A light-load current detection device and method based on the light-load mode of a switching power supply

Abstract

The present invention relates to a light-load current detection device and method based on a light-load mode of a switching power supply. The device includes a switching power supply and a timing module; the switching power supply includes a light-load mode detection module and a switching power supply control module; the light-load mode detection module compares the output voltage of the switching power supply with a reference voltage, and outputs a sleep signal to the switching power supply control module based on the comparison result to control the output of the output voltage of the switching power supply; the timing module receives the sleep signal and outputs a light-load current confirmation signal when the sleep signal indicates that the switching power supply has been in light-load mode for more than a predetermined time. The present invention does not require the addition of additional sampling resistor sampling circuits and packaging costs, does not rely on the accuracy of the sampling circuit, can detect smaller load currents, the switching power supply is intermittently turned on, and the device operates in a high-efficiency mode before it goes into sleep mode, thereby improving the device's battery life.

Description

Technical Field

[0001] The present invention relates to a light-load current detection device and method, and in particular to a light-load current detection device and method based on a light-load mode of a switching power supply. Technical Background

[0002] Light load mode is a mode in which the switching power supply turns off the power tube for a period of time and then turns on the power tube in order to improve the efficiency of low current output. Intermittent switching will generate light load ripple, such as Figure 1 As shown in Figure 2(b). Light-load current detection determines that the load current is less than a certain value and generates a signal, which automatically shuts down the system or takes other actions. Portable devices often need to detect light-load current and then go into sleep mode to save power. Light-load detection in switching power supplies is a design challenge. One traditional detection method is to connect a resistor in series with the output path and use a high-precision op amp to collect the voltage difference across the resistor, as shown in Figure 2(b). Another traditional detection method is to sample the average current in the inductor, as shown in Figure 2(a).

[0003] Both of the above methods have significant drawbacks. The series resistor adds additional power consumption and circuit cost, and requires additional sampling pins on the package. Sampling the inductor current requires the switching power supply to operate in continuous conduction mode, resulting in a significant loss of efficiency under light loads. With the increasing popularity of various low-power devices, maintaining high efficiency under light loads by using burst mode (intermittent switching) has become increasingly important. This makes it difficult to simultaneously detect light loads and maintain high efficiency. Furthermore, light load detection requires high precision in the detection circuit; lower set currents make it more likely that detection will go undetected. Summary of the Invention

[0004] Purpose of the invention: In view of the deficiencies in the prior art, the present invention provides a light-load current detection device based on the light-load mode of a switching power supply, so as to efficiently detect the light-load current, and the detection device has a simple structure.

[0005] Another aspect of the present invention provides a light-load current detection method based on a light-load mode of a switching power supply.

[0006] Technical Solution: A light-load current detection device based on a light-load mode of a switching power supply of the present invention includes a switching power supply and a timing module. The switching power supply includes a light-load mode detection module and a switching power supply control module. The light-load mode detection module compares the output voltage of the switching power supply with a reference voltage and outputs a sleep signal to the switching power supply control module based on the comparison result to control the output voltage of the switching power supply. The timing module receives the sleep signal and, when the sleep signal indicates that the switching power supply has been in light-load mode for more than a predetermined time, outputs a signal indicating that a light-load current has been detected.

[0007] The predetermined time is calculated by the following formula:

[0008]

[0009] Wherein, T is the predetermined time, Vr is the light-load ripple of the designed switching power supply in the light-load mode, Cout is the output capacitance value, and I is the set target light-load current to be detected.

[0010] Furthermore, the timing module includes one or more D flip-flops; the reset terminal of each of the multiple D flip-flops receives the sleep signal Vsleep from the light-load mode detection module; except for the last D flip-flop, the input terminal d of each flip-flop is connected to its own output terminal q; the input terminal d of the last D flip-flop is connected to the high potential Vdd, and the output terminal outputs a signal indicating that a light-load current has been detected to the switching power supply control module; the clock signal input terminal of the first D flip-flop is connected to the clock signal Clk, and the clock signal input terminals of subsequent flip-flops are connected to the output terminal q of the previous D flip-flop.

[0011] Furthermore, the light-load mode detection module includes a comparator, two input terminals of the comparator are respectively connected to the output voltage and the reference voltage, and an output terminal of the comparator is connected to the input of the light-load mode detection module.

[0012] A light-load current detection method based on a light-load mode of a switching power supply of the present invention comprises the following steps:

[0013] (1) Calculating the predetermined time T based on the light-load ripple Vr, the output capacitance Cout, and the target light-load current I to be detected in the light-load mode of the designed switching power supply;

[0014] (2) designing a timing module based on the calculated predetermined time T so that when the timing module detects that the input sleep signal lasts longer than T, it outputs a signal indicating that a light load current has been detected;

[0015] (3) The input end of the timing module designed in step (2) receives the sleep signal of the existing switching power supply. When it is detected that the timing module outputs a signal indicating that a light load current has been detected, it is considered that a light load current has been detected.

[0016] The predetermined time T in step (1) is calculated by the following formula:

[0017]

[0018] Beneficial effects: Compared with the existing technology, the present invention does not require additional sampling resistor sampling circuit and packaging costs, does not rely on the accuracy of the sampling circuit, can detect smaller load currents, the switching power supply is intermittently turned on, and the device always works in high-efficiency mode before sleeping, thereby improving the device's battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a waveform diagram of an existing switching power supply;

[0020] FIG2( a ) is a schematic diagram showing the structure of a detection circuit corresponding to a light-load current detection method of an existing switching power supply;

[0021] FIG2( b ) is a schematic diagram of the structure of another detection circuit corresponding to the light-load current detection method of the existing switching power supply;

[0022] Figure 3 4 is a structural block diagram of the light-load current detection device of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that the examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0024] Based on the existing switching power supply with light load mode, the present invention determines the load current by calculating the light load mode time interval, so that the switching power supply can maintain a high-efficiency burst mode under light load and detect the light load current.

[0025] Specifically, assuming the light-load ripple of the switching power supply in burst mode is Vr, and the target light-load current to be detected is set to I. The amount of charge on the output capacitor Cout during each interval is equal to the amount of discharge. Therefore, we have:

[0026] Vr×Cout=I×T

[0027]

[0028] In this way, by calculating the burst mode (light load mode) interval, i.e., the time the power supply stops switching, the light load current can be determined. For example, if the detection current I is less than 10mA, simply use a timer to measure the time the power supply stops switching > T to determine that the load current is less than 10mA. The chip can then shut down or hibernate to save power. To detect a current I less than 1mA, simply multiply the time by 10. The smaller the current, the longer the detection time, eliminating the problem of failure to detect. Traditional detection methods rely on the accuracy of op amps or comparators. If the detection current is too small, the current below the target value will not be detected, resulting in the system failing to automatically shut down.

[0029] like Figure 3Based on the above principles, the light-load current detection method of the present invention includes a switching power supply and a timing module. The switching power supply includes a light-load mode detection module and a switching power supply control module. The light-load mode detection module includes a comparator that compares the output voltage Vout of the switching power supply with a reference voltage Vref and outputs a sleep signal Vsleep to the switching power supply control module to control the output voltage Vout of the switching power supply. The timing module receives the sleep signal Vsleep and, when the sleep signal Vsleep indicates that the switching power supply has been in light-load mode for a predetermined time T, outputs a signal indicating that a light-load current has been detected.

[0030] The timing module can be implemented by cascading multiple triggers. For example, Figure 3 The timing module includes multiple D flip-flops, and the reset terminal of each of the multiple flip-flops receives the sleep signal Vsleep from the light-load mode detection module; except for the last D flip-flop, the input terminal d of each flip-flop is connected to its own output terminal q; the input terminal d of the last D flip-flop is connected to the high potential Vdd, and the output terminal outputs a signal used to indicate that a light-load current has been detected; the clock signal input terminal of the first D flip-flop is connected to the clock signal Clk, and the clock signal input terminals of subsequent flip-flops are connected to the output terminal q of the previous D flip-flop.

[0031] The detection method based on the above light-load current detection device includes the following steps:

[0032] Step 1: Calculate the burst mode (light load mode) interval time T using the following formula based on the designed switching power supply's light load ripple Vr, output capacitance Cout, and the target light load current I to be detected:

[0033]

[0034] Step 2: Design a timing module based on the calculated interval time T, so that when the timing module detects that the input signal duration exceeds T, it outputs a signal indicating that a light load current is detected.

[0035] Specifically, if the clock clk period of the timing module is t, n is the number of D flip-flops. Taking t = 1us as an example, t×2 n-1 =1×2 8-1=128us, 8 D flip-flops are needed to calculate a time greater than T=128us. In other cases, the number of D flip-flops can be reversed based on the calculated interval time T. After determining the number of D flip-flops, these n D flip-flops are cascaded so that the reset terminal of each of the multiple flip-flops receives the sleep signal Vsleep from the light-load mode detection module. Except for the last D flip-flop, the input terminal d of each flip-flop is connected to its own output terminal q. The input terminal d of the last D flip-flop is connected to the high potential Vdd, and the output terminal outputs a light-load current to indicate the detection of the light-load current to the switching power supply control module. The clock signal input terminal of the first D flip-flop is connected to the clock signal Clk, and the clock signal input terminals of subsequent flip-flops are connected to the output terminal q of the previous D flip-flop.

[0036] It should be noted that the timing module can be implemented in more than one way as described above. The function of the timing module can also be implemented by programming programmable logic or using a pure analog circuit.

[0037] Step 3: The input end of the timing module designed in step 2 receives the sleep signal Vsleep of the existing switching power supply. When the timing module outputs the signal noload indicating that a light load current has been detected, it is considered that a light load current has been detected.

[0038] It should be noted that although the signal "noload" indicating the detection of a light load current is input to the switching power supply control module in FIG2 , its purpose is to allow the switching power supply to perform other actions based on the noload signal, such as shutting down, hibernating, or notifying other systems. In other embodiments, the output of the timing module does not necessarily need to be input to the switching power supply control module.

[0039] The above describes in detail the specific embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by ordinary technicians in this field, various changes can be made to the specific operating steps and various reactants and reaction conditions can be changed and replaced without departing from the purpose of the present invention.

Claims

1. A light-load current detection device based on a light-load mode of a switching power supply, characterized in that: The invention comprises a switching power supply and a timing module; the switching power supply comprises a light-load mode detection module and a switching power supply control module; the light-load mode detection module compares the output voltage of the switching power supply with a reference voltage and outputs a sleep signal to the switching power supply control module based on the comparison result to control the output voltage of the switching power supply; the timing module receives the sleep signal and outputs a signal indicating that a light-load current has been detected when the sleep signal indicates that the switching power supply has been in light-load mode for more than a predetermined time; The predetermined time is calculated by the following formula: Wherein, T is the predetermined time, Vr is the light-load ripple of the designed switching power supply in the light-load mode, Cout is the output capacitance value, and I is the set target light-load current to be detected.

2. The light-load current detection device based on the light-load mode of the switching power supply according to claim 1, characterized in that: The timing module includes one or more D flip-flops; the reset terminal of each of the multiple D flip-flops receives the sleep signal Vsleep from the light-load mode detection module; except for the last D flip-flop, the input terminal of each flip-flop is connected to its own output terminal; the input terminal of the last D flip-flop is connected to the high potential Vdd, and the output terminal outputs the signal used to indicate the detection of light-load current; the clock signal input terminal of the first D flip-flop is connected to the clock signal Clk, and the clock signal input terminals of subsequent flip-flops are connected to the output terminal of the previous D flip-flop.

3. The light-load current detection device based on the light-load mode of the switching power supply according to claim 1, characterized in that: The light-load mode detection module includes a comparator, two input terminals of the comparator are connected to the output voltage and the reference voltage respectively, and an output terminal of the comparator is connected to the input of the light-load mode detection module.

4. A light-load current detection method based on a light-load mode of a switching power supply, characterized in that: The steps include: (1) Calculating the predetermined time T based on the light-load ripple Vr, the output capacitance Cout, and the set target light-load current I to be detected in the light-load mode of the designed switching power supply; (2) designing a timing module based on the calculated predetermined time T so that when the timing module detects that the input sleep signal lasts longer than T, it outputs a signal indicating that a light load current has been detected; (3) enabling the input end of the timing module designed in step (2) to receive a sleep signal of the existing switching power supply, and when it is detected that the timing module outputs a signal indicating that a light load current has been detected, it is considered that a light load current has been detected; The predetermined time T in step (1) is calculated by the following formula:

Images