Inductive current detection and overcurrent protection circuit

Abstract

The invention discloses an inductive current detection and overcurrent protection circuit, and belongs to the field of power management. The circuit comprises an input voltage VIN, a current detection resistor RTRACE, a resistor R1, a resistor R2, a switch tube Q1, a switch tube Q2, a high-frequency filter capacitor C1, an inductor L1, an output capacitor COUT, an input capacitor CIN, a current comparator, a current limiting circuit and a PWM controller. According to the invention, real-time detection of the inductive current can be realized without additional components, system loss is hardly increased, and overcurrent protection can be realized when the output current exceeds a set value. A current detection resistor RTRACE is arranged through PCB line impedance, and a voltage dividing network composed of R1 and R2 divides the voltage on the RTRACE so as to be matched with the current limiting threshold value of the current comparator. The capacitor C1 is used for filtering high-frequency noise on the resistor R2. When the voltage ripples at the two ends of the R2 exceed the threshold value of the current comparator, the output of the current comparator enables the current limiting circuit to work, and therefore overcurrent protection is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power management, and in particular to an inductor current detection and overcurrent protection circuit. Background Art

[0002] With the continuous development of electronic technology, various high-performance processors have higher and higher requirements for power supplies. High current, high efficiency and high reliability have gradually become the development direction of load point power supplies. Overcurrent protection is one of the most important indicators of power supply circuit reliability, and low-cost, real-time and accurate current detection is the prerequisite for achieving overcurrent protection.

[0003] In non-isolated power supplies, it is a common method to implement output overcurrent protection by detecting the inductor current. There are two main traditional detection methods: one is to directly use the DC resistance of the inductor itself and connect an RC oscillation circuit in parallel at both ends of the inductor for current detection. This method does not increase additional losses, but the detection accuracy is low and is greatly affected by the inductor temperature; the other is to connect a precision detection resistor in series with the inductor for current detection. This method has high accuracy and is less affected by temperature, but it increases additional losses and costs of the system. At the same time, the volume of the detection resistor is generally large, and it will occupy valuable PCB area in a highly integrated power supply system. Summary of the invention

[0004] The object of the present invention is to provide an inductor current detection and overcurrent protection circuit to solve the problems in the background technology.

[0005] In order to solve the above technical problems, the present invention provides an inductor current detection and overcurrent protection circuit, comprising: an input voltage V IN , current detection resistor R TRACE , resistors R1 and R2, switches Q1 and Q2, high-frequency filter capacitor C1, inductor L1, output capacitor C OUT , input capacitor C IN , current comparator, current limiting circuit and PWM controller;

[0006] Input voltage V IN The first end of the input capacitor C IN The first end of the switch tube Q1 and the drain end of the switch tube Q1 are interconnected, and the input voltage V IN The second end of the input capacitor C IN The second end of the switch tube Q1 and the source end of the switch tube Q2 are both grounded, the gate end of the switch tube Q1 and the gate end of the switch tube Q2 are both connected to the PWM controller, the source end of the switch tube Q1 and the drain end of the switch tube Q2 are commonly connected to the first end of the inductor L1, and the second end of the inductor L1 is simultaneously connected to the current detection resistor R TRACE a first end of a resistor R1;

[0007] The second end of the resistor R1, the first end of the high-frequency filter capacitor C1 and the first end of the resistor R2 are simultaneously connected to the positive input end of the current comparator; the current detection resistor R TRACE The second end of the high frequency filter capacitor C1, the second end of the resistor R2, the output capacitor C OUT The first end of the current comparator is connected to the negative input terminal at the same time.

[0008] The output end of the current comparator is connected to the PWM controller through a current limiting circuit. By controlling the drive signal output by the PWM controller, the duty cycle of the switch tube is controlled, thereby achieving overcurrent protection when the output current exceeds the set value.

[0009] In one embodiment, the current detection resistor R TRACE The impedance of the PCB line is set by the copper thickness, line width and length of the PCB line to control the line impedance.

[0010] In one implementation, the resistor R1 and the resistor R2 form a voltage divider network, and the voltage divider ratio is adjusted by adjusting the resistance values ​​of the resistor R1 and the resistor R2 to match the threshold of the current comparator.

[0011] In one embodiment, when the voltage ripple on the resistor R2 is less than the threshold of the current comparator, the current comparator outputs a low level and the current limiting circuit does not work; when the voltage ripple on the resistor R2 is greater than the threshold of the current comparator, the current comparator outputs a high level and the current limiting circuit starts to work.

[0012] In one implementation, the setting requirements for the resistance and capacitance of the resistor R1 and the resistor R2 are as follows: when the output current reaches the set value, the voltage ripple across the resistor R2 just reaches the threshold of the current comparator.

[0013] The present invention provides an inductor current detection and overcurrent protection circuit, which has the following beneficial effects:

[0014] 1. The present invention provides an inductor current detection and overcurrent protection method, which has a simple design and can realize current detection and overcurrent protection at the same time.

[0015] 2. No additional components are required in the main circuit, and the system loss is hardly increased. The traditional detection resistor is replaced by PCB line impedance, saving cost and PCB area.

[0016] 3. The current detection accuracy is high, the detection signal is proportional to the inductor current, and all the information of the inductor current can be obtained in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural diagram of an inductor current detection and overcurrent protection circuit proposed by the present invention;

[0018] Figure 2 is the inductor current waveform;

[0019] Figure 3 This is the current detection signal waveform. DETAILED DESCRIPTION

[0020] The following is a further detailed description of an inductor current detection and overcurrent protection circuit proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0021] like Figure 1 As shown, the present invention provides an inductor current detection and overcurrent protection circuit, which mainly uses the PCB line impedance R TRACE , a voltage divider network composed of resistors R1 and R2, a high-frequency filter capacitor C1, a current comparator, a current limiting circuit and a PWM controller.

[0022] To design an inductor current detection circuit, we must first calculate the actual inductor current. When the switch Q1 is turned on, the voltage across the inductor L1 is:

[0023] V ON =V IN -V OUT

[0024] When the switch Q2 is turned on, the voltage across the inductor is:

[0025] V OFF =-V OUT

[0026] The duty cycle of the switch tube Q1 is:

[0027]

[0028] When the operating frequency of the switch tube is f, the output current is I O When the inductor current I L It can be decomposed into the DC component I O and the superposition of the AC component of the current ripple, such as Figure 2 As shown. O is the output load current, ΔI L is the amplitude of the AC ripple component, and its value is:

[0029]

[0030] So the peak value of the inductor current is:

[0031]

[0032] R TRACE is the inductor L1 and the output capacitor C OUT The line impedance of the PCB between is used to convert the inductor current information into a voltage signal. Resistors R1 and R2 are connected in series with the PCB line impedance R TRACE In parallel, for R TRACE The sampled voltage signal is divided to match the threshold of the current comparator to complete the output current limit setting. TRACE , so the current flowing through the inductor L1 almost flows through R TRACE reaches the output terminal, thus at R TRACE The voltage V is generated at both ends TRACE . V TRACE The calculation formula is as follows:

[0033] V TRACE =I L *R TRACE

[0034] Since the resistors R1 and R2 are connected in series with R TRACE In parallel, the voltage after resistors R1 and R2 are connected in series is also equal to V TRACE The voltage divider network composed of resistors R1 and R2 has a TRACE After voltage division, the voltage V across R2 is SENSE for:

[0035]

[0036] The two input terminals of the current comparator are connected to the two ends of the resistor R2, and the output terminal of the current comparator is connected to the current limiting circuit. Capacitor C1 is connected in parallel with R2 to filter out the high-frequency noise on the resistor R2 and avoid false triggering of the current comparator. The voltage divided on the resistor R2 is used as the input signal of the current comparator to control the output of the current comparator. When the voltage peak value ΔV on the resistor R2 SENSE is less than the current comparator threshold V TH When the current comparator outputs a low level, the current limiting circuit does not work; when the voltage ripple peak on the resistor R2 is greater than the threshold value V of the current comparator TH When the current comparator outputs a high level, the current limiting circuit starts to work. The working condition of the current limiting circuit is the peak voltage ΔV across the resistor R2. SENSE satisfy:

[0037]

[0038] To realize the overcurrent protection function of the circuit, it is necessary to reasonably select R TRACE , the values ​​of resistors R1 and R2 are such that the output current I OReaching the set value I LIM When the voltage peak value ΔV across the resistor R2 is SENSE Just reaches the current comparator threshold V TH . R TRACE is the line impedance of the PCB, and the commonly used calculation formula is:

[0039]

[0040] Where: ρ is the resistivity of the conductor, L is the length of the conductor, H is the thickness of the conductor, and W is the width of the conductor.

[0041] The above formula is only a rough calculation formula. Affected by factors such as process, routing shape, and placement of sampling points, the actual processed PCB line impedance often deviates from the designed value. TRACE When designing, the design value should be slightly larger than the ideal value, and it is recommended to be about 20% larger. The specific value can be determined according to the actual circuit. The part exceeding the ideal value can be compensated by adjusting the voltage divider ratio of resistors R1 and R2. In addition, the accuracy of the PCB line impedance design value can be improved with the help of simulation software.

[0042] When R TRACE Once determined, the values ​​of resistors R1 and R2 can be determined by the following formula:

[0043]

[0044] This formula calculates the proportional relationship between the resistors R1 and R2. When selecting the resistance values ​​of the resistors R1 and R2, care should be taken to ensure that the resistance value of R1+R2 is much greater than R TRACE It is recommended that the resistance of R1+R2 be above kΩ. O Reach I LIM When the current limiting circuit starts to work, the output current limiting point of the circuit is I LIM In actual use, a certain margin should be reserved to reasonably set the current limit point according to the use environment.

[0045] The current limiting circuit is connected to the PWM controller and adjusts the drive signal output by the PWM controller to limit the output current I O Reach I LIM When the duty cycle of the switch tube is adjusted in time, the output current I O Overcurrent protection is achieved when the set value is exceeded.

[0046] It should be noted that this embodiment only takes the BUCK topology structure as the main circuit as an example for explanation, and other topologies can change the calculation equation of the inductor current according to the actual circuit, and the rest of the design process is consistent with this application.

[0047] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. An inductor current detection and overcurrent protection circuit, characterized in that: include: Input voltage V IN , current detection resistor R TRACE , resistors R1 and R2, switches Q1 and Q2, high-frequency filter capacitor C1, inductor L1, output capacitor C OUT , input capacitor C IN , current comparator, current limiting circuit and PWM controller; Input voltage V IN The first end of the input capacitor C IN The first end of the switch tube Q1 and the drain end of the switch tube Q1 are interconnected, and the input voltage V IN The second end of the input capacitor C IN The second end of the switch tube Q1 and the source end of the switch tube Q2 are both grounded, the gate end of the switch tube Q1 and the gate end of the switch tube Q2 are both connected to the PWM controller, the source end of the switch tube Q1 and the drain end of the switch tube Q2 are commonly connected to the first end of the inductor L1, and the second end of the inductor L1 is simultaneously connected to the current detection resistor R TRACE a first end of a resistor R1; The second end of the resistor R1, the first end of the high-frequency filter capacitor C1 and the first end of the resistor R2 are simultaneously connected to the positive input end of the current comparator; the current detection resistor R TRACE The second end of the high frequency filter capacitor C1, the second end of the resistor R2, the output capacitor C OUT The first end of the current comparator is connected to the negative input terminal at the same time. The output end of the current comparator is connected to the PWM controller through a current limiting circuit. By controlling the drive signal output by the PWM controller, the duty cycle of the switch tube is controlled, thereby achieving overcurrent protection when the output current exceeds the set value.

2. The inductor current detection and overcurrent protection circuit according to claim 1, characterized in that: The current detection resistor R TRACE The impedance of the PCB line is set by the copper thickness, line width and length of the PCB line to control the line impedance.

3. The inductor current detection and overcurrent protection circuit according to claim 1, characterized in that: The resistor R1 and the resistor R2 form a voltage divider network, and the voltage divider ratio is adjusted by adjusting the resistance values ​​of the resistor R1 and the resistor R2 to match the threshold of the current comparator.

4. The inductor current detection and overcurrent protection circuit according to claim 1, characterized in that: When the voltage ripple on the resistor R2 is smaller than the threshold of the current comparator, the current comparator outputs a low level and the current limiting circuit does not work; when the voltage ripple on the resistor R2 is larger than the threshold of the current comparator, the current comparator outputs a high level and the current limiting circuit starts working.

5. The inductor current detection and overcurrent protection circuit according to claim 1, characterized in that: The setting requirements of the resistance and capacitance of the resistor R1 and the resistor R2 are as follows: when the output current reaches the set value, the voltage ripple across the resistor R2 just reaches the threshold of the current comparator.

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