Patent Publication Number: US-2019196528-A1

Title: Current-limiting circuit and controlling method thereof

Description:
BACKGROUND 
     1. Technology Field 
     The present disclosure relates to a current-limiting circuit and a controlling method thereof, particularly to a current-limiting circuit capable of suppressing instantaneous large currents and a controlling method thereof. 
     2. Description of the Related Art 
     Under power line operations in the prior art, when the load terminal needs to consume a large current instantaneously, instability of the load voltage and the source voltage may result and the output noise becomes large, which seriously affects the overall performance of the system. For example, in the power supplied to the WIFI line, when the system sends a beacon detection signal in the idle state, the load will consume a large current instantaneously. At this time, the current will have a large dynamic load. As a result, the power supply design of the input must be large enough to start the over power protection (OPP), which causes unstable output voltage. High-power wireless transmission electronic products, such as wireless APs, radio transceivers and radios, are prone to such application conditions. 
     To solve the aforementioned problem in the prior art, a filter with a larger amount of inductance or a larger capacitance is usually used to filter and suppress instantaneous large currents, or an input power supply with a higher specification is used. As a result, the design cost and space will be increased, and it is not cost-effective. 
     Accordingly, it is necessary to devise a new current-limiting circuit and a controlling method thereof to solve the problem in the prior art. 
     SUMMARY 
     It is a major objective of the present disclosure to provide a current-limiting circuit that provides the effect of suppressing instantaneous large currents. 
     It is another objective of the present disclosure to provide a controlling method used for the structure described above. 
     To achieve the above objectives, the current-limiting circuit of the present disclosure includes a current input terminal, a current output terminal, a switch module, a differential amplifier, a first resistor and a first capacitor. The switch module includes a signal input end, a signal output end and a control end. The signal input end is electrically connected to the current input terminal. The signal output end is electrically connected to the current output terminal. The differential amplifier includes a positive input end, a negative input end and an amplified output end, wherein the positive input end is electrically connected to the signal output end of the switch module, the negative input end is electrically connected to the current output terminal, and the amplified output end is electrically connected to the control end of the switch module. An end of the first resistor is electrically connected to the signal output end and the positive input end of the switch module, and the opposite end of the first resistor is electrically connected to the negative input end and the current output terminal. An end of the first capacitor is electrically connected between the first resistor and the current output terminal, and the opposite end of the first capacitor is connected to a ground. 
     A method of controlling the current limiting circuit of the present disclosure includes the following steps: inputting an initial current signal by a current input terminal to flow through two ends of the first resistor to generate a voltage difference; outputting a control signal by a differential amplifier according to the voltage difference; determining whether the voltage of the control signal is less than a cut-off voltage; when the voltage of the control signal is less than the cut-off voltage, keeping the switch module on to cause the current output terminal to output an initial current signal; charging the first capacitor by the initial current signal; when the voltage of the control signal is greater than the cut-off voltage, turning off the switch module so that the current output terminal does not output the initial current signal; and discharging from the first capacitor to output a discharge current signal through a current output terminal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an architecture diagram of a current-limiting circuit of the present invention; and 
         FIG. 2  is a flowchart showing steps in a method for controlling the current limiting circuit of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereafter, the technical content of the present invention will be better understood with reference to preferred embodiments. 
     Hereafter, please first refer to  FIG. 1 , which is an architecture diagram of a current-limiting circuit of the present invention. 
     In the embodiment of the present invention, a current-limiting circuit  1  is used to ensure a stable power output. The current-limiting circuit  1  includes a current input terminal  10 , a current output terminal  20 , a switch module  30 , a differential amplifier  40 , a first resistor R 1  and a first capacitor C 1 . The current input terminal  10  is used to input an initial current signal. The current output terminal  20  is used to output the current signal to a load  50 . The switch module  30  has a signal input end  31 , a signal output end  32  and a control end  33 . In an embodiment of the present invention, the switch module  30  is a P-type metal-oxide-semiconductor field-effect transistor (MOSFET), but the present invention is not limited thereto. Thus, the source of the switch module  30  is the signal input end  31 , the drain thereof is the signal output end  32 , and the gate thereof is the control end  33 . The signal input end  31  is electrically connected to the current input terminal  10 , and the signal output end  32  is electrically connected to the current output terminal  20 . The switch module  30  has a cut-off voltage. When the signal voltage inputted by the control end  33  exceeds the cut-off voltage, the MOSFET is activated to turn off the signal transmission between the signal input end  31  and the signal output end  32 . 
     The differential amplifier  40  has a positive input end  41 , a negative input end  42  and an amplified output end  43 , wherein the positive input end  41  is electrically connected to the signal output end  32  of the switch module  30 , the negative input end  42  is electrically connected to the current output terminal  20 , and the amplified output end  43  is electrically connected to the control end  33  of the switch module  30 . The differential amplifier  40  is a rail-to-rail amplifier, which is activated by receiving a power signal supplied by the power supply Vcc. Therefore, in the best case, the voltage of the power signal inputted by the power supply Vcc can be outputted through the amplified output end  43 , so there is no need to supply additional power or other ICs with the switch module  30 . An end of the first resistor R 1  is electrically connected to the signal output end  32  and the positive input end  41  of the switch module  30 , and the opposite end of the first resistor R 1  is electrically connected to the negative input end  42  and the current output terminal  20 ; that is, the first resistor R 1  is connected between the positive input end  41  and the negative input end  42 . An end of the first capacitor C 1  is electrically connected between the first resistor R 1  and the current output terminal  20 , and the opposite end of the first capacitor C 1  is connected to a ground G. The first capacitor C 1  may be 100 μF, and the first resistor R 1  may be 10Ω, but the present invention is not limited thereto. 
     In addition to the above components, the positive input end  41  of the differential amplifier  40  is connected to the first resistor R 1  via the second resistor R 2 , and the negative input end  42  is connected to the first resistor R 1  via the third resistor R 3 . Also, the negative input end  42  is connected to the amplified output end  43  via the fourth resistor R 4 , and the positive input end  41  is connected to the ground G via the fifth resistor R 5 . In the embodiment of the present invention, the second resistor R 2  and the third resistor R 3  have the same resistance value, e.g., 1 kΩ, and the fourth resistor R 4  and the fifth resistor R 5  have the same resistance value, e.g., 91 kΩ. Therefore, the magnification of the differential amplifier  40  is equivalent to the second resistor R 2  divided by the fourth resistor R 4 . Also, the current-limiting circuit  1  further includes a second capacitor C 2 , a third capacitor C 3  and a sixth resistor R 6 , wherein the second capacitor C 2  is connected in parallel with the first resistor R 1 , the third capacitor C 3  is connected in parallel with the fourth resistor R 4 , and the sixth resistor R 6  is connected in series between the differential amplifier  40  and the switch module  30 . The second capacitor C 2  and the third capacitor C 3  may be 1000 pF, and the sixth resistor R 6  may be 0.1Ω, but the present invention is not limited thereto. Since the other passive components in the current-limiting circuit  1  are not the focus of the improvement, they will not be described in detail herein. 
     After an initial current signal is inputted by the current input terminal  10  of the present invention, it will flow to the two ends of the first resistor R 1  via the switch module  30 , so the two ends of the first resistor R 1  will have a voltage difference. The positive input end  41  and the negative input end  42  of the differential amplifier  40  are electrically connected to two ends of the first resistor R 1 . Therefore, the differential amplifier  40  outputs a control signal to the control end  33  of the switch module  30  via the amplified output end  43  according to the voltage difference. When the load  50  requires a small current, the current value of the initial current signal will be smaller, so the voltage of the control signal outputted from the amplified output terminal  43  will be less than the cut-off voltage of the switch module  30 , and the switch module  30  will be kept ON. In this way, the current output terminal  20  continuously outputs the initial current signal to the load  50  and simultaneously charges the first capacitor C 1 . When the load  50  requires a large instantaneous current, the current value of the initial current signal increases beyond the current value that the original circuit can carry. At this time, the voltage difference of the two ends of the first resistor R 1  is also increased, and the amplified output end  43  outputs a control signal with a larger voltage. When the voltage of the control signal outputted from the amplified output terminal  43  is greater than the cut-off voltage of the switch module  30 , the switch module  30  is switched to cut off the output of the initial current signal. At this time, the first capacitor C 1  is discharged to output the discharge current signal to the load  50  through the current output terminal  20  so that the current output terminal  20  can still maintain the current output. This will not cause instability of the output voltage due to the large instantaneous current required by load  50 . 
     Now please refer to  FIG. 2 , which is a flowchart showing steps in a method of controlling the current limiting circuit of the present invention. It should be noted here that the method of controlling the current limiting circuit of the present invention is described by taking the current-limiting circuit  1  as an example, but the method is not limited to using the current-limiting circuit  1  described above. 
     First, the method performs Step  201 : inputting, by the current input terminal, an initial current signal to flow through the two ends of the first resistor to generate a voltage difference. 
     First, when an initial current signal is inputted by the current input terminal  10 , it will flow through the two ends of the first resistor R 1 , and the two ends of the first resistor R 1  will have a voltage difference. 
     Then the method performs Step  202 : outputting, by the differential amplifier, a control signal according to the voltage difference. 
     The positive input end  41  and the negative input end  42  of the differential amplifier  40  are electrically connected to the two ends of the first resistor R 1 . Thus, the differential amplifier  40  outputs a control signal via the amplified output end  43  according to the voltage difference. 
     Next, the method performs Step  203 : determining whether a voltage of the control signal is less than the cut-off voltage. 
     When the switch module  30  receives the control signal, it will determine whether the voltage of the control signal is less than the cut-off voltage of the switch module  30 . 
     When the voltage of the control signal is less than the cut-off voltage, the method performs Step  204 : Keeping the switch module on so that the current output terminal outputs the initial current signal. 
     When the load  50  requires a small current, the current value of the initial current signal is smaller, so the voltage of the control signal outputted from the amplified output end  43  is less than the cut-off voltage of the switch module  30 , and the switch module  30  is kept on. As a result, the current output terminal  20  will continue to output the initial current signal to the load  50 . 
     Then the method performs Step  205 : Charging the first capacitor by the initial current signal. 
     The initial current signal will synchronously charge the first capacitor C 1 . 
     When the voltage of the control signal is greater than the cut-off voltage, the method performs Step  206 : The switch module is turned off so that the current output terminal does not output the initial current signal. 
     When the load  50  requires a large instantaneous current, the current value of the initial current signal increases, so the voltage of the control signal outputted from the amplified output end  43  is greater than the cut-off voltage of the switch module  30 . Consequently, the switch module  30  will not continue with the output of the initial current signal. 
     Finally, the method performs Step  207 : Discharging from the first capacitor to output a discharge current signal through the current output terminal. 
     Finally, the first capacitor C 1  is discharged to output the discharge current signal to the load  50  through the current output terminal  20  so that the current output terminal  20  can still maintain the current output. 
     It should be noted here that the method of controlling the current limiting circuit of the present invention is not limited to the order of the above steps and that the order of the above steps may be changed as long as the objectives of the present invention can be achieved. 
     With the current-limiting circuit  1 , the impact on the output voltage due to the requirement of an instant high current signal by the load  50  can be avoided, and the cost due to the use of large capacitors or inductive components can be reduced. 
     Although the invention has been described with reference to the above embodiments, it will be apparent to those of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims rather than by the above detailed descriptions.