Light load current detection circuit

Abstract

The invention provides a light load current detection circuit, which is used for acquiring the output current of a DC-DC conversion circuit, the output current is the average value of the inductive current, and the light load current detection circuit comprises a first counter, a second counter and an output current determination module; the first counter is set to count the upper tube turn-off trigger signals; the second counter is set to count the period number of the periodic signal, and the period of the periodic signal is in direct proportion to the sum of the upper tube conduction time and the lower tube conduction time; and the output current determination module determines the output current according to the count value of the first counter and the count value of the second counter. The first counter of the light-load current detection circuit is set to count the upper tube turn-off trigger signal, and the second counter is set to count the number of cycles of the periodic signal, so that the obtained ratio can be used for obtaining the output current.

Description

Technical Field

[0001] The invention relates to the field of voltage conversion circuits, and in particular to a light-load current detection circuit. Background Art

[0002] The step-down DC-DC converter (i.e., buck converter circuit) will enter the switching current discontinuous mode (DCM mode) under light load mode, which is conducive to reducing switching losses and improving work efficiency. The switch will work for a period of time and then stop for a period of time until the next time the upper tube needs to be turned on again to charge the inductor. In this working state, the working cycle of the buck converter circuit is very long, and the output current is difficult to sample. The traditional current sampling method is to sample and average the output current, so the voltage obtained by sampling is very low, and the circuit accuracy requirements are very high; the non-sampling time is very long, and a large sampling capacitor is required, which is not conducive to circuit design. Summary of the invention

[0003] An object of the present invention is to provide a light-load current detection circuit to obtain the output current of a DC-DC conversion circuit when the DC-DC converter operates in a DCM mode.

[0004] In order to achieve the above-mentioned purpose, the present invention provides a light-load current detection circuit, which is used to obtain the output current of a DC-DC conversion circuit, the output current is the average value of the inductor current, and includes a first counter, a second counter and an output current determination module; the first counter is configured to count the upper tube shutdown trigger signal; the second counter is configured to count the number of cycles of a periodic signal, and the period of the periodic signal is proportional to the sum of the upper tube conduction time and the lower tube conduction time; the output current determination module determines the output current according to the count value of the first counter and the count value of the second counter.

[0005] The second counter is connected to an output end of a periodic signal generating device, and the periodic signal generating device is configured to generate a periodic signal having a period equal to the sum of an upper tube conduction time and a lower tube conduction time.

[0006] The periodic signal generating device includes a first capacitor and a second capacitor, the low-voltage sides of the first capacitor and the second capacitor are both grounded, the high-voltage sides of the first capacitor and the second capacitor are respectively connected to the first charging current and the second charging current and are respectively connected to the two input ends of the first voltage comparator, and the output end of the first voltage comparator is the output end of the periodic signal generating device; the first charging current charges the first capacitor only when the upper tube is turned on or the lower tube is turned on; the high-voltage side of the second capacitor is connected to a second voltage clearing switch tube, and the gate of the second voltage clearing switch tube is connected to the output end of the first voltage comparator, so that when the periodic signal output by the periodic signal generating device becomes a high level, the second capacitor is cleared through the second voltage clearing switch tube.

[0007] The first capacitor is also connected to a first voltage clearing switch tube, and the gate of the first voltage clearing switch tube is connected to the upper tube conduction start signal output by the driving circuit, so that each time the upper tube starts to turn on or when the upper tube starts to turn on again after a fixed time, the first voltage clearing switch tube clears the voltage of the first capacitor.

[0008] The output current determination module includes a division register and a current value calculation module. The division register is configured to continuously calculate and update the ratio n / m of the count value of the second counter and the count value of the second counter in the DCM mode and store it; and the current value calculation module is configured to continuously calculate the output current according to the ratio n / m in the DCM mode.

[0009] The first charging current is equal to the second charging current, and the period of the periodic signal is equal to the sum of the upper tube conduction time and the lower tube conduction time.

[0010] For the step-down converter circuit, the output current calculated by the current value calculation module for: , For the boost converter circuit, the output current calculated by the current value calculation module for: , in, is the internal reference current, n is the count value of the first voltage comparator, and m is the count value of the second comparator.

[0011] The DC-DC conversion circuit comprises an error amplifier, a driving circuit, a pair of parallel switching tubes and a filtering circuit connected in sequence, and an inductor current comparator and a zero-crossing detection module connected to the driving circuit.

[0012] The positive input terminal and the negative input terminal of the error amplifier are connected to the feedback voltage and the reference voltage respectively, and the output terminal of the error amplifier is connected to the input terminal of the driving circuit; when the feedback voltage is lower than or equal to the reference voltage, the inductor current comparator outputs an upper tube start trigger signal to the driving circuit, so that the upper tube is turned on; The inductor current comparator is used to compare the inductor detection current with the internal reference current. When the inductor detection current is greater than or equal to the internal reference current, the inductor current comparator outputs an upper tube shutdown trigger signal to the drive circuit, and the drive circuit outputs a signal to shut down the upper tube and turn on the lower tube; When the zero-crossing detection module detects that the inductor current is 0, the zero-crossing detection module outputs a lower tube shutdown trigger signal, and the drive circuit outputs a signal to shut down the lower tube.

[0013] The parallel switch tubes include an upper tube and a lower tube, the two output ends of the drive circuit are respectively connected to the gates of the upper tube and the lower tube, the drains of the upper tube and the lower tube are connected, and the source of the lower tube is grounded; The filter circuit includes an inductor with one end connected to the drains of the upper tube and the lower tube and a grounded capacitor connected to the other end of the inductor, and the connection point of the inductor and the grounded capacitor serves as a voltage output terminal, and the source of the upper tube serves as a voltage input terminal; or, the filter circuit includes an inductor with one end connected to the drains of the upper tube and the lower tube and a grounded capacitor connected to the source of the upper tube, and the source of the upper tube serves as a voltage output terminal, and the other end of the inductor serves as a voltage input terminal.

[0014] The first counter of the light-load current detection circuit of the present invention is configured to count the upper tube shutdown trigger signal, and the second counter is configured to count the number of cycles of the periodic signal, so that the obtained ratio can be used to obtain the output current. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A circuit block diagram of a light-load current detection circuit according to an embodiment of the present invention is shown, which illustrates an application scenario of the light-load current detection circuit of the present invention.

[0016] Figure 2 The output current waveform diagram of a buck converter circuit using the light-load current detection circuit of the present invention working in DCM mode is shown.

[0017] Figure 3 This is another application scenario diagram of the light-load current detection circuit of the present invention. DETAILED DESCRIPTION

[0018] like Figure 1 The circuit block diagram of a light-load current detection circuit according to an embodiment of the present invention is shown, which is used to obtain the output current iout of the DC-DC conversion circuit. The output current iout is the average value of the inductor current isw, and the output current iout can be used for other functional modules of the circuit. The light-load current detection circuit of the present invention is suitable for DC-DC conversion circuits, and is particularly suitable for all DC-DC conversion circuits that can operate in a switching current discontinuous mode (DCM mode), including buck-type conversion circuits and boost-type conversion circuits.

[0019] The control principle of the light-load current detection circuit of the present invention is: like Figure 1 As shown, the existing DC-DC conversion circuit includes an error amplifier 100, a drive circuit 200, a pair of parallel switch tubes 300 and a filter circuit 400 which are connected in sequence.

[0020] The non-inverting input terminal and the inverting input terminal of the error amplifier 100 are connected to the feedback voltage Vfb and the reference voltage Vref, respectively, and the output terminal of the error amplifier 100 is connected to the input terminal of the driving circuit 200. The feedback voltage Vfb is a feedback signal of the output voltage Vout, which is usually obtained by resistor voltage division, and Vref is a built-in or external reference signal. The error amplifier 100 is configured to compare the feedback voltage Vfb and the reference voltage Vref. When the feedback voltage Vfb is lower than or equal to the reference voltage Vref, the inductor current comparator outputs an upper tube start trigger signal hs_on to the driving circuit 200, so that the upper tube is turned on.

[0021] In addition, the DC-DC conversion circuit also includes an inductor current comparator 600 connected to the drive circuit 200, which is used to compare the inductor detection current isense and the internal reference current ipeak. When the inductor detection current isense reaches the internal reference current ipeak, the inductor current comparator outputs an upper tube shutdown trigger signal hs_off to the drive circuit 200, so that the upper tube is turned off and the lower tube is turned on. The inductor detection current isense is obtained by sampling the inductor current isw by the output current sampling module, which is usually isense=1 / N×isw, where N is the sampling ratio. There are many classic forms of the output current sampling module, which will not be repeated here. The size of the internal reference current ipeak is adjustable.

[0022] In this embodiment, the inductor current comparator 600 is implemented by a current mirror formed by a pair of NMOS switch tubes with a common gate, and the two NMOS switch tubes are respectively connected to the inductor detection current isense and the internal reference current ipeak, and the gate of the NMOS switch tube connected to the internal reference current ipeak is connected to an inverter, and the output end of the inverter is the output signal of the inductor current comparator 600. Therefore, when the inductor detection current isense is less than the internal reference current ipeak, the output level of the inductor current comparator 600 is low, that is, no upper tube shutdown trigger signal hs_off is generated, and when the inductor detection current isense is greater than or equal to the internal reference current ipeak, the output level of the inductor current comparator 600 is high, that is, the inductor current comparator 600 outputs the upper tube shutdown trigger signal hs_off. In other embodiments, the inductor current comparator 600 can be implemented in other ways.

[0023] The DC-DC conversion circuit also includes a zero-crossing detection module 500 connected to the driving circuit 200. When the zero-crossing detection module 500 detects that the inductor current is 0, the zero-crossing detection module 500 outputs a lower tube shutdown trigger signal ls_off, so that the lower tube conduction signal gls output by the driving circuit 200 is switched to a low level, that is, the driving circuit 200 outputs a signal to shut down the lower tube.

[0024] The parallel switch tube 300 includes an upper tube and a lower tube. The two output ends of the drive circuit 200 are respectively connected to the gates of the upper tube and the lower tube, and the drains of the upper tube and the lower tube are connected, and the source of the lower tube is grounded.

[0025] In one embodiment, since the DC-DC conversion circuit is a step-down conversion circuit, the filter circuit 400 includes an inductor having one end connected to the drain of the upper tube and the lower tube and a grounded capacitor connected to the other end of the inductor, and the connection point between the inductor and the grounded capacitor serves as a voltage output terminal, and the source of the upper tube serves as a voltage input terminal.

[0026] Therefore, if Figure 1 and Figure 2 As shown, when the feedback voltage Vfb is lower than the reference voltage Vref, the error amplifier 100 outputs the upper tube start trigger signal hs_on to the driving circuit 200, so that the upper tube conduction signal ghs output by the driving circuit 200 is switched to a high level, that is, the driving circuit 200 outputs a signal to turn on the upper tube, and the inductor current isw starts to increase from 0.

[0027] When the inductor detection current isense corresponding to the inductor current isw reaches the internal reference current ipeak (set value, adjustable), the inductor current comparator outputs an upper tube turn-off trigger signal hs_off to the drive circuit 200, so that the upper tube conduction signal ghs output by the drive circuit 200 switches to a low level, and the lower tube conduction signal gls switches to a high level, that is, the drive circuit 200 outputs a signal to turn off the upper tube and turn on the lower tube. The upper tube conduction time is ton.

[0028] After the lower tube is turned on, the inductor current starts to decrease from the internal reference current ipeak. When the zero-crossing detection module 500 detects that the inductor current is 0, the zero-crossing detection module 500 outputs the lower tube shutdown trigger signal ls_off, so that the lower tube conduction signal gls output by the driving circuit 200 is switched to a low level, that is, the driving circuit 200 outputs a signal to turn off the lower tube. The lower tube conduction time is toff. Thus, a triangular output waveform is formed.

[0029] It should be noted that, in this embodiment, Figure 2 As shown, the waveforms of the upper tube conduction signal ghs and the lower tube conduction signal gls output by the driving circuit 200 are only for the case where the corresponding switch tube is turned on when the level is high and the corresponding switch tube is turned off when the level is low, which is only an exemplary description. In other embodiments, the upper tube conduction signal ghs and the lower tube conduction signal gls do not necessarily turn on the corresponding switch tube when the level is high, so the corresponding waveforms will also change, as long as the turn-on and turn-off time of the switch tube remains unchanged.

[0030] Then, when the voltage at the VFB terminal of the error amplifier is lower than the Vref voltage, the upper tube is turned on again. It can be seen that the waveform of the inductor current is discontinuous and has no regularity. In this case, current sampling becomes very difficult.

[0031] See also Figure 1 Based on the control principle of the present invention, the implemented light-load current detection circuit includes a first counter 10, a second counter 20 and an output current determination module.

[0032] The first counter 10 is configured to count the upper tube shut-off trigger signal hs_off. Thus, the first counter 10 accumulates the number of times the upper tube is shut off and the lower tube is turned on within the time of the discontinuous mode of the switching current (such as within the mT time), and the count value of the first counter 10 increases by 1 each time. The count value of the first counter 10 is n.

[0033] The second counter 20 is configured to count the number of periods of the periodic signal, wherein the period of the periodic signal is equal to the sum of the upper tube conduction time ton and the lower tube conduction time toff. The count value of the second counter 20 is m.

[0034] The second counter 20 is connected to the output end of a periodic signal generating device 50, and the periodic signal generating device 50 is configured to generate a periodic signal having a period equal to the sum of the upper tube conduction time ton and the lower tube conduction time toff. In this embodiment, the periodic signal generating device 50 includes a first capacitor c1 and a second capacitor c2, the low-voltage sides of the first capacitor c1 and the second capacitor c2 are both grounded, the high-voltage sides of the first capacitor c1 and the second capacitor c2 are respectively connected to the first charging current i1 and the second charging current i2 and are respectively connected to the two input ends (i.e., the negative input end and the positive input end) of the first voltage comparator cp1, and the output end of the first voltage comparator cp1 is the output end of the periodic signal generating device 50.

[0035] The first charging current i1 is connected to a first driving switch K1, and the first driving switch K1 is closed only when the upper tube is turned on or the lower tube is turned on. Therefore, the first charging current i1 charges the first capacitor c1 only when the upper tube is turned on or the lower tube is turned on, and the total charging time is equal to the sum of the upper tube on time ton and the lower tube on time toff (that is, equal to ton+toff). Therefore, when the charging of the ton+toff time is completed: i1(ton+toff)=c1×Vc1, Wherein, i1 is the first charging current, ton is the upper tube conduction time, toff is the lower tube conduction time, c1 is the first capacitor, and Vc1 is the first capacitor voltage.

[0036] Then Vc1=i1(ton+toff) / c1.

[0037] Since there is no discharge path, the voltage on the first capacitor c1 will always maintain the first capacitor voltage Vc1.

[0038] In some embodiments, the first capacitor c1 is also connected to the first voltage clearing switch tube, and the gate of the first voltage clearing switch tube is connected to the upper tube conduction start signal output by the driving circuit 200, so that each time the upper tube starts to conduct or after a fixed time, the upper tube starts to conduct again, the first voltage clearing switch tube quickly clears the first capacitor voltage Vc1 (that is, the second charging current charging ends). The duration of the upper tube conduction start signal is very short, generally on the order of a few ns. In other embodiments, the shorter the duration, the better. Therefore, after the first capacitor voltage Vc1 is quickly cleared, the first capacitor c1 immediately starts to charge through the first charging current i1. In other embodiments, if there is no leakage in the entire circuit (ideally), the first voltage clearing switch tube can also be omitted, so that the first capacitor voltage Vc1 is not cleared, and the first capacitor voltage Vc1 is always maintained.

[0039] The high voltage side of the second capacitor c2 is connected to a second voltage reset switch tube, and the gate of the second voltage reset switch tube is connected to the output end of the first voltage comparator cp1, so that when the periodic signal output by the periodic signal generating device 50 becomes a high level, the second capacitor c2 is reset by the second voltage reset switch tube, so that the periodic signal returns to a low level and starts the timing of the next cycle. Thus, the period T of the periodic signal is the charging time of the second capacitor c2. In this embodiment, the second voltage reset switch tube is an NMOS tube, and in other embodiments, the second voltage reset switch tube can be a PMOS tube, as long as it satisfies the condition that when the periodic signal output by the periodic signal generating device 50 becomes a high level, the second capacitor c2 is reset by the second voltage reset switch tube.

[0040] The first voltage comparator cp1 is configured to make the periodic signal become a high level when the second capacitor voltage Vc2 is greater than or equal to the first capacitor voltage Vc1, and at this time, the second voltage clearing switch tube discharges and clears c2.

[0041] The second capacitor voltage Vc2 satisfies the formula: i2×t=c2×Vc2, Among them, i2 is the second charging current, c2 is the resistance of the second capacitor, t is the charging time, and Vc2 is the second capacitor voltage.

[0042] Since every time Vc2=Vc1, that is, every time the charging time t reaches the total time of a single charge of the second capacitor c2, the first voltage comparator cp1 will output a high level, and then the second capacitor voltage Vc2 will start charging again (that is, the charging time t returns to 0). Therefore, every time the charging time t reaches the total charging time of the second capacitor c2, the high level output by the first voltage comparator cp1 forms a periodic signal pulse, and the period T of the periodic signal pulse is the total time of a single charge of the second capacitor c2.

[0043] In this embodiment, the first charging current i1 is equal to the second charging current i2. After calculation, the period of the periodic signal T=ton+toff. Thus, the second counter 20 can count the number of periods of the periodic signal, and the period of the periodic signal is equal to the sum of the upper tube conduction time ton and the lower tube conduction time toff.

[0044] In other embodiments, the values ​​of the first charging current i1 and the second charging current i2 are different, and the period of the periodic signal is proportional to the sum of the upper tube conduction time and the lower tube conduction time.

[0045] In some embodiments, the second charging current i2 is connected to a second driving switch K2. In DCM, the output stage sometimes works and sometimes does not work. The second driving switch K2 is set to remain closed when both the upper tube and the lower tube are disconnected, so that the result of the second counter can be obtained. When one of the upper tube and the lower tube is turned on (i.e., ton or toff), the second driving switch K2 is turned off, so that the second counter is suspended.

[0046] Since in DCM mode, the output current All satisfy the following formula: , Therefore, the output current for: , in, is the internal reference current, n is the count value of the first counter, and m is the count value of the second counter.

[0047] The output current determination module is used to determine the output current according to the count value n of the first counter 10 and the count value m of the second counter 20. In this embodiment, the output current determination module includes a division register 30 and a current value calculation module 40 .

[0048] The divider register 30 is configured to continuously calculate and update the ratio n / m of the count value of the first counter 10 to the count value of the second counter 20 in the DCM mode and store it, and the current value calculation module 40 is configured to continuously calculate the output current according to the ratio n / m in the DCM mode.

[0049] The divider register 30 uses 12-bit data. The current value calculation module 40 may be a digital circuit. Due to the above formula, the output current calculated by the current value calculation module 40 is for: , in, is the internal reference current, n is the count value of the first voltage comparator, and m is the count value of the second comparator.

[0050] In this embodiment, in the DCM mode, the count values ​​of the first counter ct1 and the second counter ct2 continue to increase (and will not be reset to zero), and the ratio n / m calculated by the division register 30 continues to be updated. This is because for a load of a fixed size, the output current It is a constant value, so the ratio n / m obtained by the formula will be unstable at the beginning, but as the counting time becomes longer, the ratio n / m will stabilize. The circuit is always in dynamic adjustment, so the ratio n / m will be calculated all the time.

[0051] Considering that the step-down DC-DC converter does not need to calculate the output current when exiting the DCM mode, in this embodiment, the first counter ct1 and the second counter ct2 are set to end their work and be cleared when exiting the DCM mode, and the output current determination module ends its work.

[0052] Can be combined with digital circuit, so that the output current can be easily obtained The value of .

[0053] In another embodiment, Figure 3 As shown, since the DC-DC conversion circuit is a step-up conversion circuit (i.e., a boost conversion circuit), the filter circuit 400 includes an inductor having one end connected to the drains of the upper tube and the lower tube and a grounded capacitor connected to the source of the upper tube, and the source of the upper tube serves as a voltage output terminal, and the other end of the inductor serves as a voltage input terminal.

[0054] against Figure 3 The light-load current detection circuit implemented by the DC-DC conversion circuit shown also includes a first counter, a second counter, and an output current determination module connected to the output ends of the first counter and the second counter.

[0055] The first counter is configured to count the number of times the upper tube is turned off and the lower tube is turned on. The second counter is configured to count the number of cycles of a periodic signal, wherein the cycle of the periodic signal is equal to the sum of the upper tube conduction time ton and the lower tube conduction time toff, and the count value of the second counter is m. The output current determination module is configured to determine the output current according to the count value n of the first counter and the count value m of the second counter. .

[0056] The specific structures of the first counter and the second counter can be the same as those described above. Figure 1 In the illustrated embodiment, the first counter 10 and the second counter 20 are identical.

[0057] For boost converter circuits, the output current Satisfies the following formula: , Therefore, the output current for: , in, is the internal reference current, n is the count value of the first voltage comparator, and m is the count value of the second comparator.

[0058] Therefore, in this embodiment, the output current determination module includes a division register and a current value calculation module, the division register 30 is configured to continuously calculate and update the ratio n / m of the count value of the first counter 10 and the count value of the second counter 20 in the DCM mode and store it; and the current value calculation module 40 is configured to continuously calculate the output current according to the ratio n / m in the DCM mode. The calculation formula is: .

[0059] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiments of the present invention can also be modified in various ways. All simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A light load current detection circuit, which is used to obtain the output current of a DC-DC conversion circuit, the output current is the average value of the inductor current, characterized in that: It includes a first counter, a second counter and an output current determination module; the first counter is set to count the upper tube shutdown trigger signal; the second counter is set to count the number of cycles of the periodic signal, and the cycle of the periodic signal is proportional to the sum of the upper tube conduction time and the lower tube conduction time; the output current determination module determines the output current according to the count value of the first counter and the count value of the second counter.

2. The light load current detection circuit according to claim 1, characterized in that: The second counter is connected to an output end of a periodic signal generating device, and the periodic signal generating device is configured to generate a periodic signal having a period equal to the sum of an upper tube conduction time and a lower tube conduction time.

3. The light load current detection circuit according to claim 2, characterized in that: The periodic signal generating device comprises a first capacitor and a second capacitor, the low voltage sides of the first capacitor and the second capacitor are both grounded, the high voltage sides of the first capacitor and the second capacitor are respectively connected to a first charging current and a second charging current and are respectively connected to two input ends of a first voltage comparator, and the output end of the first voltage comparator is the output end of the periodic signal generating device; The first charging current charges the first capacitor only when the upper tube is turned on or the lower tube is turned on; The high voltage side of the second capacitor is connected to a second voltage clearing switch tube, and the gate of the second voltage clearing switch tube is connected to the output end of the first voltage comparator, so that when the periodic signal output by the periodic signal generating device becomes a high level, the second capacitor is cleared through the second voltage clearing switch tube.

4. The light load current detection circuit according to claim 3, characterized in that: The first capacitor is also connected to a first voltage clearing switch tube. The DC-DC conversion circuit includes a driving circuit. The gate of the first voltage clearing switch tube is connected to the upper tube conduction start signal output by the driving circuit, so that each time the upper tube starts to turn on or when the upper tube starts to turn on again after a fixed time, the first voltage clearing switch tube clears the voltage of the first capacitor.

5. The light load current detection circuit according to claim 3, characterized in that: The output current determination module includes a division register and a current value calculation module. The division register is configured to continuously calculate and update the ratio n / m of the count value of the second counter and the count value of the second counter in the DCM mode and store it; and the current value calculation module is configured to continuously calculate the output current according to the ratio n / m in the DCM mode.

6. The light load current detection circuit according to claim 3, characterized in that: The first charging current is equal to the second charging current, and the period of the periodic signal is equal to the sum of the upper tube conduction time and the lower tube conduction time.

7. The light load current detection circuit according to claim 5, characterized in that: For the step-down converter circuit, the output current calculated by the current value calculation module for: ， For the boost converter circuit, the output current calculated by the current value calculation module for: ， in, is the internal reference current, n is the count value of the first voltage comparator, and m is the count value of the second comparator.

8. The light load current detection circuit according to claim 1, characterized in that: The DC-DC conversion circuit comprises an error amplifier, a driving circuit, a pair of parallel switching tubes and a filtering circuit connected in sequence, and an inductor current comparator and a zero-crossing detection module connected to the driving circuit.

9. The light load current detection circuit according to claim 8, characterized in that: The positive input terminal and the negative input terminal of the error amplifier are connected to the feedback voltage and the reference voltage respectively, and the output terminal of the error amplifier is connected to the input terminal of the driving circuit; when the feedback voltage is lower than or equal to the reference voltage, the inductor current comparator outputs an upper tube start trigger signal to the driving circuit, so that the upper tube is turned on; The inductor current comparator is used to compare the inductor detection current with the internal reference current. When the inductor detection current is greater than or equal to the internal reference current, the inductor current comparator outputs an upper tube shutdown trigger signal to the drive circuit, and the drive circuit outputs a signal to shut down the upper tube and turn on the lower tube; When the zero-crossing detection module detects that the inductor current is 0, the zero-crossing detection module outputs a lower tube shutdown trigger signal, and the drive circuit outputs a signal to shut down the lower tube.

10. The light load current detection circuit according to claim 8, characterized in that: The parallel switch tubes include an upper tube and a lower tube, the two output ends of the driving circuit are respectively connected to the gates of the upper tube and the lower tube, the drains of the upper tube and the lower tube are connected, and the source of the lower tube is grounded; The filter circuit includes an inductor with one end connected to the drains of the upper tube and the lower tube and a grounded capacitor connected to the other end of the inductor, and the connection point of the inductor and the grounded capacitor serves as a voltage output terminal, and the source of the upper tube serves as a voltage input terminal; or, the filter circuit includes an inductor with one end connected to the drains of the upper tube and the lower tube and a grounded capacitor connected to the source of the upper tube, and the source of the upper tube serves as a voltage output terminal, and the other end of the inductor serves as a voltage input terminal.

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