CN211656009U

CN211656009U - Control device and chip of switching power supply and switching power supply

Info

Publication number: CN211656009U
Application number: CN201921640496.3U
Authority: CN
Inventors: 宗强; 刘准; 吴寿化; 方芳
Original assignee: Shenzhen Chip Hope Micro-Electronics Ltd
Current assignee: Shenzhen Chip Hope Micro-Electronics Ltd
Priority date: 2019-09-27
Filing date: 2019-09-27
Publication date: 2020-10-09
Anticipated expiration: 2029-09-27

Abstract

The application discloses switching power supply's controlling means, chip and switching power supply, wherein, switching power supply contains power switch tube and transformer, controlling means includes: the switch unit is electrically connected between the secondary winding of the transformer and a grounding end; the detection unit is connected with two ends of the switch unit in parallel and used for controlling the switch unit to generate an oscillation signal on the secondary winding of the transformer when the load is determined to be insufficient in power supply by detecting an electric signal of the secondary winding when the switch unit is in an off state; and the primary side driving unit is coupled to the secondary side winding and used for driving the power switching tube to be conducted based on the oscillation signal. The switching power supply control device, the chip and the switching power supply can reduce the energy consumption of the switching power supply and improve the dynamic performance of the switching power supply.

Description

Control device and chip of switching power supply and switching power supply

Technical Field

The application relates to the technical field of control circuits, in particular to a control device of a switching power supply, a chip and the switching power supply.

Background

The switching power supply is a device for converting electric energy, converts alternating current provided by a power grid into various direct current output voltages, and is widely applied to occasions such as electronic equipment adapters and the like because the switching power supply has the advantages of few peripheral system components, low cost, simple structure, low standby power consumption and the like.

In order to maintain the output voltage provided by the switching power supply stable, the switching power supply needs to control its switching frequency to maintain normal operation. In order to reduce the standby power consumption of the system when the system works in light load or no load, the switching power supply reduces the working frequency in the period so that the conducting times of the switching power supply in the same time period are reduced. However, the low minimum switching frequency will have a great influence on the dynamic performance of the system, and when the system is switched from light load to heavy load instantly due to the limitation of the minimum switching frequency, the switching power supply cannot compensate energy immediately, so that the dynamic performance of the system is very poor.

Disclosure of Invention

In view of the above-mentioned drawbacks of the related art, an object of the present application is to provide a control apparatus for a switching power supply, which is used to solve the problem that the prior art switching power supply cannot achieve both low power consumption and dynamic response.

To achieve the above and other related objects, a first aspect of the present application discloses a control device for a switching power supply, wherein the switching power supply includes a power switch tube and a transformer, and the control device includes: the switch unit is electrically connected between the secondary winding of the transformer and a grounding end; the detection unit is connected with two ends of the switch unit in parallel and used for controlling the switch unit to generate an oscillation signal on the secondary winding of the transformer when the load is determined to be insufficient in power supply by detecting an electric signal of the secondary winding when the switch unit is in an off state; and the primary side driving unit is coupled to the secondary side winding and used for driving the power switching tube to be conducted based on the oscillation signal.

In certain embodiments of the first aspect of the present application, the detection unit comprises: the detection circuit is connected in parallel with two ends of the switch unit and is used for detecting the electric signal of the secondary winding; the comparison circuit is electrically connected to the detection circuit and used for comparing the electric signal of the secondary winding with a reference signal to output a first indication signal when the switch unit is in an off state; and the logic control circuit is electrically connected with the comparison circuit and the switch unit and used for outputting a secondary side control signal to the switch unit based on the first indication signal.

In certain embodiments of the first aspect of the present application, the reference signal is a predetermined fixed value.

In certain embodiments of the first aspect of the present application, the detection unit further includes a reference signal generation circuit, electrically connected to the comparison circuit, for outputting a reference signal reflecting an average power supply of the load.

In certain embodiments of the first aspect of the present application, the detection unit further comprises: the synchronous rectification circuit is electrically connected with the detection circuit and the logic control circuit and used for outputting a second indicating signal to the logic control circuit based on the electric signal of the detection secondary winding; wherein the logic control circuit outputs the secondary side control signal to the switching unit based on the first and second indication signals; and the enabling circuit is electrically connected with the synchronous rectification circuit and the comparison circuit and is used for enabling the comparison circuit based on the first quasi-position delay of the second indication signal or disabling the comparison circuit based on the second quasi-position of the second indication signal.

In certain embodiments of the first aspect of the present application, the primary side drive unit includes a feedback circuit, coupled to the secondary winding, for generating a feedback signal based on the oscillating signal; the judging circuit is electrically connected to the feedback circuit and used for outputting a primary side control signal based on the feedback signal; and the driving circuit is electrically connected to the judging circuit and used for driving the power switch tube to be conducted based on the primary side control signal.

In certain embodiments of the first aspect of the present application, the determining circuit includes a negative voltage determining circuit, configured to determine a negative voltage of the feedback signal according to a voltage of the feedback signal and a preset value to output the primary side control signal.

In some embodiments of the first aspect of the present application, the primary side driving unit further includes a shielding circuit electrically connected to the determining circuit and the driving circuit, and configured to shield the primary side control signal during a non-timeout period of the timing based on the primary side control signal.

A second aspect of the present application discloses a chip that encapsulates at least part of the circuitry of the control device of the switching power supply as described above.

A third aspect of the present application discloses a switching power supply device including: the rectifying circuit is used for rectifying the accessed alternating current and outputting the rectified alternating current to the power supply bus; the driving end of the power switch tube is electrically connected to the control device of the switching power supply, and the input end of the power switch tube is connected to the power supply bus; and the transformer is electrically connected between the power supply bus and the input end of the power switch tube and used for providing stable power supply for a load based on the on or off of the power switch tube.

To sum up, switching power supply's controlling means, chip and switching power supply that this application provided are through setting up detecting element and switch element at the output for can be at the change of output direct monitoring load power supply, and give the input in time when the load power supply suddenly drops, make switching power supply work still can in time respond to the change of load when under extremely low operating frequency, thereby improved its dynamic behavior when reducing switching power supply energy consumption.

Drawings

Fig. 1 shows a block diagram of a switching power supply.

Fig. 2 is a block diagram of a control device of a switching power supply according to an embodiment of the present invention.

Fig. 3 is a voltage waveform diagram of a control device of the switching power supply according to an embodiment of the present invention.

Fig. 4 is a schematic structural diagram of a detection unit in an embodiment of the control device of the switching power supply of the present application.

Fig. 5 is a schematic structural diagram of a reference signal generating circuit in an embodiment of a control apparatus of a switching power supply according to the present application.

Fig. 6 is a schematic structural diagram of a detection unit in another embodiment of the control device of the switching power supply of the present application.

Fig. 7 is a schematic structural diagram of a switch unit in an embodiment of the control device of the switching power supply of the present application.

Fig. 8 is a schematic structural diagram of a primary side driving unit in an embodiment of the control device of the switching power supply of the present application.

Fig. 9 is a schematic structural diagram of a negative voltage determining circuit in an embodiment of the control device of the switching power supply of the present application.

Fig. 10 is a schematic structural diagram of a primary side driving unit in another embodiment of the control device of the switching power supply of the present application.

Detailed Description

The following description of the embodiments of the present application is provided for illustrative purposes, and other advantages and capabilities of the present application will become apparent to those skilled in the art from the present disclosure.

Although the terms first, second, etc. may be used herein to describe various elements or parameters in some instances, these elements or parameters should not be limited by these terms. These terms are only used to distinguish one element or parameter from another element or parameter. For example, the first switching frequency may be referred to as the second switching frequency, and similarly, the second switching frequency may be referred to as the first switching frequency, without departing from the scope of the various described embodiments. The first switching frequency and the second switching frequency are both describing one switching frequency, but they are not the same switching frequency unless the context clearly dictates otherwise. Similar situations also include the first and second indication signals Sig1 and Sig2, or the first and second secondary power switching light pipes.

Also, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used in this specification, specify the presence of stated features, steps, operations, elements, components, items, species, and/or groups, but do not preclude the presence, or addition of one or more other features, steps, operations, elements, components, species, and/or groups thereof. The terms "or" and/or "as used herein are to be construed as inclusive or meaning any one or any combination. Thus, "A, B or C" or "A, B and/or C" means "any of the following: a; b; c; a and B; a and C; b and C; A. b and C ". An exception to this definition will occur only when a combination of elements, functions, steps or operations are inherently mutually exclusive in some way.

The switch power supply is a device for converting electric energy, converts alternating current provided by a power grid into various direct current output voltages, and can be used for providing output voltages of 5V, 3.3V, 2.5V and the like required by a digital circuit and output voltages of +/-12V, +/-15V and the like required by an analog circuit in various electronic devices and household appliances requiring power supply of multiple paths of different voltages. The switching power supply has the advantages of few peripheral system components, low cost, simple structure, low standby power consumption and the like, and is widely applied to occasions such as electronic equipment adapters and the like.

Referring to fig. 1, a block diagram of a switching power supply is shown, where the switching power supply includes a rectifier circuit 10, a transformer 11, a power switch tube 12, and a control circuit 13, where the rectifier circuit 10 is configured to rectify an input ac into a dc input voltage Vin and input the dc input voltage Vin to a power supply bus, an input end of the power switch tube 12 is connected to the power supply bus through the transformer 11, a driving end of the power switch tube is electrically connected to the control circuit 13 to be controlled to be turned on and off, and the transformer 11 includes a primary winding Np, a secondary winding Ns, and an auxiliary winding Na, and is configured to provide stable power supply for a load based on the turning on and off of the power switch tube 12.

In the switching power supply shown in fig. 1, the control circuit 13 has a feedback terminal FB and a detection terminal CS, the feedback terminal FB obtains a voltage division signal from a voltage division circuit formed by a resistor R1 and a resistor R2 electrically connected to the auxiliary winding Na, the detection terminal CS obtains a current detection signal of the primary winding Np from a resistor Rs, wherein the voltage division signal is used for reflecting the output voltage Vout, the current detection signal is used for reflecting a peak current when the primary winding Np is turned on, and the control circuit 13 controls the on/off of the power switching tube 12 based on the voltage division signal obtained from the feedback terminal FB and the current detection signal obtained from the detection terminal CS.

In order to maintain the output voltage provided by the switching power supply stable, the switching power supply adjusts the switching frequency by sampling the FB signal at the feedback end to maintain the normal operation. In order to reduce the standby power consumption of the system when the system works under light load or no load, the switching power supply reduces the lowest working frequency of the switching power supply, so that the conducting times of the switching power supply are reduced in the same time period.

In view of this, the present application provides a control device for a switching power supply, where the switching power supply includes the power switch tube and the transformer, and the control device for the switching power supply provided in the present application enables the switching power supply to respond to the load change in time when the switching power supply operates at an extremely low operating frequency. Referring to fig. 2, a block diagram of a control device of a switching power supply according to an embodiment of the present invention is shown, and the control device includes a switching unit 20, a detection unit 21, and a primary side driving unit 22.

The switch unit is electrically connected between the secondary winding of the transformer and the ground terminal.

In the switching power supply shown in fig. 1, the power switching tube 12 is disposed on the primary side of the transformer 11, and a rectifying diode D1 is disposed on the secondary side of the transformer 11 to achieve secondary side rectification, so that stable power supply can be provided to a load. In order to further reduce internal consumption and improve system operation efficiency, as shown in fig. 2, the switching unit 20 is turned on or off at a first switching frequency to implement secondary side rectification in cooperation with the power switching tube 12. It should be noted that, when the switching unit 20 operates at the first switching frequency, it needs to be turned off before the power switching tube 12 is turned on, that is, the switching unit 20 and the power switching tube 12 cannot be simultaneously turned on, and the specific structure and the control manner of the switching unit 20 will be described in detail later.

The detecting unit 21 is connected in parallel to two ends of the switching unit 20, and is configured to control the switching unit 20 to generate an oscillating signal on the secondary winding Ns of the transformer 11 when it is determined that the load is short of power supply by detecting an electrical signal of the secondary winding Ns during the off state of the switching unit 20.

In practical applications, the detecting unit 21 is connected in parallel to two ends of the switching unit 20, that is, the detecting unit 21 is electrically connected between the secondary winding Ns of the transformer 11 and the ground terminal, and is used for detecting an electrical signal of the secondary winding Ns. In the embodiment, the electrical signal may be, for example, an electrical parameter such as a voltage value and a current value that can reflect the power supply state of the secondary winding Ns, and the following description will be given by taking the electrical signal for detecting the secondary winding Ns as the voltage value, but the electrical signal for detecting the secondary winding Ns is not limited thereto, and other embodiments that can reflect the power supply state of the secondary winding Ns as the electrical signal for the secondary winding Ns are also within the scope of the present application.

Referring to fig. 3 in conjunction with fig. 2, fig. 3 is a voltage waveform diagram of the control device of the switching power supply in an embodiment of the present invention, as shown in the figure, when the switching power supply is under light load or no load, in order to reduce power consumption, the power switch tube 12 operates at an extremely low switching frequency (in a waveform of Pgate in fig. 3), the switch unit 20 is matched with the power switch tube 12 to operate at a first switching frequency (in a waveform of Sgate in fig. 3), and the electrical signal of the secondary winding Ns detected by the detection unit 21 is a waveform corresponding to Vds. It should be noted that, when the power switch tube 12 is turned on, the transformer 11 is in the excitation stage, and the electrical signal of the secondary winding Ns detected by the detecting unit 21 reflects the voltage value of the excitation stage on the secondary winding Ns; when the switching unit 20 is turned on in cooperation with the turn-off of the power switching tube 12, the loop on the secondary winding Ns of the transformer 11 is turned on, the transformer 11 is in a demagnetization stage, and the electrical signal of the secondary winding Ns detected by the detecting unit 21 is a short-circuit signal; after the demagnetization of the transformer 11 is finished, the switching unit 20 is turned off, and the power switching tube 12 is still kept in the off state to reduce the power consumption because the power switching tube 12 operates at an extremely low switching frequency, at this time, the electrical signal of the secondary winding Ns detected by the detecting unit 21 reflects the load supply, that is, the output voltage Vout.

In view of this, in order to respond to the change of the load supply (from light load to heavy load) in time during the time when the power switch tube 12 is turned off, the detection unit 21 determines that the load supply is insufficient (voltage dip 23 appearing in the waveform of Vds in fig. 3) according to the electrical signal of the secondary winding Ns detected by the device when the switch unit 20 is in the off state, and controls the switch unit 20 to generate an oscillation signal (oscillation signal 24 appearing in the waveform of Vds) on the secondary winding Ns of the transformer 11.

In an embodiment, please refer to fig. 4, which is a schematic structural diagram of a detection unit of the control device of the switching power supply of the present application in an embodiment, as shown in the figure, the detection unit 21 includes a detection circuit 210, a comparison circuit 211, and a logic control circuit 212.

The detection circuit 210 is connected in parallel to two ends of the switching unit 20, and is configured to detect an electrical signal of the secondary winding. Here, the detection circuit 210 is electrically connected between the secondary winding of the transformer and the ground, and obtains the electrical signal of the secondary winding through a wire.

The comparing circuit 211 is electrically connected to the detecting circuit 210, and is configured to compare the electrical signal of the secondary winding with a reference signal to output a first indication signal Sig1 during the period that the switch unit 20 is in the off state.

As can be seen from the above, the electrical signal of the secondary winding reflects the power supply of the load during the off period of the switch unit 20, and the comparison circuit 211 compares the electrical signal of the secondary winding with a reference signal during the off period of the switch unit 20 to determine whether the power supply of the load is insufficient or not, and outputs the first indication signal Sig1 when the power supply is insufficient.

In one embodiment, as shown in fig. 4, the comparing circuit 211 includes a comparator 2110, a first input terminal of the comparator 2110 is used for obtaining a reference signal REF, and a second input terminal of the comparator 2110 is electrically connected to the detecting circuit 210 and is used for obtaining an electrical signal of the secondary winding detected by the detecting circuit 210. In order to enable the comparator 2110 to operate in the off state of the switch unit 20, the enable terminal of the comparator 2110 may further be electrically connected to the switch unit 20 through a switch detection circuit 2111, the switch detection circuit 2111 is configured to obtain the state of the switch unit 20, the comparator 2110 is disabled when the switch unit 20 is in the on state, the comparator 2110 is enabled when the switch unit 20 is in the off state so as to enable the comparator 2110 to compare signals obtained by two input terminals thereof, and it is determined that the load power supply is insufficient to output the first indication signal Sig1 when the comparison result is that the electrical signal of the secondary winding is lower than the reference signal REF. It should be noted that, in practical applications, at the moment that the switch unit 20 is turned off, demagnetization of the transformer is finished, but parasitic parameter oscillation (such as parasitic parameter oscillation 25 in Vds waveform in fig. 3) may be generated on the secondary winding due to the discharging function of the parasitic element, in order to avoid the comparator 2110 making a false determination according to the parasitic parameter oscillation detected by the detection circuit 210, the enable terminal of the comparator 2110 is further electrically connected to the switch detection circuit 2111 through a delay circuit 2112, the delay circuit 2112 starts timing based on the enable signal output by the switch detection circuit 2111, the comparator 2110 is enabled when the timing is overtime, and the delay circuit 2112 directly disables the comparator 2110 based on the disable signal output by the switch detection circuit 2111, so that the comparator 2110 does not output a comparison result.

The reference signal REF is a voltage threshold used for measuring whether the output voltage of the switching power supply suddenly drops. In one example, the reference signal REF is a predetermined constant value, which can be provided by dividing a voltage with a constant voltage source or a constant voltage source and a voltage dividing resistor (not shown). But not limited to this, the preset fixed value is also provided by the sampling voltage obtained by the constant current source and the sampling resistor.

In another example, the reference signal is set to an average value reflecting the average supply to the load in order to accommodate switching power supply applications with different output voltages. In view of this, the detection unit further includes a reference signal generation circuit electrically connected to the comparison circuit for outputting a reference signal reflecting the load average power supply to the comparison circuit. For example, please refer to fig. 5, which is a schematic structural diagram of a reference signal generating circuit of a control device of a switching power supply in an embodiment of the present invention, as shown in the figure, the reference signal generating circuit includes a first switch S1, a second switch S2, a buffer BUF, a capacitor C1 and a capacitor C2, wherein one end of the first switch S1 is electrically connected to the detecting circuit, the other end of the first switch S1 is electrically connected to one end of the second switch S2, the other end of the second switch S2 is electrically connected to the comparing circuit through the buffer BUF, the capacitor C1 is electrically connected to a node between the first switch S1 and the second switch S2, and the capacitor C2 is electrically connected to a node between the second switch S2 and the buffer BUF. Specifically, the first switch S1 is closed during the off phase of the switch unit, so that the electrical signal of the secondary winding detected by the detection circuit is transmitted to the capacitor C1, the second switch S2 operates during the off phase of the first switch S1, the electrical signal on the capacitor C1 is equally divided to the capacitor C2, and the average value of the previous multiple output voltages is obtained at the input end of the buffer BUF by setting the first switch S1 and the second switch S2 to be on and off and matching with the energy storage and the energy release of the capacitor C1 and the capacitor C2, and the buffer is used for generating the reference signal based on the average value of the multiple output voltages. For example, the buffer may reduce the average value of the output voltage for a plurality of times by a certain proportion, so that the obtained reference signal is the voltage threshold of the actually required output voltage dip.

As shown in fig. 4, the logic control circuit 212 is electrically connected to the comparison circuit 211 and the switch unit 20, and is configured to output a secondary control signal to the switch unit 20 based on the first indication signal Sig 1.

When the comparison circuit 211 determines that the load is under-supplied with power and outputs the first indication signal Sig1, the logic control circuit 212 outputs a secondary control signal based on the logic of the first indication signal Sig1, which may be, for example, a switching pulse signal for controlling the switching unit 20 to be turned on and off at a second switching frequency to generate an oscillation signal on the secondary winding of the transformer. The logic control circuit 212 includes, but is not limited to, flip-flops, timers, selectors, AND gates, OR gates, NAND gates, NOT gates, etc. according to control logic.

In another embodiment, please refer to fig. 6, which is a schematic structural diagram of a detection unit in another embodiment of the control device of the switching power supply of the present application, as shown in the figure, the detection unit 21 further includes a synchronous rectification circuit 213 and an enable circuit 214.

The synchronous rectification circuit 213 is electrically connected to the detection circuit 210 and the logic control circuit 212, and is configured to output a second indication signal Sig2 to the logic control circuit 212 based on the electrical signal of the secondary winding; wherein the logic control circuit 212 outputs the secondary control signal to the switch unit 20 based on the first and second indication signals Sig1 and Sig 2.

As described above, the switching means 20 is turned on or off at the first switching frequency to perform the secondary side rectification in accordance with the power switching tube, and the electric signal of the secondary side winding detected by the detection circuit 210 is processed by the synchronous rectification circuit 213 to output the second indication signal Sig 2.

Here, the logic control circuit 212 receives both the first indication signal Sig1 and the second indication signal Sig2, and the logic control circuit 212 generates a secondary side control signal through logic control based on the first indication signal Sig1 and the second indication signal Sig2, wherein the secondary side control signal includes a synchronous rectification signal and a switching pulse signal, the synchronous rectification signal is used for controlling the switching unit 20 to be switched at a first switching frequency so as to realize secondary side synchronous rectification, and the switching pulse signal is used for controlling the switching unit 20 to be switched at a second switching frequency so as to generate an oscillation signal on a secondary side winding of the transformer. The logic control circuit 212 includes, but is not limited to, flip-flops, timers, selectors, AND gates, OR gates, NAND gates, NOT gates, etc. according to control logic.

The enabling circuit 214 is electrically connected to the synchronous rectification circuit 213 and the comparing circuit 211, and is configured to delay enable the comparing circuit 211 based on the first level of the second indication signal Sig 2; or disable the comparator 211 based on the second level of the second indication signal Sig 2.

Here, the comparison circuit 211 is operated during the off state of the switching unit 20 by the enable circuit 214. The second indication signal Sig2 includes a first level, such as a low level, for indicating that the logic control circuit 212 controls the switch unit 20 to turn off, and a second level, such as a high level, for indicating that the logic control circuit 212 controls the switch unit 20 to turn on.

In one embodiment, the enabling circuit 214 includes a timer, the timer triggers the start of timing based on the first level of the second indication signal Sig2, the comparing circuit 211 is enabled when the timing is over, and the enabling circuit 214 directly disables the comparing circuit 211 based on the second level of the second indication signal Sig2, so that the comparing circuit 211 does not output the comparison result.

The switch unit 20 is electrically connected to the logic control circuit 212, and is configured to perform secondary synchronous rectification based on the secondary control signal, or generate an oscillation signal on a secondary winding of the transformer based on the secondary control signal.

In one embodiment, the switching unit includes a power switch tube (not shown), and for distinguishing from a power switch tube located at a primary side in the switching power supply, the power switch tube in the switching unit is referred to as a secondary side power switch tube, and the secondary side power switch tube operates at a first switching frequency based on a synchronous rectification signal in the secondary side control signal to perform a synchronous rectification state, and is turned on and off at a second switching frequency based on a switching pulse signal in the secondary side control signal to generate an oscillation signal on a secondary side winding of the transformer during an off state in which the secondary side power switch tube operates at the first switching frequency. The secondary power switch may be, for example, an insulated gate field effect transistor (MOSFET) with a very low on-state resistance, but not limited thereto, and in other embodiments, the secondary power switch may also be, for example, a Junction Field Effect Transistor (JFET).

In another embodiment, please refer to fig. 7, which is a schematic structural diagram of a switch unit in an embodiment of the control device of the switching power supply of the present application, as shown in the figure, the switch unit includes a selection circuit 200, a first secondary side power switch 201 and a second secondary side power switch 202, the selection circuit 200 is electrically connected to the detection unit 21, the first secondary side power switch 201 and the second secondary side power switch 202 are electrically connected in parallel between a secondary side winding and a ground terminal of the transformer, control terminals of the first secondary side power switch 201 and the second secondary side power switch 202 are electrically connected to the selection circuit 200, the selection circuit 200 is configured to select two secondary side power switches (201, 202) based on the secondary side control signal, so that the first secondary side power switch 201 operates at a first switching frequency based on a synchronous rectification signal in the secondary side control signal to perform synchronous rectification, the second secondary side power switch tube 202 is switched on and off at a second switching frequency based on the switching pulse signal in the secondary side control signal to generate an oscillating signal on the secondary side winding of the transformer. The first secondary power switch 201 may be, for example, an insulated gate field effect transistor (MOSFET) or a Junction Field Effect Transistor (JFET) with a very low on-state resistance, and the second secondary power switch 202 may be, for example, a triode or a field effect transistor.

The primary side driving unit is coupled to the secondary side winding and used for driving the power switch tube to be conducted based on the oscillation signal. Therefore, when the switching power supply works in a light load or no-load state at an extremely low switching frequency, the primary side driving unit can also respond to the change of load power supply (from light load or no-load to heavy load) in time to drive the power switching tube to be conducted, so that the energy at the input end of the switching power supply is transmitted to the output end, and the output voltage can rise in time.

Referring to fig. 8, which is a schematic structural diagram of a primary side driving unit of the control device of the switching power supply of the present application in an embodiment, as shown in the figure, the primary side driving unit 22 includes a feedback circuit 220, a judgment circuit 221, and a driving circuit 222.

The feedback circuit 220 is coupled to the secondary winding Ns for generating a feedback signal based on the oscillation signal. Taking the circuit structure shown in fig. 8 as an example, the feedback circuit 220 includes a voltage dividing circuit formed by a resistor R1 and a resistor R2, the voltage dividing circuit formed by the resistor R1 and the resistor R2 is electrically connected to the auxiliary winding Na of the transformer to be coupled to the secondary winding Ns through the auxiliary winding Na, so that the oscillation signal is transmitted from the secondary winding Ns to the auxiliary winding Na, and the feedback circuit 220 outputs the feedback signal based on the oscillation signal.

The determining circuit 221 is electrically connected to the feedback circuit 220, and is configured to output a primary side control signal based on the feedback signal. Here, the determination circuit 221 obtains the voltage of the feedback signal from the feedback circuit 220, and outputs the primary side control signal when determining that the secondary winding Ns generates the oscillation signal based on the voltage of the feedback signal.

In one embodiment, the determining circuit 221 includes a negative voltage determining circuit for determining a negative voltage of the feedback signal according to a voltage of the feedback signal and a predetermined value to output the primary side control signal. For example, please refer to fig. 9, which is a schematic structural diagram of a negative voltage determining circuit of the control apparatus of the switching power supply of the present application in an embodiment, as shown in the figure, the negative voltage determining circuit includes a comparator 2210, a positive input terminal of the comparator 2210 is electrically connected to a voltage dividing circuit composed of a current source I2 and a transistor N2, that is, an input value of the positive input terminal of the comparator 2210 is a tube voltage drop of a switching tube N2, a negative input terminal of the comparator 2210 is electrically connected to the voltage dividing circuit composed of a current source I1, a resistor R and a transistor N1, wherein a base of the transistor N1 is electrically connected to the feedback circuit for obtaining a voltage of the feedback signal, that is, an input value of the negative input terminal of the comparator 2210 is a sum of the voltage of the feedback signal, the tube voltage drop of the switching tube N1 and the divided voltage of the resistor R, the triode N1 and the triode N2 adopt triodes with the same parameters, namely, the tube voltage drop of the switch tube N1 is the same as that of the switch tube N2. The comparator 2210 compares the input values of the two input terminals, and outputs the primary side control signal when the positive input terminal is larger than the negative input terminal, that is, the voltage of the feedback signal is smaller than-I1 ar. Therefore, the negative pressure judgment circuit can determine that the feedback signal is caused by the oscillation signal according to the judgment of the negative pressure of the feedback signal so as to output the primary side control signal. In practical application, a proper current source I1 and a proper resistor R can be selected according to the specific circuit structure of the switching power supply to obtain a proper threshold value for judging the negative voltage of the feedback signal.

As can be seen from the above, the switching power supply is not a pure resistive circuit structure, the oscillation signal is coupled to the feedback circuit 220 by the secondary winding, and then the clipping distortion occurs, and the negative voltage determination circuit determines the oscillation signal by determining the negative voltage of the feedback signal, thereby improving the determination accuracy. However, the implementation manner of the negative voltage determining circuit is not limited to this, and in other embodiments, a negative voltage to positive voltage circuit formed by a switching tube and a current mirror may be used to perform polarity conversion on the voltage of the feedback signal, and then the comparator compares the voltage of the feedback signal after the polarity conversion with a preset value to output the primary side control signal.

As shown in fig. 8, the driving circuit 222 is electrically connected to the determining circuit 221, and is configured to drive the power switching tube 12 to be turned on based on the primary side control signal.

It should be noted that the primary side driving unit in the embodiment of the present application may also include a control circuit, which has the same function as the control circuit in the prior art shown in fig. 1, and may also be disposed outside the primary side driving unit according to actual needs. Referring to fig. 10, which is a schematic structural diagram of a primary side driving unit of another embodiment of the control device of the switching power supply of the present application, the control circuit 223 is electrically connected to the driving circuit 222 and the feedback circuit 220, and is configured to control the driving circuit 222 to drive the power switching tube 12 to be turned on or off based on the current detection signal and the feedback signal obtained by the detection terminal CS during normal operation. The normal work comprises a light load working mode, a heavy load working mode and a no-load working mode.

In a circuit of a switching power supply, when an EFT (Electrical Fast Transient/burst) test is performed, an interference pulse needs to be coupled to an internal circuit from the outside of the switching power supply, but when the interference pulse is coupled to the internal circuit, a feedback signal of a feedback circuit is severely interfered, which may cause a false trigger dynamic response, so that the power switch tube is mistakenly switched on and off to output unnecessary energy, and an output voltage of the circuit is abnormally increased.

In view of this, the primary side driving unit 22 further includes a shielding circuit (not shown) electrically connected to the determining circuit 221 and the driving circuit 222 for shielding the primary side control signal during a timing non-timeout period based on the primary side control signal.

In an example, the shielding circuit clocks and controls the driving circuit 222 to drive the power switch tube 12 to be turned on based on the primary side control signal, and the shielding circuit does not respond to the primary side control signal output by the subsequent determining circuit 221 in the non-timed-out period until the clocking is finished to reset the shielding circuit. It should be noted that the timing duration of the shielding circuit is a preset fixed value, the conduction of the power switch tube 12 does not change the load power supply (i.e., the output voltage Vout) within the preset fixed value, but by the conduction of the power switch tube 12 at this time, the control circuit 223 determines whether the load power supply suddenly drops, if the load power supply actually suddenly drops, that is, the primary side control signal is triggered by the oscillation signal, the control circuit 223 controls the driving circuit 222 to drive the power switch tube 12 to turn on or off in the heavy load operating mode, and if the load power supply does not suddenly drop, that is, the primary side control signal is triggered by the EFT test, the control circuit 223 controls the driving circuit 222 to drive the power switch tube 12 to turn on or off in the original operating mode.

The application also discloses a chip, the chip is packaged with at least part of the circuit of the control device of the switching power supply. The chip further comprises a plurality of pins, wherein the plurality of pins comprise a first pin for obtaining an electric signal of the secondary winding, a second pin for obtaining power supply of the chip, and a third pin for grounding.

In an embodiment, the chip is packaged with the switching unit and the detection unit in the control device of the switching power supply, wherein the switching unit and the detection unit are both electrically connected between the first pin and the third pin in the chip, and the detection unit is configured to control the switching unit to generate an oscillation signal on the secondary winding of the transformer when it is determined that the load is insufficiently supplied by detecting an electrical signal of the secondary winding during a period in which the switching unit is in an off state. The circuit structures of the switch unit and the detection unit are the same as those described above, and are not described herein again.

In a further embodiment, the chip is packaged with a detection unit and has a fourth pin for connecting a control terminal of a switching unit located outside the chip.

The application also discloses a switching power supply device, the switching power supply comprises a rectifying circuit, a transformer, a power switch tube and the control device in the embodiment, and the structure of the control device is not repeated herein.

As shown in fig. 10, the rectifier circuit 10 is configured to rectify an incoming ac into a dc input voltage Vin to a power supply bus, and when the switching power supply is started, the power supply VCC of the primary side driving unit 22 is supplied with power through a starting resistor Ri and a capacitor Ci.

The transformer 11 is composed of a primary winding Np, a secondary winding Ns and an auxiliary winding Na, the input end of the power switch tube 12 is connected to the power supply bus through the transformer 11, the drive end is electrically connected to the control device, and the on or off of the power switch tube 12 controls the storage or release of energy in the transformer 11 to provide stable power supply for a load.

When the power switch tube 12 is switched on, the power supply bus, the primary winding Na and the power switch tube 12 form a switching-on loop, the transformer 11 stores energy, and the resistor Rs induces primary inductance.

When the power switch tube 12 is closed, the power supply bus, the primary winding Na and the power switch tube 12 form a loop and are disconnected, the energy stored by the transformer is transmitted to the secondary winding Ns and the auxiliary winding Na, and the current of the secondary winding Ns is rectified by a switch unit 20 in the control device and filtered by a capacitor C0 to supply Vout to the load. On the one hand, the current of the auxiliary winding Na supplies power to the power source VCC of the primary side driving unit 22 in the control device through the rectifier diode D2, on the other hand, the auxiliary winding Na senses the voltage of the secondary winding Ns, when the power switch tube 12 is turned off, the voltage on the auxiliary winding Na supplies the voltage of the feedback signal to the control circuit 223 through the FB terminal through the voltage division circuit formed by the resistor R1 and the resistor R2 in the feedback circuit 220 in the control device, and the control circuit 223 controls the driving circuit 222 to drive the power switch tube 12 to be turned on or off based on the voltage of the feedback signal at the FB terminal and the voltage at the CS terminal.

In order to reduce the standby power consumption of the switching power supply, when the switching power supply is operated at idle or light load, the operating frequency of the power switch tube 12 is very low, when the switching power supply is switched from no-load or light-load to heavy-load instantly, the output voltage Vout of the power supply of the load is reflected to drop suddenly, at this time, the detection unit 21 determines that the power supply of the load is insufficient by detecting the electric signal of the secondary winding Ns during the period that the switching unit 20 is in the turn-off state, thereby controlling the switching unit 20 to generate an oscillating signal on the secondary winding Ns of the transformer 11, the oscillating signal is coupled to the auxiliary winding Na, the feedback circuit 220 outputs a voltage of the feedback signal to the determining circuit 221 based on the oscillating signal coupled to the auxiliary winding Na, the determining circuit 221 determines the feedback signal as the oscillating signal by the voltage of the feedback signal and a predetermined value, and outputs a primary control signal to the driving circuit 222 to control the power switch tube 12 to be conducted and supplement the output voltage Vout. Subsequently, the control circuit 223 of the switching power supply continues to control the driving circuit 222 to drive the power switch tube 12 to turn on or off based on the voltage of the feedback signal at the FB terminal and the voltage at the CS terminal, so that the switching power supply operates in the heavy load mode.

In addition, in order not to respond to the false determination generated by the EFT test, the primary driving unit 22 further includes a shielding circuit (not shown), which is electrically connected to the determining circuit 221 and the driving circuit 222, and configured to shield the primary control signal during the non-timeout period of the timing based on the primary control signal.

At this time, when the judging circuit 221 outputs the primary side control signal based on the judging result, the primary side control signal is sent to the shielding circuit, the shielding circuit times and controls the driving circuit 222 to drive the power switch tube 12 to be conducted based on the primary side control signal, and the shielding circuit does not respond to the primary side control signal output by the subsequent judging circuit 221 at the timing non-overtime stage until the timing is over, so that the shielding circuit is reset. By turning on the power switch tube 12 at this time, the control circuit 223 determines whether the output voltage Vout suddenly drops based on the voltage of the feedback signal at the FB terminal and the voltage at the CS terminal, if the output voltage Vout actually suddenly drops, that is, the primary side control signal is triggered by the oscillation signal, the control circuit 223 controls the driving circuit 222 to drive the power switch tube 12 to turn on or turn off in the heavy load operating mode, and if the load power supply does not suddenly drop, that is, the primary side control signal is triggered by the EFT test, the control circuit 223 controls the driving circuit 222 to still drive the power switch tube 12 to turn on or turn off in the original no-load or light load operating mode.

The above embodiments are merely illustrative of the principles and utilities of the present application and are not intended to limit the application. Any person skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present application. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical concepts disclosed in the present application shall be covered by the claims of the present application.

Claims

1. A control apparatus for a switching power supply, wherein the switching power supply includes a power switch tube and a transformer, the control apparatus comprising:

the switch unit is electrically connected between the secondary winding of the transformer and a grounding end;

the detection unit is connected with two ends of the switch unit in parallel and used for controlling the switch unit to generate an oscillation signal on the secondary winding of the transformer when the load power supply is determined to be insufficient by detecting an electric signal of the secondary winding during the switch unit is in an off state;

and the primary side driving unit is coupled to the secondary side winding and used for driving the power switching tube to be conducted based on the oscillation signal.

2. The control device of the switching power supply according to claim 1, wherein the detection unit includes:

the detection circuit is connected in parallel with two ends of the switch unit and is used for detecting the electric signal of the secondary winding;

the comparison circuit is electrically connected to the detection circuit and used for comparing the electric signal of the secondary winding with a reference signal to output a first indication signal when the switch unit is in an off state;

and the logic control circuit is electrically connected with the comparison circuit and the switch unit and used for outputting a secondary side control signal to the switch unit based on the first indication signal.

3. The apparatus according to claim 2, wherein the reference signal is a predetermined fixed value.

4. The apparatus according to claim 2, wherein the detection unit further comprises a reference signal generating circuit electrically connected to the comparison circuit for outputting a reference signal reflecting an average power supply of the load.

5. The control device of the switching power supply according to any one of claims 2 to 4, wherein the detection unit further includes:

the synchronous rectification circuit is electrically connected with the detection circuit and the logic control circuit and used for outputting a second indicating signal to the logic control circuit based on the electric signal of the detection secondary winding; wherein the logic control circuit outputs the secondary side control signal to the switching unit based on the first and second indication signals;

and the enabling circuit is electrically connected with the synchronous rectification circuit and the comparison circuit and is used for enabling the comparison circuit based on the first quasi-position delay of the second indication signal or disabling the comparison circuit based on the second quasi-position of the second indication signal.

6. The control device for the switching power supply according to claim 1, wherein the primary side drive unit comprises

The feedback circuit is coupled to the secondary winding and used for generating a feedback signal based on the oscillation signal;

the judging circuit is electrically connected to the feedback circuit and used for outputting a primary side control signal based on the feedback signal;

and the driving circuit is electrically connected to the judging circuit and used for driving the power switch tube to be conducted based on the primary side control signal.

7. The apparatus of claim 6, wherein the determining circuit comprises a negative voltage determining circuit for determining a negative voltage of the feedback signal according to the voltage of the feedback signal and a predetermined value to output the primary side control signal.

8. The apparatus of claim 6, wherein the primary driving unit further comprises a shielding circuit electrically connected to the determining circuit and the driving circuit, for shielding the primary control signal during a non-timeout period based on the timing of the primary control signal.

9. A chip, characterized in that it encloses at least part of the circuitry of the control device of the switching power supply according to any of claims 1-5.

10. A switching power supply, comprising:

the rectifying circuit is used for rectifying the accessed alternating current and outputting the rectified alternating current to the power supply bus;

the driving end of the power switch tube is electrically connected with the control device of the switching power supply according to any one of the claims 1-8, and the input end of the power switch tube is connected with the power supply bus;

and the transformer is electrically connected between the power supply bus and the input end of the power switch tube and used for providing stable power supply for a load based on the on or off of the power switch tube.