Blanking circuit and switching power supply

Abstract

The embodiment of the utility model discloses a blanking circuit and a switching power supply, and relates to the technical field of switching power supply blanking, the blanking circuit comprises a coupling unit and a first switch unit; the switching power supply comprises a switching power supply chip, a second switch unit and a transformer; the switching power supply chip comprises an output pin and a current detection pin; the output pin is respectively connected with the coupling unit and the second switch unit, the coupling unit is connected with the first switch unit, and the second switch unit is connected with a primary winding of the transformer and the current detection pin; the first switch unit is connected with the current detection pin and is grounded; according to the technical scheme, the coupling unit couples and transmits the PWM signal output by the switching power supply chip to the first switching unit, the first switching unit is switched on at the moment that the second switching unit is switched on, and the current detection pin of the switching power supply chip is pulled down, so that false triggering caused by peak current when the switching power supply works can be effectively avoided.

Description

Technical Field

[0001] The utility model relates to the technical field of switch power supply blanking, in particular to a blanking circuit and a switch power supply. Background Art

[0002] With the development of power electronics technology, the integration of circuits makes the volume of circuit systems smaller. The power density of the output load of general linear regulators is small and can no longer meet the requirements of circuit system miniaturization. Switching power supplies that replace such linear regulators begin to appear. Among them, flyback switching power supplies are widely used in medium and small power scenarios due to their simple circuit, high conversion efficiency, small turns ratio of transformers, and stable output.

[0003] However, due to the parasitic capacitance between turns and layers in the primary winding of the flyback switching power supply, this parasitic capacitance will cause large spikes in the peak current of the primary side. Even if the switching power supply chip adds leading-edge blanking internally, it will be mis-triggered when the spike current is too high, affecting the stable output of the power supply. At the same time, too high current spikes (di / dt) will also seriously affect the EMI filter, increase the loss when the MOS tube is turned on, and reduce the power supply efficiency.

[0004] It can be seen that how to reduce the spike current of the power supply and ensure that it will not be mis-triggered by the spike current during the normal operation of the power supply has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Utility Model

[0005] The technical problem to be solved by the embodiments of the utility model is: how to reduce the spike current of the power supply and ensure that it will not be mis-triggered by the spike current during the normal operation of the power supply.

[0006] To solve the above problems, in a first aspect, an embodiment of the utility model provides a blanking circuit applied to a switching power supply. The blanking circuit includes a coupling unit and a first switching unit; the switching power supply includes a switching power supply chip, a second switching unit, and a transformer. The switching power supply chip includes an output pin and a current detection pin; the output pin is respectively connected to the coupling unit and the second switching unit, the coupling unit is connected to the first switching unit, the second switching unit is connected to the primary winding of the transformer and the current detection pin; the first switching unit is connected to the current detection pin and grounded.

[0007] A further technical solution thereof is that the coupling unit includes a coupling capacitor, one end of the coupling capacitor is connected to the output pin, and the other end of the coupling capacitor is connected to the first switching unit.

[0008] A further technical solution thereof is that the first switching unit includes a first switching tube, a control end of the first switching tube is connected to the coupling capacitor, an input end of the first switching tube is connected to the current detection pin, and an output end of the first switching tube is grounded.

[0009] A further technical solution thereof is that the blanking circuit further includes a first current limiting unit, and the coupling capacitor is connected to the control end of the first switching tube through the first current limiting unit.

[0010] A further technical solution thereof is that the second switching unit includes a second switching tube, a control end of the second switching tube is connected to the output pin, an input end of the second switching tube is connected to the primary winding of the transformer, and an output end of the second switching tube is connected to the current detection pin.

[0011] A further technical solution thereof is that the switching power supply further includes a second current limiting unit, and the current detection pin is connected to the output end of the second switching tube through the second current limiting unit.

[0012] A further technical solution thereof is that the switching power supply further includes a current detection unit, the current detection unit includes a sampling resistor and a filtering unit, the sampling resistor is connected to the output end of the second switching tube and grounded, and the filtering unit is respectively connected to the sampling resistor, the output end of the second switching tube, and the current detection pin.

[0013] A further technical solution thereof is that the filtering unit includes a filtering resistor and a filtering capacitor, the filtering resistor is respectively connected to the sampling resistor, the output end of the second switching tube, and the current detection pin, and the filtering capacitor is connected to the filtering resistor and grounded.

[0014] A further technical solution thereof is that the first switching tube is a MOS tube.

[0015] In a second aspect, an embodiment of the present invention provides a switching power supply, including the blanking circuit as described in the first aspect.

[0016] Compared with the prior art, the technical effects that can be achieved by the embodiments of the present invention include:

[0017] In the technical solution of the embodiment of the present utility model, the blanking circuit includes a coupling unit and a first switching unit; the switching power supply includes a switching power supply chip, a second switching unit and a transformer, and the switching power supply chip includes an output pin and a current detection pin; the output pin is respectively connected to the coupling unit and the second switching unit, the coupling unit is connected to the first switching unit, and the second switching unit is connected to the primary winding of the transformer and the current detection pin; the first switching unit is connected to the current detection pin and grounded; through the above technical solution, the coupling unit couples and transmits the PWM signal output by the switching power supply chip to the first switching unit. At the moment when the second switching unit is turned on, the first switching unit is turned on, pulling down the current detection pin of the switching power supply chip, so as to effectively avoid the mis-triggering of the switching power supply due to the peak current during operation. Description of the Drawings

[0018] The drawings here are incorporated into the specification and form a part of this specification, showing the embodiments consistent with the present utility model, and are used together with the specification to explain the principles of the present utility model.

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, unless otherwise stated, and the drawings in the drawings do not constitute a proportional limitation.

[0021] Figure 1 It is a circuit schematic diagram of a switching power supply proposed by the embodiment of the present utility model;

[0022] Figure 2 It is a circuit diagram of a switching power supply proposed by the embodiment of the present utility model;

[0023] Figure 3 It is a waveform diagram of the PWM signal output by the output pin of the switching power supply chip and the current signal detected by the current detection pin when the blanking circuit is not configured;

[0024] Figure 4 It is a waveform diagram of the PWM signal output by the output pin of the switching power supply chip and the current signal detected by the current detection pin when the blanking circuit is configured.

[0025] Reference numeral

[0026] The blanking circuit 10, the coupling unit 11, the first switching unit 12, the first current limiting unit 13, the switching power supply chip U1, the second switching unit 20, the transformer L1, the second current limiting unit 30, the current detection unit 40, the filtering unit 41, the coupling capacitor C1, the first switching transistor Q1, the first current limiting resistor R1, the second switching transistor Q2, the second current limiting resistor R4, the sampling resistor R2, the filtering resistor R3, the filtering capacitor C2, the output pin OUT, and the current detection pin CS. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Similar component numbers in the drawings represent similar components. Obviously, the embodiments to be described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0028] It should be understood that when used in this specification and the appended claims, the terms "comprises" and "comprising" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0029] It should also be understood that the terms used in the specification of the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present invention. As used in the specification of the embodiments of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0030] See Figure 1 - Figure 2 , an embodiment of the present invention provides a blanking circuit 10, and the blanking circuit 10 is applied to a switching power supply. The blanking circuit 10 includes a coupling unit 11 and a first switching unit 12. The switching power supply may be a flyback switching power supply, and the switching power supply includes a switching power supply chip U1, a second switching unit 20, and a transformer L1. The specific structure is introduced as follows:

[0031] The model of the switching power supply chip U1 may be UC3844. The switching power supply chip U1 includes an output pin OUT and a current detection pin CS; the output pin OUT is used to output a PWM signal to the second switching unit 20 and the coupling unit 11. The current detection pin CS is used to detect the conduction current of the second switching unit 20.

[0032] Specifically, the output pin OUT is respectively connected to the coupling unit 11 and the second switching unit 20, and is used to output a PWM signal to the second switching unit 20 and the coupling unit 11.

[0033] The coupling unit 11 is connected to the first switching unit 12, and is used to couple the PWM signal output by the output pin OUT to the first switching unit 12.

[0034] The second switching unit 20 is connected to the primary winding of the transformer L1 and the current detection pin CS; the first switching unit 12 is connected to the current detection pin CS and grounded. The current detection pin CS is used to detect the conduction current of the second switching unit 20. The first switching unit 12 is used to eliminate the spike current when the second switching unit 20 conducts, avoiding mis-triggering of the switching power supply during operation.

[0035] In the technical solution of the embodiment of the present invention, the blanking circuit 10 includes a coupling unit 11 and a first switching unit 12; the switching power supply includes a switching power supply chip U1, a second switching unit 20, and a transformer L1. The switching power supply chip U1 includes an output pin OUT and a current detection pin CS; the output pin OUT is respectively connected to the coupling unit 11 and the second switching unit 20, the coupling unit 11 is connected to the first switching unit 12, and the second switching unit 20 is connected to the primary winding of the transformer L1 and the current detection pin CS; the first switching unit 12 is connected to the current detection pin CS and grounded; through the above technical solution, the coupling unit 11 couples and transmits the PWM signal output by the switching power supply chip U1 to the first switching unit 12. At the moment when the second switching unit 20 is turned on, the first switching unit 12 conducts, pulling down the current detection pin CS of the switching power supply chip U1, so as to effectively avoid mis-triggering of the switching power supply due to spike current during operation.

[0036] Specifically, when the blanking circuit 10 is not configured, refer to Figure 3 , Figure 3 The waveform on the upper side in is the waveform diagram of the PWM signal output by the output pin OUT of the switching power supply chip U1, and the waveform on the lower side is the current waveform diagram detected by the current detection pin CS of the switching power supply chip U1. It can be seen that when the blanking circuit 10 is not configured, at the moment when the second switching unit 20 conducts, a spike current is generated at the CS pin of the switching power supply chip U1, which may cause mis-triggering of the switching power supply.

[0037] When the blanking circuit 10 is configured, refer to Figure 4 , Figure 4The waveform on the upper side is the waveform diagram of the PWM signal output from the output pin OUT of the switching power supply chip U1, and the waveform on the lower side is the current waveform diagram detected by the current detection pin CS of the switching power supply chip U1. It can be seen that after configuring the blanking circuit 10 of the embodiment of the present invention, at the moment when the second switching unit 20 is turned on, no spike current will be generated at the CS pin of the switching power supply chip U1, thereby effectively avoiding mis-triggering of the switching power supply.

[0038] Further, the coupling unit 11 includes a coupling capacitor C1. One end of the coupling capacitor C1 is connected to the output pin OUT, and the other end of the coupling capacitor C1 is connected to the first switching unit 12. The coupling capacitor C1 has the function of passing alternating current and blocking direct current, and can effectively couple the high-frequency PWM signal of the output pin OUT of the switching power supply chip U1 to the first switching unit 12.

[0039] Further, the first switching unit 12 includes a first switching transistor Q1. The control end of the first switching transistor Q1 is connected to the coupling capacitor C1, the input end of the first switching transistor Q1 is connected to the current detection pin CS, and the output end of the first switching transistor Q1 is grounded. The first switching transistor Q1 can specifically be a MOS transistor. For example, in this embodiment, the first switching transistor Q1 is an NMOS transistor. For an NMOS transistor, its control end is the gate, the input end is the drain, and the output end is the source.

[0040] Further, the blanking circuit 10 further includes a first current limiting unit 13. The coupling capacitor C1 is connected to the control end of the first switching transistor Q1 through the first current limiting unit 13. The first current limiting unit 13 functions to limit the magnitude of the current and is used to drive the first switching transistor Q1 to turn on / off. The first current limiting unit 13 includes at least one current limiting resistor. For example, in this embodiment, the first current limiting unit 13 includes a first current limiting resistor R1.

[0041] Further, the second switching unit 20 includes a second switching transistor Q2. The control end of the second switching transistor Q2 is connected to the output pin OUT, the input end of the second switching transistor Q2 is connected to the primary winding of the transformer L1, and the output end of the second switching transistor Q2 is connected to the current detection pin CS. The second switching transistor Q2 can specifically be a MOS transistor. For example, in this embodiment, the second switching transistor Q2 is an NMOS transistor. For an NMOS transistor, its control end is the gate, the input end is the drain, and the output end is the source.

[0042] Further, the switching power supply further includes a second current limiting unit 30. The current detection pin CS is connected to the output end of the second switching transistor Q2 through the second current limiting unit 30. The second current limiting unit 30 functions to limit the magnitude of the current and is used to drive the second switching transistor Q2 to conduct / turn off. The second current limiting unit 30 includes at least one current limiting resistor. For example, in this embodiment, the second current limiting unit 30 includes a second current limiting resistor R4.

[0043] Further, the switching power supply further includes a current detection unit 40. The current detection unit 40 includes a sampling resistor R2 and a filtering unit 41. The sampling resistor R2 is connected to the output end of the second switching transistor Q2 and grounded. The filtering unit 41 is respectively connected to the sampling resistor R2, the output end of the second switching transistor Q2, and the current detection pin CS. The sampling resistor R2 is used to collect the conduction current of the second switching transistor Q2. The filtering unit 41 functions to filter and can effectively filter out the clutter in the circuit, thereby improving the accuracy of detection.

[0044] Further, the filtering unit 41 includes a filtering resistor R3 and a filtering capacitor C2. The filtering resistor R3 is respectively connected to the sampling resistor R2, the output end of the second switching transistor Q2, and the current detection pin CS. The filtering capacitor C2 is connected to the filtering resistor R3 and grounded. The filtering resistor R3 and the filtering capacitor C2 form an RC filtering circuit, thereby being able to achieve a good filtering effect.

[0045] An embodiment of the present utility model provides a switching power supply, which includes the blanking circuit 10 described in any of the above embodiments.

[0046] In the above embodiments, the descriptions of the respective embodiments have their own focuses. For the parts not described in detail in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

[0047] In the description of the present utility model, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present utility model.

[0048] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present utility model, "a plurality of" means two or more unless otherwise specifically defined.

[0049] In the present utility model, unless otherwise clearly specified and defined, terms such as "installed", "connected", "connected to", "fixed", etc. shall be understood in a broad sense. For example, it may be a connection, a detachable connection, or an integral body; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0050] In the present utility model, unless otherwise clearly specified and defined, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but in contact through additional features therebetween. Moreover, the first feature being "above", "above and over", and "on the top of" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "below", "below and under", and "under the bottom of" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0051] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present utility model. In this specification, the schematic descriptions of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0052] Obviously, those skilled in the art can make various modifications and variations to the present utility model without departing from the spirit and scope of the present utility model. Thus, provided that these modifications and variations of the present utility model fall within the scope of the claims of the present utility model and their equivalent technologies, the present utility model also intends to include these modifications and variations therein.

[0053] The above are the specific embodiments of the present utility model, but the protection scope of the present utility model is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present utility model can easily conceive of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present utility model. Therefore, the protection scope of the present utility model shall be subject to the protection scope of the claims.

Claims

1. A blanking circuit, characterized in that, Applied to a switching power supply, the blanking circuit includes a coupling unit and a first switching unit; the switching power supply includes a switching power supply chip, a second switching unit, and a transformer, and the switching power supply chip includes an output pin and a current detection pin; the output pin is respectively connected to the coupling unit and the second switching unit, the coupling unit is connected to the first switching unit, the second switching unit is connected to the primary winding of the transformer and the current detection pin; the first switching unit is connected to the current detection pin and grounded.

2. The blanking circuit according to claim 1, wherein The coupling unit includes a coupling capacitor, one end of the coupling capacitor is connected to the output pin, and the other end of the coupling capacitor is connected to the first switching unit.

3. The blanking circuit according to claim 2, wherein The first switching unit includes a first switching transistor, the control end of the first switching transistor is connected to the coupling capacitor, the input end of the first switching transistor is connected to the current detection pin, and the output end of the first switching transistor is grounded.

4. The blanking circuit according to claim 3, wherein The blanking circuit further includes a first current limiting unit, and the coupling capacitor is connected to the control end of the first switching transistor through the first current limiting unit.

5. The blanking circuit according to claim 1, wherein The second switching unit includes a second switching transistor, the control end of the second switching transistor is connected to the output pin, the input end of the second switching transistor is connected to the primary winding of the transformer, and the output end of the second switching transistor is connected to the current detection pin.

6. The blanking circuit according to claim 5, wherein The switching power supply further includes a second current limiting unit, and the current detection pin is connected to the output end of the second switching transistor through the second current limiting unit.

7. The blanking circuit according to claim 5, wherein The switching power supply further includes a current detection unit, the current detection unit includes a sampling resistor and a filtering unit, the sampling resistor is connected to the output end of the second switching transistor and grounded, and the filtering unit is respectively connected to the sampling resistor, the output end of the second switching transistor, and the current detection pin.

8. The blanking circuit according to claim 7, wherein The filtering unit includes a filtering resistor and a filtering capacitor, the filtering resistor is respectively connected to the sampling resistor, the output end of the second switching transistor, and the current detection pin, and the filtering capacitor is connected to the filtering resistor and grounded.

9. The blanking circuit according to claim 3, characterized in that The first switching transistor is a MOS transistor.

10. A switching power supply, characterized in that, Including the blanking circuit according to any one of claims 1-9.

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