CN109962604A - Driving circuit and zero passage detection method with zero crossing detection function - Google Patents
Driving circuit and zero passage detection method with zero crossing detection function Download PDFInfo
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- CN109962604A CN109962604A CN201711403770.0A CN201711403770A CN109962604A CN 109962604 A CN109962604 A CN 109962604A CN 201711403770 A CN201711403770 A CN 201711403770A CN 109962604 A CN109962604 A CN 109962604A
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- 238000001514 detection method Methods 0.000 title claims abstract description 81
- 238000005070 sampling Methods 0.000 claims abstract description 7
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- 230000005347 demagnetization Effects 0.000 claims description 12
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- 239000003990 capacitor Substances 0.000 claims description 5
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
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- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/083—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the ignition at the zero crossing of the voltage or the current
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Abstract
The present invention provides a kind of driving circuit with zero crossing detection function and zero passage detection method, comprising: power switch tube, pulling drive pipe, the first drop-down driving tube, the second drop-down driving tube and current limliting module；The output end of inductance in the drain electrode connection switch power supply of power switch tube, the source electrode of power switch tube are grounded via current sampling resistor；The grid of power switch tube is connected to supply voltage via pulling drive pipe, and the control terminal of pulling drive pipe connects the first driving signal；The grid of power switch tube is grounded via the series circuit after the first drop-down driving tube and the second drop-down driving tube and current limliting block coupled in series respectively, and the control terminal of the first drop-down driving tube connects the second driving signal；The control terminal of second drop-down driving tube connects third driving signal；Current limliting module controls drop signal and falls amplitude with preset for controlling the second pull-down current less than the first pull-down current.The present invention can avoid a possibility that failure or error detection of conventional driver circuits zero passage detection.
Description
Technical Field
The invention relates to the field of switching power supply control, in particular to a driving circuit with a zero-crossing detection function and a zero-crossing detection method.
Background
With the global emphasis on energy problems, the energy consumption problem of electronic products will be more and more prominent, and how to reduce the standby power consumption and improve the power supply efficiency becomes a problem to be solved urgently. Although the traditional linear voltage-stabilized power supply has simple circuit structure and reliable work, the traditional linear voltage-stabilized power supply has the defects of low efficiency (only 40-50%), large volume, large copper and iron consumption, high working temperature, small adjustment range and the like. In order to improve the efficiency, people develop a switch type voltage-stabilized power supply, the efficiency of which can reach more than 85 percent, the voltage-stabilized range is wide, and in addition, the switch type voltage-stabilized power supply has the characteristics of high voltage-stabilized precision, no use of a power transformer and the like, and is an ideal voltage-stabilized power supply.
A switching power supply operating in a critical conduction mode is a common switching voltage-stabilized power supply, and performs zero-crossing detection after demagnetization of an inductive current to ensure normal operation of the switching power supply.
In the prior art, a zero-crossing detection method directly uses a Cgd capacitive coupling signal of a power switch in a power supply system to perform zero-crossing detection, does not need an additional detection device or circuit to realize zero-crossing detection, can reduce the area of a control chip, and has obvious cost advantage.
In the existing zero-crossing detection scheme, after demagnetization of a system is finished, a drop signal is coupled to a grid electrode of a power switch through a Cgd capacitor, and a pull-down tube keeps strong pull-down capability on the grid electrode of the power switch, so that the coupled drop signal has large loss, and the problem that the signal cannot be detected is caused if the signal is too weak; in the prior art, in order to detect a weak drop signal, the threshold of the comparator is designed to be too close to the ground, so that false detection can occur, and the power supply system is abnormal in function and even explodes due to failure of zero-crossing detection or false detection, thereby bringing potential reliability hazards to the system.
Therefore, how to improve the accuracy of zero-crossing detection and the reliability of the system has become one of the problems to be solved urgently by workers in the field.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a driving circuit with zero-crossing detection function and a zero-crossing detection method, which are used to solve the reliability problem caused by the error detection of zero-crossing detection of the demagnetization of the inductor current in the prior art.
To achieve the above and other related objects, the present invention provides a driving circuit with zero-crossing detection function, which at least includes:
the power switch tube, the pull-up driving tube, the first pull-down driving tube, the second pull-down driving tube and the current limiting module;
the drain electrode of the power switch tube is connected with the output end of an inductor in a switch power supply, the source electrode of the power switch tube is grounded through a current sampling resistor and is used for controlling output voltage through the conduction and the cut-off of the power switch tube, and meanwhile, a parasitic capacitor between the drain electrode and the grid electrode of the power switch tube is coupled with a falling signal of the demagnetization end of the inductor;
the grid electrode of the power switch tube is connected to a power supply voltage through the pull-up driving tube, and the control end of the pull-up driving tube is connected with a first driving signal and used for providing a pull-up current for the grid electrode of the power switch tube in the starting process of the power switch tube;
the grid electrode of the power switch tube is grounded through a series circuit formed by connecting the first pull-down driving tube and the second pull-down driving tube in series with the current limiting module, and the control end of the first pull-down driving tube is connected with a second driving signal and used for providing a first pull-down current for the grid electrode of the power switch tube at the initial stage of closing of the power switch tube; the control end of the second pull-down driving tube is connected with a third driving signal and used for providing a second pull-down current for the grid electrode of the power switch tube in the closing process of the power switch tube; the current limiting module is used for controlling the second pull-down current provided by the second pull-down driving tube to be smaller than the first pull-down current provided by the first pull-down driving tube and controlling the drop signal to have a preset drop amplitude.
Preferably, the input end of the inductor is connected with an input voltage, two ends of the inductor are connected with a freewheeling diode in parallel, the cathode of the freewheeling diode is connected with the input end of the inductor, and the anode of the freewheeling diode is connected with the output end of the inductor.
Preferably, the pull-up driving tube is an NMOS tube, a drain of the pull-up driving tube is connected to the power supply voltage, a source of the pull-up driving tube is connected to a gate of the power switching tube, and the gate of the pull-up driving tube is connected to the first driving signal; when the first driving signal is at a high level, the pull-up driving tube is conducted to provide a pull-up current for the grid electrode of the power switch tube.
Preferably, the first pull-down driving tube is an NMOS tube, a drain of the first pull-down driving tube is connected to a gate of the power switch tube, a source of the first pull-down driving tube is grounded, and the gate of the first pull-down driving tube is connected to the second driving signal; when the second driving signal is at a high level, the first pull-down driving tube is turned on to provide the first pull-down current for the grid electrode of the power switch tube.
Preferably, the second pull-down driving tube is an NMOS tube, a drain of the second pull-down driving tube is connected to a gate of the power switching tube, a source of the second pull-down driving tube is grounded via the current limiting module, and the gate of the second pull-down driving tube is connected to the third driving signal; when the third driving signal is at a high level, the second pull-down driving tube is turned on to provide the second pull-down current for the gate of the power switch tube.
More preferably, the on time of the first pull-down driving pipe is set to 0-5 μ sec.
Preferably, the first pull-down driving pipe has a size 10 to 100 times larger than that of the second pull-down driving pipe.
Preferably, the current limiting module includes: the circuit comprises a first current limiting resistor, a second current limiting resistor and a diode; wherein,
one end of the first current limiting resistor is connected with the second pull-down driving tube, and the other end of the first current limiting resistor is grounded; one end of the second current limiting resistor is connected with the second pull-down driving tube, and the other end of the second current limiting resistor is connected with the anode of the diode; the cathode of the diode is grounded.
Preferably, the driving circuit with the zero-crossing detection function further includes a comparator, and an input end of the comparator is respectively connected to the gate of the power switching tube and a reference voltage, and is configured to convert the detected falling signal after the demagnetization of the inductor into a logic signal.
In order to achieve the above and other related objects, the present invention provides a zero-crossing detection method based on a driving circuit with zero-crossing detection function as defined in any one of the above solutions, applied in a switching power supply circuit operating in critical conduction mode, the zero-crossing detection method at least comprising:
when the inductor starts to discharge, a first pull-down current provided by the first pull-down driving tube and a second pull-down current provided by the second pull-down driving tube pull down the grid of the power switch tube together, so that the power switch tube is in a cut-off state; after a set time, the first pull-down driving tube is turned off, the second pull-down driving tube continues to pull down the power switch tube, and the power switch tube is still in a cut-off state; in the process of pulling down the grid of the power switch tube, the second pull-down current is smaller than the first pull-down current; wherein the set time is less than the time for the inductor to discharge;
when the inductor finishes discharging, the parasitic capacitance between the drain electrode and the grid electrode of the power switch tube is coupled with a falling signal after the inductor demagnetizes, after the falling signal is detected, the second pull-down driving tube is switched off, the pull-up driving tube provides pull-up current to pull up the grid electrode of the power switch tube, so that the power switch tube is in a conducting state, and the inductor starts to charge.
Preferably, the set time is 0-5 microseconds.
More preferably, the set time is 1 to 2 microseconds.
Preferably, the first pull-down current is 10 to 100 times the second pull-down current.
Preferably, the falling signal is coupled to the gate of the power switch tube and then compared with a reference voltage, when the coupling signal of the falling signal is smaller than the reference voltage, the zero-crossing detection signal is activated, and the pull-up current is formed.
As described above, the driving circuit with zero-cross detection function and the zero-cross detection method of the present invention have the following beneficial effects:
the driving circuit with the zero-crossing detection function and the zero-crossing detection method avoid the possibility of failure or false detection of the zero-crossing detection of the conventional driving circuit by optimizing the driving time sequence, and improve the reliability of the system.
Drawings
Fig. 1 is a schematic structural diagram of a driving circuit with zero-crossing detection function according to the present invention.
Fig. 2 is a schematic diagram showing the operation timing of the driving circuit with zero-crossing detection function according to the present invention.
Description of the element reference numerals
2 driving circuit with zero-crossing detection function
20 power switch tube
21 pull-up driving tube
22 first pull-down drive tube
23 second Pull-Down drive tube
24 comparator
25 current limiting module
251 first current limiting resistor
252 second current limiting resistor
253 diode
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1-2. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
As shown in fig. 1, the present invention provides a driving circuit 2 having a zero-cross detection function, where the driving circuit 2 having a zero-cross detection function includes:
a power switch tube 20, a pull-up driving tube 21, a first pull-down driving tube 22, a second pull-down driving tube 23 and a current limiting module 25.
As shown in fig. 1, an input end of an inductor L is connected to a power supply voltage Vin and a cathode of a freewheeling diode D, and an output end of the inductor L is connected to an anode of the freewheeling diode D.
As shown in fig. 1, the drain of the power switch tube 20 is connected to the output end of the inductor L, and the source of the power switch tube 20 is connected to ground via a current sampling resistor Rsense for controlling the output voltage by turning on and off the power switch tube 20, and meanwhile, a parasitic capacitance Cgd between the drain and the gate of the power switch tube 20 couples the droop signal of the demagnetization end of the inductor L.
Specifically, the power switch tube 20 is an NMOS tube, and when the gate of the power switch tube 20 is at a high level, the power switch tube 20 is turned on, and the current flows to the ground through the inductor L, the power switch tube 20 and the current sampling resistor Rsense. The power switch tube 20 controls a power path, and a parasitic capacitance Cgd between a drain and a gate of the power switch tube is used for coupling a demagnetized drop signal; the current sampling resistor Rsense is used for setting the peak current of the system.
As shown in fig. 1, the gate of the power switch tube 20 is connected to a power voltage via the pull-up driving tube 21, and the control terminal of the pull-up driving tube 21 is connected to a first driving signal Driver1 for providing a pull-up current to the gate of the power switch tube 20 during the turn-on process of the power switch tube 20.
Specifically, in this embodiment, the pull-up driving transistor 21 is an NMOS transistor, a drain of the pull-up driving transistor 21 is connected to the power voltage, a source of the pull-up driving transistor 21 is connected to a gate of the power switching transistor 20, and a gate of the pull-up driving transistor 21 is connected to the first driving signal Driver 1; when the first driving signal Driver1 is at a high level, the pull-up driving transistor NM is turned on to provide a pull-up current to the gate of the power switching transistor 20. The pull-up driving transistor 21 may also be a PMOS transistor, and the pull-up function can be realized by adaptively adjusting the connection relationship and the polarity of the driving signal, which is not limited to the devices and the connection relationship listed in this embodiment.
As shown in fig. 1, the gate of the power switch tube 20 is grounded via the first pull-down driving tube 22, and the control terminal of the first pull-down driving tube 22 is connected to the second driving signal Driver2 for providing the first pull-down current to the gate of the power switch tube 20 during the initial stage of turning off the power switch tube 20.
Specifically, in this embodiment, the first pull-down driving transistor 22 is an NMOS transistor, a drain of the first pull-down driving transistor 22 is connected to the gate of the power switch 20, a source of the first pull-down driving transistor 22 is grounded, and a gate of the first pull-down driving transistor 22 is connected to the second driving signal Driver 2; when the second driving signal Driver2 is at a high level, the first pull-down driving transistor 22 is turned on to provide the first pull-down current to the gate of the power switch 20. The first pull-down driving transistor 22 may be a PMOS transistor, and the pull-up function can be realized by adaptively adjusting the connection relationship and the polarity of the driving signal, which is not limited to the devices and the connection relationship listed in this embodiment.
As shown in fig. 1, the gate of the power switch tube 20 is grounded via the second pull-down driving tube 23, and the control end of the second pull-down driving tube 23 is connected to a third driving signal Driver3 for providing a second pull-down current to the gate of the power switch tube 20 during the turn-off process of the power switch tube 20; the current limiting module 25 is configured to control the second pull-down current provided by the second pull-down driving tube 23, so as to ensure that the second pull-down current is smaller than the first pull-down current provided by the first pull-down driving tube 22, and control the drop amplitude of the drop signal, so that the drop signal has a preset drop amplitude with a certain amplitude.
Specifically, in this embodiment, the second pull-down driving transistor 23 is an NMOS transistor, a drain of the second pull-down driving transistor 23 is connected to a gate of the power switching transistor 20, a source of the second pull-down driving transistor 23 is connected in series with the current limiting module 25, and is grounded via the current limiting module 25, and a gate of the second pull-down driving transistor 23 is connected to the third driving signal Driver 3; when the third driving signal Driver3 is at a high level, the second pull-down driving transistor 23 is turned on to provide the second pull-down current to the gate of the power switch transistor 20.
More specifically, while the power switch tube 20 is turned off, the first pull-down driving tube 22 and the second pull-down driving tube 23 are simultaneously turned on to discharge the gate of the power switch tube 20, but the first pull-down driving tube 22 is turned on for only a small fixed time and then turned off, and in this embodiment, the on-time of the first pull-down driving tube 22 is set to 0 μ sec to 5 μ sec, and more preferably, the on-time of the first pull-down driving tube 22 is further set to 1 μ sec to 2 μ sec. The second pull-down driving tube 23 is always turned on during the turn-off of the power switching tube 20, the on-time of the second pull-down driving tube 23 is determined by the whole driving circuit, the on-time range of the second pull-down driving tube 23 varies greatly according to the driving circuit, and the on-time of the second pull-down driving tube 23 may be between several microseconds and several hundred microseconds. The first pull-down current is greater than the second pull-down current, the first pull-down driving tube 22 provides a larger pull-down for the gate of the power switching tube 20, and the second pull-down driving tube 23 provides a weak pull-down for the gate of the power switching tube 20, in this embodiment, the first pull-down driving tube 22 has a larger size, the second pull-down driving tube 23 has a smaller size, and the first pull-down driving tube 22 is 10 to 100 times larger than the second pull-down driving tube 23. The existence of the current limiting module 25 can effectively control the pull-down strength provided by the gate of the power switch tube 20 by the second pull-down driving tube 23, so that the second pull-down driving tube 23 can provide a weak pull-down for the gate of the power switch tube 20, namely, the pull-down of the gate of the power switch tube 20 is very weak, in the application, the pull-down strength provided by the gate of the power switch tube 20 by the structure formed by connecting the second pull-down driving tube 23 and the current limiting module 25 in series is far less than that provided by the gate of the power switch tube 20 by only one second pull-down driving tube 23.
As an example, the current limiting module 25 includes: a first current limiting resistor 251, a second current limiting resistor 252, and a diode 253; one end of the first current limiting resistor 251 is connected to the second pull-down driving tube 23, and the other end is grounded, specifically, one end of the first current limiting resistor 251 is connected to the source of the second pull-down driving tube 23; one end of the second current limiting resistor 252 is connected to the second pull-down driving transistor 23, and the other end is connected to the anode of the diode 253, specifically, one end of the second current limiting resistor 252 is connected to the source of the second pull-down driving transistor 23; the cathode of the diode 253 is grounded. The second current-limiting resistor 253 can limit reverse high-temperature leakage of the diode 253, so that a falling signal with a large amplitude can be obtained by the gate of the power switch tube 20, great benefits are provided for subsequent signal comparison and processing, and problems such as undetected signal due to too weak signal can be avoided.
As an example, the falling amplitude of the falling signal obtained by the gate of the power switch tube 20 may reach 190mV to 210mV, and preferably, in this embodiment, the falling amplitude of the falling signal obtained by the gate of the power switch tube 20 is 200 mV.
As shown in fig. 1, the driving circuit with zero-crossing detection function further includes a comparator 24, and the input end of the comparator 24 is respectively connected to the gate of the power switch 20 and a reference voltage VREF, and is configured to convert the detected droop signal after the demagnetization of the inductor L into a zero-crossing detection signal ZCD.
Specifically, in this embodiment, the inverting input terminal of the comparator 24 is connected to the gate of the power switch 20, the non-inverting input terminal of the comparator 24 is connected to the reference voltage VREF, and the zero-crossing detection signal ZCD is asserted when the coupling signal of the droop signal is smaller than the reference voltage VREF.
Compared with a driving circuit without the current limiting module 25, the driving circuit without the current limiting module 25 can design the threshold of the comparator 24 to be too close to the ground in order to detect a weak drop signal, which can cause false detection and affect the reliability of the system; in the application, after the current limiting module 25 is additionally arranged, a drop signal with a large amplitude can be obtained, and false detection can be avoided, so that the reliability of the system is ensured.
Referring to fig. 1 and fig. 2, in combination with a working timing diagram of the driving circuit 2 with the zero-crossing detection function of the present invention, the present invention provides a zero-crossing detection method based on the driving circuit with the zero-crossing detection function, which is applied to a switching power supply circuit working in a critical conduction mode, and in this embodiment, the zero-crossing detection method is implemented based on the driving circuit 2 with the zero-crossing detection function, and the zero-crossing detection method at least includes:
when the inductor L starts to discharge, the first pull-down current provided by the first pull-down driving tube 22 and the second pull-down current provided by the second pull-down driving tube 23 pull down the gate of the power switching tube 20 together, so that the power switching tube 20 is in a cut-off state; after a set time, the first pull-down driving tube 23 is turned off, the second pull-down driving tube 23 continues to pull down the power switch tube 20, and the power switch tube 20 is still in a cut-off state; in the process of pulling down the gate of the power switch tube 20, the second pull-down current is smaller than the first pull-down current; wherein the set time is less than the time for the inductor L to discharge.
Specifically, in the inductor discharging phase, the first driving signal Driver1 jumps to a low level, the second driving signal Driver2 and the third driving signal Driver3 jump to a high level, the first pull-down current provided by the first pull-down driving transistor 22 and the second pull-down current provided by the second pull-down driving transistor 23 jointly pull down the GATE of the power switching transistor 20, the GATE voltage GATE of the power switching transistor 20 jumps to a low level, the power switching transistor 20 is in an off state, and the Drain voltage Drain of the power switching transistor 20 rises. After a set time, the second driving signal Driver2 jumps to a low level, the first pull-down driving transistor 22 is turned off, that is, the first pull-down current is turned off, the second pull-down driving transistor 23 continues to provide the second pull-down current to keep pulling down the power switching transistor 20, the GATE voltage GATE of the power switching transistor 20 maintains a low level, and the power switching transistor 20 is still in an off state. In the present embodiment, the set time is 0 to 5 microseconds, and more specifically, the set time is further set to 1 to 2 microseconds. The first pull-down current provided by the first pull-down driving tube 22 provides a larger pull-down for the gate of the power switching tube 20, and the second pull-down current provided by the second pull-down driving tube 23 provides a weak pull-down for the gate of the power switching tube 20, where in this embodiment, the first pull-down current is 10 to 100 times of the second pull-down current. At this time, the zero-crossing detection signal ZCD output by the comparator 24 does not act, and in this embodiment, the zero-crossing detection signal ZCD is at a low level.
When the discharge of the inductor L is finished, the parasitic capacitance Cgd between the drain and the gate of the power switch tube 20 couples with the falling signal after the demagnetization of the inductor L is finished, and when the falling signal is detected, the second pull-down driving tube 23 is turned off, and the pull-up driving tube 21 provides a pull-up current to pull up the gate of the power switch tube 20, so that the power switch tube 20 is in a conducting state, and the inductor L starts to charge. The current limiting module 25 connected to the source of the second pull-down tube 23 and including the first current limiting resistor 251, the second current limiting resistor 252 and the diode 253 ensures that no leakage current flows into the gate of the power switch tube 20, so as to ensure that a large-amplitude drop signal can be obtained.
As an example, the falling amplitude of the falling signal may reach 190mV to 210mV, and preferably, in this embodiment, the falling amplitude of the falling signal is 200 mV.
Specifically, when the discharge of the inductor L is about to end, the Drain voltage Drain of the power switch tube 20 starts to fall, at this time, only the second pull-down current provided by the second pull-down driver 23 provides a weak pull-down for the gate of the power switch tube 20, the falling signal is coupled to the gate of the power switch tube 20 and then compared with the reference voltage VREF, and when the coupled signal of the falling signal is smaller than the reference voltage VREF, the zero-crossing detection signal ZCD takes effect, in this embodiment, it is a high-level pulse. After the high-level pulse is ended, the first driving signal Driver1 jumps to a high level, the second driving signal Driver2 and the third driving signal Driver3 jump to a low level, the pull-up driving tube 21 provides a pull-up current to pull up the GATE of the power switching tube 20, the GATE voltage GATE of the power switching tube 20 jumps to a high level, the power switching tube 20 is in a conducting state, and the Drain voltage Drain of the power switching tube 20 drops. The inductor L is in a charging state.
During the turn-on process of the power switch tube 20, the pull-up driving tube 21 provides a pull-up current to the gate of the power switch tube 20. In the closing process of the power switch tube 20, the first pull-down driving tube 22 and the second pull-down driving tube 23 are simultaneously turned on to discharge the grid electrode of the power switch tube 20, but the first pull-down driving tube 22 is only turned on for a small fixed time, and then turned off, and only the second pull-down driving tube 23 is kept on. After the demagnetization of the system is finished, after the falling signal is coupled to the gate of the power switch tube 20 through the capacitor Cgd between the gate and the drain of the power switch tube 20, the driving method in the prior art still keeps strong pull-down capability on the gate break of the power switch tube 20, so that the coupled falling signal has large loss.
In summary, the present invention provides a driving circuit with zero-crossing detection function and a zero-crossing detection method, where the driving circuit with zero-crossing detection function at least includes: the power switch tube, the pull-up driving tube, the first pull-down driving tube, the second pull-down driving tube and the current limiting module; the drain electrode of the power switch tube is connected with the output end of an inductor in a switch power supply, the source electrode of the power switch tube is grounded through a current sampling resistor and is used for controlling output voltage through the conduction and the cut-off of the power switch tube, and meanwhile, a parasitic capacitor between the drain electrode and the grid electrode of the power switch tube is coupled with a falling signal of the demagnetization end of the inductor; the grid electrode of the power switch tube is connected to a power supply voltage through the pull-up driving tube, and the control end of the pull-up driving tube is connected with a first driving signal and used for providing a pull-up current for the grid electrode of the power switch tube in the starting process of the power switch tube; the grid electrode of the power switch tube is grounded through a series circuit formed by connecting the first pull-down driving tube and the second pull-down driving tube in series with the current limiting module, and the control end of the first pull-down driving tube is connected with a second driving signal and used for providing a first pull-down current for the grid electrode of the power switch tube at the initial stage of closing of the power switch tube; the control end of the second pull-down driving tube is connected with a third driving signal and used for providing a second pull-down current for the grid electrode of the power switch tube in the closing process of the power switch tube; the current limiting module is used for controlling the second pull-down current provided by the second pull-down driving tube to be smaller than the first pull-down current provided by the first pull-down driving tube and controlling the drop signal to have a preset drop amplitude. The driving circuit with the zero-crossing detection function and the zero-crossing detection method avoid the possibility of failure or false detection of the zero-crossing detection of the conventional driving circuit by optimizing the driving time sequence, and improve the reliability of the system.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (14)
1. A driving circuit having a zero-cross detection function, characterized in that the driving circuit having a zero-cross detection function at least comprises:
the power switch tube, the pull-up driving tube, the first pull-down driving tube, the second pull-down driving tube and the current limiting module;
the drain electrode of the power switch tube is connected with the output end of an inductor in a switch power supply, the source electrode of the power switch tube is grounded through a current sampling resistor and is used for controlling output voltage through the conduction and the cut-off of the power switch tube, and meanwhile, a parasitic capacitor between the drain electrode and the grid electrode of the power switch tube is coupled with a falling signal of the demagnetization end of the inductor;
the grid electrode of the power switch tube is connected to a power supply voltage through the pull-up driving tube, and the control end of the pull-up driving tube is connected with a first driving signal and used for providing a pull-up current for the grid electrode of the power switch tube in the starting process of the power switch tube;
the grid electrode of the power switch tube is grounded through a series circuit formed by connecting the first pull-down driving tube and the second pull-down driving tube in series with the current limiting module, and the control end of the first pull-down driving tube is connected with a second driving signal and used for providing a first pull-down current for the grid electrode of the power switch tube at the initial stage of closing of the power switch tube; the control end of the second pull-down driving tube is connected with a third driving signal and used for providing a second pull-down current for the grid electrode of the power switch tube in the closing process of the power switch tube; the current limiting module is used for controlling the second pull-down current provided by the second pull-down driving tube to be smaller than the first pull-down current provided by the first pull-down driving tube and controlling the drop signal to have a preset drop amplitude.
2. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the input end of the inductor is connected with input voltage, two ends of the inductor are connected with a freewheeling diode in parallel, the cathode of the freewheeling diode is connected with the input end of the inductor, and the anode of the freewheeling diode is connected with the output end of the inductor.
3. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the pull-up driving tube is an NMOS tube, the drain electrode of the pull-up driving tube is connected with the power supply voltage, the source electrode of the pull-up driving tube is connected with the grid electrode of the power switch tube, and the grid electrode of the pull-up driving tube is connected with the first driving signal; when the first driving signal is at a high level, the pull-up driving tube is conducted to provide a pull-up current for the grid electrode of the power switch tube.
4. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the first pull-down driving tube is an NMOS tube, the drain electrode of the first pull-down driving tube is connected with the grid electrode of the power switch tube, the source electrode of the first pull-down driving tube is grounded, and the grid electrode of the first pull-down driving tube is connected with the second driving signal; when the second driving signal is at a high level, the first pull-down driving tube is turned on to provide the first pull-down current for the grid electrode of the power switch tube.
5. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the second pull-down driving tube is an NMOS tube, the drain electrode of the second pull-down driving tube is connected with the grid electrode of the power switch tube, the source electrode of the second pull-down driving tube is grounded through the current limiting module, and the grid electrode of the second pull-down driving tube is connected with the third driving signal; when the third driving signal is at a high level, the second pull-down driving tube is turned on to provide the second pull-down current for the gate of the power switch tube.
6. A drive circuit having a zero-cross detection function according to claim 1 or 5, characterized in that: the conduction time of the first pull-down driving tube is set to be 0-5 microseconds.
7. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the size of the first pull-down driving pipe is 10-100 times larger than that of the second pull-down driving pipe.
8. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the current limiting module includes: the circuit comprises a first current limiting resistor, a second current limiting resistor and a diode; wherein,
one end of the first current limiting resistor is connected with the second pull-down driving tube, and the other end of the first current limiting resistor is grounded; one end of the second current limiting resistor is connected with the second pull-down driving tube, and the other end of the second current limiting resistor is connected with the anode of the diode; the cathode of the diode is grounded.
9. A drive circuit having a zero-cross detection function according to claim 1, characterized in that: the driving circuit with the zero-crossing detection function further comprises a comparator, wherein the input end of the comparator is respectively connected with the grid electrode of the power switch tube and a reference voltage, and the comparator is used for converting the detected falling signal of the end of the demagnetization of the inductor into a logic signal.
10. A zero-crossing detection method based on a driving circuit with zero-crossing detection function according to any one of claims 1 to 9, applied to a switching power supply circuit operating in critical conduction mode, wherein the zero-crossing detection method at least comprises:
when the inductor starts to discharge, a first pull-down current provided by the first pull-down driving tube and a second pull-down current provided by the second pull-down driving tube pull down the grid of the power switch tube together, so that the power switch tube is in a cut-off state; after a set time, the first pull-down driving tube is turned off, the second pull-down driving tube continues to pull down the power switch tube, and the power switch tube is still in a cut-off state; in the process of pulling down the grid of the power switch tube, the second pull-down current is smaller than the first pull-down current; wherein the set time is less than the time for the inductor to discharge;
when the inductor finishes discharging, the parasitic capacitance between the drain electrode and the grid electrode of the power switch tube is coupled with a falling signal after the inductor demagnetizes, after the falling signal is detected, the second pull-down driving tube is switched off, the pull-up driving tube provides pull-up current to pull up the grid electrode of the power switch tube, so that the power switch tube is in a conducting state, and the inductor starts to charge.
11. A zero-crossing detection method as claimed in claim 10, wherein: the set time is 0-5 microseconds.
12. A zero-crossing detection method as claimed in claim 11, wherein: the set time is 1 microsecond to 2 microseconds.
13. A zero-crossing detection method as claimed in claim 10, wherein: the first pull-down current is 10-100 times of the second pull-down current.
14. A zero-crossing detection method as claimed in claim 10, wherein: and the falling signal is coupled to the grid of the power switch tube and then is compared with a reference voltage, when the coupling signal of the falling signal is smaller than the reference voltage, a zero-crossing detection signal acts, and the pull-up current is formed.
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