Choke

An electronic device including a core, at least a wire and a magnetic material is provided. The core includes a pillar, a top board and a bottom board. The pillar is disposed between the top board and the bottom board. An area of the top board is smaller than an area of the bottom board. A winding space is formed among the top board, the bottom board and the pillar. The wire is winded around the pillar and located in the winding space. The magnetic material fills the winding space to encapsulate the wire. The magnetic material includes a resin and a metallic powder, wherein an average particle diameter of the magnetic powder is smaller than 20 μm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a choke. More particularly, the present invention relates to a choke having a relatively small height and size.

2. Description of Related Art

A choke is used for stabilizing a circuit current to achieve a noise filtering effect, and a function thereof is similar to that of a capacitor, by which stabilization of the current is adjusted by storing and releasing electrical energy of the circuit. Compared to the capacitor that stores the electrical energy by an electrical field (electric charge), the choke stores the same by a magnetic field.

In the past, the chokes are generally applied in electronic devices such as DC/DC converters and battery chargers, and applied in transmission devices such as modems, asymmetric digital subscriber lines (ADSL) or local area networks (LAN), etc. However, in recent years, with development and demands of electronics technology, various electronic products are continually developed, and have a general trend of lightness, slimness, shortness and smallness. The chokes are widely applied to information products such as notebooks, mobile phones, LCD displays, and digital cameras, etc. Though, a height and size of the choke can be a problem in utilization.

FIG. 1is a cross-sectional view of a conventional choke. Referring toFIG. 1, the choke10has a coil12and a magnetic material14encapsulating the coil12, wherein a shape size of the choke10is above 4 mm×4 mm, and a height thereof is above 2.5 mm. A method of fabricating the choke10is as follows. First, a wire is winded into the coil12, and the winded coil12is disposed in a mold. Next, the magnetic material14fills in the mold for encapsulating the coil12, wherein the magnetic material14is, for example, insulated magnetic powder with particles. Next, a pressure molding and a firing process are performed to form the choke10.

In the fabrication process of the choke10, since the magnetic material14has the particles, and the coil12is a hollow structure, during the pressure molding process, the particles of the magnetic material14can press the coil12under the pressure, so that the coil12can be cracked or deformed. Moreover, if the height of the choke10is reduced to be less than or equal to 2.5 mm, a relatively fine wire (especially having high inductance) can be applied to wind the coil12. However, the coil12winded by such fine wire has a poor strength, and the pressure molding cannot be performed, so that reduction of the size of the choke10cannot be implemented.

FIG. 2is a cross-sectional view of another conventional choke. Referring toFIG. 2, the choke20disclosed by the U.S. Pat. No. 7,209,022 includes a drum-core30, a wire40, an exterior resin50, and a pair of external electrodes60. The drum-core30includes a pillar32, a top board34and a bottom board36, and the pillar32, the top board34and the bottom board36form a winding space S. The wire40is winded around the pillar32, and is located in the winding space S. The exterior resin50fills in the winding space S, and encapsulates the wire40, wherein the exterior resin50is coated by a dispenser, and a glass transition temperature that the exterior resin50is transited from a glass state to a plastic state is below −20° C. The pair of external electrodes60is disposed on a lower surface of the bottom board36.

Since the exterior resin50of the choke20has a volatile solvent, and is a mixed material formed by a plurality of formulations, after it is coated in the winding space S, it has to be rested at a room temperature for 30 minutes to vaporize the solvent, so as to perform a heat-curing process. Therefore, a fabrication time of the choke20is relatively long. Moreover, since the exterior resin50is formed by a plurality of the formulations having the solvent, and the glass transition temperature is below −20° C., a pot-life and a heat time of the exterior resin50are influenced by a formulation ratio, so that the pot-life of the exterior resin50is shortened, and a part of the formulations cannot be used for a mass production.

SUMMARY OF THE INVENTION

The present invention is directed to a choke having a magnetic material that can be directly heat-cured without being rested in a room temperature for some time, so as to shorten a fabrication time.

The present invention provides an electronic device including a core, at least a wire and a magnetic material. The core includes a pillar, a top board and a bottom board. The pillar is disposed between the top board and the bottom board. An area of the top board is smaller than an area of the bottom board. A winding space is formed among the top board, the bottom board and the pillar. The wire is winded around the pillar and located in the winding space. The magnetic material fills the winding space to encapsulate the wire. The magnetic material includes a resin and a metallic powder, wherein an average particle diameter of the magnetic powder is smaller than 20 μm.

In an embodiment of the present invention, the average particle diameter of the magnetic powder is smaller than or equal to 12 μm.

In an embodiment of the present invention, the average particle diameter of the magnetic powder is smaller than or equal to 7 μm.

In an embodiment of the present invention, the average particle diameter of the magnetic powder is smaller than or equal to 5 μm.

In an embodiment of the present invention, the shape of the magnetic powder is substantially a circle.

The present invention provides a choke including a drum-core, at least a wire and a magnetic material. The drum-core includes a pillar, a top board and a bottom board. The pillar is disposed between the top board and the bottom board. An area of the top board is smaller than that of the bottom board. A winding space is formed among the top board, the bottom board and the pillar. The wire is winded around the pillar and is located in the winding space. The magnetic material fills the winding space and encapsulates the wire. The magnetic material includes a thermosetting resin and a metallic powder, wherein a viscosity of the thermosetting resin is between 12000 c.p.s. and 30000 c.p.s., and a content of the metallic powder in the magnetic material is between 60 wt % and 80 wt %.

In an embodiment of the present invention, the top board and the bottom board of the drum-core are respectively a quadrate board. The top board has a first upper surface and a first lower surface, and the bottom board has a second upper surface and a second lower surface. The pillar is a column, and a diameter of the pillar is less than a length of a side of the top board.

In an embodiment of the present invention, a height between the first upper surface and the second lower surface is H, a height between the first lower surface and the second upper surface is h, and 0.3≤h/H≤0.5.

In an embodiment of the present invention, a length of a side of the top board is L1, a length between a side of the top board and an adjacent side of the pillar is L2, and 0.2≤L2/L1≤0.3.

In an embodiment of the present invention, a diameter of the wire is d, a height between the first lower surface and the second upper surface is h, and d≤h/2.

In an embodiment of the present invention, a height between the first lower surface and the second upper surface is h, a length between a side of the top board and an adjacent side of the pillar is L2, and h≤L2≤3h.

In an embodiment of the present invention, the bottom board has at least two arc-shaped guide slots and two bar-shaped guide slots respectively connected to the arc-shaped guide slots.

In an embodiment of the present invention, the arc-shaped guide slots are located at two opposite sides of the bottom board.

In an embodiment of the present invention, the choke further includes a pair of electrodes and a solder paste. The pair of electrodes and the solder paste are respectively disposed on the bar-shaped guide slots, wherein the pair of electrodes is formed by laminated metal layers, two ends of the wire are disposed on the pair of electrodes, and the solder paste covers the wire.

In an embodiment of the present invention, the choke further includes a pair of electrodes, and the pair of electrodes only covers a middle region of the bar-shaped guide slots.

In an embodiment of the present invention, the choke further includes a pair of electrodes, and the pair of electrodes only covers two ends of the bar-shaped guide slots.

In an embodiment of the present invention, the drum-core is formed by pressure molding a ferrite powder.

In an embodiment of the present invention, a material of the drum-core includes Ni—Zn ferrite or Mn—Zn ferrite, and the metallic powder includes an iron powder.

In an embodiment of the present invention, a permeability of the magnetic material is between 4 and 6.

In an embodiment of the present invention, the thermosetting resin is an organic material of polymer, and does not contain a volatile solvent.

In an embodiment of the present invention, the thermosetting resin includes a polymethylallyl (PMA) synthesize resin.

In an embodiment of the present invention, a linear expansion coefficient of the thermosetting resin is between 1×10−5/° C. and 20×10−5/° C.

In an embodiment of the present invention, a glass transition temperature of the thermosetting resin is between 130° C. and 170° C.

In an embodiment of the present invention, a content of the magnetic powder in the magnetic material is between 50 wt % and 90 wt %.

In an embodiment of the present invention, a glass transition temperature of the magnetic material and a glass transition temperature of the thermosetting resin are substantially the same.

The present invention provides a choke including a drum-core, at least a wire and a magnetic material. The drum-core includes a pillar and a winding space. The wire is winded around the pillar and is located in the winding space. The magnetic material fills the winding space and encapsulates the wire. The magnetic material includes a thermosetting resin and a metallic powder, wherein a viscosity of the thermosetting resin is between 12000 c.p.s. and 30000 c.p.s., and a content of the metallic powder in the magnetic material is between 60 wt % and 80 wt %.

The present invention further provides a choke including a core, at least a wire and a magnetic material. The core includes a pillar and a winding space. The wire is winded around the pillar and located in the winding space. The magnetic material fills in the winding space, encapsulating the wire and includes a resin and a magnetic powder, wherein an average particle diameter of the magnetic powder is smaller than 20 μm.

In an embodiment of the present invention, the magnetic powder comprises an iron powder and the iron powder in the magnetic material is between 50 wt % and 90 wt %.

In an embodiment of the present invention, the magnetic powder comprises an iron powder and the iron powder in the magnetic material is between 50 wt % and 90 wt %, and the magnetic powder is void of ferrite.

In an embodiment of the present invention, an electronic device is disclosed, wherein the electronic device comprises: a core comprising a pillar and a winding space; at least a wire, winded around the pillar and located in the winding space; and a magnetic material, filling the winding space and encapsulating the wire, wherein the magnetic material comprises resin and magnetic powder, wherein the magnetic powder comprises iron powder, wherein a content of the iron powder in the magnetic material is between 50 wt % and 90 wt %. In one embodiment, the electronic device as described above, the magnetic powder is void of ferrite.

In an embodiment of the present invention, an electronic device, comprising: a core comprising a pillar and a winding space; at least a wire, winded around the pillar and located in the winding space; and a magnetic material, filling the winding space and encapsulating the wire, wherein the magnetic material comprises resin and magnetic powder, wherein the magnetic powder comprises metallic powder, wherein the magnetic powder is void of ferrite and a content of the metallic powder in the magnetic material is between 50 wt % and 90 wt %. In one embodiment, the electronic device as described above, the content of the metallic powder in the magnetic material is between 60 wt % and 80 wt %.

In the present invention, since the choke applies the magnetic material formed by the thermosetting resin and the iron powder, after the magnetic material is coated in the winding space, it can be directly heat-cured without being rested in the room temperature for some time. Compared to the conventional technique, not only the fabrication time of the choke can be shortened, but also cracking and deforming of the drum-core can be avoided after the magnetic material is heated. Moreover, the magnetic material is also suitable for a mass production.

In order to make the aforementioned and other features and advantages of the present invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below.

DESCRIPTION OF EMBODIMENTS

In the embodiment of the invention, an electronic device including a core, at least a wire and a magnetic material is provided. The electronic device is a choke, for example. The core includes a pillar, a top board and a bottom board. The pillar is disposed between the top board and the bottom board. An area of the top board is smaller than an area of the bottom board. A winding space is formed among the top board, the bottom board and the pillar. The wire is winded around the pillar and located in the winding space. The magnetic material fills the winding space to encapsulate the wire. The magnetic material includes a resin and a metallic powder, wherein an average particle diameter of the magnetic powder is smaller than 20 μm. The resin includes a thermosetting resin, for example.

Moreover, the average particle diameter of the magnetic powder is smaller than or equal to 12 μm. In more detail, the average particle diameter of the magnetic powder is smaller than or equal to 7 μm. Perfectly, the average particle diameter of the magnetic powder is smaller than or equal to 5 μm, and the average particle diameter of the magnetic powder includes peak values of Gaussian Distribution. The shape of the magnetic powder is substantially a circle. It should be noted that magnetic powder of small mean particle diameter is, the better effects of the inductance value of the electronic device will be. The following embodiment uses a choke as an example, and persons of ordinary skill in the art may make modifications to the embodiments of the electronic device of the present invention without departing from the spirit of the present invention.

FIG. 3is a three-dimensional view of a choke according to an embodiment of the present invention,FIG. 4is a bottom view of the choke depicted inFIG. 3,FIG. 5is a cross-sectional view of the choke depicted inFIG. 3, andFIG. 6is a front view of a drum-core of the choke depicted inFIG. 3. Referring toFIG. 3,FIG. 4andFIG. 5, in the present embodiment, the choke100includes a drum-core110, at least a wire120(only one is illustrated inFIG. 5) and a magnetic material130. The choke100is suitable for a small size application, for example, a shape size of the chock100is below 4 mm×4 mm, and a height thereof is below 2.5 mm.

In detail, the drum-core110includes a pillar112, a top board114and a bottom board116, wherein the pillar112is disposed between the top board114and the bottom board116, and a winding space S′ is formed among the top board114, the bottom board116and the pillar112. The pillar112, the top board114and the bottom board116can be formed integrally, or can be respectively fabricated, and then are integrated by adhesion or locking. Particularly, in the present embodiment, the drum-core110is formed by pressure molding and firing an adhesive mixed with a ferrite powder. Namely, the pillar112, the top board114and the bottom board116are formed integrally. Moreover, the ferrite powder includes Ni—Zn ferrite powder or Mn—Zn ferrite powder. Preferably, in the present embodiment, the drum-core110is formed by the Ni—Zn ferrite powder. The adhesive includes a polymethylallyl (PMA) synthesize resin, and a linear expansion coefficient thereof is between 1×10−5/° C. and 20×10−5/° C. In the present embodiment, the linear expansion coefficient is about 13.8×10−5/° C.

According to a design of the choke100of the present embodiment, the top board114and the bottom board116are respectively a quadrate board, wherein an area of the top board114is smaller than that of the bottom board116. Namely, a side length of the top board114is smaller than that of the bottom board116. In detail, referring toFIG. 6, the top board114has a first upper surface114aand a first lower surface114b, and the bottom board116has a second upper surface116aand a second lower surface116b, wherein the a height H is between the first upper surface114aand the second lower surface116b, and a height h is between the first lower surface114band the second upper surface116a, and preferably 0.3≤h/H≤0.5, though the present embodiment is not limited thereto. Moreover, the side length of the top board114is L1, a length L2 is between a side of the top board114and an adjacent side of the pillar112, and preferably 0.2≤L2/L1≤0.3, though the present embodiment is not limited thereto.

Referring toFIG. 5andFIG. 6again, the wire120of the choke100is winded around the pillar112, and is located in the winding space S′, wherein the wire120is formed by a copper wire coated with an enamelled layer, and the enamelled layer is an insulating layer. The wire120can be linear or spiral. In the present embodiment, the pillar112is a column, and two ends of the pillar112are respectively connected to the first lower surface114band the second upper surface116a, wherein a diameter of the pillar112is less than the side length of the top board114. Since the pillar112is a column, when the wire120is winded around the pillar112, besides the wire120can be attached to an outer wall of the pillar112to effectively wind the wire120, a relatively low direct current resistance (DCR) can also be obtained under an equivalent permeability effect.

Further, a diameter of the wire120is d (including a diameter of the copper wire and a thickness of the enamelled layer), and the height of the pillar112(i.e. a distance between the first lower surface114band the second upper surface116a) is h. Preferably, d≤h/2, though the present embodiment is not limited thereto. In brief, in a design of the present embodiment, a size of the winding space S′ is defined according to the above equation 0.3≤h/H≤0.5 or 0.2≤L2/L1≤0.3, and a relation between the diameter d of the wire120and the winding space S′ can be defined by d≤h/2 and h≤L2≤3h, though the present embodiment is not limited thereto.

During the fabrication of the choke100of the present embodiment, the pillar112, the top board114and the bottom board116are first formed, and then the wire120is winded around the pillar112. Compared to the conventional technique that the coil12is first winded, and then the magnetic material14and the coil12are pressure-molded to form the choke10(referring toFIG. 1), in the present embodiment, cracking or deforming of the coil12caused by the coil12being pressed by the particles of the magnetic material14during the pressure-molding process can be avoided.

Moreover, an overall height and the size of the choke100are related to the height and the size of the drum-core110, while the height and the size of the conventional choke10are related to the diameter of the coil12and an amount of the filled magnetic material14. During the fabrication of the choke100of the present embodiment, the drum-core110is first formed, and then the wire120is winded, so that compared to the conventional fabrication method that the wire is first winded to form the coil12, and then the magnetic material14fills and pressure-molded to formed the choke10, the overall height and size of the choke100can be accurately controlled.

Referring toFIG. 3,FIG. 4andFIG. 5, in the present embodiment, the bottom board116further has two arc-shaped guide slots116cand two bar-shaped guide slots116drespectively connected to the arc-shaped guide slots116c. The arc-shaped guide slots116care located at a same side of the bottom board116(referring toFIG. 4) or two opposite sides of the bottom board116(referring toFIG. 7andFIG. 8). The arc-shaped guide slots116cconnect the second upper surface116aand the second lower surface116b, and the bar-shaped guide slots116dare disposed on the second lower surface116b. Particularly, in the present embodiment, longitudinal sections of the arc-shaped guide slot116cand longitudinal sections of the bar-shaped guide slots116dare all ladder-shaped.

Moreover, in the present embodiment, the choke100further includes a pair of electrodes140. The pair of electrodes140is disposed on the second lower surface116b, wherein the pair of electrodes140is formed by laminated metal layers, while the metal layer is formed by, for example, coating, and the laminated metal layers include a silver paste142serving as a base material, a nickel layer144formed by electroplating, and a tin layer146formed by electroplating. The pair of electrodes140can be respectively disposed on the bar-shaped guide slots116dand the second lower surface116bat two sides of the bar-shaped guide slots116d, wherein the electrode140covers the whole bar-shaped guide slot116d(referring toFIG. 4), only covers a middle region of the bar-shaped guide slot116d(referring toFIG. 7) or covers two ends of the bar-shaped guide slot116d(referring toFIG. 8). Two ends of the wire120can be respectively bended to the bar-shaped guide slots116dalong the arc-shaped guide slots116c, and can be disposed on the pair of electrodes140to electrically connect the pair of electrodes140. Then, a solder paste150can be soldered to cover the wire120, so as to fix the wire120on the bar-shaped guide slots116d. The choke100is suitable for electrically connecting to external through the pair of electrodes140on the bottom board116according to a surface mount technology (SMT). Since the electrode140of the present invention is formed by laminating a plurality of metal layers on the bar-shaped guide slot116d, compared to the conventional technique that applies a lead frame as an electrode, the height of the choke100of the present invention is not increased since the electrode140is disposed in the bar-shaped guide slot116d. Regarding a choke with a relatively small size, the conventional fabrication method that applies the lead frame may have a problem of uneasy soldering between the lead frame and the wire. However, in the present invention, the electrodes are formed by directly coating the metal layers, and then the wire120is covered by the solder paste150for electrically connecting the wire120and the electrode140, so that the uneasy soldering problem between the lead frame and the wire can be resolved.

In the present embodiment, since the bar-shaped guide slots116dare designed on the bottom board116, besides the pair of electrodes140can be directly fabricated on the bar-shaped guide slots116d, the wire120can also be fixed on the bar-shaped guide slots116d, so that the overall height of the choke100can be effectively controlled. Moreover, the electrode140is disposed on the bar-shaped guide slot116dand extends to the second lower surface116blocated at two sides of the bar-shaped guide slot116d, which may avail forming the nickel layer144and the tin layer146by electroplating process, and avails the solder paste150protruding out from the second lower surface116b, so as to facilitate an external electrical connection. In addition, the longitudinal section of the bar-shaped guide slot116dis arc-shaped, so that the silver paste142can be sufficiently coated in the bar-shaped guide slot116d, and a problem that corners of the bar-shaped guide slot116dare difficult to be coated with the silver paste142is avoided.

Referring toFIG. 3andFIG. 5again, in the present embodiment, the magnetic material130fills in the winding space S′ and encapsulates the wire120, wherein the magnetic material130fills in the winding space S′ by coating. The magnetic material130is composed of a thermosetting resin and a metallic powder, wherein the thermosetting resin is an organic material not containing volatile solvent, and a viscosity of the thermosetting resin is between 12000 c.p.s. and 30000 c.p.s. A content of the metallic powder in the magnetic material130is between 50 wt % and 90 wt %, perfectly, is between 60 wt % and 80 wt %, and a content of the thermosetting resin is less than 40 wt %. In one embodiment, the content of the metallic powder in the magnetic material130is between 50 wt % and 90 wt %, perfectly, is between 60 wt % and 80 wt %, and the magnetic material130is void of ferrite.

In the present embodiment, the viscosity of the thermosetting resin is between 12000 c.p.s. and 18000 c.p.s., and the metallic powder includes an iron powder.

In detail, a reason that the thermosetting resin and the iron powder are used to compose the magnetic material130lies in: the thermosetting resin can bear a high temperature of more than 350° C. when a heating temperature exceeds a glass transition temperature, so as to satisfy a demand of a desolder temperature, and a permeability of the magnetic material130can be easily controlled due to utilization of the iron powder. Moreover, since the viscosity of the thermosetting resin is between 12000 c.p.s. and 30000 c.p.s., the iron powder is easy to be mixed with the thermosetting resin to form the magnetic material130, and a tolerance range of a mixing ratio thereof is relatively great, and the thermosetting resin is easy to be coated in the winding space S′. Since a content of the thermosetting resin in the magnetic material130is less than 40 wt %, and the thermosetting resin does not contain the volatile solvent, during a heat-curing process, a thermal stress generated due to expansion and contraction of the thermosetting resin can be reduced, and blow holes are relatively less, so that cracking of the drum-core110can be avoided. In addition, in the present embodiment, the permeability of the magnetic material130is between 4 and 6, and the thermosetting resin is a polymer, for example, a polymethylallyl (PMA) synthesize resin, wherein a linear expansion coefficient of the thermosetting resin is between 1×10−5/° C. and 20×10−5/° C., and the glass transition temperature is between 130° C. and 170° C. In one embodiment, the content of the iron powder in the magnetic material130is between 50 wt % and 90 wt %, perfectly, is between 60 wt % and 80 wt %, and the magnetic material130is void of ferrite.

Particularly, in the present embodiment, the glass transition temperature of the magnetic material130is substantially the same to the glass transition temperature of the thermosetting resin, and the linear expansion coefficient is about 13.8×10−5/° C., and the glass transition temperature is 150° C.

Since the top board114and the bottom board116of the drum-core110of the present embodiment are all quadrate boards, and an area of the top board114is less than that of the bottom board116, and the viscosity of the magnetic material130is between 12000 c.p.s. and 30000 c.p.s., and the content of the thermosetting resin130is less than 40 wt %, after the magnetic material130is filled in the winding space S′ by coating, a flash phenomenon of the magnetic material130is not liable to be occurred.

It should be noted that since the magnetic material130of the present embodiment does not contain the volatile solvent, after the magnetic material130is coated, it can be directly heat-cured without being rested in the room temperature for some time, and cracking and deforming of the drum-core can be avoided when the magnetic material130is heat-cured, so that compared to the conventional technique, not only a fabrication time of the choke100can be shortened, but also a pot-life of the magnetic material130is not influenced by a formulation ratio, and the magnetic material130is suitable for a mass production.

Moreover, in the drum-core110of the present embodiment, the top board114and the bottom board116are designed to be quadrate, so that not only the choke100may have a relatively high permeability effect, but also the DCR can be reduced, and a saturation current can be increased. Moreover, in the present embodiment, since the pair of electrodes140is designed on the second lower surface116bof the bottom board116, and the bottom board116is the quadrate board, when the choke100is electrically connected to the external through the pair of electrodes140on the bottom board116, a positioning and a direction-selecting problem can be avoided, and the choke100can be directly connected to the external according to the SMT without using the lead frame. By such means, not only the choke100may have a relatively small overall height, but also a designable size of the drum-core110can be increased.

In brief, in the present embodiment, since the choke100applies the magnetic material130composed of the thermosetting resin and the metallic powder, after the magnetic material130is coated in the winding space S′, it can be directly heat-cured without being rested in the room temperature for some time. Compared to the conventional technique, not only the fabrication time of the choke100can be shortened, but also cracking and deforming of the drum-core can be avoided after the magnetic material130is heated. Moreover, a pot-life of the magnetic material130is not influenced by the formulation ratio, and the magnetic material130is suitable for a mass production.

Experiment

In the present invention, since an inductance, the DCR and the saturation current of the choke100are all related to winding turns that the wire120wraps around the pillar112, the diameter of the wire120(the diameter of the copper wire and the thickness of the enamelled layer), and the size of the drum-core110, three groups of measured results are provided below for comparing relations among the winding turns of the wire120and the diameter of the wire120, and the inductance, the DCR and the saturation current.

In the present embodiment, the three groups of measured results are all obtained by comparing the drum-cores30and110of the chokes20and100with the same material and similar size, wherein a difference between the choke100of the present embodiment and the choke20ofFIG. 2is that the magnetic material130used by the choke100does not contain the volatile solvent, and the magnetic material130is composed of the thermosetting resin and the iron powder, though the magnetic material30used by the choke20ofFIG. 2contains the volatile solvent, and is formed according to a plurality of formulations. It should be noted that the following three groups of measured results are all obtained in case that no cracking is occurred to the drum-cores30and110during the heat-curing process.

In detail, the table one presents the experiment and calculation data of two chokes20and100having a size of 3 mm×3 mm×1 mm and respectively applying five different wire diameters and winding turns, wherein the data includes the inductances, the DCRs and the saturation currents. According to the data of the table one, in case of the same wire diameter and the same winding turns, the choke100has a relatively better DCR and saturation current. Namely, compared to the choke20, the choke100has advantages of the low DCR and the high saturation current. Moreover, in case of the same wire diameter and different winding turns, the inductances and the DCRs of the chocks20and100are all proportional to the winding turns, and the saturation currents of the chocks20and100are all inversely proportional to the winding turns.

In detail, the table two presents the experiment and calculation data of two chokes20and100having a size of 3 mm×3 mm×1.2 mm and respectively applying five different wire diameters and winding turns, wherein the data includes the inductances, the DCRs and the saturation currents. According to the data of the table two, in case of the same wire diameter and the same winding turns, the choke100has a relatively better DCR and saturation current. Namely, compared to the choke20, the choke100has advantages of the low DCR and the high saturation current. Moreover, when the temperature in increased for 40° C., an increment of the saturation current of the choke100is greater than that of the choke20. Namely, compared to the choke20, the choke100has a better saturation current. Moreover, in case of the same wire diameter and different winding turns, the inductances and the DCRs of the chocks20and100are all proportional to the winding turns, and the saturation currents of the chocks20and100are all inversely proportional to the winding turns.

In detail, the table three presents the experiment and calculation data of two chokes20and100having a size of 4 mm×4 mm×1.2 mm and respectively applying four different wire diameters and winding turns, wherein the data includes the inductances, the DCRs and the saturation currents. According to the data of the table three, in case of the same wire diameter and the same winding turns, the choke100has a relatively better DCR and saturation current. Namely, compared to the choke20, the choke100has advantages of the low DCR and the high saturation current. Moreover, in case of the same wire diameter and different winding turns, the inductances and the DCRs of the chocks20and100are all proportional to the winding turns, and the saturation currents of the chocks20and100are all inversely proportional to the winding turns.

In brief, according to the experiment data, it is known that in case of the drum-cores30and110of the chokes20and100applying the same material, and having the similar size, and the wire diameter and the winding turns being the same, and in case that only the magnetic material130used by the choke100does not contain the volatile solvent, and the magnetic material130is composed of the thermosetting resin and the iron powder, though the magnetic material30used by the choke20ofFIG. 2contains the volatile solvent, and is formed according to a plurality of formulations, compared to the choke20, the choke100has the better DCR and the saturation current.

In summary, since the choke of the present invention applies the magnetic material composed of the thermosetting resin and the metallic powder, the choke of the present invention has at least the following advantages:

1. After the magnetic material is coated in the winding space, it can be directly heat-cured without being rested in the room temperature for some time, so as to shorten the fabrication time of the choke.

2. When the magnetic material is heated, cracking or deforming of the drum-core can be avoided.

3. A pot-life of the magnetic material is not influenced by a formulation ratio, so that the magnetic material is suitable for a mass production.

4. A content of the thermosetting resin in the magnetic material is less than 40 wt %, so that during the heat-curing process, a thermal stress generated due to expansion and contraction of the thermosetting resin can be reduced, and cracking of the drum-core can be avoided.

5. The inductance, the shape size, the saturation current and the DCR of the choke all meet a required specification.

6. The choke is suitable for applications that require a shape size of the choke being below 4 mm×4 mm and a height being below 1.5 mm.