Power converter with dual injection control and control circuit thereof

Abstract

The invention discloses a control circuit and a power converter thereof, the control circuit is used for the power converter, the power converter is provided with an input voltage and an output voltage, and the control circuit comprises a ramp generator, an operational circuit and a comparator. The ramp generator is used for receiving the input voltage or the output voltage to generate a ramp voltage. The operation circuit is used for generating a second error voltage according to a first error voltage and an operation result of the input voltage, and the first error voltage is generated by the output voltage. The comparator is coupled to the ramp generator and the operational circuit and is used for comparing the second error voltage with the ramp voltage to generate a control signal.

Description

TECHNICAL FIELD

[0001] The present invention relates to a power converter, and more particularly to a power converter with double injection control. BACKGROUND

[0002] Power converters are widely used in various electronic systems to provide a stable voltage supply. Power converters generally include two types: switching capacitor and switching inductor, to meet different requirements, such as power efficiency, stability, or for different load sizes. A hybrid converter is a type of power converter, whose power stage employs an inductor plus a capacitor. Since the hybrid converter has a flying capacitor, a smaller inductor can be used to achieve the same output power, thereby improving the power density and reducing the circuit cost.

[0003] Generally, the hybrid converter employs a voltage mode control technique, which sets up a feedback circuit to generate a control signal for switching the internal switching components of the power converter to generate a desired output voltage level. Voltage mode control usually faces the problem of line transition, that is, when the input voltage changes, the output voltage can overshoot or undershoot. In view of this, the prior art needs to be improved. SUMMARY

[0004] Therefore, the main purpose of the present invention is to provide a new power converter using double injection technology and its control circuit to solve the line transition problem of the power converter.

[0005] One embodiment of the present invention discloses a control circuit for a power converter having an input voltage and an output voltage. The control circuit includes a ramp generator, an arithmetic circuit, and a comparator. The ramp generator is configured to receive the input voltage or the output voltage to generate a ramp voltage. The arithmetic circuit is configured to generate a second error voltage based on a first error voltage and a calculation result of the input voltage, wherein the first error voltage is generated from the output voltage. The comparator is coupled to the ramp generator and the arithmetic circuit and is configured to compare the second error voltage with the ramp voltage to generate a control signal.

[0006] Another embodiment of the present invention discloses a power converter comprising a power stage and a control circuit. The power stage is configured to receive an input voltage to generate an output voltage. The control circuit is coupled to the power stage and comprises a ramp generator, an operational circuit, and a comparator. The ramp generator is configured to receive the input voltage or the output voltage to generate a ramp voltage. The operational circuit is configured to generate a second error voltage based on a first error voltage and an operational result of the input voltage, wherein the first error voltage is generated from the output voltage. The comparator is coupled to the ramp generator and the operational circuit and is configured to compare the second error voltage with the ramp voltage to generate a control signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram of a power converter.

[0008] Figure 2A The line conversion problems associated with voltage mode control are shown.

[0009] Figure 2B shows that the height of the ramp voltage increases as the input voltage rises.

[0010] Figure 2C Correcting or adjusting the error voltage in a double injection scheme is shown.

[0011] Figure 3 FIG. 1 is a schematic diagram of a power converter according to an embodiment of the present invention.

[0012] Figure 4 Schematic diagram of a detailed implementation of the control circuit according to an embodiment of the present invention.

[0013] Figure 5 Waveform diagram showing the comparison between the dual injection control proposed in the present invention and the conventional voltage mode control for a power converter.

[0014] Figure 6 FIG. 4 is a schematic diagram of a detailed implementation of a power converter according to an embodiment of the present invention.

[0015] Figure 7 FIG. 1 is a schematic diagram of a hybrid step-down converter for which the control circuit of the present embodiment is applied.

[0016] Wherein the reference numerals are explained as follows:

[0017] 10, 30 power converter

[0018] 100, 300, 700 power stage

[0019] V IN input voltage

[0020] V OUT output voltage

[0021] 102, 302 error amplifier

[0022] 104, 402 ramp generator

[0023] 106, 406 comparator

[0024] 108, 308 processing circuit

[0025] V REF reference voltage

[0026] V EA error voltage

[0027] V RAMP ramp voltage

[0028] V C control signal

[0029] V PWM , V PWM1 , V PWM2 , V PWM3 pulse width modulation signal

[0030] V IN1 , V IN2 voltage level

[0031] ΔV IN , ΔV EA , ΔV EA2 voltage difference

[0032] V EA2 corrected error voltage

[0033] 305, 705 control circuit

[0034] 404 arithmetic circuit

[0035] C fly capacitance

[0036] LS inductor

[0037] SW1-SW3 switchers

[0038] R FB1 , R FB2 voltage dividing resistor

[0039] 602 compensation device

[0040] 612 soft start circuit

[0041] 614 dead time control circuit

[0042] 616 driving device

[0043] 70 hybrid buck converter DETAILED DESCRIPTION

[0044] Figure 1 is a schematic diagram of a power converter 10. The power converter 10 includes a power stage 100, which can be composed of a power component and a plurality of switchers, for receiving an input voltage Vin IN to generate an output voltage Vout OUT . Depending on the type of the power converter 10, which can be a switching capacitor or a switching inductor, the power component can be a capacitor or an inductor. To implement a hybrid converter, the power stage 100 can be provided with a plurality of power components, which include both capacitors and inductors.

[0045] To control the power converter 10 to generate a stable output voltage Vout OUT , the power converter 10 can employ a voltage mode control scheme through a feedback circuit, which includes an error amplifier 102, a ramp generator 104, a comparator 106 and a processing circuit 108. The error amplifier 102 can receive the output voltage Vout OUT and a reference voltage Vref REF to generate an error voltage Verr EA . With a well-designed reference voltage Vref REF , the output voltage Vout OUT can be maintained at a desired level. The ramp generator 104 can generate a ramp voltage Vramp RAMP and provide the ramp voltage Vramp RAMP to the comparator 106. The comparator 106 can compare the error voltage Verr EA with the ramp voltage Vramp RAMP to generate a control signal Vctrl C , which is transmitted to the processing circuit 108 for reception. According to the control signal VctrlC The processing circuit 108 can generate one or more pulse width modulation (PWM) signals V PWM to control the switching of the switches in the power stage 100 to adjust the output voltage level of the power converter 10. In some embodiments, the processing circuit 108 can also be used to implement various functions that can be used to improve the efficiency of the switching control, such as soft start and dead-time control.

[0046] As mentioned above, a line transition problem occurs during the transition of the input voltage V IN . When the level of the input voltage V IN changes, the output voltage V OUT will change rapidly with the input voltage V IN . The feedback circuit of the power converter 10 can control the output voltage V OUT to eventually settle at a certain level, but the response of the feedback circuit is usually slow, causing the error voltage V EA to settle slowly. In this case, the output voltage V OUT may have a large overshoot or undershoot, which is undesirable for the circuitry receiving the voltage supply from the power converter 10.

[0047] Figure 2A A line transition problem associated with voltage mode control is shown, which shows the waveforms of the input voltage V IN and the error voltage V EA compared to the ramp voltage V RAMP . The input voltage V IN rises from a first voltage level V IN1 to a second voltage level V IN2 , with a voltage difference ΔV IN . In response to the transition of the input voltage V IN , the error voltage V EA drops by a voltage difference ΔV EA , which changes the duty cycle of the pulse width modulation signal V PWM , causing the output power to decrease, thus controlling the output voltage V OUT to return to its target level. However, the limitation of the loop bandwidth causes the error voltage V EA to drop slower than the rise of the input voltage V IN , thus, during the transition of the input voltage V IN , the output voltage V OUTA large overshoot or undershoot will occur.

[0048] In one embodiment, in order to increase the speed of duty cycle adjustment, the ramp generator 104 can be controlled according to the input voltage V IN The level is used to output the ramp voltage V RAMP For example, Figure 2B As shown, when the input voltage V IN When rising, the ramp voltage V RAMP The height will also increase, representing the ramp voltage V RAMP The peak-to-peak value of the duty cycle increases, thereby improving the stabilization speed of the duty cycle. In a boost converter application, the duty cycle D can be expressed as:

[0049]

[0050] Among them, V M is the ramp voltage V RAMP Please note that when the input voltage V IN As the error voltage V increases, the duty cycle D should decrease. Although overshoot or undershoot may occur due to the slower settling error voltage V EA The output voltage V OUT The change problem can still be solved by changing the ramp voltage V RAMP (or V M ) and improved.

[0051] However, in Figure 2B In the embodiment, the error voltage V EA is generated without any additional processing, so the error voltage V EA will still change to the new value during the line conversion, which means that the output voltage V OUT Improvement of overshoot or undershoot issues is still limited.

[0052] Therefore, in another embodiment, a double injection technique is used to further improve the line conversion problem. Based on the double injection implementation, the error voltage output to the comparator can be corrected along with the input voltage, so that the output of the error amplifier remains consistent.

[0053] For example, if Figure 2C As shown, when the double injection scheme is adopted, the error voltage V output by the error amplifier EA Can be corrected or adjusted to generate a corrected error voltage V EA2 , which can be further output to the comparator for comparison. Therefore, the calculation of duty cycle D can be modified as follows:

[0054]

[0055] Since the comparator receives the corrected error voltage V EA2 Reduces the input voltage V IN The error amplifier outputs an error voltage V EA In this way, the output voltage V OUT Voltage changes occur during line switching.

[0056] Depend on Figure 2C From the waveform, we can see that when the input voltage V IN When rising, the error voltage V EA2 will still drop (it has a voltage difference ΔV EA2 ) to control the duty cycle D to its target value, but the error amplifier actually outputs the error voltage V EA In essence, it remains unchanged, that is, the voltage difference ΔV EA Approaching 0.

[0057] To achieve the above-mentioned error voltage control, a control circuit may be added to the feedback loop of the power converter. Figure 3 FIG2 is a schematic diagram of a power converter 30 according to an embodiment of the present invention. Power converter 30 includes a power stage 300, an error amplifier 302, a control circuit 305, and a processing circuit 308. The circuit structures and operations of power stage 300, error amplifier 302, and processing circuit 308 are similar to those of power stage 100, error amplifier 102, and processing circuit 108, respectively, and are not described here for simplicity. The difference between power converter 30 and power converter 10 is that power converter 30 also includes control circuit 305 to improve the aforementioned line conversion problem.

[0058] like Figure 3 As shown, the control circuit 305 can be implemented in the feedback circuit and coupled between the error amplifier 302 and the processing circuit 308 to receive the error voltage V from the error amplifier 302. EA , and the corresponding output control signal V C To the processing circuit 308. The control signal V C It can be used to control and adjust the duty cycle of the power converter 30, that is, to control the pulse width modulation signal V PWM duty cycle.

[0059] Figure 4 FIG. 4 is a schematic diagram of a detailed implementation of the control circuit 305 according to an embodiment of the present invention. The control circuit 305 includes a ramp generator 402, an operation circuit 404, and a comparator 406. Specifically, the ramp generator 402 can be used to receive an input voltage V IN , to generate a ramp voltage V RAMPWhen the level of the input voltage V IN is changed, the peak-to-peak amplitude of the ramp voltage V RAMP may be changed accordingly to improve the duty cycle adjustment speed, as shown in the embodiment of FIG. 4. Figure 2B

[0060] The operation circuit 404 can be configured to receive the error voltage V EA and the input voltage V IN and perform operations on these two voltages. Based on the operation results of the error voltage V EA and the input voltage V IN , the operation circuit 404 can generate a modified error voltage V EA2 , which can be further output to the comparator 406 for comparison. In some embodiments, the operation circuit 404 can include a subtractor configured to subtract the input voltage V IN from the error voltage V EA to generate the modified error voltage V EA2 . The structure of the control circuit 305 can be configured to implement the embodiment shown in FIG. 4, in which the error voltage V EA output by the error amplifier 302 can be maintained at a substantially constant level, while the modified error voltage V EA2 is decreased to achieve the desired duty cycle. Figure 2C

[0061] Then, the comparator 406 can compare the modified error voltage V EA2 with the ramp voltage V RAMP to generate the control signal V C and output the control signal V C to the processing circuit 308.

[0062] In the control circuit 305, the input voltage V IN is injected to the ramp generator 402 to modify the size of the ramp voltage V RAMP and is also injected to the operation circuit 404 to modify the error voltage V EA , thereby implementing a double-injection control. This double-injection scheme improves the response speed of the feedback loop from two aspects, i.e., the two injection points of the input voltage V IN , which can greatly improve the line switching problem caused by the change of the input voltage V IN , i.e., the amount of change of the output voltage V OUT is reduced.

[0063] Figure 5 A waveform diagram for comparing the double-injection control proposed by the present application with the general voltage mode control for power converters, which shows the input voltage V IN , the output voltage V OUT , and the ramp voltage V​​RAMP and the error voltage V EA and V EA2 Compare the waveforms. Figure 5 As shown, when the input voltage V IN When the double injection control proposed in the present invention changes, a more stable output voltage V OUT , its variation is smaller than that of general voltage mode control. Based on double injection control, the ramp voltage V RAMP Can respond to input voltage V IN The error voltage V EA2 With the input voltage V IN The error amplifier outputs an error voltage V EA maintained at a substantially constant level.

[0064] Figure 6 FIG. 1 is a schematic diagram of a detailed implementation of a power converter 30 according to an embodiment of the present invention. In this example, the power converter 30 may be a KY boost converter, which includes a capacitor C fly and an inductor L S , controlled by three switches SW1~SW3. Figure 6 A detailed implementation of the feedback circuit is also shown. In this example, when the output voltage V OUT When entering the feedback circuit, you can first pass the voltage divider resistor R FB1 and R FB2 The error amplifier 302 can be optionally configured with a compensation device 602 to improve the stability of the feedback loop. The control circuit 305 uses Figure 4 The processing circuit 308 includes a soft start circuit 612, a dead time control circuit 614 and a driving device 616. The soft start circuit 612 can be used to output a pulse width modulation signal V PWM3 To switch SW3, while preventing the circuit components inside the power stage 300 from being damaged by the rush current. The dead time control circuit 614 can provide timing control so that the switches SW1 to SW3 are not turned on at the same time, thereby avoiding unnecessary leakage current. The driving device 616 is used to provide a suitable driving signal (such as a pulse width modulation signal V PWM1 and V PWM2 ) to the corresponding switch.

[0065] It is worth noting that the purpose of the present invention is to provide a new control circuit for a power converter to reduce the overshoot and undershoot of the output voltage during the input voltage conversion process. Those skilled in the art may make modifications or changes accordingly, without limitation. For example,Figure 6 The circuit structure shown is only one of many embodiments of the power converter of the present application, in which the compensation device 602 can employ any type of compensation architecture or be omitted, and / or the voltage dividing resistors R FB1 and R FB2 may be implemented in another way or omitted. In addition, the processing circuit can include any function capable of improving the efficiency of the power converter, which is not limited to that described in the present specification.

[0066] In addition, the double injection control method proposed by the present application can be applied to any type of power converter, including the hybrid converter (e.g., the KY boost converter) in the above-described embodiments, but is not limited thereto. In another embodiment, the double injection control method can also be applied to a buck converter or a buck-boost converter, the duty cycle of which can be determined in response to the input voltage V IN and the output voltage V OUT . In this case, the slope generator can receive the input voltage V IN or the output voltage V OUT to generate a variable slope voltage V RAMP . According to the duty cycle formula, the operation circuit can perform operations in the same or different ways, such as using appropriate addition and / or subtraction, to maintain the error voltage V EA output by the error amplifier constant.

[0067] Figure 7 is a schematic diagram of a control circuit applied to a hybrid buck converter 70 according to an embodiment of the present application. The hybrid buck converter 70 includes a power stage 700 controlled by a control circuit 705. Other components in the hybrid buck converter 70 are similar to those in the above-described embodiments and are omitted in the Figure 7 description of the present embodiment without affecting the description of the present embodiment. The structure of the control circuit 705 is similar to that of the control circuit 305, so signals or components with similar functions are denoted by the same symbols. The hybrid buck converter 70 also includes a capacitor C fly and an inductor L S controlled by three switches SW1-SW3.

[0068] In this example, in response to the duty cycle formula of the hybrid buck converter 70, the slope generator 402 can receive the output voltage V OUT to change the size of the slope voltage V OUT according to the level of the output voltage V RAMP , and the duty cycle D can be calculated as follows:

[0069] In addition, the double injection control method proposed by the present application can be applied to any type of power converter, including the hybrid converter (e.g., the KY boost converter) in the above-described embodiments, but is not limited thereto. In another embodiment, the double injection control method can also be applied to a buck converter or a buck-boost converter, the duty cycle of which can be determined in response to the input voltage V IN and the output voltage V OUT . In this case, the slope generator can receive the input voltage V IN or the output voltage V OUT to generate a variable slope voltage V RAMP . According to the duty cycle formula, the operation circuit can perform operations in the same or different ways, such as using appropriate addition and / or subtraction, to maintain the error voltage V EA output by the error amplifier constant.

[0070] Embodiments of controlling the hybrid buck converter 70 to operate with a duty cycle D are well known to those skilled in the art and will not be described in detail here.

[0071] In summary, the present application proposes a dual-injection technique for power converters. The feedback loop of a power converter can include a control circuit, in which a comparator is used to compare a modified error voltage and a ramp voltage to generate a control signal with a desired duty cycle. The modified error voltage can be generated by an operational circuit, and the ramp voltage can be generated by a ramp generator. One injection is applied to the operational circuit, which provides appropriate logic operations to control the error voltage outputted by the error amplifier to remain constant during the line transition of the input voltage. Another injection is applied to the ramp generator, which can change the magnitude of the ramp voltage according to the level of the input voltage or the output voltage. In this way, the overshoot and undershoot on the output voltage during the input voltage transition can be alleviated, while the amount of change in the output voltage is reduced.

[0072] The preferred embodiments of the present application have been described above with the specific embodiments. The present application may, however, be practiced with the various modifications and variations which can be effected by persons skilled in the art without departing from the spirit and scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. A control circuit for a power converter having an input voltage and an output voltage, characterized by, The control circuit includes: a slope generator configured to receive the input voltage or the output voltage to generate a slope voltage; an operation circuit configured to generate a second error voltage according to an operation result of the input voltage and a first error voltage, wherein the first error voltage is generated from the output voltage; and 2. The control circuit of claim 1, wherein, a comparator coupled to the slope generator and the operation circuit, and configured to compare the second error voltage with the slope voltage to generate a control signal.

3. The control circuit of claim 1, wherein, The operation circuit includes a subtractor configured to subtract the input voltage from the first error voltage to generate the second error voltage.

4. The control circuit of claim 1, wherein, The control signal is configured to control a duty cycle of the power converter.

5. The control circuit of claim 1, wherein, The control circuit is further coupled to a processing circuit configured to receive the control signal and generate a plurality of driving signals configured to control a plurality of switchers in the power converter according to the control signal.

6. The control circuit of claim 5, wherein, The control circuit is further coupled to an error amplifier configured to receive the first error voltage from the error amplifier.

7. The control circuit of claim 1, wherein, The error amplifier is configured to generate the first error voltage according to the output voltage.

8. The control circuit of claim 1, wherein, The slope generator is configured to vary a magnitude of the slope voltage according to the input voltage or the output voltage.

9. A power converter, characterized by, The first error voltage is substantially maintained during a conversion of the input voltage. The control circuit includes: a power stage configured to receive an input voltage to generate an output voltage; and a control circuit coupled to the power stage, the control circuit including: a slope generator configured to receive the input voltage or the output voltage to generate a slope voltage; an operation circuit configured to generate a second error voltage according to an operation result of the input voltage and a first error voltage, wherein the first error voltage is generated from the output voltage; and 10. The power converter of claim 9, wherein, a comparator coupled to the slope generator and the operation circuit, and configured to compare the second error voltage with the slope voltage to generate a control signal.

11. The power converter of claim 9, wherein, The operation circuit includes a subtractor configured to subtract the input voltage from the first error voltage to generate the second error voltage.

12. The power converter of claim 9, wherein, The control signal is configured to control a duty cycle of the power converter. The control circuit further includes:

13. The power converter of claim 9, wherein, a processing circuit coupled to the control circuit and the power stage, and configured to receive the control signal and generate a plurality of driving signals configured to control a plurality of switchers in the power stage according to the control signal. The control circuit further includes:

14. The power converter of claim 13, wherein, an error amplifier coupled to the control circuit, and configured to output the first error voltage to the control circuit.

15. The power converter of claim 9, wherein, The error amplifier is further coupled to the power stage to generate the first error voltage according to the output voltage.

16. The power converter of claim 9, wherein, The slope generator is configured to vary a magnitude of the slope voltage according to the input voltage or the output voltage. The first error voltage is substantially maintained during a conversion of the input voltage.

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