CN102170232A - Self-driven active buffer and flyback switching mode power supply - Google Patents

Abstract

The invention provides a self-driven active buffer and flyback switching mode power supply, which has no need for external drive circuit. The self-driven active buffer comprises a first terminal, a second terminal, a first capacitor, a second capacitor and an MOS ransistor wherein one end of the first capacitor is connected with the first terminal, and another end is connected with the second terminal through the series MOS transistor and the second capacitor; the substrate of the MOS transistor is shorted with the source, and the grid is connected with the second terminal. Due to the respective two connections comprising the grid of the MOS transistor with one end of the second capacitor and source with another end of the second capacitor, the voltage of the second capacitor provides driving voltage for MOS, therefore, the MOS transistor can realize self-driven through the voltage of the second capacitor. In addition, the active buffer can absorb the spike voltage which can not be consumed away in the form of heat, thereby not reducing the efficiency of the switching mode power supply.

Description

A kind of self-driven active snubber and inverse-excitation type switch power-supply

Technical field

The present invention relates to the switch power technology field, particularly a kind of self-driven active snubber and inverse-excitation type switch power-supply.

Background technology

It is little that Switching Power Supply has a volume, and therefore the advantage that efficient height and electric current are big is widely used in occasions such as charger for mobile phone and notebook adapter.In recent years, because high conversion efficiency and low standby power loss are emphasized in the rise of green power supply notion more.

In all types of Switching Power Supplies, inverse-excitation type switch power-supply is the most general.And transformer is one of core devices in the inverse-excitation type switch power-supply, and the effect of transformer provides the electrostatic isolation of power input and output.

Along with the development of technology, the development trend of Switching Power Supply is smart dimensions and high switching frequency.But high switching frequency will bring switching loss and high heat problem.In order to solve the switching loss that high switching frequency brings, Switching Power Supply often adopts the design of quasi-resonance control type at present.In quasi-resonance control type design, with the mains switch closure, the mains switch loss is just more little like this when the drain voltage of mains switch is minimum.

Referring to Fig. 1, this figure is a kind of structure chart that has the Switching Power Supply of voltage shutoff type buffer of the prior art.

Voltage shutoff type buffer comprises resistance 102, electric capacity 103 and diode 104.

The closed and disconnected of mains switch 101 is controlled by drive signal S1.

When mains switch 101 is closed, the induced electricity on transformer 105 former limits linear the increasing that fail to be convened for lack of a quorum.

When mains switch 101 disconnects, a due to voltage spikes will appear in the drain electrode of mains switch 101.The origin cause of formation of this due to voltage spikes mainly is the former limit leakage inductance of transformer 105.When mains switch 101 disconnects, the energy of the former limit leakage inductance of transformer 105 will produce this due to voltage spikes to the parasitic capacitance charging of former limit inductance.

This due to voltage spikes will cause serious electromagnetic interference, and therefore, voltage shutoff type buffer is used for absorbing this due to voltage spikes.

When this due to voltage spikes is higher than input voltage vin, diode 104 conductings, electric capacity 103 absorbs energy, this due to voltage spikes hour.Resistance 102 is heat energy with the power conversion that electric capacity 103 absorbs.

But the heat energy that resistance 102 consumes will reduce the efficient of Switching Power Supply.In order to improve the efficient of Switching Power Supply, utilize active snubber shown in Figure 2 to absorb peak voltage in the prior art.

Referring to Fig. 2, this figure is the structure chart that has the Switching Power Supply of another kind of buffer in the prior art.

Active snubber among Fig. 2 comprises first capacitor C 1 and metal-oxide-semiconductor M2.

The closed and disconnected of mains switch M1 is controlled by drive signal S1.

When mains switch M1 disconnected, due to voltage spikes appeared in the drain electrode of metal-oxide-semiconductor M2.When M1 disconnected, M2 will conducting suppress due to voltage spikes, and C1 helps to reveal the energy that due to voltage spikes produces.

This active snubber is not fallen the energy that due to voltage spikes produces with thermal energy consumption, therefore improved the efficient of Switching Power Supply, but M2 needs complicated drive circuit to produce the on off state that drive signal S2 controls M2, existing U.S. Pat 2007/0263415A1 discloses a kind of self-driven active snubber, but the structure more complicated has increased the cost of entire circuit.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of self-driven active snubber and inverse-excitation type switch power-supply, and simple in structure, cost is lower.

The invention provides a kind of self-driven active snubber, comprising: the first terminal, second terminal, first electric capacity, second electric capacity and metal-oxide-semiconductor;

One end of described first electric capacity connects the first terminal, and the other end is connected second terminal by the metal-oxide-semiconductor of series connection with second electric capacity successively;

The substrate of described metal-oxide-semiconductor and source shorted, grid connect second terminal.

Preferably, also comprise the parasitic body diode of metal-oxide-semiconductor, the anode of the parasitic body diode of described metal-oxide-semiconductor connects the source electrode of described metal-oxide-semiconductor, and the negative electrode of the parasitic body diode of described metal-oxide-semiconductor connects the drain electrode of described metal-oxide-semiconductor.

Preferably, also comprise the parasitic capacitance of metal-oxide-semiconductor, an end of the parasitic capacitance of described metal-oxide-semiconductor connects the source electrode of described metal-oxide-semiconductor, and the other end connects the drain electrode of described metal-oxide-semiconductor.

Preferably, described the first terminal connects an end of the former limit of transformer connecting line voltage in the Switching Power Supply, and described second terminal connects the other end on the former limit of transformer in the described Switching Power Supply.

Preferably, described metal-oxide-semiconductor is the NMOS pipe.

The present invention also provides a kind of inverse-excitation type switch power-supply with described self-driven active snubber, comprising: self-driven active snubber, mains switch, transformer and switch power controller;

The first terminal of described self-driven active snubber connects an end of the former limit of transformer connecting line voltage in the Switching Power Supply, and second terminal connects the other end on the former limit of transformer in the described Switching Power Supply;

Described switch power controller is used to export pwm pulse, to control the on off state of described mains switch.

Preferably, also comprise the parasitic body diode of mains switch, the anode of the parasitic body diode of described mains switch connects the source electrode of mains switch, and the negative electrode of the parasitic body diode of described mains switch connects the drain electrode of mains switch.

Preferably, also comprise the parasitic capacitance of mains switch, an end of the parasitic capacitance of described mains switch connects the source electrode of mains switch, and the other end connects the drain electrode of mains switch.

Preferably, described metal-oxide-semiconductor is the NMOS pipe.

Compared with prior art, the present invention has the following advantages:

Self-driven active snubber and inverse-excitation type switch power-supply that the embodiment of the invention provides do not need external drive circuit, because the grid of metal-oxide-semiconductor and source electrode are connected the two ends of second electric capacity respectively, voltage on second electric capacity provides driving voltage for MOS, so metal-oxide-semiconductor can be realized self-driven by the voltage on second electric capacity.And this active snubber can absorb peak voltage, and can not consume with the form of heat, thereby can not reduce the efficient of Switching Power Supply.

Description of drawings

Fig. 1 is a kind of structure chart that has the Switching Power Supply of voltage shutoff type buffer of the prior art;

Fig. 2 is the structure chart that has the Switching Power Supply of another kind of buffer in the prior art;

Fig. 3 is self-driven active snubber embodiment one structure chart that is used for Switching Power Supply provided by the invention;

Fig. 4 is self-driven active snubber embodiment two structure charts that are used for Switching Power Supply provided by the invention;

Fig. 5 is the voltage oscillogram of key point among Fig. 4 of the present invention.

Embodiment

For above-mentioned purpose of the present invention, feature and advantage can be become apparent more, the specific embodiment of the present invention is described in detail below in conjunction with accompanying drawing.

Referring to Fig. 3, this figure is self-driven active snubber embodiment one structure chart that is used for Switching Power Supply provided by the invention.

The self-driven active snubber circuit that is used for Switching Power Supply that present embodiment provides comprises: the first terminal, second terminal, first capacitor C 1, second capacitor C 2 and metal-oxide-semiconductor M2;

One end of described first capacitor C 1 connects the first terminal, in the time of in being applied to Switching Power Supply, the first terminal is the end of the connecting line voltage Vin on the former limit of transformer T in the Switching Power Supply, the other end is connected second terminal by the metal-oxide-semiconductor M2 of series connection with second capacitor C 2 successively, in the time of in being applied to Switching Power Supply, second terminal is the other end on the former limit of transformer T in the Switching Power Supply;

The substrate of described metal-oxide-semiconductor M2 and source shorted, grid connects the different name end on the former limit of transformer T.

The self-driven active snubber that the embodiment of the invention provides does not need external drive circuit, because the grid of metal-oxide-semiconductor M2 and source electrode are connected the two ends of second capacitor C 2 respectively, voltage on the C2 provides driving voltage for M2, so metal-oxide-semiconductor M2 can realize self-driven by the voltage on second capacitor C 2.And this active snubber can absorb peak voltage, and can not consume with the form of heat, thereby can not reduce the efficient of Switching Power Supply.

Describe the operation principle of the self-driven active snubber that the embodiment of the invention provides in detail below in conjunction with Fig. 4.

Referring to Fig. 4, this figure is self-driven active snubber embodiment two structure charts that are used for Switching Power Supply provided by the invention.

This circuit also comprises the parasitic body diode D2 of metal-oxide-semiconductor M2, and the anode of the parasitic body diode D2 of described metal-oxide-semiconductor M2 connects the source electrode of described metal-oxide-semiconductor M2, and the negative electrode of the parasitic body diode D2 of described metal-oxide-semiconductor M2 connects the drain electrode of described metal-oxide-semiconductor M2.

This circuit also comprises the parasitic capacitance Cds2 of metal-oxide-semiconductor M2, and the end of the parasitic capacitance Cds2 of described metal-oxide-semiconductor M2 connects the source electrode of described metal-oxide-semiconductor M2, and the other end connects the drain electrode of described metal-oxide-semiconductor M2.

This circuit also comprises the parasitic body diode D1 of mains switch M1, and the anode of the parasitic body diode D1 of described mains switch M1 connects the source electrode of mains switch M1, and the negative electrode of the parasitic body diode D1 of described mains switch M1 connects the drain electrode of mains switch M1.

This circuit also comprises the parasitic capacitance Cds1 of mains switch M1, and the end of the parasitic capacitance Cds1 of described mains switch M1 connects the source electrode of mains switch M1, and the other end connects the drain electrode of mains switch M1.

When mains switch M1 conducting, the grid voltage of metal-oxide-semiconductor M2 will be pulled down to 0.The parasitic body diode D2 of metal-oxide-semiconductor M2 turn-offs, and the voltage at second capacitor C, 2 two ends is dividing potential drops that Vin passes through first capacitor C 1, Cds2 and C2.So the grid of metal-oxide-semiconductor M2 to the voltage Vgs of source electrode can by below formula (1) obtain:

$\mathrm{Vgs}=\mathrm{<figure-callout\; id="1"\; label="Vin"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">Vin</figure-callout>}\frac{1/{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}{1/C_2+1/C_1+1/C_{\mathrm{ds}2}}---\left(1\right)$

In actual applications, the value of C1 will be far longer than the value of Cds2, and when the M1 conducting, the Vgs of M2 almost is 0 like this, and this moment, M2 realized automatically shutting down.

When M1 disconnected, transformer T secondary diode in series 411 was with conducting, and the voltage of M1 drain electrode will equal line voltage Vin and the voltage sum of turning back.The N that the described voltage of turning back is output voltage V out times, N is the turn ratio of former limit of transformer and secondary.The parasitic body diode of M2 is with conducting, and the voltage across poles of C2 can obtain by following formula (2):

$\mathrm{Vgs}=(N\&times;\mathrm{Vout}-\mathrm{Vd})\frac{1/{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">C</figure-callout>}}_1}{1/C_2+1C_1}---\left(2\right)$

Vd in the formula (2) is the voltage of the parasitic body diode of M2.

In actual applications, the value of C1 and C2 can be designed as the requirement of satisfying Vgs.For example, if Vout=5V, N=10 then can design the Vgs that C1=(2/3) * C2 obtains about 10V.

In the moment that M1 disconnects, because the leakage inductance Lm on the former limit of transformer T, the drain voltage of M1 will rise and surpass the voltage of turning back, and the numerical value that surpasses is Vm, and according to law of conservation of energy, this voltage Vm can calculate by following formula (3).

$\mathrm{Vm}=\mathrm{Ip}\sqrt{\frac{L_m}{C_{\mathrm{node}1}}}---\left(3\right)$

Ip is the peak current on the former limit of transformer T, and Cnode1 is the capacitance of drain sum of M1;

When M1 turn-offed, M2 was with conducting; So in the moment that M1 turn-offs, Cnode1 can draw by following formula (4):

${\mathrm{<figure-callout\; id="1"\; label="C\; node"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{node}}=\frac{C_1{C}_2}{{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+C_2}+\mathrm{Cm}+\mathrm{Cds}1---\left(4\right)$

Cm is the parasitic shunt capacitance on the former limit of transformer T.Cds1 is the parasitic capacitance of the drain-to-source of M1.Parameter [C1C2/ (C1+C2)] is the appearance value after C1 and the C2 series connection.

In actual applications, can reasonably select the absolute value of C1 and C2 to satisfy the demand of EMI.

When the electric current of transformer T secondary dropped to 0, the drain voltage of M1 also began to descend, and voltage and line voltage sum drop to line voltage from turning back.Because the drain voltage of described M1 still is higher than line voltage, so metal-oxide-semiconductor M2 conducting still, M1 drain voltage period of oscillation is by the magnetizing inductance and the Cnode1 decision on the former limit of transformer.When the drain voltage of described M1 drops to line voltage when following, metal-oxide-semiconductor M2 will turn-off, and will be recharged at the parasitic capacitance Cnode2 of the drain node of M1, and the value of Cnode2 charging can pass through formula (5) calculating.

$C_{\mathrm{node}2}=\frac{1}{1/{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">C</figure-callout>}}_1+1/C_2+1/C_{\mathrm{ds}2}}\mathrm{Cm}+\mathrm{<figure-callout\; id="1"\; label="Cds"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">Cds</figure-callout>}1\&ap;\mathrm{Cm}+\mathrm{<figure-callout\; id="1"\; label="Cds"\; filenames="HDA0000051671280000022.png"\; state="\{\{state\}\}">Cds</figure-callout>}1+\mathrm{Cds}2---\left(5\right)$

Cds2 compares very little with C1 with C2.

When the drain voltage of described M1 equaled 0, energy was stored in the former limit inductance of transformer T with the form of electric current.Then owing to continuous induced current, the drain voltage of described M1 will descend.When induced current is reduced to 0, the drain voltage of described M1 can drop to its minimum Vlow, if do not consider thermal losses, Vlow can calculate by following formula (7).

$V_{\mathrm{low}}=V_{\mathrm{in}}-N*V_{\mathrm{out}}\sqrt{\frac{C_{\mathrm{node}1}}{C_{\mathrm{mode}2}}}---\left(6\right)$

Can obtain the voltage of several important node among Fig. 4 by above the separate equations.Referring to Fig. 5, this figure is the voltage oscillogram of key node among Fig. 4.

The mode of operation of Fig. 5 correspondence is the quasi-resonance pattern.

Mains switch is with conducting when the voltage of M1 drops to its minimum voltage.

With reference to figure 5, ton is the duration of M1 conducting.The voltage Vgs2 of metal-oxide-semiconductor M2 almost is 0 in the ton time period among Fig. 4.In the toff time period, the voltage Vgs2 of described metal-oxide-semiconductor M2 will raise and then conducting metal-oxide-semiconductor M2, and this moment, Cnode1 absorbed the leakage energy.

Because described big capacitor C node1, due to voltage spikes will reduce, and electromagnetic interference problem also will be enhanced.

In time, owing to there is not electric current to flow through the secondary diode 411 of transformer T, the drain voltage Vc of described mains switch M1 begins to descend, and described big capacitor C node1 begins discharge at t1.When Vc drops to line voltage Vin when following, Vgs2 will drop to 0, and the metal-oxide-semiconductor M2 among Fig. 4 will turn-off, and Cnode1 will be reduced to Cnode2.If capacitor C among Fig. 41 and C2 are enough big, voltage Vc will drop to 0, when the minimum Vlow of Vc at it, mains switch M1 will conducting, because M1 conducting when the drain voltage of M1 is minimum, the switching loss of correspondence is less during the M1 conducting like this, can reduce loss like this.

M1 conducting during at first low ebb of Vc or at second low ebb reduces switching loss on the basis of mode of operation.

In sum, the self-driven active snubber circuit that the embodiment of the invention provides not only can reduce switching loss, and can not cause energy loss, thereby has improved the efficient of power supply.

Need to prove that the present invention also provides a kind of inverse-excitation type switch power-supply with above-described self-driven active snubber, comprising: self-driven active snubber, mains switch, transformer, switch power controller;

The first terminal of described self-driven active snubber connects an end of the former limit of transformer connecting line voltage in the Switching Power Supply, and second terminal connects the other end on the former limit of transformer in the described Switching Power Supply;

Described switch power controller is used to export pwm pulse, to control the on off state of described mains switch.

The above only is preferred embodiment of the present invention, is not the present invention is done any pro forma restriction.Though the present invention discloses as above with preferred embodiment, yet be not in order to limit the present invention.Any those of ordinary skill in the art, do not breaking away under the technical solution of the present invention scope situation, all can utilize the method and the technology contents of above-mentioned announcement that technical solution of the present invention is made many possible changes and modification, or be revised as the equivalent embodiment of equivalent variations.Therefore, every content that does not break away from technical solution of the present invention, all still belongs in the scope of technical solution of the present invention protection any simple modification, equivalent variations and modification that above embodiment did according to technical spirit of the present invention.

Claims (9)

1. a self-driven active snubber is characterized in that, comprising: the first terminal, second terminal, first electric capacity, second electric capacity and metal-oxide-semiconductor;

One end of described first electric capacity connects the first terminal, and the other end is connected second terminal by the metal-oxide-semiconductor of series connection with second electric capacity successively;

The substrate of described metal-oxide-semiconductor and source shorted, grid connect second terminal.

2. self-driven active snubber according to claim 1, it is characterized in that, the parasitic body diode that also comprises metal-oxide-semiconductor, the anode of the parasitic body diode of described metal-oxide-semiconductor connects the source electrode of described metal-oxide-semiconductor, and the negative electrode of the parasitic body diode of described metal-oxide-semiconductor connects the drain electrode of described metal-oxide-semiconductor.

3. self-driven active snubber according to claim 2 is characterized in that, also comprises the parasitic capacitance of metal-oxide-semiconductor, and an end of the parasitic capacitance of described metal-oxide-semiconductor connects the source electrode of described metal-oxide-semiconductor, and the other end connects the drain electrode of described metal-oxide-semiconductor.

4. self-driven active snubber according to claim 1 is characterized in that, described the first terminal connects an end of the former limit of transformer connecting line voltage in the Switching Power Supply, and described second terminal connects the other end on the former limit of transformer in the described Switching Power Supply.

5. according to each described self-driven active snubber of claim 1-4, it is characterized in that described metal-oxide-semiconductor is the NMOS pipe.

6. the inverse-excitation type switch power-supply with the described self-driven active snubber of claim 1 is characterized in that, comprising: self-driven active snubber, mains switch, transformer and switch power controller;

The first terminal of described self-driven active snubber connects an end of the former limit of transformer connecting line voltage in the Switching Power Supply, and second terminal connects the other end on the former limit of transformer in the described Switching Power Supply;

Described switch power controller is used to export pwm pulse, to control the on off state of described mains switch.

7. inverse-excitation type switch power-supply according to claim 6, it is characterized in that, the parasitic body diode that also comprises mains switch, the anode of the parasitic body diode of described mains switch connects the source electrode of mains switch, and the negative electrode of the parasitic body diode of described mains switch connects the drain electrode of mains switch.

8. inverse-excitation type switch power-supply according to claim 7 is characterized in that, also comprises the parasitic capacitance of mains switch, and an end of the parasitic capacitance of described mains switch connects the source electrode of mains switch, and the other end connects the drain electrode of mains switch.

9. according to each described inverse-excitation type switch power-supply of claim 6-8, it is characterized in that described metal-oxide-semiconductor is the NMOS pipe.

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