Current sensing method and overcurrent protection method for ac chopper circuit

Abstract

The application provides a current detection method and overcurrent protection method applied to an alternating current chopper circuit. The alternating current chopper circuit comprises a first switch tube coupled between an alternating current power supply and a load, a second switch tube coupled between the load and a reference ground, a third switch tube coupled between a second end of the alternating current power supply and a second end of the load, and a fourth switch tube coupled between a reference end and the second end of the load. The current detection method comprises detecting a current flowing through the first switch tube and / or detecting a current flowing through the third switch tube. The current detection method and the overcurrent protection method are suitable for current detection and overcurrent protection in a bridgeless alternating current chopper circuit, and have high current detection response speed and system reliability.

Description

Technical Field

[0001] This invention relates to the field of electronics, and specifically, but not limited to, a current detection method and an overcurrent protection method for an AC chopper circuit. Background Technology

[0002] A single-phase motor generally refers to an asynchronous motor powered by a single-phase AC power source provided by mains electricity. Because mains power is very convenient and economical, and is widely used in household electricity consumption, single-phase motors are not only widely used in production but are also closely related to people's daily lives. Especially with the continuous improvement of people's living standards, the use of single-phase motors in household appliances such as electric fans is also increasing. Single-phase motors regulate their speed through a speed control circuit.

[0003] Existing speed control circuits include inductive mechanical switch speed control, series reactor stepless speed control, thyristor speed control, and frequency converter speed control, but they have one or more disadvantages such as low efficiency, high cost, and large size.

[0004] Another method employs a bridged AC chopper, which shapes the input AC power supply into a half-wave voltage via a freewheeling bridge, then uses a high-frequency bridge circuit to achieve chopping, and reverses the negative half-cycle to restore the original voltage. This type of chopper can effectively overcome the shortcomings of thyristor choppers, achieving low harmonics and lower cost. However, the high-power freewheeling bridge at the input still occupies a large volume and consumes a significant amount of power.

[0005] As mentioned earlier, the bridged AC chopper speed control scheme introduces a rectifier bridge to simplify the drive, which not only introduces additional conduction losses and reduces efficiency, but also requires solving heat dissipation problems, increasing size and cost. In fact, with proper optimization of the control logic, the second-stage H-bridge can perform power frequency rectification, thereby integrating the two-stage system into a single-stage system, reducing semiconductor devices and conduction losses, and achieving higher power density integration. Based on this concept, Figure 1A A more optimized and lower-cost speed control circuit based on a bridgeless AC chopper is provided (patent pending).

[0006] However, there is currently no relevant literature mentioning overcurrent detection and protection methods for this type of circuit. Figure 1BThis is an H-bridge chopper circuit quite similar to a single-phase bridgeless chopper topology. Traditional H-bridges typically detect the current of two lower-side switches, as shown in IS1 and IS2 in the figure. The advantages of this approach are obvious: signal grounding and simplified processing. However, a careful comparison of the two topologies reveals that in a bridgeless AC chopper, the two lower-side switches (the second and fourth switches) mostly function as freewheeling diodes, with only the two upper-side switches (the first and third switches) acting as the main switches for energy transfer from the power supply to the load. Detecting only the current of the lower-side switches is insufficient for true protection. Furthermore, when overcurrent occurs, the common protection measure in traditional H-bridges is to turn off all four switches. However, if a bridgeless chopper experiences an overcurrent, a similar protection method (i.e., turning off all four switches) will cause voltage spikes, damaging the switches. Therefore, this invention proposes a current detection and overcurrent protection method for a bridgeless AC chopper circuit that differs from the traditional H-bridge. Summary of the Invention

[0007] To address one or more problems in the prior art, this invention proposes a current detection method and an overcurrent protection method for AC chopper circuits.

[0008] According to one aspect of the present invention, a current detection method for an AC chopper circuit is provided. The AC chopper circuit includes: a first switch coupled between a first input terminal and a first output terminal; a second switch coupled between a reference terminal and the first output terminal; a third switch coupled between a second input terminal and a second output terminal; and a fourth switch coupled between the reference terminal and the second output terminal, wherein the first input terminal is coupled to a first terminal of an AC power supply, the second input terminal is coupled to a second terminal of the AC power supply, the first output terminal is coupled to a first terminal of a load, and the second output terminal is coupled to a second terminal of the load; the current detection method includes detecting the current flowing through the first switch and / or detecting the current flowing through the third switch.

[0009] In one embodiment, the current flowing through the first switch is detected by detecting the voltage at the first input terminal relative to the first output terminal or the reference terminal, and the current flowing through the third switch is detected by detecting the voltage at the second input terminal relative to the second output terminal or the reference terminal.

[0010] In one embodiment, the current sensing method includes: connecting a first sensing resistor in series with a first switching transistor; connecting a second sensing resistor in series with a third switching transistor; coupling the cathode of a first diode to a first input terminal; coupling the cathode of a second diode to a second input terminal; and coupling the output terminal of a current source to the anode of the first diode and the anode of the second diode to provide a bias current, such that the voltage at the output terminal of the current source reflects the load current.

[0011] In one embodiment, the current sensing method further includes coupling a first end of a bias resistor to the output of a current source, and a second end of the bias resistor to the anode of a first diode and the anode of a second diode, for setting a reference threshold for current sensing.

[0012] In one embodiment, the current detection method includes: detecting the voltage at a first input terminal based on the equivalent on-resistance of a first switch; detecting the voltage at a second input terminal based on the equivalent on-resistance of a third switch; coupling the cathode of a first diode to the first input terminal; coupling the cathode of a second diode to the second input terminal; and coupling the output terminal of a current source to the anode of the first diode and the anode of the second diode to provide a bias current, such that the voltage at the output terminal of the current source reflects the load current.

[0013] In one embodiment, the current detection method further includes coupling a first end of a bias resistor to the output of a current source, and a second end of the bias resistor to the anode of a first diode and the anode of a second diode.

[0014] In one embodiment, the current detection method includes: connecting a first detection resistor in series with a first switching transistor; coupling the cathode of a first diode to a first input terminal; coupling the input terminal of a first current source to a first output terminal, with its output terminal coupled to the anode of the first diode to provide a bias current, such that the voltage at the output terminal of the first current source reflects the current flowing through the first switching transistor; connecting a second detection resistor in series with a third switching transistor; coupling the cathode of a second diode to a second input terminal; and coupling the input terminal of a second current source to a second output terminal, with its output terminal coupled to the anode of the second diode to provide a bias current, such that the voltage at the output terminal of the second current source reflects the current flowing through the third switching transistor.

[0015] In one embodiment, the current detection method further includes: setting a first bias resistor between the output terminal of the first current source and the anode of the first diode to set a reference threshold for current detection; and setting a second bias resistor between the output terminal of the second current source and the anode of the second diode to set a reference threshold for current detection.

[0016] In one embodiment, the first sensing resistor is the equivalent on-resistance of the first switching transistor, and the second sensing resistor is the equivalent on-resistance of the third switching transistor.

[0017] In one embodiment, the current detection method further includes: connecting a first transistor and a first detection resistor connected in series in parallel with a first switching transistor, wherein the control terminal of the first transistor is coupled to the control terminal of the first switching transistor, such that the current flowing through the first transistor is proportional to the current flowing through the first switching transistor and such that the voltage drop across the first detection resistor reflects the current flowing through the first switching transistor; and connecting a second transistor and a second detection resistor connected in series in parallel with a third switching transistor, wherein the control terminal of the second transistor is coupled to the control terminal of the third switching transistor, such that the voltage drop across the second detection resistor reflects the current flowing through the third switching transistor.

[0018] In one embodiment, the first transistor and the first switch are integrated on the same semiconductor wafer, and the second transistor and the third switch are integrated on the same semiconductor wafer.

[0019] According to another aspect of the present invention, an overcurrent protection method includes the current detection method as described in any of the above embodiments, and when the current flowing through the first switch or the third switch is greater than a preset threshold, overcurrent / short circuit protection is performed.

[0020] In one embodiment, the AC chopper circuit further includes an auxiliary power supply circuit, wherein the input terminal of the auxiliary power supply circuit is coupled to the first input terminal and the second input terminal, the reference ground terminal of the auxiliary power supply circuit is coupled to the reference terminal, and the output terminal of the auxiliary power supply circuit provides auxiliary power. The overcurrent protection method includes turning off the first switch, the second switch, the third switch and the fourth switch simultaneously when the current flowing through the first switch or the third switch is greater than a preset threshold.

[0021] In one embodiment, the overcurrent protection method includes controlling the load, the second switch, and the fourth switch to form a freewheeling circuit when the current flowing through the first switch or the third switch exceeds a preset threshold.

[0022] In one embodiment, the overcurrent protection method includes turning off the first and third switches and turning on the second and fourth switches when the current flowing through the first or third switch exceeds a preset threshold.

[0023] The current detection method and overcurrent protection method for AC chopper circuits proposed in this invention can be applied to current detection in AC chopper circuits without a front-stage rectifier bridge, and provide an overcurrent protection method suitable for bridgeless AC chopper circuits, with high current detection response speed and system reliability. Attached Figure Description

[0024] Figure 1A A schematic diagram of a bridgeless AC chopper circuit is shown.

[0025] Figure 1BAn existing H-bridge circuit for converting a DC signal into a chopped signal is shown.

[0026] Figure 2 A schematic diagram of a current detection method for an AC chopper circuit according to an embodiment of the present invention is shown;

[0027] Figure 3 A schematic diagram of an AC chopper circuit including a current detection circuit is shown according to a first embodiment of the present invention;

[0028] Figure 4 A waveform diagram according to an embodiment of the present invention is shown;

[0029] Figure 5 A schematic diagram of an AC chopper circuit according to a second embodiment of the present invention is shown;

[0030] Figure 6A A schematic diagram of an AC chopper circuit according to a third embodiment of the present invention is shown;

[0031] Figure 6B A schematic diagram of an AC chopper circuit in another embodiment of the present invention is shown;

[0032] Figure 7 A schematic diagram of an AC chopper circuit according to a fourth embodiment of the present invention is shown;

[0033] Figure 8 A schematic diagram of an AC chopper circuit according to a fifth embodiment of the present invention is shown;

[0034] Figure 9 A schematic diagram of an AC chopper circuit according to a sixth embodiment of the present invention is shown;

[0035] Figure 10 A schematic diagram of an AC chopper circuit according to a seventh embodiment of the present invention is shown;

[0036] Figure 11 A schematic flowchart of an overcurrent protection method according to an embodiment of the present invention is shown;

[0037] Figure 12 A schematic diagram of an overcurrent protection method according to an embodiment of the present invention is shown;

[0038] Figure 13 A schematic diagram of an overcurrent protection method according to an embodiment of the present invention is shown. Detailed Implementation

[0039] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0040] The description in this section pertains to only a few typical embodiments, and the present invention is not limited to the scope of the embodiments described. Combinations of different embodiments, substitution of some technical features in different embodiments, and substitution of similar or identical prior art with some technical features in the embodiments are also within the scope of the description and protection of the present invention.

[0041] The terms "coupled" or "connected" in this specification include both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a connection through an electrically conductive medium like a conductor, which may contain parasitic inductance or capacitance. It can also be a connection through an intermediate circuit or component described in the embodiments of this specification, such as a connection through a sensing resistor. Indirect connections may also include connections through other active or passive devices that achieve the same or similar functions. "A and / or B" indicates either a case including both A and B, or a case including only A or only B.

[0042] Figure 2 A schematic diagram of a current detection method for an AC chopper circuit according to an embodiment of the present invention is shown. The AC chopper circuit includes a switching circuit. The switching circuit has a first input terminal 211, a second input terminal 212, a first output terminal 213, and a second output terminal 214, wherein the first input terminal 211 is coupled to a first terminal of an AC power supply Vac, the second input terminal 212 is coupled to a second terminal of the AC power supply Vac, the first output terminal 213 is coupled to a first terminal of an AC load M, and the second output terminal 214 is coupled to a second terminal of the AC load M.

[0043] The AC power supply Vac provides a power source with alternating polarity. In one embodiment, the AC power supply Vac is AC mains power, such as a 220V / 50Hz sinusoidal AC voltage source. In one embodiment, the AC power supply further includes a capacitor C1 coupled across the AC voltage source and / or an EMI (electromagnetic interference) filter circuit for filtering high-frequency spike signals. The switching circuit 11 receives the alternating polarity AC signal Vac and uses its outputs 213 and 214 to drive the AC load M.

[0044] In one embodiment, the AC load includes a single-phase AC motor.

[0045] By controlling the states of multiple switching transistors Q1-Q4 in the switching circuit, the input AC power supply Vac is AC chopped, and an AC chopped signal is provided at the output of the switching circuit to power the load M.

[0046] Specifically, the switching circuit includes: a first switching transistor Q1, coupled between the first input terminal 211 and the first output terminal 213 of the switching circuit; a second switching transistor Q2, coupled between the reference terminal RG and the first output terminal 213 of the switching circuit; a third switching transistor Q3, coupled between the second input terminal 212 and the second output terminal 214 of the switching circuit; and a fourth switching transistor Q4, coupled between the reference terminal RG and the second output terminal 214 of the switching circuit. Each switching transistor includes a body diode connected in parallel. The first switching transistor Q1 includes a first body diode D1 connected in parallel, wherein the anode of the first body diode D1 is coupled to the first output terminal 213 of the switching circuit, and the cathode of the first body diode D1 is coupled to the first input terminal 211 of the switching circuit. The second switching transistor Q2 includes a second body diode D2 connected in parallel, wherein the anode of the second body diode D2 is coupled to the reference terminal RG of the switching circuit, and the cathode of the second body diode D2 is coupled to the first output terminal 213 of the switching circuit. The third switch Q3 includes a third body diode D3 connected in parallel, wherein the anode of the third body diode D3 is coupled to the second output terminal 214 of the switching circuit, and the cathode of the second body diode D2 is coupled to the second input terminal 212 of the switching circuit. The fourth switch Q4 includes a fourth body diode D4 connected in parallel, wherein the anode of the fourth body diode D4 is coupled to the reference terminal RG of the switching circuit, and the cathode of the fourth body diode D4 is coupled to the second output terminal 214 of the switching circuit. Switches Q1-Q4 may include field-effect transistors such as metal-oxide-semiconductor field-effect transistors (MOSFETs), junction field-effect transistors (JFETs), or insulated-gate bipolar transistors (IGBTs). Preferably, switches Q1-Q4 include parasitic body diodes for implementing asynchronous freewheeling functionality. In another embodiment, switches Q1-Q4 may also each have discrete diodes connected in parallel. Each of switches Q1-Q4 may be replaced by a combination of multiple switches or a combination of switches and diodes.

[0047] In other embodiments, the switching circuit may have other topologies, such as a bridgeless three-phase switching circuit, and the load may be a three-phase AC motor.

[0048] When working within the positive half-cycle of the working interval, such as Figure 2The polarity of the AC power supply is shown. The voltage at the first input terminal 211 of the switching circuit is less than the voltage at the second input terminal 212 of the switching circuit. The AC chopper circuit controls the first switch Q1 and the second switch Q2 to conduct simultaneously. The second half-bridge drive circuit 233 controls the third switch Q3 to switch with a duty cycle. The fourth switch Q4 operates in freewheeling mode. The fourth switch Q4 can be in synchronous rectification (controlled by the control terminal) or asynchronous rectification mode (conducted through the body diode D4). When operating in the negative half-cycle operating range, the voltage at the first input terminal 211 of the switching circuit is greater than the voltage at the second input terminal 212 of the switching circuit. The AC chopper circuit controls the third switch Q3 and the fourth switch Q4 to conduct simultaneously. The first switch Q1 switches with a duty cycle. The second switch Q2 operates in freewheeling mode. The second switch Q2 can be in synchronous rectification (controlled by the control terminal) or asynchronous (conducted through the body diode D2) freewheeling mode. In this topology, the switching circuit is directly coupled to the AC power supply. By controlling the switching circuit, the AC power supply is chopped to output an AC chopped signal, eliminating the need for a high-power freewheeling circuit at the input end and improving power density and efficiency.

[0049] In this topology and operating mode, the two lower switching transistors Q2 and Q4 mostly function as freewheeling switches, while the two upper switching transistors Q1 and Q3 can reflect the current state when the power supply is providing power. Therefore, only the current of the two upper transistors Q1 and Q3, which are directly connected to the power supply, can accurately and directly reflect the current value during the energy transfer stage, enabling timely detection and response to current changes, and achieving timely system overcurrent or short-circuit protection.

[0050] In this AC chopper circuit topology, to detect the load current Io during AC power supply Vac, the current detection method includes detecting the current flowing through the first switch Q1 and / or detecting the current flowing through the third switch Q3. Preferably, the detection method detects the current flowing through the first switch Q1 during its on-state and / or detects the current flowing through the third switch Q3 during its on-state.

[0051] In one embodiment, the current flowing through the first switch Q1 is detected by detecting the voltage at the first input terminal 211 relative to the first output terminal 213 or the reference terminal RG, and the current flowing through the third switch Q3 is detected by detecting the voltage at the second input terminal 212 relative to the second output terminal 214 or the reference terminal RG.

[0052] Figure 3A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown to illustrate a current detection method used in the AC chopper circuit. The AC chopper circuit includes a switching circuit 31 and a current detection circuit 32. The current detection circuit 32 includes a first detection resistor Rs1, a second detection resistor Rs2, a first diode Ds1, a second diode Ds2, and a current source Is. The first detection resistor Rs1 is connected in series with a first switching transistor Q1, and the second detection resistor Rs2 is connected in series with a third switching transistor Q3. In the illustrated embodiment, the first detection resistor Rs1 is coupled between the first input terminal 311 of the switching circuit and the first switching transistor Q1; however, the positions of the first detection resistor Rs1 and the switching transistor Q1 can be interchanged. The cathode of the first diode Ds1 is coupled to the first input terminal 311 of the switching circuit 31, and the anode of the first diode Ds1 is coupled to the output terminal of the current source Is. The cathode of the second diode Ds2 is coupled to the second input terminal 312 of the switching circuit 31, and the anode of the second diode Ds1 is also coupled to the output terminal of the current source Is. The current source Is is used to provide bias current to turn on diodes Ds1 or Ds2, and to provide a voltage signal at the output of the current source Is as a current detection signal Vcs. The following will combine... Figure 4 The waveform diagram illustrates the working mode of the AC chopper circuit and the current detection method.

[0053] Figure 4A waveform diagram according to an embodiment of the present invention is shown. From top to bottom, the signal AC power supply Vac, output voltage Vo, current detection signal Vcs, first synchronization signal ST1, second synchronization signal ST2, and switch control signals PWM1-PWM4 are shown. The AC power supply Vac is a sinusoidal AC signal applied between the first and second input terminals of the switching circuit. The output voltage Vo is the AC chopped signal obtained by chopping the sinusoidal AC signal Vac, which is the voltage difference between the first and second output terminals of the switching circuit, applied across the AC load. The synchronization signals ST1 and ST2 are state signals related to the polarity of the AC power supply Vac. When the first synchronization signal ST1 is high, the voltage at the first input terminal of the switching circuit is less than the voltage at the second input terminal, indicating that the switching circuit is operating in the positive half-cycle operating range. When the second synchronization signal ST2 is high, the voltage at the first input terminal of the switching circuit is greater than the voltage at the second input terminal, indicating that the switching circuit is operating in the negative half-cycle operating range. When both signals ST1 and ST2 are low, it indicates that the switching circuit is operating in the dead zone operating range. In one embodiment, the operating region can be defined by comparing the input voltage Vac with two threshold voltages or based on the phase of the voltage zero-crossing point. Taking the two threshold voltage comparison method as an example, the operating time period when the input voltage Vac is higher than the first comparison threshold (positive) is defined as the positive half-cycle operating region; the operating time period when the input voltage is lower than the first comparison threshold but higher than the second comparison threshold (negative) is defined as the dead zone operating region; and the operating region when the input voltage is lower than the second comparison threshold is defined as the negative half-cycle operating region. The switch control signals PWM1-PWM4 are the switching control signals that drive the switching transistors Q1-Q4. When the switch control signal is high, the corresponding switching transistor is turned on. When the switch control signal is low, the corresponding switch does not form a channel, the switch is turned off, but the parasitic diode of the switch can carry current in one direction.

[0054] During the positive half-cycle operating range, the synchronization signal ST1 is high, and the voltage at the second terminal 312 of the AC power supply is greater than the voltage at the first terminal 311. That is, the voltage at the second terminal 312 is positive relative to the reference terminal, and the voltage at the first terminal 311 is negative. At this time, signals PWM1 and PWM2 are high, and switches Q1 and Q2 are turned on. Signal PWM3 is a pulse width modulation signal that causes switch Q3 to switch with a duty cycle. The fourth switch Q4 operates in synchronous freewheeling or asynchronous freewheeling, complementing the switching action of the third switch Q3. At this time, the AC power supply is applied positively to the right bridge arm shown in the figure. The right bridge arm switches with a set duty cycle (Q3), generating a voltage signal at the output terminal with the same envelope and input voltage waveform, and whose average value is proportional to the duty cycle, which is applied positively to the load M. At this time, the third switch Q3 is the main switch, and the fourth switch Q4 is the freewheeling switch. At this time, the fourth switch Q4 does not need a drive signal, and the current flows through the body diode. When the third switch Q3 is turned on, the current Io flows out through the second terminal 312 of the AC power supply Vac, passing through Q3, the load M, Q1, and resistor Rs1, and then to the first terminal 311 of the AC power supply Vac. At this time, since Q1 and Q2 are turned on, the voltage at the first input terminal 311 is Rs1*Io. The voltage at the first terminal 311 of the AC power supply Vac is negative, the second diode Ds2 is turned on, and the first diode Ds1 is turned off. The sum of the sampling resistor voltage Rs1*Io and the fixed diode forward bias voltage (Vdiode) is reflected at the current sampling output terminal, making the current detection signal Vcs = Vdiode - Rs1*Io, where Vdiode is the forward voltage drop of diode Ds2, a constant value such as 0.7 volts, and voltage Vcs uses the reference terminal RG as ground. Therefore, Vcs can reflect the current Io flowing through the load, and at this time, the current flowing through the first switch Q1 is detected. When the switch Q3 is turned off, the current in the inductive load M forms a loop through the body diodes of the conducting Q2 and Q4. At this time, the voltage on terminal 311 reflects the voltage drop Vq2 on Q2, Vcs=Vq2+Vdiode.

[0055] During the negative half-cycle operating interval, the synchronization signal ST2 is high, and signals PWM3 and PWM4 are also high. Switches Q3 and Q4 are turned on. Signal PWM1, a pulse width modulation signal, causes switch Q1 to switch with a duty cycle. Switch Q2 operates in synchronous freewheeling or asynchronous freewheeling, complementing the switching action of switch Q1. At this time, the first diode Ds1 is turned on. When switch Q1 is turned on, current Io flows out through the first terminal 311 of the AC power supply Vac, through Q1, the load M, Q3, and resistor Rs2, to the second terminal 312 of the AC power supply Vac. The current detection circuit detects the current flowing through switch Q3 and obtains the current detection signal Vcs = Vdiode - Rs2 * Io, with the reference terminal RG as the reference ground. By fixing Rs1 and Rs2, Vcs reflects the current Io flowing through the load. When the switch Q3 is turned off, the current in the inductive load M forms a loop through the body diodes of the conducting Q2 and Q4. At this time, the voltage on terminal 311 reflects the voltage drop Vq2 on Q2, Vcs=Vq2+Vdiode.

[0056] During the dead-time operating range, the two switches Q2 and Q4 closest to the reference terminal RG can be turned on, while the two switches Q1 and Q3 at the corresponding input terminals are turned off, forming a freewheeling loop between the inductive load and the reference terminal. During the dead-time operating range, both upper transistors are in the off state. Figure 3 The two detection diodes Ds1 and Ds2 shown are turned off, and the Vcs voltage is clamped to a higher fixed voltage (Vclamp).

[0057] Figure 5 A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown. The current detection circuit includes a first diode Ds1, a second diode Ds2, and a current source Is. Figure 3 Compared to the previous embodiment, in this embodiment, the first detection resistor in the current detection circuit is the equivalent on-resistance of the first switching transistor Q1, such as the channel resistance or the body diode resistance, and the second detection resistor Rs2 is the equivalent on-resistance of the third switching transistor Q3. In this embodiment, when the first switching transistor Q1 or the third switching transistor Q3 is turned on, the voltage difference across it changes with the load current Io, so the load current Io can be reflected through this voltage difference. The on-state voltage difference of Q1 or Q3 can be reflected in the voltage value of the current detection signal Vcs.

[0058] Figure 6A A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown. Figure 3Compared to the previous embodiment, the current detection circuit in this embodiment further includes a bias resistor Ros, whose first end is coupled to the output of the current source Is, and whose second end is coupled to the anode of the first diode Ds1 and the second diode Ds2. The output of the current source Is provides a current detection signal Vcs. During the positive half-cycle operating interval, when the switching transistor Q3 is turned on, the current detection signal Vcs = Vdiode + Ros * Is - Rs1 * Io. During the negative half-cycle operating interval, when Q1 is turned on, the current detection signal Vcs = Vdiode + Ros * Is - Rs2 * Io. When the current detection signal is used to compare with a preset current threshold signal to further control the switching circuit, the resistance value of the bias resistor Ros can be selected to adjust the current control level, such as for adjusting the overcurrent protection point.

[0059] Figure 6B A schematic diagram of an AC chopper circuit, representing another embodiment of the present invention, is shown. Figure 6A As shown, the current detection circuit includes a first detection resistor Rs1 and a second detection resistor Rs2. In one embodiment, Figure 6A In this embodiment, the first detection resistor Rs1 and the second detection resistor Rs2 are additionally provided resistive elements, connected in series with the first switch Q1 and the third switch Q3, respectively. In another embodiment, the first detection resistor Rs1 and the second detection resistor Rs2 are the equivalent on-resistances of the first switch Q1 and the third switch Q3, respectively, instead of being additional resistive elements. To reflect this feature, Figure 6B It shows Figure 6A Another possible embodiment of the present invention is described. In this embodiment, the AC chopper circuit detects the voltage at the first input terminal 611 based on the equivalent on-resistance of the first switch Q1; detects the voltage at the second input terminal 612 based on the equivalent on-resistance of the third switch Q3; couples the cathode of the first diode Ds1 to the first input terminal; couples the cathode of the second diode to the second input terminal; and...

[0060] The output of the current source is coupled to the anode of the first diode and the anode of the second diode to provide bias current, so that the voltage at the output of the current source reflects the load current.

[0061] Figure 7 A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown. Figure 3 Compared to the previous embodiment, the current source in this embodiment includes a voltage source Vcc and a resistor R1.

[0062] Figure 8A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown. The current detection circuit includes a first detection circuit and a second detection circuit. The first detection circuit includes: a first detection resistor Rs1, connected in series with a first switch Q1; a first diode Ds1, whose cathode is coupled to a first input terminal 811 of the switch circuit; and a first current source Is1, whose input terminal is coupled to a first output terminal 813 of the switch circuit, and whose output terminal is coupled to the anode of the first diode Ds1 to provide a bias power supply and provide a first current detection signal Vcs1. The second detection circuit includes a second detection resistor Rs2, connected in series with a third switch Q3; a second diode Ds2, whose cathode is coupled to a second input terminal 812 of the switch circuit; and a second current source Is2, whose input terminal is coupled to a second output terminal 814 of the switch circuit, and whose output terminal is coupled to the anode of the second diode Ds2 to provide a bias power supply and provide a second current detection signal Vcs2. The current detection circuit generates a current detection signal based on the first current detection signal Vcs1 and the second current detection signal Vcs2. When the switches are operating in the positive half-cycle, transistors Q1 and Q2 are turned on, Q3 is in switching mode, and Q4 is in freewheeling mode. Both transistors in the left half-bridge are simultaneously turned on. When Q3 is on, diode Ds2 is forward-biased and conducts, and the voltage drop across Rs2 is reflected in the Vcs2 signal. When Q3 is off, Ds2 is reverse-biased and cut off, clamping the Vcs2 signal to a certain voltage. Similarly, when in the negative half-cycle, both transistors in the right half-bridge are simultaneously turned on. When Q1 is on, diode Ds1 is forward-biased and conducts, and the voltage drop across Rs1 is reflected in the Vcs1 signal. In one embodiment, the first sensing resistor Rs1 is the on-channel resistance of the first switching transistor Q1, and the second sensing resistor Rs2 is the on-channel resistance of the third switching transistor Q3. The current detection circuit does not include the discrete first and second sensing resistors.

[0063] Figure 9 A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown. Figure 8 Compared to the previous embodiment, in this embodiment, the first current detection circuit further includes a first bias resistor Ros1, whose first end is coupled to the output terminal of the first current source Is1, and whose second end is coupled to the anode of the first diode Ds1; the second current detection circuit further includes a second bias resistor Ros2, whose first end is coupled to the output terminal of the second current source Is2, and whose second end is coupled to the anode of the second diode Ds2. By adjusting the resistance values ​​of the first bias resistor Ros1 and the second bias resistor Ros2, the overcurrent protection threshold can be adjusted.

[0064] Figure 10A schematic diagram of an AC chopper circuit according to an embodiment of the present invention is shown. In this AC chopper circuit, the current detection circuit includes a first detection circuit and a second detection circuit. The first detection circuit is connected in parallel with a first switch Q1. The first detection circuit includes a first transistor SN1 and a first detection resistor Rs1 connected in series. The control terminal of the first transistor SN1 is coupled to the control terminal of the first switch Q1. The coupling point of the first transistor SN1 and the first detection resistor Rs1 provides a first detection current signal Vcs1. The second detection circuit is connected in parallel with a third switch Q3. The second detection circuit includes a second transistor SN2 and a second detection resistor Rs2 connected in series. The control terminal of the second transistor SN2 is coupled to the control terminal of the third switch Q3. The coupling point of the second transistor SN2 and the second detection resistor Rs2 provides a second detection current signal Vcs2. The first transistor SN1 and the first switch Q1 can be integrated on the same semiconductor wafer, and the second transistor SN2 and the third switch Q3 can be integrated on the same semiconductor wafer. In the illustrated embodiment, switching transistors Q1 and Q3, and detection transistors SN1 and SN2 are all MOSFETs. The current flowing through the load M through the aforementioned connections is in a fixed ratio to the current flowing through the detection transistors. Therefore, the detection signal Vcs2 when Q3 is on or the detection signal Vcs1 when Q1 is on can be used to provide a current detection signal. Because they are manufactured using the same semiconductor process, consistency is high, and current detection is more accurate. During the positive half-cycle operating region, the current when Q3 is on reflects the voltage drop across the second detection resistor Rs2 as signal Vcs2. During the negative half-cycle operating region, the current when Q1 is on reflects the voltage drop across the first detection resistor Rs1 as signal Vcs1.

[0065] In one embodiment, the first detection circuit may employ Figure 8 or Figure 9 The first detection circuit shown can be replaced by the second detection circuit shown in Figure 10. Alternatively, the second detection circuit can be used instead of the one shown in Figure 10.

[0066] Figure 11 A schematic flowchart of an overcurrent protection method according to an embodiment of the present invention is shown. The overcurrent protection method includes detecting in step 1101... Figure 2 The current flowing through the first switch Q1 and / or the third switch Q3 in the AC chopper circuit shown. Current detection methods can be implemented through... Figures 2 to 10The current detection circuit and corresponding method are implemented in the above. The overcurrent protection method includes, in step 1102, executing overcurrent / short-circuit protection when an overcurrent is detected flowing through the first or third switching transistor. The overcurrent state can be manifested as the current flowing through the first or third switching transistor exceeding a preset threshold, or it can be determined according to specific operating requirements or other conditions. Specifically, an overcurrent / short-circuit indication signal can be generated by comparing the current detection signal with a set current threshold signal through a comparison circuit. When the overcurrent / short-circuit indication signal indicates an overcurrent, the switching circuit is controlled to execute overcurrent or short-circuit protection action. The overcurrent or short-circuit protection methods in two embodiments are described below.

[0067] Figure 12 A schematic diagram of an overcurrent protection method according to an embodiment of the present invention is shown. The AC chopper circuit includes an auxiliary power supply circuit 1201. The input terminal of the auxiliary power supply circuit is coupled to the first input terminal 1211 and the second input terminal 1212 of the switching circuit. The reference ground terminal of the auxiliary power supply circuit 1201 is coupled to the reference terminal RG of the switching circuit. The output terminal of the auxiliary power supply circuit 1201 provides an auxiliary power supply Vaux for powering other circuits, such as control circuits. In this AC chopper circuit, when the overcurrent / short-circuit indication signal indicates an overcurrent, the overcurrent protection circuit controls the switching circuit to perform a protection action, including controlling the first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 to turn off simultaneously. At this time, the residual current of the inductive load M forces the corresponding body diode of the switching circuit to conduct, and forms a current path with the auxiliary power supply circuit 1201 through the reference terminal RG, providing a freewheeling path for the inductive load. This provides overcurrent protection while preventing overvoltage damage to the switching transistors caused by excessive voltage fluctuations. Figure 12 As shown, when operating in the negative half-cycle, the current detection circuit detects overcurrent and simultaneously turns off Q1-Q4. At this time, the current flowing through the inductive load M provides a freewheeling path through the body diode D3 of switch Q3, diode D5 in the auxiliary power supply circuit, capacitor C2, the reference terminal RG, and the body diode D2 of switch Q2. Residual inductive energy is absorbed by the second capacitor C2 in the auxiliary power supply circuit 1201. The voltage of the switch is also clamped by capacitor C2 to prevent overvoltage. It should be noted that in this case, the turn-off and turn-on signals from the third and second switches are equivalent.

[0068] Figure 12In this circuit, the auxiliary power supply circuit 1201 includes diodes D5 and D6, capacitor C2, and a DC / DC converter circuit. The anode of diode D6 is coupled to the first input terminal 1211 of the switching circuit, and the cathode is coupled to the input terminal of the DC / DC converter circuit. The anode of diode D5 is coupled to the second input terminal 1212 of the switching circuit, and the cathode is coupled to the input terminal of the DC / DC converter circuit. The ground terminal of the DC / DC converter is coupled to the reference terminal RG of the switching circuit and serves as the system ground. The output terminal of the DC / DC converter circuit provides the auxiliary power supply Vaux. Capacitor C2 is coupled between the input terminal and the ground terminal of the DC / DC converter circuit. When the switching circuit operates in the positive half-cycle, Q1 and Q2 conduct, causing the reference ground of the auxiliary power supply circuit 1201 to be coupled to the low-level voltage terminal of the AC power supply. Diode D5 conducts, causing the high-level voltage terminal of the AC power supply Vac to be applied to the auxiliary power supply circuit of the DC / DC converter circuit. When the switching circuit operates in the negative half-cycle operating range, Q3 and Q4 are turned on, causing the reference ground of the auxiliary power supply circuit 1201 to be coupled to the low voltage terminal of the AC power supply, and diode D6 is turned on, causing the high voltage terminal of the AC power supply Vac to be applied to the auxiliary power supply circuit of the DC / DC circuit.

[0069] Figure 13 A schematic diagram of an overcurrent protection method according to another embodiment of the present invention is shown. Figure 12 In the overcurrent protection method shown, during the negative half-cycle operating range and when the voltage value is at its maximum, the voltage stress on the first switch Q1 is at its maximum, which is the sum of the absolute values ​​of the clamping capacitor C2 voltage and the AC source voltage Vac. To address this issue, in one embodiment, when the overcurrent / short-circuit indication signal indicates an overcurrent, the load, the second switch, and the fourth switch form a freewheeling circuit. See [reference needed] Figure 13 When the overcurrent / short circuit indicator signal indicates an overcurrent, the first switch Q1 and the third switch Q3 of the control switching circuit are turned off, while the second switch Q2 and the fourth switch Q4 are turned on. This allows the residual current flowing through the inductive load to form a loop through the body diode of the turned-on lower switch and another lower switch. The second switch Q2 or the fourth switch Q4 can also operate in a non-synchronous freewheeling state. Figure 13The diagram illustrates that during the positive half-cycle operating period, when the voltage at the first input terminal 1301 of the switching circuit is less than the voltage at the second input terminal 1302, if the current flowing through switch Q1 exceeds a preset threshold, the switching control circuit controls the second switch Q2 to conduct, while the first switch Q1 and the third switch Q3 are turned off. In another embodiment, the first switch Q1 and the second switch Q2 of the first bridge arm are simultaneously conducted, while the third switch Q3 and the fourth switch Q4 of the second bridge arm are simultaneously turned off. At this time, the power supply Vac stops supplying power to the load M. As shown in the figure, the residual current in the inductive load M forms a freewheeling loop through the body diode D4 of the conducting second switch Q2 and fourth switch Q4 to prevent voltage surges that could damage the switches. The residual inductive current is consumed by the loop resistor, and the voltage across the third switch Q3 is clamped to the input AC source voltage Vac. During the negative half-cycle operating period, when the voltage at the first input terminal 1301 is greater than the voltage at the second input terminal 1302, the switching control circuit controls the fourth switch Q4 to conduct, while the other switches are turned off. In another embodiment, the first switch Q1 and the second switch Q2 of the first bridge arm can be turned off, while the third switch Q3 and the fourth switch Q4 of the second bridge arm can be turned on. The residual current forms a freewheeling circuit through the turned-on Q4 and the body diode D2, and the voltage of the first switch Q3 is clamped to the input AC source voltage Vac. Figure 12 Compared to the overcurrent protection methods shown in the previous embodiment, the overcurrent protection measures in this embodiment allow the device to withstand lower voltage stress.

[0070] In one embodiment, in Figure 13 In the overcurrent protection method shown, the turn-off duration Toff of the third switch Q3 in the positive half-cycle operating interval and the first switch Q1 in the negative half-cycle operating interval can be maintained for a period of time until the system restarts. In one embodiment, the turn-off duration Toff can also be maintained for several pulse width modulation cycles. In yet another embodiment, when an overcurrent is detected, the corresponding Q3 or Q1 is turned off, but in the next pulse width modulation cycle, switch Q3 (positive half-cycle operating interval) or switch Q1 (negative half-cycle operating interval) is turned on again normally. In this way, the overcurrent protection can seamlessly switch with the normal operating mode, realizing cycle-by-cycle control of the overcurrent protection.

[0071] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "non-inverting" and "inverting" in the above logic control can be interchanged or changed, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic control.

[0072] The description and application of the present invention herein are illustrative and not intended to limit the scope of the invention to the embodiments described above. The effects or advantages described in the specification may not be apparent in actual experimental cases due to uncertainties in specific conditions or other factors, and such descriptions are not intended to limit the scope of the invention. Variations and modifications to the embodiments disclosed herein are possible, and various substitutions and equivalents of the components in the embodiments are well known to those skilled in the art. It should be understood by those skilled in the art that the invention can be implemented in other forms, structures, arrangements, proportions, and with other components, materials, and parts without departing from the spirit or essential characteristics of the invention. Other variations and modifications can be made to the embodiments disclosed herein without departing from the scope and spirit of the invention.

Claims

1. A current detection method for an AC chopper circuit, wherein the AC chopper circuit comprises: The first switching transistor is coupled between the first input terminal and the first output terminal; The second switch is coupled between the reference terminal and the first output terminal; The third switch is coupled between the second input terminal and the second output terminal; as well as The fourth switch is coupled between the reference terminal and the second output terminal, wherein the first input terminal is coupled to the first terminal of the AC power supply, the second input terminal is coupled to the second terminal of the AC power supply, the first output terminal is coupled to the first terminal of the load, and the second output terminal is coupled to the second terminal of the load. The current detection method includes detecting the current flowing through the first switching transistor and / or detecting the current flowing through the third switching transistor; The current detection method includes: Connect the first detection resistor in series with the first switching transistor; Connect the second detection resistor in series with the third switching transistor; The cathode of the first diode is coupled to the first input terminal; Couple the cathode of the second diode to the second input terminal; and The output of the current source is coupled to the anode of the first diode and the anode of the second diode to provide bias current, so that the voltage at the output of the current source reflects the load current.

2. The current detection method as described in claim 1 further includes coupling a first end of a bias resistor to the output terminal of a current source, and coupling a second end of the bias resistor to the anode of a first diode and the anode of a second diode.

3. A current detection method for an AC chopper circuit, wherein the AC chopper circuit includes: The first switching transistor is coupled between the first input terminal and the first output terminal; The second switch is coupled between the reference terminal and the first output terminal; The third switch is coupled between the second input terminal and the second output terminal; as well as The fourth switch is coupled between the reference terminal and the second output terminal, wherein the first input terminal is coupled to the first terminal of the AC power supply, the second input terminal is coupled to the second terminal of the AC power supply, the first output terminal is coupled to the first terminal of the load, and the second output terminal is coupled to the second terminal of the load. The current detection method includes detecting the current flowing through the first switching transistor and / or detecting the current flowing through the third switching transistor; The current detection method includes: The voltage at the first input terminal is detected based on the equivalent on-resistance of the first switching transistor. The voltage at the second input terminal is detected based on the equivalent on-resistance of the third switch. The cathode of the first diode is coupled to the first input terminal; Couple the cathode of the second diode to the second input terminal; and The output of the current source is coupled to the anode of the first diode and the anode of the second diode to provide bias current, so that the voltage at the output of the current source reflects the load current.

4. The current detection method as described in claim 3 further includes coupling a first end of a bias resistor to the output terminal of a current source, and coupling a second end of the bias resistor to the anode of a first diode and the anode of a second diode.

5. A current detection method for an AC chopper circuit, wherein the AC chopper circuit includes: The first switching transistor is coupled between the first input terminal and the first output terminal; The second switch is coupled between the reference terminal and the first output terminal; The third switch is coupled between the second input terminal and the second output terminal; as well as The fourth switch is coupled between the reference terminal and the second output terminal, wherein the first input terminal is coupled to the first terminal of the AC power supply, the second input terminal is coupled to the second terminal of the AC power supply, the first output terminal is coupled to the first terminal of the load, and the second output terminal is coupled to the second terminal of the load. The current detection method includes detecting the current flowing through the first switching transistor and / or detecting the current flowing through the third switching transistor; The current detection method includes: Connect the first detection resistor in series with the first switching transistor; The cathode of the first diode is coupled to the first input terminal; The input terminal of the first current source is coupled to the first output terminal, and its output terminal is coupled to the anode of the first diode to provide bias current, so that the voltage at the output terminal of the first current source reflects the current flowing through the first switching transistor. Connect the second detection resistor in series with the third switching transistor; Couple the cathode of the second diode to the second input terminal; and The input terminal of the second current source is coupled to the second output terminal, and its output terminal is coupled to the anode of the second diode to provide bias current, so that the voltage at the output terminal of the second current source reflects the current flowing through the third switching transistor.

6. The current detection method as described in claim 5, further comprising: The first bias resistor is set between the output terminal of the first current source and the anode of the first diode to set the reference threshold for current detection. as well as A second bias resistor is placed between the output terminal of the second current source and the anode of the second diode to set a reference threshold for current detection.

7. The current detection method as described in claim 6, wherein the first detection resistor is the equivalent on-resistance of the first switching transistor, and the second detection resistor is the equivalent on-resistance of the third switching transistor.

8. A current detection method for an AC chopper circuit, wherein the AC chopper circuit includes: The first switching transistor is coupled between the first input terminal and the first output terminal; The second switch is coupled between the reference terminal and the first output terminal; The third switch is coupled between the second input terminal and the second output terminal; as well as The fourth switch is coupled between the reference terminal and the second output terminal, wherein the first input terminal is coupled to the first terminal of the AC power supply, the second input terminal is coupled to the second terminal of the AC power supply, the first output terminal is coupled to the first terminal of the load, and the second output terminal is coupled to the second terminal of the load. The current detection method includes detecting the current flowing through the first switching transistor and / or detecting the current flowing through the third switching transistor; The current detection method further includes: The first transistor and the first sensing resistor, which are connected in series, are connected in parallel with the first switching transistor, wherein the control terminal of the first transistor is coupled to the control terminal of the first switching transistor, so that the voltage drop across the first sensing resistor reflects the current flowing through the first switching transistor. as well as The second transistor and the second sensing resistor, which are connected in series, are connected in parallel with the third switching transistor, wherein the control terminal of the second transistor is coupled to the control terminal of the third switching transistor, so that the voltage drop across the second sensing resistor reflects the current flowing through the third switching transistor.

9. The current detection method as described in claim 8, comprising integrating a first transistor and a first switching transistor on the same semiconductor wafer, and integrating a second transistor and a third switching transistor on the same semiconductor wafer.

10. An overcurrent protection method, comprising the current detection method as described in any one of claims 1-9, and performing overcurrent / short-circuit protection when an overcurrent occurs in the current flowing through a first switching transistor or a third switching transistor.

11. The overcurrent protection method as described in claim 10, wherein the AC chopper circuit further includes an auxiliary power supply circuit, the input terminal of the auxiliary power supply circuit is coupled to the first input terminal and the second input terminal, the reference ground terminal of the auxiliary power supply circuit is coupled to the reference terminal, the output terminal of the auxiliary power supply circuit provides auxiliary power, and the overcurrent protection method includes turning off the first switch, the second switch, the third switch and the fourth switch simultaneously when the current flowing through the first switch or the third switch is greater than a preset threshold.

12. The overcurrent protection method as described in claim 10, comprising controlling the load, the second switch and the fourth switch to form a freewheeling circuit when the current flowing through the first switch or the third switch is greater than a preset threshold.

13. The overcurrent protection method as described in claim 12, wherein when the current flowing through the first switch or the third switch is greater than a preset threshold, the first switch and the third switch are turned off, and the second switch and the fourth switch are turned on.

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