Isolation switch converter, control circuit and power supply method thereof

Abstract

The present application discloses an isolating switch converter and its control circuit and power supply method. The isolating switch converter includes a primary circuit, a secondary circuit and a control circuit, wherein the control circuit has a loop controller and a driver, the loop controller is powered by an output voltage, and the driver is powered by the output voltage or the secondary winding according to the magnitude of the output voltage. The isolating switch converter does not require an auxiliary winding, and the driver and the loop controller are powered by the combination of the output voltage and the secondary winding, thereby ensuring the normal operation of the circuit.

Description

Technical Field

[0001] The present invention relates to an electronic circuit, and more particularly to an isolation switch converter and a control circuit and a power supply method thereof. Background Art

[0002] Isolation switch converters usually use transformers to isolate the primary and secondary sides. In order to better obtain high efficiency, SR (synchronous rectification) technology is usually used on the secondary side. The so-called SR means that in the power stage circuit, a controllable power tube (such as a metal oxide field effect transistor MOSFET) is used to replace the diode. As the slave switch tube of the power stage circuit, it cooperates with the main control switch tube to periodically turn on and off to convert the input voltage into the desired output voltage. Since the on-resistance of the controllable power tube is lower than the on-resistance of the diode. Therefore, the use of a controllable power tube consumes less power and has a higher conversion efficiency.

[0003] In order to better control the main control switch tube and the secondary-side controllable power tube, a control circuit is usually set on the secondary side to control the main control switch tube and the secondary-side controllable power tube. Therefore, it is necessary to power both the logic control part and the driver of the control circuit. For example, the prior art powers the logic control part and the driver of the control circuit together. In situations where the output voltage range is relatively wide and the minimum output voltage is relatively low, the prior art usually uses self-power supply or additional auxiliary windings to power the above-mentioned logic control part and the driver. However, when the load is light, the self-power supply may have insufficient power supply capacity, and it is difficult to power the logic control part and the drive circuit at the same time. The auxiliary winding power supply is costly and the circuit is complex. Summary of the invention

[0004] Therefore, the purpose of the present invention is to solve the above-mentioned technical problems in the prior art and to provide an improved isolating switch converter and its control circuit and power supply method.

[0005] According to an embodiment of the present invention, an isolating switch converter is proposed, comprising: a primary circuit, receiving an input voltage, the primary circuit having a main power switch coupled to a primary winding; a secondary circuit, providing an output voltage, the secondary circuit having a secondary power switch coupled to a secondary winding; a control circuit, comprising a loop controller and a driver, the loop controller providing a control signal, the driver generating a drive signal in response to the control signal, and controlling the conduction and disconnection of the secondary power switch; a first power supply capacitor, providing a first power supply voltage, supplying power to the loop controller, wherein the first power supply voltage is derived from the output voltage; a second power supply capacitor, providing a second power supply voltage, supplying power to the driver, wherein the second power supply voltage is derived from the output voltage or from the secondary winding.

[0006] According to an embodiment of the present invention, a control circuit for an isolating switch converter is also proposed, wherein the isolating switch converter has a main power switch coupled to a primary winding and a secondary power switch coupled to a secondary winding, and the control circuit comprises: a loop controller, which provides a control signal; and a driver, which generates a drive signal in response to the control signal to control the conduction and disconnection of the secondary power switch; wherein: the power supply voltage of the loop controller is provided by the output voltage of the isolating switch converter; and the power supply voltage of the driver is provided by the output voltage or the secondary winding.

[0007] According to an embodiment of the present invention, a power supply method for an isolating switch converter is also proposed, wherein the isolating switch converter includes: a main power switch coupled to a primary winding, a secondary power switch coupled to a secondary winding, a loop controller that provides a control signal, and a driver that responds to the control signal and drives the secondary power switch. The power supply method includes: converting the output voltage to provide a power supply voltage to the loop controller and the driver, respectively; judging the power supply capacity of the output voltage to the driver, and when the output voltage cannot provide sufficient power supply voltage to the driver, providing the power supply voltage to the driver through the secondary winding; when the output voltage can provide sufficient power supply voltage to the driver, continuing to provide the power supply voltage to the driver through the output voltage.

[0008] According to the above-mentioned isolation switch converter and its control circuit and power supply method in various aspects of the present invention, no auxiliary winding is required. Through the combination of output voltage and secondary winding, power is provided to the driver and loop controller, thereby ensuring the normal operation of the circuit and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of a circuit structure of an isolating switch converter 100 according to an embodiment of the present invention;

[0010] Figure 2 is a schematic diagram of a circuit structure of an isolating switch converter 200 according to an embodiment of the present invention;

[0011] Figure 3 is a schematic diagram of a circuit structure of an isolating switch converter 300 according to an embodiment of the present invention;

[0012] Figure 4 is a schematic diagram of a circuit structure of an isolating switch converter 400 according to an embodiment of the present invention;

[0013] Figure 5 is a schematic diagram of a circuit structure of an isolating switch converter 500 according to an embodiment of the present invention;

[0014] Figure 6 The flowchart 600 of a power supply method for an isolated switching converter according to an embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0015] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not have to be used to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, materials or methods are not specifically described.

[0016] Throughout the specification, reference to "one embodiment", "embodiment", "one example" or "example" means that a particular feature, structure or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment", "in an embodiment", "one example" or "example" that appear in various places throughout the specification do not necessarily refer to the same embodiment or example. In addition, specific features, structures or characteristics can be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. In addition, it should be understood by those of ordinary skill in the art that the drawings provided herein are for illustrative purposes, and the drawings are not necessarily drawn to scale. It should be understood that when an element is said to be "coupled to" or "connected to" another element, it can be directly coupled or coupled to another element or there can be an intermediate element. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, there is no intermediate element. The same reference numerals indicate the same element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0017] Figure 1 FIG. 1 is a schematic diagram of a circuit structure of an isolating switch converter 100 according to an embodiment of the present invention. Figure 1 In the illustrated embodiment, the isolating switch converter 100 comprises: a primary circuit 110, receiving an input voltage V IN The primary circuit 110 has a main power switch Q0 coupled to the primary winding T0; the secondary circuit 111 provides an output voltage V O The secondary circuit 111 has a secondary power switch (i.e., a synchronous rectifier switch) Q1 coupled to the secondary winding T1; the control circuit 112 includes a loop controller 11 and a driver 12, wherein the loop controller 11 provides a control signal C SR The driver 12 responds to the control signal C SR Generate drive signal G SR , used to control the on and off of the secondary power switch Q1; the first power supply capacitor C1, provides a first power supply voltage V DD , to power the loop controller 11, wherein the first power supply voltage VDD Derived from the output voltage V O ; The second power supply capacitor C2 provides a second power supply voltage V SR , to power the driver 12, wherein the second power supply voltage V SR Derived from the output voltage V O Or it may come from the secondary winding T1.

[0018] In one embodiment of the present invention, when the output voltage V O Can provide sufficient supply voltage (such as output voltage V O Or the output voltage V O When the power supply voltage provided is higher than the threshold voltage, the second power supply voltage V SR Derived from the output voltage V O ; When the output voltage V O Cannot provide enough supply voltage (such as output voltage V O Or the output voltage V O When the power supply voltage provided is lower than the threshold voltage, the second power supply voltage V SR Derived from the secondary winding T1.

[0019] In another embodiment of the present invention, when the output voltage V O When the power supply voltage provided is lower than the power supply voltage provided by the secondary winding T1, the second power supply voltage V SR Derived from the secondary winding T1, when the output voltage V O When the power supply voltage provided is higher than the power supply voltage provided by the secondary winding T1, the second power supply voltage V SR Derived from the output voltage V O .

[0020] That is, the power supply of the loop controller 11 is provided by the output voltage V O Provided; the power supply of the driver 12 is provided by the output voltage V O Or the voltage V1 across the secondary winding T1 provides: When the output voltage V O When the output voltage V O When the output voltage V O supply.

[0021] In one embodiment of the present invention, according to different application scenarios, the output voltage V O The voltage range is wide, such as the output voltage V O It can be as low as 3.3V or as high as tens of volts (such as 28V or higher). OWhen the voltage rises to a certain value, which is enough to drive the secondary power switch Q1, the output voltage V O The second power supply capacitor C2 is charged to obtain a second power supply voltage V SR ; When the output voltage V O Drop to a certain voltage value, such as the output voltage V O Drops to 3.3V, at which point the output voltage V O The provided power supply voltage cannot guarantee the normal operation of the driver 12. At this time, the power supply of the driver 12 is switched to the secondary winding T1.

[0022] In one embodiment of the present invention, the isolation switch converter may include isolation circuits such as a flyback circuit, a forward circuit, a resonant circuit (LLC circuit), etc. The control circuit 112 may control the secondary power switch Q1 alone, or may control the main power switch Q0 and the secondary power switch Q1 simultaneously (i.e., all-in-one control well known to those skilled in the art: the control circuits for controlling the main power switch and the secondary power switch are integrated on an integrated circuit, and the control signal is transmitted from the secondary side to the primary side through, for example, an isolation capacitor).

[0023] Figure 1 The embodiment discloses a control circuit 112 for an isolation switch converter, wherein the isolation switch converter has a main power switch Q0 coupled to a primary winding T0 and a secondary power switch Q1 coupled to a secondary winding T1. The control circuit 112 includes: a loop controller 11, providing a control signal C SR ; Driver 12, responds to control signal C SR Generate drive signal G SR , controls the conduction and disconnection of the secondary power switch O1; wherein the power supply voltage of the loop controller 11 is provided by the output voltage of the isolation switch converter; the power supply voltage of the driver 12 is provided by the output voltage V O Or the secondary winding T1 provides. When the output voltage V O Can provide sufficient supply voltage (such as output voltage V O The power supply voltage provided is higher than the power supply voltage or output voltage V provided by the secondary winding T1 O When the power supply voltage provided is higher than the threshold voltage), the power supply voltage V SR Derived from the output voltage V O ; When the output voltage V O Failure to provide sufficient supply voltage (such as output voltage V O The power supply voltage provided is lower than the power supply voltage or output voltage V provided by the secondary winding T1 O When the power supply voltage provided is lower than the threshold voltage, the power supply voltage of the driver 12 is derived from the secondary winding T1.

[0024] Figure 2 FIG. 2 is a schematic diagram of a circuit structure of an isolating switch converter 200 according to an embodiment of the present invention. Figure 2 The isolated switch converter 200 specifically shows the output voltage V according to one embodiment of the present invention. O The voltage V1 across the secondary winding T1 charges the first capacitor C1 and the second capacitor C2. Figure 2 In the embodiment shown, the control circuit 112 further includes: a first conversion unit 13, which converts the output voltage V O Converted into the first supply voltage V DD , to power the loop controller 11, and at the same time, the output voltage V O Converted into the second supply voltage V SR , supplying power to the driver 12; the second conversion unit 14, when the output voltage V O When the voltage V1 across the secondary winding T1 is insufficient to supply power to the driver 12, the second conversion unit 14 converts the voltage V1 across the secondary winding T1 into a second power supply voltage V SR , power the driver 12.

[0025] In one embodiment of the present invention, when the power supply voltage V converted by the first conversion unit 13 SR is smaller than the power supply voltage converted by the second conversion unit 14 (eg Figure 2 The intermediate voltage V M ), indicating the output voltage V O is not enough to power the driver 12. At this time, the driver 12 is powered by the secondary winding T1. Figure 2 In the illustrated embodiment, the control circuit 112 further includes an intermediate circuit 15, when the second power supply voltage V converted by the first conversion unit 13 SR Less than the middle voltage V M When the intermediate circuit 15 converts the intermediate voltage V M The voltage is transmitted to the second power supply capacitor C2 to supply power to the driver 12 .

[0026] In one embodiment of the present invention, the intermediate circuit 15 may include a diode.

[0027] In another embodiment of the present invention, when the output voltage V O Or when the supply voltage it provides is less than the threshold voltage, it means the output voltage V O The current is not enough to power the driver 12. At this time, the driver 12 is powered by the secondary winding T1. Figure 3 shown.

[0028] Figure 3 FIG. 4 is a schematic diagram of a circuit structure of an isolating switch converter 300 according to an embodiment of the present invention. Figure 3The isolated switch converter 300 specifically shows the output voltage V according to another embodiment of the present invention. O The voltage V1 across the secondary winding T1 charges the first capacitor C1 and the second capacitor C2. Figure 3 In the embodiment shown, the control circuit 112 further includes: a first conversion unit 13, which converts the output voltage V O Converted into the first supply voltage V DD , to power the loop controller 11, and at the same time, the output voltage V O Converted into the second supply voltage V SR , supplying power to the driver 12; the comparison unit 16 compares the second supply voltage V SR and threshold voltage V th The second conversion unit 14, when the second supply voltage V SR Less than the threshold voltage V th When the second conversion unit 14 converts the voltage V1 across the secondary winding T1 into a second power supply voltage V SR , power the driver 12.

[0029] Figure 4 FIG. 4 is a schematic diagram of a circuit structure of an isolating switch converter 400 according to an embodiment of the present invention. Figure 4 The isolating switch converter 400 specifically shows a schematic diagram of the circuit structure of the first conversion unit 13 and the second conversion unit 14 according to an embodiment of the present invention. Figure 4 In the embodiment shown, the first conversion unit includes: a first switch S1, which converts the output voltage V O Converted into the second supply voltage V SR , stored at both ends of the second power supply capacitor C2. The second conversion unit 14 includes: a second switch S2, which converts the voltage V1 at both ends of the secondary winding T1 into a second power supply voltage V SR , stored at both ends of the second power supply capacitor C2.

[0030] In one embodiment of the present invention, the first switch S1 is O (or the second supply voltage V SR ) is greater than the threshold voltage, and is turned on to increase the output voltage V O Converted into the second supply voltage V SR ; The second switch S2 is at the output voltage V O (or the second supply voltage V SR ) is less than the threshold voltage to convert the voltage V1 across the secondary winding T1 into the second supply voltage V SR , as mentioned above Figure 3 The comparison unit 16 of the embodiment shown in the figure is used to determine the output voltage V O (or the second supply voltage VSR In another embodiment of the present invention, the first switch S1 and the second switch S2 are both kept turned on when the isolating switch converter is operating normally, and Figure 2 The intermediate circuit 14 is shown for selecting the supply voltage of the driver 12 .

[0031] In one embodiment of the present invention, the first switch S1 or the second switch S2 is turned on, indicating that the first switch S1 or the second switch S2 is either operating in a linear mode, such as operating in a low dropout regulator (LDO) mode, to increase the output voltage V O Or the voltage V1 across the secondary winding T1 is converted into the second supply voltage V SR .

[0032] In another embodiment of the present invention, the first switch S1 or the second switch S2 is turned on, indicating that the first switch S1 or the second switch S2 operates in the saturation region, that is, operates in the switching mode, so as to increase the output voltage V O Alternatively, the voltage V1 across the secondary winding T1 is transmitted to the second power supply capacitor C2.

[0033] exist Figure 4 In the embodiment shown, the output voltage V O is directly used to charge the first power supply capacitor C1 to obtain the first power supply voltage V DD However, those skilled in the art should know that in other embodiments of the present invention, the output voltage V O It can be transferred to the first power supply capacitor C1 after conversion. Figure 5 shown.

[0034] Figure 5 FIG. 5 is a schematic diagram of a circuit structure of an isolating switch converter 500 according to an embodiment of the present invention. Figure 5 The isolating switch converter 500 specifically shows a schematic diagram of the circuit structure of the first conversion unit 13 according to another embodiment of the present invention. Figure 5 In the embodiment shown, the first conversion unit 13 further includes: a third switch S3, which is turned on when the isolation switch converter is working, and the output voltage V O Converted into the first supply voltage V DD , stored at both ends of the first power supply capacitor C1.

[0035] In one embodiment of the present invention, the third switch S3 being turned on indicates that the third switch S3 operates in an LDO mode or a switch mode.

[0036] Figure 6A flowchart 600 of a power supply method for an isolation switch converter according to an embodiment of the present invention is schematically shown. The isolation switch converter comprises: a main power switch coupled to a primary winding, a secondary power switch coupled to a secondary winding, a loop controller providing a control signal, and a driver responding to the control signal and driving the secondary power switch. The power supply method comprises:

[0037] Step 601, converting the output voltage to provide supply voltage to the loop controller and the driver respectively;

[0038] Step 602, determine the power supply capacity of the output voltage to the driver. When the output voltage cannot provide sufficient power supply voltage to the driver, go to step 603; otherwise, return to step 601 and continue to provide power supply voltage to the driver through the output voltage.

[0039] Step 603: providing a supply voltage to the driver through the secondary winding.

[0040] In one embodiment of the present invention, determining the power supply capacity of the output voltage to the driver includes: comparing the power supply voltage provided by the output voltage to the driver with a threshold voltage. When the power supply voltage is less than the threshold voltage, it indicates that the output voltage cannot provide sufficient power supply voltage to the driver.

[0041] In another embodiment of the present invention, determining the power supply capacity of the output voltage to the driver includes: comparing the power supply voltage provided by the output voltage to the driver with the power supply voltage provided by the secondary winding to the driver, and when the power supply voltage provided by the output voltage to the driver is less than the power supply voltage provided by the secondary winding to the driver, it indicates that the output voltage cannot provide sufficient power supply voltage to the driver.

[0042] The aforementioned isolating switch converter and power supply method according to multiple embodiments of the present invention adjust the power supply condition of the driver through different voltage levels of the output voltage. When the output voltage can provide sufficient power supply capacity for the driver, the output voltage is used to continuously power the loop controller and the driver. When the output voltage cannot provide sufficient power supply capacity for the driver, the output voltage is used to power only the loop controller, and the secondary winding voltage is used to power the driver, thereby ensuring the normal operation of the circuit, eliminating the auxiliary winding, and reducing the cost.

[0043] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. An isolating switch converter, comprising: A primary circuit receives an input voltage, wherein the primary circuit has a main power switch coupled to the primary winding; A secondary circuit provides an output voltage, wherein the secondary circuit has a secondary power switch coupled to the secondary winding; The control circuit includes a loop controller and a driver, wherein the loop controller provides a control signal, and the driver generates a drive signal in response to the control signal to control the conduction and disconnection of the secondary power switch; A first power supply capacitor, providing a first power supply voltage to power the loop controller, wherein the first power supply voltage is derived from the output voltage; A second power supply capacitor provides a second power supply voltage to power the driver, wherein the second power supply voltage is derived from the output voltage or from the secondary winding; wherein: When the output voltage can provide sufficient supply voltage for the driver, the second supply voltage is derived from the output voltage; When the output voltage cannot provide sufficient supply voltage for the driver, the second supply voltage is derived from the secondary winding.

2. The isolating switch converter according to claim 1, wherein the control circuit further comprises: A first conversion unit converts the output voltage into a first power supply voltage to supply power to the loop controller, and converts the output voltage into a second power supply voltage to supply power to the driver; A second conversion unit converts the voltage across the secondary winding into an intermediate voltage; The intermediate circuit transmits the intermediate voltage to the second power supply capacitor to supply power to the driver when the second power supply voltage converted by the first conversion unit is lower than the intermediate voltage.

3. The isolating switch converter according to claim 1, wherein the control circuit further comprises: A first conversion unit converts the output voltage into a first power supply voltage to supply power to the loop controller, and converts the output voltage into a second power supply voltage to supply power to the driver; A comparison unit, for comparing the second supply voltage with the threshold voltage; The second conversion unit converts the voltage across the secondary winding into the second power supply voltage to supply power to the driver when the second power supply voltage is less than the threshold voltage.

4. A control circuit for an isolating switch converter, the isolating switch converter having a main power switch coupled to a primary winding and a secondary power switch coupled to a secondary winding, the control circuit comprising: A loop controller, providing a control signal; The driver generates a driving signal in response to the control signal to control the on and off of the secondary power switch; wherein: The power supply voltage of the loop controller is provided by the output voltage of the isolation switch converter; The power supply voltage of the driver is provided by the output voltage or the secondary winding; wherein: When the supply voltage provided by the output voltage to the driver is lower than the supply voltage provided by the secondary winding to the driver, the supply voltage of the driver is derived from the secondary winding; When the supply voltage provided by the output voltage to the driver is higher than the supply voltage provided by the secondary winding to the driver, the supply voltage of the driver is derived from the output voltage.

5. The control circuit as claimed in claim 4, wherein: When the supply voltage provided by the output voltage to the driver is higher than the threshold voltage, the supply voltage of the driver is derived from the output voltage; When the supply voltage provided by the output voltage to the driver is lower than the threshold voltage, the supply voltage of the driver is derived from the secondary winding.

6. A power supply method for an isolating switch converter, the isolating switch converter comprising: A main power switch coupled to the primary winding, a secondary power switch coupled to the secondary winding, a loop controller providing a control signal, and a driver responding to the control signal and driving the secondary power switch, the power supply method comprising: Convert the output voltage to provide supply voltage to the loop controller and driver respectively; The power supply capacity of the output voltage to the driver is determined. When the output voltage cannot provide sufficient power supply voltage to the driver, the power supply voltage is provided to the driver through the secondary winding; when the output voltage can provide sufficient power supply voltage to the driver, the power supply voltage continues to be provided to the driver through the output voltage.

7. The power supply method according to claim 6, wherein determining the power supply capability of the output voltage to the driver comprises: The supply voltage provided by the output voltage to the driver is compared with the threshold voltage. When the supply voltage is less than the threshold voltage, it indicates that the output voltage cannot provide sufficient supply voltage to the driver.

8. The power supply method according to claim 6, wherein determining the power supply capability of the output voltage to the driver comprises: Compare the power supply voltage provided by the output voltage to the driver with the power supply voltage provided by the secondary winding to the driver. When the power supply voltage provided by the output voltage to the driver is less than the power supply voltage provided by the secondary winding to the driver, it means that the output voltage cannot provide sufficient power supply voltage to the driver.

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