Switching power converter controller for digital control of constant power mode

Abstract

A switching power converter with digital control of a constant power mode is provided. During the constant power mode, the switching power converter may approximate the simulated constant power mode by incrementing or decrementing the output voltage by a discrete voltage step. At each discrete voltage step, the output current may vary over a range while the output voltage remains constant. Alternatively, the switching power converter may approximate the simulated constant power mode by incrementally or incrementally decreasing the output current by discrete current steps. At each discrete current step, the output voltage may vary over a range while the output current remains constant.

Description

Technical Field

[0001] The present application relates to switching power converters, and more particularly to a digitally controlled switching power converter controller for constant power mode. Background Art

[0002] Depending on the output voltage and output current, the switching power converter can transition between constant voltage mode and constant current mode, such as during battery charging. Figure 1 An example of such a transition between constant current mode and constant voltage mode is shown in . During constant voltage mode, the output current is below a maximum value (Imax), while the output voltage is regulated to be equal to a constant value Vmax. If the output current increases to equal or exceed Imax during constant voltage mode, the switching power converter transitions to constant current mode. Conversely, if the output voltage increases to equal or exceed Vmax during constant current mode, the switching power converter transitions to constant voltage mode.

[0003] To further enhance battery charging, switching power converters with constant power mode have been developed. Figure 1 The direct transition between the constant voltage mode and the constant current mode shown in FIG. Alternatively, the switching power converter transitions from the constant power mode to the constant voltage mode or the constant current mode. Figure 2 An example of transition between constant voltage mode, constant power mode, and constant current mode is shown in . During constant voltage mode, the switching power converter adjusts the output voltage to be equal to a constant value Vmax, while the output current is less than the maximum value IP1. When the output current is equal to or exceeds IP1, the switching power converter transitions to constant power mode at node P1. During constant power mode, the switching power converter reduces the output voltage in response to an increase in the output current, so that the product of the output voltage and the output current produces a constant output power. Conversely, the switching power converter increases the output voltage in response to a decrease in the output current to maintain a constant output power again. If the output voltage drops to equal to or less than the minimum voltage value VP2 during constant power mode, the switching power converter transitions to constant current mode at point P2.

[0004] Although battery charging is enhanced using a constant power mode, the control method has proven to be complex to implement.Therefore, there is a need in the art for improved constant power operation. Summary of the invention

[0005] According to aspects of the present disclosure, a switching power converter is provided, comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is connected to an output node for an output voltage; a power switch, wherein the power switch is connected in series with the primary winding; and a controller, wherein the controller is configured to: control the cycle of the power switch during a constant voltage mode to adjust the output voltage to be equal to a maximum voltage; transition from the constant voltage mode to a constant power mode in response to an output current being greater than a maximum current of the constant voltage mode; and control the cycle of the power switch to adjust the output voltage to be equal to a first constant voltage when the output current of the switching power converter is within a first current range, wherein the first constant voltage is a discrete voltage step less than the maximum voltage, and a first constant power reference current is calculated by dividing the constant power of the constant power mode by the first constant voltage, wherein the first current range includes the first constant power reference current.

[0006] According to another aspect of the present disclosure, a switching power converter is provided, comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is connected to an output node for an output voltage; a power switch, wherein the power switch is connected in series with the primary winding; a controller, wherein the controller is configured to control the cycle of the power switch so that the output current of the switching power converter is equal to the constant current during a constant current mode; transition from the constant current mode to the constant power mode in response to the output voltage being greater than the maximum voltage of the constant current mode; controlling the cycle of the power switch to adjust the output voltage to be equal to a first constant voltage when the output current of the switching power converter is within a first current range, wherein the first constant voltage is less than the maximum voltage by a discrete voltage step, and calculating a first constant power reference current by dividing the constant power of the constant power mode by the first constant voltage, wherein the first current range includes the first constant power reference current.

[0007] According to another aspect of the present disclosure, a switching power converter is provided, comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is connected to an output node for an output voltage; a power switch, wherein the power switch is connected in series with the primary winding; and a controller, wherein the controller is configured to control a cycle of the power switch during a constant voltage mode to adjust the output voltage to be equal to a maximum voltage, wherein the controller is further configured to: transition from a constant voltage mode to a constant power mode in response to an output current being greater than a maximum current of the constant voltage mode; control a cycle of the power switch when the output voltage of the switching power converter is within a first voltage range to adjust the output current to be equal to a first constant current, wherein the first constant current is greater than the maximum current by a discrete current step, and a first constant power reference voltage is calculated by dividing the constant power of the constant power mode by the first constant current, wherein the first voltage range includes the first constant power reference voltage.

[0008] Finally, according to another aspect of the present disclosure, a switching power converter is provided, comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is connected to an output node for an output voltage; a power switch, wherein the power switch is connected in series with the primary winding; and a controller, wherein the controller is configured to: control the cycle of the power switch during a constant current mode to adjust the output current of the switching power converter to be equal to a maximum constant current; transition from a constant current mode to a constant power mode in response to an output voltage greater than a maximum voltage of the constant current mode; control the cycle of the power switch when the output voltage of the switching power converter is within a first voltage range to adjust the output current to be equal to a first constant current, wherein the first constant current is smaller than the maximum constant current by a discrete current step, and a first constant power reference voltage is calculated by dividing the constant power of the constant power mode by the first constant current, wherein the first voltage range includes the first constant power reference voltage.

[0009] These advantageous features can be better understood by considering the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The current and voltage output waveforms of a flyback converter transitioning between constant voltage mode and constant current mode are shown.

[0011] Figure 2 The current and voltage output waveforms of a flyback converter transitioning between constant voltage mode, simulated constant power mode, and constant current mode are shown.

[0012] Figure 3 A flyback converter configured with a digitally controlled constant power mode according to an aspect of the present disclosure is shown.

[0013] Figure 4 is a flow chart of a method of transitioning from a constant voltage mode to a constant power mode according to an aspect of the present disclosure, wherein the output voltage is varied digitally.

[0014] Figure 5 The current and voltage output waveforms of an analog constant power mode according to an aspect of the present disclosure are illustrated, along with a digitally varied output voltage and a corresponding constant power reference current.

[0015] Figure 6 The diagram shows a method according to one aspect of the present disclosure. Figure 4 The method generates current and voltage output waveforms.

[0016] Figure 7is a flow chart of a method of transitioning from a constant current mode to a constant power mode, wherein the output voltage is varied digitally, according to an aspect of the present disclosure.

[0017] Figure 8 is a flow chart of a method of transitioning from a constant voltage mode to a constant power mode according to an aspect of the present disclosure, wherein the output current is varied digitally.

[0018] Fig. 9 is a flow chart of a method of transitioning from a constant current mode to a constant power mode according to an aspect of the present disclosure, wherein the output current is varied digitally.

[0019] Fig.10 The current and voltage output waveforms of the simulated constant power mode according to an aspect of the present disclosure are illustrated along with the digitally varied output current and the corresponding constant power reference current.

[0020] Fig.11 The diagram shows a method according to one aspect of the present disclosure. Figure 8 or Fig. 9 The method generates current and voltage output waveforms.

[0021] Embodiments of the present disclosure and their advantages are best understood by referring to the following detailed description.It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the accompanying drawings. DETAILED DESCRIPTION

[0022] The switching power converter has an advantageous digital control of the constant power mode. Compared with the analog constant power mode, the digital control is easy to implement and stable. In this digital control, the constant power output is approximated by discrete steps of the output voltage or output current. The desired constant output power is therefore approximated by digitally increasing / decreasing the output voltage or output current. For example, assume that the output voltage is increased or decreased by discrete voltage steps during the constant power mode. At each discrete voltage step, the cycle of the power switch is controlled to adjust the output voltage to be constant at its increasing / decreasing value, but the output current can vary in an analog manner within the current range. The center of this current range is equal to the constant power reference current, which is equal to the constant output power of the constant power mode divided by the increasing (or decreasing) output voltage. It can therefore be understood that when the output current is equal to the constant power reference current, the output power is equal to the desired constant power. If the output current changes so that it is no longer within the current range, the output voltage is decreased or increased according to the error between the output current and the desired current range.

[0023] If the output current is instead digitally incremented / decremented in discrete current steps, the output voltage can vary within a voltage range while the output current is maintained constant at its incrementing / decrementing value. For each incrementing / decrementing value, the center of the corresponding voltage range is equal to a constant power reference voltage, which is equal to the constant output power divided by the increasing (or decreasing) output current. It can therefore be understood that when the output voltage is equal to the constant power reference voltage, the output power is equal to the desired constant power. The choice between digitally varying the output voltage or digitally varying the output current depends on whether it is desired to minimize the output voltage ripple or the output current ripple during the constant power mode.

[0024] The resulting digital control can be implemented in a secondary side or primary side controller. As the name implies, a secondary side controller resides on the secondary side of the transformer of a switching power converter. Conversely, a primary side controller is located on the primary side of the transformer. It should be noted that the primary side controller is isolated from the output voltage and output current by the transformer. In contrast, the secondary side controller can sense both the output voltage and the output current directly. Since both the output voltage and the output current must be measured in the digital control disclosed herein, the following discussion will focus on the secondary side controller implementation, but it will be understood that the primary side implementation of the digital control can also be implemented.

[0025] exist Figure 3 An exemplary flyback converter 300 of a digitally controlled secondary side controller implementation with a constant power mode is shown in FIG. The primary side controller U1 controls the cycle of the power switch transistor S1 in response to a received control signal (e.g., a received control signal voltage) from the optocoupler 110. The power switch transistor S1 is connected between ground and the primary winding T1 of the transformer T. In each cycle, a rectified input voltage Vin, such as from an AC power supply voltage, drives a primary current into the primary winding when the power switch transistor S1 is turned on. While the primary current flows, the secondary controller U2 maintains the synchronous rectifier (SR) switch transistor off. For example, the secondary controller U2 can monitor the drain (D) to source (S) voltage of the SR switch transistor to determine when the primary winding current is turned on. After a sufficient amount of magnetic energy is stored in the transformer T1, the primary side controller U1 turns off the power switch transistor S1. The secondary controller U2 senses this shutdown and accordingly turns on the SR switching transistor to conduct the secondary winding T2 of the transformer T so as to charge the output capacitor C1 with the output voltage Vout and conduct the output current Iout to the load (e.g., a mobile device battery). In an alternative embodiment, the SR switching transistor can be replaced by an output diode D1.

[0026] To control whether the constant voltage, constant current or constant power mode is effective, the secondary side controller U2 directly senses the output voltage Vout. In addition, the secondary side controller U2 can sense the output current Iout by sensing the voltage across the sense resistor R and converting this voltage into current through Ohm's law. Figure 2 , when the output current Iout is less than IP1, the secondary side controller U2 regulates the output voltage Vout in the constant voltage mode. Similarly, when the output voltage Vout is less than VP2, the secondary side controller U2 regulates the output current Iout in the constant current mode. Since these modes are conventional, the following discussion will focus on the constant power mode.

[0027] It should be noted that there are essentially an infinite number of voltage-current combinations that meet constant output power, because output power is the product of output voltage and output current. When one of the output voltage or output current increases, the other must decrease, and vice versa, to meet the constant power requirement. This infinite number of possibilities leads to design complexity in previous constant power regulation attempts. But this complexity is alleviated in this article by digital technology that digitally changes the reference voltage or reference current. The digitally varied voltage / current is referred to as a digitally varied reference signal in this article. As used herein, the digitally varied reference signal is incremented or decremented in discrete steps. For example, the reference voltage is changed by a positive or negative multiple of a voltage step (ΔV). Similarly, the reference current is changed according to a positive or negative multiple of a current step (ΔI). The following discussion will first address the implementation of the reference voltage being a digitally varied reference signal, and then discuss the implementation of the reference current being a digitally varied reference signal.

[0028] The transition from constant voltage mode to constant power mode is triggered by the secondary side controller U2 sensing that the output current has exceeded the output current limit. Prior to this transition, the feedback loop regulates the output voltage to a constant voltage (CV), wherein an error signal regarding the difference between the output voltage and the CV reference voltage is generated in the feedback loop. Therefore, it is convenient for the secondary side controller U2 to subtract the voltage increment ΔV from the CV reference voltage to calculate the initial value of the CP reference voltage when transitioning to the constant power (CP) mode. The secondary side controller U2 can then calculate the CP reference current by dividing the constant power by the CP reference voltage. By monitoring whether the output current is greater than the CP reference current by a threshold amount or less than the CP reference current by the threshold amount, the secondary side controller U2 increases or decreases the CP reference voltage accordingly.

[0029] exist Figure 4A flow chart of the calculation of the reference voltage and reference current by the secondary side controller U2 when transitioning from the constant voltage mode to the constant power mode is shown in . At the transition 400 from the CV mode to the CP mode, the variable N is set to 1. In the calculation step 405, the secondary side controller U2 calculates the CP reference voltage (CP Vref) by subtracting N*ΔV from the CV reference voltage (CV Vref), where ΔV is the voltage step discussed above. Since the CP reference voltage can be increased or decreased, in step 410, the secondary side controller U2 tests whether the CP reference voltage is greater than the CV reference voltage. If this test is positive, the secondary side controller U2 transitions back to the CV mode in step 415. If step 410 is negative, the secondary side controller U2 divides the constant power (CP) of the constant power mode by the CP reference voltage in step 420 to calculate the CP reference current (CPIref). In the case where the CP reference current is calculated, the secondary side controller U2 checks in step 425 whether the CP reference current is greater than the constant current reference current (CC Iref) used during the constant current mode. If the CP reference current is greater than the CC reference current, the secondary side controller U2 transitions to the constant current mode in step 430. Otherwise, in step 435, the secondary side controller U2 tests whether the difference between the output current (Iout) and the CP reference current is greater than the positive threshold Ith. If the output current is greater, the secondary side controller U2 increments the variable N in step 440, whereupon control returns to step 405, such that the CP reference voltage is incremented. However, if the output current is not greater, the secondary side controller U2 continues to test in step 450 whether the difference between the output current and the CP reference current is less than the negative threshold -Ith. If the result of step 450 is positive, the secondary side controller U2 continues to decrement the variable N in step 445, whereupon control returns to step 405, such that the CP reference voltage is decremented. If the result of step 450 is negative, control returns to step 435.

[0030] Referring again to step 405, it should be noted that once the secondary side controller U2 has calculated the CP reference voltage, the secondary side controller U2 generates a control voltage such that the output voltage is regulated to be equal to the CP reference voltage during the time period when the CP reference voltage is neither increasing nor decreasing. In this regard, the secondary side controller U2 can perform steps 435 and 440 by integrating the current error (the difference between the output current and the CP reference current) over an integration period. In the event that this error changes sign (from positive to negative or from negative to positive), the integration period is reset. The integration period will therefore be the minimum length of time that the output voltage will be regulated relative to a given setting of the CP reference voltage. The end result is that the output voltage on the CP mode will increase or decrease in response to an increase or decrease in the CP reference voltage.

[0031] exist Figure 5 Multiple exemplary CP reference voltages and corresponding CP reference currents are shown. The magnitude of the exemplary CP reference voltages decreases starting from the CP reference voltage Vref1. Thus, the second CP reference voltage Vref2 is less than Vref1 by ΔV. Similarly, the third CP reference voltage Vref3 is less than Vref2 by ΔV, the fourth CP reference voltage Vref4 is less than Vref3 by ΔV, and the fifth CP reference voltage Vref5 is less than Vref4 by ΔV. The corresponding CP reference currents are designated as Iref1, Iref2, Iref3, Iref4, and Iref5 respectively. The ideal analog CP regulation curve intersects each Vref, Iref pair.

[0032] This ideal CP regulation curve is advantageously approximated by regulating the output voltage with respect to a series of exemplary CP reference voltages Vref1 to Vref5 as Figure 6 shown. When using a given CP reference voltage to generate a control voltage for output voltage regulation, the output voltage is regulated in the CV manner to be equal to the CP reference voltage. However, this constant voltage regulation will only vary with the output current, which is not less than the negative threshold amount ΔI of the corresponding CP reference current and not greater than the positive threshold amount ΔI of the corresponding CP reference current. For example, consider the constant voltage regulation where the output voltage is equal to Vref2. The corresponding CP reference current is Iref2. Thus, the output voltage is only equal to Vref2, while the output current error satisfies the inequality -Ith < output current error < Ith. If the output current error is less than -Ith, the output voltage regulation will change to be equal to Vref1. If the output current error is greater than Ith, the output voltage regulation will change to be equal to Vref3. It should be noted that the value of Ith is a design choice as it results in a trade-off. As Ith decreases, the approximation to the ideal CP curve becomes better, but at the cost of more frequent transitions from one CP reference voltage to another.

[0033] In Figure 7 shown is a flowchart of the transition from the CC mode to the CP mode. At the transition 700 from the CC mode to the CP mode, the variable N is set to 1. In the calculation step 705, the secondary side controller U2 makes N*ΔV equal to the CC mode output voltage VP2 ( Figure 2) are added to calculate the CP reference voltage (CP Vref). Since the CP reference voltage can be increased or decreased, in step 710, the secondary side controller U2 tests whether the CP reference voltage is greater than the CV reference voltage. If this test is affirmative, the secondary side controller U2 transitions back to CV mode in step 715. If step 710 is negative, the secondary side controller U2 divides the constant power (CP) of the constant power mode by the CP reference voltage to calculate the CP reference current (CPIref) in step 720. In the case where the CP reference current is calculated, the secondary side controller U2 checks in step 725 whether the CP reference current is greater than the constant current reference current (CC Iref) used during the constant current mode. If the CP reference current is greater than the CC reference current, the secondary side controller U2 transitions to the constant current mode in step 730. Otherwise, in step 735, the secondary side controller U2 tests whether the difference between the output current (Iout) and the CP reference current is greater than the positive threshold value Ith. If the output current is greater, then in step 740 the secondary side controller U2 decrements the variable N, whereupon control returns to step 705, causing the CP reference voltage to decrement. However, if the output current is not greater, then in step 750 the secondary side controller U2 continues to evaluate whether the difference between the output current and the CP reference current is less than the negative threshold -Ith. If the result of step 750 is positive, then in step 745 the secondary side controller U2 continues to increment the variable N, whereupon control returns to step 705, causing the CP reference voltage to increment. If the result of step 750 is negative, then control returns to step 735.

[0034] Compare Figure 4 and Figure 7 , it can be seen that the difference between the two is related to the desired constant power behavior. When transitioning from CV mode to CP mode and then from CP mode to CV mode, it can be seen that the output current must be gradually increased until it eventually reaches the CC reference current limit. Step 740 is therefore the variable N being incremented in response to the increase in output current so that the CP reference voltage is decremented, which results in the desired gradual increase in output current. In contrast, during the transition from CC mode to CP mode and finally to CV mode, the output current is gradually reduced to model the desired constant power behavior. Therefore, step 745 is the variable N being incremented in response to the decrease in output current so that the CP reference voltage is increased, which results in the desired gradual decrease in output current.

[0035] Reference again Figure 3It should be noted that the primary side controller U1 can also implement a stepped constant voltage digital emulation that simulates a constant power mode. For example, the primary side controller U1 can sense the output voltage through primary feedback only or through signaling from the secondary side controller U2 (such as through an opto-isolator). Similarly, the primary side controller U2 can sense the output current indirectly by sensing the primary winding current through a sense resistor (not shown).

[0036] Regardless of whether the digital simulation of the simulated constant power mode is controlled by the secondary side controller U2 or the primary side controller U1, this control may involve a step constant current regulation rather than a step constant voltage regulation. In the step constant current simulation of the simulated constant power mode, the CP reference current is incremented or decremented in digital steps. At each digital value of the CP reference current, the switching power converter continues to regulate the output current to be equal to the CP reference current. Based on the CP reference current, the switching power converter calculates the CP reference voltage by dividing the constant power (CP) by the CP reference current. Whether the CP reference current is then further increased or decreased depends on the error between the output voltage and the CP reference voltage.

[0037] For the implementation of digitally varying the CP reference current, Figure 8 8 shows a flow chart of calculating the CP reference voltage and CP reference current by the secondary side controller U2 when transitioning from the constant voltage mode to the constant power mode. At the transition 800 from the CV mode to the CP mode, the variable N is set to 1. In the calculation step 805, the secondary side controller U2 calculates the CP reference voltage and CP reference current by making N*ΔI equal to the constant voltage current IP1 ( Figure 2) are added to calculate the CP reference current (CP Iref), where ΔI is a current step similar to the voltage step ΔV discussed above. Due to this increment, in step 810, the secondary side controller U2 tests whether the CP reference current is greater than the CC reference current (CC Iref). If this test is affirmative, the secondary side controller U2 transitions back to CC mode in step 815. If step 810 is negative, in step 820 the secondary side controller U2 divides the constant power (CP) of the constant power mode by the CP reference current to calculate the CP reference voltage (CP Vref). In the case where the CP reference voltage is calculated, in step 825, the secondary side controller U2 checks whether the CP reference voltage is greater than the constant voltage reference voltage (CV Vref) used during the constant voltage mode. If the CP reference voltage is greater than the CV reference voltage, the secondary side controller U2 transitions to the constant voltage mode in step 830. Otherwise, in step 835, the secondary side controller U2 tests whether the difference between the output voltage (Vout) and the CP reference voltage is less than the negative threshold -Vth. If this difference is less than the negative threshold -Vth, then in step 840 the secondary side controller U2 increments the variable N, whereupon control returns to step 805, causing the CP reference current to increment. However, if the difference is greater, then in step 850 the secondary side controller U2 continues to test whether the difference between the output voltage and the CP reference voltage is greater than the positive threshold Vth. If the result of step 850 is positive, then in step 845 the secondary side controller U2 continues to decrement the variable N, whereupon control returns to step 805, causing the CP reference current to decrement. If the result of step 850 is negative, then control returns to step 835.

[0038] Referring again to step 805, it should be noted that once the secondary side controller U2 has calculated the CP reference current, the secondary side controller U2 generates a control signal such that the output current is regulated to be equal to the CP reference current during the time period when the CP reference current is neither increasing nor decreasing. In this regard, the secondary side controller U2 can perform steps 835 and 840 by integrating the voltage error (the difference between the output voltage and the CP reference voltage) over an integration period. In the event that this error changes sign (from positive to negative or from negative to positive), the integration period is reset. The integration period will therefore be the minimum length of time that the output current will be regulated relative to a given setting of the CP reference current. The end result is that the output current on the CP mode will increase or decrease in response to an increase or decrease in the CP reference current.

[0039] In the embodiment where the CP reference current is digitally varied, the transition from CC mode to CP mode is similar to Fig. 9As shown in the flowchart of . At the transition 900 from CC mode to CP mode, the variable N is set to 1. In the calculation step 905, the secondary side controller U2 calculates the CP reference current (CP Iref) by subtracting N*ΔI from the CC reference current. Since the variable N can also be decremented, in step 910, the secondary side controller U2 tests whether the CP reference current is greater than the CC reference current (CC Iref). If this test is affirmative, the secondary side controller U2 transitions back to CC mode in step 915. If step 910 is negative, the secondary side controller U2 divides the constant power (CP) of the constant power mode by the CP reference current in step 920 to calculate the CP reference voltage (CP Vref). In the case where the CP reference voltage is calculated, in step 925, the secondary side controller U2 checks whether the CP reference voltage is greater than the constant voltage reference voltage (CVVref) used during the constant voltage mode. If the CP reference voltage is greater than the CV reference voltage, the secondary side controller U2 transitions to the constant voltage mode in step 930. Otherwise, in step 935, the secondary side controller U2 tests whether the difference between the output voltage (Vout) and the CP reference voltage is greater than the positive threshold Vth. If this difference is greater than the threshold Vth, then in step 940 the secondary side controller U2 increments the variable N, whereupon control returns to step 905, causing the CP reference current to be decremented. However, if the difference is less than the positive threshold Vth, then in step 950 the secondary side controller U2 continues to test whether the difference between the output voltage and the CP reference voltage is less than the negative threshold Vth. If the result of step 950 is positive, then in step 945 the secondary side controller U2 continues to decrement the variable N, whereupon control returns to step 905, causing the CP reference current to be incremented. If the result of step 950 is negative, then control returns to step 935.

[0040] exist Fig.10 . A plurality of exemplary digitally varied CP reference currents and corresponding CP reference voltages are shown in FIG. The magnitude of the exemplary CP reference currents rises from the CP reference current Iref1. Thus, the second CP reference current Iref2 is ΔI greater than Iref1. Similarly, the third CP reference current Iref3 is ΔI greater than Vref3, the fourth CP reference current Iref4 is ΔI greater than Iref3, and the fifth CP reference current Iref5 is ΔI less than Iref4. The corresponding CP reference voltages are designated as Vref1, Vref2, Vref3, Vref4, and Vref5, respectively. The ideal analog CP regulation curve cuts across each Vref, Iref pair.

[0041] This ideal simulated CP regulation curve is advantageously expressed by comparing it to Fig.11A series of exemplary CP reference currents Iref1 to Iref5 shown in [reference] regulate the output current for approximation. When a given CP reference current is selected, the output current is regulated in the CC mode to be equal to the CP reference current. However, during this constant current regulation, the range of the output voltage will be from not less than a negative threshold amount Vth lower than the corresponding CP reference voltage to not greater than a positive threshold amount Vth higher than the corresponding CP reference voltage. For example, consider the constant current regulation where the output current is equal to Iref2. The corresponding CP reference voltage is Vref2. Thus, the output current is only equal to Vref2, and the output voltage error satisfies the inequality -Vth < output voltage error < Vth. If the output voltage error is less than -Vth, the output current regulation will change to be equal to Iref1. If the output voltage error is greater than Vth, the output current regulation will change to be equal to Iref3. As discussed regarding the threshold Ith, the magnitude of the threshold voltage Vth is a design choice.

[0042] Referring again to Figure 4 , it should be noted that after the transition from the constant voltage mode to the constant power mode, the initial value of the constant power reference voltage can be expressed as a first constant voltage, which is a threshold voltage increment less than the maximum voltage value of the output voltage during the constant voltage mode. The corresponding constant power reference current can be expressed as a first constant power reference current. While the output voltage is regulated to be equal to the first constant voltage, the output current can vary within a first current range extending from -ΔI below the constant power reference current to ΔI above the constant power reference current. If the output current is greater than the first current range, the output voltage regulation changes to be equal to a second constant voltage, which is a threshold voltage increment less than the first constant voltage. In this way, the output voltage regulation can continue to change to a third constant voltage, and so on. The threshold voltage increments from one constant voltage to another can be unequal, such that non-linear increments (or decrements) can be utilized in alternative embodiments.

[0043] Referring again to Figure 8, it should be noted that the initial value of the constant power reference current after the transition from the constant voltage mode to the constant power mode can be expressed as a first constant current, which is a threshold current increment greater than IP1. The corresponding constant power reference voltage can be expressed as a first constant power reference voltage. Although the output current is adjusted to be equal to the first constant current, the output voltage can vary within a first voltage range extending from -ΔV below the constant power reference current to ΔV above the constant power reference voltage. If the output voltage is less than the first voltage range, the output current regulation is transformed to be equal to the second constant current, which is a threshold current increment greater than the first constant current. In this way, the output current regulation can continue to change to a third constant current, and so on. The threshold current increment from one constant current to another constant current can be unequal, so that nonlinear increment (or decrement) can be utilized in alternative embodiments.

[0044] As some skilled in the art will now appreciate and depending on the particular application at hand, many modifications, substitutions and changes may be made to the materials, devices, configurations and methods of use of the apparatus of the present disclosure without departing from the spirit and scope of the present disclosure. In view of this, the scope of the present disclosure should not be limited to the scope of the specific embodiments illustrated and described herein, as the embodiments are merely by way of some examples thereof, but on the contrary, should be fully commensurate with the scope of the claims appended hereto and their functional equivalents.

Claims

1. A switching power converter, comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is coupled to an output node for outputting a voltage; a power switch connected in series with the primary winding; and A controller, the controller being configured to: controlling cycling of the power switch during a constant voltage mode to regulate the output voltage equal to a maximum voltage; transitioning from the constant voltage mode to a constant power mode in response to the output current being greater than a maximum current of the constant voltage mode; When the output current of the switching power converter is within a first current range, controlling the cycle of the power switch to regulate the output voltage to be equal to a first constant voltage, wherein the first constant voltage is less than the maximum voltage by a discrete voltage step, and A first constant power reference current is calculated by dividing the constant power of the constant power mode by the first constant voltage, wherein the first current range includes the first constant power reference current.

2. The switching power converter of claim 1, wherein: The controller is a secondary side controller coupled to the output node.

3. The switching power converter of claim 1, wherein: The controller is a primary side controller coupled to the power switch.

4. The switching power converter of claim 1, wherein: The controller is further configured to: decreasing the first constant voltage by the discrete voltage steps to provide a second constant voltage in response to the output current being greater than a maximum current of the first current range; determining a second constant power reference current by dividing the constant power by the second constant voltage; and When the output current of the switching power converter is within a second current range that includes the second constant power reference current, the cycling of the power switch is controlled to regulate the output voltage to be equal to the second constant voltage.

5. The switching power converter of claim 4, wherein: The controller is further configured to: decreasing the second constant voltage by the discrete voltage steps to provide a third constant voltage in response to the output current being greater than a maximum current of the second current range; determining a third constant power reference current by dividing the constant power by the third constant voltage; and When the output current of the switching power converter is within a third current range including the third constant power reference current, the cycling of the power switch is controlled to regulate the output voltage to be equal to the third constant voltage.

6. The switching power converter of claim 4, wherein: The controller is further configured to: In response to the output current being less than a minimum current of the second current range, increasing the second constant voltage by the discrete voltage steps to provide a third constant voltage; determining a third constant power reference current by dividing the constant power by the third constant voltage; and When the output current of the switching power converter is within a third current range including the third constant power reference current, the cycling of the power switch is controlled to regulate the output voltage to be equal to the third constant voltage.

7. The switching power converter of claim 1, wherein: The controller is further configured to: transitioning to a constant current mode in response to the output current exceeding a maximum current; and Cycling of the power switch is controlled during the constant current mode to regulate the output current equal to the maximum current.

8. A switching power converter comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is coupled to an output node for outputting a voltage; a power switch, the power switch being connected in series with the primary winding; a controller configured to control cycling of the power switch such that an output current of the switching power converter during a constant current mode is equal to a constant current; transitioning from the constant current mode to a constant power mode in response to the output voltage being greater than a maximum voltage of the constant current mode; When the output current of the switching power converter is within a first current range, controlling the cycle of the power switch to regulate the output voltage to be equal to a first constant voltage, wherein the first constant voltage is greater than the maximum voltage by a discrete voltage step, and A first constant power reference current is calculated by dividing the constant power of the constant power mode by the first constant voltage, wherein the first current range includes the first constant power reference current.

9. The switching power converter of claim 8, wherein: The controller is a secondary side controller coupled to the output node.

10. The switching power converter of claim 8, wherein: The controller is a primary side controller coupled to the power switch.

11. The switching power converter of claim 8, wherein: The controller is further configured to: In response to the output current being less than a minimum current of the first current range, increasing the first constant voltage by the discrete voltage steps to provide a second constant voltage; determining a second constant power reference current by dividing the constant power by the second constant voltage; and When the output current of the switching power converter is within a second current range that includes the second constant power reference current, the cycling of the power switch is controlled to regulate the output voltage to be equal to the second constant voltage.

12. The switching power converter of claim 11, wherein: The controller is further configured to: In response to the output current being less than a minimum current of the second current range, increasing the second constant voltage by the discrete voltage steps to provide a third constant voltage; determining a third constant power reference current by dividing the constant power by the third constant voltage; and When the output current of the switching power converter is within a third current range including the third constant power reference current, the cycling of the power switch is controlled to regulate the output voltage to be equal to the third constant voltage.

13. The switching power converter of claim 11, wherein: The controller is further configured to: decreasing the second constant voltage by the discrete voltage steps to provide a third constant voltage in response to the output current being greater than a maximum current of the second current range; determining a third constant power reference current by dividing the constant power by the third constant voltage; and When the output current of the switching power converter is within a third current range including the third constant power reference current, the cycling of the power switch is controlled to regulate the output voltage to be equal to the third constant voltage.

14. The switching power converter of claim 8, wherein: The controller is further configured to: transitioning to a constant voltage mode in response to the output voltage exceeding a maximum voltage; and Cycling of the power switch is controlled during the constant voltage mode to regulate the output voltage equal to the maximum voltage.

15. A switching power converter comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is coupled to an output node for outputting a voltage; a power switch, the power switch being connected in series with the primary winding; a controller configured to control cycling of the power switch during a constant voltage mode to regulate the output voltage to be equal to a maximum voltage, wherein the controller is further configured to: transitioning from the constant voltage mode to a constant power mode in response to the output current being greater than a maximum current of the constant voltage mode; When the output voltage of the switching power converter is within a first voltage range, controlling the cycle of the power switch to regulate the output current to be equal to a first constant current, wherein the first constant current is greater than the maximum current by a discrete current step, and A first constant power reference voltage is calculated by dividing the constant power of the constant power mode by the first constant current, wherein the first voltage range includes the first constant power reference voltage.

16. The switching power converter of claim 15, wherein: The controller is further configured to: In response to the output voltage being less than a minimum voltage of the first voltage range, incrementing the first constant current by the discrete current steps to provide a second constant current; determining a second constant power reference voltage by dividing the constant power by the second constant current; and When the output voltage is within a second voltage range including the second constant power reference voltage, the cycling of the power switch is controlled to regulate the output current to be equal to the second constant current.

17. The switching power converter of claim 15, wherein: The controller is further configured to: transitioning to a constant current mode in response to the output current being greater than a maximum constant current; and The output current is regulated to be equal to the maximum constant current during the constant current mode.

18. A switching power converter comprising: a transformer having a primary winding and a secondary winding, wherein the secondary winding is coupled to an output node for outputting a voltage; a power switch connected in series with the primary winding; and A controller, the controller being configured to: controlling the cycling of the power switch during a constant current mode to regulate the output current of the switching power converter to be equal to a maximum constant current; transitioning from the constant current mode to a constant power mode in response to the output voltage being greater than a maximum voltage of the constant current mode; When the output voltage of the switching power converter is within a first voltage range, controlling the cycle of the power switch to regulate the output current to be equal to a first constant current, wherein the first constant current is less than the maximum constant current by a discrete current step, and A first constant power reference voltage is calculated by dividing the constant power of the constant power mode by the first constant current, wherein the first voltage range includes the first constant power reference voltage.

19. The switching power converter of claim 18, wherein: The controller is further configured to: In response to the output voltage being greater than a maximum voltage of the first voltage range, decreasing the first constant current by the discrete current steps to provide a second constant current; determining a second constant power reference voltage by dividing the constant power by the second constant current; and When the output voltage is within a second voltage range including the second constant power reference voltage, the cycling of the power switch is controlled to regulate the output current to be equal to the second constant current.

20. The switching power converter of claim 18, wherein: The controller is further configured to: transitioning to a constant voltage mode in response to the output voltage being greater than a maximum constant voltage; and The output current is regulated to be equal to the maximum constant voltage during the constant voltage mode.

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