Voltage converter controller, voltage converter, and method of operating a voltage converter

Abstract

A voltage converter controller, a voltage converter, and a method of operating a voltage converter are disclosed for regulating the on-time of an auxiliary switch of the voltage converter. A first voltage and a second voltage are measured before and during conduction of a main switch of the voltage converter, and the on-time is regulated based on these voltages.

Description

Technical Field

[0001] This application generally relates to voltage converters, voltage converter controllers, and corresponding methods. Background Art

[0002] A voltage converter is used to provide an input voltage based on an output voltage. Voltage converters are used as power supplies for various applications such as mobile phones or other electrical appliances, for example. Some voltage converters provide electrical isolation between the input and any output, for example by using a transformer. Examples of such voltage converters include flyback converters. A particular type of flyback converter is an asymmetric pulse width modulation (PWM) half-bridge flyback converter, where the inductor of the converter is substantially split to form a transformer such that the voltage ratio is multiplied based on the winding ratio of the transformer, and also has the additional advantage of providing electrical isolation.

[0003] In some converters, a main switch is used for the primary side circuit of the converter, i.e., the side coupled to the input terminal to receive the input voltage. The side coupled to the output terminal to output the output voltage is referred to herein as the secondary side circuit, and the primary side circuit and the secondary side circuit can be electrically isolated from each other. The switching of such a main switch is typically implemented as a transistor, such as a metal oxide semiconductor (MOS) field effect transistor (FET). In some implementations, such a field effect transistor has a parasitic capacitance, also referred to herein as an output capacitance. If such a switch is switched by the voltage applied across the transistor, the capacitance is charged, and charge may be lost during the switching event, resulting in overall losses in the converter.

[0004] Therefore, various methods have been taken to obtain so-called zero voltage switching (ZVS), which means that the main switch is switched, particularly turned on, while no voltage is applied across the switch (e.g., between the source and drain of a MOSFET switch). Such methods typically involve using an auxiliary switch that injects energy such that zero voltage switching is obtained. Controlling the timing of such an auxiliary switch is important on the one hand for obtaining zero voltage switching and on the other hand for preventing energy losses that may occur when such an auxiliary switch is closed for a long time.

[0005] In current methods, an additional pin of a controller that controls the voltage converter is used to configure and adjust the on-time of such an additional switch. Such additional pins increase the manufacturing cost. In addition, current methods do not provide an optimal timing for the auxiliary switch. Summary of the Invention

[0006] A voltage converter controller, a voltage converter, and a method for operating a voltage converter are provided.

[0007] According to an embodiment, a voltage converter controller is provided, comprising:

[0008] A drive circuit configured to control switching of a main switch on a primary side circuit of a voltage converter and switching of an auxiliary switch for regulating a switching voltage of the main switch.

[0009] A terminal configured to receive a voltage from an auxiliary winding of a transformer of the voltage converter.

[0010] A sampling circuit configured to provide a first voltage based on a voltage at the terminal before the main switch is turned on and a second voltage based on a voltage at the terminal when the main switch is turned on, and

[0011] An adjustment circuit configured to adjust an on-time of the auxiliary switch based on the first voltage and the second voltage.

[0012] According to another embodiment, there is provided a voltage converter controller, comprising:

[0013] A drive circuit configured to control switching of a main switch on a primary side circuit of a voltage converter and switching of an auxiliary switch for regulating a switching voltage of the main switch, and

[0014] An adjustment circuit configured to adjust an on-time of the auxiliary switch to obtain a switching voltage of the main switch, the switching voltage being greater than zero and lower than an inflection point of a curve of charge stored in an output capacitor of the main switch with respect to voltage.

[0015] According to another embodiment, there is provided a voltage converter, comprising:

[0016] A primary side circuit configured to receive an input voltage,

[0017] A secondary side circuit configured to output an output voltage,

[0018] A transformer coupled to the primary side circuit and the secondary side circuit,

[0019] wherein the primary side circuit includes a main switch, and wherein the voltage converter further includes an auxiliary switch configured to regulate a switching voltage across the main switch when the main switch is turned on, and

[0020] The voltage converter controller as described above.

[0021] According to another embodiment, there is provided a method, comprising:

[0022] Measuring a first voltage using an auxiliary winding of a transformer of a voltage converter before closing a main switch of a primary side circuit of the voltage converter and measuring a second voltage using the auxiliary winding when the main switch is turned on, and

[0023] Adjust the conduction time of the auxiliary switch based on the first voltage and the second voltage to adjust the switching voltage across the main switch when the main switch is conducting.

[0024] According to another embodiment, a method is provided, comprising:

[0025] Operate the main switch of a voltage converter and adjust the conduction time of the auxiliary switch of the voltage converter to obtain a switching voltage of the main switch, the switching voltage being greater than zero and lower than the inflection point of the curve of the charge stored in the output capacitance of the main switch with respect to voltage.

[0026] The above summary is only intended to provide a brief overview of some aspects of some embodiments and should not be construed as limiting. In particular, other embodiments may include other features in addition to those explicitly given above. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a block diagram of a voltage converter according to an embodiment;

[0028] Figure 2 is a flowchart showing a method according to an embodiment;

[0029] Figure 3 is a circuit diagram of a voltage converter according to an embodiment;

[0030] Figure 4 is a circuit diagram showing an adjustment circuit of a voltage converter controller according to an embodiment;

[0031] Figure 5 is a flowchart showing a method according to an embodiment;

[0032] Figure 6 is a signal diagram showing the operation of an embodiment of Figure 3 ;

[0033] Figures 7A to 7C is a signal diagram showing the operation of an embodiment of Figure 3 ;

[0034] Figure 8 is a circuit diagram of a voltage converter according to another embodiment;

[0035] Figure 9 is a signal diagram showing the operation of an embodiment of Figure 8 ;

[0036] Figure 10 is a schematic diagram of a voltage converter according to another embodiment;

[0037] Figures 11 to 13 is a diagram showing the selection of a switching voltage according to some embodiments. Detailed Embodiments

[0038] In the following, various embodiments will be described in detail with reference to the accompanying drawings. These embodiments are given only as examples and should not be construed in any way as limiting. For example, although an embodiment may be described as including multiple features or elements, this should not be construed as limiting, and in other embodiments, some features or elements may be omitted and / or may be replaced by alternative features or elements. In addition to the features or elements explicitly shown and described, other features or elements may be provided, such as features or elements typically provided in a voltage converter such as a flyback converter, such as protection mechanisms like overcurrent protection or feedback control.

[0039] Unless otherwise stated, features from different embodiments may be combined with each other to form other embodiments. Variations and modifications described with respect to one of the embodiments may also be applicable to other embodiments.

[0040] In the embodiments shown and described, any direct electrical connection or coupling between elements, i.e., a connection or coupling without intervening elements (such as metal traces), may be replaced by an indirect connection or coupling, i.e., a connection or coupling including one or more additional intervening elements, and vice versa, as long as the general purpose of the connection or coupling, such as providing a certain signal, a certain information, or a certain control, is substantially maintained. In other words, the connections and couplings may be modified as long as the general purpose and function of the connection or coupling remain substantially unchanged.

[0041] The embodiments relate to a voltage converter, a controller for the voltage converter, and related methods. Although a flyback converter is used as an example of a voltage converter in some of the embodiments described below, this is for illustrative purposes only, and other voltage converters may be used, particularly voltage converters that provide electrical isolation through a transformer.

[0042] The embodiments described herein use switches, particularly transistor switches. As used herein, when a switch is substantially non-conductive between its load terminals, e.g., between the source terminal and the drain terminal in the case of a MOS transistor-based switch, the switch is off, in the off state, or open. Substantially non-conductive in this regard means non-conductive except for possible undesired leakage terminal currents that may occur in the device. When the switch provides a low-ohm connection between its load terminals, the switch is described as on, in the on state, or closed.

[0043] Now turning to the drawings, Figure 1 a voltage converter 10 according to an embodiment is shown. Figure 1 The voltage converter includes a primary side circuit 11 that receives an input voltage Vin. In addition, Figure 1The voltage converter includes a secondary-side circuit 13 that outputs an output voltage Vout. A transformer 12 couples a primary-side circuit 11 and the secondary-side circuit 13 while providing electrical isolation. In some implementations, the voltage converter 10 can be a flyback converter.

[0044] In addition, the voltage converter 10 includes a controller 14 that contains an adjustment circuit. The controller 14 controls the operation of the voltage converter 10, particularly by closing a main switch of the primary-side circuit 11 to selectively transfer energy from the primary-side circuit 11 to the secondary-side circuit 13 to control the operation of the voltage converter 10. By adjusting the on-time of such a main switch, the output voltage Vout can be modulated to a predetermined value.

[0045] In addition, the controller 14 controls an auxiliary switch to ensure switching of the main switch at a desired voltage across the main switch, such as switching at zero voltage to obtain zero-voltage switching, or switching at a voltage slightly above zero as will be further described below. As will be further described in detail below, the auxiliary switch can be provided on the primary-side circuit 11 or the secondary-side circuit 13.

[0046] The adjustment circuit of the controller 14 measures a first voltage before closing the main switch and a second voltage when closing the main switch. The first voltage and the second voltage respectively indicate the drain voltage of the main switch before closing the main switch and the drain voltage of the main switch when closing the main switch. As will be described in more detail later, based on these voltages, the off-time (closing time) of the auxiliary switch is adjusted to obtain switching of the main switch at a desired voltage. When the main switch switches, such as conducts (closes), the voltage across the main switch is also referred to as the switching voltage herein.

[0047] Figure 2 A flowchart of a method according to an embodiment is shown. Although Figure 2 the method is shown and described as a series of actions or events, the order of describing these actions or events should not be construed as limiting. Figure 2 the method can be implemented using Figure 1 the voltage converter, particularly its controller 14, but can also be implemented independently of Figure 1 the voltage converter.

[0048] At step 20, the method includes: measuring a first voltage using an auxiliary winding of a transformer of the voltage converter before closing the main switch of the voltage converter. The first voltage can indicate the drain voltage of the main switch before closing the main switch. "Indicate" means that the measured voltage is not necessarily the drain voltage itself, but some voltage that varies with the drain voltage, so the measured voltage can be used as an indication of the drain voltage.

[0049] The term "before closing" may indicate a measurement within a short time before closing, e.g., immediately before a control signal is provided to the main switch to close the main switch or when the control signal is provided to the main switch to close the main switch.

[0050] At step 21, the method includes: measuring a second voltage using an auxiliary winding when the main switch is closed. The second voltage may indicate the DC link voltage when the main switch is closed. In some embodiments, as will be described in more detail below, an auxiliary winding coupled to transformer 12 may be used to measure the first voltage and the second voltage.

[0051] At step 22, the method includes: adjusting the on-time of the auxiliary switch based on the first voltage and the second voltage to regulate the voltage at the time of switching the main switch to a predetermined value, e.g., to 0V or a value slightly higher than 0. Examples will be described in further detail below.

[0052] Next, specific examples of voltage converters that can implement the above techniques and implementation examples will be discussed. These are for illustrative purposes only and should not be construed as limiting.

[0053] Figure 3 is a circuit diagram of a voltage converter according to an embodiment - in this case a flyback converter. Figure 3 The voltage converter receives an input voltage on the primary side circuit 37 and outputs an output voltage to the load 310 through the secondary side circuit 39. The primary side circuit 37 and the secondary side circuit 39 are coupled through a transformer 38. In Figure 3 the embodiment, the primary side circuit 37 receives an input voltage as an AC (alternating current) input voltage at terminal 30 and rectifies the AC voltage via a rectifier 32 to obtain a DC (direct current) input voltage.

[0054] The primary side circuit 37 includes a main switch 311 controlled by a primary side circuit controller 33. The primary side circuit controller 33 controls the main switch 311, for example, according to a pulse width modulation (PWM) control scheme, to regulate the output voltage provided to the load 310 to a predetermined value. For this purpose, the primary side circuit controller 33 receives information indicating the output voltage via a feedback loop 312.

[0055] In addition, Figure 3 the voltage converter includes an active clamp 34, which includes an auxiliary switch transistor 35 and is coupled to an inductor 313. By turning on the auxiliary transistor 35 before turning on the main switch 311, the voltage across the main switch 311 when the main switch 311 is turned on can be regulated to, for example, approximately 0V to obtain zero voltage switching, or as will be further explained below, to a value slightly higher than 0V to further optimize energy loss.

[0056] In addition,Figure 3 The voltage converter includes an auxiliary transformer winding 36 coupled to the primary side circuit controller 33. Via the auxiliary winding 36, the primary side circuit controller 33 can measure the voltage indicative of the drain voltage of the main switch 311, and can regulate the switching of the auxiliary switch 35 according to the techniques discussed in Figure 1 and Figure 2 and further discussed with reference to Figure 4 to FIG. 7. In this way, the operation of the active clamp 34 can be regulated to obtain the desired voltage across the main switch 311 when the main switch 311 is conducting.

[0057] Figure 4 FIG. is a circuit diagram showing a part of the primary side circuit controller 33 according to an embodiment, particularly its regulation circuit. Figure 3 The auxiliary winding 36 of is coupled to a terminal 42 (e.g., a pin) of the primary side circuit controller 33. The terminal 42 is also referred to as a zero crossing detection (ZCD) terminal.

[0058] As Figure 4 shown, in the present embodiment, the auxiliary winding 36 is coupled to the terminal 42 via a resistor 40R ZCD_high and the resistor 41R ZCD_low couples the node between the resistor 40 and the terminal 42 to ground.

[0059] The auxiliary winding 36 together with the resistors 40, 41 enables the detection of the voltage indicative of the drain voltage of the main switch 311 during the operation of the voltage converter. The voltage V bulk (the input voltage after the rectifier 32 corresponding to the drain voltage) is reflected back to the ZCD terminal 42 through the auxiliary winding 36 and thus can be measured. Therefore, when the main switch 311 is conducting, the voltage provided to the terminal 42 is a negative voltage. In Figure 4 the embodiment, an inverter formed by an operational amplifier 44 and a feedback resistor 43 converts this negative voltage to a positive voltage V pos . In other embodiments, a negative voltage can be used without conversion to a positive voltage.

[0060] The positive voltage V pos is sampled in a first sampling circuit 45 and a second sampling circuit 46. The sampling circuits 45, 46 can be implemented as latches or flip - flops, for example. The first sampling circuit 45 is controlled by a signal sample_01 to sample V pos before the main switch 311 conducts. The sampled voltage is referred to as V smvbulk here. The second sampling circuit 46 is controlled by a signal sample_02 to sample the voltage V pos when the main switch 311 is conducting. This sampled voltage is referred to as V smbottom. The comparison, judgment, and update logic circuit 47 processes the voltage V smvbulk , V smbottom and updates the on-time of the second auxiliary switch 35 based on this comparison.

[0061] Specifically, the circuit 47 can compare the difference between V smvbulk and V smbottom with a threshold value to determine whether the on-time of the auxiliary switch 35 should be increased, decreased, or remain unchanged.

[0062] For example, in an embodiment, if V smvbulk - V smbottom is greater than the first reference voltage V ref1 , this can indicate that the on-time of the auxiliary switch 35 must be increased. For example, this can indicate that the main switch 311 conducts at a non-zero voltage, and the on-time of the auxiliary switch 35 is increased to ensure zero-voltage switching. As discussed later, in other embodiments, switching at another predetermined voltage can be achieved.

[0063] If V smvbulk - V smbottom is lower than the second reference voltage V ref2 , this can indicate that the main switch 311 conducts at the correct switching point (e.g., at zero voltage), but the on-time of the auxiliary switch 35 may be unnecessarily long. An on-time longer than the required on-time may result in unnecessary losses. Therefore, in this case, in an embodiment, the on-time of the auxiliary switch 35 can be reduced.

[0064] If V ref2 < V smvbulk - V smbottom < V ref1 , this means that the main switch 311 conducts at the desired voltage (e.g., zero voltage), such that the on-time of the auxiliary switch 35 does not need to be modified. V ref1 and V ref2 are selected based on the desired switching voltage of the main switch 311, for example, to ensure zero-voltage switching or switching at a voltage slightly above zero. The on-time of the auxiliary switch 35 can be modified, for example, by changing the pulse width of the pulse-width modulation signal that controls the auxiliary switch 35. Example signals will be discussed in further detail below.

[0065] Figure 3 The operation of the embodiment of

[0066] is as follows: When the auxiliary switch 35 is on, the clamping voltage across the clamping capacitor of the active clamp 34 discharges to magnetize the output induction of the active clamp 34. When the auxiliary switch 35 is turned off again, the remaining current will continue to cause the drain voltage of the main switch 311 to change from Vin +n P / n S x V out Discharge to 0, where V in is the input voltage after rectification (after rectifier 32), V out is the output voltage, and n P / n S is the winding ratio between the primary side circuit and the secondary side circuit of the transformer 38. Figure 2 The corresponding voltage seen at the ZCD terminal 42 is -V when the main switch 311 is turned on. bulk xn A / n P x(R ZCD_low / R ZCD_low +R ZCD_high ), where n A / n P is the winding ratio between the auxiliary winding 36 and the primary winding of the transformer 38. In order to achieve zero voltage switching, for example, the energy stored in the magnetizing inductor should be greater than 1 / 2 x C OSS x V DS 2 , where V DS is the drain-source voltage of the main switch 311, and C OSS is the output capacitance of the main switch 311 .

[0067] Therefore, by turning on the auxiliary switch for a short time, the drain-source voltage of the main switch 311 is discharged to a desired level before the main switch 311 is turned on.

[0068] During the on-time of the main switch 311, the voltage at the terminal 42 will be negative, as explained above. bulk xn A / n P x(R ZCD_low / R ZCD_low +R ZCD_high ). The drain-source voltage of the main switch 311 before the main switch 311 is turned on depends on the length of the on-time of the auxiliary switch 35. By setting the above threshold V accordingly ref1 and V ref2 , the on-time required for zero voltage switching or another desired switching voltage can be obtained.

[0069] To further illustrate, Figure 5 is a flowchart illustrating a method according to an embodiment. Figure 5 The method can be Figure 3 and Figure 4 In the embodiment of the present invention, in particular, the primary side circuit controller 33 is used, and for ease of description, reference will be made to Figure 3 andFigure 4 is explained. However, Figure 5 the use of the method is not limited to Figure 3 and Figure 4 the embodiments.

[0070] Figure 5 The method is shown as a series of actions or events and can be part of the continuous operation of a voltage converter. Therefore, as will be explained in more detail below, the actions or events described below with reference to Figure 5 can be repeatedly executed.

[0071] At step 50 of Figure 5 , the method includes turning on the main power MOSFET serving as the main switch, such as Figure 3 the main switch 311 of

[0072] At step 51, the method includes: sampling the voltage at the ZCD terminal (or a voltage derived therefrom, such as Figure 4 the V at pos ) when the power MOSFET is on. In Figure 4 the embodiment, this is accomplished by controlling the sampling circuit 45.

[0073] After that, the main power MOSFET is turned off.

[0074] At step 52, when the voltage at terminal 42 has the highest (peak) value, an auxiliary power MOSFET such as an active clamp, such as Figure 3 the auxiliary switch 35 in

[0075] At step 53, the method includes sampling and holding the voltage at the ZCD terminal, which is also the reflected drain voltage or body voltage. The body voltage (sometimes called V bulk ) is Figure 3 the voltage across the capacitor C1 in Figure 8 the C in BULK . The drain voltage, sometimes called V drain , is the voltage across the switch 311 of the main switch such as Figure 8 . Figure 5 In the embodiment of [[ID=No. 56]]

[0076] As described above, at step 56, the sampling results at steps 51 and 53 are processed. For example, by taking the difference between the sampling results at steps 51 and 53 and the above such as V ref1 , V ref2The sampled results are processed by comparing them with a reference voltage. Based on this comparison, the conduction time of the auxiliary power MOSFET is modified, for example, by modifying the pulse width of the corresponding control signal.

[0077] In step 55, after a certain dead time after turning off the auxiliary power MOSFET, the main power MOSFET conducts again. Step 54 is a repetition of step 50 in the next cycle. Thus, as shown at step 55, this method is repeated.

[0078] Next, the operation of the embodiments of Figure 3 and Figure 4 and the method of Figure 5 will be further illustrated using example signals.

[0079] It should be noted that the signal waveforms shown herein are only illustrative examples, and the signal waveforms may vary according to specific device implementations.

[0080] In Figure 6 , V gs represents the gate-source voltage. The portion labeled S a shows the gate-source voltage applied to close the auxiliary switch 35 of Figure 3 , and the portion labeled S w shows the gate-source voltage applied to close the main switch 311. The currents I p , I Lm , I c and I s are shown in Figure 3 , and represent the primary-side circuit current, the current through the inductor 313, the current through the auxiliary switch 35, and the secondary-side circuit current, respectively. V ds_Sw represents the drain-source voltage of the main switch 311. The block 60 shows the behavior before the main switch 311 conducts. By closing the auxiliary switch 35, the drain-source voltage V ds_Sw becomes zero at the moment when the main switch Sw conducts (the moment t8 in Figure 6 ). As will be discussed later, in other embodiments, the conduction time of the auxiliary switch 35 is used to provide switching at a drain-source voltage V ds_Sw slightly above zero.

[0081] Figures 7A to 7C is a waveform diagram further showing the above operation. In Figures 7A to 7C , V pos is the voltage V Figure 4 , V pos , V ZCD(V) is the voltage at terminal 42 (V pos is substantially -V ZCD ), V outis the output voltage of the voltage converter, V ds is the drain-source voltage of the main switch 311, V fb is the feedback voltage provided by the feedback loop 312, V GD1 shows the control voltage applied to the auxiliary switch 35, V GD0 shows the control voltage (correspondingly the gate-source voltage) applied to the main switch 311, and V bulk corresponds to Figure 3 the above-mentioned voltage V shown in bulk . Figure 7A shows the case where the on-time of the auxiliary switch 35 is too short for zero-voltage switching, such that when the main switch conducts according to the voltage V GD0 conducts, some drain-source voltage V ds still remains. The reference numeral 70 shows the time point of sampling the voltage V pos before conducting the switch ( Figure 4 the sampling circuit 46 of Figure 5 53) to obtain the voltage V smbottom and the reference numeral 70 indicates the time point of sampling the voltage V pos during the conduction of the main switch ( Figure 4 the sampling circuit 45 of to obtain V smbulk , Figure 5 51). Based on the voltage sampled in this way, if zero-voltage switching is obtained based on the voltage in Figure 7A , the pulse width of the signal V GD1 will increase.

[0082] For example, this may result in Figure 7B the case where the drain-source voltage is zero when the main switch is conducted, as shown by the reference numeral 72.

[0083] Only a non-limiting example is given. In Figure 7A , the on-time of the auxiliary switch can be 225 ns, which can be increased to Figure 7B 440 ns in

[0084] Figure 7C shows the case where the on-time of the auxiliary switch is further increased. The reference numerals 73 and 74 respectively indicate the sampling points corresponding to the reference numerals 70 and 71 in Figure 7A , that is, the sampling before conducting the main switch and the sampling when the main switch is conducted. Although zero-voltage switching is also achieved in the case of Figure 7C , compared with Figure 7B , the relatively long on-time of the auxiliary switch 35 results in additional losses.

[0085] In this case, the update performed by the comparison, judgment and update circuit 47 and / or in Figure 5The comparison and determination performed at step 56 in [it] will result in a reduction in the conduction time of the auxiliary switch 35.

[0086] Above, embodiments have been described in which the auxiliary switch in the active clamp is used to provide switching of the main switch at a desired voltage (e.g., zero voltage switching). In other embodiments, other arrangements of the auxiliary switch can be used to provide switching of the main switch at a desired voltage, such as zero voltage switching. Next, examples of such alternative arrangements will be described with reference to Figures 8 to 10 Describe examples of such alternative arrangements.

[0087] Figure 8 A voltage converter according to another embodiment is shown. To avoid repetition, the Figure 3 voltage converter corresponding to Figure 8 has the same reference numerals for its elements and will not be discussed in detail again.

[0088] Instead of Figure 3 the active clamp 34 of Figure 8 the voltage converter includes an additional auxiliary winding 84 coupled to the auxiliary switch 81. A primary side circuit controller 82 that performs functions similar to those described for the primary side circuit controller 33 of Figure 3 controls the switching of the main switch 311 and the auxiliary switch 81. In particular, by closing the auxiliary switch 81 before closing the main switch 311, switching of the main switch 311 at a desired voltage (e.g., zero voltage switching) can be obtained.

[0089] For this, the primary side circuit controller 82 uses the auxiliary winding 36, for example, to sample the voltage received at the terminal 42 by using a circuit as shown in Figure 4 In other words, the conduction time of the auxiliary switch 81 can be adjusted to be the same as the conduction time of the auxiliary switch 35 as described above.

[0090] In addition, in Figure 8 the embodiment of

[0091] Figure 9 A sample operation of the embodiment of Figure 8 is shown. In Figure 9 where V GD1 shows the control signal applied to the auxiliary switch 81, and V GD0 shows the control voltage applied to the gate terminal of the main switch 311. As shown, for example, in block 90, the auxiliary switch 81 is conducted for a short duration before the main switch 311 is conducted. This causes asFigure 9 the voltage V in ZVS the discharge at the auxiliary winding 84 indicated. The current in the auxiliary winding generates a negative current in the magnetization induction, and this negative current in turn causes the drain voltage V of the main switch 311 to drain discharge, such that zero voltage switching can be obtained in the example of Figure 9 . I mag shows the magnetization current.

[0092] Therefore, by also using an additional auxiliary winding 84 coupled to the auxiliary switch 81, switching of the main switch at a desired voltage, such as zero voltage switching, can be obtained.

[0093] Figure 10 Schematically shows a part of a voltage converter according to another embodiment. Again, reference is made to Figure 3 and Figure 8 the elements already discussed have the same reference numerals and will not be discussed again. In addition, Figure 10 only some components of the voltage converter are shown, and other components such as the feedback loop 312 and the primary side circuit controller 33 or 82 and the auxiliary winding 36 have been omitted in Figure 10 , but they can be implemented in the same manner as discussed in reference to Figure 3 , Figure 4 and Figure 8 . In Figure 10 , the auxiliary switch 101 is provided on the secondary side circuit 39 and is coupled to the voltage source 100 and the secondary side winding 102. By closing the switch 101, energy is injected from the secondary side circuit 39 into the primary side circuit 37, and the primary side circuit 37 can again be used to discharge the voltage across the main switch 311 to ensure switching at a desired voltage. In a manner similar to the way already described above, the on-time of the auxiliary switch can be regulated based on the voltage measurements described in reference to Figure 4 and Figure 5 to obtain switching of the main switch 311 at a desired voltage, such as zero voltage switching.

[0094] Therefore, it can be seen that the techniques discussed herein can be applied to various configurations in a voltage converter to regulate the on-time of the auxiliary switch at the primary side circuit or the secondary side circuit to obtain a desired switching voltage for the main switch, such as zero voltage switching.

[0095] As described above, in some embodiments, zero voltage switching is obtained. In other embodiments, switching at a voltage slightly above zero can be obtained to optimize the total losses, which will now be described in reference to Figures 11 to 13 .

[0096] In particular, achieving zero voltage switching across a main switch such as main switch 311 requires energy, for example from Figure 10 The energy injected into the secondary side circuit in Figure 3 The energy used for active clamping in Figure 8 As will be discussed below, in some embodiments, the total energy loss can be optimized by selecting the switching voltage of the main switch not to be exactly at 0V but slightly above 0V.

[0097] In some embodiments, the auxiliary switch 101 on the secondary side circuit 39 can be a synchronous rectification switch of a synchronous rectifier, which is used in this embodiment to obtain a desired switching voltage on the primary side circuit.

[0098] Figure 11 The charge and energy in the output capacitance (e.g., the parasitic capacitance described above) of the main switch (in this example, a superjunction power switch) for various switching voltages are shown. In particular, curve 110 shows the stored charge Qoss, and curve 111 shows the stored energy Eoss as a function of the voltage across the main switch. Figure 11 As can be seen in the figure, approximately 10% of the maximum charge Qoss is injected into the main switch, reducing the voltage from 500V to 28V. This charging / discharging requires closing the auxiliary switch. In this case, if the device is discharged to only 28V instead of 0V, for example, 90% of the losses can be saved, and in this case, the energy stored in the output capacitor is reduced by more than two-thirds, as shown in bar 112.

[0099] In particular, from Figure 11 It can be seen that at lower voltages (at Figure 11 At a point slightly below 25V (in the figure), there is a sharp bend in curves 110 and 111, where the slope of the curve may vary significantly, for example, by more than 20%. This bend is also referred to herein as an inflection point or inflection region. The inflection point can be defined as the voltage at which the first-order derivative p = d(Ron * Qoss) / dV corresponds to a predetermined threshold, for example, 0.1, where Ron is the on-resistance of the main switch. In other words, the parameter p is the first-order derivative of the product of Ron and Qoss. This parameter p decreases monotonically from 2.3 to 0.003 in the voltage range 0V to 500V. According to this definition, Figure 11 The inflection point is 26.5V.

[0100] Figure 12 Another example considering various conduction losses is shown. Figure 12 For example, assuming the use of Figure 10 The synchronous rectification switch is used to inject energy.

[0101] existFigure 12 In it, curve 120 shows the loss (Eoss loss) of the energy stored in the main switch as already described with respect to Figure 11 and the energy loss is zero for zero voltage switching. Curve 121 shows the additional switching loss on the secondary side circuit, which is caused by turning off the current through the synchronous rectifier switch on the secondary side circuit. Curve 122 shows the conduction loss from the positive current on the secondary side, curve 123 shows the conduction loss on the secondary side circuit due to the additional negative (synchronous rectifier) current, and curve 124 shows the additional primary conduction loss due to the slightly higher peak current on the primary side. All losses are plotted as a function of the voltage across the main switch when the main switch is conducting. It can be seen that although the loss according to curve 120 is zero at 0V, the other losses have their highest values at 0V and then decrease towards higher voltages as the energy required to achieve zero voltage switching.

[0102] Figure 13 shows the loss balance, where zero loss balance indicates the minimum total loss when all the Figure 12 losses are added together. It can be seen that the lowest loss is not at the switching voltage of 0V, i.e., at zero voltage switching, but at a slightly higher voltage, at about 10V in the example of Figure 13 . Switching at 0V results in 0.5 μJ or more loss compared to this optimum point, while switching at the inflection point of Figure 11 (at about 26V in the example of Figure 11 ) results in 0.9 μJ or more loss per switching event. Therefore, the optimum switching voltage is approximately halfway between zero volts and the inflection point, for example, between 30% and 70% of the voltage at the inflection point or between 40% and 60% of the voltage at the inflection point.

[0103] Although the injection of energy from the secondary side circuit as shown with respect to Figure 10 has been used as an example in Figure 12 and Figure 13 , similar considerations apply to other arrangements, such as the arrangements discussed with reference to Figure 3 and Figure 8 . Basically, through all these methods, the output capacitance of the main switch is charged / discharged.

[0104] In addition to the loss aspect, in some embodiments, using a switching voltage slightly higher than 0V may also be advantageous in terms of the loss of the duty cycle. In some embodiments, due to injecting too much energy, such as discharging the main switch completely to 0V, more duty cycle is occupied, and in some cases, it will cause the controller to limit the dead time required to allow the output capacitance of the main switch to discharge.

[0105] It should be noted that, at least for modern superjunction power switches, the Qoss curve is relatively flat for voltages above the inflection point, referring to Figure 13 The discussed optimal switching voltage basically does not change with the input voltage of the voltage converter. For example, discharging from 500V or from 200V basically does not change the optimal switching voltage. In both cases, for the example switch discussed in reference Figures 11 to 13 , the optimal switching voltage is between 10V and 11V. Regarding Figures 11 to 13 the specific value parameters, these values depend on the specific switch implementation.

[0106] In other embodiments, where the behavior of the Qoss curve of curve 110 as in Figure 11 is less obvious, that is, for higher voltages, there is no strong inflection point and steeper slope, an offset of the optimal voltage depending on the input voltage may occur. For example, at a lower input voltage, the switching voltage can be adjusted to a lower volt value compared to a higher input voltage. The exact optimal voltage, i.e., the voltage with the minimum loss, generally depends on the topology, the on-resistances of the primary-side circuit switch and the secondary-side circuit switch, the peak currents on the primary-side circuit and the secondary-side circuit, etc.

[0107] In addition, the conduction loss on the primary-side circuit and the conduction loss from the positive current on the secondary-side circuit (see Figure 12 ) respectively include linear terms depending on the load current of the primary-side circuit and the secondary-side circuit. Therefore, the optimal voltage slightly depends on the load. As the load increases, the voltage is higher, while the Eoss loss (curve 120) remains constant independently of the load current. Therefore, in some embodiments, the switching voltage can be adjusted according to the load current. In other embodiments, the switching voltage can be kept constant independently of the load current. It should also be noted that in an embodiment, it is not necessary to adjust to the optimal value, but the value between the inflection point of the Qoss / Eoss curve and 0V can be selected to be, for example, a value that can only approximate the optimal value.

[0108] It should be noted that although setting the switching voltage of the primary-side switch to the voltage between zero and the inflection point as described above can be performed using the control techniques discussed above, that is, using the two voltages measured using the auxiliary winding, it can also be used in combination with other control techniques, such as conventional techniques.

[0109] As already explained above, this concept is applicable to various converter topologies that actively reduce the voltage across the main switch by injecting energy using an auxiliary switch, such as those illustrated in reference Figure 3 , Figure 8 or Figure 1 .

[0110] Therefore, the specific implementations discussed above are merely examples and should not be construed in any way as limiting.

[0111] At least some embodiments are defined by the examples given below.

[0112] Example 1: A voltage converter controller, comprising:

[0113] A drive circuit configured to control the switching of a main switch and an auxiliary switch for regulating the switching voltage of the main switch on the primary side circuit of the voltage converter,

[0114] A terminal configured to receive a voltage from an auxiliary winding of a transformer of the voltage converter,

[0115] A sampling circuit configured to provide a first voltage based on the voltage at the terminal before the main switch conducts and a second voltage based on the voltage at the terminal when the main switch conducts, and

[0116] A regulation circuit configured to regulate the on-time of the auxiliary switch based on the first voltage and the second voltage.

[0117] Example 2: The voltage converter controller according to Example 1, wherein the regulation circuit is configured to regulate the on-time of the auxiliary switch based on a comparison of the difference between the first voltage and the second voltage with at least one threshold voltage.

[0118] Example 3: The voltage converter controller according to Example 2, wherein the regulation circuit is configured to: increase the on-time of the auxiliary switch when the difference is higher than a first threshold voltage of at least one threshold voltage, and decrease the on-time of the auxiliary switch when the difference between the first voltage and the second voltage is lower than a second threshold voltage of at least one threshold voltage.

[0119] Example 4: The voltage converter controller according to any one of Examples 1 to 3, wherein the regulation circuit is configured to regulate the on-time of the auxiliary switch to obtain zero voltage switching of the main switch.

[0120] Example 5: The voltage converter controller according to any one of Examples 1 to 3, wherein the voltage converter controller is configured to regulate the on-time of the auxiliary switch to obtain switching of the main switch at a switching voltage on both sides of the main switch, the switching voltage being greater than zero and lower than the voltage at the inflection point in the curve of the charge stored in the output capacitance of the main switch with respect to the switching voltage.

[0121] Example 6: The voltage converter controller according to Example 5, wherein the switching voltage is between 8V and 15V.

[0122] Example 7: The voltage converter controller according to any one of Examples 1 to 6, wherein the regulating circuit is configured to regulate the on-time of the auxiliary switch according to the load current of the voltage converter controller.

[0123] Example 8: A voltage converter, comprising:

[0124] A primary side circuit configured to receive an input voltage,

[0125] A secondary side circuit configured to output an output voltage,

[0126] A transformer coupled to the primary side circuit and the secondary side circuit,

[0127] wherein the primary side circuit includes a main switch, and wherein the voltage converter further includes an auxiliary switch configured to regulate the switching voltage across the main switch when the main switch is on, and

[0128] The voltage converter controller according to any one of Examples 1 to 7.

[0129] Example 9: The voltage converter according to Example 8, further comprising an auxiliary winding of the transformer, wherein the auxiliary winding is coupled to a terminal of the voltage converter controller.

[0130] Example 10: The voltage converter controller according to any one of Examples 8 or 9, wherein the auxiliary switch is one of an active clamp auxiliary switch, an auxiliary switch coupled to an additional auxiliary winding, and an auxiliary switch of the secondary side circuit.

[0131] Example 11: The voltage converter according to any one of Examples 8 to 10, wherein the voltage converter is a flyback converter.

[0132] Example 12: A method, comprising:

[0133] Before closing the main switch of the primary side circuit of the voltage converter, measuring a first voltage using an auxiliary winding of the transformer of the voltage converter,

[0134] When the main switch is on, measuring a second voltage using the auxiliary winding, and

[0135] Based on the first voltage and the second voltage, regulating the on-time of the auxiliary switch to regulate the switching voltage across the main switch when the main switch is on.

[0136] Example 13: The method according to Example 12, wherein the regulation includes comparing the difference between the first voltage and the second voltage with at least one threshold voltage.

[0137] Example 14: The method according to Example 13, wherein the comparison includes: increasing the conduction time of the auxiliary switch when the difference is higher than a first threshold voltage of at least one threshold voltage, and decreasing the conduction time of the auxiliary switch when the difference is lower than a second threshold voltage of at least one threshold.

[0138] Example 15: The method according to Example 13 or 14, wherein at least one threshold is selected to obtain zero voltage switching.

[0139] Example 16: The method according to any one of Examples 13 or 14, wherein at least one threshold is selected to obtain a switching at a switching voltage that is greater than zero and lower than the voltage at an inflection point in a curve of the energy stored in the output capacitance of the main switch with respect to the switching voltage, at which inflection point the slope of the curve changes by at least 20%.

[0140] Example 17: The method according to any one of Examples 12 to 16, further comprising regulating the conduction time of the auxiliary switch based on the load current output by the voltage converter.

[0141] Example 18: The method according to any one of Examples 12 to 17, wherein the auxiliary switch is one of an active clamp switch, a switch coupled to an auxiliary winding, or a switch on the secondary side circuit of the voltage converter.

[0142] Example 19: A voltage converter controller, comprising:

[0143] A drive circuit configured to control the switching of a main switch on the primary side circuit of the voltage converter and an auxiliary switch for regulating the switching voltage of the main switch, and

[0144] A regulation circuit configured to regulate the conduction time of the auxiliary switch to obtain a switching voltage of the main switch that is greater than zero and lower than the voltage at an inflection point in a curve of the charge stored in the output capacitance of the main switch with respect to the switching voltage.

[0145] Example 20: The voltage converter controller according to Example 19, wherein the inflection point is at a voltage where the first derivative with respect to voltage of the product of the on-resistance of the main switch and the charge stored in the output capacitance corresponds to a predetermined threshold.

[0146] Example 21: The voltage converter controller according to Example 20, wherein the predetermined threshold is 0.1.

[0147] Example 22: The voltage converter controller according to any one of Examples 19 to 21, wherein the switching voltage is selected to minimize the total energy loss.

[0148] Example 23: The voltage converter according to any one of Examples 19 to 22, wherein the switching voltage is adjusted to be between 30% and 70% of the voltage at the inflection point.

[0149] Example 24: The voltage converter according to any one of Examples 19 to 23, wherein the switching voltage is adjusted to be between 8V and 15V.

[0150] Example 25: A voltage converter, comprising:

[0151] A primary side circuit configured to receive an input voltage,

[0152] A secondary side circuit configured to output an output voltage,

[0153] A transformer coupled to the primary side circuit and the secondary side circuit,

[0154] wherein the primary side circuit includes a main switch, and wherein the voltage converter further includes an auxiliary switch configured to adjust the switching voltage across the main switch when the main switch is conducting, and

[0155] A voltage converter controller according to any one of Examples 19 to 24.

[0156] Example 26: The voltage converter according to Example 25, wherein the auxiliary switch is one of an active clamp auxiliary switch, an auxiliary switch coupled to an additional auxiliary winding, and an auxiliary switch of the secondary side circuit.

[0157] Example 27: The voltage converter according to Example 25 or 26, wherein the voltage converter is a flyback converter.

[0158] Example 28: A method, comprising:

[0159] Operating a main switch of a voltage converter and adjusting the on-time of an auxiliary switch of the voltage converter to obtain a switching voltage of the main switch, the switching voltage being greater than zero and lower than the voltage at the inflection point in a curve of the charge stored in the output capacitor of the main switch with respect to the switching voltage.

[0160] Example 29: The method according to Example 28, wherein the inflection point is at a voltage where the first derivative of the product of the on-resistance of the main switch and the charge stored in the output capacitor with respect to the voltage corresponds to a predetermined threshold.

[0161] Example 30: The method according to Example 29, wherein the predetermined threshold is 0.1.

[0162] Example 31: The method according to any one of Examples 28 to 30, wherein the switching voltage is selected to minimize the total energy loss.

[0163] Example 32: The method according to any one of Examples 28 to 31, wherein the switching voltage is adjusted to be between 30% and 70% of the inflection point voltage.

[0164] Example 33: The method according to any one of Examples 28 to 32, wherein the switching voltage is adjusted to be between 8V and 15V.

[0165] As can be seen from the various modifications and variations discussed above, the embodiments shown and described are only used as non-limiting examples and should not be construed as restrictive.

Claims

1. A voltage converter controller comprising: a drive circuit configured to control switching of a main switch on a primary side circuit of a voltage converter and switching of an auxiliary switch for regulating a switching voltage of the main switch, a terminal configured to receive a voltage from an auxiliary winding of a transformer of the voltage converter, a sampling circuit configured to provide a first voltage based on a voltage at the terminal before the main switch is turned on, and to provide a second voltage based on the voltage at the terminal when the main switch is turned on, and A regulation circuit is configured to regulate the on-time of the auxiliary switch to obtain switching of the main switch at a switching voltage across the main switch, the switching voltage being greater than zero and lower than a voltage at an inflection point in a curve of charge stored in an output capacitance of the main switch versus the switching voltage.

2. The voltage converter controller according to claim 1, wherein: The regulation circuit is further configured to regulate an on-time of the auxiliary switch based on a comparison of a difference between the first voltage and the second voltage and at least one threshold voltage.

3. The voltage converter controller according to claim 2, wherein: The regulation circuit is further configured to increase the on-time of the auxiliary switch when the difference is higher than a first threshold voltage of the at least one threshold voltage, and to decrease the on-time of the auxiliary switch when the difference between the first voltage and the second voltage is lower than a second threshold voltage of the at least one threshold voltage.

4. The voltage converter controller according to claim 1 , wherein: The regulation circuit is further configured to regulate an on-time of the auxiliary switch to obtain zero voltage switching of the main switch.

5. The voltage converter controller according to claim 1 , wherein: The switching voltage is between 8V and 15V.

6. The voltage converter controller according to claim 1, wherein: The regulation circuit is further configured to adjust an on-time of the auxiliary switch according to a load current of the voltage converter controller.

7. A method for operating a voltage converter, comprising: Before closing a main switch of a primary-side circuit of a voltage converter, measuring a first voltage using an auxiliary winding of a transformer of the voltage converter, When the main switch is turned on, the auxiliary winding is used to measure a second voltage, and The on-time of the auxiliary switch is adjusted to obtain switching of the main switch at a switching voltage across the main switch, the switching voltage being greater than zero and lower than a voltage at an inflection point in a curve of charge stored in an output capacitance of the main switch versus the switching voltage.

8. The method of claim 7 , further comprising comparing a difference between the first voltage and the second voltage with at least one threshold voltage, and adjusting a conduction time of an auxiliary switch based on a result of the comparison to adjust a switching voltage across the main switch when the main switch is turned on.

9. The method according to claim 8, wherein Adjusting the on-time of the auxiliary switch based on the result of the comparison includes increasing the on-time of the auxiliary switch when the difference is higher than a first threshold voltage of the at least one threshold voltage, and decreasing the on-time of the auxiliary switch when the difference is lower than a second threshold voltage of the at least one threshold voltage.

10. The method according to claim 8, wherein The at least one threshold voltage is selected to obtain zero voltage switching.

11. The method according to claim 8, wherein The at least one threshold voltage is selected to obtain switching at a switching voltage that is greater than zero and lower than a voltage at an inflection point in a curve of energy stored in the output capacitance of the main switch versus the switching voltage, at which inflection point the slope of the curve changes by at least 20%. 12 . The method of claim 7 , further comprising adjusting an on-time of the auxiliary switch based on a load current output by the voltage converter.

13. The method according to claim 7, wherein: The auxiliary switch is one of an active clamp switch, a switch coupled to an auxiliary winding, and a switch on a secondary side circuit of the voltage converter.

14. A voltage converter controller comprising: a drive circuit configured to control switching of a main switch on a primary side circuit of a voltage converter and switching of an auxiliary switch for regulating a switching voltage of the main switch, and a regulating circuit configured to regulate the on-time of the auxiliary switch to obtain switching of the main switch at a switching voltage that is greater than zero and lower than a voltage at an inflection point in a curve of charge stored in an output capacitance of the main switch versus the switching voltage, The inflection point is at a voltage at which a first-order derivative of a product of an on-resistance of the main switch and a charge stored in the output capacitor with respect to voltage corresponds to a predetermined threshold, and at the inflection point, a slope of the curve changes by at least 20%.

15. The voltage converter controller according to claim 14, wherein: The predetermined threshold is 0.

1.

16. The voltage converter controller according to claim 14, wherein: The switching voltage is selected to minimize the overall energy loss.

17. The voltage converter controller of claim 14, wherein: The switching voltage is adjusted to be between 30% and 70% of the voltage at the knee point.

18. The voltage converter controller of claim 14, wherein: The switching voltage is regulated between 8V and 15V.

19. A voltage converter comprising: a primary side circuit configured to receive an input voltage, A secondary side circuit configured to output an output voltage, a transformer coupling the primary-side circuit and the secondary-side circuit, wherein the primary side circuit includes a main switch, and wherein the voltage converter further includes an auxiliary switch configured to adjust a switching voltage across the main switch when the main switch is turned on, and A voltage converter controller comprising: a drive circuit configured to control switching of a main switch on a primary side circuit of a voltage converter and switching of an auxiliary switch for regulating a switching voltage of the main switch, a terminal configured to receive a voltage from an auxiliary winding of a transformer of the voltage converter, a sampling circuit configured to provide a first voltage based on a voltage at the terminal before the main switch is turned on, and to provide a second voltage based on the voltage at the terminal when the main switch is turned on, and A regulation circuit is configured to regulate the on-time of the auxiliary switch to obtain switching of the main switch at a switching voltage across the main switch that is greater than zero and lower than a voltage at an inflection point in a curve of charge stored in an output capacitance of the main switch versus the switching voltage.

20. The voltage converter according to claim 19, wherein The regulation circuit is further configured to regulate an on-time of the auxiliary switch based on a comparison of a difference between the first voltage and the second voltage and at least one threshold voltage.

21. The voltage converter according to claim 19, wherein The auxiliary switch is one of an active clamp auxiliary switch, an auxiliary switch coupled to an additional auxiliary winding, and an auxiliary switch of the secondary side circuit.

22. The voltage converter according to claim 19, wherein The voltage converter is a flyback converter.

23. The voltage converter according to claim 19, wherein The voltage converter controller is a voltage converter controller according to any one of claims 1 to 6, the voltage converter further comprising an auxiliary winding of the transformer, wherein the auxiliary winding is coupled to the terminal of the voltage converter controller.

24. A method for operating a voltage converter, comprising: operates the main switch of the voltage converter, and adjusting the on-time of the auxiliary switch of the voltage converter to obtain switching of the main switch at a switching voltage that is greater than zero and lower than a voltage at an inflection point in a curve of charge stored in an output capacitance of the main switch versus the switching voltage, The inflection point is at a voltage at which a first-order derivative of a product of an on-resistance of the main switch and a charge stored in the output capacitor with respect to voltage corresponds to a predetermined threshold, and at the inflection point, a slope of the curve changes by at least 20%.

25. The method according to claim 24, wherein The predetermined threshold is 0.

1.

26. The method according to claim 24, wherein The switching voltage is selected to minimize the overall energy loss.

27. The method according to claim 24, wherein The switching voltage is adjusted to be between 30% and 70% of the voltage at the knee point.

28. The method according to claim 24, wherein The switching voltage is regulated between 8V and 15V.

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