CN103929048B - A kind of zero cross detection circuit of Switching Power Supply - Google Patents

A kind of zero cross detection circuit of Switching Power Supply Download PDF

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CN103929048B
CN103929048B CN201410177999.7A CN201410177999A CN103929048B CN 103929048 B CN103929048 B CN 103929048B CN 201410177999 A CN201410177999 A CN 201410177999A CN 103929048 B CN103929048 B CN 103929048B
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voltage
switching tube
power supply
module
zero cross
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CN103929048A (en
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陈后鹏
胡佳俊
王倩
宋志棠
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Shanghai Institute of Microsystem and Information Technology of CAS
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Shanghai Institute of Microsystem and Information Technology of CAS
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Abstract

The invention provides a kind of zero cross detection circuit of Switching Power Supply, at least comprise voltage input module; Be connected to the voltage output module of described voltage input module; By the inductance of charge and discharge control output voltage; Control the switching tube of inductance discharge and recharge; Resonance signal between inductance and the drain electrode of switching tube is coupled to the coupling circuit of switching tube grid; For taking out the proportional electric current of the negative voltage that outputs signal with described coupling circuit and being converted into the resonance sampling module that voltage exports; Produce the comparison control module of control signal according to the voltage that described resonance sampling module exports and produce the control driver module of described switching tube gate voltage.The zero cross detection circuit of Switching Power Supply of the present invention significantly can reduce the area of pulse width modulated power supply chip, improving product competitiveness.

Description

A kind of zero cross detection circuit of Switching Power Supply
Technical field
The present invention relates to microelectronic, particularly relate to a kind of zero cross detection circuit of Switching Power Supply.
Background technology
Switching Power Supply adopts power semiconductor as switch, turns on and off by control switch a kind of power supply maintaining regulated output voltage or electric current.Compared with linear power supply, Switching Power Supply is less than linear power supply volume, efficiency is higher, energy-saving and environmental protection more.Linear power supply is instead of completely in some field.Especially constantly reduce in current power equipment volume, voltage constantly reduces, and under the trend that mobile device generally uses, the application of Switching Power Supply is more and more extensive.At present, Switching Power Supply is just towards high frequency, miniaturized future development.
Because electronic technology is at constantly de-velopment and innovation, also constantly there is new form in switching power source chip control technology.Which kind of control mode all needs the internal circuit of chip to remove sampling and outputting voltage or electric current all the time, is adjusted self by the change of sample throughput.The structure of system, the feedback control technology etc. of employing is made according to the size of power output.
In the course of work of Switching Power Supply, if the electric current in inductance does not discharge completely in switching process, then belong to continuous current mode (CCM); If the electric current in inductance discharges completely, recharge after a while, then belong to discontinuous mode; If after the electric current in inductance discharges completely, charged immediately again, then belong to critical conduction mode (BCM).No matter be discontinuous mode, or critical conduction mode, the electric current in inductance all will discharge completely.Be that zero this feature is born and different Sampling techniques and control circuit according to electric current in inductance.
Be illustrated in figure 1 the zero cross detection circuit 1 of a kind of source drive generally used at present.This circuit comprises voltage input module 11, voltage output module 12, inductance L m, diode D, coupling circuit 13, switching tube M1, switching tube M2, resonance sampling module 14, comparator 15, trigger 16 and sampling resistor Rcs, wherein voltage input module 11, voltage output module 12, inductance L m, diode D, coupling circuit 13, switching tube M1 and sampling resistor Rcs are the outer device of sheet, and switching tube M2, resonance sampling module 14, comparator 15 and trigger 16 is device in sheet.Described coupling circuit 13 is coupled to the drain terminal of the described switching tube M2 in sheet the resonance signal between described inductance L m and described switching tube M1, then described resonance sampling module 14 is to this signal sampling, the sampled signal of described switching tube M2 drain terminal and reference voltage compare by described comparator 15 simultaneously, described trigger 16 receives the output signal of described resonance sampling module 14 and described comparator 15, and exports the described conducting of switching tube M2 of control and the control signal of disconnection.In this sample mode, electric current in inductance L m all will flow through the switching tube M2 of chip internal, this switching tube M2 needs very large area, and electric current in inductance L m is larger, the area of the switching tube M2 of chip internal is larger, corresponding chip area is larger, and the manufacturing cost based on this point chip just substantially increases, and the competitiveness of product is also just corresponding to be reduced.
How to improve the cost of the zero passage detection chip of Switching Power Supply, improving product competitiveness is those skilled in the art's problem demanding prompt solution.
Summary of the invention
The shortcoming of prior art in view of the above, the object of the present invention is to provide a kind of zero cross detection circuit of Switching Power Supply, and the cost for the zero passage detection chip solving prior art breaker in middle power supply is high, the problem that product competitiveness is low.
For achieving the above object and other relevant objects, the invention provides a kind of zero cross detection circuit of Switching Power Supply, the zero cross detection circuit of described Switching Power Supply at least comprises:
Voltage input module, voltage output module, inductance, switching tube, coupling circuit, resonance sampling module, compare control module and control driver module;
Described voltage output module is connected to described voltage input module, for output voltage;
Described inductance is connected to described voltage output module, carrys out regulation output voltage by the charge and discharge of described inductance, makes it be stabilized in set point;
Described switching tube is connected to described inductance, controls described inductance charge and discharge by the turn-on and turn-off of described switching tube, when described switching tube conducting, and described induction charging, when described switching tube turns off, described inductive discharge;
The input of described coupling circuit is connected between the drain electrode of described inductance and described switching tube, the output of described coupling circuit is connected to the grid of described switching tube, for the resonance signal between described inductance and the drain electrode of described switching tube being coupled to the grid of described switching tube;
Described resonance sampling module is connected to described coupling circuit, for taking out the proportional electric current of the negative voltage that outputs signal with described coupling circuit, and is converted into voltage and exports;
The described control module that compares is connected to described resonance sampling module, produces control signal according to the voltage that described resonance sampling module exports;
Described control driver module is connected to the described output comparing control module and described switching tube, for generation of the gate voltage controlling described switching tube turn-on and turn-off.
Preferably, the zero cross detection circuit of described Switching Power Supply is applicable to the pulse width modulated power supply of discontinuous mode or critical conduction mode.
Preferably, described voltage input module comprises power supply and is connected to the filter capacitor of described power supply.
Preferably, described voltage output module comprises output capacitance and is parallel to the load of described output capacitance.
Preferably, described switching tube is NMOSFET.
Preferably, described coupling circuit is electric capacity or by the electric capacity circuit formed in series with a resistor.
Preferably, the described control module that compares comprises the first comparator, the first trigger and buffer; The input of described first comparator connects described resonance sampling module and the first reference voltage respectively, the output signal of described resonance sampling module and described first reference voltage is compared; Described first trigger is connected to described first comparator, and described in when described first comparator exports high level signal, the first trigger exports high level pulse; Described buffer is connected to described first trigger, for buffer output signal.
More preferably, described first trigger is d type flip flop.
Preferably, described control drive circuit comprises the second comparator and the second trigger, the voltage signal corresponding with described switching tube output current and the second reference voltage are made comparisons by described second comparator, and comparative result being exported to described second trigger, described second trigger drives the gate voltage of described switching tube for exporting.
More preferably, described second trigger can be d type flip flop or rest-set flip-flop.
Preferably, also comprise diode, the anode of described diode is connected between the drain electrode of described inductance and described switching tube, and the negative electrode of described diode is connected to described voltage input module, when described switching tube conducting, and described diode cut-off; When described switching tube turns off, described diode current flow, provides path to described inductance and described voltage output module.
Preferably, also comprise sampling resistor, one end of described sampling resistor is connected to the output of described switching tube, other end ground connection, for gathering the voltage corresponding with described switching tube output current.
As mentioned above, the zero cross detection circuit of Switching Power Supply of the present invention, has following beneficial effect:
The zero cross detection circuit of Switching Power Supply of the present invention is optimized circuit structure, the switching tube of chip internal and the switching tube of chip exterior are synthesized a switch, and be positioned over chip exterior, the area of chip can be reduced widely, improve the competitiveness of product.
Accompanying drawing explanation
Fig. 1 is shown as the schematic diagram of the zero cross detection circuit of Switching Power Supply of the prior art.
Fig. 2 is shown as the schematic diagram of the zero cross detection circuit of Switching Power Supply of the present invention.
Fig. 3 is shown as the circuit diagram of the resonance sampling module of the zero cross detection circuit of Switching Power Supply of the present invention.
Fig. 4 (a) is shown as the waveform schematic diagram of zero cross detection circuit inductance discharge and recharge under discontinuous mode of Switching Power Supply of the present invention.
Fig. 4 (b) is shown as the waveform schematic diagram of zero cross detection circuit Lx node under discontinuous mode of Switching Power Supply of the present invention.
Fig. 4 (c) is shown as the waveform schematic diagram of zero cross detection circuit Gs node under discontinuous mode of Switching Power Supply of the present invention.
The waveform schematic diagram of the zero cross detection circuit that Fig. 5 (a) is shown as Switching Power Supply of the present invention inductance discharge and recharge in a critical mode.
The waveform schematic diagram of the zero cross detection circuit that Fig. 5 (b) is shown as Switching Power Supply of the present invention Lx node in a critical mode.The waveform schematic diagram of the zero cross detection circuit that Fig. 5 (c) is shown as Switching Power Supply of the present invention Gs node in a critical mode.Element numbers explanation
The zero cross detection circuit of 1 Switching Power Supply
11 voltage input modules
12 voltage output module
13 coupling circuits
14 resonance sampling modules
15 comparators
16RS trigger
The zero cross detection circuit of 2 Switching Power Supplies
21 voltage input modules
22 voltage output module
221 loads
23 coupling circuits
24 resonance sampling modules
25 comparison control circuits
251 first comparators
252 first triggers
253 buffers
26 control driver module
261 second comparators
262 second triggers
CT filter capacitor
Cout output capacitance
Lm inductance
M switching tube
M1 switching tube
M2 switching tube
D diode
Rcs sampling resistor
Embodiment
Below by way of specific instantiation, embodiments of the present invention are described, those skilled in the art the content disclosed by this specification can understand other advantages of the present invention and effect easily.The present invention can also be implemented or be applied by embodiments different in addition, and the every details in this specification also can based on different viewpoints and application, carries out various modification or change not deviating under spirit of the present invention.
Refer to Fig. 2 ~ Fig. 5 (c).It should be noted that, the diagram provided in the present embodiment only illustrates basic conception of the present invention in a schematic way, then only the assembly relevant with the present invention is shown in graphic but not component count, shape and size when implementing according to reality is drawn, it is actual when implementing, and the kenel of each assembly, quantity and ratio can be a kind of change arbitrarily, and its assembly layout kenel also may be more complicated.
As shown in Figure 2, the invention provides a kind of zero cross detection circuit 2 of Switching Power Supply, the zero cross detection circuit 2 of described Switching Power Supply at least comprises:
Voltage input module 21, voltage output module 22, inductance L m, switching tube M, coupling circuit 23, resonance sampling module 24, compare control module 25, control driver module 26, diode D and sampling resistor Rcs.
Described voltage input module 21 is for providing input voltage vin.
As shown in Figure 2, described voltage input module 21 comprises power supply Vin and filter capacitor CT, described filter capacitor CT one end is connected with the output of described voltage input module 21, other end ground connection, carries out filtering for the voltage Vin exported described voltage input module 21.
Described voltage output module 22 is connected to described voltage input module 21, for the voltage of stable output.
As shown in Figure 2, described voltage output module 22 comprises output capacitance Cout and is parallel to the load 221 of described output capacitance Cout.Described output capacitance Cout is for storing electric charge and powering to described load 221.
Described inductance L m is connected to described voltage output module 22, carrys out regulation output voltage by the discharge and recharge of described inductance L m, makes it be stabilized in set point.
As shown in Figure 2, one end of described inductance L m is connected to output capacitance Cout and load 221, and the other end is connected to the drain terminal of described switching tube M.
Described switching tube M is connected to described inductance L m, described inductance L m charge and discharge are controlled by the turn-on and turn-off of described switching tube M, when described switching tube M conducting, input voltage vin gives described inductance L m charging, when described switching tube M turns off, described inductance L m electric discharge, provides power supply to described voltage output module 22.In the present embodiment, described switching tube M is preferably NMOSFET.
The anode of described diode D is connected between described inductance L m and described switching tube M, the negative electrode of described diode D is connected to described voltage input module 21, when described switching tube M turns off, described diode D provides path to described inductance L m and described voltage output module 22.
As shown in Figure 2, the drain electrode of described switching tube M is connected to described inductance L m, and when described switching tube M conducting, described input voltage vin gives described inductance L m charging; When described switching tube M turns off, charging path disconnects, and the loop that described inductance L m is formed to diode D and output module 22 provides power supply.
One end of described sampling resistor Rcs is connected to the source electrode of described switching tube M, other end ground connection, for gathering the voltage corresponding with described switching tube M output current.
The input of described coupling circuit 23 is connected between the drain electrode of described inductance L m and described switching tube M, and the output of described coupling circuit 23 is connected to the grid of described switching tube M.Described coupling circuit 23 is electric capacity or by the electric capacity circuit formed in series with a resistor.In the present embodiment, described coupling circuit 23 is an electric capacity.
As shown in Figure 2, the input of described coupling circuit 23 is connected between the drain electrode of described inductance L m and described switching tube M, the output of described coupling circuit 23 is connected to the grid of described switching tube M, the starting of oscillation when described inductance L m zero crossing, resonance signal, every straight-through friendship, is coupled to the grid of described switching tube M by described electric capacity 23.
Described resonance sampling module 24 is connected to described coupling circuit 23, for taking out the proportional electric current of the negative voltage that outputs signal with described coupling circuit 24, and is that voltage exports by described current conversion.
Be illustrated in figure 3 an embodiment of described resonance sampling module 24, resistance Rs one end is connected to the output Gs of described coupling circuit 23, metal-oxide-semiconductor Mn1 and metal-oxide-semiconductor Mn2 forms current-mirror structure, and due to the source electrode b ground connection of metal-oxide-semiconductor Mn2, the source electrode a point current potential of metal-oxide-semiconductor Mn1 is also 0.As the voltage V of Gs point gSwhen being less than zero, there is the path that current flowing resistance Rs, metal-oxide-semiconductor Mn1, metal-oxide-semiconductor Mp1 and metal-oxide-semiconductor Mp2 are formed, this electric current I rS=| V gS|/Rs.Mirror image between Mp1, Mp2 and Mp5, Mp6, produces sampling current: Isense=K × I rS, wherein K is the scale factor of mirror image, the voltage V of this electric current and Gs point gSthe proportional relation of negative voltage.Be converted into voltage via resistance Rsense again to export, described voltage Vsense=Isense × Rsense.Resonance zero passage is larger, i.e. the voltage V of Gs point gSmore be less than 0, I rSlarger, corresponding Isense and Vsense is also larger.If the voltage V of Gs point gSbe more than or equal to 0, Vsense also just to equal zero.
The described control module 25 that compares is connected to described resonance sampling module 24, produces pulse signal Dpulse according to the voltage that described resonance sampling module 24 exports.
As shown in Figure 2, in the present embodiment, the described control module 25 that compares comprises the first comparator 251; First trigger 252, in the present embodiment, described first trigger is preferably d type flip flop; And buffer 253.The input of described first comparator 251 connects described resonance sampling module 24 and the first reference voltage Vref 1 respectively, as shown in Figure 2, the positive input of described first comparator 251 is connected to the output of described resonance sampling module 24, the reverse input end of described first comparator 251 connects the first reference voltage Vref 1, the output signal of described resonance sampling module 24 and described first reference voltage Vref 1 compare by described first comparator 251, high level signal is exported when the signal that described resonance sampling module 24 exports is greater than described first reference voltage Vref 1, otherwise, output low level signal.Described first trigger 252 is connected to described first comparator 251, and when described first comparator 251 exports high level signal, described first trigger 252 produces high level pulse signal.Described buffer 253 is connected to the output of described first trigger 252, plays cushioning effect, and ensure the synchronous transmission of data or clock, the output signal of described buffer 253 is pulse signal Dpulse.
Described control driver module 26 is connected to the described output comparing control module 25 and described switching tube M, for generation of the gate voltage V controlling described switching tube M turn-on and turn-off gS.
As shown in Figure 2, in the present embodiment, described control drive circuit 26 comprises the second comparator 261 and the second trigger 262, and described second trigger 262 can be d type flip flop or rest-set flip-flop, and in the present embodiment, described second trigger 262 is rest-set flip-flop.The voltage signal Vcs corresponding with described switching tube M output current and the second reference voltage Vref 2 make comparisons by described second comparator 261, and exporting comparative result to described rest-set flip-flop, described rest-set flip-flop drives the gate voltage V of described switching tube M for exporting gS, the signal Dpulse exported when described buffer 253 is high level, when the signal Vcs that described second comparator 261 exports is low level, and described gate voltage V gSfor high level, other situations are low level.
Zero cross detection circuit 2 operation principle of above-mentioned Switching Power Supply is as follows:
When described switching tube M conducting, described voltage input module 21, described voltage output module 22, described inductance L m, described switching tube M and described sampling resistor Rcs form loop, and described input presses Vin to described inductance L m charging; When described switching tube M turns off, loop disconnects, and described output module 22, described inductance L m and described diode D form new loop, and now, described inductance L m electric discharge, for described output module 22 provides the energy.
The zero cross detection circuit 2 of described Switching Power Supply is applicable to the pulse width modulated power supply of discontinuous mode or critical conduction mode.
Under discontinuous mode, when the discharging current in described inductance L m is slowly down to 0, the electric current in described inductance L m starts to occur resonance, and as shown in Fig. 4 (a), the electric current in described inductance L m occurs resonance 0 position.Also there is resonance, as shown in Fig. 4 (b) in the voltage of the node Lx between the drain electrode of described inductance L m and described switching tube M thereupon.This resonance signal is coupled to the gate voltage V of described switching tube M by described coupling circuit 23 gS, as shown in Fig. 4 (c), during due to described inductance L m electric discharge, described switching tube M is off state, and in the present embodiment, described switching tube is NMOSFET, so gate voltage V gSlow level partial coupling resonance signal, shows as the voltage of 0V in the present embodiment.
Gate voltage V gSthe voltage lower than 0V will be produced at 0V voltage location generation resonance, when the voltage lower than 0V is collected by described resonance sampling module 24, by electric current proportional with this negative voltage for generation one, and export in the form of voltage, and produce high level signal by the described control module 25 that compares; Simultaneously, sampled voltage Vcs and reference voltage Vref 2 make comparisons by described first comparator 261, because inductance L m is in discharge condition, so described switching tube M turns off, the voltage Vcs corresponding with described switching tube M output current is less than described reference voltage Vref 2, described second comparator 261 output low level signal; The described high level signal comparing control module 25 generation is connected to the R end of described rest-set flip-flop 262, the low level signal that described second comparator 261 exports is connected to the S end of described rest-set flip-flop 262, and described rest-set flip-flop 262 produces the gate voltage V of described switching tube M gS, this gate voltage V gSfor high level pulse, act on the grid of described switching tube M, described switching tube M conducting, described inductance L m enters charge mode.
Described inductance L m starts charging, and current value increases gradually, as shown in Fig. 4 (a).The voltage of the node Lx between described inductance L m and described switching tube M is 0V, as shown in Fig. 4 (b).The gate voltage V of described switching tube M gSfor high level signal, as gate voltage V gSwhen being more than or equal to 0V, the described control module 25 that compares produces low level signal.The output current of described switching tube M increases gradually, when the voltage Vcs corresponding with described switching tube M output current is greater than reference voltage Vref 1, the saltus step of described rest-set flip-flop 262 is low level, and described switching tube M turns off, and described inductance L m reenters discharge mode.
By controlling the gate voltage V of described switching tube M grid gScontrol the shutoff of the conducting of described switching tube M, control the charge and discharge of described inductance L m further, regulate the output voltage of described voltage output module 22, make it be stable at a certain set point.
Under critical conduction mode, principle is consistent, does not repeat one by one, unlike under this pattern, after the electric current in described inductance L m discharges completely, charges immediately again, only have a zero crossing, can not occur resonance for a long time at this.As Fig. 5 (a) is depicted as the waveform schematic diagram of inductance L m discharge and recharge under critical conduction mode.Fig. 5 (b) is depicted as the waveform schematic diagram of Lx node under critical conduction mode.Fig. 5 (c) is shown as the waveform schematic diagram of Gs node under critical conduction mode.
In the zero cross detection circuit 2 of Switching Power Supply of the present invention, described voltage input module 21, voltage output module 22, inductance L m, diode D, coupling circuit 23, switching tube M and sampling resistor Rcs are the outer device of sheet; Resonance sampling module 24, comparator 15 and trigger 16 is device in sheet.The zero cross detection circuit of Switching Power Supply of the present invention is guaranteed at optimized circuit on the basis of stable output voltage, the large area metal-oxide-semiconductor in sheet is merged into the metal-oxide-semiconductor outside sheet, greatly reduces chip area, effectively reduce costs, improving product competitiveness.
In sum, the zero cross detection circuit of Switching Power Supply of the present invention, at least comprises the voltage input module providing power supply; Be connected to described voltage input module, due to the voltage output module of output voltage; By the inductance of charge and discharge control output voltage; Control the switching tube of inductance discharge and recharge; Resonance signal is coupled to the coupling circuit of switching tube grid; Gather the described resonance sampling module of described switching tube gate voltage zero cross signal; Produce the comparison control module of pulse signal and produce the control driver module of described switching tube gate voltage.When inductive current is zero, occur resonance between switching tube and inductance, this resonance signal is coupled to the grid of described switching tube by described coupling circuit.The grid that resonance signal is coupled to switching tube shows as the oscillator signal of zero crossing.Described resonance sample circuit takes out the resonance current be directly proportional to this resonance signal negative voltage, and this resonance current converts voltage to and outputs to described comparison control circuit, then produces by controlling driver module the conducting that control signal controls described switching tube.The zero cross detection circuit of Switching Power Supply of the present invention significantly can reduce the area of pulse width modulated power supply chip.So the present invention effectively overcomes various shortcoming of the prior art and tool high industrial utilization.
Above-described embodiment is illustrative principle of the present invention and effect thereof only, but not for limiting the present invention.Any person skilled in the art scholar all without prejudice under spirit of the present invention and category, can modify above-described embodiment or changes.Therefore, such as have in art usually know the knowledgeable do not depart from complete under disclosed spirit and technological thought all equivalence modify or change, must be contained by claim of the present invention.

Claims (12)

1. a zero cross detection circuit for Switching Power Supply, is characterized in that, the zero cross detection circuit of described Switching Power Supply at least comprises:
Voltage input module, voltage output module, inductance, switching tube, coupling circuit, resonance sampling module, compare control module and control driver module;
Described voltage output module is connected to described voltage input module, for output voltage;
Described inductance is connected to described voltage output module, carrys out regulation output voltage by the charge and discharge of described inductance, makes it be stabilized in set point;
Described switching tube is connected to described inductance, controls described inductance charge and discharge by the turn-on and turn-off of described switching tube, when described switching tube conducting, and described induction charging, when described switching tube turns off, described inductive discharge;
The input of described coupling circuit is connected between the drain electrode of described inductance and described switching tube, the output of described coupling circuit is connected to the grid of described switching tube, for the resonance signal between described inductance and the drain electrode of described switching tube being coupled to the grid of described switching tube;
Described resonance sampling module is connected to described coupling circuit, for taking out the proportional electric current of the negative voltage that outputs signal with described coupling circuit, and is converted into voltage and exports;
The described control module that compares is connected to described resonance sampling module, produces control signal according to the voltage that described resonance sampling module exports;
Described control driver module is connected to the described output comparing control module and described switching tube, for generation of the gate voltage controlling described switching tube turn-on and turn-off.
2. the zero cross detection circuit of Switching Power Supply according to claim 1, is characterized in that: the zero cross detection circuit of described Switching Power Supply is applicable to the pulse width modulated power supply of discontinuous mode or critical conduction mode.
3. the zero cross detection circuit of Switching Power Supply according to claim 1, is characterized in that: described voltage input module comprises power supply and is connected to the filter capacitor of described power supply.
4. the zero cross detection circuit of Switching Power Supply according to claim 1, is characterized in that: described voltage output module comprises output capacitance and is parallel to the load of described output capacitance.
5. the zero cross detection circuit of Switching Power Supply according to claim 1, is characterized in that: described switching tube is NMOSFET.
6. the zero cross detection circuit of Switching Power Supply according to claim 1, is characterized in that: described coupling circuit is electric capacity or by the electric capacity circuit formed in series with a resistor.
7. the zero cross detection circuit of Switching Power Supply according to claim 1, is characterized in that: the described control module that compares comprises the first comparator, the first trigger and buffer; The input of described first comparator connects described resonance sampling module and the first reference voltage respectively, the output signal of described resonance sampling module and described first reference voltage is compared; Described first trigger is connected to described first comparator, and described in when described first comparator exports high level signal, the first trigger exports high level pulse; Described buffer is connected to described first trigger, for buffer output signal.
8. the zero cross detection circuit of Switching Power Supply according to claim 7, is characterized in that: described first trigger is d type flip flop.
9. the zero cross detection circuit of Switching Power Supply according to claim 1, it is characterized in that: described control drive circuit comprises the second comparator and the second trigger, the voltage signal corresponding with described switching tube output current and the second reference voltage are made comparisons by described second comparator, and comparative result being exported to described second trigger, described second trigger drives the gate voltage of described switching tube for exporting.
10. the zero cross detection circuit of Switching Power Supply according to claim 9, is characterized in that: described second trigger is d type flip flop or rest-set flip-flop.
The zero cross detection circuit of 11. Switching Power Supplies according to claim 1, it is characterized in that: also comprise diode, the anode of described diode is connected between the drain electrode of described inductance and described switching tube, the negative electrode of described diode is connected to described voltage input module, when described switching tube conducting, described diode cut-off; When described switching tube turns off, described diode current flow, provides path to described inductance and described voltage output module.
The zero cross detection circuit of 12. Switching Power Supplies according to claim 1, it is characterized in that: also comprise sampling resistor, one end of described sampling resistor is connected to the output of described switching tube, other end ground connection, for gathering the voltage corresponding with described switching tube output current.
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