlG. 2, the switching unit 100 according to the first embodiment of the present invention includes the Triac 110, which is a bi-directional switching device capable of directly controlling the AC power, but the switching unit 100 according to the second embodiment of the present invention includes an SCR (silicon controlled rectifier) 130 capable of controlling the DC power, so the switching unit 100 according to the second embodiment of the present invention is connected to the rectifying unit including bridge diodes Dl to D4. [39] According to the second embodiment of the present invention, similarly to the first embodiment of the present invention, the power source supplies AC power to terminals Tl and T2 for driving the electric motor. The AC power inputted into the terminals Tl and T2 is full- wave rectified through the rectifying unit including bridge diodes Dl to D4. Then, the full-wave rectified AC power is applied to a P terminal as shown in FlG. 4, and then, applied to the Q2 and Q3 of the control signal generating unit 220 through the fourth resistor R4 so that the second and third transistors Q2 and Q3 of the control signal generating unit 220 are turned on. As the third transistor Q3 is turned on, the power is fed into the SCR 130 through the emitter of the third transistor Q3. Ac¬ cordingly, the power is applied to the starting coil (not shown) of the electric motor through the terminals Tl and T2, so the electric motor is driven. [40] In addition, the power applied to the P terminal is applied to the charging unit 210 through the fifth diode D5, and then, inputted into the second resistor R2 and the ca¬ pacitance diode CDl while being smoothed by means of the first resistor Rl and the first capacitor Cl. If charge of the capacitance diode CDl has been completed within a capacitance range of the zener diode ZDl during the predetermined charge time determined according to the R*C time constant of the second resistor R2 and the ca¬ pacitance diode CDl, the power inputted into the second resistor R2 and the ca¬ pacitance diode CDl is applied to the base of the first transistor Ql of the control signal generating unit 220 through the third resistor R3. Thus, the first transistor Ql is turned on and the power of the P terminal inputted into the base of the second transistor Q2 through the fourth resistor R4 flows into the emitter of the first transistor Ql so that the second transistor Q2 is turned off. In addition, the third transistor Q3 having the base connected to the emitter of the second transistor Q2 is also turned off. Accordingly, the power being applied to the SCR 130 from the emitter of the third transistor Q3 is shut off, so the SCR 130 is turned off. Accordingly, the power being applied to the starting coil (not shown) of the electric motor through the terminals Tl and T2 is also shut off. [41] As shown in FlG. 5, the protecting unit 120 may include at least one diode having a potential barrier. [42] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.

Claims

Claims [1] A starting circuit for an electric motor, the starting circuit comprising: a switching unit for switching power applied to a starting coil of the electric motor from a power source; a rectifying unit including bridge diodes for full- wave rectifying AC power generated from the power source; a charging unit receiving the full- wave rectified power from the rectifying unit and restricting generation of a control signal used for controlling the switching unit during a predetermined period of time; and a control signal generating unit for receiving the full- wave rectified power from the rectifying unit and generating the control signal according to signals outputted from the charging unit in order to control the switching unit. [2] The starting circuit as claimed in claim 1, wherein the switching unit includes a Triac (triode ac switch), which is a bi-directional switching device interposed between terminals in order to control the AC power inputted into the terminals, and a protecting unit connected to one end of the Triac in order to prevent the electric motor from being damaged due to a short-circuit of the Triac when over- current is applied to the Triac. [3] The starting circuit as claimed in claim 1, wherein the switching unit includes an SCR (silicon controlled rectifier), which is connected to the rectifying unit including the bridge diodes for full- wave rectifying the AC power, and a protecting unit connected to one end of the SCR in order to prevent the electric motor from being damaged due to a short-circuit of the SCR when over-current is applied to the SCR. [4] The starting circuit as claimed in claim 2 or 3, wherein the protecting unit includes a resistor. [5] The starting circuit as claimed in claim 2 or 3, wherein the protecting unit includes a fuse. [6] The starting circuit as claimed in claim 2 or 3, wherein the protecting unit includes at least one diode having a potential barrier according to the kind of power (AC power or DC power) applied to the switching unit. [7] The starting circuit as claimed in claim 1, wherein the charging unit includes a first resistor connected to a cathode of a fifth diode, which receives the full-wave rectified power from the rectifying unit through an anode thereof; a first capacitor connected to a first branch of an output terminal of the first resistor in order to smooth the rectified power; a capacitance diode having a cathode connected to a second branch of the output terminal of the first resistor through a second resistor used for adjusting charge time, and a zener diode connected to the cathode of the capacitance diode. [8] The starting circuit as claimed in claim 7, wherein the control signal generating unit includes first to third transistors, the first transistor has a base connected between the second resistor and the ca¬ pacitance diode of the charging unit through the zener diode and a third resistor and a collector for receiving the full-wave rectified power from the rectifying unit through a fourth resistor, the second transistor has a base connected to the collector of the first transistor and a collector for receiving the full-wave rectified power from the rectifying unit through a fifth resistor to amplify the full- wave rectified power, and the third transistor has a base connected to an emitter of the second transistor, a collector for receiving the full- wave rectified power from the rectifying unit through a seventh resistor, and an emitter connected to a gate of the Triac through a diode. [9] The starting circuit as claimed in claim 8, wherein, in the control signal generating unit, the collector of the first transistor is directly connected to the base of the third transistor without having the fifth register, which receives the full- wave rectified power from the rectifying unit, and the second transistor, which receives the power through the collector thereof and the ninth resistor and amplifies the power.