专利汇可以提供Primary-side control of a switching power converter with feed forward delay compensation专利检索,专利查询,专利分析的服务。并且An electronic system includes controller to control a switching power converter to provide power to a load. To control the amount of power provided to the load, in at least one embodiment, the controller senses a current value representing a current in the switching power converter and detects when the current value reaches a target peak value. However, due to delays in the controller and/or the switching power converter, the detected target peak value will not be the actual current peak value generated by the switching power converter. In at least one embodiment, the controller adjusts the detected target peak value with a post-detection delay compensation factor to generate a delay compensated current value that more accurately represents an actual peak current value associated with the current in the switching power converter.,下面是Primary-side control of a switching power converter with feed forward delay compensation专利的具体信息内容。
What is claimed is:
This application claims the benefit under 35 U.S.C. §119(e) and 37 C.F.R. §1.78 of U.S. Provisional Application No. 61/493,104, filed Jun. 3, 2011, and entitled “Peak Current Compensation for Better Line Regulation,” which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates in general to the field of electronics, and more specifically to a method and system for exercising primary-side control of a switching power converter with feed-forward delay compensation.
2. Description of the Related Art
Many electronic systems utilize switching power converters to efficiently convert power from one source into power useable by a device (referred to herein as a “load”). For example, power companies often provide alternating current (AC) power at specific voltages within a specific frequency range. However, many loads utilize power at a different voltage and/or frequency than the supplied power. For example, some loads, such as light emitting diode (LED) based lamps operate from a direct current (DC). “DC current” is also referred to as “constant current”. “Constant” current does not mean that the current cannot change over time. The DC value of the constant current can change to another DC value. Additionally, a constant current may have noise or other minor fluctuations that cause the DC value of the current to fluctuate. “Constant current devices” have a steady state output that depends upon the DC value of the current supplied to the devices.
LEDs are becoming particularly attractive as main stream light sources in part because of energy savings through high efficiency light output, long life, and environmental incentives such as the reduction of mercury. LEDs are semiconductor devices and are best driven by direct current. The brightness of the LED varies in direct proportion to the DC current supplied to the LED. Thus, increasing current supplied to an LED increases the brightness of the LED and decreasing current supplied to the LED dims the LED.
The controller 106 provides a pulse width modulated (PWM) control signal CS0 to current control switch 108 in a flyback-type, switching power converter 110 to control the conversion of input voltage VIN into a primary-side voltage VP and secondary voltage VS. The switch 108 is, for example, a field effect transistor (FET). When control signal CS0 causes switch 108 to conduct, a primary-side current iPRIMARY flows into a primary coil 114 of transformer 116 to energize the primary coil 114. When control signal CS0 opens switch 112, primary coil 114 deenergizes. Energizing and deenergizing the primary coil 114 induces a secondary voltage VS across a secondary coil 118 of transformer 116. Primary voltage VP is N times the secondary voltage VS, i.e. VP=N·VS, and “N” is a ratio of coil turns in the primary coil 114 to the coil turns in the secondary coil 118. The secondary-side current iSECONDARY is a direct function of the secondary voltage VS and the impedance of diode 120, capacitor 122, and load 104. Diode 120 allows the secondary-side current iSECONDARY to flow in one direction. The secondary-side current iSECONDARY charges capacitor 120, and capacitor 120 maintains an approximately DC voltage VLOAD across load 104. Thus, secondary-side current iSECONDARY is a DC current.
The load 104 has a certain power demand, and the controller 106 generates the switch signal CS0 in an attempt to cause the switching power converter 110 to meet the power demand of the load 104. Ideally, the power PPRIMARY provided by the primary-side of the switching power converter 110 equals the power PLOAD that is provided to the load 104. However, power losses due to non-idealities in the electronic system 100 result in the power PPRIMARY provided by the primary-side being greater than the power PLOAD delivered to the load 104, i.e. PPRIMARY>PLOAD. To meet the power demand of the load 104, controller 106 utilizes feedback to determine the amount of power actually delivered to the load 104. The controller 106 attempts to generate the control signal CS0 to control the primary-side current iPRIMARY so that the power PPRIMARY meets the power demand of the load 104.
Controller 106 utilizes a feedback control loop to control the power PLOAD delivered to the load 104. To control the power PLOAD, the controller 106 controls the control signal CS0 and thereby controls the primary-side current iPRIMARY. Controlling the primary-side current iPRIMARY controls the primary-side power PPRIMARY provided by the primary-side of the switching power converter 110. The controller 106 adjusts the primary-side current iPRIMARY so that the primary-side power PPRIMARY is sufficient to transfer enough power PLOAD to the load 104 to meet the power demand of the load 104.
To generate the primary-side power PPRIMARY, controller 106 utilizes either secondary-side, feedback-based control via a secondary-side feedback path 124 or primary-side control via sense resistor 126. The secondary-side, feedback path 124 is shown with a ‘dashed’ line to indicate use in the alternative to primary-side feedback. For secondary-side, feedback-based control, the controller 106 senses the secondary current iSECONDARY via the signal iS_SENSE. The secondary-side feedback path 124 generally includes components, such as an opto-isolator or optocoupler, that provide electrical isolation between the controller 106 and the secondary-side of the transformer 110. Since the controller 106 knows the primary-side voltage VP and the turns ratio N, the controller 106 also knows the secondary side voltage VS and knows the secondary-side current iSECONDARY from the feedback signal iS_SENSE. Thus, the controller 106 can directly determine the power PLOAD delivered to the load 104. The controller 106 generates the control signal CS0 to generate the primary-side current iPRIMARY to meet the power demand of the load 104 so that the power demand of the load equals the power provided to the load 104.
The actual peak value of the primary-side current iPRIMARY is directly proportional to the amount of power delivered to the load 104. Thus, for primary-side only control, determination of the actual peak value iPK of the primary-side current iPRIMARY dominates the accuracy of the determination of the amount of power delivered to the load 104. The foregoing statement is especially the case during low power applications since the range of the primary-side current iPRIMARY is reduced. The switch 108 does not turn OFF instantaneously upon detection of a target peak value iPK of the primary-side current iPRIMARY by the controller 106. Once the controller 106 senses that the primary-side peak current iPK_SENSE equals a target peak value iPK and turns switch 108 OFF, the actual primary-side current iPRIMARY has already overshot the sensed peak current iPK_SENSE.
To compensate for the delay in turning switch 108 OFF, the electronic system 100 introduces a feed forward, scaled voltage compensation factor
to boost the current conducted by the sense resistor 126. RSENSE is the resistance value of the sense resistor 126, R128 is the resistance value of the resistor 128, R130 is the resistance value of the resistor 130. Boosting the current across the sense resistor 126 prior to the controller 106 sensing the primary-side current causes the controller 106 to determine a higher peak current iPK_SENSE that can compensate for the delay in turning off the switch 108. Equation [1] represents the value of the estimated peak current iPK_EST using the fixed, feed forward compensation factor:
iPK_EST is the estimated peak value of the primary current iPRIMARY, and iPK_SENSE is the sensed peak value of the primary-side current. As previously stated, RSENSE is the resistance value of the sense resistor 126, R128 is the resistance value of the resistor 128, R130 is the resistance value of the resistor 130, L is the inductance value of the primary-side coil 114, and tDELAY, as defined by Equation [2], is the delay due to the switch 108 OFF. Since the compensation factor
tracks well with the input voltage VIN, for a given inductance value L of the primary-side coil 114, the compensation factor
effectively cancels out delays in turning the switch 108 OFF.
However, secondary-side sensing requires additional, potentially relatively expensive components. Using primary-side sensing and applying the compensation factor
which equals
works for a particular inductance value L of the primary-side coil 114. However, the inductance value L of the primary-side coil 114 can vary from transformer to transformer by, for example, at least +/−10%. Thus, if the inductance value L used by the controller 106 differs from the actual inductance value L for the primary-side coil 114, then the estimation of the peak value of the primary-side current iPRIMARY can result in errors providing power to the load 104. Additionally, altering the primary-side current value across the sense resistor RSENSE prior to sensing a representative value of the primary-side current iPRIMARY utilizes external components, which increase the cost of the electronic system 100.
In one embodiment of the present invention, a method includes sensing a value of a current in a switching power converter during a switching cycle of the switching power converter. The method also includes detecting a target peak value of the current value and adjusting the detected target peak value of the current value with a post-detection delay compensation factor to generate a delay compensated current value. The method further includes determining an amount of current provided to a load coupled to the switching power converter based on the delay compensated current value and generating a switch control signal to control the value of the current in the switching power converter to provide energy to the load in accordance with the delay compensated current value.
In another embodiment of the present invention, an apparatus includes a controller a controller having an input to sense a value of a current in a switching power converter during a switching cycle of the switching power converter. The controller is capable to detect a target peak value of the current value and adjust the detected target peak value of the current value with a post-detection delay compensation factor to generate a delay compensated current value. The controller is further capable to determine an amount of current provided to a load coupled to the switching power converter based on the delay compensated current value and generate a switch control signal to control the value of the current in the switching power converter to provide energy to the load in accordance with the delay compensated current value.
In a further embodiment of the present invention, an apparatus includes a switching power converter, wherein the switching power converter includes a transformer having a primary-side and a secondary-side. The apparatus also includes a controller having an input to sense a value of a current in a switching power converter during a switching cycle of the switching power converter. The controller is capable to detect a target peak value of the current value and adjust the detected target peak value of the current value with a post-detection delay compensation factor to generate a delay compensated current value. The controller is further capable to determine an amount of current provided to a load coupled to the switching power converter based on the delay compensated current value and generate a switch control signal to control the value of the current in the switching power converter to provide energy to the load in accordance with the delay compensated current value. The apparatus further includes a load coupled to the secondary-side of the transformer of the switching power converter.
The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.
An electronic system includes a controller to control a switching power converter to provide power to a load. To control the amount of power provided to the load, in at least one embodiment, the controller senses a current value representing a current in the switching power converter and detects when the current value reaches a target peak value. However, due to delays in the controller and/or the switching power converter, the detected target peak value will not be the actual current peak value generated by the switching power converter. In at least one embodiment, the controller adjusts the detected target peak value with a post-detection delay compensation factor to generate a delay compensated current value that more accurately represents an actual peak current value associated with the current in the switching power converter. In at least one embodiment, the controller utilizes the delay compensated current value to determine an amount of current provided to the load and to determine a subsequent target peak current value.
one embodiment, the post-detection delay compensation factor models an extrapolation of the value of the current that changes as a result of delays in the controller and/or the switching power converter. Exemplary delays occur between detecting the approximate peak value of the current value by the controller and discontinuing the current by the switching power converter. In at least one embodiment, the current value increases linearly as delay increases and, thus, is modeled using a linear extrapolation. However, the particular model is a matter of design choice and depends on the characteristic effects of delays on the current value. In at least one embodiment, the post-detection delay compensation factor represents a dynamically determined, approximate delay between the detected peak value of the current and an actual peak value of the current.
In at least one embodiment, the controller 202 targets a particular output current iOUT_TARGET to provide to the load 212. The target output current iOUT_TARGET represents the amount of charge provided to the load 212 during a period of time. In at least one embodiment, the target output current iOUT_TARGET is a target amount of charge provided to the load 212 over a cyclic period, (for example, “TT” in
Delays occur between the time the sensor 217 detects that the current value equals the target peak current value iPK_TARGET and when the switch 208 turns OFF. The delays can arise from any number of sources such as:
During the delays, the input current iIN continues to increase. Thus, the delays result in the switching power converter 204 providing an additional amount of current iOUT to the load 212 after the sensor 217 detects that the current value CV has reached the target peak current value iPK_TARGET(n). The sensor 217 also provides the peak reached signal PKR to the delay compensator 216. To compensate for the delays, in operation 308, the delay compensator 216 receives the peak reached signal PKR and adjusts the detected target peak current value iPK_TARGET(n) with a delay compensation factor DELAY_COMP to generate an estimated peak current iPK_EST. In at least one embodiment, the adjustment of the target peak current value iPK_TARGET(n) by the delay compensation factor DELAY_COMP models the increase in the input current iIN that occurs due to the delays. The particular model depends on the characteristics of the input current iIN and a desired degree of accuracy in estimating the actual peak value of the input current iIN. In at least one embodiment, the input current iIN increases linearly over time, and the adjustment of the target peak current value iPK_TARGET (n) by the delay compensation factor DELAY_COMP represents a linear extrapolation of the input current iIN that occurs during the delays.
Once the delay compensator 216 determines the estimated peak current iPK_EST, and, based on the estimated peak current iPK_EST, operation 310 determines the amount of output current iOUT provided to the load 212. In at least one embodiment, the particular quantification of the value of the output current iOUT provided to the load 212 is a matter of design choice. In at least one embodiment, operation 310 quantifies the current iOUT provided to the load 212 as an amount of charge provided to the load 212 during a period TT of the control signal CS1.
Operation 312 sets the next target peak current value iPK_TARGET(n+1) to minimize a difference between the amount of estimated actual output current iOUT provided to the load 212 and the target output current iOUT_TARGET. In at least one embodiment, operation 312 sets the value of the target peak current value iPK_TARGET(n+1) by responding to any difference between the output current iOUT provided to the load 212, as determined using estimated peak current iPK_EST, and the target output current iOUT_TARGET for provision to the load 212. If the estimated actual output current iOUT is greater than the target output current iOUT _TARGET, then operation 312 reduces the value of the target peak current value iPK_TARGET(n+1). If the estimated actual output current iOUT is less than the target output current iOUT_TARGET, then operation 312 increases the value of the target peak current value iPK_TARGET(n+1). In at least one embodiment, operation 312 adjusts the target peak current value iPK_TARGET(n+1) every cycle of the control signal CS1 to minimize the difference between the estimated output current iOUT provided to the load 212 and the target output current iOUT_TARGET. The particular convergence algorithm used to select the values of each subsequent target peak current value iPK_TARGET(n+1) so that the output current iOUT converges to the target output current iOUT_TARGET is a matter of design choice and can be any custom or well-known convergence algorithm. The delay compensator 216 provides the target peak current value iPK_TARGET(n+1) to the sensor 217. The target peak current value iPK_TARGET(n+1) then becomes the current target peak current value iPTARGET(n) for the next cycle of control process 300.
In operation 314, the switch control signal generator 218 generates the switch control signal CS1 to turn the switch 208 ON. The particular time at which the switch control signal generator 218 turns the switch 208 ON is a matter of design choice and, in at least one embodiment, depends on the operational mode of the switching power converter 204. In at least one embodiment, the switching power converter 204 operates in quasi-resonant mode and/or discontinuous conduction mode as described, for example, in U.S. patent application Ser. No. 13/486,625, filed Jun. 1, 2012, entitled “Control Data Determination From Primary-Side Sensing of a Secondary-Side Voltage in a Switching Power Converter”, assignee Cirrus Logic, Inc., and inventors Robert T. Grisamore and Zhaohui He, which is hereby incorporated by reference in its entirety (referred to herein as “Grisamore-He”).
In at least one embodiment, the electronic system 400 operates in accordance with an embodiment of the exemplary control process 300. During the pulse 502, the primary-side current iPRIMARY flows through the switch 406 and develops a voltage across sense resistor 417. In operation 302, the comparator 418 receives the current sense signal iCS, which represents one embodiment of the current value CV in
The delay compensator 422 conceptually includes two functional units, the secondary output current and peak primary current estimator with post-target current detection delay compensation 423 (referred to as the “currents estimator 423”) and the peak target current generator 425. In operation 308, the currents estimator 423 adjusts the target peak current value iPK_TARGET(n) by a delay compensation factor DELAY_COMP to generate an estimated peak current iPK_EST in order to determine the amount of secondary-side current iSECONDARY delivered to the load 208. As previously discussed, various delays occur between the time when the comparator 418 detects that the current sense signal iCS reaches the target peak current value iPK_TARGET(n) and when the FET 406 stops conducting the primary-side current iPRIMARY.
VIN is the input voltage, L is the inductance value of the primary-side coil 408, and a dT_cscmp_dly is the detection delay between when the comparator 418 actually detects that the current sense voltage VCS equals the target peak current value iPTARGET(n).
A further delay is a propagation delay dT_logic_dly from an output of the comparator 418 to the transition of the control signal CS2 at the gate of the FET 406. The propagation delay dT_logic_dly is due to, for example, delays in inverters, flip-flops, level shifters, etc., which allow the primary-side current to continue to linearly increase. In at least one embodiment, Equation [4] represents change in the peak value ΔiPK of the primary-side current iPRIMARY due to the propagation delay dT_logic_dly:
VIN is the input voltage, L is the inductance value of the primary-side coil 408, and a dT_logic_dly is the propagation delay from an output of the comparator 418 to the transition of the control signal CS2 at the gate of the FET 406.
Another delay is the delay in turning OFF the FET 406. Turning the FET 406 involves, for example, removing charge from the gate of the FET 406 and depleting charge in the conducting channel of the FET 406. In at least one embodiment, Equation [5] represents change in the peak value ΔiPK of the primary-side current iPRIMARY due to the turn OFF delay of FET 406:
VIN is the input voltage, L is the inductance value of the primary-side coil 408, and a dT_gdrv_dly is the delay in turning the FET 406 OFF.
By summing Equations [3], [4], [5], Equation [6] represents the estimated peak current iPK_EST of the primary-side current iPRIMARY.
dT_dly_total=dT_cscmp_dly+dT_logic_dly+dT_gdrv_dly is the estimated delay duration of the primary-side current iPRIMARY during a cycle of the control signal CS2. The quantity
represents an embodiment of a delay compensation factor DELAY_COMP. T1_meas is a measured value of T1 since the actual value of T1 is unknown. The measured value also incurs a delay error. However, dT_dly_total is much smaller than the actual T1, so the delay due to measuring T1 is not included in the delay compensation factor. In at least one embodiment, the value of the delay compensation factor DELAY_COMP equal to
is empirically or analytically predetermined based on knowledge of the components used on the electronic system 400 and is stored in the memory 424. The delay compensation factor DELAY_COMP is used by the currents estimator 423 to determine the estimated peak current iPK_EST after detection of the target peak value of the primary-side current. In at least one embodiment, this “post-detection” delay compensation factor DELAY_COMP reduces external components and is flexible to represent multiple delay types. Additionally, in at least one embodiment, the delay compensation factor DELAY_COMP is not sensitive to variations in inductance values of the primary-side coil 408.
In at least one other embodiment, the value of the delay compensation factor DELAY_COMP is measured as dT_meas by measuring changes in the drain to source VDS voltage of FET 406 as shown in waveform 602. However, this measurement also incurs a delay that is, in at least one embodiment, accounted for by adding dT_cscmp_dly to dT_meas.
In operation 310, in accordance with Equation [7], the currents estimator 423 uses the estimated peak current iPK_EST of Equation [6] to determine the secondary current iSECONDARY delivered to the load 208 during the period TT of the control signal CS2. The area beneath the secondary-side current iSECONDARY represents the amount of charge delivered to the load 208. Equation [7] represents the amount of charge provided to the load 208 during the period TT of the control signal CS2;
Q is the charge provided to the load 208, TT is the period of the control signal CS2, iPK_EST is the estimated peak value of the primary-side current iPRIMARY as adjusted by the delay compensation factor DELAY_COMP, and T2 is the duration of the secondary-side current iSECONDARY from the end of the period T1 until the secondary-side current iSECONDARY decays to zero. Grisamore-He describes an exemplary system and method to determine the values of T2 and TT.
The currents estimator 423 provides a peak primary-side current target adjustment signal TARG_ADJ to the peak target current generator 425. In operation 312, the delay compensator 422 sets the next value of the target peak current value iPTARGET(n+1) based on how the amount of secondary-side current iSECONDARY provided to the load 208 as determined by Equation [7] compares to the targeted amount of secondary-side current iSECONDARY_TARGET. The peak target current generator 425 increases the target peak current value iPK_TARGET(n+1) if the comparison indicates a desired increase in the amount of energy provided to load 208 and decreases the target peak current value iPK_TARGET(n+1) if the comparison indicates a desired decrease in the amount of current provided to the load 208. The peak target current generator 425 provides the next target peak current value iPK_TARGET(n+1) to a digital-to-analog converter 426 to provide an analog version of the target peak current value iPK_TARGET(n+1) to the comparator 418 for the next cycle of process 300. Thus, the target peak current value iPK_TARGET(n+1) then becomes the current target peak current value iPK_TARGET for use by the comparator 418. The peak target current generator 425 also provides the next target peak current value iPK_TARGET(n−1) to the currents estimator 423 for use in conjunction with Equation [6].
Thus, an electronic system includes controller to control a switching power converter to provide power to a load. In at least one embodiment, the controller adjusts a detected target peak value with a post-detection delay compensation factor to generate a delay compensated current value that more accurately represents an actual peak current value associated with the current in the switching power converter. In at least one embodiment, the controller utilizes the delay compensated current value to determine an amount of current provided to the load and to determine a subsequent target peak current value.
Although embodiments have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.
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