TW201624890A - Current sensing circuit and method thereof for power converting device - Google Patents

Abstract

A current sensing circuit and a method thereof for a power converting device are provided. The current sensing circuit includes a sensing unit, an amplifier, a sensing switch and a compensating circuit. The sensing unit detects an output current of the power converting device and provides a sensing signal. The amplifier has an output end and is coupled to the sensing unit to receive the sensing signal. The sensing switch is coupled to the output end of the amplifier. The compensating circuit is coupled to the sensing switch and a first input end of the amplifier. When the sensing signal is smaller than a threshold value, the compensating circuit activates a current compensation mechanism so as to maintain the sensing switch in a turned-on state.

Description

Current sensing circuit and method of power conversion device

The present invention relates to a current sensing circuit and method, and more particularly to a current sensing circuit and method suitable for use in a power conversion device.

In general, the power conversion device is provided with a current sensing circuit. Thereby, the power conversion device can use the feedback signal generated by the current sensing circuit to perform feedback control to improve the reliability and stability of the system. For example, when the load driven by the power conversion device is too small, the current sensing circuit can detect the reverse current (ie, the negative current) in the power conversion device, thereby causing the power conversion device to switch to a different operation mode.

However, when the reverse current in the power conversion device is excessive, the sensing switch in the existing current sensing circuit tends to be turned off, thereby causing the current sensing circuit to fail to operate normally. In contrast, when the power conversion device stops generating reverse current, the existing current sensing circuit will not turn on the sensing switch in time, thereby causing the power conversion device to fail to utilize the existing current sensing circuit. Feedback control to reduce system reliability and stability.

The invention provides a current sensing circuit and method for a power conversion device, which utilizes a current compensation mechanism to prevent the sensing switch from being switched to a non-conducting state, thereby contributing to improving the reliability and stability of the power conversion device.

The current sensing circuit of the power conversion device of the present invention comprises a sensing unit, an amplifier, a sensing switch and a compensation circuit. The sensing unit is configured to sense an output current of the power conversion device and provide a sensing signal. The amplifier has an output and is coupled to the sensing unit to receive the sensing signal. The sense switch is coupled to the output of the amplifier. The compensation circuit is coupled to the sensing switch and the first input of the amplifier. When the sense signal is less than the threshold, the compensation circuit activates the current compensation mechanism to maintain the sense switch in an on state.

The current sensing method of the power conversion device of the present invention includes the following steps. The output current of the power conversion device is sensed through the sensing unit, and a sensing signal is provided. The power conversion device includes a sensing unit, an amplifier, and a sensing switch. The amplifier is coupled to the sensing unit, and the sensing switch is coupled to the first input end and the output end of the amplifier. When the sense signal is less than the threshold, the current compensation mechanism is activated to maintain the sense switch in an on state.

Based on the above, the present invention provides a sensing signal through the sensing unit, and when the sensing signal is less than the threshold, the current compensation mechanism is activated to maintain the sensing switch in an on state. Thereby, the voltage-controlled current source will provide the compensation current in a timely manner. The sensing switch is prevented from being switched to the non-conducting state, thereby improving the reliability and stability of the power conversion device.

The above described features and advantages of the invention will be apparent from the following description.

100‧‧‧Power conversion device

10‧‧‧ Controller

11‧‧‧Switching circuit

12‧‧‧ Impedance circuit

13‧‧‧ Current sensing circuit

PU11, PU12‧‧‧ pulse wave signal

VI‧‧‧Input voltage

VO‧‧‧ output voltage

SW11, SW12‧‧‧ switch

L1‧‧‧Inductance

C11, C12, C4‧‧‧ capacitors

IL‧‧‧Output current

110‧‧‧Sensor unit

120‧‧‧Amplifier

130‧‧‧Sensing switch

140, 412‧‧‧ current source

150‧‧‧compensation circuit

151‧‧‧voltage controlled current source

S11, S12‧‧‧ sensing signals

R11, R12, R41‧‧‧ resistance

ND1‧‧‧ node

Isen‧‧‧Sensing current

I11‧‧‧First current

I12‧‧‧second current

Icp‧‧‧compensation current

VT‧‧‧ control voltage

210, 220, 310, 320‧‧‧ curves

VG‧‧‧ sense the voltage at the control terminal

Vth‧‧‧ threshold voltage

410‧‧‧ Current Detector

420‧‧‧current compensator

430‧‧‧Stable circuit

411, 413‧‧‧current mirror

421‧‧‧Control unit

MP41~MP44‧‧‧P type transistor

MN41~MN44‧‧‧N type transistor

R41‧‧‧ load components

Ist‧‧‧Starting current

S510, S520, S521~S524‧‧‧ steps in Figure 5

1 is a schematic diagram of a power conversion device in accordance with an embodiment of the present invention.

2 and 3 are schematic diagrams of signals according to an embodiment of the invention, respectively.

4 is a schematic diagram of a current sensing circuit in accordance with an embodiment of the present invention.

FIG. 5 is a flow chart of a current sensing method of a power conversion device according to an embodiment of the invention.

1 is a schematic diagram of a power conversion device in accordance with an embodiment of the present invention. As shown in FIG. 1, the power conversion device 100 includes a controller 10, a switching circuit 11, an impedance circuit 12, and a current sensing circuit 13. The controller 10 generates pulse signals PU11 and PU12. The switching circuit 11 switches a plurality of transmission paths in accordance with the pulse signals PU11 and PU12 to control the current flowing through the impedance circuit 12. Thereby, the power conversion device 100 can convert the input voltage VI into the output voltage VO.

For example, the switching circuit 11 includes a switch SW11 and a switch SW12. In addition, the embodiment of FIG. 1 is an example of a buck impedance circuit 12, so the impedance circuit 120 Including inductor L1 and capacitor C11. The switches SW11 and SW12 are connected in series with each other and used to form the plurality of transmission paths. The first end of the inductor L1 is coupled to a node between the switches SW11 and SW12. The first end of the capacitor C11 is coupled to the second end of the inductor L1, and the second end of the capacitor C11 is coupled to the ground. Further, the controller 10 controls the switches SW11 and SW12 using the pulse signals PU11 and PU12. Thereby, as the switches SW11 and SW12 are switched, the output current IL flowing through the inductor L1 will be correspondingly varied, thereby causing the power conversion device 100 to generate a corresponding output voltage VO.

On the other hand, the current sensing circuit 13 can be used to sense the output current IL of the power conversion device 100, and can generate a corresponding feedback signal according to the sensing result. In addition, the controller 10 can generate the pulse signals PU11 and PU12 according to the feedback signals from the current sensing circuit 13. In other words, the power conversion device 100 can perform feedback control using the feedback signal of the current sensing circuit 13.

Looking further, the current sensing circuit 13 includes a sensing unit 110, an amplifier 120, a sensing switch 130, an offset current 140, and a compensation circuit 150. The sensing switch 130 can be, for example, an N-type transistor. The sensing unit 110 can sense the output current IL and accordingly provide the sensing signals S11 and S12. In addition, in an embodiment, as shown in FIG. 1 , the sensing unit 110 includes a resistor R11 , a resistor R12 , and a capacitor C12 . The first end of the resistor R11 is coupled to the first end of the inductor L1, and the second end of the resistor R11 is coupled to the second input end of the amplifier 120. The first end of the resistor R12 is coupled to the second end of the resistor R11, and the second end of the resistor R12 is coupled to the first input end of the amplifier 120. The first end of the capacitor C12 is coupled to the second end of the inductor L1, and the second end of the capacitor C12 is coupled to the second end of the resistor R11. In addition, the sensing unit 110 transmits the resistor R11. The sensing signals S11 and S12 are outputted with R12. In other words, the current sensing circuit 130 generates the sensing signals S11 and S12 according to the DC impedance of the inductor L1. Although the embodiment of FIG. 1 exemplifies the implementation of current sensing circuit 130, it is not intended to limit the invention. For example, in another embodiment, the current sensing circuit 130 is coupled to the switch SW12 in the switching circuit 11 and can provide a sensing signal related to the output current IL. In contrast, the output current IL can also be referred to as a load current or an inductor current.

The amplifier 120 has a first input, a second input, and an output. put The first input end and the second input end of the amplifier 120 are coupled to the sensing unit 110 to receive the sensing signals S11 and S12. The control end of the sense switch 130 is coupled to the output of the amplifier 120, and the second end of the sense switch 130 is coupled to the first input of the amplifier 120. Thereby, the amplifier 120 and the sensing switch 130 will form a feedback loop, and the corresponding sensing current Isen can be generated through the first end of the sensing switch 130. In addition, the offset current 140 is coupled to the second end of the sensing switch 130. The compensation circuit 150 is coupled to the first end of the sensing switch 130 and the first input of the amplifier 120.

In operation, when the output current IL of the power conversion device 100 is a forward current (ie, a positive current), the sensing unit 110 receives the first current I11 from the node ND1 in response to the forward current, that is, the flow. The current through resistor R12 will be as indicated by the first current I11. At this time, the sensing switch 130 will remain in a conducting state, and the sensing current Isen generated by the sensing switch 130 will be greater than the critical current Ith, thereby causing the compensation circuit 150 to fail to initiate a current compensation mechanism. In addition, the larger the forward current, the larger the first current I11. Since the offset current 140 provides a fixed current, the sense current Isen becomes correspondingly larger as the first current I11 becomes larger. In other words, When the output current IL of the power conversion device 100 is a forward current, the sensing switch 130 will be continuously turned on, and the compensation circuit 150 does not need to activate a current compensation mechanism.

On the other hand, when the output current IL of the power conversion device 100 is a negative current (ie, a negative current), the sensing unit 110 transmits the second current I12 to the node ND1 in response to the negative current, that is, flows through the resistor. The current of R12 will be as shown by the second current I12. In addition, the larger the negative current, the larger the second current I12 flowing to the node ND1, which in turn causes the sensing current Isen generated by the sensing switch 130 to correspondingly become smaller. In addition, when the negative current of the power conversion device 100 is larger and reaches a preset value, the sensing signal provided by the sensing unit 110 will be less than a threshold, thereby causing the sensing current Isen to be smaller than the critical current Ith. At this point, the compensation circuit 150 will initiate a current compensation mechanism such that the sense switch 130 can be continuously maintained in an on state.

For example, the compensation circuit 150 includes a voltage-controlled current source 151, and the voltage-controlled current source 151 is coupled to the second end of the sensing switch 130. When the current compensation mechanism is activated, the voltage controlled current source 151 will generate a compensation current Icp according to the control voltage VT, thereby providing a compensation current Icp flowing from the node ND1 to the ground. As the compensation current Icp is generated, it can be avoided that the sensing current Isen rapidly decreases as the second current I12 increases, thereby preventing the sensing switch 130 from being switched to the non-conducting state. In this way, when the power conversion device 100 stops generating the reverse current, the current sensing circuit 13 can immediately return the feedback signal to the controller 10 according to the sensing current Isen, thereby contributing to the improvement of the reliability of the power conversion device 100. Sex and stability.

It is worth mentioning that the compensation current Icp is proportional to the difference between the critical current Ith and the sensing current Isen. That is, when the sensing current Isen is smaller than the critical current Ith When the compensation circuit 150 starts the voltage-controlled current source 151, the control voltage VT is adjusted according to the sensing current Isen, so that the level of the control voltage VT increases as the sensing current Isen becomes smaller. As such, when the negative current in the power conversion device 100 is larger, the voltage-controlled current source 151 will provide a larger compensation current Icp in response to the smallering of the sensing current Isen. Thereby, the sensing range of the current sensing circuit 13 for the negative current can be effectively expanded.

For example, FIG. 2 and FIG. 3 are respectively a message according to an embodiment of the present invention. No. Schematic. The X axis of FIG. 2 and FIG. 3 is used to represent the first current I11, and the Y axis of FIG. 2 and FIG. 3 is the voltage VG of the sensing current Isen and the control terminal of the sensing switch 130, respectively. It is worth mentioning that the first current I11 and the second current I12 are used to indicate the current flowing through the resistor R12 in different current directions, so the second current I12 is a negative value of the first current I11, that is, FIG. 2 and FIG. The negative X-axis in 3 is also used to indicate the change in the second current I12.

When the output current IL flowing through the inductor L1 is a forward current, flowing through the resistor The current of R12 is the first current I11, that is, the operation of current sensing circuit 13 at this time will be as shown in the first quadrant of the coordinate axis of Figures 2-3. Therefore, referring to the first quadrant in the coordinate axis of FIG. 2-3, when the output current IL flowing through the inductor L1 is a forward current, the sensing current Isen will correspondingly become larger as the first current I11 becomes larger. Become bigger. Furthermore, the sense current Isen is greater than the critical current Ith, which in turn causes the compensation circuit 150 to fail to activate the voltage controlled current source 151. Moreover, the voltage VG at the control terminal of the sense switch 130 is greater than the threshold voltage Vth of the sense switch 130, thereby causing the sense switch 130 to remain in an on state.

On the other hand, when the output current IL flowing through the inductor L1 is a negative current, the current flowing through the resistor R12 is the second current 112, that is, the operation of the current sensing circuit 13 at this time will be as shown in FIGS. 2 and 3. The second quadrant in the coordinate axis is shown. Therefore, referring to the second quadrant in the coordinate axis of FIG. 2, when the negative current in the power conversion device 100 is generated, initially, as shown by the curve 210, the sensing current Isen changes with the second current I12. Big and lower. Furthermore, when the sense current Isen is less than the critical current Ith, the compensation circuit 150 will activate the voltage controlled current source 151. At this time, as shown by the curve 220, the magnitude of the decrease in the sense current Isen will be moderated as the voltage-controlled current source 151 is activated. In this way, in the process of the second current I12 rising from the first limiting current Ineg to the second limiting current Iscp, the current sensing circuit 13 can still detect the negative current in the power conversion device 100, thereby effectively The current sensing circuit 13 is extended for the sensing range of the negative current.

In contrast, referring to the second quadrant in the coordinate axis of FIG. 3, when the negative current in the power conversion device 100 is generated, as shown by the curve 310 of FIG. 3, initially, the voltage VG of the control terminal of the sense switch 130 is generated. It will decrease as the second current I12 becomes larger. In addition, when the sensing current Isen is less than the critical current Ith, as shown by the curve 320 of FIG. 3, the falling amplitude of the voltage VG of the control terminal of the sensing switch 130 is moderated, thereby preventing the sensing switch 130 from being switched to the non-conducting state. .

4 is a schematic diagram of a current sensing circuit in accordance with an embodiment of the present invention. As shown in FIG. 4, the compensation circuit 150 includes a current detector 410 and a current compensator 420. The current detector 410 is coupled to the first end of the sensing switch 130 , and the current detector 410 can detect the sensing current Isen generated by the sensing switch 130 . Current supplement The compensator 420 includes a voltage controlled current source 151 , and the current compensator 420 is coupled to the second end of the sensing switch 130 and the current detector 410 . In addition, when the sensing current Isen is less than the critical current Ith, the current detector 410 generates a starting current Ist, and the current compensator 420 generates the control voltage VT according to the starting current Ist to thereby activate the voltage-controlled current source 151.

Further, the current detector 410 includes a current mirror 411, a current source 412, and a current mirror 413, and the current compensator 420 further includes a control unit 421. The input end of the current mirror 411 is coupled to the first end of the sensing switch 130 to thereby detect the sensing current Isen. The current source 412 is coupled to the output of the current mirror 411 and is used to generate a critical current Ith. The input end of the current mirror 413 is coupled to the output end of the current mirror 411. The control unit 421 is coupled to the output end of the current mirror 413. Thereby, when the sensing current Isen is smaller than the critical current Ith, the output terminal of the current mirror 413 can generate the starting current Ist. In addition, the control unit 421 generates a control voltage VT according to the startup current Ist to control the voltage control current source 151.

It is worth mentioning that the current source 412 provides a fixed critical current Ith. Therefore, when the sense current Isen becomes small, the current generated at the output of the current mirror 411 is smaller. In contrast, the starting current Ist generated by the current mirror 413 is also larger, thereby causing the control unit 421 to increase the level of the control voltage VT. In other words, when the voltage-controlled current source 151 is activated, the level of the control voltage VT increases as the sense current Isen becomes smaller. Thereby, when the negative current in the power conversion device 100 is larger, the sensing current Isen will correspondingly become smaller, and the voltage-controlled current source 151 will provide greater compensation in response to the smallering of the sensing current Isen. Current Icp.

Further, the current mirror 411 includes a P-type transistor MP41 and a P-type transistor MP42. The first end of the P-type transistor MP41 is coupled to the first end of the sensing switch 130. The second end of the P-type transistor MP41 is coupled to the power terminal. The control end of the P-type transistor MP41 is electrically connected to the first end. The first end of the P-type transistor MP42 is coupled to the current source 412. The second end of the P-type transistor MP42 is coupled to the power terminal. The control end of the P-type transistor MP42 is coupled to the control end of the P-type transistor MP41.

The current mirror 413 includes a P-type transistor MP43 and a P-type transistor MP44. The first end of the P-type transistor MP43 is coupled to the first end of the P-type transistor MP42. The second end of the P-type transistor MP43 is coupled to the power terminal. The control end of the P-type transistor MP43 is electrically connected to the first end. The first end of the P-type transistor MP44 is coupled to the current compensator 420. The second end of the P-type transistor MP44 is coupled to the power terminal. The control end of the P-type transistor MP44 is coupled to the control end of the P-type transistor MP43.

The control unit 421 includes an N-type transistor MN41, and the voltage-controlled current source 151 includes an N-type transistor MN42. The first end of the N-type transistor MN41 is coupled to the output end of the current mirror 413, that is, the first end of the P-type transistor MP44. The second end of the N-type transistor MN41 is coupled to the ground. The control end of the N-type transistor MN41 is electrically connected to the first end and used to generate the control voltage VT. The first end of the N-type transistor MN42 is coupled to the second end of the sensing switch 130. The second end of the N-type transistor MN42 is coupled to the ground. The control terminal of the N-type transistor MN42 is coupled to the control terminal of the N-type transistor MN41.

It is worth mentioning that, in an embodiment, the width-to-length ratio of the P-type transistor MP41 is equal to the aspect ratio of the P-type transistor MP42, and the P-type The width to length ratio of the transistor MP43 is equal to the aspect ratio of the P-type transistor MP44. That is, in one embodiment, both the current mirror 411 and the current mirror 413 replicate the current at a magnification of one. Therefore, when the sensing current Isen is smaller than the critical current Ith, the starting current Ist generated by the current mirror 413 is equal to the difference between the critical current Ith and the sensing current Isen, that is, Ist=Ith-Isen. Further, the width-to-length ratio of the N-type transistor MN42 is N times the aspect ratio of the N-type transistor MN41, where N is a value greater than zero. In other words, in one embodiment, the compensation current Icp is N times the starting current Ist, that is, Icp=N*Ist.

In addition, as far as the current of the node ND1 is concerned, Isen+I12=Icp+Ineg, that is, I12=N*(Ith-Isen)+Ineg-Isen, where Ineg is the current supplied by the offset current 140 (ie, the first A limiting current Ineg). Thereby, according to the above equation, the second limiting current Iscp in FIG. 2 can be obtained, and Iscp=N*Ith+Ineg can be obtained. Further, if Ineg=10uA, Ith=5uA, and N=5, the second limiting current Iscp will be equal to 35uA. In other words, if the voltage-controlled current source 151 does not start when the sense current Isen is less than the threshold current Ith, as shown by the curve 210 of FIG. 2, the second current I12 rises to 10 uA (that is, the first limit current Ineg). The test switch 130 will be turned off, which in turn causes the current sensing circuit 13 to fail to operate normally.

In contrast, if the voltage-controlled current source 151 is activated when the sense current Isen is less than the threshold current Ith, as shown by the curve 220 of FIG. 2, the second current I12 rises from 10 uA (ie, the first limit current Ineg) to During the 35uA (ie, the second limiting current Iscp), the sensing switch 130 will be continuously turned on, thereby causing the current sensing circuit 13 to still detect the negative current in the power conversion device 100. according to Thus, it can be clearly seen that with the activation of the voltage controlled current source 151, the sensing range of the current sensing circuit 13 for the negative current can be effectively expanded.

Further, the current source 412 includes a load element R41, an N-type transistor MN43, and an N-type transistor MN44. The first end of the load component R41 is coupled to the power terminal. The first end of the N-type transistor MN43 is coupled to the second end of the load element R41. The second end of the N-type transistor MN43 is coupled to the ground. The control end of the N-type transistor MN43 is electrically connected to the first end. The first end of the N-type transistor MN44 is coupled to the first end of the P-type transistor MP42. The second end of the N-type transistor MN44 is coupled to the ground. The control terminal of the N-type transistor MN44 is coupled to the control terminal of the N-type transistor MN43. In operation, load element R41 can provide a reference current to N-type transistor MN43. In addition, the N-type transistor MN43 and the N-type transistor MN44 form a current mirror to map the critical current Ith according to the reference current. The critical current Ith is smaller than the current supplied by the offset current 140 (that is, the first limiting current Ineg).

Further, in an embodiment, the current sensing circuit 13 further includes a stabilization circuit 430. The stabilization circuit 430 includes a resistor R41 and a capacitor C4. The first end of the resistor R41 is coupled to the output of the amplifier 120. The first end of the capacitor C4 is coupled to the second end of the resistor R41, and the second end of the capacitor C4 is coupled to the ground. Thereby, the current sensing circuit 13 will pass through the stabilization circuit 430 to stabilize the voltage at the control terminal of the sensing switch 130.

Viewed from another perspective, FIG. 5 is a flow chart of a current sensing method of a power conversion device according to an embodiment of the invention. Referring to FIG. 1 and FIG. 5 simultaneously, as shown in step S510, the current sensing circuit 13 senses the power conversion device 100. The output current IL is generated according to the sensing result. In addition, when the negative current of the power conversion device 100 is larger and reaches a preset value, the sensing signal provided by the sensing unit 110 will be less than a threshold. In addition, as shown in step S520, when the sensing signal is less than the threshold, the compensation circuit 150 will initiate a current compensation mechanism to cause the sensing switch 130 to remain in the conducting state.

It is worth mentioning that the amplifier 120 in the compensation circuit 150 is responsive to The sensing signal is controlled to control the sensing switch 130, so the sensing current Isen flowing through the sensing switch 130 is related to the sensing signal provided by the sensing unit 110. For example, when the sensing signal provided by the sensing unit 110 is less than a critical value, the sensing current Isen will also be less than the critical current Ith. Therefore, in an embodiment, whether to activate the current compensation mechanism may be determined according to the sense current Isen flowing through the sense switch 130.

For example, referring to FIG. 4 and FIG. 5 simultaneously, as shown in step S521, the current detecting device 410 can detect the sensing current Isen flowing through the sensing switch 130 as shown in step S521. . Moreover, as shown in step S522, when the sensing current Isen is less than the critical current Ith, it means that the sensing signal is less than the critical value. At this time, the current detector 410 generates a starting current Ist. In addition, as shown in steps S523 and S524, the current compensator 420 generates the control voltage VT according to the starting current Ist, and controls the voltage-controlled current source 151 by using the control voltage VT, thereby causing the voltage-controlled current source 151 to generate a compensation current Icp. As the compensation current Icp is generated, it is possible to prevent the sensing current Isen from rapidly decreasing as the negative current of the power conversion device 100 increases, thereby preventing the sensing switch 130 from being switched to the non-conduction state. The detailed description of each step of FIG. 5 has been included in the above embodiments, and thus will not be described herein.

In summary, the present invention senses the output current of the power conversion device through the sensing unit and provides a sensing signal accordingly. In addition, when the sense signal is less than the threshold, a current compensation mechanism is activated to cause the sense switch to remain in an on state. Thereby, when the reverse current in the power conversion device is excessively large, the compensation current can be timely provided, thereby preventing the sensing switch from being switched to the non-conduction state. In this way, when the power conversion device stops generating the reverse current, the current sensing circuit can immediately return the feedback signal to the controller according to the sensing current, thereby contributing to improving the reliability and stability of the power conversion device.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

100‧‧‧Power conversion device

10‧‧‧ Controller

11‧‧‧Switching circuit

12‧‧‧ Impedance circuit

13‧‧‧ Current sensing circuit

PU11, PU12‧‧‧ pulse wave signal

VI‧‧‧Input voltage

VO‧‧‧ output voltage

SW11, SW12‧‧‧ switch

L1‧‧‧Inductance

C11, C12‧‧‧ capacitor

IL‧‧‧Output current

110‧‧‧Sensor unit

120‧‧‧Amplifier

130‧‧‧Sensing switch

140‧‧‧current source

150‧‧‧compensation circuit

151‧‧‧voltage controlled current source

S11, S12‧‧‧ sensing signals

R11, R12‧‧‧ resistance

ND1‧‧‧ node

Isen‧‧‧Sensing current

I11‧‧‧First current

I12‧‧‧second current

Icp‧‧‧compensation current

VT‧‧‧ control voltage

Claims (15)

A current sensing circuit of a power conversion device includes: a sensing unit for sensing an output current of the power conversion device and providing a sensing signal; an amplifier having an output coupled to the sense The measuring unit receives the sensing signal; a sensing switch coupled to the output end of the amplifier; and a compensation circuit coupled to the sensing switch and a first input end of the amplifier, wherein when the sensing When the signal is less than a threshold, the compensation circuit initiates a current compensation mechanism to maintain the sense switch in an on state. The current sensing circuit of claim 1, wherein the threshold value is related to a negative current. The current sensing circuit of claim 1, further comprising: an offset current coupled to the compensation circuit, the sensing switch, and the first input of the amplifier. The current sensing circuit of claim 1, wherein the compensation circuit has a voltage-controlled current source coupled to the sensing switch, and when the current compensation mechanism is activated, the compensation circuit transmits the voltage control The current source provides a compensation current. The current sensing circuit of claim 4, wherein the compensation circuit comprises: a current detector coupled to the first end of the sensing switch and detecting a sense of flowing through the sensing switch Measuring current, wherein when the sensing current is less than a critical current, the The current detector generates a starting current; and a current compensator includes the voltage controlled current source, and is coupled to the second end of the sensing switch and the current detector, wherein the current compensator generates the current according to the starting current A control voltage is applied to activate the voltage controlled current source. The current sensing circuit of claim 5, wherein when the sensing current is less than the critical current, the voltage-controlled current source generates the compensation current according to a control voltage, and the compensation circuit is based on the sensing current The control voltage is adjusted such that the compensation current is proportional to the difference between the critical current and the sense current. The current sensing circuit of claim 5, further comprising: an offset current coupled to the compensation circuit, the sensing switch and the first input of the amplifier, wherein the critical current is less than the bias The current supplied by the current is shifted. The current sensing circuit of claim 5, wherein the current detector comprises: a first current mirror having an input terminal electrically connected to the switching element; and a second current source electrically connected to the first An output terminal of the current mirror generates the critical current; and a second current mirror having an input end electrically connected to the output end of the first current mirror, and when the sensing current is less than the critical current, the second The starting current is generated at the output of the current mirror. The current sensing circuit of claim 8, wherein the current compensator further comprises: a control unit electrically connected to the output end of the second current mirror, wherein the control The unit generates the control voltage according to the starting current to control the voltage controlled current source. A current sensing method for a power conversion device, wherein the power conversion device includes a sensing unit, an amplifier, and a sensing switch, and the current sensing method includes: sensing one of the power conversion devices through the sensing unit Outputting a current, and providing a sensing signal, wherein the amplifier is coupled to the sensing unit, and the sensing switch is coupled to a first input end and an output end of the amplifier; and when the sensing signal is less than a threshold A current compensation mechanism is initiated to cause the sense switch to remain in an on state. The current sensing method of claim 10, wherein the threshold value is related to a negative current. The current sensing method of claim 10, wherein the step of activating the current compensation mechanism comprises: providing a compensation current through a voltage controlled current source, wherein the voltage control current source is coupled to the sensing switch. The current sensing method of claim 10, wherein when the sensing signal is less than the threshold, the step of starting the current compensation mechanism to maintain the sensing switch in the conducting state comprises: detecting the flow Passing a sensing current of the sensing switch; generating a starting current when the sensing current is less than a threshold current; generating a control voltage according to the starting current; and controlling a voltage controlled current source according to a control voltage to generate a Compensation current, where The voltage controlled current source is coupled to the sensing switch. The current sensing method of claim 13, wherein the compensation current is proportional to a difference between the critical current and the sensing current. The current sensing method of claim 13, wherein the power conversion device further includes an offset current coupled to the sensing switch and the first input of the amplifier, and the threshold The current is less than the current provided by the offset current.