Electrical Component Comprising an Electrical Resistor

Abstract

In an embodiment an electrical component includes an electrical resistor having a PTC ceramic with a reference temperature exceeding 150° C., wherein, at the reference temperature, a reference resistance is twice an amount of a minimum resistance of the PTC ceramic.

Claims

1-27. (canceled)

28. An electrical component comprising: an electrical resistor comprising a PTC ceramic with a reference temperature exceeding 150° C., wherein, at the reference temperature, a reference resistance is twice an amount of a minimum resistance of the PTC ceramic.

29. The electrical component of claim 28, wherein the reference temperature exceeds 165° C.

30. The electrical component of claim 28, wherein dimensions and materials of the electrical resistor are selected to provide an optimized trade-off between dielectric strength and current carrying capacity.

31. The electrical component of claim 28, wherein the electrical resistor has a cuboid shape.

32. The electrical component of claim 28, wherein dimensions of the electrical resistor do not exceed 11 × 5 × 9 mm.

33. The electrical component of claim 28, wherein a dimension of the electrical resistor along a current path does not exceed 5 mm.

34. The electrical component of claim 33, wherein the dimension of the electrical resistor along the current path is larger than or equal to 3 mm.

35. The electrical component of claim 28, wherein the electrical component is adapted to be used in applications with a voltage level of up to 1400 V.

36. The electrical component of claim 28, further comprising a housing enclosing the electrical resistor.

37. The electrical component of claim 36, wherein the housing comprises a thermo-resistant plastic material.

38. The electrical component of claim 36, wherein the housing has a compact, cuboid shape.

39. The electrical component of claim 36, wherein a mass of the electrical component does not exceed 7 g.

40. The electrical component of claim 36, wherein the housing comprises a bottom and a cover both enclosing the electrical resistor in a cavity.

41. The electrical component of claim 36, further comprising contact springs permanently incorporated in the housing and comprising at least an inner portion inside the housing in a cavity and an outer portion outside the housing.

42. The electrical component of claim 41, wherein the inner portions of the contact springs which are located on the resistor are shaped like a barb, wherein a central, curved part of a barbed shaped portion of the contact spring is arranged on the resistor, and wherein an inner terminus of the spring arranged on an inner wall of a cover of the housing and the barbs of at least two springs on opposite sides of the resistor are clamped between the resistor and the cover of the housing providing a hard force to the housing to keep the cover closed and to fix the resistor in between.

43. The electrical component of claim 41, wherein the contact springs are a fixed, non-interchangeable part of the housing comprising a central portion incorporated by a bottom of the housing.

44. The electrical component of claim 41, wherein the contact springs comprise stainless steel.

45. The electrical component of claim 41, wherein the contact springs electrically contact the electrical resistor inside the cavity in the housing from at least two opposite sides at contact areas and electrically connect the electrical resistor with an electric contact outside the housing.

46. The electrical component of claim 41, wherein the inner portions of the contact springs are arranged to contact and fix the electrical resistor within the housing from at least two opposite sides thereby fixing it inside the cavity of the housing.

47. The electrical component of claim 28, wherein the electrical component is surface-mounted on a surface of a printed circuit board.

48. The electrical component of claim 47, wherein the electrical component is surface-mounted on the surface of the printed circuit board by solder.

49. The electrical component of claim 47, wherein outer portions of contact springs comprise contact pads mounted on an outer side of a bottom of a housing for electrically contacting the contact springs and thus the electrical resistor with the printed circuit board and for mechanically fixing the contact springs and thus the housing to the printed circuit board.

50. The electrical component of claim 49, wherein the contact pads form a flat surface together with the bottom of the housing and all contact pads are arranged coplanar.

51. The electrical component of claim 47, wherein dimension of the resistor in a height direction perpendicular to the printed circuit board is smaller than or equal to 11 mm.

52. The electrical component of claim 47, wherein dimension of the electrical component in a height direction perpendicular to the printed circuit board is smaller than or equal to 14 mm.

53. The electrical component of claim 28, wherein the PTC ceramic comprises a specific ceramic composition with the formula Ba.sub.(1-x-y-z)Pb.sub.xCa.sub.ySr.sub.zTiO.sub.3, wherein 0.1 < x < 0.3, 0 < y < 0.1 and 0 < z < 0.1 are fulfilled.

54. An electrical circuit comprising: the electrical component of claim 28.

55. The electrical circuit of claim 54, wherein the electrical circuit is an inrush current limiter.

56. The electrical circuit of claim 54, wherein the electrical circuit is a discharge resistor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0134] In the following, the invention will be explained in more detail with reference to accompanied figures.

[0135] Similar or apparently identical elements in the figures are marked with the same reference signs. The figures and the proportions in the figures are not scalable.

[0136] The figures show:

[0137] FIG. 1 shows a first embodiment of the electrical component in a cross-sectional view;

[0138] FIG. 2 shows the first embodiment of the electrical component in a perspective view from the top;

[0139] FIG. 3 shows a first embodiment of the electrical component in a perspective view from the bottom;

[0140] FIG. 4 shows a resistance-to-temperature-profile of the PTC ceramic included in the resistor according to the first embodiment used for high-voltage applications (≥ 800 V DC);

[0141] FIG. 5 shows a resistance-to-temperature-profile of the PTC ceramic included in the resistor according to a second embodiment used for low-voltage applications (230 V AC);

[0142] FIG. 6 shows electrical components according to the first embodiment mounted on a PCB; and

[0143] FIG. 7 shows a circuit diagram of an exemplary circuit comprising electrical components according to the first embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0144] The FIGS. 1, 2 and 3 show an embodiment of the electrical component 1 according to the invention from different views. The electrical component 1 comprises an electrical resistor 2. The electrical resistor consists of a ceramic with a positive temperature coefficient (PTC).

[0145] The electrical resistor 2 has a cuboid shape. The dimensions of the electrical resistor are selected to optimize the dielectric strength and the current carrying capacity of the resistor.

[0146] The cuboid resistor 2 has three dimensions. In the first embodiment electric current can pass the resistor from a first side to a second side. The distance between these two sides is estimated as the width of the resistor. Therefore, the width of the resistor corresponds to the length of the current path through the resistor.

[0147] The dimensions normal to the width are designated as the height and the length of the resistor.

[0148] In the present embodiment the dimensions of the resistor 2 amount 4.2 mm in width, 10.2 mm in height and 8.1 mm in length.

[0149] The ceramic material of the electrical resistor comprises a mixture of different ceramic materials which are typically used in electrical resistors and have PTC properties.

[0150] These ceramic materials are mixed with different ratios in order to obtain a PTC ceramic with a resistance-to-temperature-profile as shown in the FIGS. 4 and 5.

[0151] In the first embodiment, the PTC ceramic’s composition is optimized to be applied in high voltage applications ≥ 800 V DC (direct current).

[0152] The PTC ceramic is characterized by a resistance-to-temperature-profile according to FIG. 4. The profile is measured at low-level-voltage (1 V, pulse signal).

[0153] The reference temperature of the PTC ceramic amounts as shown in FIG. 4 around 165° C.

[0154] The ability of a PTC ceramic resistor applied as an inrush current limiter or a discharge resistor in an electric circuit to transfer energy is calculated by the following formula:

[00002]$\text{E}={\text{c}}_{\text{th}}\ast \text{V}\ast \left({\text{T}}_{\text{Ref}}-{\text{T}}_{\text{Amb}}\right)$

[0155] Due to the ceramic’s high reference temperature, the volume and thus the mass of the resistor can be minimized.

[0156] In comparison to a conventional PTC ceramic resistor the volume of the electrical resistor can be reduced by approximately 60%.

[0157] The high reference temperature further allows a variation of the dimensions in order to optimize the properties of the resistor 2 regarding its current carrying capability and dielectric strength.

[0158] The described electrical resistor 2, comprising the described ceramic material and having a width of 4.2 mm, shows an optimized trade-off between an improved current carrying capability and an improved dielectric strength.

[0159] The high reference temperature further allows a variation of the dimensions in order to optimize the properties of the resistor regarding its current carrying capability and dielectric strength.

[0160] Therefore, the electrical resistor is adapted to be used in high voltage applications with a voltage level of up to 1000 V.

[0161] Nevertheless, the same electrical resistor can be used in applications with a lower voltage level.

[0162] In a second embodiment the PTC ceramic’s composition is optimized to be applied in a lower voltage applications (230 V AC (alternating current)).

[0163] The PTC ceramic of the second embodiment is characterized by a resistance-to-temperature-profile according to FIG. 5. The profile is measured at low-level-voltage (1V, pulse signal).All other properties of the resistor are the same as in the first embodiment.

[0164] As can be seen in FIG. 5, the resistance of the electrical resistor in the working range below 165° C. is lower at the same temperature than in high-voltage applications.

[0165] In this case, the volume of the resistor can be even more decreased or the transmitted electrical energy can be increased.

[0166] The electrical resistor 2 is enclosed by a housing 3. The housing 3 comprises a bottom part and a cover part arranged along the height of the resistor 2. The bottom 4 encloses a lower portion of the resistor 2 and the cover 5 encloses an upper portion of the resistor 2.

[0167] The dimensions of the housing do not exceed 14 × 10 × 12 mm. The wall thickness of the housing does not exceed 2 mm. For example, the housing has a height of 13.5 mm, a length of 10 mm and a width of 11 mm.

[0168] The both parts of the housing 3 are connected by snap locks applied on each side of the housing 3.

[0169] The outer side of the housing 3 shows a cuboid shape adapted to the shape of the resistor 2. In the inside, the housing 3 provides a cavity 6 in which the resistor 2 is embedded.

[0170] During the assembling process, first the bottom 4 of the housing 3 is provided. The resistor 2 is arranged in a recess in the bottom 4 provided for this purpose.

[0171] Furthermore, the housing 3 comprises four metallic contact springs 7 incorporated in the bottom 4. These metal springs 7 press on the resistor 2 from two opposite sides at four contact areas, two at each side. Thereby the springs 7 get stretched and fix the resistor 2 in the cavity 6 inside the housing 3.

[0172] Two springs, each arranged at the same side, hang together and are cut from one metal piece.

[0173] By using four springs 7 the mechanical fixation and the electrical connection of the resistor 2 is improved.

[0174] In a further step, the cover 5 is arranged on the bottom 4 in order to form the housing 3 and the cavity 6 enclosed by the housing 3 and accommodating the resistor 2.

[0175] The both parts of the housing 3 are injection molded.

[0176] The metal springs 7 are incorporated into the bottom 3 during the injection molding process.

[0177] The housing 3 of the present embodiment consists of a polymer material. For example, the housing 3 consists of a liquid-crystal polymer material showing high strength and high robustness against thermal stress.

[0178] In another example, the housing 3 consists of PET or PPT mixed with up to 30 wt% of glass fiber material. The glass fiber material gives the material of the housing 3 high strength and high robustness against thermal stress.

[0179] The housing 3 protects the electrical resistor 2 against damaging mechanical impacts. Furthermore, it insulates the resistor 2 thermally. The thermal insulation protects ambient devices if the resistor 2 heats up.

[0180] In addition, the outside of the housing 3 offers a smooth and even surface that allows the housing 3 to be easily mounted on a carrier such as a printed circuit board.

[0181] Standardized dimensions of the housing 3 allow a mass assembly process of the electrical component 1 according to the described embodiment on a PCB.

[0182] The metal springs 7 comprise inner portions contacting and fixing the resistor 2 comprising the PTC ceramic in the cavity 6 of the housing 3.

[0183] Furthermore, the metal springs 7 also comprise outer portions exposed at the outside of the housing 3 comprising contact pads 8.

[0184] The springs 7 protrude from the housing 3 on a side surface normal to the bottom side. The outer portion of the springs 7 is tightly attached to the outer surface of the housing 3.

[0185] The contact pads 8 are portions of the springs 7 tightly attached to the bottom side of the bottom 4. The bottom side is the outer side of the of the housing’s bottom 4 opposite to the cover 5.

[0186] In the shown first embodiment, the contact pads 8 are arranged in the four corners of the rectangular bottom side.

[0187] The dimensions of the bottom side are defined as the width and the length of the resistor 2. The dimension normal to the bottom side is designated as the height of the resistor 2.

[0188] These contact pads 8 can be fixed on the printed circuit board (PCB) 9 as shown in FIG. 6.

[0189] When providing four springs 7 with in total four contact pads 8, a reliable fixation of the electrical component 1 on the PCB 9 can be accomplished.

[0190] The metallic contact pads 8 are fixed on solder pads 10 on the PCB 9. The solder pads 10 are attached on electrical contact points of the PCB 9. Therefore, the device 1 is electrically contacted with a circuit on the PCB 9. Providing four contact pads 8 and four solder pads 10, a reliable contact between the PCB 9 and the device 1 can be accomplished.

[0191] In this way, the electrical component 1 can be incorporated in an electrical circuit printed on the PCB 9.

[0192] The circuit diagram in FIG. 7 shows two examples for applications of the electrical component 1 according to the invention incorporated in an electrical circuit.

[0193] The two electrical components ICL 101 and DCR 102 are incorporated in the circuit of an automotive onboard battery charger (OBC) 100 as shown in the circuit diagram.

[0194] The devices 1 comprising a PTC ceramic material according to the invention serve as electrical resistors in the circuit.

[0195] A device 1 designated as ICL 101 is applied as an inrush current limiter, whereas another device 1 designated as DCR 102 is applied as a discharge resistor.

[0196] For charging a capacitor 103 the three shown switches S2, S3 and S4 are open and a 3-phase switch S1 (main switch) is closed. The inrush current limiter ICL 101 limits the inrush current peak of a charging current to a level which does not damage the diodes D1 to D6 incorporated in the circuit and does not blow fuses at the power distribution of the electrical grid.

[0197] The ICL 101 has to transfer the charging energy E.sub.c of the capacitor 103.

[0198] The charging energy E.sub.c is given by

[00003]${\text{E}}_{\text{c}}=\frac{\text{C}\ast {\text{U}}^2}{2}$

wherein U is the voltage level to which the capacitor 103 is charged and C is the capacity of the capacitor 103.

[0199] In order that the temperature of the PTC ceramic T.sub.PTC does not rise too much and the PTC ceramic does not change to a high-resistance state (T.sub.PTC < T.sub.Ref) E ≥ 0.96 ∗ E.sub.c must be fulfilled, wherein 0.96 ∗ E.sub.c corresponds to the energy level at the ICL 101.

[0200] Once the capacitor 103 is charged to the voltage level U, the ICL 101 is short-circuited by closing the switch S2. To integrate the electrical load 104 in the circuit the switch S.sub.3 (load switch) is closed.

[0201] In case of a malfunction of the circuit (e.g. short-circuit of terminals of the capacitor 103 or the switch S2 does not close) a fault current occurs. The resulting high electrical power heats-up the ICL 101. Therefore, the ICL 101 becomes high-resistant and reduces the fault current to a low value.

[0202] For discharging the capacitor 103 the switches S1 and S3 are opened, whereas the switch S2 remains closed and the switch S4 is additionally closed. The energy stored in the capacitor 103 (E.sub.c according to the formula above) is then discharged over the DCR 102. The DCR 102 working as a discharge resistor converts the electrical energy of the capacitor 103 into heat energy.

[0203] In order that the DCR 102 is not heated up above its reference temperature it has to fulfill E ≥ E.sub.c.

[0204] In case of a malfunction of the circuit (e.g. S1 is not opened) the supply voltage from the grid would be connected directly to the discharge resistor DCR 102 causing a high thermal load on the resistor. In this case, the DCR 102 is heated up and decreases the fault current by its high resistance. In this case, the resistor DCR 102 works as a fuse.

[0205] Although the invention has been illustrated and described in detail by means of the preferred embodiment examples, the present invention is not restricted by the disclosed examples and other variations may be derived by the skilled person without exceeding the scope of protection of the invention.