CN111025035A - Demagnetization detection circuit and control circuit and method thereof - Google Patents
Demagnetization detection circuit and control circuit and method thereofDownload PDFInfo
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- CN111025035A CN111025035ACN201811175200.5ACN201811175200ACN111025035ACN 111025035 ACN111025035 ACN 111025035ACN 201811175200 ACN201811175200 ACN 201811175200ACN 111025035 ACN111025035 ACN 111025035A
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Abstract
Description
Technical Field
The invention relates to the field of electronics, in particular to a demagnetization detection circuit and a control circuit and method thereof.
Background
As shown in fig. 1, the conventional Boost PFC power circuit often operates in a DCM mode (critical current mode), especially when the output power is less than 200W, or CRM mode. In the DCM mode, the switch Q1 is turned on when the current in the inductor L drops to zero, and the switch Q1 can achieve zero voltage conduction at this time, so that the switching loss of the switch Q1 is the lowest. The current in the inductor L starts to rise after conduction. Q1 turns off after a predetermined time of turn-on and the current in inductor L begins to drop. Therefore, in DCM, it is necessary to detect the time when the current in the inductor drops to zero, or demagnetization detection.
One demagnetization detection technique in the prior art employs an auxiliary winding to decouple the inductor L in the Boost PFC circuit, and additionally employs a dc blocking circuit to detect the time point when the current of the inductor L drops to zero, as shown in fig. 2. The detection mode adopts an additional winding, and the winding has larger volume, higher cost and higher detection complexity.
Another degaussing test is to add an extra capacitor between the source and gate of the transistor Q1 and to detect the point in time when the inductor current drops to zero by detecting the discharge current on the capacitor. However, the detection method needs to draw current upwards from the ground terminal, is easily interfered, and has poor detection accuracy. Especially when a plurality of lamps are connected in parallel or a high-power supply condition exists, the scheme cannot be applied due to large interference.
Disclosure of Invention
With respect to one or more problems of the prior art, it is an object of the present invention to provide a demagnetization detection circuit, a control circuit and a method that obviate at least some of the disadvantages set forth above.
According to an aspect of the present invention, there is provided a demagnetization detection circuit for a switching circuit, wherein the switching circuit includes an inductor, a switch coupled between a second terminal of the inductor and a ground terminal, and a rectifying device coupled between the second terminal of the inductor and an output terminal, and the demagnetization detection circuit obtains demagnetization time information that an inductor current drops to zero based on a voltage at the second terminal of the inductor.
In one embodiment, a demagnetization detection circuit includes: the input end of the differential circuit is coupled with the second end of the inductor; and the input end of the comparison circuit is coupled with the output end of the differential circuit, and the output end of the comparison circuit provides a degaussing detection signal.
In one embodiment, the differentiating circuit includes: the first end of the capacitor receives a voltage signal representing the voltage of the second end of the inductor; and the first end of the resistor is coupled with the second end of the capacitor, the second end of the resistor is coupled with the grounding end, and the coupling point of the capacitor and the resistor is used as the output end of the differential circuit.
In one embodiment, the demagnetization detection circuit further includes a voltage divider circuit, an input terminal of the voltage divider circuit is coupled to the second terminal of the inductor, and an output terminal of the voltage divider circuit is coupled to an input terminal of the differential circuit.
According to another aspect of the present invention, there is provided a control circuit for a Boost PFC circuit, wherein the Boost PFC circuit includes a rectifying circuit, an inductor coupled to the rectifying circuit at a first end, a switch coupled between a second end of the inductor and a ground end, and a rectifying tube coupled between the second end of the inductor and an output end, the control circuit including: a demagnetization detection circuit according to any of the above embodiments; the loop control circuit is used for controlling the conducting time of the switch; the demagnetizing detection circuit comprises a trigger, a first input end, a second input end and an output end, wherein the first input end of the trigger is coupled with the output end of the demagnetizing detection circuit, and the second input end of the trigger is coupled with the output end of the loop control circuit; and the input end of the driving circuit is coupled with the output end of the trigger, and the output end of the driving circuit is coupled with the control end of the switch.
In one embodiment, the loop control circuit has an input terminal coupled to an output terminal of the Boost PFC circuit for receiving a detection signal indicative of the output voltage, wherein the Boost PFC circuit further has an output capacitor coupled between a second terminal of the rectifier and a ground terminal, and wherein the second terminal of the rectifier serves as the output terminal of the Boost PFC circuit.
In one embodiment, the flip-flop is an RS flip-flop, the first input of the flip-flop is a set input, and the second input of the flip-flop is a reset input.
According to yet another aspect of the present invention, there is provided a demagnetization detection method for a switching circuit, wherein the switching circuit includes an inductor, a switch coupled between a second terminal of the inductor and a ground terminal, and a rectifier tube coupled between the second terminal of the inductor and an output terminal, the method includes detecting a voltage at the second terminal of the inductor, and obtaining demagnetization time information that an inductor current drops to zero from the voltage.
According to still another aspect of the present invention, there is provided a demagnetization detection circuit for detecting information of demagnetization time of an inductor, including: the input end of the differentiating circuit is coupled with the inductor and used for acquiring a voltage signal at one end of the inductor; and the input end of the comparison circuit is coupled with the output end of the differential circuit, and the output end of the comparison circuit provides a demagnetization detection signal.
In one embodiment, the differentiating circuit includes: the first end of the capacitor receives a voltage signal representing the voltage of the second end of the inductor; the first end of the resistor is coupled with the second end of the capacitor, the second end of the resistor is coupled with the grounding end, and the coupling point of the capacitor and the resistor is used as the output end of the differential circuit.
The demagnetization detection circuit, the control circuit and the method provided by the invention avoid adopting an auxiliary winding to carry out demagnetization detection, can effectively reduce the volume and the detection complexity of a system, and are easy to integrate. And because the two ends of the switch are provided with parasitic capacitors, the voltage of the second end of the inductor can inhibit spike pulses, and the resonance of the capacitor and the inductor ensures that the voltage of the second end of the inductor has the characteristics of slow drop and stability when the follow current is finished, the detection has good anti-interference performance and reliability.
Drawings
Fig. 1 shows a prior art Boost PFC power supply circuit diagram;
FIG. 2 shows a prior art demagnetization detection circuit;
FIG. 3 shows a schematic diagram of a switching circuit according to an embodiment of the invention;
FIG. 4 shows a schematic diagram of a control circuit according to an embodiment of the invention;
FIG. 5 illustrates a demagnetization detection circuit according to an embodiment of the invention.
The same reference numbers in different drawings identify the same or similar elements or components.
Detailed Description
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
The description in this section is for several exemplary embodiments only, and the present invention is not limited only to the scope of the embodiments described. Combinations of different embodiments, and substitutions of features from different embodiments, or similar prior art means may be substituted for or substituted for features of the embodiments shown and described.
"coupled" in this specification includes direct connection and also includes indirect connection, such as connection through an electrically conductive medium, such as a conductor, where the electrically conductive medium may include parasitic inductance or parasitic capacitance. But also may include connections through other active or passive devices, such as through switches, follower circuits, etc., that are known to those skilled in the art for achieving the same or similar functional objectives.
Fig. 3 shows a schematic diagram of a switching circuit according to an embodiment of the invention. A demagnetization detection circuit in thecontrol circuit 32 performs demagnetization detection based on the voltage VDS at the switch node. Preferably, the switching circuit is a Boost PFC circuit, and includes a rectifyingcircuit 31, an inductor L having a first end coupled to the rectifying circuit, a switch Q1 coupled between a second end of the inductor L and a ground end, a rectifying tube D coupled between the second end of the inductor L and the output Vo, and acontrol circuit 32. Therectifier circuit 31 rectifies the alternating-current power supply AC. Thecontrol circuit 32 comprises a demagnetization detection circuit which obtains information on the demagnetization time when the inductor current drops to zero based on the voltage VDS at the second end of the inductor L, i.e. at the switching node as shown in the figure.
In the illustrated embodiment, the rectifying device employs a diode D, but the rectifying diode D may be replaced by a rectifying switch, and the on and off are controlled by a switching signal. In the illustrated embodiment, the switch Q1 is a junction field effect transistor, and one skilled in the art will appreciate that the switch Q1 may also be a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or other type of transistor. The switching circuit may also be other circuits such as a Boost (Boost) circuit that does not include a rectifying circuit, or other possible switching circuits.
The switch circuit may further have an output capacitor Co coupled between a second terminal of the rectifier D and a ground terminal, wherein the second terminal of the rectifier D serves as an output terminal of the switch circuit to provide the output voltage Vo.
When the current in the inductor L finishes the follow current through the rectifier tube D, the switch node voltage VDS is reduced from a high value. The switch node voltage VDS slowly drops due to resonance generated by the inductor L and the parasitic capacitance Cp between the source and drain of the switch Q1. And acquiring demagnetization time information of the inductor current reduced to zero by acquiring an inflection point when the VDS is reduced. In addition, in a preferred embodiment, due to the existence of the parasitic capacitance Cp at two ends of the transistor source drain, a spike signal can be inhibited, the switch node voltage VDS is stable, interference in detection can be inhibited, and the application range is wide.
FIG. 4 shows a control circuit schematic according to an embodiment of the invention. The control circuit includes adegaussing detection circuit 41, aloop control circuit 42, a flip-flop 43 and adrive circuit 44. Thedemagnetization detection circuit 41 receives a signal representing the voltage VDS at the second terminal (switch node voltage) of the inductor L and generates a demagnetization detection signal S1. In the illustrated embodiment, thedegaussing detection circuit 41 includes a differentiatingcircuit 411 and acomparing circuit 412, wherein an input terminal of the differentiatingcircuit 411 is coupled to the second terminal of the inductor for receiving the signal indicative of the switch node voltage VDS, an input terminal of thecomparing circuit 412 is coupled to an output terminal of the differentiatingcircuit 411, and an output terminal of the comparingcircuit 412 provides the degaussing detection signal S1.Loop control circuit 42 is used to control the on-time of switch Q1. In one embodiment, the on-time is set to a preset fixed length. In another embodiment, the on-time may vary depending on the characteristics of the output signal. In one embodiment, theloop control circuit 42 may further have an input terminal coupled to the output terminal of the Boost PFC circuit for receiving a detection signal indicative of the output voltage Vo and adjusting the length of the on-time according to the detection signal.
The flip-flop 43 has a first input terminal S, a second input terminal R and an output terminal Q, wherein the first input terminal S of the flip-flop 43 is coupled to the output terminal of thedemagnetization detection circuit 41, and the second input terminal R of the flip-flop 43 is coupled to the output terminal of theloop control circuit 42. The degaussing detection signal S1 is input to a first input of the flip-flop for controlling the turn-on of the switch Q1. Theloop control circuit 42 is used for controlling the switch Q1 to be on for a long time, and the output end of the loop control circuit is input to the second input end of the flip-flop 43 for turning off the switch Q1. The drivingcircuit 44 has an input terminal coupled to the output terminal Q of the flip-flop 43, an output terminal coupled to a control terminal of the switch Q1, and an output terminal outputting a control signal CTRL for controlling the on and off of the Q1. In the illustrated embodiment, the flip-flop is an RS flip-flop, the first input terminal of the flip-flop 43 is a set terminal S, and the second input terminal is a reset terminal R. In other embodiments, other types of flip-flops may be used; or the set input end is coupled with the loop control circuit, the reset end is coupled with the demagnetization detection circuit, and then the same or similar control is realized through the setting of the driving circuit or the selection of the switch type.
In one embodiment, the loop control circuit has an input terminal coupled to the output terminal of the Boost PFC circuit for receiving a detection signal indicative of the output voltage Vo, as shown in fig. 3. The Boost PFC circuit further comprises an output capacitor coupled between the second end of the rectifying tube and the ground terminal, wherein the second end of the rectifying tube is used as the output end of the Boost PFC circuit.
FIG. 5 illustrates a demagnetization detection circuit according to an embodiment of the invention. The demagnetization detection circuit includes a differentiation circuit and acomparison circuit 51. In the illustrated embodiment, the differentiating circuit includes a capacitor C and a resistor R3. The first terminal of the capacitor C receives a voltage signal representing the voltage VDS of the second terminal of the inductor, the first terminal of the resistor R3 is coupled to the second terminal of the capacitor C, the second terminal of the resistor R3 is coupled to the ground terminal, and the coupling point of the capacitor C and the resistor R3 serves as the output terminal of the differential circuit.
In the illustrated embodiment, the demagnetization detection circuit may further include a voltage divider circuit, which is composed of R1 and R2, wherein a first terminal of the resistor R1 is coupled to the second terminal of the inductor L as an input terminal of the voltage divider circuit for receiving the voltage VDS, and an output terminal of the voltage divider circuit is coupled to the input terminal of the differential circuit for providing a voltage signal indicative of the voltage VDS at the second terminal of the inductor. Of course, in another embodiment, the differentiating circuit in the degaussing detection circuit may also receive the VDS voltage signal directly.
In the illustrated embodiment, the differentiating circuit further includes a bias voltage such that the voltage output by the differentiating circuit is positive. However, the bias circuit may be located elsewhere, such as inside the comparison circuit.
The first terminal of the capacitor C is configured to receive a voltage signal representing the voltage VDS of the second terminal of the inductor, the first terminal of the resistor R3 is coupled to the second terminal of the capacitor C, the second terminal of the resistor R3 is coupled to the ground, and a coupling point of the capacitor C and the resistor R3 is used as an output terminal of the differential circuit and coupled to a non-inverting input terminal of thecomparison circuit 51. The inverting input terminal of the comparison circuit is coupled to a reference signal Vref. The output of the comparison circuit provides a degaussing detection signal S.
When a signal A representing VDS drops, a negative current is generated through a resistor R3 by the blocking action of a capacitor C, the voltage VB on a node B drops, and when VB < Vref, thecomparison circuit 51 is turned over to output an effective degaussing detection signal S1.
The demagnetization detection circuit eliminates the auxiliary winding, so that the detection circuit is smaller in size and easy to integrate in an integrated circuit, and the cost and the detection complexity of the system are reduced. In addition, because parasitic capacitance exists between the source and the drain of the switch Q1, spike pulse can be inhibited, and the switch node voltage VDS is stable, so that the detection anti-interference capability is strong. Is easy to be applied to various occasions.
Although the demagnetization detection circuit in some embodiments is used in the Boost PFC circuit, the demagnetization detection circuit of the present invention is not limited to be applied in the Boost PFC circuit, and may also be applied in any other type of circuit topology that needs to detect the demagnetization time information of the inductor whose inductance current drops to zero for further control, such as a Boost switch circuit or other circuits that do not include a rectification circuit.
In one embodiment, a degaussing detection circuit for detecting inductance degaussing time information includes: the input end of the differentiating circuit is coupled with the inductor and used for acquiring a voltage signal at one end of the inductor; and the input end of the comparison circuit is coupled with the output end of the differential circuit, and the output end of the comparison circuit provides a degaussing detection signal. Wherein the differentiating circuit may comprise: the first end of the capacitor receives a voltage signal representing the voltage of the second end of the inductor; the first end of the resistor is coupled with the second end of the capacitor, the second end of the resistor is coupled with the grounding end, and the coupling point of the capacitor and the resistor is used as the output end of the differential circuit.
According to an embodiment of the present invention, there is provided a demagnetization detection method for a switching circuit, wherein the switching circuit includes an inductor, a switch coupled between a second terminal of the inductor and a ground terminal, and a rectifier coupled between the second terminal of the inductor and an output terminal, the method includes detecting a voltage at the second terminal of the inductor, and obtaining demagnetization time information that an inductor current decreases to zero from the voltage. Therefore, the auxiliary winding can be avoided, and the volume and the detection complexity of the system can be effectively reduced. Preferably, the switch circuit is a Boost circuit or a Boost PFC circuit, the switch is a junction field effect transistor or a MOSFET, and the voltage of the second end of the inductor has the characteristics of slow drop and stability due to the existence of parasitic capacitance at two ends of the switch, so that the switch has good anti-interference performance. In one embodiment, the demagnetization detection method comprises the steps of obtaining the differential characteristic of the voltage at the second end of the inductor and comparing the obtained differential value with a certain threshold value to obtain the demagnetization time information that the inductor current drops to zero.
The description and applications of the invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. Variations and modifications of the embodiments disclosed herein are possible, and alternative and equivalent various components of the embodiments will be apparent to those skilled in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other components, materials, and parts, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.
Claims (10)
1. A degaussing detection circuit for a switching circuit, wherein the switching circuit comprises an inductor, a switch coupled between a second terminal of the inductor and ground, and a rectifying device coupled between the second terminal of the inductor and an output terminal, the degaussing detection circuit obtaining degaussing time information for the inductor current to drop to zero based on a voltage at the second terminal of the inductor.
2. The demagnetization detection circuit of claim 1, comprising:
the input end of the differential circuit is coupled with the second end of the inductor;
and the input end of the comparison circuit is coupled with the output end of the differential circuit, and the output end of the comparison circuit provides a demagnetization detection signal.
3. The demagnetization detection circuit of claim 2, wherein the differentiating circuit comprises:
the first end of the capacitor receives a voltage signal representing the voltage of the second end of the inductor;
the first end of the resistor is coupled with the second end of the capacitor, the second end of the resistor is coupled with the grounding end, and the coupling point of the capacitor and the resistor is used as the output end of the differential circuit.
4. The demagnetization detection circuit of claim 2, further comprising a voltage divider circuit, wherein an input terminal of the voltage divider circuit is coupled to the second terminal of the inductor, and an output terminal of the voltage divider circuit is coupled to an input terminal of the differential circuit.
5. A control circuit for a Boost PFC circuit, wherein the Boost PFC circuit includes a rectifying circuit, an inductor coupled with a first end to the rectifying circuit, a switch coupled between a second end of the inductor and a ground terminal, and a rectifier coupled between the second end of the inductor and an output terminal, the control circuit comprising:
the demagnetization detection circuit according to any of claims 1 to 4;
the loop control circuit is used for controlling the conducting time of the switch;
the demagnetizing detection circuit comprises a trigger, a first input end, a second input end and an output end, wherein the first input end of the trigger is coupled with the output end of the demagnetizing detection circuit, and the second input end of the trigger is coupled with the output end of the loop control circuit; and
and the input end of the driving circuit is coupled with the output end of the trigger, and the output end of the driving circuit is coupled with the control end of the switch.
6. The control circuit of claim 5, wherein the loop control circuit has an input terminal coupled to the output terminal of the Boost PFC circuit for receiving the detection signal indicative of the output voltage, wherein the Boost PFC circuit further has an output capacitor coupled between the second terminal of the rectifier and the ground terminal, wherein the second terminal of the rectifier serves as the output terminal of the Boost PFC circuit.
7. The control circuit of claim 5, wherein the flip-flop is an RS flip-flop, the first input of the flip-flop is a set input, and the second input of the flip-flop is a reset input.
8. A degaussing detection method for a switching circuit, wherein the switching circuit comprises an inductor, a switch coupled between a second end of the inductor and a ground terminal, and a rectifier tube coupled between the second end of the inductor and an output terminal, the method comprises the steps of detecting the voltage of the second end of the inductor, and obtaining degaussing time information that the current of the inductor drops to zero according to the voltage.
9. A demagnetization detection circuit for detecting inductance demagnetization time information, comprising:
the input end of the differentiating circuit is coupled with the inductor and used for acquiring a voltage signal at one end of the inductor;
and the input end of the comparison circuit is coupled with the output end of the differential circuit, and the output end of the comparison circuit provides a demagnetization detection signal.
10. The demagnetization detection circuit of claim 9, wherein the differentiating circuit comprises:
the first end of the capacitor receives a voltage signal representing the voltage of the second end of the inductor;
the first end of the resistor is coupled with the second end of the capacitor, the second end of the resistor is coupled with the grounding end, and the coupling point of the capacitor and the resistor is used as the output end of the differential circuit.
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| CN201811175200.5ACN111025035A (en) | 2018-10-10 | 2018-10-10 | Demagnetization detection circuit and control circuit and method thereof |
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| CN201811175200.5ACN111025035A (en) | 2018-10-10 | 2018-10-10 | Demagnetization detection circuit and control circuit and method thereof |
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| CB02 | Change of applicant information | Address after:Room 3303, block a, block 8, block C, Wanke Yuncheng phase III, Liuxin 4th Street, Xili community, Nanshan District, Shenzhen City, Guangdong Province Applicant after:Shenzhen Biyi Microelectronics Co.,Ltd. Address before:518055 2 302, nine Xiang Ling new industrial zone, 4227 Xili Hu Road, Nanshan District, Shenzhen, Guangdong. Applicant before:SHENZHEN KIWI MICROELECTRONIC Co.,Ltd. | |
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| RJ01 | Rejection of invention patent application after publication | Application publication date:20200417 | |
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