CONTROL CIRCUIT FOR MULTI-OUTPUT SWITCHING CONVERTER
A control circuit, for controlling a switching converter having a primary switch, an energy storage component and a plurality of rectifiers, the control circuit having: a sample and hold circuit, configured to sample and hold a power source winding voltage provided by a power source winding of the energy storage component during when any one of the plurality of rectifiers is on, and to provide a sample&hold voltage based thereon; and a feedback circuit, configured to receive the sample&hold voltage and a power supply voltage of the control circuit, and to provide a feedback voltage based thereon; wherein the primary switch is controlled to be on and off based on the feedback voltage.
This application claims priority to and the benefit of Chinese Patent Application No. 202011519080.3, filed on Dec. 21, 2020, which is incorporated herein by reference in its entirety.
FIELDThe present invention relates generally to electronic circuits, and more particularly but not exclusively to a control circuit for multi-output switching converter.
BACKGROUNDIn a switching converter comprising a transformer, multiple outputs could be obtained by adding secondary windings to the transformer. However, there is usually only one control loop for controlling all the outputs, which means only one of the outputs is fed back to the control loop to regulate all the outputs. The fed back output maybe the output providing the highest power, or the output providing low power but with high accuracy requirement. The output fed back to the control loop could be regulated accurately and timely. But the other outputs are barely regulated.
For better regulation to all the outputs, one of the solutions is that all the outputs are weighted and then fed back to the control loop. However, in some applications, e.g., primary side controlled flyback converter, the opto-coupler transferring signal between the primary side and the secondary side of the flyback converter is omitted to save cost, which makes the output at the secondary side hardly fed back to the primary side, let alone the multiple outputs. In these applications, how to provide a proper feedback and regulate all the outputs effectively is a big challenge.
SUMMARYIt is an object of the present invention to provide a control circuit for a switching converter with multiple outputs to effectively regulate the multiple outputs and the method thereof.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a
A control circuit, for controlling a switching converter having a primary switch, an energy storage component and a plurality of rectifiers, the control circuit comprising: a sample and hold circuit, configured to sample and hold a power source winding voltage provided by a power source winding of the energy storage component during when any one of the plurality of rectifiers is on, and to provide a sample&hold voltage based thereon; and a feedback circuit, configured to receive the sample&hold voltage and a power supply voltage of the control circuit, and to provide a feedback voltage based on the power supply voltage and the sample&hold voltage; wherein the primary switch of the switching converter is controlled to be on and off based on the feedback voltage.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a switching converter having a flyback topology, comprising: a primary switch, coupled to a primary winding of an energy storage component; a sample and hold circuit, configured to sample and hold a power source winding voltage provided by a power source winding of the energy storage component during when any one of rectifiers of the switching converter is on, and to provide a sample&hold voltage based thereon; and a feedback circuit, configured to receive a power supply voltage and the sample&hold voltage, and to provide a feedback voltage based on the power supply voltage and the sample&hold voltage; wherein the primary switch is controlled to be on and off based on the feedback voltage.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a control circuit, used with a switching converter having a flybuck topology, wherein the switching converter has an energy storage component, a primary switch and a rectifier, the control circuit comprising: a sample and hold circuit, configured to sample and hold a primary winding voltage provided by a primary winding of the energy storage component during when the rectifier is on, and to provide a sample&hold voltage based thereon; a feedback circuit, configured to receive a power supply voltage and the sample&hold voltage, and to provide a feedback voltage based on the power supply voltage and the sample&hold voltage; wherein the primary switch of the switching converter is controlled to be on and off based on the feedback voltage.
The control circuit and the feedback circuit of the switching converter provided by the present invention has simple circuit structure, and could effectively regulate the multiple outputs and improve the accuracy of each output of the switching converter.
The use of the same reference label in different drawings indicates the same or like components.
DETAILED DESCRIPTIONIn the present invention, numerous specific details are provided, such as examples of circuits, components, and methods, to provide a thorough understanding of embodiments of the invention. Persons of ordinary skill in the art would recognize, however, that the invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the invention.
The flyback converter 10 turns on and off the primary switch PM1, the rectifiers D11, D12 and D13, to transfer energy from the primary side to the secondary sides (each secondary side includes a secondary winding and all the elements attached thereto, the power source winding Lt1 is a secondary winding too, used to provide power to the control circuit 105) of the flyback converter. By setting the turns ratio of the primary winding Lp1 to the secondary windings Ls11, Ls12, Lt1, and controlling the duty cycle of the primary switch PM1, the flyback converter 10 could provide the first output voltage Va1, the second output voltage Va2 and the power supply voltage Vcc1 with required voltage levels.
In the primary side controlled flyback converter 10, the primary side and the secondary sides are isolated, with no opto-coupler feeding back output information. In prior art, the power source winding voltage VL1 during a freewheeling period of the rectifiers is provided as a feedback voltage to the control loop of the flyback converter 10 to regulate the duty cycle of the primary switch PM1. However, in some cases, e.g., output loads are very different, or the output with the lowest power has high accuracy requirement, the output with low power could not be effectively regulated when the power source winding voltage VL1 is used as the feedback voltage.
The sample and hold circuit 24 receives the power source winding voltage VL1, then samples the power source winding voltage VL1 during when any one of the rectifiers (D11, D12 and D13) is on and the ringing of the power source winding voltage VL1 is over, and then holds the sampled value to generate the sample&hold voltage Vs&h1. In application, persons of ordinary skill in the art could calculate the on time periods of the rectifiers, and estimate the ringing time period of the power source winding voltage VL1, based on the specs of the application, thereby avoid the ringing time period of the power source winding voltage VL1, and find a proper sampling point to sample the power source winding voltage VL1.
Any circuit which could generate the switching control signal G1 with a certain duty cycle could be adopted by the present invention, e.g., pulse width modulation (PWM) circuit, pulse frequency modulation (PFM) circuit, a combination of the PWM circuit and the PFM circuit. In one embodiment, when the feedback voltage Vfb1 decreases, the compensation signal Vcomp1 increases. Then after the regulation of the pulse control circuit 23, a duty cycle of the switching control signal G1 increases, wherein the duty cycle of the switching control signal G1 is defined as a ratio of an on time period of the primary switch PM1 to a switching cycle of the primary switch PM1, and wherein the switching cycle of the primary switch PM1 is defined as a repeated time period having an on time period and an off time period of the primary switch PM1. The energy transferred from the primary side to the secondary sides increases as the duty cycle of the switching control signal G1 increases.
In the embodiment of
The power supply voltage Vcc1 powers the control circuit 105 that could be regarded as a light load of the flyback converter 10. By contrast, the sample&hold voltage Vs&h1 represents an output voltage provided to a heavy load. The feedback circuit 21 in
In the embodiment of
The states of the selecting signal S1 are decided by the requirement of the application. In some embodiments, logical high level represents the first state of the selecting signal S1, and logical low level represents the second state of the selecting signal S1, or just the opposite.
In the embodiment of
In the embodiment of
In one embodiment, K3=1.2 and K4=0.8. When 0.8×Vcc1<Vs&h1<1.2×Vcc1, the first comparison signal CR1 and the second comparison signal CR2 are logical high, then the logic circuit 406 provides a logical high selecting signal S1. Under the control of the logical high selecting signal S1, the selecting circuit 407 provides the sample&hold voltage Vs&h1 as the feedback voltage Vfb1. When Vs&h1≤0.8×Vcc1 or Vs&h1≥1.2×Vcc1, the second comparison signal CR2 or the first comparison signal CR1 is logical low. Then the logic circuit 406 provides a logical low selecting signal S1. Under the control of the logical low selecting signal S1, the selecting circuit 407 provides the power supply voltage Vcc1 as the feedback voltage Vfb1.
In the embodiment of
In the embodiment of
In the embodiment of
In
Under the control of the feedback circuit 61, the control circuit 60 takes the sample&hold voltage Vs&h1 as the feedback voltage Vfb1 to focus on regulating the output with a heavier load when the overall load is heavy, and takes the power supply voltage Vcc1 as the feedback voltage Vfb1 to focus on regulating the output with a lighter load when the overall load is light, so as to effectively regulate both the output with heavier load and the output with lighter load.
The threshold signal Vth is adopted to determine the load condition of the system, and the value of the threshold signal Vth could be decided according to the application.
In prior art, the power supply voltage Vcc2 is provided as a feedback voltage to the control circuit 705, to participate in the control control to regulate the outputs of the flybuck converter 70. However, when the load of the second output voltage Vb2 is heavy, the outputs of the flybuck converter 70 could not be regulated effectively by feeding back the power supply voltage Vcc2.
When the secondary side of the flybuck converter 70, i.e., the second output voltage Vb2 is heavily loaded, the sample&hold voltage Vs&h2 is needed in the control loop to fast recover the first output voltage Vb1 and the second voltage Vb2.
The present invention is illustrated by embodiments of dual-output switching converters, namely the flyback converter 10 in
Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. It should be understood, of course, the foregoing disclosure relates only to a preferred embodiment (or embodiments) of the invention and that numerous modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims. Various modifications are contemplated and they obviously would be resorted to by those skilled in the art without departing from the spirit and the scope of the invention as hereinafter defined by the appended claims as only a preferred embodiment(s) thereof has been disclosed.
Claims
1. A control circuit, for controlling a switching converter having a primary switch, an energy storage component and a plurality of rectifiers, the control circuit comprising:
- a sample and hold circuit, configured to sample and hold a power source winding voltage provided by a power source winding of the energy storage component during when any one of the plurality of rectifiers is on, and to provide a sample&hold voltage based thereon; and
- a feedback circuit, configured to receive the sample&hold voltage and a power supply voltage of the control circuit, and to provide a feedback voltage based on the power supply voltage and the sample&hold voltage; wherein
- the primary switch of the switching converter is controlled to be on and off based on the feedback voltage.
2. The control circuit of claim 1, further comprising:
- an error amplifier, configured to receive the feedback voltage and a reference voltage, and based on an amplified error between the feedback voltage and the reference voltage, the error amplifier provides a compensation signal; and
- a pulse control circuit, configured to receive the compensation signal, and based on the compensation signal, the pulse control circuit provides a switching control signal to control the primary switch.
3. The control circuit of claim 1, wherein the feedback circuit comprises:
- a first scaling circuit, configured to receive the power supply voltage, and to provide a first scaling voltage which is a product of the power supply voltage and a first scale factor;
- a second scaling circuit, configured to receive the sample&hold voltage, and to provide a second scaling voltage which is a product of the sample&hold voltage and a second scale factor; and
- an operational circuit, configured to receive the first scaling voltage and the second scaling voltage, and based on the first scaling voltage and the second scaling voltage, the operational circuit provides a feedback voltage which is a sum of the first scaling voltage and the second scaling voltage; wherein
- both the first scale factor and the second scale factor are constants having values between 0 and 1, and a sum of the first scale factor and the second scale factor is 1.
4. The control circuit of claim 1, wherein the feedback circuit comprises:
- a third scaling circuit, configured to receive the power supply voltage, and to provide a third scaling voltage which is a product of the power supply voltage and a third scale factor, wherein the third scale factor is a constant having a value between 1 and 2;
- a fourth scaling circuit, configured to receive the power supply voltage, and to provide a fourth scaling voltage which is a product of the power supply voltage and a fourth scale factor, wherein the fourth scale factor is a constant having a value between 0 and 1;
- a hysteresis comparator, configured to receive the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, and based on a comparison result of the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, the hysteresis comparator provides a selecting signal; and
- a selecting circuit, configured to receive the selecting signal, the power supply voltage and the sample&hold voltage, wherein one of the power supply voltage and the sample&hold voltage is selected to be the feedback voltage based on the selecting signal.
5. The control circuit of claim 1, wherein the feedback circuit comprises:
- a third scaling circuit, configured to receive the power supply voltage, and to provide a third scaling voltage which is a product of the power supply voltage and a third scale factor, wherein the third scale factor is a constant having a value between 1 and 2;
- a fourth scaling circuit, configured to receive the power supply voltage, and to provide a fourth scaling voltage which is a product of the power supply voltage and a fourth scale factor, wherein the fourth scale factor is a constant having a value between 0 and 1;
- a hysteresis comparator, configured to receive the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, and based on a comparison result of the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, the hysteresis comparator provides a selecting signal;
- a weighting circuit, configured to receive the power supply voltage and the sample&hold voltage, and based on the power supply voltage and the sample&hold voltage, the weighting circuit provides a weighted voltage; and
- a selecting circuit, configure to receive the selecting signal, the power supply voltage, and the weighted voltage, wherein one of the power supply voltage and the weighted voltage is selected as the feedback voltage based on the selecting signal.
6. The control circuit of claim 5, wherein the weighting circuit comprises:
- a first scaling circuit, configured to receive the power supply voltage, and to provide a first scaling voltage which is a product of the power supply voltage and a first scale factor;
- a second scaling circuit, configured to receive the sample&hold voltage, and to provide a second scaling voltage which is a product of the sample&hold voltage and a second scale factor; and
- an operational circuit, configured to receive the first scaling voltage and the second scaling voltage, and based on the first scaling voltage and the second scaling voltage, the operational circuit provides a weighted voltage which is a sum of the first scaling voltage and the second scaling voltage; wherein both the first scale factor and the second scale factor are constants having values between 0 and 1, and a sum of the first scale factor and the second scale factor is 1.
7. The control circuit of claim 2, wherein the feedback circuit comprises:
- a load comparison circuit, configured to receive the compensation signal and a threshold signal, based on a comparison result of the compensation signal and the threshold signal, the load comparison circuit provides a selecting signal; and
- a selecting circuit, configured to receive the selecting signal, the power supply voltage and the sample&hold voltage, wherein one of the power supply voltage and the sample&hold voltage is selected as the feedback voltage based on the selecting signal.
8. A switching converter having a flyback topology, comprising:
- a primary switch, coupled to a primary winding of an energy storage component;
- a sample and hold circuit, configured to sample and hold a power source winding voltage provided by a power source winding of the energy storage component during when any one of a plurality of rectifiers of the switching converter is on, and to provide a sample&hold voltage based thereon; and
- a feedback circuit, configured to receive a power supply voltage and the sample&hold voltage, and to provide a feedback voltage based on the power supply voltage and the sample&hold voltage; wherein
- the primary switch is controlled to be on and off based on the feedback voltage.
9. The switching converter of claim 8, further comprising:
- an error amplifier, configured to receive the feedback voltage and a reference voltage, and based on an amplified error between the feedback voltage and the reference voltage, the error amplifier provides a compensation signal; and
- a pulse control circuit, configured to receive the compensation signal, and based on the compensation signal, the pulse control circuit provides a switching control signal to control the primary switch.
10. The switching converter of claim 8, further comprising:
- an energy storage component, having a primary winding, a power source winding, and at least two secondary windings, wherein the primary switch is coupled to the primary winding.
- at least three rectifiers, coupled respectively to the power source winding and the at least two secondary windings, wherein one of the rectifiers has a first terminal coupled to the power source winding to receive the power source winding voltage, and a second terminal configured to provide the power supply voltage.
11. The switching converter of claim 8, wherein the feedback circuit comprises:
- a first scaling circuit, configured to receive the power supply voltage, and to provide a first scaling voltage which is a product of the power supply voltage and a first scale factor;
- a second scaling circuit, configured to receive the sample&hold voltage, and to provide a second scaling voltage which is a product of the sample&hold voltage and a second scale factor; and
- an operational circuit, configured to receive the first scaling voltage and the second scaling voltage, and based on the first scaling voltage and the second scaling voltage, the operational circuit provides a feedback voltage which is a sum of the first scaling voltage and the second scaling voltage; wherein
- both the first scale factor and the second scale factor are constants having values between 0 and 1, and a sum of the first scale factor and the second scale factor is 1.
12. The switching converter of claim 8, wherein the feedback circuit comprises:
- a third scaling circuit, configured to receive the power supply voltage, and to provide a third scaling voltage which is a product of the power supply voltage and a third scale factor, wherein the third scale factor is a constant having a value between 1 and 2;
- a fourth scaling circuit, configured to receive the power supply voltage, and to provide a fourth scaling voltage which is a product of the power supply voltage and a fourth scale factor, wherein the fourth scale factor is a constant having a value between 0 and 1;
- a hysteresis comparator, configured to receive the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, and based on a comparison result of the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, the hysteresis comparator provides a selecting signal; and
- a selecting circuit, configured to receive the selecting signal, the power supply voltage and the sample&hold voltage, wherein one of the power supply voltage and the sample&hold voltage is selected to be the feedback voltage based on the selecting signal.
13. The switching converter of claim 8, wherein the feedback circuit comprises:
- a third scaling circuit, configured to receive the power supply voltage, and to provide a third scaling voltage which is a product of the power supply voltage and a third scale factor, wherein the third scale factor is a constant, and has a value between 1 and 2;
- a fourth scaling circuit, configured to receive the power supply voltage, and to provide a fourth scaling voltage which is a product of the power supply voltage and a fourth scale factor, wherein the fourth scale factor is a constant and has a value between 0 and 1;
- a hysteresis comparator, configured to receive the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, and based on a comparison result of the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, the hysteresis comparator provides a selecting signal; and
- a weighting circuit, configured to receive the power supply voltage and the sample&hold voltage, and based on the power supply voltage and the sample&hold voltage, the weighting circuit provides a weighted voltage; and
- a selecting circuit, configure to receive the selecting signal, the power supply voltage, and the weighted voltage, wherein one of the power supply voltage and the weighted voltage is selected as the feedback voltage based on the selecting signal.
14. The control circuit of claim 13, wherein the weighting circuit comprises:
- a first scaling circuit, configured to receive the power supply voltage, and to provide a first scaling voltage which is a product of the power supply voltage and a first scale factor;
- a second scaling circuit, configured to receive the sample&hold voltage, and to provide a second scaling voltage which is a product of the sample&hold voltage and a second scale factor; and
- an operational circuit, configured to receive the first scaling voltage and the second scaling voltage, and based on the first scaling voltage and the second scaling voltage, the operational circuit provides a weighted voltage which is a sum of the first scaling voltage and the second scaling voltage; wherein
- both the first scale factor and the second scale factor are constants having values between 0 and 1, and a sum of the first scale factor and the second scale factor is 1.
15. The control circuit of claim 9, wherein the feedback circuit comprises:
- a load comparison circuit, configured to receive the compensation signal and a threshold signal, and based on a comparison result of the compensation signal and the threshold signal, the load comparison circuit provides a selecting signal; and
- a selecting circuit, configured to receive the selecting signal, the power supply voltage and the sample&hold voltage, wherein one of the power supply voltage and the sample&hold voltage is selected as the feedback voltage based on the selecting signal.
16. A control circuit, used with a switching converter having a flybuck topology, wherein the switching converter has an energy storage component, a primary switch and a rectifier, the control circuit comprising:
- a sample and hold circuit, configured to sample and hold a primary winding voltage provided by a primary winding of the energy storage component during when the rectifier is on, and to provide a sample&hold voltage based thereon;
- a feedback circuit, configured to receive a power supply voltage and the sample&hold voltage, and to provide a feedback voltage based on the power supply voltage and the sample&hold voltage; wherein
- the primary switch of the switching converter is controlled to be on and off based on the feedback voltage.
17. The control circuit of claim 16, further comprising:
- an error amplifier, configured to receive the feedback voltage and a reference voltage, and based on an amplified error between the feedback voltage and the reference voltage, the error amplifier provides a compensation signal; and
- a pulse control circuit, configured to receive the compensation signal, and based on the compensation signal, the pulse control circuit provides a switching control signal to control the primary switch.
18. The switching converter of claim 16, wherein the feedback circuit comprises:
- a first scaling circuit, configured to receive the power supply voltage, and to provide a first scaling voltage which is a product of the power supply voltage and a first scale factor;
- a second scaling circuit, configured to receive the sample&hold voltage, and to provide a second scaling voltage which is a product of the sample&hold voltage and a second scale factor; and
- an operational circuit, configured to receive the first scaling voltage and the second scaling voltage, and based on the first scaling voltage and the second scaling voltage, the operational circuit provides a feedback voltage which is a sum of the first scaling voltage and the second scaling voltage; wherein
- both the first scale factor and the second scale factor are constants having values between 0 and 1, and a sum of the first scale factor and the second scale factor is 1.
19. The switching converter of claim 16, wherein the feedback circuit comprises:
- a third scaling circuit, configured to receive the power supply voltage, and to provide a third scaling voltage which is a product of the power supply voltage and a third scale factor, wherein the third scale factor is a constant having a value between 1 and 2;
- a fourth scaling circuit, configured to receive the power supply voltage, and to provide a fourth scaling voltage which is a product of the power supply voltage and a fourth scale factor, wherein the fourth scale factor is a constant having a value between 0 and 1;
- a hysteresis comparator, configured to receive the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, and based on a comparison result of the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, the hysteresis comparator provides a selecting signal; and
- a selecting circuit, configured to receive the selecting signal, the power supply voltage and the sample&hold voltage, wherein one of the power supply voltage and the sample&hold voltage is selected to be the feedback voltage based on the selecting signal.
20. The switching converter of claim 16, wherein the feedback circuit comprises:
- a third scaling circuit, configured to receive the power supply voltage, and to provide a third scaling voltage which is a product of the power supply voltage and a third scale factor, wherein the third scale factor is a constant having a value between 1 and 2;
- a fourth scaling circuit, configured to receive the power supply voltage, and to provide a fourth scaling voltage which is a product of the power supply voltage and a fourth scale factor, wherein the fourth scale factor is a constant having a value between 0 and 1;
- a hysteresis comparator, configured to receive the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, and based on a comparison result of the third scaling voltage, the fourth scaling voltage, and the sample&hold voltage, the hysteresis comparator provides a selecting signal;
- a weighting circuit, configured to receive the power supply voltage and the sample&hold voltage, and based on the power supply voltage and the sample&hold voltage, the weighting circuit provides a weighted voltage; and
- a selecting circuit, configure to receive the selecting signal, the power supply voltage, and the weighted voltage, wherein one of the power supply voltage and the weighted voltage is selected as the feedback voltage based on the selecting signal.
Type: Application
Filed: Dec 7, 2021
Publication Date: Jun 23, 2022
Inventor: Siran Wang (Hangzhou)
Application Number: 17/543,995