CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority under 35 U.S.C. § 119(e) to U.S.

Provisional Patent Application No. 61/238,379 filed October 7, 2015, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present application relates to a noise suppression circuit for use with a noise source such as a motor.

BACKGROUND

[0003] In driving a motor, one concern is the generation of noise at certain frequencies. For example, Figure 1 shows an example of a conventional noise suppression circuit. Figure 1 shows a motor 1000 having brushes 1012, 1014. Inductors 1020, 1022 are connected to each of brushes 1012, 1014. An "X capacitor" 1034 connects the motor terminals 1050, 1052, and "Y capacitors" 1030, 1032 connect motor terminals 1050, 1052 to ground.

[0004] As seen in Figure 2, radiated noise is produced due to RF current 1100 on the wiring harness 1110 resulting from capacitance between the harness 1110 and the motor housing 1010. At low frequencies, Y capacitors 1030, 1032 short circuit this voltage to suppress the noise (see current 1102 in Figure 2). However, it has been found that at high frequencies (e.g., above 200 MHz), the connection to the motor housing 1010 results in a higher level of RF noise than would exist if there was no connection to the motor housing 1010. It is presumed that this higher level of noise is due to resonance of current 1100 and 1102.

[0005] Removing Y capacitors 1030, 1032 to eliminate the connection to the motor housing 1010 would remove this resonant radiated noise at high frequencies (see Figure 3). However, the connection to the motor housing 1010 must be maintained to suppress low frequency noise.

[0006] Additionally, Figure 4 shows an example of a conventional Printed Circuit

Board

(PCB) trace layout for a noise suppression circuit. For example, traces 1200, 1202, and 1204 in Figure 4 all have large widths to keep impedance low. However, when large width traces are adjacent to each other in a PCB layout, there is a possibility of high frequency shorting paths occurring due to capacitance between the traces. This high frequency shorting path can have implications in noise suppression when trying to implement a solution to the problem of high frequency radiated noise.

[0007] It may be possible to use feed-through capacitors to help suppress noise in some applications. However, it is important to note that the size of feed through capacitors make them unsuitable for use in small motors. Additionally, the cost of feed-through capacitors is prohibitive for widespread use.

[0008] Thus, there is a need for a reasonable cost structure that maintains connection to the

motor housing at low frequencies and also suppressing radiated noise at high frequencies, while accounting for the possible issues caused by high frequency shorting paths in a PCB layout with large trace widths.

SUMMARY

[0009] At least an embodiment of a noise suppression circuit for use with a motor may include a first brush, a second brush, and a motor housing, may include a first inductor having a first terminal and a second terminal, the first terminal of the first inductor being connected to the first brush; a second inductor having a first terminal and a second terminal, the first terminal of the second inductor being connected to the second brush; a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being connected to the second terminal of the first inductor; a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being connected to the second terminal of the second inductor; a third capacitor having a first terminal and a second terminal, the first terminal of the third capacitor being connected to the first terminal of the first capacitor and the second terminal of the first inductor, and the second terminal of the third capacitor being connected to the first terminal of the second capacitor and the second terminal of the second inductor; and one of a group consisting of a first ferrite bead having a first terminal and a second terminal, the first terminal of the first ferrite bead being connected to the second terminal of the first capacitor and the second terminal of the second capacitor and the second terminal of the first ferrite bead being connected to ground; and a first ferrite bead having a first and second terminal and a second ferrite bead having a first and second terminal; the first terminal of the first ferrite beading being connected to the second terminal of the first capacitor, and the second terminal of the first ferrite bead being connected to ground; and the first terminal of the second ferrite bead being connected to the second terminal of the second capacitor, and the second terminal of the second ferrite bead being connected to ground. The motor housing may be connected to ground.

[0010] At least an embodiment of a motor may include a first brush; a second brush; a motor housing; and a noise suppression circuit. The noise suppression circuit may include a first inductor having a first terminal and a second terminal, the first terminal of the first inductor being connected to the first brush; a second inductor having a first terminal and a second terminal, the first terminal of the second inductor being connected to the second brush; a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being connected to the second terminal of the first inductor; a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being connected to the second terminal of the second inductor; a third capacitor having a first terminal and a second terminal, the first terminal of the third capacitor being connected to the first terminal of the first capacitor and the second terminal of the first inductor, and the second terminal of the third capacitor being connected to the first terminal of the second capacitor and the second terminal of the second inductor; and one of a group consisting of a first ferrite bead having a first terminal and a second terminal, the first terminal of the first ferrite bead being connected to the second terminal of the first capacitor and the second terminal of the second capacitor and the second terminal of the first ferrite bead being connected to ground; and a first ferrite bead having a first and second terminal and a second ferrite bead having a first and second terminal; the first terminal of the first ferrite beading being connected to the second terminal of the first capacitor, and the second terminal of the first ferrite bead being connected to ground; and the first terminal of the second ferrite bead being connected to the second terminal of the second capacitor, and the second terminal of the second ferrite bead being connected to ground. The motor housing may be connected to ground.

[0011] At least an embodiment of a noise suppression circuit for use with a noise

source

connected to ground may include a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being connected to the noise source; and a first impedance element having a first terminal and a second terminal, the first terminal of the first impedance element being connected to the second terminal of the first capacitor and the second terminal of the first impedance element being connected to the ground.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] Embodiments will now be described, by way of example only, with reference to the

accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:

[0013] Figure 1 is a diagram of a conventional noise suppression circuit;

[0014] Figure 2 is a diagram showing currents that can flow in a noise suppression circuit;

[0015] Figure 3 is a diagram of a noise suppression circuit with Y capacitors removed;

[0016] Figure 4 is a conventional PCB trace layout for a noise suppression circuit;

[0017] Figure 5 is a diagram of a noise suppression circuit according to an

embodiment;

[0018] Figure 6 is a diagram of a noise suppression circuit according to an

embodiment;

[0019] Figure 7 is a diagram of a noise suppression circuit according to an

embodiment;

[0020] Figure 8 is a diagram of a noise suppression circuit according to an

embodiment;

[0021] Figure 9 is a diagram showing the effect of an embodiment of a noise

suppression circuit at low frequency and high frequency;

[0022] Figure 10 is a PCB trace layout for a noise suppression circuit according to at least an embodiment;

[0023] Figure 11 shows the implementation of a noise suppression circuit with a motor according to at least an embodiment.

DETAILED DESCRIPTION

[0024] Figure 5 illustrates one embodiment of a noise suppression circuit. The noise suppression circuit may be used with a noise source 10, and may include a capacitor 30 and impedance element 40. Capacitor 30 has a first terminal and a second terminal, the first terminal of capacitor 30 being connected to the noise source 10. Impedance element 40 has a first terminal and a second terminal. The first terminal of impedance element 40 may be connected to a second terminal of capacitor 30, and the second terminal of impedance element may be connected to ground. Impedance element 40 may be a resistor, a low pass filter, a ferrite bead, or other suitable structure. [0025] Figure 6 illustrates another embodiment of a noise suppression circuit. In Figure 6,

the noise source may be embodied as a motor comprising housing 110, first brush 112, and second brush 114. Housing 110 may be connected to ground. The noise suppression circuit may include a first inductor 120 having a first and second terminal, a second inductor 122 having a first and second terminal, a first capacitor 130 having a first and second terminal, a second capacitor 132 having a first and second terminal, a third capacitor 134 having a first and second terminal, a first ferrite bead 140 having a first and second terminal, and a second ferrite bead 142 having a first and second terminal. The first terminal of the first inductor 120 may be connected to first brush 112. The first terminal of the second inductor 122 may be connected to second brush 114. The first terminal of the first capacitor 130 may be connected to the second terminal of the first inductor 120. The first terminal of the second capacitor 132 may be connected to the second terminal of the second inductor 122. The first terminal of the third capacitor 134 may be connected to the first terminal of the first capacitor 130 and the second terminal of the first inductor 120. The second terminal of the third capacitor 134 may be connected to the first terminal of the second capacitor 132 and the second terminal of the second inductor 122. The first terminal of the first ferrite bead 140 may be connected to the second terminal of the first capacitor 130. The second terminal of the first ferrite bead 140 may be connected to ground. The first terminal of the second ferrite bead 142 may be connected to the second terminal of the second capacitor 132. The second terminal of the second ferrite bead 142 may be connected to ground. The addition of first ferrite bead 140 and second ferrite bead 142 will reduce the resonant frequency by adding inductance to the circuit, and will also reduce the magnitude of the resonance of currents 1100 and 1102 by adding resistance. In other words, the ferrite bead has both resistive and inductive properties.

[0026] Figure 7 illustrates another embodiment of a noise suppression circuit. In

Figure 7,

the noise source 10 of Figure 5 may be embodied as a motor comprising first brush housing 210, first brush 212, and second brush 214. Housing 210 may be connected to ground. The noise suppression circuit may include a first inductor 220 having a first and second terminal, a second inductor 222 having a first and second terminal, a first capacitor 230 having a first and second terminal, a second capacitor 232 having a first and second terminal, a third capacitor 234 having a first and second terminal, and a first ferrite bead 244 having a first and second terminal. The first terminal of the first inductor 220 may be connected to first brush 212. The first terminal of the second inductor 222 may be connected to second brush 214. The first terminal of the first capacitor 230 may be connected to the second terminal of the first inductor 220. The first terminal of the second capacitor 232 may be connected to the second terminal of the second inductor 222. The first terminal of the third capacitor 234 may be connected to the first terminal of the first capacitor 230 and the second terminal of the first inductor 220. The second terminal of the third capacitor 234 may be connected to the first terminal of the second capacitor 232 and the second terminal of the second inductor 222. The first terminal of the first ferrite bead 240 may be connected to the second terminal of the first capacitor 230 and the second terminal of the second capacitor 232. The second terminal of the first ferrite bead 240 may be connected to ground. The addition of first ferrite bead 240 will reduce the resonant frequency by adding inductance to the circuit, and will also reduce the magnitude of the resonance of currents 1100 and 1102 by adding resistance. In other words, the ferrite bead has both resistive and inductive properties.

[0027] Figure 8 illustrates another embodiment of a noise suppression circuit. In

Figure 8,

the noise source may be embodied as a motor comprising housing 310, first brush 312, and second brush 314. Housing 310 may be connected to ground. The noise suppression circuit may include a first inductor 320 having a first and second terminal, a second inductor 322 having a first and second terminal, a first capacitor 330 having a first and second terminal, a second capacitor 332 having a first and second terminal, a third capacitor 334 having a first and second terminal, a first resistor 340 having a first and second terminal, and a second resistor 342 having a first and second terminal. The first terminal of the first inductor 320 may be connected to first brush 312. The first terminal of the second inductor 322 may be connected to second brush 314. The first terminal of the first capacitor 330 may be connected to the second terminal of the first inductor 320. The first terminal of the second capacitor 332 may be connected to the second terminal of the second inductor 322. The first terminal of the third capacitor 334 may be connected to the first terminal of the first capacitor 330 and the second terminal of the first inductor 320. The second terminal of the third capacitor 334 may be connected to the first terminal of the second capacitor 332 and the second terminal of the second inductor 322. The first terminal of the first resistor 340 may be connected to the second terminal of the first capacitor 330. The second terminal of the first resistor 340 may be connected to ground. The first terminal of the second resistor 342 may be connected to the second terminal of the second capacitor 332. The second terminal of the second resistor 342 may be connected to ground. The addition of first resistor 340 and second resistor 342 will reduce the magnitude of the resonance of currents 1100 and 1102 (see Figure 2).

[0028] Figure 9 is a diagram showing the effect of embodiments of the noise

suppression

circuit. For example, at low frequencies, the ferrite beads 140, 142 will have relatively low impedance, such that the low frequency current can be shorted to the housing through capacitors 130, 132. In contrast, at high frequencies, the impedances of the ferrite beads 140, 142 becomes relatively high so as to effectively disconnect the circuit from the housing 110, thereby suppressing the high frequency noise generated by resonant currents.

[0029] Figure 10 shows how the noise suppression circuit of Figure 6 may be

implemented

on a circuit board 160. For example, first capacitor 130 may have first land 130a and second land 130b on the circuit board 160. Second capacitor 132 may have first land 132a and second land 132b on the circuit board 160. First ferrite bead 140 (i.e., first impedance element) may have first land 140a and second land 140b on the circuit board 160. Second ferrite bead 142 may have first land 142a and second land 142b on the circuit board 160. Second land 130b of first capacitor 130 may be connected to first land 140a of first ferrite bead 140 by first trace 162. Second land 132b of second capacitor 132 may be connected to first land 142a of second ferrite bead 142 by second trace 164. Second land 140b of first ferrite bead 140 may be connected to ground terminal 150 by third trace 166. Second land 142b of second ferrite bead 142 may be connected to ground terminal 150 by fourth trace 168.

[0030] As further seen in Figure 10, a width of first trace 162 may be narrower than a width of a second land 130b of first capacitor 130 and narrower than a width of first land 140a of first ferrite bead 140. Additionally, a width of second trace 164 may be narrower than a width of a second land 132b of second capacitor 132 and narrower than a width of first land 142a of second ferrite bead 142. Figure 10 further shows that a width of second land 140b of first ferrite bead 140 and a width of third trace 166 are wider than a width of first land 140a of first ferrite bead 140. Additionally, a width of second land 142b of second ferrite bead 142 and a width of fourth trace 168 are wider than a width of first land 142a of second ferrite bead 142. This arrangement of widths of the lands and traces helps to prevent high frequency shorting paths due to capacitance between lands.

[0031] Figure 11 shows that circuit board 160 may be fixed to a brush card 180 as part of a motor. Additionally, the ground terminal of circuit board 160 may be connected to ground via a screw 152. In other words, the second terminals of first ferrite bead (i.e., impedance element) and second ferrite bead may be connected to ground via screw 152. The screw 152 may be directly connected to a motor cover and therefore electric noise can escape outside the motor.

[0032] Thus, overall, the structures described above impart the benefits of suppressing noise at both low frequency and high frequency with the same circuit, while avoiding issues of high frequency shorting paths when implementing the circuit in a PCB layout.

[0033] While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.

[0034] The presently disclosed embodiments are therefore to be considered in all respects

as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.