Output overpower compensation circuit and switching power supply

Abstract

The utility model discloses an output overpower compensation circuit and a switching power supply, and the output overpower compensation circuit comprises a sampling circuit which samples a first voltage signal representing the magnitude of the output voltage of the switching power supply; the comparison circuit is used for comparing the first voltage signal with a set voltage and generating a second voltage signal; the compensation resistor and the switch control circuit are connected in series and then are connected between the sampling pin and the grounding pin of the control chip, and the switch control circuit is controlled by a second voltage signal; when the switching power supply works and a first voltage signal is smaller than a set voltage, the output of the switching control circuit presents a high-resistance open circuit, and the compensation resistor does not participate in bus voltage regulation; and when the first voltage signal is greater than or equal to the set voltage, the output of the switch control circuit presents low-resistance short circuit, and the compensation resistor participates in bus voltage regulation. According to the utility model, the working frequency and the output overpower point deviation in a wide output voltage range are reduced, and the reliability of the switching power supply is improved.

Description

Technical Field

[0001] This utility model relates to the field of power supply technology, and in particular to an output overpower compensation circuit and a switching power supply. Background Technology

[0002] Conventional AC / DC switching power supplies, based on the requirements of wide input range and high efficiency, typically use a PFC+LLC cascaded topology. However, because the LLC topology operates over a wide gain range with an excessively wide frequency adjustment range, it leads to larger magnetic components and increased power losses. Therefore, a PFC stage is usually added after AC input rectification to stabilize the PFC output voltage, which in turn stabilizes the input voltage of the LLC topology. (See attached...) Figure 1 The diagram shows a common PFC+LLC cascade topology application. The PFC stage samples the PFC output bus voltage through sampling resistors R001, R002, R003, and R004. After comparing it with a fixed reference, the duty cycle is adjusted through the PFC voltage loop to achieve stable output of the PFC output voltage. The primary-side overpower protection (OPP) is implemented by detecting the voltage change ΔVcr of the resonant capacitor during the period from the turn-off of the lower transistor Q3 to the drive-off point of the upper transistor Q2, and limiting it below the set maximum reference power point ΔVcr_max.

[0003] The inventor of this application utilizes Figure 1 When designing the circuit and the aforementioned overpower protection method, it was found that the PFC output voltage of this circuit is fixed. Although it can achieve normal full-load operation over a wide output voltage range to a certain extent, the output overpower protection point will vary greatly under different output voltages. Specifically, when the output voltage is at the rated power limit, the voltage increment ΔVcr1 of the resonant capacitor is smaller, and the distance from the overpower protection point ΔVcr_max is lower, resulting in a higher output overpower protection point. When the output voltage is at the rated power limit, the voltage increment ΔVcr2 of the resonant capacitor is larger, and the distance from the overpower protection point ΔVcr_max is closer, resulting in a lower output overpower protection point.

[0004] The deviation of the above-mentioned overpower protection point causes the following problems in the application design:

[0005] The first setting prioritizes setting the upper limit of the output voltage to meet the rated power. The problem with this is that the lower limit of the output voltage, corresponding to the overpower point, will be set to be very large, even to the point that the circuit components cannot withstand the stress, leading to component damage.

[0006] Another scenario is that the over-power point corresponding to the lower limit of the output voltage is set to be safe enough, but when the upper limit of the output voltage is reached, the over-power point is very small, causing the rated power to be protected and unable to drive the load, which in turn affects the normal use of the overall switching power supply.

[0007] Therefore, it is necessary to improve the prior art. Content of the utility model

[0008] The technical problem to be solved by the utility model is to provide an over-power compensation circuit and a switching power supply, which at least solve one of the technical problems existing in the prior art to some extent.

[0009] As a first aspect of the utility model, the technical scheme of the embodiment of the over-power compensation circuit provided is as follows:

[0010] An output over-power compensation circuit is applied to a switching power supply, wherein the switching power supply comprises a PFC circuit, an LLC resonant converter and a control chip, an input end of the PFC circuit is connected to an input end of the switching power supply, an output end of the PFC circuit outputs a bus voltage to an input end of the LLC resonant converter, an output end of the LLC resonant converter is connected to an output end of the switching power supply, and a sampling circuit for sampling the bus voltage is connected in parallel between a sampling pin and a ground pin of the control chip, wherein the control chip adjusts the size of the bus voltage according to a sampling signal obtained by the sampling pin, and the output over-power compensation circuit comprises:

[0011] The sampling circuit is used for sampling a first voltage signal representing the size of the output voltage of the switching power supply.

[0012] The comparison circuit is used for comparing the first voltage signal with a set voltage to generate a second voltage signal.

[0013] The compensation resistor and the switch control circuit are connected in series and are connected between the sampling pin and the ground pin of the control chip, and the switch control circuit is controlled by the second voltage signal; when the switching power supply is working: when the first voltage signal is smaller than the set voltage, the switch control circuit outputs a high-resistance open circuit, and the compensation resistor does not participate in the bus voltage adjustment; when the first voltage signal is greater than or equal to the set voltage, the switch control circuit outputs a low-resistance short circuit, and the compensation resistor participates in the bus voltage adjustment.

[0014] Preferably, the sampling circuit comprises an auxiliary winding, one end of the auxiliary winding outputs the first voltage signal, and the other end of the auxiliary winding is used for grounding.

[0015] Further, the auxiliary winding is close to the secondary winding of the main power transformer when being wound.

[0016] Further, the sampling circuit further comprises a rectifier diode, one end of the auxiliary winding is connected to an anode of the rectifier diode, and a cathode of the rectifier diode outputs the first voltage signal.

[0017] Further, the sampling circuit further comprises a first filter capacitor, which is connected between the cathode of the rectifier diode and the other end of the auxiliary winding.

[0018] Further, the cathode of the rectifier diode is further used for connecting a power supply pin of the control chip, and the first voltage signal is used as the working voltage of the control chip.

[0019] Preferably, the comparison circuit comprises a zener diode, the cathode of the zener diode inputs the first voltage signal, and the anode of the zener diode generates the second voltage signal.

[0020] Preferably, the switch control circuit comprises a first voltage dividing device, a second voltage dividing device and a switch tube, one end of the compensation resistor is used for connecting a sampling pin of the control chip, the other end of the compensation resistor is connected to the drain of the switch tube, the source of the switch tube is used for connecting a ground pin of the control chip, one end of the first voltage dividing device inputs the second voltage signal, the other end of the first voltage dividing device is connected to the control end of the switch tube and one end of the second voltage dividing device at the same time, and the other end of the second voltage dividing device is used for grounding.

[0021] Preferably, the first voltage dividing device and / or the second voltage dividing device is a resistor.

[0022] Further, the switch control circuit further comprises a second filter capacitor, which is connected in parallel with the second voltage dividing device.

[0023] As a second aspect of the utility model, the embodiment technical scheme of the switching power supply is as follows:

[0024] The switching power supply comprises a PFC circuit, an LLC resonant converter and a control chip, the input end of the PFC circuit is connected to the input end of the switching power supply, the output end of the PFC circuit outputs a bus voltage to the input end of the LLC resonant converter, the output end of the LLC resonant converter is connected to the output end of the switching power supply, and a sampling circuit for sampling the bus voltage is connected in parallel between the sampling pin and the ground pin of the control chip; the control chip adjusts the size of the bus voltage according to the sampling signal obtained by the sampling pin, wherein the switching power supply further comprises the output over-power compensation circuit of any one of the first aspect.

[0025] Preferably, the control chip is NXP TEA2016.

[0026] The utility model has the following beneficial effects compared with the prior art:

[0027] The compensation resistor and the switch control circuit are connected in series and connected between the sampling pin and the grounding pin of the control chip, when the switch power supply works, the bus voltage has two voltage values, which are a first voltage value and a second voltage value, the first voltage value is less than the second voltage value, when the first voltage signal is less than a set voltage, it means that the output voltage of the switch power supply is lower than a reference set value, the switch control circuit output presents high resistance open circuit, the compensation resistor does not participate in bus voltage regulation, at this time, the bus voltage is maintained at the first voltage value, the first voltage value is a normal set low value (such as 390VDC), so that the LLC resonant converter output voltage lower limit corresponding resonant cavity working frequency can be limited, thereby reducing the corresponding over-power protection point; when the first voltage signal is greater than or equal to the set voltage, it means that the output voltage of the switch power supply is higher than or equal to the reference set value, at this time, the switch control circuit output presents low resistance short circuit, the compensation resistor participates in bus voltage regulation, and the bus voltage is raised to the second voltage value, the second voltage value is a normal set high value (such as 420VDC), so that the LLC resonant converter output voltage upper limit corresponding resonant cavity working frequency can be raised, thereby improving the corresponding over-power protection point.

[0028] In conclusion, the embodiment of the utility model reduces the working frequency and output over-power point deviation of the LLC resonant converter under the wide output voltage range, makes the over-power points corresponding to the adjustable upper limit voltage and the adjustable lower limit voltage of the switch power supply output better consistent, and improves the reliability of the product. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the principle of the prior art background;

[0030] Figure 2 It is Figure 1 It is a working waveform diagram of the circuit;

[0031] Figure 3 It is a schematic diagram of the principle of the switch power supply to which the over-power compensation circuit of the first embodiment of the utility model is applied. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purposes, features and advantages of the utility model more obvious and easy to understand, the specific embodiments of the utility model will be described in detail below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0033] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of the present application are intended to cover both non-exclusive inclusion, for example, containing a series of elements, unit circuits or control timing not necessarily limited to those clearly listed, but can include elements, unit circuits or control timing not clearly listed or inherent to these circuits.

[0034] In addition, the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0035] It should be understood that in the specification and claims, when it is described that an element is "connected" to another element, the element can be "directly connected" to the other element, or "connected" to the other element through a third element; when it is described that a step is followed by another step, the step can be directly followed by the other step, or followed by the other step through a third step.

[0036] According to the background art problem, under the condition of direct current wide output application, under the condition of the same output power, the lower limit value of the output voltage corresponds to a smaller ΔVcr1, and the upper limit value of the output voltage corresponds to a larger ΔVcr2. The present inventors have found that the main reasons for the above deviation are as follows:

[0037] Figure 2 For Figure 1 The working waveform diagram of the circuit is shown in Figure 2 As shown, based on the half-bridge LLC half-cycle symmetry working characteristic, from the turn-off time t1 of the lower tube Q3 to the turn-off time t2 of the upper tube Q2, the amplitude of the resonant inductor current does not change only because the direction is changed, so it can be known that the resonant inductor energy does not change in the half-cycle time from t1 to t2. During this process, part of the LLC input (PFC output) energy is stored on the resonant capacitor Cr, and this energy is recorded as P_cr1. Another part of the energy is transmitted to the output load, and this energy is recorded as Po1. From the turn-off time t2 of the upper tube Q2 to the turn-off time t3 of the lower tube, the resonant inductor energy also does not change, and at this time, the resonant capacitor Cr supports the load output power Po, and this energy is recorded as Po2. According to the symmetric conduction characteristic of the secondary side full-wave rectifier tube, Po1=Po2=1 / 2*Po, so P_cr1=1 / 2*Po. That is, half of the LLC input energy is stored on Cr and the other half is provided to the load in the half-cycle time from the turn-off t1 of the lower tube Q3 to the turn-off t2 of the upper tube Q2. In the other half cycle from the turn-off time t2 of the upper tube Q2 to the turn-off time t3 of the lower tube, the resonant capacitor Cr provides 1 / 2 of the load power. It can be known that:

[0038] P_cr1=1 / 2*Po=(1 / 2*Cr*Vcr_H 2 -1 / 2*Cr*Vcr_L2 ) / (Ts / 2)

[0039] =Cr*(Vcr_H+Vcr_L)*(Vcr_H-Vcr_L) *fs---①

[0040] Where P_cr1 is the energy stored in the resonant capacitor Cr during the half cycle from t1 to t2, Cr is the resonant capacitor capacity, Vcr_H is the resonant capacitor voltage corresponding to the upper tube off, Vcr_L is the resonant capacitor voltage corresponding to the lower tube off, Ts is the switching period, and fs is the switching frequency.

[0041] Since the average value of the half-bridge LLC resonant inductance and the working voltage of the transformer is 0, the average value of the midpoint voltage of the resonant upper and lower MOS tubes is:

[0042] Vmid_av=Vcr_av=(Vcr_H+Vcr_L) / 2=Vin_bus / 2---②

[0043] Where: Vcr_av is the center value of the resonant capacitor voltage, which is also the average value; Vin_bus is the PFC output bus voltage, which is also the input voltage of LLC.

[0044] And Vcr_H-Vcr_L=ΔVcr---③

[0045] Combining the above ①, ②, ③ formulas, we get:

[0046] ΔVcr=1 / 2*Po / (Cr*Vin_bus*fs)---④

[0047] From the above formula ④, it can be seen that under the condition of the same output power Po and different output voltages, the fluctuation value ΔVcr of the resonant capacitor working voltage is inversely proportional to the bus voltage Vin_bus and the switching frequency.

[0048] According to the above analysis, under the condition of the same output power, the Vin_bus is kept unchanged when working at different output voltages, so the corresponding ΔVcr deviation is mainly caused by the switching frequency deviation: the switching frequency is too high when the output voltage is too low, resulting in a smaller ΔVcr1; the switching frequency is too low when the output voltage is too high, resulting in a larger ΔVcr1.

[0049] According to the above research conclusion, if we want to reduce the over-power deviation corresponding to the upper and lower limits of the output voltage, we must reduce the ΔVcr deviation corresponding to different output voltages under the same output power. If we want to reduce the above deviation, we start from formula ④ and propose the following innovative scheme:

[0050] At the output adjustable voltage upper limit, the corresponding switching frequency fs is lower than the adjustable lower limit voltage, if the adjustable upper limit voltage corresponding Vin_bus is improved, the Vin_bus*fs corresponding to the output adjustable upper limit voltage and the output adjustable lower limit voltage corresponding deviation will be reduced, thereby reducing the AVcr deviation, for the need to reach the AVcr_max corresponding over power point deviation is also reduced simultaneously, for the need to reach the AVcr_max corresponding over power point deviation is also reduced simultaneously, thereby improving the consistency of different output voltages corresponding over power point.

[0051] First embodiment

[0052] The embodiment provided is an output over power compensation circuit, applied to a switching power supply, the switching power supply comprising a PFC circuit, an LLC resonant converter and a control chip, the input end of the PFC circuit being connected to the input end of the switching power supply, the output end of the PFC circuit outputting a bus voltage to the input end of the LLC resonant converter, the output end of the LLC resonant converter being connected to the output end of the switching power supply, a sampling circuit for sampling the bus voltage being connected in parallel between the sampling pin and the ground pin of the control chip, and the control chip adjusting the size of the bus voltage according to the sampling signal obtained by the sampling pin.

[0053] Figure 3 The over power compensation circuit of the first embodiment of the utility model is a specific circuit applied to a switching power supply, wherein the switching power supply comprises:

[0054] The PFC circuit comprises an input filter capacitor C1, a PFC inductor L1, a MOS tube Q1, a diode D1, a capacitor C2, an input end, an output end and a ground end, one end of the capacitor C1 and one end of the PFC inductor L1 are connected together and serve as the input end of the PFC circuit, and are connected to the input end of the switching power supply, the other end of the inductor L1 is connected to the anode of the diode D1 and the drain of the MOS tube Q1 at the same time, the other end of the capacitor C1, the source of the MOS tube Q1 and the cathode of the capacitor C2 are connected together and serve as the ground end of the PFC circuit, and are connected to the primary side ground GND of the switching power supply, the cathode of the diode D1 is connected to the anode of the capacitor C2, and serves as the output end of the PFC circuit and outputs the bus voltage VBUS;

[0055] An LLC resonant converter includes MOSFETs Q2 and Q3, a resonant inductor Lr, a transformer T1, diodes D2 and D3, a capacitor C3, and input positive, input negative, output positive, and output negative terminals. The positive input terminal of the LLC resonant converter is simultaneously connected to the output terminal of the PFC circuit and the drain of MOSFET Q2. The source of MOSFET Q2 is simultaneously connected to the drain of MOSFET Q3 and one end of the resonant inductor Lr. The other end of the resonant inductor Lr is connected to the same-name terminal of the primary winding Np of transformer T1. The opposite-name terminal of the primary winding Np of transformer T1 is connected to one end of the resonant capacitor Cr. The other end of the resonant capacitor Cr is connected to the MOSFETs... The source of Q3 is also connected to the ground terminal of the PFC circuit, serving as the negative input terminal of the LLC resonant converter. The same-name terminal of the secondary winding Ns1 of transformer T1 is connected to the cathode of diode D2. The anode of diode D2, the anode of diode D3, and the cathode of capacitor C3 are connected together to form the negative output terminal of the LLC resonant converter, which is connected to the negative output terminal Vout- of the switching power supply. The same-name terminal of the secondary winding Ns2 of transformer T1 and the opposite-name terminal of the secondary winding Ns1 are connected together to form the positive output terminal of the LLC resonant converter, which is connected to the positive output terminal Vout+ of the switching power supply. The opposite-name terminal of the secondary winding Ns2 is also connected to the cathode of diode D3.

[0056] The control chip U001 has a sampling circuit connected in parallel between its sampling pin 8 and ground pin 6 to sample the bus voltage. The control chip adjusts the bus voltage based on the sampling signal obtained from the sampling pin.

[0057] It should be noted that, Figure 3 The switching power supply circuit is merely an example and should not limit the scope of protection of this utility model. Those skilled in the art can design specific switching power supply circuits for the output overpower compensation circuit of this utility model as needed. For example, if the switching power supply is an AC switching power supply, the voltage input to the input terminal of the switching power supply is first rectified into DC by a rectifier bridge before being connected to the PFC circuit. At this time, the input terminal of the PFC circuit is connected to the positive output terminal of the rectifier bridge, and the ground terminal of the PFC circuit is connected to the negative output terminal of the rectifier bridge. As another example, the secondary circuit of transformer T1 in the LLC resonant converter can also be designed as a full-bridge rectifier circuit, etc.

[0058] Please continue reading Figure 3 The output overpower compensation circuit includes:

[0059] The sampling circuit is used to sample the first voltage signal that characterizes the magnitude of the output voltage of the switching power supply.

[0060] A comparator circuit is used to compare a first voltage signal with a set voltage to generate a second voltage signal;

[0061] The compensation resistor R005 and the switch control circuit are connected between the sampling pin and the ground pin of the control chip in series, and the switch control circuit is controlled by the second voltage signal; when the switch power supply is working: when the first voltage signal is less than the set voltage, the switch control circuit output presents high resistance open circuit, and the compensation resistor does not participate in the bus voltage regulation; when the first voltage signal is greater than or equal to the set voltage, the switch control circuit output presents low resistance short circuit, and the compensation resistor participates in the bus voltage regulation.

[0062] As a specific embodiment, please continue to refer to Figure 3 The sampling circuit includes an auxiliary winding Nf, one end of the auxiliary winding outputs the first voltage signal, and the other end is used for grounding. The voltage of the primary winding rectification filter under heavy load is linearly proportional to the secondary winding voltage, and the ratio of the two is the winding ratio of the transformer. The secondary winding voltage is approximately equal to the output voltage, so the first voltage signal representing the output voltage of the switch power supply can be sampled through the auxiliary winding.

[0063] Since there is a deviation in the accuracy of sampling the output voltage through the primary winding of the LLC transformer, the auxiliary winding is preferably close to the secondary winding of the main power transformer during winding, so that the output voltage can be accurately sampled under heavy load, and the realization of the purpose of the present embodiment is not affected.

[0064] As a specific embodiment, please continue to refer to Figure 3 The sampling circuit further includes a rectifier diode D5, one end of the auxiliary winding is connected to the anode of the rectifier diode D5, and the cathode of the rectifier diode D5 outputs the first voltage signal. The function of adding the rectifier diode is to rectify the auxiliary winding alternating voltage into a pulsating direct current voltage.

[0065] As a specific embodiment, please continue to refer to Figure 3 The sampling circuit further includes a first filter capacitor C4, which is connected between the cathode of the rectifier diode and the other end of the auxiliary winding. The function of adding the first filter capacitor is to filter the above-mentioned rectified pulsating direct current voltage, and output a low-ripple direct current voltage after filtering. The direct current voltage is used as the input of the subsequent switch circuit on the one hand, and on the other hand, it can also be used as the power supply Vcc of the chip.

[0066] As a specific embodiment, please continue to refer to Figure 3 The cathode of the rectifier diode D5 is also used for connecting the power supply pin 1 of the control chip, and the first voltage signal is used as the working voltage of the control chip.

[0067] As a specific embodiment, please continue to refer to Figure 3The comparison circuit comprises a Zener diode Z001, a cathode of the Zener diode Z001 inputs the first voltage signal, and an anode of the Zener diode Z001 generates the second voltage signal.

[0068] As a specific embodiment, please continue to refer to Figure 3 The switch control circuit comprises a first voltage dividing device R006, a second voltage dividing device R007, and a switch tube Q001, one end of a compensation resistor R005 is used for connecting a sampling pin of the control chip, the other end of the compensation resistor R005 is connected to a drain of the switch tube, a source of the switch tube is used for connecting a ground pin of the control chip, one end of the first voltage dividing device inputs the second voltage signal, the other end of the first voltage dividing device is connected to a control end of the switch tube and one end of the second voltage dividing device at the same time, and the other end of the second voltage dividing device is used for grounding.

[0069] As a specific embodiment, please continue to refer to Figure 3 The first voltage dividing device and / or the second voltage dividing device is a resistor.

[0070] As a specific embodiment, please continue to refer to Figure 3 The switch control circuit further comprises a second filter capacitor C002, and the second filter capacitor C002 is connected in parallel with the second voltage dividing device R007.

[0071] The output over-power compensation circuit of the embodiment is analyzed below in combination with the specific circuit of Figure 3 , and the specific circuit is as follows:

[0072] The auxiliary winding Nf couples an output voltage, the output voltage is rectified by a rectifier diode D5, is filtered by a first filter capacitor C4, and a stable direct current voltage Vcc (i.e. the first voltage signal) is obtained. The direct current voltage Vcc is compared with a stable voltage value of the Zener diode Z001, when the output voltage exceeds a set reference voltage value, the direct current voltage Vcc is greater than the stable voltage value of the Zener diode Z001, the Zener diode Z001 is turned on, when a voltage divided by the second voltage dividing device R007 is greater than a GS turn-on threshold Vgs(th) of the N-MOS tube Q001, the N-MOS tube Q001 is turned on, a drain-source of the N-MOS tube Q001 is equivalent to a low-resistance short circuit, and is equivalent to that the compensation resistor R005 is connected in parallel between the Vbus_sense pin and the GND pin of the control chip, and the compensation resistor R005 that enters is equivalent to reducing a sampling ratio, and finally causes the PFC output voltage Vin_bus to increase to Vc2.

[0073] The circuit of the embodiment Figure 1 is compared with the background art Figure 3 circuit, and the actual measurement of the over-power point deviation effect corresponding to an output voltage of 23-30VDC in a range of 120W is shown in the following Table 1:

[0074] Table 1. Overpower points corresponding to different output voltages

[0075]

[0076] Note: Po_nom represents the rated power 120W, and the maximum deviation ratio refers to the maximum overpower value divided by the minimum overpower value.

[0077] As can be seen from the above display effect, ​ After adding the overpower compensation circuit, the maximum overpower value and the minimum overpower value deviation ratio is reduced from 1.715 times to 1.26 times, which better improves the overpower deviation in the wide output voltage range.

[0078] Second embodiment

[0079] The embodiment provides a switching power supply, which comprises a PFC circuit, an LLC resonant converter and a control chip. The input end of the PFC circuit is connected with the input end of the switching power supply. The output end of the PFC circuit outputs a bus voltage to the input end of the LLC resonant converter. The output end of the LLC resonant converter is connected with the output end of the switching power supply. A sampling circuit for sampling the bus voltage is connected in parallel between the sampling pin and the ground pin of the control chip. The control chip adjusts the size of the bus voltage according to the sampling signal obtained by the sampling pin. The switching power supply further comprises the output overpower compensation circuit of any one of the first embodiment.

[0080] The switching power supply of the embodiment can reduce the working frequency and the output overpower point deviation of the LLC resonant converter in the wide output voltage range, so that the switching power supply has better consistency of the overpower points corresponding to the adjustable upper limit voltage and the adjustable lower limit voltage. When the output adjustable upper limit voltage meets the rated power, the output adjustable lower limit voltage also corresponds to the overcurrent point in the safe area that can be borne by the device, and the reliability of the product is improved.

[0081] As a specific embodiment, the control chip is TEA2016 of NXP.

[0082] The above embodiments are only preferred embodiments of the utility model patent, and it should be pointed out that the above preferred embodiments should not be regarded as the limitation of the utility model patent. For ordinary skilled persons in the art, the rectifier filter circuit of the above embodiment can be replaced from half-wave rectification to full-bridge rectification, and the auxiliary winding can be replaced from single winding to double winding based on the center tap. The MOS tube of the above embodiment can be replaced by a triode, and the like, which can also achieve the purpose of the application. In addition, without departing from the spirit and scope of the utility model patent, a number of improvements and refinements can be made, which are obvious to those skilled in the art. These improvements and refinements should also be regarded as the protection scope of the utility model patent, and will not be described in detail here.

Claims

1. An output overpower compensation circuit, applied to a switching power supply, the switching power supply including a PFC circuit, an LLC resonant converter, and a control chip, wherein the input terminal of the PFC circuit is connected to the input terminal of the switching power supply, the output terminal of the PFC circuit outputs a bus voltage to the input terminal of the LLC resonant converter, the output terminal of the LLC resonant converter is connected to the output terminal of the switching power supply, a sampling circuit for sampling the bus voltage is connected in parallel between the sampling pin and the ground pin of the control chip, and the control chip adjusts the magnitude of the bus voltage according to the sampling signal obtained from the sampling pin, characterized in that... The output overpower compensation circuit includes: A sampling circuit is used to sample a first voltage signal that characterizes the magnitude of the output voltage of the switching power supply. A comparator circuit is used to compare the first voltage signal with a set voltage to generate a second voltage signal; The compensation resistor and the switch control circuit are connected in series between the sampling pin and the ground pin of the control chip. The switch control circuit is controlled by the second voltage signal. When the switching power supply is working: when the first voltage signal is less than the set voltage, the output of the switch control circuit presents a high-impedance open circuit, and the compensation resistor does not participate in the bus voltage regulation; when the first voltage signal is greater than or equal to the set voltage, the output of the switch control circuit presents a low-impedance short circuit, and the compensation resistor participates in the bus voltage regulation.

2. The output overpower compensation circuit according to claim 1, characterized in that: The sampling circuit includes an auxiliary winding, one end of which outputs the first voltage signal, and the other end is used for grounding.

3. The output overpower compensation circuit according to claim 2, characterized in that: The auxiliary winding is wound in close contact with the secondary winding of the main power transformer.

4. The output overpower compensation circuit according to claim 2, characterized in that: The sampling circuit also includes a rectifier diode, one end of the auxiliary winding is connected to the anode of the rectifier diode, and the cathode of the rectifier diode outputs the first voltage signal.

5. The output overpower compensation circuit according to claim 4, characterized in that: The sampling circuit also includes a first filter capacitor, which is connected between the cathode of the rectifier diode and the other end of the auxiliary winding.

6. The output overpower compensation circuit according to claim 5, characterized in that: The cathode of the rectifier diode is also used to connect to the power supply pin of the control chip, with the first voltage signal serving as the operating voltage of the control chip.

7. The output overpower compensation circuit according to claim 1, characterized in that: The comparison circuit includes a Zener diode, the cathode of which receives the first voltage signal, and the anode of which generates the second voltage signal.

8. The output overpower compensation circuit according to claim 1, characterized in that: The switch control circuit includes a first voltage divider, a second voltage divider, and a switching transistor. One end of the compensation resistor is connected to the sampling pin of the control chip, and the other end of the compensation resistor is connected to the drain of the switching transistor. The source of the switching transistor is connected to the ground pin of the control chip. One end of the first voltage divider receives the second voltage signal, and the other end of the first voltage divider is simultaneously connected to the control terminal of the switching transistor and one end of the second voltage divider. The other end of the second voltage divider is grounded.

9. The output overpower compensation circuit according to claim 8, characterized in that: The first voltage divider and / or the second voltage divider are resistors.

10. The output overpower compensation circuit according to claim 8 or 9, characterized in that: The switch control circuit also includes a second filter capacitor, which is connected in parallel with the second voltage divider.

11. A switching power supply, comprising a PFC circuit, an LLC resonant converter, and a control chip, wherein the input terminal of the PFC circuit is connected to the input terminal of the switching power supply, the output terminal of the PFC circuit outputs a bus voltage to the input terminal of the LLC resonant converter, the output terminal of the LLC resonant converter is connected to the output terminal of the switching power supply, a sampling circuit for sampling the bus voltage is connected in parallel between the sampling pin and the ground pin of the control chip, and the control chip adjusts the magnitude of the bus voltage according to the sampling signal obtained from the sampling pin, characterized in that: The switching power supply further includes the output overpower compensation circuit as described in any one of claims 1 to 10.

12. The switching power supply according to claim 11, characterized in that: The control chip is NXP TEA2016.

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