Active Y-rated capacitor control option for common mode electromagnetic interference (EMI) reduction

Abstract

The system includes an input voltage supply (102) and a switching converter coupled to the input voltage supply (102). The switching converter includes a transformer (T2) having a primary coil and a secondary coil. The switching converter also includes a Y-rated capacitor (C7) having a top plate and a bottom plate, the top plate being coupled to a first end of the secondary coil. The switching converter also includes a push-pull current source (301) coupled to the bottom plate of the Y-rated capacitor. The switching converter further includes a controller (401) coupled to the push-pull current source (301).

Description

[Technical field]

[0001] Power supplies and power converters are used in a variety of electronic systems. Electrical power is typically transmitted over long distances as an alternating current (AC) signal. The AC signal is often split and metered as desired at different locations in a business or home and converted to direct current (DC) for use by individual electronic devices and components. Battery-powered devices are also common. Modern electronic systems often employ devices and components that are designed to operate using different DC voltages. As such, different switching converters (AC-DC converters and / or DC-DC converters) are required for such systems. [Background technology]

[0002] There are many different switching converter topologies. The available topologies vary based on the components used, the amount of power they handle, the input voltage, the output voltage, efficiency, reliability, size, and / or other characteristics. One exemplary switching converter is called a flyback converter. One existing challenge with flyback converters is that it is difficult to meet common-mode electromagnetic interference (EMI) specifications for offline flyback converters, despite large common-mode chokes. The presence of parasitic capacitance across the transformer boundary makes this problem difficult to solve. Efforts are ongoing to improve switching converter designs, including overcoming the EMI problems mentioned above. Summary of the Invention

[0003] In one example, a system includes an input voltage supply and a switching converter coupled to the input voltage supply. The switching converter includes a transformer having a primary coil and a secondary coil. The switching converter also includes a Y-rated capacitor having a top plate and a bottom plate, the top plate coupled to a first end of the secondary coil. The switching converter also includes a push-pull current source coupled to the bottom plate of the Y-rated capacitor. The switching converter also includes a controller coupled to the push-pull current source.

[0004] In one example, a switching converter circuit includes a first Y-rated capacitor node and a push-pull current source coupled to the first Y-rated capacitor node. The switching converter also includes a controller coupled to the push-pull current source. The controller includes a sample-and-hold circuit coupled to the second Y-rated capacitor node. The controller also includes an integrator circuit coupled to the sample-and-hold circuit.

[0005] In one example, an integrated circuit includes a first Y-rated capacitor node and a second Y-rated capacitor node. The integrated circuit also includes a push-pull current source coupled to the first Y-rated capacitor node. The integrated circuit also includes a controller coupled to the push-pull current source, the controller configured to monitor a voltage change at the second Y-rated capacitor node and selectively push current to or pull current from the first Y-rated capacitor node. [Brief description of the drawings]

[0006] For a detailed description of various examples, reference is made to the accompanying drawings, in which:

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a switching converter in some examples.

[0008] [Diagram 2]FIG. 2 is a schematic diagram of another switching converter according to some examples.

[0009] [Figure 3A] FIG. 1 is a schematic diagram illustrating another switching converter in a pull operation scenario in some examples.

[0010] [Figure 3B] FIG. 3B is a schematic diagram illustrating the switching converter of FIG. 3A in a push operation scenario in some examples.

[0011] [Figure 4] FIG. 2 is a schematic diagram of another switching converter according to some examples.

[0012] [Figure 5A] 4 is a timing diagram illustrating waveforms associated with a switching converter in some examples. [Figure 5B] 4 is a timing diagram illustrating waveforms associated with a switching converter in some examples. [Figure 5C] 4 is a timing diagram illustrating waveforms associated with a switching converter in some examples. [Figure 5D] 4 is a timing diagram illustrating waveforms associated with a switching converter in some examples.

[0013] [Figure 6A] FIG. 2 is a schematic diagram of another switching converter according to some examples.

[0014] [Figure 6B] 6B is a timing diagram associated with the switching converter of FIG. 6A in some examples.

[0015] [Figure 7] FIG. 2 is a schematic diagram of another switching converter according to some examples.

[0016] [Figure 8A-1] FIG. 2 is a schematic diagram of another switching converter according to some examples. [Figure 8A-2] FIG. 2 is a schematic diagram of another switching converter according to some examples.

[0017] [Figure 8B] 8B is a timing diagram associated with the switching converter of FIG. 8A in accordance with some examples.

[0018] [Figure 9A] FIG. 2 is a schematic diagram of another switching converter according to some examples. [Figure 9B] FIG. 2 is a schematic diagram of another switching converter according to some examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Described herein are active Y-rated capacitor control options for common mode electromagnetic interference (EMI) reduction. A capacitor that complies with safety standards for preventing electric shock hazards (e.g., failure to open circuit, not short circuit) is referred to herein as a "Y-rated capacitor." Exemplary Y-rated capacitor standards include UL1414 and UL1283. In some examples, the described active Y-rated capacitor control options are used in a switching converter. In one example, the switching converter includes a transformer having a primary coil and a secondary coil. The switching converter also includes a Y-rated capacitor having a top plate and a bottom plate, the top plate being coupled to a first end of the secondary coil. The switching converter also includes a push-pull current source coupled to the bottom plate of the Y-rated capacitor. The switching converter also includes a controller coupled to the push-pull current source, the controller providing at least some of the control options described herein. One control option includes selectively pushing current to the bottom plate of the Y-rated capacitor. Another control option includes selectively pulling current from the bottom plate of the Y-rated capacitor. In some examples, the active Y-rated capacitor control option is combined with other switching converter options, such as a discontinuous conduction mode (DCM) circuit (eg, with a DCM amplifier and / or a DCM clamp).

[0020] The switching converters described herein have various modes of operation. When the required output power is higher than a predetermined level, the converter operates in a continuous mode where pulse width modulation operation is applied continuously in response to the output voltage of the switching converter. A second mode of operation, utilized when the output power is at a lower level, is "burst mode" where pulse width modulation operation is turned on and off in response to the output voltage of the switching converter. As used herein, burst mode operation includes PWM on mode and PWM off mode. For better understanding, the various switching converter options are described below with reference to the figures.

[0021] FIG. 1 is a schematic diagram illustrating a switching converter 100 in some examples. The switching converter 100 is an example of an offline flyback converter. As shown, the switching converter 100 includes an alternating current (AC) source 102 having a first end 103A coupled to a first winding of a common mode choke (T1) having depolarization (represented by a dot on the same side of the winding of T1) via a circuit including L1, C1, and R1. More specifically, a first end of L1 is coupled to a first end 103A of the AC source 102, and a second end of L1 is coupled to a first winding of T1. The first winding of T1 is also coupled to a top plate of C1. As shown, a bottom plate of C1 is coupled to a first end of R1, and a second end of R1 is coupled to an earth ground node 110.

[0022] In the example of Figure 1, the second end 103B of the AC source 102 is coupled to the second winding of T1 via a circuit including L2, C2, and R2. More specifically, a first end of L2 is coupled to the second end 103B of the AC source 102, and a second end of L2 is coupled to the second winding of T1. The second winding of T1 is also coupled to the top plate of C2. As shown, the bottom plate of C2 is coupled to a first end of R2, and a second end of R2 is coupled to the earth ground node 110.

[0023] In the example of FIG. 1, the output from T1 is rectified by a set of diodes D1-D4. More specifically, the anode of D1 and the cathode of D3 are coupled to a first winding of T1. The anode of D2 and the cathode of D4 are coupled to a second winding of T1. The cathodes of D1 and D2 are coupled to a top plate of a capacitor (C3) and a first end of an inductor (L3). The anodes of D3 and D4 are coupled to a bottom plate of C3 and a primary (local) ground node 108. As shown, the second end of L3 is coupled to a top plate of another capacitor (C4) and to a first winding of a transformer (T2) with additive polarity (represented by a dot on the opposite side of the winding of T2). The bottom plate of C4 is coupled to the primary ground node 108. Meanwhile, the second winding of T2 has a first end coupled to the anode of a diode (D5) and a second end coupled to a secondary ground node 115. As shown, the cathode of D5 is coupled to the top plate of an output capacitor (COUT) and to a load 106 in parallel with COUT. Specifically, the top plate of COUT is coupled to the cathode of D5 and the bottom plate of COUT is coupled to the secondary ground node 115.

[0024] In the example of FIG. 1, turning transistor M1 on and off controls the amount of power provided to load 106. As shown, M1 has a first current terminal coupled to the first winding of T2, a second current terminal coupled to primary ground node 108, and a control terminal coupled to a controller (not shown) for switching converter 100. FIG. 1 also shows two additional capacitors C5 and C6, where C5 represents the interwinding capacitance of T2 and C6 represents the stray capacitance between secondary ground node 115 and earth ground node 110. During the switching action of M1, a voltage change 112 at the first winding of T2 causes a voltage change 114 at node 115. The switching action of C5 and C6, M1, and the associated voltage change 114 inject a current 116 from secondary ground node 115 to earth ground node 110. This current 116 flows back from node 110 through resistors R1 and R2 of a line impedance stabilization network (LISN). The resulting voltage drop across R1 and R2 contributes significantly to the measured EMI, which is undesirable.

[0025] FIG. 2 is a schematic diagram illustrating another switching converter 200 in some examples. In the example of FIG. 2, the switching converter 200 includes many of the same components as described for the switching converter 100 of FIG. 1. The switching converter 200 also includes a Y-rated capacitor (C7) coupled between the secondary ground node 115 and the primary ground node 108. During the switching action of M1, a voltage change 112 at the first winding of T2 causes a voltage change 214 at the secondary ground node 115. C5 and C6 cause the switching action of M1 and the associated voltage change 214 to contribute to the LISN EMI measured across R1 and R2. C7 reduces the voltage change 214 at node 115 compared to the voltage change 114 of FIG. 1, thereby reducing the LISN EMI for the switching converter 200 compared to the switching converter 100 of FIG. 1. In the example of FIG. 2, C7 provides a current path 216 to the primary ground node 108 that reduces the amount of current along current path 218 to the earth ground node 110 via C6.

[0026] FIG. 3A is a schematic diagram illustrating another switching converter 300 in a pull operation scenario in some examples. In the example of FIG. 3A, the switching converter 300 includes many of the same components as described for the switching converters 100, 200 of FIG. 1 and FIG. 2. The switching converter 300 also includes a push-pull current source 301 coupled to the bottom plate of C7. In the example of FIG. 3A, the push-pull current source 301 includes four transistors: M2A, M2B, M3, and M4. As shown, a first current terminal of M2A is coupled to an input voltage supply (VDD) node 305, a second current terminal of M2A is coupled to a first current terminal of M2B (referred to herein as a push regulation transistor), and a control terminal of M2A is coupled to a driver circuit 302. In the example of FIG. 3A, the driver circuit 302 is powered by the input voltage supply (VDD) provided by node 305. In operation, driver circuit 302 selectively provides a drive signal to M2 based on VDD in response to a control signal (DVDT-) input to node 307 to perform a push operation (see, e.g., FIG. 3B). In some examples, DVDT- is a digital signal that goes high when the drain of M1 swings down. In such examples, "DVDT" represents the dv / dt at the drain of M1. Note: FIG. 3A simply represents operation with the drain of M1 swinging up.

[0027] In the example of FIG. 3A, the second current terminal of M2B is coupled to the first current terminal of M3, while the control terminal of M2B is coupled to control node 310. Also, the second current terminal of M3 is coupled to the first current terminal of M4, and the control terminal of M3 is coupled to control node 309. As shown, a node 312 between the second current terminal of M2B and the first current terminal of M3 is coupled to the bottom plate of C7. Also, the second current terminal of M4 is coupled to the primary ground node 108, and the control terminal of M4 is coupled to the driver circuit 306. In the example of FIG. 3A, the driver circuit 306 is powered by an input voltage supply (VDD) provided by node 305. During the pull operation depicted in FIG. 3A, the driver circuit 306 provides a drive signal to M4 based on VDD in response to a control signal (DVDT+) input to node 311, DVDT+ being a digital signal that goes high when the drain of transistor M1 swings up. As a result of the pulling action, current flows as represented by current flow path 316 .

[0028] The pull action depicted in Figure 3A reduces the voltage change 314 at the secondary ground node 115 as a result of the voltage change 112 at the first winding of T2. C5 and C6 cause the switching action of M1 and the associated voltage change 314 to contribute to the EMI measured across the LISN resistors R1 and R2. However, C7 and the push-pull current source 301 reduce the voltage change 314 at node 115 compared to the voltage change 114 in Figure 1 or the voltage change 214 in Figure 2. In the example of Figure 3A, the voltage change 314 is reduced by using the push-pull current source 301 to pull current from the bottom plate of C7 through transistors M3 and M4 to the primary ground node 108. This reduces the voltage change 314 at the secondary ground node 115 due to the reversed polarity voltage change 318 at the bottom plate of C7. By reducing the voltage change 314 at the secondary ground node 115, the amount of current that flows from the secondary ground node 115 through C6 to the earth ground node 110 is also reduced. In this manner, LISN EMI is reduced. Note: The example voltage changes 112, 314, and 318 in FIG. 3A are not drawn to scale. In some scenarios, the voltage change 318 may be up to 1 / 100th of the voltage change 112.

[0029] FIG. 3B is a schematic diagram illustrating the switching converter 300 of FIG. 3A in a push operation scenario in some examples. In the example of FIG. 3B, the switching converter 300 includes many of the same components as described for the switching converters 100, 200 of FIG. 1 and FIG. 2. Again, the switching converter 300 includes a push-pull current source 301 coupled to the bottom plate of C7. In the example of FIG. 3B, the push-pull current source 301 performs a push operation that can drive current as represented by current flow path 326. More specifically, the driver circuit 302 directs M2A to close in response to DVDT- going high (indicating M1 being pulled down). Also, M2B can drive current while M3 and M4 are open, thereby preventing current from flowing to the primary ground node 108. Closing M2A and M2B and opening M3 and / or M4 pushes current to the bottom plate of C7. M2B allows the amount of current during a push operation to be adjusted between a minimum current and a maximum current. In another example, M2B is replaced by a resistor, which corresponds to the current used for the push operation (versus using M2B) being maximized.

[0030] The pushing action reduces the voltage change 324 at the secondary ground node 115 as a result of the voltage change 322 at the first winding of T2. C5 and C6 cause the switching action of M1 and the associated voltage change 324 to contribute to the EMI measured across the LISN resistors R1 and R2. However, C7 and the push-pull current source 301 reduce the voltage change 324 at node 115 compared to the voltage change 114 in FIG. 1 or the voltage change 214 in FIG. 2. In one example, the voltage change 324 is reduced by using the push-pull current source 301 to push current from the VDD node 305 through transistors M2A and M2B to the bottom plate of C7. This reduces the voltage change 324 at the secondary ground node 115 due to the reversed polarity voltage change 328 at the bottom plate of C7. By reducing the voltage change 324 at the secondary ground node 115, the amount of current that flows from the secondary ground node 115 through C6 to the earth ground node 110 is also reduced. In this manner, LISN EMI is reduced. Note: The example voltage changes 322, 324, and 328 in Figure 3B are not drawn to scale. In some scenarios, voltage change 328 may be up to 1 / 100th of voltage change 322.

[0031] Figure 4 is a schematic diagram of another switching converter 400 in some examples. In the example of Figure 4, switching converter 400 includes many of the same components as described for switching converters 100, 200, and 300 of Figures 1-3. Switching converter 400 also includes a controller 401 for push-pull current source 301 that is coupled to the bottom plate of C7.

[0032] As shown, the controller 401 includes a sample and hold (S&H) circuit 404 coupled to an integrator circuit 405. More specifically, the S&H circuit 404 includes a switch (S1) and a capacitor (C10), where S1 is coupled between an input node 403 of the controller 401 and a top plate of C10, while the bottom plate of C10 is coupled to the primary ground node 108. In the example of FIG. 4, the input node 403 of the controller 401 is coupled to a sensing array including C8 and C9. In some examples, C7 is a first Y-rated capacitor of the switching converter 400, and C8 is a second Y-rated capacitor. As shown, the top plate of C8 is coupled to the secondary ground node 115, and the bottom plate of C8 is coupled to the top plate of C9. Additionally, the bottom plate of C9 is coupled to the primary ground node 108. C8 and C9 provide a sense signal 402 related to the voltage change 414 to the S&H circuit 404.

[0033] The output of the S&H circuit 404 is provided to an integrator circuit 405. As shown, the integrator circuit 405 includes a resistor (R5) and a capacitor (C11) at the positive input (+) node of an operational amplifier 406. More specifically, R5 is between the output of the S&H circuit 404 and the + node of the operational amplifier 406. Also, C11 is between the + node of the operational amplifier 406 and the primary ground node 108. The integrator circuit 405 also includes a resistor (R4) at the negative input (-) node of the operational amplifier 406. In the example of FIG. 4, the integrator circuit 405 also includes a feedback loop 408 with a capacitor (C12) between the output of the operational amplifier 406 and the - node of the operational amplifier 406. The output of the integrator circuit 405 is coupled to the control node 309 at the control terminal for M3.

[0034] During the switching action of M1, a voltage change 112 at the first winding of T2 causes a voltage change 414 at node 115. Due to C5 and C6, the switching action of M1 and the associated voltage change 414 contribute to the EMI measured across the LISN resistors R1 and R2. Due to C7-C9, the push-pull current source 301, and the controller 401, the voltage change 414 at node 115 is reduced compared to the voltage change 114 in FIG. 1 or the voltage change 214 in FIG. 2. In one example, the voltage change 414 is the result of the controller 401 directing the push-pull current source 301 to pull current from the bottom plate of C7 when there is a voltage change 414 at node 115 as indicated by the sense signal 402. In some examples, the operation of the controller 401 and the push-pull current source 301 reduces the voltage change at node 115 by an amount 418, resulting in the voltage change 414. 4, C7 provides a current flow path 416 to the primary ground node 108 through M3 and M4, thereby reducing the amount of current flowing through C6 to the secondary ground node 110. In this way, the EMI measured across the LISN resistors R1 and R2 is reduced.

[0035] 5A-5D are timing diagrams illustrating waveforms associated with a switching converter in some examples. In timing diagram 510 of FIG. 5A, waveform 512 represents a primary drain voltage (e.g., the voltage at a first current terminal of M1). As shown, the primary drain voltage transitions between low and high voltage values ​​(e.g., 0-300 volts) as represented by pulses 514A-514C, with the control signal for M1 determining the timing of pulses 514A-514C.

[0036] In timing diagram 520 of Figure 5B, waveform 522 represents the secondary ground voltage (e.g., the voltage at node 115) when a Y-rated capacitor (e.g., C7) is used. As shown, the secondary ground voltage transitions between low and high voltages (e.g., 0 to 4 volts) represented by pulses 524A-524C, with the control signal for M1 determining the timing of pulses 524A-524C.

[0037] In timing diagram 530 of Figure 5C, waveform 532 represents the secondary ground voltage (e.g., the voltage at node 115) when using a Y-rated capacitor (e.g., C7) and an active push-pull current source (e.g., push-pull current source 301 with controller 401 of Figure 4). As shown, the secondary ground voltage represented by waveform 532 decreases through short pulses 534A-534F corresponding to each low-to-high and high-to-low transition of the primary drain voltage represented in timing diagram 510 of Figure 5A.

[0038] In timing diagram 540 of Figure 5D, waveform 542 represents a control signal provided (e.g., from controller 401) to control node 309 at the control terminal for M3. As shown, waveform 542 includes pulses 544A-544C that are inverted relative to pulses 514A-514C of the primary drain voltage represented in timing diagram 510 of Figure 5A.

[0039] FIG. 6A is a schematic diagram showing another switching converter 600 in some examples. In the example of FIG. 6A, the switching converter 600 includes the same components as those described for the switching converter 400 of FIG. 4, and the difference between FIG. 6A and FIG. 4 is that instead of a square wave pulse (or other non-sinusoidal pulse) corresponding to the voltage change 112, there is a sinusoidal signal 602 at the first coil of T2 of FIG. 6A. The sinusoidal signal 602 may be present due to resonant oscillation during the converter "off" phase when the switching converter 600 is controlled in burst mode (also called PWM on / off control). The sinusoidal signal 602 and the associated voltage change are referred to as discontinuous conduction mode (DCM) ringing. The DCM ringing results in a sinusoidal voltage change 604 at node 115. As shown in FIG. 6A and FIG. 4, the sinusoidal voltage change 604 is not reduced as effectively as the voltage change 414 using C7, push-pull current source 301, and controller 401. In some examples, C7 is a first Y-rated capacitor and C8 is a second Y-rated capacitor of switching converter 600.

[0040] FIG. 6B is a timing diagram 610 associated with the switching converter 600 of FIG. 6A in some examples. In the timing diagram 610, a secondary ground waveform 611 during burst mode operation is depicted. More specifically, during the converter "on" phase 612, the secondary ground voltage is a fixed voltage (approximately 10V in FIG. 6B) with short, small value pulses maintained by the action of the push-pull current source described above. During the converter "off" phase 614, the secondary ground voltage rings between a high voltage (e.g., approximately 12V) and a low voltage (e.g., approximately 0V). During this phase, there are no switching edges and the push-pull is not active. Therefore, the ringing does not decay. During the next "on" phase 615, the secondary ground voltage returns to approximately the fixed voltage due to the introduction of a burst frequency voltage change 616. During the next "off" phase 618, the secondary ground voltage again rings between a high voltage (e.g., approximately 12V) and a low voltage (e.g., approximately 0V). The ringing shown in Figure 6B causes undesired EMI measured across the LISN resistors R1 and R2. The burst frequency voltage change 616 shown in Figure 6B causes additional undesired EMI measured across the LISN resistors R1 and R2.

[0041] Figure 7 is a schematic diagram of another switching converter 700 in some examples. In the example of Figure 7, switching converter 700 includes many of the same components as those described for switching converters 100, 200, 300, and 400 of Figures 1-4. Also, in the example of Figure 7, switching converter 700 includes a DCM circuit 701 coupled to the bottom plate of C7 instead of push-pull current source 301.

[0042] As shown, the DCM circuit 701 includes a S&H circuit 714 coupled to an integrator circuit 715. More specifically, the S&H circuit 714 includes a switch (S2) and a capacitor (C13), where S2 is coupled between an input node 703 of the amplifier circuit 701 and a top plate of C13, while the bottom plate of C13 is coupled to the primary ground node 108. In the example of Figure 7, the input node 703 of the DCM circuit 701 is coupled to a sense array including C8 and C9. C8 and C9 provide a sense signal 708 related to the burst frequency voltage change 616 (see Figure 6B) to the S&H circuit 714.

[0043] The output of the S&H circuit 714 is provided to an integrator circuit 715. As shown, the integrator circuit 715 includes a resistor (R7) and a capacitor (C14) at a positive input (+) node of an operational amplifier 716. More specifically, R7 is between the output of the S&H circuit 714 and the + node of the operational amplifier 716. C14 is also between the + node of the operational amplifier 716 and the primary ground node 108. The integrator circuit 715 also includes a resistor (R6) at a negative input (-) node of the operational amplifier 716. In the example of FIG. 7, the integrator circuit 715 also includes a feedback loop 717 with a capacitor (C15) between the output of the operational amplifier 716 and the - node of the operational amplifier 716. The output of the integrator circuit 715 is coupled to an amplifier circuit 720.

[0044] As shown, the amplifier circuit 720 includes two resistors (R9 and R10) at the positive input (+) node of the operational amplifier 722. More specifically, R9 is between the output of the integrator circuit 715 and the + node of the operational amplifier 722. Also, R10 is between the + node of the operational amplifier 722 and the primary ground node 108. The amplifier circuit 720 also includes a resistor (R8) at the negative input (-) node of the operational amplifier 722. As shown, the - node of the operational amplifier 722 is coupled to the input node 703 of the DCM circuit 701 via R8. In the example of FIG. 7, the amplifier circuit 720 also includes a feedback loop 724 with a resistor (R11) between the output of the operational amplifier 722 and the - node of the operational amplifier 722. As shown, the operational amplifiers 716 and 722 are powered by the input supply voltage (VDD) node. In the example of FIG. 7, the values ​​of R8-R11 determine the gain of the amplifier circuit 720. In operation, the S&H circuit 714 stores the secondary ground burst frequency voltage change (ΔV) between the "on" and "off" periods. The integrator circuit 715 minimizes this burst frequency voltage change (ΔV) by creating an appropriate DC reference voltage for the amplifier circuit 720 so that the DC component of the voltage at the amplifier output node (which is also the bottom plate of the Y-rated capacitor C7) is equal during the "on" and "off" phases of the converter. The amplifier circuit 720 also damps the sinusoidal DCM ringing 704 at the secondary ground node 115 and generates an out-of-phase sinusoidal signal 706 at the bottom plate of the Y-rated capacitor C7. In some examples, C7 is the first Y-rated capacitor of the switching converter 700 and C8 is the second Y-rated capacitor.

[0045] 8A-1 and 8A-2 are schematic diagrams illustrating another switching converter 800 in some examples. In the example of FIG. 8A-1 and 8A-2, the switching converter 800 includes many of the same components as those described for the switching converters 100, 200, 300, 400, 600, and 700 in FIG. 1-4, FIG. 6, and FIG. 7. In some examples, C7 is a first Y-rated capacitor of the switching converter 800, and C8 is a second Y-rated capacitor. As shown in FIG. 8A-1 and 8A-2, the switching converter 800 includes a push-pull current source 301 and a DCM circuit 701 coupled to the bottom plate of C7 via respective switches S3 and S4. More specifically, S3 is closed during the "on" phase of the switching converter 800, so that the push-pull current source 301 can selectively push or pull current to or from the bottom plate of C7. Meanwhile, S4 is open during the “on” phase of switching converter 800. In contrast, S4 is closed during the “off” phase of switching converter 800 so that DCM circuit 701 can apply current to the bottom plate of C7 to reduce ringing of the secondary ground signal during the “off” phase. Also, S3 is open during the “off” phase of switching converter 800.

[0046] In some examples, during PWM-based switching operation of M1, the push-pull current source 301 and controller 401 operate as described herein to reduce the voltage change (e.g., voltage change 414 in FIG. 4) applied to the secondary ground node 110. Also, during burst mode switching operation of M1 (when the switching converter is turned on and off periodically), the DCM circuit 701 operates as described herein to reduce ringing on the secondary ground signal.

[0047] FIG 8B is a timing diagram 820 associated with the switching converter of FIG 8A in some examples. In the timing diagram 820, secondary ground waveforms 821 are depicted during different converter operations. More specifically, during the "on" phase of the converter, the secondary ground voltage is a fixed voltage (approximately 10V in FIG 8B) due to the operation of the push-pull current source 301 and the controller 401. During the "off" phase of the converter, the secondary ground voltage remains at a fixed voltage due to the operation of the DCM circuit 701 minimizing burst frequency voltage changes and damping secondary ground voltage DCM ringing.

[0048] 9A and 9B are schematic diagrams illustrating another switching converter 900 in some examples. In the example of FIG. 9, the switching converter 900 includes many of the same components as those described for the switching converters 100, 200, 300, and 400 of FIGS. 1-4. The switching converter 900 also includes an additional push-pull current source 901 coupled to the bottom plate of C7. In the example of FIGS. 9A and 9B, the push-pull current source 901 includes three transistors M5-M7. As shown, a first current terminal of M5 is coupled to the VDD node 305, a second current terminal of M5 is coupled to a first end of a resistor (R12), and a control terminal of M5 is coupled to the drive circuit 902. R12 sets the amount of current during the push operation to a maximum level. In another example, R12 is replaced with a transistor (see, for example, M2B in FIG. 3A) that can be used to adjust the current flow during the push operation from a minimum to a maximum level.

[0049] 9A and 9B, the driver circuit 902 is powered by VDD provided by node 305. In operation, the driver circuit 902 selectively provides a drive signal to M5 based on VDD in response to a control signal (DVDT-_BURST_1STCYC) input to node 707. In the example of FIGS. 9A and 9B, DVDT-_BURST_1STCYC is a high-going digital signal during the first switching transition of the drain voltage of M1 (at the beginning of the PWM ON mode of the switching converter 900). This switching transition occurs when M1 is first turned on in the PWM ON mode.

[0050] Also, a first current terminal of M6 is coupled to the second end of R12, a second current terminal of M6 is coupled to a first current terminal of M7, and a control terminal of M6 is coupled to a control node 909. As shown, a node 912 between R12 and the first current terminal of M6 is coupled to the bottom plate of C7. Also, a second current terminal of M7 is coupled to the primary ground node 108, and a control terminal of M7 is coupled to the driver circuit 906. In the example of FIG. 9, the driver circuit 906 is powered by VDD provided by node 305. In operation, the driver circuit 906 selectively provides a drive signal to M7 based on VDD in response to a control signal (DVDT-_BURST_LASTCYC) input to node 307. In the example of FIGS. 9A and 9B, DVDT-_BURST_LASTCYC is a high-going digital signal during the last switching transition of the drain voltage of M1 (at the end of the PWM ON mode of the switching converter 900). This switching transition occurs because M1 is the last to be turned off in PWM ON mode.

[0051] The switching converter 900 also includes a controller 908 for the push-pull current source 901 coupled to the bottom plate of C7. As shown, the controller 908 includes a S&H circuit 914 coupled to an integrator circuit 915. More specifically, the S&H circuit 914 includes a switch (S5) and a capacitor (C16), where S5 is coupled between an input node 903 of the controller 908 and a top plate of C16, while the bottom plate of C16 is coupled to the primary ground node 108. In the example of Figures 9A and 9B, the input node 903 of the controller 908 is coupled to a sense arrangement including C8 and C9. C8 and C9 provide the sense signal 402 related to the burst frequency voltage change at node 115 to the S&H circuit 914. In some examples, C7 is the first Y-rated capacitor of the switching converter 900 and C8 is the second Y-rated capacitor.

[0052] The output of the S&H circuit 915 is provided to an integrator circuit 915. As shown, the integrator circuit 915 includes a resistor (R14) and a capacitor (C17) at the positive input (+) node of an operational amplifier 916. More specifically, R14 is between the output of the S&H circuit 914 and the + node of the operational amplifier 916. C17 is also between the + node of the operational amplifier 916 and the primary ground node 108. The integrator circuit 915 also includes a resistor (R13) at the negative input (-) node of the operational amplifier 916. In the example of Figures 9A and 9B, the integrator circuit 915 also includes a feedback loop 918 with a capacitor (C18) between the output of the operational amplifier 916 and the - node of the operational amplifier 916. The output of the integrator circuit 915 is coupled to the control node 909 at the control terminal for M6.

[0053] During the switching action of M1, a voltage change at the first winding of T2 causes a voltage change at node 115. C5 and C6 cause the switching action of M1 and the associated voltage change to contribute to the EMI measured across LISN resistors R1 and R2. C7-C9, push-pull current source 301, and controller 401 reduce the voltage change at node 115 during PWM operation. C7-C9, push-pull current source 901, and controller 908 reduce the burst frequency voltage change at node 115 during burst mode operation. In one example, the voltage change at node 115 is the result of controller 908 directing push-pull current source 901 to pull current from the bottom plate of C7 when there is a burst frequency voltage change at node 115 as indicated by sense signal 402. In some examples, the operation of controller 908 and push-pull current source 901 causes the secondary ground burst frequency voltage change to zero.

[0054] With reference to switching converters 400, 600, 800, and 900 (see FIGS. 4, 6A, 8A-1, 8A-2, 9A, 9B), a switching converter circuit with a first Y-rated capacitor node (e.g., the bottom plate of C7) is depicted with a push-pull current source (e.g., push-pull current source 301 of FIGS. 4, 6A, 8A-2, 9B) coupled to the first Y-rated capacitor node. The switching converter circuit also includes a controller (e.g., controller 410 of FIGS. 4, 6A, 8A-2, 9B) coupled to the push-pull current source. In some examples, the controller includes a sample-and-hold circuit (e.g., sample-and-hold circuit 404) coupled to the second Y-rated capacitor node (at the bottom plate of C8). The controller also includes an integrator circuit (e.g., integrator circuit 405) coupled to the sample-and-hold circuit.

[0055] In some examples, the sample and hold circuit is a first sample and hold circuit, the integrator circuit is a first integrator circuit, and the switching converter circuit further includes a DCM circuit (e.g., DCM circuit 701 of FIG. 8A-2) coupled to the second Y-rated capacitor node. The DCM circuit includes a second sample and hold circuit (e.g., sample and hold circuit 714 of FIG. 8A-2) and a second integrator circuit (e.g., integrator circuit 715 of FIG. 8A-2) coupled to the sample and hold circuit. The DCM circuit also includes an amplifier (e.g., amplifier 720 of FIG. 8A-2) coupled to the second integrator circuit, which is coupled to the first Y-rated capacitor node via a switch (e.g., S4 of FIG. 8A-2). In some examples, the switch is a first switch, and the switching converter circuit includes a second switch (e.g., S3 of FIG. 8A-2) between the push-pull current source and the first Y-rated capacitor node. During a PWM on mode of the switching converter, the second switch is closed and the first switch is open. During a PWM off mode of the switching converter, the second switch is open and the first switch is closed.

[0056] In some examples, the push-pull current source is a first push-pull current source and the switching converter circuit further includes a second push-pull current source (e.g., push-pull current source 908 of FIG. 9B) coupled to the second Y-rated capacitor node, the first push-pull current source configured to operate during a PWM on mode of the switching converter circuit and the second push-pull current source configured to operate during a first and last switching cycle of a burst mode of the switching converter circuit.

[0057] In some examples, the integrated circuit includes a first Y-rated capacitor node (e.g., the bottom plate of C7) and a second Y-rated capacitor node (e.g., the bottom plate of C8). The integrated circuit further includes a push-pull current source (e.g., push-pull current source 301 of FIGS. 4, 6A, 8A-2, 9B) coupled to the first Y-rated capacitor node. The integrated circuit further includes a controller (e.g., controller 410 of FIGS. 4, 6A, 8A-2, 9B) coupled to the push-pull current source, the controller configured to monitor a voltage change at the second Y-rated capacitor node and selectively push a current to or pull a current from the first Y-rated capacitor node. In some examples, the controller includes a sample and hold circuit (e.g., sample and hold circuit 404 of FIG. 4) coupled to the second Y-rated capacitor node. The controller further includes an integrator circuit (e.g., integrator circuit 405) coupled to the sample and hold circuit.

[0058] The integrated circuit push-pull current source also includes a push transistor (e.g., M2A in FIGS. 4, 6A, 8A-2) or push adjustment transistor (e.g., M2B in FIGS. 4, 6A, 8A-2) having a first current terminal coupled to the input voltage source (VDD) and a second current terminal coupled to the first Y-rated capacitor node via a resistor (e.g., R12 in FIG. 9B), and a control terminal coupled to the first driver circuit (e.g., driver circuit 302 in FIGS. 3A, 3B, 4, 6A, 8A-2, and 9B). The push-pull current source further includes a pull transistor (e.g., M4 in FIGS. 3A, 3B, 4, 6A, 8A-2, and 9B) having a first current terminal, a second current terminal, and a control terminal, the second current terminal of the pull transistor being coupled to the ground node. The push-pull current source further includes a control transistor (e.g., M3 in FIGS. 3A, 3B, 4, 6A, 8A-2, and 9B) having a first current terminal, a second current terminal, and a control terminal. The first current terminal of the control transistor is coupled to one end of a resistor (e.g., R12 in FIG. 9B) or to a second current terminal of a push adjustment transistor (e.g., M2B in FIGS. 4, 6A, and 8A-2). The second current terminal of the control transistor is coupled to the first current terminal of the pull transistor. Also, the control terminal of the control transistor is coupled to the sense controller.

[0059] In some examples, the sample and hold circuit (e.g., sample and hold circuit 404 of FIG. 4) is the first sample and hold circuit, and the integrator circuit (e.g., integrator circuit 405) is the first integrator circuit. In such examples, the integrated circuit also includes a DCM circuit (e.g., DCM circuit 701 of FIG. 8A-2) coupled to the second Y-rated capacitor node. The DCM circuit includes a second sample and hold circuit (e.g., sample and hold circuit 714 of FIG. 8A-2) and a second integrator circuit (e.g., integrator circuit 715 of FIG. 8A-2) coupled to the second sample and hold circuit. The DCM circuit further includes an amplifier (e.g., amplifier 720 of FIG. 8A-2) coupled to the second integrator circuit, which is coupled to the first Y-rated capacitor node via a switch (e.g., S4 of FIG. 8A-2). In some examples, the switch is a first switch, and the integrated circuit also includes a second switch (e.g., S3 in FIG. 8A-2) between the push-pull current source and the first Y-rated capacitor node. During a PWM on mode of the switching converter, the second switch is closed and the first switch is open. During a PWM off mode of the switching converter, the second switch is open and the first switch is closed.

[0060] Also, in some examples, the push-pull current source (e.g., push-pull current source 301 of FIGS. 4, 6A, 8A-2, 9B) is a first push-pull current source, and the integrated circuit further includes a second push-pull current source (e.g., push-pull current source 908 of FIG. 9B) coupled to the second Y-rated capacitor node, the first push-pull current source configured to operate during a PWM ON mode of the switching converter, and the second push-pull current source configured to operate during a PWM OFF mode of the switching converter.

[0061] The term "coupled" is used throughout this specification. This term may encompass a connection, communication, or signal path that enables a functional relationship consistent with the description herein. For example, in a first example, device A is coupled to device B when device A generates a signal to control device B to perform an operation, or in a second example, device A is coupled to device B through an intervening component C. The second example is when the intervening component C does not substantially change the functional relationship between device A and device B such that device B is controlled by device A through a control signal generated by device A.

[0062] Modifications in the described embodiments are possible, and other embodiments are possible, within the scope of the claims.

Claims

1. 1. A system comprising: a voltage supply input; a switching converter coupled to the voltage supply input, a transformer having a primary coil coupled to the voltage supply input and a secondary coil having a first end and a second end; a first Y-rated capacitor having a top plate and a bottom plate, the top plate being coupled to a first end of the secondary coil; a second Y-rated capacitor having a top plate and a bottom plate, the top plate being coupled to a first end of the secondary coil; and a first push-pull current source coupled to a bottom plate of the first Y-rated capacitor; a controller coupled to the first push-pull current source, the controller including a sample and hold circuit coupled to a bottom plate of the second Y-rated capacitor; the switching converter, Including, the system.

2. 2. The system of claim 1, The system, wherein the controller further includes an integrator circuit coupled to the sample and hold circuit.

3. 2. The system of claim 1, a discontinuous conduction mode (DCM) circuit coupled to a bottom plate of the second Y-rated capacitor, an integrator circuit coupled to the sample and hold circuit; an amplifier coupled to the integrator circuit and coupled to a bottom plate of the first Y-rated capacitor through a first switch; The system further comprises the DCM circuit.

4. 4. The system of claim 3, a second switch between the first push-pull current source and a bottom plate of the first Y-rated capacitor; the second switch is closed and the first switch is open during a pulse width modulation (PWM) on mode of the switching converter; The system, wherein the second switch is open and the first switch is closed during a PWM off mode of the switching converter.

5. 2. The system of claim 1, a second push-pull current source coupled to a bottom plate of the second Y-rated capacitor; the first push-pull current source is configured to operate during a pulse width modulation (PWM) on mode of the switching converter; The system wherein the second push-pull current source is configured to operate during a first and a last switching cycle of a burst mode of the switching converter.

6. 2. The system of claim 1, The system further includes a discontinuous conduction mode (DCM) clamp coupled to the transformer.

7. 1. A switching converter circuit, comprising: a first Y-rated capacitor node; a second Y-rated capacitor node; and a first push-pull current source coupled to the first Y-rated capacitor node; a controller coupled to the first push-pull current source, a first sample and hold circuit coupled to the second Y-rated capacitor node; a first integrator circuit coupled to the first sample and hold circuit; The controller including:

1. A switching converter circuit comprising:

8. 8. A switching converter circuit as claimed in claim 7, a discontinuous conduction mode (DCM) circuit coupled to the second Y-rated capacitor node, a second sample and hold circuit; a second integrator circuit coupled to the second sample and hold circuit; an amplifier coupled to the second integrator circuit and coupled to the first Y-rated capacitor node through a first switch; The switching converter circuit further comprises the DCM circuit.

9. 9. A switching converter circuit as claimed in claim 8, comprising: a second switch between the first push-pull current source and the first Y-rated capacitor node; the second switch is closed and the first switch is open during a pulse width modulation (PWM) on mode of the switching converter circuit; A switching converter circuit, wherein the second switch is open and the first switch is closed during a PWM off mode of the switching converter circuit.

10. 8. A switching converter circuit as claimed in claim 7, a second push-pull current source coupled to the second Y-rated capacitor node; the first push-pull current source is configured to operate during a pulse width modulation (PWM) on mode of the switching converter circuit; The switching converter circuit, wherein the second push-pull current source is configured to operate during a first and a last switching cycle of a burst mode of the switching converter circuit.

11. 8. A switching converter circuit as claimed in claim 7, a transformer having a primary coil and a secondary coil, the secondary coil having a first end coupled to the first Y-rated capacitor node; a discontinuous conduction mode (DCM) clamp coupled to the transformer; The switching converter circuit further comprises:

12. 8. A switching converter circuit as claimed in claim 7, A switching converter circuit, wherein the first Y-rated capacitor node, the second Y-rated capacitor node, the first push-pull current source, and the controller are components of an integrated circuit.

13. 13. A switching converter circuit as claimed in claim 12, comprising: a transformer having a primary coil and a secondary coil, the secondary coil having a first end coupled to the first Y-rated capacitor node; a first Y-rated capacitor having a top plate coupled to a first end of the secondary coil and a bottom plate coupled to the first Y-rated capacitor node; a second Y-rated capacitor having a top plate coupled to a first end of the secondary coil and a bottom plate coupled to the controller; The switching converter circuit further comprises:

14. 1. An integrated circuit comprising: a first Y-rated capacitor node; a second Y-rated capacitor node; and a first push-pull current source coupled to the first Y-rated capacitor node; a controller coupled to the first push-pull current source and configured to monitor a voltage change at the second Y-rated capacitor node and selectively push current to or pull current from the first Y-rated capacitor node; a first sample and hold circuit coupled to the second Y-rated capacitor node; an integrator circuit coupled to the first sample and hold circuit; The controller including:

4. An integrated circuit comprising:

15. 15. An integrated circuit according to claim 14, comprising: The first push-pull current source comprises: a push transistor having a first current terminal coupled to an input voltage supply, a second current terminal coupled through a resistor to the first Y-rated capacitor node, and a control terminal coupled to a first driver circuit; a pull transistor having a first current terminal, a second current terminal coupled to the ground node, and a control terminal; a control transistor having a first current terminal coupled to one end of the resistor, a second current terminal coupled to the first current terminal of the pull transistor, and a control terminal coupled to the controller; 4. An integrated circuit comprising:

16. 15. An integrated circuit according to claim 14, comprising: a discontinuous conduction mode (DCM) circuit coupled to the second Y-rated capacitor node, a second sample and hold circuit; a second integrator circuit coupled to the second sample and hold circuit; an amplifier coupled to the second integrator circuit and coupled to the first Y-rated capacitor node through a first switch; 4. An integrated circuit further comprising the DCM circuit.

17. 17. An integrated circuit according to claim 16, comprising: a second switch between the push-pull current source and the first Y-rated capacitor node; the second switch is closed and the first switch is open during a pulse width modulation (PWM) on mode of a switching converter; The second switch is open and the first switch is closed during a PWM off mode of the switching converter.

18. 15. An integrated circuit according to claim 14, comprising: a second push-pull current source coupled to the second Y-rated capacitor node; the first push-pull current source is configured to operate during a pulse width modulation (PWM) on mode of a switching converter; The second push-pull current source is configured to operate during PWM off of the switching converter.

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