A method and a circuit for detecting the peak value of an inductance current

Abstract

This invention relates to a method and circuit for detecting peak inductor current. In the method, the inductor is an energy storage inductor of a switching power supply; the switching power supply operates in continuous mode; and the method includes the following steps: obtaining the valley value I_valley of the inductor current; obtaining the median value I_m of the inductor current; and calculating the peak value I_peak of the inductor current based on the valley value and the median value, using the calculation method: I_peak = I_valley + (1 / n)*(I_m - I_valley). This invention calculates the peak value of the inductor current by detecting the valley value and the median value, avoiding direct detection of the peak value and preventing the influence of blank time and loop establishment time on the detection accuracy of the peak value of the energy storage inductor current.

Description

Technical Field

[0001] This invention relates to power supply circuits, and more specifically to an inductor current peak detection circuit and detection method. Background Technology

[0002] A switching circuit is a type of DC-DC converter, and the BUCK type is a topology of a switching circuit. Figure 1 This is a schematic diagram of the BUCK circuit structure. (Example:) Figure 1 As shown, the BUCK-type switching circuit includes an upper power transistor M1, a lower power transistor M2, and an energy storage inductor L. The load is connected to the output voltage Vout. During the operation of the switching circuit, the upper power transistor M1 and the lower power transistor M2 are controlled to turn on or off by a pulse signal with a variable duty cycle. When the upper power transistor M1 is on, the lower power transistor M2 is off, and the input voltage provides energy to the energy storage inductor L. When the upper power transistor M1 is off, the lower power transistor M2 is on, and the energy storage inductor L releases the stored energy to the load. In the analysis of the BUCK-type switching circuit, it is often necessary to detect the peak current of the energy storage inductor L. The traditional method is to directly detect the peak current of the inductor. However, direct detection has many drawbacks. For example, in order to eliminate voltage spikes, the switching circuit will set a blanking time after the upper power transistor M1 is turned off. Also, if it is necessary to detect the peak current of the inductor, the loop establishment of the traditional inductor current peak detection circuit requires a certain amount of time. The blanking time and the loop establishment time will affect the detection accuracy of the peak current of the energy storage inductor. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention discloses a method and detection circuit for detecting peak inductor current.

[0004] The technical solution adopted in this invention is as follows:

[0005] A method for detecting peak inductor current, wherein the inductor is an energy storage inductor of a switching power supply; the switching power supply operates in continuous mode; the method includes the following steps:

[0006] Obtain the valley value I_valley of the inductor current;

[0007] Obtain the intermediate value I_m of the inductor current;

[0008] The peak value I_peak of the inductor current is calculated based on the valley value and the median value. The calculation method is as follows:

[0009] I_peak=I_valley+(1 / n)*(I_m-I_valley);

[0010] Where n = t_m / T; t_m is the time it takes for the inductor current to change from the intermediate value I_m to the valley value I_valley, and T is the total time it takes for the inductor current to change from the peak value I_peak to the valley value I_valley, or t_m is the time it takes for the inductor current to change from the valley value I_valley to the intermediate value I_m, and T is the total time it takes for the inductor current to change from the valley value I_valley to the peak value I_peak.

[0011] A further technical solution is that n = 1 / 2; the peak value I_peak of the inductor current is calculated based on the valley value and the median value. The calculation method is as follows:

[0012] I_peak=I_valley+2*(I_m-I_valley).

[0013] A further technical solution is that the switching power supply includes an upper power transistor and a lower power transistor; the valley value I_valley of the inductor current and the median value I_m of the inductor current are measured during the conduction period of the lower power transistor, t_m is the time for the inductor current to change from the median value I_m to the valley value I_valley, and T is the total time for the inductor current to change from the peak value I_peak to the valley value I_valley.

[0014] A further technical solution is that the switching power supply includes an upper power transistor and a lower power transistor; the valley value I_valley and the median value I_m of the inductor current are measured during the conduction period of the upper power transistor, t_m is the time for the inductor current to change from the valley value I_valley to the median value I_m, and T is the total time for the inductor current to change from the valley value I_valley to the peak value I_peak.

[0015] A further technical solution is that the valley value I_valley of the inductor current is the inductor current value measured at the time when the lower power transistor is turned off and the upper power transistor is turned on, and the peak value I_peak of the inductor current is the inductor current value at the time when the upper power transistor is turned off and the lower power transistor is turned on.

[0016] A further technical solution is that the working process of the switching power supply includes multiple cycles; one cycle is selected as the current detection cycle; in the current detection cycle, the valley value I_valley of the inductor current is obtained, and the median value I_m of the inductor current is obtained; and the peak value I_peak of the inductor current in the next cycle adjacent to the current detection cycle is calculated.

[0017] An inductor current detection circuit for implementing the inductor current peak detection method as described in any of the preceding claims, comprising:

[0018] An inductor current intermediate value detection circuit is used to obtain the intermediate value I_m of the inductor current;

[0019] Inductor current valley detection circuit, used to obtain the valley value I_valley of inductor current;

[0020] A calculation circuit is used to calculate the peak value I_peak of the inductor current based on the valley value I_valley and the intermediate value I_m. The calculation method is as follows:

[0021] Where n = t_m / T; t_m is the time it takes for the inductor current to change from the intermediate value I_m to the valley value I_valley, and T is the total time it takes for the inductor current to change from the peak value I_peak to the valley value I_valley, or t_m is the time it takes for the inductor current to change from the valley value I_valley to the intermediate value I_m, and T is the total time it takes for the inductor current to change from the valley value I_valley to the peak value I_peak.

[0022] A further technical solution is to provide a first voltage buffer circuit between the inductor current intermediate value detection circuit and the calculation circuit; and to provide a second voltage buffer circuit between the inductor current valley value detection circuit and the calculation circuit.

[0023] A further technical solution is that the detection circuit includes an operational amplifier, a first resistor, and a second resistor; the first end of the first resistor is connected to the output terminal of the operational amplifier circuit; the second end of the first resistor is connected to the first end of the second resistor; the second end of the second resistor is used to input the valley value I_valley of the inductor current; the common terminal of the first resistor and the second resistor is connected to the inverting input terminal of the operational amplifier; the non-inverting input terminal of the operational amplifier is used to input the intermediate value I_m of the inductor current; the output terminal of the operational amplifier outputs the peak value I_peak of the inductor current; and the resistance ratio of the first resistor and the second resistor is (1-n) / n.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention calculates the peak value of the inductor current by detecting the valley and median values ​​of the inductor current, avoiding direct detection of the peak value of the inductor current and avoiding the impact of blank time and loop establishment time on the detection accuracy of the peak value of the energy storage inductor current. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the BUCK circuit structure.

[0027] Figure 2 This is a schematic diagram of the inductor current detection time according to an embodiment of the present invention.

[0028] Figure 3This is a schematic diagram of the detection circuit structure according to an embodiment of the present invention. Detailed Implementation

[0029] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0030] Example 1.

[0031] Example 1 discloses a method for detecting peak inductor current, wherein the inductor is the energy storage inductor of a switching power supply; the switching power supply includes an upper power transistor and a lower power transistor. The switching power supply operates in continuous mode. Figure 2 This is a schematic diagram of the inductor current detection time according to an embodiment of the present invention. Figure 2 The horizontal axis represents time, and the vertical axis represents inductor current. For example... Figure 1 As shown in Example 1, specifically during the on-time t1 of the upper power transistor, the valley value I_valley and the median value I_m of the inductor current are obtained. The peak value detection method for the inductor current specifically includes the following steps:

[0032] Step 1a: At the first time point, obtain the valley value I_valley of the inductor current; specifically, the valley value I_valley of the inductor current is the inductor current value measured at the time point when the lower power transistor is turned off and the upper power transistor is turned on.

[0033] Step 2a: At the second time point, obtain the intermediate value of the inductor current I_m = I_m1; specifically, the peak value of the inductor current I_peak is the inductor current value at the time point when the upper power transistor is turned off and the lower power transistor is turned on.

[0034] The first and second time points are preset based on the change period of the inductor current. When the change period of the inductor current is known, the first time point can be determined, and the second time point is set according to the required calculation ratio.

[0035] Step 3a. Calculate the peak inductor current I_peak based on the valley and median values. The calculation method is as follows:

[0036] I_peak=I_valley+(1 / n)*(I_m-I_valley);

[0037] Where n = t / T; in Example 1, t = t3, which is the time for the inductor current to change from the valley value I_valley to the intermediate value I_m, and T = t1, which is the total time for the inductor current to change from the valley value I_valley to the peak value I_peak. The intermediate value I_m = I_m1, where I_m1 is any current value between the valley value I_valley and the peak value I_peak. Preferably, I_m1 is any current value between 1.1 * I_valley and 0.9 * peak value I_peak.

[0038] Specifically, the operation of a switching power supply consists of multiple cycles. One cycle is selected as the current sensing cycle. During the current sensing cycle, the valley value I_valley of the inductor current is obtained, and the median value I_m of the inductor current is obtained; and the peak value I_peak of the inductor current in the next cycle adjacent to the current sensing cycle is calculated.

[0039] The reason why the above calculation method can obtain the peak inductor current is that, in the CCM mode of the BUCK circuit, when the upper power transistor is turned on, the rate of change of the inductor current is:

[0040] di / dt = (Vin - Vout) / L;

[0041] Where Vout is the output voltage of the BUCK circuit, and L is the inductance value. The input voltage Vin, output voltage Vout, and inductance value L are all constants. Therefore, during the conduction of the power transistor, the change in current changes uniformly with time; that is, the ratio of current change to time change is consistent. When the time t3 for the inductor current to change from its trough to its median value is n times the total time t1 for the inductor current to change from its trough to its peak value, the change in current from its trough to its median value is also n times greater than the total change in current from its trough to its peak value. In other words:

[0042] The time required for the inductor current to change from the valley value I_valley to the intermediate value I_m1 is t3 = n*t1;

[0043] The time required for the inductor current to change from the intermediate value I_m1 to the peak value I_peak is (1-n)*t1.

[0044] Then we have:

[0045] (I_valley-I_m1) / n*t1=(I_m1-I_peak) / (1-n)*t1;

[0046] After performing basic mathematical operations, we have:

[0047] I_peak=I_valley+(1 / n)*(I_m1-I_valley).

[0048] Preferably, the intermediate value I_m can be obtained at the midpoint between the valley value I_valley and the peak value I_peak of the inductor current. In this case, n = 1 / 2, and we have:

[0049] I_peak=I_valley+2*(I_m-I_valley).

[0050] In a physical sense, this is because the change in current is equal in the first half and the second half of the current change. Therefore, this special time point was chosen, namely I_peak-I_m=I_m-I_valley, which gives I_peak=2*I_m-I_valley, and further gives I_peak=I_valley+2*(I_m-I_valley).

[0051] Example 2.

[0052] Example 2 discloses a method for detecting peak inductor current. The difference between Example 2 and Example 1 is that, as shown in Example 1... Figure 2 As shown in Example 2, during the conduction period t2 of the lower power transistor, the valley value I_valley and the median value I_m of the inductor current are obtained. The peak value detection method for the inductor current specifically includes the following steps:

[0053] Step 1b: At the third time point, obtain the intermediate value I_m of the inductor current;

[0054] Step 2b: At the fourth time point, obtain the valley value I_valley of the inductor current;

[0055] Step 3b: Calculate the peak inductor current I_peak based on the valley and median values. The calculation method is as follows:

[0056] I_peak=I_valley+(1 / n)*(I_m-I_valley);

[0057] The third and fourth time points are preset based on the change period of the inductor current. When the change period of the inductor current is known, the fourth time point can be determined, while the third time point is set according to the required calculation ratio.

[0058] Where n = t / T; t = t4, is the time it takes for the inductor current to change from the intermediate value I_m to the valley value I_valley; T = t2, is the total time it takes for the inductor current to change from the peak value I_peak to the valley value I_valley. The intermediate value I_m = I_m2, and I_m2 takes any current value between the valley value I_valley and the peak value I_peak. Preferably, I_m2 takes any current value between 1.1*I_valley and 0.9*peak value I_peak.

[0059] The calculation principle of Example 2 is the same as that of Example 1. In Example 2, when the time t4 for the inductor current to change from the intermediate value to the valley value is n times the total time t2 for the inductor current to change from the peak value to the valley value, the current change value from the intermediate value to the valley value is also n times greater than the total current change value from the peak value to the valley value. That is:

[0060] The time required for the inductor current to change from the intermediate value I_m2 to the valley value I_valley is t4 = n*t2;

[0061] The time required for the inductor current to change from its peak value I_peak to its intermediate value I_m2 is (1-n)*t2;

[0062] Then we have:

[0063] (I_m2-I_valley) / n*t2=(I_peak-I_m2) / (1-n)*t2;

[0064] After performing basic mathematical operations, we have:

[0065] I_peak=I_valley+(1 / n)*(I_m2-I_valley).

[0066] Other details and variations of Example 2 can be found in Example 1.

[0067] Example 3.

[0068] Example 3 illustrates an inductor current detection circuit for implementing the inductor current peak detection method of Example 1 or Example 2. Figure 3 This is a schematic diagram of the detection circuit structure according to an embodiment of the present invention, as shown below. Figure 3 As shown, the circuit includes:

[0069] An inductor current intermediate value detection circuit is used to obtain the intermediate value I_m of the inductor current;

[0070] Inductor current valley detection circuit, used to obtain the valley value I_valley of inductor current;

[0071] A calculation circuit is used to calculate the peak value I_peak of the inductor current based on the valley and median values. The calculation method is as follows:

[0072] I_peak=I_valley+(1 / n)*(I_m-I_valley);

[0073] Where n = t / T; t is the time it takes for the inductor current to change from the midpoint I_m to the valley I_valley, and T is the total time it takes for the inductor current to change from the peak I_peak to the valley I_valley, or t is the time it takes for the inductor current to change from the valley I_valley to the midpoint I_m, and T is the total time it takes for the inductor current to change from the valley I_valley to the peak I_peak.

[0074] The calculation circuit specifically includes an operational amplifier and two resistors, R1 and R2. The first terminal of R1 is connected to the output of the operational amplifier circuit. The second terminal of R1 is connected to the first terminal of R2. The second terminal of R2 is used to input the valley value I_valley of the inductor current. The common terminal of R1 and R2 is connected to the inverting input of the operational amplifier. The non-inverting input of the operational amplifier is used to input the intermediate value I_m of the inductor current. The ratio of the resistance of R1 to that of R2 is (1-n) / n. According to the basic principle of the operational amplifier, the output of the operational amplifier is:

[0075] I_peak=I_valley+(1 / n)*(I_m-I_valley).

[0076] When the resistance of the first resistor R1 is equal to that of the second resistor R2, then n = 1 / 2. At this time:

[0077] I_peak=I_valley+2*(I_m-I_valley).

[0078] A first voltage buffer circuit is provided between the inductor current intermediate value detection circuit and the calculation circuit; a second voltage buffer circuit is provided between the inductor current valley value detection circuit and the calculation circuit to protect the subsequent circuits.

[0079] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. The present invention can be modified in any form without departing from its basic structure.

Claims

1. A method for detecting peak inductor current, characterized in that, The inductor is an energy storage inductor of a switching power supply; the switching power supply operates in continuous mode; the process includes the following steps: Obtain the valley value I_valley of the inductor current; Obtain the intermediate value I_m of the inductor current; The peak value I_peak of the inductor current is calculated based on the valley value and the median value. The calculation method is as follows: I_peak=I_valley+(1 / n)*(I_m-I_valley); Where n = t_m / T; t_m is the time it takes for the inductor current to change from the intermediate value I_m to the valley value I_valley, and T is the total time it takes for the inductor current to change from the peak value I_peak to the valley value I_valley, or t_m is the time it takes for the inductor current to change from the valley value I_valley to the intermediate value I_m, and T is the total time it takes for the inductor current to change from the valley value I_valley to the peak value I_peak.

2. The inductor current peak detection method according to claim 1, characterized in that, n = 1 / 2; Calculate the peak value I_peak of the inductor current based on the valley value and the median value. The calculation method is as follows: I_peak=I_valley+2*(I_m-I_valley).

3. The inductor current peak detection method according to claim 1, characterized in that, The switching power supply includes an upper power transistor and a lower power transistor; the valley value I_valley and the median value I_m of the inductor current are measured during the conduction period of the lower power transistor, t_m is the time for the inductor current to change from the median value I_m to the valley value I_valley, and T is the total time for the inductor current to change from the peak value I_peak to the valley value I_valley.

4. The inductor current peak detection method according to claim 1, characterized in that, The switching power supply includes an upper power transistor and a lower power transistor; the valley value I_valley and the median value I_m of the inductor current are measured during the conduction period of the upper power transistor, t_m is the time it takes for the inductor current to change from the valley value I_valley to the median value I_m, and T is the total time it takes for the inductor current to change from the valley value I_valley to the peak value I_peak.

5. The inductor current peak detection method according to claim 1, characterized in that, The valley value of the inductor current, I_valley, is the inductor current value measured at the time when the lower power transistor is turned off and the upper power transistor is turned on. The peak value of the inductor current, I_peak, is the inductor current value at the time when the upper power transistor is turned off and the lower power transistor is turned on.

6. The inductor current peak detection method according to claim 1, characterized in that, The working process of the switching power supply includes multiple cycles; one cycle is selected as the current detection cycle; in the current detection cycle, the valley value I_valley of the inductor current is obtained, and the median value I_m of the inductor current is obtained; The peak value I_peak of the inductor current in the next cycle adjacent to the current detection cycle is calculated.

7. An inductor current detection circuit for implementing the inductor current peak detection method according to any one of claims 1 to 6, characterized in that, include: An inductor current intermediate value detection circuit is used to obtain the intermediate value I_m of the inductor current; Inductor current valley detection circuit, used to obtain the valley value I_valley of inductor current; A calculation circuit is used to calculate the peak value I_peak of the inductor current based on the valley value I_valley and the intermediate value I_m. The calculation method is as follows: Where n = t_m / T; t_m is the time it takes for the inductor current to change from the intermediate value I_m to the valley value I_valley, and T is the total time it takes for the inductor current to change from the peak value I_peak to the valley value I_valley, or t_m is the time it takes for the inductor current to change from the valley value I_valley to the intermediate value I_m, and T is the total time it takes for the inductor current to change from the valley value I_valley to the peak value I_peak.

8. The inductor current detection circuit of the inductor current peak detection method according to claim 7, characterized in that, A first voltage buffer circuit is provided between the inductor current intermediate value detection circuit and the calculation circuit; a second voltage buffer circuit is provided between the inductor current valley value detection circuit and the calculation circuit.

9. The inductor current detection circuit of the inductor current peak detection method according to claim 7, characterized in that, The detection circuit includes an operational amplifier, a first resistor, and a second resistor. The first end of the first resistor is connected to the output of the operational amplifier circuit. The second end of the first resistor is connected to the first end of the second resistor. The second end of the second resistor is used to input the valley value I_valley of the inductor current. The common end of the first resistor and the second resistor is connected to the inverting input of the operational amplifier. The non-inverting input of the operational amplifier is used to input the intermediate value I_m of the inductor current. The output of the operational amplifier outputs the peak value I_peak of the inductor current. The resistance ratio of the first resistor and the second resistor is (1-n) / n.

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