Switching power supply control circuit and control method

Abstract

The present invention proposes a switching power supply control circuit and control method, which compensates for the error between the feedback signal and the reference signal to obtain a compensation signal; when the compensation signal is greater than the threshold voltage, the conduction time of the main power tube is detected; if the conduction time of the main power tube is greater than the first threshold time, the working mode of the switching power supply is determined; if the switching power supply works in the intermittent conduction mode, the inductance value of the switching power supply is detected; when the inductance value is less than the first threshold, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal. The present invention can accurately detect the state of a strong magnetic field and provide sufficient output power.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a switching power supply control circuit and a control method. Background Art

[0002] In the application of electric meters, there will be a transient strong magnetic field environment. Under the condition of external strong magnetic field, due to the saturation of the transformer, the inductance becomes smaller, so the output power decreases, and the output voltage cannot be maintained. In order to overcome this problem, the peak current remains unchanged (without aggravating the saturation of the transformer), and the switching frequency needs to be increased to maintain the output voltage. The usual technical solution is to increase the switching frequency when the output voltage becomes low, that is, when the inductor peak current reaches the maximum set value. The problem brought about by this is that it is impossible to distinguish whether it is a normal over-power output condition or a strong magnetic field condition. Under normal circumstances, it will cause the over-power point to increase, affecting the reliability of the system. Summary of the invention

[0003] The purpose of the present invention is to provide a switching power supply control circuit and control method that can accurately detect the strong magnetic field state and provide sufficient output power, so as to solve the problem that the prior art cannot distinguish between normal over-power output conditions and strong magnetic field conditions.

[0004] To achieve the above object, the present invention provides a switching power supply control circuit, which compensates for the error between a feedback signal and a reference signal to obtain a compensation signal, characterized in that: when the compensation signal is greater than a threshold voltage, the conduction time of the main power tube is detected;

[0005] If the conduction time of the main power tube is greater than the first threshold time, the switching power supply working mode is determined;

[0006] If the switching power supply operates in the intermittent conduction mode, the inductance value of the switching power supply is detected; when the inductance value is less than a first threshold value, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal.

[0007] Optionally, if the on-time of the main power tube is less than the first threshold time, the switching power supply enters an adjustment cycle after working at a normal switching frequency for N cycles, and extends the off-time of the main power tube during the adjustment cycle, so that the switching power supply works in a discontinuous conduction mode, and detects the inductance value of the switching power supply in the next switching cycle; when the inductance value is less than the first threshold, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal;

[0008] The off time of the main power tube in the adjustment period is adjusted according to the on time of the main power tube. The off time of the main power tube in the adjustment period does not change with the change of the on time, or changes linearly or in segments with the change of the on time.

[0009] Optionally, if the conduction time of the main power tube is greater than the first threshold time, the time taken for the inductor current to rise to the first reference is detected as the first time; the ratio of the conduction time of the main power tube to the first time is a first ratio, and the ratio of the inductor current peak to the first reference is a second ratio. If the difference between the first ratio and the second ratio is greater than the first difference, it is determined that the switching power supply is operating in a continuous conduction mode; if the difference between the first ratio and the second ratio is less than the first difference, it is determined that the switching power supply is operating in a discontinuous conduction mode.

[0010] Optionally, if the conduction time of the main power tube is greater than the first threshold time, the inductor current corresponding to the second time when the conduction time of the main power tube is detected is used as the first detection value; the ratio of the conduction time of the main power tube to the second time is a first ratio, and the ratio of the inductor current peak value to the first detection value is a second ratio. If the difference between the first ratio and the second ratio is greater than the first difference, it is determined that the switching power supply is operating in a continuous conduction mode; if the difference between the first ratio and the second ratio is less than the first difference, it is determined that the switching power supply is operating in a discontinuous conduction mode.

[0011] A switching power supply control circuit includes an operational amplifier circuit, which compensates for the error between a feedback signal and a reference signal to obtain a compensation signal, and further includes:

[0012] A detection circuit, when the compensation signal is greater than a threshold voltage, the detection circuit detects the conduction time of the main power tube;

[0013] A mode recognition circuit, if the conduction time of the main power tube is greater than the first threshold time, determines the working mode of the switching power supply and outputs a mode recognition signal; if the mode recognition signal indicates that the switching power supply operates in the intermittent conduction mode, the detection circuit detects the inductance value of the switching power supply;

[0014] The first control circuit, if the on-time of the main power tube is less than the first threshold time, then the switching power supply enters an adjustment cycle after working at a normal switching frequency for N cycles, and in the adjustment cycle, the first control circuit controls the off-time of the main power tube to be extended, so that the switching power supply works in a discontinuous conduction mode; in the next switching cycle, the detection circuit detects the inductance value of the switching power supply; the off-time of the main power tube in the adjustment cycle is adjusted according to the on-time of the main power tube, and the off-time of the main power tube in the adjustment cycle does not change with the change of the on-time, or changes linearly or in segments with the change of the on-time;

[0015] When the inductance value is less than the first threshold value, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal.

[0016] Optionally, the mode judgment circuit includes a timing circuit and a first operation circuit; if the conduction time of the main power tube is greater than the first threshold time, the timing circuit starts timing from the turn-on moment of the main switch tube, and when the inductor current rises to the first reference, the timing ends and the first time is output; the operation circuit receives the conduction time of the main power tube, the first time, the inductor current peak and the first reference, and outputs a mode recognition signal; the operation circuit calculates the ratio of the conduction time of the main power tube to the first time as the first ratio; the operation circuit calculates the ratio of the inductor current peak and the first reference as the second ratio; if the difference between the first ratio and the second ratio is greater than the first difference, the mode recognition signal indicates that the switching power supply operates in a continuous conduction mode; if the first ratio is close to the second ratio, the mode recognition signal indicates that the switching power supply operates in a discontinuous conduction mode.

[0017] Optionally, the mode judgment circuit includes a current detection circuit and a second operation circuit. If the conduction time of the main power tube is greater than the first threshold time, the current detection circuit detects the inductor current corresponding to the conduction time of the main power tube reaching the second time, and outputs a first detection value; the second operation circuit receives the conduction time of the main power tube, the second time, the inductor current peak value and the first detection value, and outputs a mode recognition signal; the second operation circuit calculates the ratio of the conduction time of the main power tube to the second time as the first ratio; the second operation circuit calculates the ratio of the inductor current peak value and the first detection value as the second ratio; if the difference between the first ratio and the second ratio is greater than the first difference, the mode recognition signal indicates that the switching power supply operates in a continuous conduction mode; if the first ratio is close to the second ratio, the mode recognition signal indicates that the switching power supply operates in a discontinuous conduction mode.

[0018] Compared with the prior art, the present invention has the following advantages: the error between the feedback signal and the reference signal is compensated to obtain a compensation signal; when the compensation signal is greater than the threshold voltage, the conduction time of the main power tube is detected; if the conduction time of the main power tube is greater than the first threshold time, the working mode of the switching power supply is determined; if the switching power supply works in the intermittent conduction mode, the inductance value of the switching power supply is detected; when the inductance value is less than the first threshold, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal. The present invention can accurately distinguish between output under strong magnetic field conditions and output under overpower conditions, and provide sufficient output power under strong magnetic field conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a working diagram of the switching power supply control circuit of the present invention;

[0020] Figure 2 It is a waveform diagram of the switching power supply of the present invention from continuous to intermittent conduction mode;

[0021] Figure 3 A waveform diagram of the present invention for determining the working mode of the switching power supply;

[0022] Figure 4 This is a schematic diagram of the switching power supply control circuit of the present invention;

[0023] Figure 5 This is a schematic diagram of a first embodiment of a pattern recognition circuit of the present invention;

[0024] Figure 6 This is a schematic diagram of a second embodiment of a pattern recognition circuit of the present invention; DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0026] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0027] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0028] In a switching power supply, the compensation voltage COMP is usually generated by the output feedback circuit, that is, the output quantity to be controlled (such as the output voltage, in this article, the output voltage feedback is used as an example) is compared with the reference signal to generate an error signal (called the compensation voltage or error voltage). Usually, if the output voltage is lower than the reference signal, the compensation voltage COMP becomes higher, so that more energy is transferred to the output, so that the output voltage is maintained at the set value. Usually, the compensation voltage COMP can be used to indicate the status of the output.

[0029] like Figure 1As shown, the working flow chart of the switching power supply control circuit of the present invention is illustrated, and the steps are as follows: determine whether the compensation voltage COMP is greater than the threshold voltage VREF. When the compensation voltage COMP is greater than the threshold voltage VREF, it means that the output voltage is less than the set value. At this time, the circuit is in an overload state or the output power is insufficient due to external influences. At this time, determine whether the conduction time of the primary main power tube is greater than a preset value T0, such as 1us. If the conduction time of the primary main power tube is greater than the set threshold T0, determine whether the switching power supply works in the intermittent conduction mode DCM; if the switching power supply works in the intermittent conduction mode DCM, the inductance is calculated according to the inductance voltage VL, the main power tube conduction time Ton and the peak current Ipk, and the formula is: Lp = VL*Ton / Lpk; if the inductance Lp is less than the set inductance value L1, it means that it is an abnormal overload situation, and the switching power supply is allowed to increase the frequency. The compensation voltage COMP continues to rise on the basis of the threshold voltage VREF, and the switching frequency rises as the voltage of COMP rises. The peak current of the inductor is maintained at the set maximum value Ipk. When the output voltage reaches the set value, the compensation voltage COMP will no longer rise, and the circuit maintains a higher frequency. If the switching power supply operates in the continuous conduction mode CCM, or the inductor L is not less than the set inductance value L1, the overload protection timer is started. If the compensation voltage COMP is greater than the threshold voltage VREF (the state where the inductor peak current reaches the first threshold current) for a duration Tp greater than the set time T1, the switching power supply enters the overload protection.

[0030] If the on-time of the primary main power tube is less than or equal to the set threshold value T0, the control circuit cannot accurately determine whether the switching power supply is working in CCM or DCM mode in a short time. In this way, it is necessary to enter an adjustment cycle every N cycles. During the adjustment cycle, after the main switch tube is turned off, wait for a set time. This time is generally longer than the original switching cycle, so that the inductor current can drop to zero during this time, such as 200us. In this way, in the next switching cycle, it is completely similar to DCM. The inductance can be calculated based on the detected inductor voltage, on-time, and maximum peak current. Based on the detected inductance, it is compared with the set inductance to decide whether to perform the frequency increase operation.

[0031] When the external abnormal influence is removed, such as the external strong magnetic field, the inductance of the switching power supply returns to normal. Since the original circuit works in the frequency increase mode, it will cause excessive output power. The compensation voltage COMP will return to below the threshold voltage VREF. At this time, the switching frequency returns to the original set value and continues to operate.

[0032] like Figure 2As shown, it schematically shows the waveform diagram of the switching power supply of the present invention from continuous conduction mode to discontinuous conduction mode. During the adjustment period, the turn-off time T_delay of the main power transistor is extended so that the inductor current of the main power circuit operates in discontinuous conduction mode.

[0033] As Figure 3 shown, it schematically shows the waveform diagram for judging the working mode of the switching power supply of the present invention. iL1 and iL2 are the waveforms when the inductor current is continuous and discontinuous respectively. Ideally, when the inductor current rises to half of the peak current, the turn-on time of the main power transistor corresponding to iL1 is less than half of the turn-on time of the main power transistor in one switching period, and the turn-on time of the main power transistor corresponding to iL2 is equal to half of the turn-on time of the main power transistor in one switching period. Assuming that the inductor current rises to Ix and the corresponding turn-on time of the main power switch is Tx, then for iL1, Ipk / Ix<Ton / Tx, and for iL2, Ipk / Ix = Ton / Tx, where Ipk is the peak current and Ton is the turn-on time of the main power transistor in one switching period. Thus, the working mode of the switching power supply can be judged.

[0034] As Figure 4 shown, it schematically shows the schematic diagram of the control circuit of the switching power supply of the present invention, including a detection circuit U01, a mode recognition circuit U02, a first control circuit U03, and an operational amplifier U04. The operational amplifier U04 compensates for the error between the feedback signal FB and the reference signal VREF to obtain a compensation signal COMP. When the compensation signal COMP is greater than the threshold voltage VREF, if the turn-on time Ton of the main power transistor is greater than the first threshold time Ton0, the mode recognition circuit U02 judges the working mode of the switching power supply and outputs a mode recognition signal PAT. If the mode recognition signal PAT indicates that the switching power supply operates in discontinuous conduction mode DCM, the detection circuit U01 detects the inductor value Lp of the switching power supply. If the turn-on time Ton of the main power transistor is less than the first threshold time T0, after the switching power supply works at the normal switching frequency for every N cycles, it enters an adjustment period. During the adjustment period, the first control circuit controls the turn-off time of the main power transistor U05 to be extended so that the switching power supply enters discontinuous conduction mode DCM. In the next switching period, the detection circuit U01 detects the inductor value Lp; the turn-off time Toff of the main power transistor during the adjustment period is adjusted according to the turn-on time Ton of the main power transistor. The turn-off time Toff of the main power transistor during the adjustment period does not change with the change of the turn-on time Ton, or changes linearly or in a segmented manner with the change of the turn-on time Ton. When the inductor value Lp is less than the first threshold L1, the switching frequency of the main power transistor is allowed to increase with the increase of the compensation signal COMP until the compensation signal COMP is stable.

[0035] As Figure 5As shown, it is a schematic diagram of a first embodiment of the pattern recognition circuit of the present invention, including a timing circuit U101 and a first operation circuit U102. If the conduction time Ton of the main power tube is greater than the first threshold time Tth, the timing circuit starts timing from the conduction moment of the main switch tube, and when the inductor current IL rises to the first reference Iref1, the timing ends and the first time T1 is output; the first operation circuit U102 receives the conduction time Ton of the main power tube, the first time T1, the inductor current peak Ipk and the first reference Iref1, and outputs a mode recognition signal; the first operation circuit U102 calculates the ratio of the conduction time Ton of the main power tube and the first time T1, which is recorded as the first ratio; the first operation circuit U102 calculates the ratio of the inductor current peak Ipk and the first reference Iref1, which is recorded as the second ratio; the first operation circuit U102 calculates the difference between the first ratio and the second ratio, and if the difference between the first ratio and the second ratio is greater than the first difference, the mode recognition signal PAT indicates that the switching power supply operates in the continuous conduction mode; if the difference between the first ratio and the second ratio is less than the first difference, the mode recognition signal PAT indicates that the switching power supply operates in the intermittent conduction mode. This embodiment corresponds to Figure 3 Waveform diagram of .

[0036] like Figure 6 As shown, it is a schematic diagram of the second embodiment of the mode recognition circuit of the present invention, including a current detection circuit U201 and a second operation circuit U202. If the conduction time Ton of the main power tube is greater than the first threshold time Tth, the current detection circuit U201 detects the inductor current corresponding to the conduction time Ton of the main power tube when it reaches the second time T2, and outputs a first detection value IL1; the second operation circuit U202 receives the conduction time Ton of the main power tube, the second time T2, the inductor current peak value Ipk and the first detection value IL1, and outputs a mode recognition signal PAT; the second operation circuit U202 calculates The ratio of the main power tube conduction time Ton to the second time T2 is calculated as the first ratio; the second operation circuit U202 calculates the ratio of the inductor current peak value Ipk to the first detection value IL1, which is recorded as the second ratio; the second operation circuit U202 calculates the difference between the first ratio and the second ratio, and if the difference between the first ratio and the second ratio is greater than the first difference, the mode recognition signal PAT indicates that the switching power supply operates in the continuous conduction mode; if the difference between the first ratio and the second ratio is less than the first difference, the mode recognition signal PAT indicates that the switching power supply operates in the intermittent conduction mode. This embodiment corresponds to Figure 3 Waveform diagram of .

[0037] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0038] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A switching power supply control method, which compensates for the error between a feedback signal and a reference signal to obtain a compensation signal, characterized in that: When the compensation signal is greater than the threshold voltage, detecting the conduction time of the main power tube; If the conduction time of the main power tube is greater than the first threshold time, it is determined whether the switching power supply operates in the intermittent conduction mode; If the switching power supply operates in the intermittent conduction mode, the inductance value of the switching power supply is detected; when the inductance value is less than a first threshold value, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal; If the on-time of the main power tube is less than the first threshold time, the switching power supply enters an adjustment cycle after working at the normal switching frequency for N cycles, and prolongs the off-time of the main power tube in the adjustment cycle, so that the switching power supply works in the intermittent conduction mode, and detects the inductance value of the switching power supply in the next switching cycle; when the inductance value is less than the first threshold, the switching frequency of the main power tube is allowed to change in the same trend as the compensation signal; The off time of the main power tube in the adjustment period is adjusted according to the on time of the main power tube. The off time of the main power tube in the adjustment period does not change with the change of the on time, or changes linearly or in segments with the change of the on time.

2. The switching power supply control method according to claim 1, characterized in that: If the conduction time of the main power tube is greater than the first threshold time, the time taken for the inductor current to rise to the first reference is detected as the first time; the ratio of the conduction time of the main power tube to the first time is a first ratio, and the ratio of the inductor current peak value to the first reference is a second ratio. If the difference between the first ratio and the second ratio is greater than the first difference, it is determined that the switching power supply operates in a continuous conduction mode; if the difference between the first ratio and the second ratio is less than the first difference, it is determined that the switching power supply operates in a discontinuous conduction mode.

3. The switching power supply control method according to claim 1, characterized in that: If the conduction time of the main power tube is greater than the first threshold time, the inductor current corresponding to the conduction time of the main power tube reaching the second time is detected as the first detection value; the ratio of the conduction time of the main power tube to the second time is the first ratio, and the ratio of the inductor current peak value to the first detection value is the second ratio. If the difference between the first ratio and the second ratio is greater than the first difference, it is determined that the switching power supply operates in the continuous conduction mode; if the difference between the first ratio and the second ratio is less than the first difference, it is determined that the switching power supply operates in the discontinuous conduction mode.

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