Current limiting circuit and method suitable for voltage step operation

Abstract

The invention provides a current limiting circuit suitable for voltage step operation, and the circuit comprises an input current detection unit which is used for detecting an input current; the current limiting unit is used for limiting the pulse current when the step voltage change occurs at the power supply input end; and the switch switching unit is used for switching on and switching off an input main line of the power supply, switching off the switch, disconnecting the input main line and enabling the current to pass through the current limiting unit when the input current is detected to be greater than a set value, and switching on the switch and recovering a current path of the input main line when the input current is recovered to be less than the set value. The invention further provides a current limiting method suitable for voltage step operation. The current limiting circuit and method have the advantages that the current limiting circuit and method suitable for voltage step operation are provided, the operation state of a power source is not affected, input pulse current is effectively limited when voltage step is input, normal operation of the power source is not affected, and the circuit is simple and reliable and has high practical value.

Description

Technical Field

[0001] The invention relates to a current limiting circuit, and in particular to a current limiting circuit and method suitable for voltage step operation. Background Art

[0002] Some power supplies need to adapt to the working conditions of instantaneous step changes in input voltage. When the input voltage changes instantaneously, due to the existence of the output capacitor of the power supply port and the input capacitor of the power supply, the voltage difference of the instantaneous step will generate a large pulse current. If the pulse current is not limited, it can reach hundreds or even thousands of amperes. Such a large pulse current will cause potential damage to the internal components of the power supply and affect the long-term reliability of the power supply. Conventional input surge current suppression circuits only suppress the instantaneous current when the input voltage is turned on, and cannot suppress the surge current during the normal operation of the power supply. Means such as series resistors and current-limiting MOSFETs cannot adapt to this working condition. Summary of the invention

[0003] In order to solve the problems in the prior art, the present invention provides a current limiting circuit and method suitable for voltage step operation, which can not affect the operating state of the power supply, so that the input pulse current can be effectively limited when the input voltage steps, and will not affect the normal operation of the power supply.

[0004] The present invention provides a current limiting circuit suitable for voltage step operation, comprising:

[0005] An input current detection unit, used for detecting an input current;

[0006] A current limiting unit is used to limit the pulse current when a step voltage change occurs at the power input terminal;

[0007] The switch switching unit is used to open and close the input main line of the power supply. When it is detected that the input current is greater than the set value, the switch is turned off to disconnect the input main line and allow the current to pass through the current limiting unit. When the input current returns to below the set value, the switch is turned on to restore the current path of the input main line.

[0008] As a further improvement of the present invention, the switch switching unit includes a resistor R3, a resistor R4 and a MOS tube Q1, wherein the source and drain of the MOS tube Q1 are connected to the input main line for opening and closing the input main line, the gate of the MOS tube Q1 is connected to one end of the resistor R4, the other end of the resistor R4 is grounded, one end of the resistor R3 is connected to the source of the MOS tube Q1, and the other end of the resistor R3 is connected to the gate of the MOS tube Q1.

[0009] As a further improvement of the present invention, the input current detection unit includes a current limiting sampling resistor R1, a resistor R2 and a transistor Q2, wherein the emitter of the transistor Q2 is connected to the power input end, the collector of the transistor Q2 is connected to the gate of the MOS tube Q1, the base of the transistor Q2 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the source of the MOS tube Q1, one end of the current limiting sampling resistor R1 is connected to the power input end, and the other end of the current limiting sampling resistor R1 is connected to the source of the MOS tube Q1.

[0010] As a further improvement of the present invention, the current limiting unit includes an inductor L1, one end of the inductor L1 is connected to the source of the MOS tube Q1, and the other end of the inductor L1 is connected to the drain of the MOS tube Q1.

[0011] As a further improvement of the present invention, the maximum current is limited by setting an inductor L1. When the input voltage rises momentarily in a step, the transistor Q2 starts to conduct, gradually reducing the turn-on of the MOS tube Q1, and the MOS tube Q1 enters a linear conduction state. At this time, the voltage across the MOS tube Q1 rises, and the current IL starts to flow through the inductor L1 connected in parallel across the MOS tube Q1. The current I1 flowing through the current limiting sampling resistor R1 further rises, and the transistor Q2 enters a saturated conduction state. The MOS tube Q1 is completely turned off, and the step voltage is all applied to the two ends of the inductor L1. By adjusting the size of the inductor L1, the maximum pulse current value can be limited. When the internal capacitor C1 of the power supply completes charging and the pulse current recovers to below the set maximum value, the transistor Q2 is gradually cut off, and the MOS tube Q1 resumes conduction.

[0012] As a further improvement of the present invention, the current limiting circuit suitable for voltage step operation also includes an internal power supply capacitor C1, one end of the internal power supply capacitor C1 is connected to the drain of the MOS tube Q1, and the other end of the internal power supply capacitor C1 is grounded.

[0013] As a further improvement of the present invention, the transistor Q2 is a PNP transistor.

[0014] As a further improvement of the present invention, the MOS tube Q1 is a PMOS tube.

[0015] The present invention also provides a current limiting method suitable for voltage step operation, wherein the current limiting circuit suitable for voltage step operation is connected to the input main line of the power supply, and when it is detected that the input current is greater than the set value, the switch is turned off to disconnect the input main line and allow the current to pass through the current limiting unit; when the input current recovers to below the set value, the switch is turned on to allow the current to pass through the input main line.

[0016] As a further improvement of the present invention, the current limiting circuit suitable for voltage step operation is applied to a switching power supply.

[0017] The beneficial effects of the present invention are as follows: through the above scheme, a current limiting circuit and method suitable for voltage step operation are provided, which can not affect the operating state of the power supply, so that the input pulse current is effectively limited when the input voltage steps, and does not affect the normal operation of the power supply. The circuit is simple and reliable and has high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other solutions can be obtained based on these drawings without paying creative work.

[0019] Figure 1 It is a block diagram of the implementation of the current limiting circuit suitable for voltage step operation of the present invention.

[0020] Figure 2 It is a realization principle diagram of the current limiting circuit suitable for voltage step operation of the present invention. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0022] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0023] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0024] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0025] like Figure 1 to Figure 2 As shown, a current limiting circuit suitable for voltage step operation includes:

[0026] An input current detection unit 101, used to detect an input current;

[0027] The current limiting unit 103 is used to limit the pulse current when a step voltage change occurs at the power input terminal;

[0028] The switch switching unit 102 is used to open and close the input main line of the power supply. When it is detected that the input current is greater than the set value, the switch is turned off to disconnect the input main line and allow the current to pass through the current limiting unit 103. When the input current returns to below the set value, the switch is turned on to restore the current path of the input main line.

[0029] The switch unit 103 includes a resistor R3, a resistor R4 and a MOS transistor Q1, wherein the source and drain of the MOS transistor Q1 are connected to the input main line for opening and closing the input main line, the gate of the MOS transistor Q1 is connected to one end of the resistor R4, the other end of the resistor R4 is grounded, one end of the resistor R3 is connected to the source of the MOS transistor Q1, and the other end of the resistor R3 is connected to the gate of the MOS transistor Q1.

[0030] The input current detection unit 101 includes a current limiting sampling resistor R1, a resistor R2 and a transistor Q2, wherein the emitter of the transistor Q2 is connected to the power input terminal, the collector of the transistor Q2 is connected to the gate of the MOS transistor Q1, the base of the transistor Q2 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the source of the MOS transistor Q1, one end of the current limiting sampling resistor R1 is connected to the power input terminal, and the other end of the current limiting sampling resistor R1 is connected to the source of the MOS transistor Q1.

[0031] The current limiting unit 102 includes an inductor L1 , one end of the inductor L1 is connected to the source of the MOS transistor Q1 , and the other end of the inductor L1 is connected to the drain of the MOS transistor Q1 .

[0032] The maximum current is limited by setting the inductor L1. When the input voltage rises momentarily in a step, the transistor Q2 starts to conduct, gradually reducing the opening of the MOS tube Q1, and the MOS tube Q1 enters a linear conduction. At this time, the voltage across the MOS tube Q1 rises, and the current IL begins to flow through the inductor L1 connected in parallel across the MOS tube Q1. The current I1 flowing through the current limiting sampling resistor R1 further rises, and the transistor Q2 enters a saturated conduction state. The MOS tube Q1 is completely turned off, and the step voltage is all applied to the two ends of the inductor L1. By adjusting the size of the inductor L1, the maximum pulse current value can be limited. When the internal capacitor C1 of the power supply is fully charged and the pulse current returns to below the set maximum value, the transistor Q2 is gradually cut off, and the MOS tube Q1 resumes conduction.

[0033] The current limiting circuit suitable for voltage step operation further includes a power supply internal capacitor C1, one end of the power supply internal capacitor C1 is connected to the drain of the MOS tube Q1, and the other end of the power supply internal capacitor C1 is grounded.

[0034] The transistor Q2 is a PNP transistor.

[0035] The MOS tube Q1 is a PMOS tube, that is, a PMOSFET.

[0036] A current limiting method suitable for voltage step operation, wherein the current limiting circuit suitable for voltage step operation is connected to the input main line of a power supply, and when it is detected that the input current is greater than a set value, the switch is turned off to disconnect the input main line and allow the current to pass through the current limiting unit; when the input current returns to below the set value, the switch is turned on to allow the current to pass through the input main line.

[0037] When the power supply is in normal working state, the voltage drop caused by the current flowing through the current limiting sampling resistor R1 is less than the conduction threshold of the transistor Q2, and the transistor Q2 is in the cut-off state. The voltage division value of the resistor R3 and the resistor R4 makes the MOS tube Q1 in the saturated conduction state. According to the power demand of the power supply, a suitable MOSFET is selected to make the power consumption of the circuit meet the requirements.

[0038] Vin is the input voltage of the power supply. When the input voltage rises instantaneously in a step, if it is not limited, the pulse current at the moment of the step is (Vin1-Vin0) / Ron, where Vin1 is the voltage value after the step, Vin0 is the voltage value before the step, and Ron is the resistance between the power input terminal and the internal capacitor (including the connector contact resistance, the current limiting sampling resistor R1, the on-resistance of the MOS tube Q1, and the connection resistance). Usually Ron is in the milliohm level, so when the step voltage reaches more than 50V, the pulse current value can reach several hundred amperes.

[0039] If the working current of the power supply is small and the step voltage difference is small, the current limiting unit L1 may not be needed. When the current limiting unit is cancelled, Q2 of the current detection unit will control the conduction voltage of Q1 in real time, so that the current flowing through the current limiting sampling resistor R1 and the MOS tube Q1 is at the maximum protection value. The MOS tube Q1 works in a linear conduction state at the moment of the input voltage step, and its maximum power consumption is the voltage difference at the input voltage step multiplied by the maximum current protection value. When the maximum current protection value required by the power supply is large (such as greater than 20A) and the step voltage difference is large (such as greater than 50V), the maximum power consumption at the moment of the input voltage step reaches more than 1000W or even greater, a lot of MOSFETs need to be connected in parallel to meet the requirements, and considering the differences in devices, the simple parallel connection of MOSFETs cannot meet the balance of power consumption, and more measures are needed to meet the design requirements, which will greatly increase the complexity of the design and the cost is also high.

[0040] The current limiting circuit suitable for voltage step operation is applied to a switching power supply.

[0041] The present invention provides a current limiting circuit suitable for voltage step operation, which has an application range in situations where the input and output ends need to adapt to instantaneous step voltage changes.

[0042] The present invention provides a current limiting circuit and method suitable for voltage step operation, which limits the maximum current by setting an inductor L1. When the input voltage rises momentarily in a step, the transistor Q2 starts to conduct, gradually reducing the opening of the MOS tube Q1, and the MOS tube Q1 enters a linear conduction. At this time, the voltage at both ends of the MOS tube Q1 rises, and the inductor L1 connected in parallel at both ends of the MOS tube Q1 begins to pass the current IL, and the current I1 flowing through the current limiting sampling resistor R1 further rises, and the transistor Q2 enters a saturated conduction state, and the MOS tube Q1 is completely turned off. The step voltage is all applied to both ends of the MOS tube Q1, that is, the inductor L1. By adjusting the size of the inductor L1, the maximum pulse current value can be conveniently limited. When the internal capacitor of the power supply is fully charged and the pulse current is restored to below the set maximum value, the transistor Q2 is gradually cut off, and the MOS tube Q1 resumes conduction.

[0043] Obviously, the invention described herein can be varied in many ways, such as adding one more mirror circuit to achieve pulse current limiting of positive and negative steps of input voltage, replacing Q1 with a PNP transistor at low power, replacing Q2 with a PMOSFET, etc. Such variations cannot be considered as departing from the spirit and scope of the invention. Therefore, all changes that are obvious to those skilled in the art are included in the scope of the claims.

Claims

1. A current limiting circuit suitable for voltage step operation, characterized in that: include: An input current detection unit, used for detecting an input current; A current limiting unit is used to limit the pulse current when a step voltage change occurs at the power input terminal; The switch switching unit is used to open and close the input main line of the power supply. When it is detected that the input current is greater than the set value, the switch is turned off to disconnect the input main line and allow the current to pass through the current limiting unit. When the input current returns to below the set value, the switch is turned on to restore the current path of the input main line.

2. The current limiting circuit suitable for voltage step operation according to claim 1, characterized in that: The switch switching unit includes a resistor R3, a resistor R4 and a MOS tube Q1, wherein the source and drain of the MOS tube Q1 are connected to the input main line for opening and closing the input main line, the gate of the MOS tube Q1 is connected to one end of the resistor R4, the other end of the resistor R4 is grounded, one end of the resistor R3 is connected to the source of the MOS tube Q1, and the other end of the resistor R3 is connected to the gate of the MOS tube Q1.

3. The current limiting circuit suitable for voltage step operation according to claim 2, characterized in that: The input current detection unit includes a current limiting sampling resistor R1, a resistor R2 and a transistor Q2, wherein the emitter of the transistor Q2 is connected to the power input terminal, the collector of the transistor Q2 is connected to the gate of the MOS transistor Q1, the base of the transistor Q2 is connected to one end of the resistor R2, the other end of the resistor R2 is connected to the source of the MOS transistor Q1, one end of the current limiting sampling resistor R1 is connected to the power input terminal, and the other end of the current limiting sampling resistor R1 is connected to the source of the MOS transistor Q1.

4. The current limiting circuit suitable for voltage step operation according to claim 3, characterized in that: The current limiting unit includes an inductor L1 , one end of the inductor L1 is connected to the source of the MOS transistor Q1 , and the other end of the inductor L1 is connected to the drain of the MOS transistor Q1 .

5. The current limiting circuit suitable for voltage step operation according to claim 4, characterized in that: The maximum current is limited by setting the inductor L1. When the input voltage rises momentarily in a step, the transistor Q2 starts to conduct, gradually reducing the opening of the MOS tube Q1, and the MOS tube Q1 enters a linear conduction. At this time, the voltage across the MOS tube Q1 rises, and the current IL begins to flow through the inductor L1 connected in parallel across the MOS tube Q1. The current I1 flowing through the current limiting sampling resistor R1 further rises, and the transistor Q2 enters a saturated conduction state. The MOS tube Q1 is completely turned off, and the step voltage is all applied to the two ends of the inductor L1. By adjusting the size of the inductor L1, the maximum pulse current value can be limited. When the internal capacitor C1 of the power supply is fully charged and the pulse current returns to below the set maximum value, the transistor Q2 is gradually cut off, and the MOS tube Q1 resumes conduction.

6. The current limiting circuit suitable for voltage step operation according to claim 4, characterized in that: The current limiting circuit suitable for voltage step operation further includes a power supply internal capacitor C1, one end of the power supply internal capacitor C1 is connected to the drain of the MOS tube Q1, and the other end of the power supply internal capacitor C1 is grounded.

7. The current limiting circuit suitable for voltage step operation according to claim 4, characterized in that: The transistor Q2 is a PNP transistor.

8. The current limiting circuit suitable for voltage step operation according to claim 4, characterized in that: The MOS tube Q1 is a PMOS tube.

9. A current limiting method suitable for voltage step operation, characterized in that: A current limiting circuit suitable for voltage step operation as described in any one of claims 1 to 8 is connected to the input main line of the power supply, and when it is detected that the input current is greater than the set value, the switch is turned off to disconnect the input main line and allow the current to pass through the current limiting unit; when the input current returns to below the set value, the switch is turned on to allow the current to pass through the input main line.

10. The current limiting method suitable for voltage step operation according to claim 9, characterized in that: The current limiting circuit suitable for voltage step operation is applied to a switching power supply.

Images