CN100431252C - Flyback power converter capable of switching zero potential in critical mode - Google Patents

Abstract

The present invention relates to a flyback power converter capable of carrying out zero potential switchover in a critical mode, which comprises a transformer, wherein at least one series circuit comprising a capacitor and a primary side power switch is connected to a primary winding of the transformer in parallel. When a secondary side power switch (diode) connected to a secondary winding of the transformer in series is switched on, the primary side power switch is also switched on, so the energy is stored into the capacitor by the primary winding. When the secondary side power switch is converted into an off state from an on state, the primary side power switch is still switched on for a period to enable the capacitor to charge the primary winding until the charged energy of the capacitor is sufficient for making a main power connected to the primary winding in series reach zero potential switchover, and then, the primary side power switch is switched; the main power switch completes the zero potential switchover. In this way, the cost is not increased and the flyback power converter has the advantages of high efficiency, high switchover frequency, low noise, etc.

Description

Can under critical conduction mode, carry out the flyback power converter that zero potential is switched

Technical field

The invention relates to a kind of flyback power converter, refer to a kind of flyback power converter that can under critical conduction mode, carry out the zero potential switching especially.

Background technology

Traditionally, operate in the power converter (Converter) under the critical conduction mode (Boundary mode), can be a ring chokes power converter (Ringing Choke Converter, be called for short RCC), consult shown in Figure 1, it is the circuit diagram of the ring chokes power converter of a standard, this ring chokes power converter is owing to operate under the critical conduction mode, therefore, when the energy of the transformer T1 on this ring chokes power converter on it, its secondary winding is given in release, and to make the output voltage of its primary side be V ₀The time, the voltage of the elementary winding of this transformer TI promptly equals V ₀N, wherein n is the turn ratio between this elementary winding and secondary winding, that is the terminal voltage V of the power switch Q1 on it _CEEqual the voltage V of input voltage vin and elementary winding ₀The summation of n, i.e. Vin+V ₀N, this energy are stored on the parasitic capacitance in its loop with voltage form.

In the traditional ring chokes power converter of this kind, remaining energy in this transformer T1, be not enough to keep when making the diode D1 conducting that this secondary winding side connected, this diode D1 promptly becomes cut-off state, and make parasitic capacitance and inductance on the loop produce resonance, at this moment, if this power switch Q1 is not switched once more, at the terminal voltage V of power switch Q1 _CECan present with Vin is sine wave (sin wave) concussion at center, and its amplitude equals V ₀N is subjected to the influence of impedance loop, and this sine wave can present exponential decay, consults this ring chokes power converter that is shown in Figure 2 and operates in oscillogram under the critical conduction mode, wherein this terminal voltage V _CESine wave (sin wave) concussion shown in the dotted line of Fig. 2, the terminal voltage V of this power switch Q1 _CEMinimum equals Vin-V ₀N.

Therefore, by the driving road that suitably designs this power switch Q1, with terminal voltage V at this power switch Q1 _CEDuring for minimum, drive this power switch Q1, then comply with the formula of following switch cost:

$\frac{C_S{\left(V_{\mathrm{CE}}\right)}^2}{2}\·f_0,$

Wherein Cs is the equivalent stray capacitance on the loop, f ₀Be the frequency of operation of this power switch Q1, can know and learn, because the terminal voltage V of this power switch Q1 _CEReduce, the switch cost of this power switch Q1 also thereby reduce many.Yet, owing to the traditional ring chokes power converter of this kind operates under the critical conduction mode, so the frequency of operation f of this power switch Q1 ₀, higher in input voltage vin, output loading is healed when light, will become higher, so the formula of complying with aforementioned switch cost is as can be known, this power switch Q1 still can produce suitable switch cost, therefore, at frequency of operation f ₀Heal when high, it is more surprising that its switch cost also will become.

In view of this, reduce to zero for making this kind operate in the switch cost that the traditional ring chokes power converter under the critical conduction mode produced, the foregoing problems that under the high-frequency operation state, is produced with effective solution, the design of power converter and manufacturer must finish following action when the control loop of this power converter of design:

(1) on the collector electrode and emitter of this power switch Q1 of this ring chokes power converter, a diode in parallel, maybe this power switch Q1 is replaced with a power switch with parasitic diode, as: metal oxide semiconductor field effect transistor (Metal-Oxid-Semiconductor Field-Effect Transistor, be called for short MOSFET), with the terminal voltage VCE that makes this power switch Q1 at resonance after zero potential, can be clamped at this current potential by this diode or parasitic diode, switch to carry out zero potential.

(2), be designed to make aforesaid sine wave that (amplitude of sinwave concussion equals Vin, even the reflected voltage also on this elementary winding is greater than Vin, so that the terminal voltage V of this power switch Q1 with the circuit of this ring chokes power converter _CEMinimum be zero potential, and when reaching zero potential, switch.

The aforementioned practice the cost that must pay, it is the pressure drop that can produce 2Vin on this power switch Q1, and force the designer to select high withstand voltage switch element for use, because the cost and the resistance value of the withstand voltage switch element of this height are all high, so practice, not only increased the cost of manufacture of this ring chokes power converter, also increased the conducting loss of this switch element, it is not desirable to the greatest extent to cause its overall efficiency, therefore, how under the condition that does not increase the loss of cost of manufacture and switch conduction, there is skill ground that the power switch Q1 circuit design of this power converter is become, under the various load states of critical conduction mode, all can carry out zero potential and switch, promptly become the important topic that each relevant design and manufacturer's desire solve.

Summary of the invention

Because traditional ring chokes power converter operates under the critical conduction mode, will be higher because of frequency of operation, cause the switch cost of its power switch high problem that heals, the inventor is at this, work out a kind of flyback power converter that can under critical conduction mode, carry out the zero potential switching, a kind of flyback power converter that can under critical conduction mode, carry out the zero potential switching, this flyback power converter comprises a transformer, be parallel with on the elementary winding of this transformer at least by a capacitor and the formed series connection circuit of a primary side power switch, when a primary side power switch (the can be a diode) conducting of being connected on this Secondary winding of transformer, this primary side power switch also is switched on, make this elementary winding with store energy to this capacitor, when this primary side power switch becomes cut-off state by conducting state, this primary side power switch will a bit of time of conducting, to make this capacitor that this elementary winding is charged, the energy that is recharged up to this transformer, reach when being enough to make a master power switch of being connected on this elementary winding to reach the condition of zero potential switching, switch this primary side power switch, and make this master power switch finish the zero potential switching.

A purpose of the present invention, be to utilize this transformer under critical conduction mode, discharged the last natural resonance phenomenon that produces of energy, the simple control loop of arranging in pairs or groups again, electric charge on this master power switch is taken away, to make this master power switch under the various load states of critical conduction mode, carry out zero potential and to switch, significantly reduce the switch cost of this master power switch.

Another object of the present invention, be under the various load states under critical conduction mode, make the operating frequency of this main electronic switch be limited in the preset range, and effective voltage peak of causing of suppressing because of leakage inductance, make this flyback power converter under the situation that does not increase cost, to possess advantages such as high efficiency, high switching frequency and low noise.

The invention provides a kind of flyback power converter that can under critical conduction mode, carry out the zero potential switching, it is characterized in that described flyback power converter comprises:

One transformer is made up of an elementary winding and secondary winding;

One series connection circuit, be in series by an at least one auxiliary capacitor and a primary side power switch, described series circuit is connected in parallel on the described elementary winding, and the connected node between wherein said primary side power switch and the described elementary winding is connected to an end of an input voltage;

One primary side power switch is connected on the described secondary winding;

One master power switch, an end of described master power switch are connected on the connected node between described elementary winding and the described auxiliary capacitor, and the other end of described master power switch is connected to the other end of described input voltage;

At least one drive circuit is connected to the junction of described master power switch and described auxiliary capacitor, in order to detecting the magnitude of voltage of described junction, and according to described magnitude of voltage, sends drive signal, switches described primary side power switch and described master power switch respectively;

During described primary side power switch conducting, described primary side power switch is switched into conducting state, described elementary winding with store energy to described auxiliary capacitor, when described primary side power switch when conducting state switches to cut-off state, described primary side power switch is with a bit of time of conducting, to make described auxiliary capacitor that described elementary winding is charged, the energy that is recharged up to described transformer, reach when being enough to make described master power switch to reach the condition of zero potential switching, by described primary side power switch, and the described master power switch of conducting.

Description of drawings

Figure 1 shows that the circuit diagram of a traditional ring chokes power converter;

This ring chokes power converter that Figure 2 shows that Fig. 1 operates in critical conduction mode following time, the terminal voltage V of its power switch Q1 _CEThe waveform schematic diagram;

Figure 3 shows that the circuit diagram of flyback power converter of the present invention;

This flyback power converter that Figure 4 shows that Fig. 3 operates in critical conduction mode following time, the terminal voltage V of its master power switch SW1 _SW1Waveform schematic diagram four periods;

This flyback power converter that Fig. 5 (a)～5 (d) is depicted as Fig. 3 is respectively at the schematic equivalent circuits of four periods;

Figure 6 shows that the circuit diagram of a specific embodiment of the present invention;

Figure 7 shows that the voltage waveform view of each element in the specific embodiment of the invention of Fig. 6.

Symbol description:

Transformer～TI

Elementary winding～N _P

Secondary winding～N _S

Input voltage～Vin

Output voltage～V ₀

Terminal voltage～V _CE, V _SW1, Vds1

Input voltage filter capacitor～Cin

Output voltage filter capacitor～C ₀

Drive circuit～DR

Master power switch～SW1

Primary side power switch～SW2

Primary side power switch～SW3

Power switch～Q1, Q2

Stray capacitance～Cs

Auxiliary capacitor～Ca

Parasitic capacitance～Cs

Diode～D1, D _SW1

Embodiment

In a preferred embodiment of the present invention, consult shown in Figure 3, be one to operate in the circuit diagram of the flyback power converter under the critical conduction mode, this power converter comprises transformer T1, an input voltage filter capacitor Cin, an auxiliary capacitor Ca, one drive circuit DR, three power switch SW1, SW2, SW3 and output voltage filter capacitor C ₀Deng element, wherein this transformer T1 mainly is in order to store and to discharge electric energy, to which is provided with an elementary winding N _PAnd level winding N _S, the turn ratio N of this winding respectively _P/ N _SEqual n, the inductance value on it is respectively L _PAnd L _S, it winds the line mark then as shown in Figure 3, the elementary winding N of this of this transformer T1 _PAn end be to be connected with the positive pole of this input voltage filter capacitor Cin, it is held in addition then is to be connected with this master power switch SW1, the both positive and negative polarity of this input voltage filter capacitor Cin is to be connected across on the both positive and negative polarity of an input voltage vin, the end of this primary side power switch SW2 is to be connected with the positive pole of this input voltage filter capacitor Cin, its other end then is to be connected with this auxiliary capacitor Ca, the other end of this auxiliary capacitor Ca then is connected with this master power switch SW1, the other end of this master power switch SW1 then is connected to the negative pole of this input voltage filter capacitor Cin, make this input voltage filter capacitor Cin that one stable input voltage can be provided, give this transformer T1 and use.In addition, be parallel with a diode D on this master power switch SW1 _SW1, this diode D _SW1P end be the negative pole that is connected to this input voltage filter capacitor Cin, its N end then is to be connected on this auxiliary capacitor Ca, this drive circuit DR is the junction that is connected to this master power switch SW1 and this auxiliary capacitor Ca, with the magnitude of voltage by this junction of detecting, decision is by the opportunity of this primary side power switch SW2.

In this embodiment, this secondary winding N _SAn end be to be connected to an output voltage filter capacitor C ₀Negative level, its in addition end then be connected with the anode of this primary side power switch SW3, the negative terminal of this primary side power switch SW3 then with this output voltage filter capacitor C ₀Positive pole be connected, make this output voltage filter capacitor C ₀One stable VD V can be provided ₀, give the load of institute's cross-over connection on the output.

When this flyback power converter operated in critical conduction mode, this transformer T1 can discharge the energy on it and give this secondary winding N _S, make that output voltage is V ₀, at this moment, the voltage of this elementary winding promptly equals V ₀N, cutting this electric energy is to be stored on the parasitic capacitance in this auxiliary capacitor Ca and loop, the remaining energy of accumulating in this transformer T1 is not enough to make this secondary winding N _SWhen this primary side power switch SW3 of side keeps conducting, this primary side power switch SW3 is promptly by conducting state, be transformed into cut-off state, simultaneously, this primary side power switch SW2 but still keeps conducting, make the elementary winding generation of this parasitic capacitance and auxiliary capacitor Ca and this resonance, and begin originally to be accumulated in the energy on this auxiliary capacitor Ca and the parasitic capacitance, to this elementary winding N of this transformer T1 _PCharge this elementary winding N _PThe energy that is recharged reaches when being enough to make this master power switch SW1 (promptly main electronic switch) to carry out the condition of zero potential switching, just makes this primary side power switch SW2 stop conducting, and begins and will be stored in this elementary winding N _POn energy return to spue and, at this moment because this primary side power switch SW2 ends, the energy of telling of dying back will all be stored on the parasitic capacitance in loop, the resonance behavior makes the change in voltage on the parasitic capacitance strengthen, and makes the terminal voltage of this master power switch SW1 cross a Vf, makes this diode D _SW1Conducting, and make this master power switch SW1 when its terminal voltage equals zero, finish zero potential and to switch.If this diode D _SW1Do not exist, then this resonance behavior meeting is that the center continues to shake with Vin, as D among Fig. 4 _SW1Dotted line shown in.

Relatively the circuit of the present invention and traditional ring chokes power converter can be known and learns, the present invention after this primary side power switch SW3 ends, the elementary winding N of this of this transformer T1 _POn the resonance that produced, because of many existence of this auxiliary capacitor Ca, make that its L-C resonance is slack-off, therefore during its resonance action, this master power switch SW1 can't be driven, so whole operation frequency of flyback power converter of the present invention, with thus the restriction of highest frequency is arranged, when output loading lightens, though frequency of operation increases, also unlikely circuit as ring chokes power converter, with frequency of operation draw too high.

Consulting shown in Figure 4ly, is that flyback power converter of the present invention operates in the oscillogram under the critical conduction mode, and wherein DR1 is that this drive circuit DR sends a drive signal of giving this master power switch SW1, V _SW1It is the terminal voltage at this master power switch SW1 two ends, DR2 is that this drive circuit DR sends a drive signal of giving this primary side power switch SW2, the present invention is the convenient operation of explaining this flyback power converter, in the special switching cycle with this master power switch SW1, the terminal voltage V of these drive signals DR1, DR2 and this master power switch SW1 _SW1Waveform separation become 4 periods, and cooperate the equivalent circuit diagram of flyback power converter of the present invention in these 4 periods, consult shown in Fig. 5 (a)～Fig. 5 (d), describe in detail respectively should the equivalence circuit as follows: (1) t0～t1 period in running behavior that respectively should the period:

Consult the equivalent electric circuit shown in Fig. 5 (a), wherein the parasitic capacitance Cs that is comprised on the element such as this transformer T1 and each power switch SW1, SW2 and SW3 is to be indicated in the elementary winding N of cross-over connection in this transformer T1 equivalently _POn the circuit at two ends, and in should the loop of equivalence circuit diagram, solid line partly be to represent the circuit of working in the circuit, and dotted line is partly then represented the circuit of not working in the circuit.Before t0, this primary side power switch SW2 and this primary side power switch SW3 are conducting state, and this transformer T1 is in energy-delivering state, and the voltage of this auxiliary capacitor Ca and this parasitic capacitance Cs equals output voltage V ₀Be reflected in the voltage on the elementary winding

During t=t0, because remaining energy in this transformer T1 is not enough to keep the conducting of this primary side power switch SW3, so this primary side power switch SW3 becomes cut-off state; At t0-t1 in the period, this auxiliary capacitor Ca and this parasitic capacitance Cs will with the elementary winding N of this transformer T1 _PInductance L _PProduce resonance, and the energy on this auxiliary capacitor Cs is sent to this elementary winding N _PInductance L _P(2) t1～t2 period:

Consult the equivalent electric circuit shown in Fig. 5 (b), this period is to make this master power switch SW1 form the zero potential conducting crucial period on opportunity, and when time t1, often this drive circuit DR detects this elementary winding N _PThe voltage at two ends (that is the voltage at this auxiliary capacitor Ca two ends) is reduced to a predetermined extent, promptly this primary side power switch SW2 is sent a drive signal DR2, make this primary side power switch SW2 end, make this auxiliary capacitor Ca become open-circuit condition, only this parasitic capacitance Cs can continue and this elementary winding N _PInductance L _PResonance.

Because, before time t1, this auxiliary capacitor Ca and this parasitic capacitance C _SOn energy passed to this elementary winding N nearly all _PInductance L _PSo, when time t1, take turns to this elementary winding N _PInductance L _PGive electric capacity with energy, at this moment, because the electric capacity in the resonant element has lacked this auxiliary capacitor Ca, so this elementary winding N _PInductance L _PEnergy, will the voltage on this parasitic capacitance Cs be increased fast, if the voltage quantities that is produced on this parasitic capacitance Cs is called V1, then according to the following relationship formula:

$\frac{1}{2}\&CenterDot;(\mathrm{Ca}+\mathrm{Cs})\&CenterDot;{\left(\frac{V_0}{n}\right)}^2\&DoubleRightArrow;\frac{1}{2}\&CenterDot;\mathrm{Lp}\&CenterDot;{i_{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="C20041002941800141.png,C20041002941800191.png"\; state="\{\{state\}\}">p</figure-callout>}}}^2\&DoubleRightArrow;\frac{1}{2}\&CenterDot;\mathrm{Cs}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C20041002941800141.png,C20041002941800162.png"\; state="\{\{state\}\}">V</figure-callout>}1}^2,$

Voltage quantities on this parasitic capacitance Cs $V$ $1=\frac{V_0}{n}\&CenterDot;\sqrt{1+\frac{\mathrm{Ca}}{\mathrm{Cs}}},$ Because, desire to carry out the key that zero potential is switched, promptly make V1＞Vin, that is:

$\frac{V_0}{n}\&CenterDot;\sqrt{1+\frac{\mathrm{Ca}}{\mathrm{Cs}}}>\mathrm{Vin}$

Therefore, as long as selected this auxiliary capacitor Ca value is enough big, the terminal voltage of this master power switch SW1 will arrive zero potential by resonance.

(3) t2～t3 period:

Consult the equivalent electric circuit shown in Fig. 5 (c), when t=t2, the terminal voltage of this master power switch SW1 will drop to and be lower than a Vf, make this master power switch SW1 go up diode connected in parallel D _SW1Conducting, the terminal voltage of master power switch SW1 therefore by nip at-Vf, at this moment, the top of promptly finishing the zero potential switching of this master power switch SW1 is equipped with action, this drive circuit DR will send a drive signal DR1 to this master power switch SW1, make this master power switch SW1 conducting, to finish the work that zero potential is switched.In addition, in the period, this transformer T1 is the beginning storage power at t2～t3.

(4) t3～t0 period:

Consult the equivalent electric circuit shown in Fig. 5 (d), when t=t3, this drive circuit DR will to this first and primary side power switch SW1, SW2 send a drive signal DR1, DR2 respectively, end to make this master power switch SW1, and make this primary side power switch SW2 conducting.At t3～t0 in the period, this transformer T1 begins to discharge the energy of being accumulated, when t=t0, this master power switch SW1 is in cut-off state, and this transformer T1 begins to release energy, with the energy of being accumulated in it, this auxiliary capacitor Ca and this parasitic capacitance Cs are given in release, and the voltage of this transformer T1 also thereby turn to makes this primary side power switch SW3 conducting, at this moment, because this drive circuit DR detects the elementary winding N of this transformer T1 _POn voltage V _NP, turn negative number to positive number, so this drive circuit DR will send a drive signal DR2 to this primary side power switch SW2, make its conducting, and the voltage on capacitor C a and this parasitic capacitance Cs also will equal output voltage V ₀See through the reflected voltage V of this transformer T1 ₀/ n.

Consult shown in Figure 6, it is a specific embodiment of the present invention, in this embodiment, this master power switch SW1 and this primary side power switch SW2 that reaches of the present invention, can be respectively with a metal oxide semiconductor field effect transistor (Metal-Oxid-Semiconductor Field-EffectTransistor, be called for short MOSFET) Q1 and Q2 replacement, this primary side power switch SW3 that reaches of the present invention, then can replace by a diode D1, when this embodiment is carried out actual test, can obtain the waveform of each element on its circuit, as shown in Figure 7, wherein can know and learn, when the terminal voltage Vds1 of this master power switch Q1 drops to when approximating input voltage vin (in this embodiment from peak, the input voltage vin value approximates 350V), it is the state that is slow decline, but when this primary side power switch Q2 ends, be that its drive signal Vgs2 is when becoming electronegative potential by high potential, the terminal voltage Vds1 of this master power switch Q1 promptly drops to fast and approximates 0V, at this moment, its drive signal Vgs1 becomes high potential by electronegative potential immediately, finishes the action that zero potential is switched to drive this master power switch Q1.

According to the above as can be known, flyback power parallel operation of the present invention system is the natural resonance phenomenon of utilizing this transformer to be produced in the back that the releases energy simple control loop of arranging in pairs or groups again, take away with the electric charge on will this main electronic switch, can make this main electronic switch under the various load states of critical conduction mode, carrying out zero potential switches, not only significantly reduced the switch cost of this main electronic switch, and make its operating frequency be limited in the preset range, and effective voltage peak of causing of suppressing because of leakage inductance, make this flyback power converter under the situation that does not increase cost, to possess high efficiency, advantages such as high switching frequency and low noise.

Claims (9)

1, a kind of flyback power converter that can carry out the zero potential switching under critical conduction mode is characterized in that described flyback power converter comprises:

One transformer is made up of an elementary winding and secondary winding;

One series connection circuit, be in series by an at least one auxiliary capacitor and a primary side power switch, described series circuit is connected in parallel on the described elementary winding, and the connected node between wherein said primary side power switch and the described elementary winding is connected to an end of an input voltage;

One primary side power switch is connected on the described secondary winding;

One master power switch, an end of described master power switch are connected on the connected node between described elementary winding and the described auxiliary capacitor, and the other end of described master power switch is connected to the other end of described input voltage;

At least one drive circuit is connected to the junction of described master power switch and described auxiliary capacitor, in order to detecting the magnitude of voltage of described junction, and according to described magnitude of voltage, sends drive signal, switches described primary side power switch and described master power switch respectively;

During described primary side power switch conducting, described primary side power switch is switched into conducting state, described elementary winding with store energy to described auxiliary capacitor, when described primary side power switch when conducting state switches to cut-off state, described primary side power switch is with a bit of time of conducting, to make described auxiliary capacitor that described elementary winding is charged, the energy that is recharged up to described transformer, reach when being enough to make described master power switch to reach the condition of zero potential switching, by described primary side power switch, and the described master power switch of conducting.

2, flyback power converter according to claim 1 is characterized in that: also comprise a diode, described diode is connected in parallel on the described master power switch.

3, flyback power converter according to claim 2, it is characterized in that: also comprise an input voltage filter capacitor, one positive pole of described input voltage filter capacitor is connected to an end of described input voltage, its negative pole is connected to the other end of described master power switch, and the both positive and negative polarity of described input voltage filter capacitor is connected across on the both positive and negative polarity of described input voltage.

4, flyback power converter according to claim 3, it is characterized in that: the connected node between described primary side power switch and the elementary winding is connected to the positive pole of described input voltage filter capacitor, and the other end of described primary side power switch is connected to described auxiliary capacitor.

5, flyback power converter according to claim 4 is characterized in that: the positive pole of described diode is connected to the negative pole of described input voltage filter capacitor, and its negative pole is connected to described auxiliary capacitor.

6, flyback power converter according to claim 5 is characterized in that: described master power switch is a metal oxide semiconductor field effect transistor.

7, flyback power converter according to claim 5 is characterized in that: described primary side power switch is a metal oxide semiconductor field effect transistor.

8, flyback power converter according to claim 1, it is characterized in that: also comprise an output voltage filter capacitor, the negative pole of described output voltage filter capacitor is connected to an end of described secondary winding, its positive pole is connected to described primary side power switch, and the both positive and negative polarity of described output voltage filter capacitor is connected across on the both positive and negative polarity of described output voltage.

9, flyback power converter according to claim 8 is characterized in that: described primary side power switch is a diode.

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