CN102891599B - Method and circuit for improving light load efficiency of direct current-direct current (DC-DC) converter - Google Patents

Abstract

The invention relates to a method and a circuit for improving the light load efficiency of a direct current-direct current (DC-DC) converter. By the technical scheme, according to the method for improving the light load efficiency of the DC-DC converter, a synchronous switching tube and a main switching tube which is connected with a load resistor and an input voltage source and is used for adjusting a connection state between the load resistor and the input voltage source are involved, wherein the gate end of the main switching tube and the gate end of the synchronous switching tube are connected with a driving circuit. The method is characterized in that the driving circuit adjusts a width to length ratio of corresponding conductive trenches of the main switching tube and/or the synchronous switching tube according to load current Iout and the voltage of the input voltage source, so that the increase amount of the conduction resistance loss of the main switching tube is smaller than the reduction amount of the driving loss of the main switching tube and/or the increase amount of the conduction resistance loss of the synchronous switching tube is smaller than the reduction amount of the driving loss of the synchronous switching tube, and the output efficiency of the load resistor is improved. By the method, the light load efficiency is improved; the circuit is simple in structure; the use cost is reduced; and the method and the circuit are safe and reliable.

Description

Improve method and the circuit of DC-DC converter light-load efficiency

Technical field

The present invention relates to a kind of method and the circuit that improve DC-DC converter light-load efficiency, specifically a kind of method and circuit being improved DC-DC converter light-load efficiency by on-off switching tube partially conductive passage, belongs to the technical field of DC-DC converter.

Background technology

In day by day universal portable electronic products, mostly adopt powered battery, the rapid expansion of limited battery capacity and product function proposes more and more higher requirement to the efficiency of power management, and integrated synchronous BUCK type DC-DC converter can keep very high efficiency within the scope of very wide input and output voltage, it is made to become first-selected Power Management Devices in a lot of occasion.

BUCK type DC-DC converter has three kinds of control models when underloading, simply can be divided into and force continuous mode, jump pulse pattern, burst mode.Force the electric current two-way flow of continuous mode, efficiency is minimum, and ripple is minimum.The time being detected the burst mode switching tube work of output voltage by hysteresis comparator is short, and efficiency is high, and ripple is maximum.Jump pulse work pattern is in DCM pattern and some pulses are gone in jumping, and efficiency and ripple are between above-mentioned two kinds of patterns.Above three kinds respectively have pluses and minuses, and different application can adopt different selections.

Summary of the invention

The object of the invention is to overcome the deficiencies in the prior art, provide a kind of method and the circuit that improve DC-DC converter light-load efficiency, it improves light-load efficiency, and implementation structure is simple, reduces use cost, safe and reliable.

According to technical scheme provided by the invention, the method of described raising DC-DC converter light-load efficiency, comprise synchro switch pipe and for connecting load resistance and input voltage source and the main switch of regulating load resistance and input voltage source connection status, the gate terminal of described main switch and the gate terminal of synchro switch pipe are all connected with drive circuit; It is characterized in that: described drive circuit is according to the breadth length ratio of the corresponding conducting channel of the voltage-regulation main switch of load current Iout, input voltage source and/or synchro switch pipe, being less than main switch to make the loss recruitment of main switch conducting resistance drives the reduction of loss and/or the loss recruitment of synchro switch pipe conducting resistance to be less than the reduction of synchro switch pipe driving loss, improves the delivery efficiency to load resistance.

Described drive circuit comprises current threshold setting module, the described output of current threshold setting module is connected with the end of oppisite phase of comparator, the in-phase end input load electric current I out of comparator, the output of comparator is connected with the first controller and second controller, the described output of the first controller is connected with the gate terminal of main switch, and the output of described second controller is connected with the gate terminal of synchro switch pipe.

Described drive circuit regulates the breadth length ratio of the conducting channel of main switch, when making the loss recruitment of main switch conducting resistance be less than the decrease of main switch driving loss, obtains

$I_{\mathrm{OUT}}<\sqrt{k*\frac{C_{\mathrm{GS}1}*V_{\mathrm{GS}}*V_{\mathrm{IN}}*F_{\mathrm{SW}}}{R_{Q1}*D}}$

Wherein, k represents proportionality coefficient, 0<k≤1, C _gS1represent the parasitic grid source electric capacity in main switch, V _gSrepresent gate source voltage, F _sWrepresent operating frequency, R _q1for the conducting resistance of main switch, D are duty ratio, V _iNrepresent the magnitude of voltage of input voltage source.

Described first controller comprises height and turns low level shift unit, with door and lowly turn high level shift unit; Described height turns low level shift unit and is connected with an input of door, the output of comparator is connected with another input of door, be connected with the low high level shift unit that turns with the output of door, the gate terminal of the described low output and main switch that turn high level shift unit is connected.

A kind of circuit improving DC-DC converter light-load efficiency, comprise synchro switch pipe and for connecting load resistance and input voltage source and the main switch of regulating load resistance and input voltage source connection status, the gate terminal of described main switch and the gate terminal of synchro switch pipe are all connected with drive circuit; The drain electrode end of synchro switch pipe is connected with the source terminal of main switch, and the drain electrode end of main switch is connected with one end of input voltage source, and the other end of input voltage source is connected with the source terminal of synchro switch pipe; The drain electrode end of synchro switch pipe is connected with load resistance by energy storage inductor; Described drive circuit is according to the breadth length ratio of the corresponding conducting channel of the voltage-regulation main switch of load current Iout, input voltage source and/or synchro switch pipe, being less than main switch to make the loss recruitment of main switch conducting resistance drives the reduction of loss and/or the loss recruitment of synchro switch pipe conducting resistance to be less than the reduction of synchro switch pipe driving loss, improves the delivery efficiency to load resistance.

Described drive circuit comprises current threshold setting module, the described output of current threshold setting module is connected with the end of oppisite phase of comparator, the in-phase end input load electric current I out of comparator, the output of comparator is connected with the first controller and second controller, the described output of the first controller is connected with the gate terminal of main switch, and the output of described second controller is connected with the gate terminal of synchro switch pipe.

Described first controller comprises height and turns low level shift unit, with door and lowly turn high level shift unit; Described height turns low level shift unit and is connected with an input of door, the output of comparator is connected with another input of door, be connected with the low high level shift unit that turns with the output of door, the gate terminal of the described low output and main switch that turn high level shift unit is connected.

The two ends of described load resistance are parallel with filter branch, the capacitor equivalent series resistance that described filter branch comprises filter capacitor and connects with described filter capacitor.

Advantage of the present invention: drive circuit is connected with the gate terminal of main switch and the gate terminal of synchro switch pipe, described drive circuit is according to load current, the breadth length ratio of the voltage-regulation main switch of input voltage source VIN and/or the corresponding conducting channel of synchro switch pipe, being less than main switch to make the loss recruitment of main switch conducting resistance drives the reduction of loss and/or the loss recruitment of synchro switch pipe conducting resistance to be less than the reduction of synchro switch pipe driving loss, improve the delivery efficiency to load resistance, implementation structure is simple, reduce use cost, safe and reliable.

Accompanying drawing explanation

Fig. 1 is the topological structure schematic diagram of existing synchronous rectification Buck type DC-DC converter.

Fig. 2 is existing PWM control Buck type DC-DC converter structure principle chart.

Fig. 3 is the schematic diagram of DC-DC converter of the present invention.

Fig. 4 is the schematic diagram of the present invention first controller.

Fig. 5 is the schematic diagram of loss of the present invention with load variations.

Embodiment

Below in conjunction with concrete drawings and Examples, the invention will be further described.

As shown in Figure 1: be the topological structure of synchronous rectification Buck type dc-dc, wherein going up pipe Q1 is main switch, and lower pipe Q2 is synchro switch pipe, and L is energy storage inductor, and C is filter capacitor, R _cfor capacitor equivalent series resistance, R is load resistance.During work, main switch Q1 connects when each cycle starts, the electric current flowing through energy storage inductor L is risen by main switch Q1, the electric energy of input voltage source VIN is converted to Magnetic Energy Storage in the inductance magnetic field of energy storage inductor L, when arriving certain duty ratio, main switch Q1 turns off, the electric current of energy storage inductor L carries out afterflow by synchro switch pipe Q2 and declines gradually, realizes magnetic energy and is converted to electric energy and is discharged into output, complete the conversion of one-period.There is the mutual conversion between electric energy and magnetic energy just, by controlling the releasable path of magnetic and time, having achieved the conversion of voltage levels and polarity.Although the electric current on energy storage inductor L is that when Buck type DC-DC normally works, its load current is the mean value equaling inductive current along with switch periods is in do periodically change.

As shown in Figure 2: be typical PWM control BUCK type DC-DC converter structure principle chart, primarily of the outer LC filtering of sheet, error amplifier, reference circuit, PWM comparator, logic control and buffering drive circuit, main switch Q1, synchro switch pipe Q2 and oscillator; First feedback resistance R _f1and the second feedback resistance R _f2form feedback circuit, wherein, the breadth length ratio of main switch Q1, the corresponding conducting channel of synchro switch pipe Q2 is W/L, normally.

Although above-mentioned typical Buck type DC-DC converter operation principle is simple, device used is few, cost is low, but this circuit also exists certain problem, major embodiment can produce certain loss in circuit at this moment, mainly comprises control circuit partition losses, conduction loss, the switching loss of main switch Q1, synchro switch pipe Q2, drive the loss of main switch Q1, synchro switch pipe Q2, dead time losses, outer member loss etc.

At present, the power output of DC-DC converter is increasing, and the conduction loss of main switch Q1, synchro switch pipe Q2 accounts for leading role during heavy duty, also namely the loss main manifestations of circuit is the conduction loss of main switch Q1, synchro switch pipe Q2, therefore in order to requirement during satisfied heavy duty, need conducting resistance now very little.And along with the reduction of load current, the conduction loss of main switch Q1, synchro switch pipe Q2 obviously reduces, and now drive main switch Q1, the driving loss of synchro switch pipe Q2 manifests relatively, affects the conversion efficiency of dc-dc during underloading.Underload and heavy duty are relatively, and general heavy duty and load current are comparatively large, and underload and the less situation of load current, known by the art.

NMOS tube is with main switch Q1, synchro switch pipe Q2, and for forcing the DC-DC converter of continuous mode to be that the present invention is further illustrated for example.

As shown in figures 1 and 3: the present invention includes synchro switch pipe Q2 and for connecting load resistance R and input voltage source VIN and the gate terminal of the main switch Q1 of regulating load resistance R and input voltage source VIN connection status, described main switch Q1 and the gate terminal of synchro switch pipe Q2 are all connected with drive circuit; The drain electrode end of synchro switch pipe Q2 is connected with the source terminal of main switch Q1, and the drain electrode end of main switch Q1 is connected with one end of input voltage source VIN, and the other end of input voltage source VIN is connected with the source terminal of synchro switch pipe Q2; The drain electrode end of synchro switch pipe Q2 is connected with load resistance R by energy storage inductor L; Described drive circuit is according to the breadth length ratio of the corresponding conducting channel of the voltage-regulation main switch Q1 of load current Iout, input voltage source VIN and/or synchro switch pipe Q2, being less than main switch Q1 to make the loss recruitment of main switch Q1 conducting resistance drives the reduction of loss and/or the loss recruitment of synchro switch pipe Q2 conducting resistance to be less than the reduction of synchro switch pipe Q2 driving loss, improves the delivery efficiency to load resistance R.

Described drive circuit comprises current threshold setting module, the described output of current threshold setting module is connected with the end of oppisite phase of comparator, the in-phase end input load electric current I out of comparator, the output of comparator is connected with the first controller and second controller, the output of described first controller is connected with the gate terminal of main switch Q1, and the output of described second controller is connected with the gate terminal of synchro switch pipe Q2.

The two ends of described load resistance R are parallel with filter branch, the capacitor equivalent series resistance R that described filter branch comprises filter capacitor C and connects with described filter capacitor C _c.

In the embodiment of the present invention, be described for main switch Q1.The width of the conducting channel of main switch Q1 is W, and the length of conducting channel is L, and namely the breadth length ratio of main switch Q1 conducting channel is W/L; When the conducting channel of main switch Q1 is all in conducting state, the conducting resistance of main switch Q1 is little, and when the conducting channel of main switch Q1 is partly turned off or all turns off, the electric conduction resistive of main switch Q1 is large.Usually, according to the ratio of main switch Q1 conducting channel, main switch Q1 equivalence can be become the situation of some paralleled power switches, in Fig. 3 of the present invention, main switch Q1 is equivalent to two switching tubes of switching tube QH1, switching tube QH2 parallel connection, meanwhile, synchro switch pipe Q2 is equivalent to two switching tubes of switching tube QL1, switching tube QL2 parallel connection, also can be equivalent to the switching tube of requirement parallel connection as required, known by the art personnel, no longer describe in detail herein.

Particularly, after main switch Q1 is equivalent to switching tube QH1 in parallel and switching tube QH2, the breadth length ratio of configuration switch pipe QH1 conducting channel is then the breadth length ratio of switching tube QH2 conducting channel is also namely the breadth length ratio sum of switching tube QH1 conducting channel corresponding to switching tube QH2 is W/L, when main switch Q1 is equivalent to the switching tube of multiple parallel connection, similar, repeats no more; K is proportionality coefficient, 0<k≤1.After main switch Q1 is equivalent to switching tube QH1 in parallel and switching tube QH2, the parallel resistance of equivalence is R _q1, then when switching tube QH1, switching tube QH2 conducting simultaneously, namely during main switch Q1 conducting, loss can be expressed as:

P _{COND_Q1}=I _OUT ²*R _Q1*D （1）

Wherein, P _{cOND_Q1}for the conduction loss of main switch Q1, I _oUTrefer to output load current, R _q1refer to the conducting resistance of main switch Q1, D is duty ratio.

The loss (being also switching loss) of driving switch pipe QH1, switching tube QH2 can be expressed as:

P _SWITCH=Q _G*V _IN*F _SW=C _GS1*V _GS*V _IN*F _SW(2)

Wherein, P _sWITCHfor switching loss, C _gS1the parasitic grid source electric capacity of equivalence during some switching tubes in parallel for main switch Q1, V _gSfor gate source voltage during upper pipe work, F _sWfor operating frequency, V _iNfor the magnitude of voltage of input voltage source.

Now, main switch Q1 total losses are two sums, can be expressed as:

P _TOTAL=P _{COND_Q1}+P _SWITCH(3)

Known loss and R from formula (1) and formula (2) two formula _q1with C _gS1contact directly, two values are all relevant with the size of main switch Q1, wherein

$R_{Q1}=\frac{1}{u_N{C}_{\mathrm{ox}}(W/L)(V_{\mathrm{GS}}-|V_{\mathrm{TN}}\left|\right)}---\left(4\right)$

C _gS1=C _oX* W*L is less by the size of formula (4) known main switch Q1, R _q1larger, and simultaneously C _gS1less, thus affect main switch Q1 loss.Wherein u _nthe channel mobility of NMOS tube, C _oXbe the gate oxide capacitance of unit are, W is the overall width of main switch Q1 conducting channel, and L is the total length of main switch Q1 conducting channel, V _gSfor the gate source voltage of main switch Q1, V _tNfor the threshold voltage of main switch Q1.

For improving the efficiency of DC-DC converter when underloading, will close the partially conductive raceway groove of main switch Q1 in the embodiment of the present invention, closes by switching tube QH2, switching tube QH1 keeps conducting, and the conducting channel of now main switch Q1 work is as shown in Figure 3, the raster data model of switching tube QH1, switching tube QH2 is driven by HDRV1 signal, HDRV2 signal respectively; The switching tube QL1 of synchro switch pipe Q2 equivalence, the raster data model of switching tube QL2 are driven by LDRV1 signal, LDRV2 signal respectively.

Drive circuit makes the breadth length ratio of the conducting channel of main switch Q1 be after turning off the switching tube QH2 of equivalence then now the conducting resistance of main switch Q1 increases to and grid source electric capacity is reduced to k*C _gS1, now the conduction loss of main switch Q1 is changed to:

${P^{\&prime;}}_{\mathrm{COND}\_Q1}={I_{\mathrm{OUT}}}^2*\frac{R_{Q1}}{k}*D---\left(5\right)$

The Dissipation change of driving main switch Q1 is:

P' _SWITCH=k*C _GS1*V _GS*V _IN*F _SW（6）

Now total losses are changed to:

P' _TOTAL=P' _{COND_Q1}+P' _SWITCH（7）

So the loss recruitment of main switch Q1 conducting resistance is:

$\mathrm{\&Delta;}{P}_{\mathrm{COND}\_Q1}={I_{\mathrm{OUT}}}^2*\left(\frac{1-k}{k}\right)*R_{Q1}*D---\left(8\right)$

The driving loss reduction of main switch Q1 is:

ΔP _SWTTCH=(1-k)C _GS1*V _GS*V _IN*F _SW（9）

In order to make the breadth length ratio regulating main switch Q1 conducting channel, reaching the object of Loss reducing, only needing to make (8) formula be less than (9) formula,

ΔP _SWITCH>ΔP _{COND_Q1}

Also be $(1-k)C_{\mathrm{GS}1}*V_{\mathrm{GS}}*V_{\mathrm{IN}}*F_{\mathrm{SW}}>{I_{\mathrm{OUT}}}^2*\left(\frac{1-k}{k}\right)*R_{Q1}*D---\left(10\right)$

$I_{\mathrm{OUT}}<\sqrt{k*\frac{C_{\mathrm{GS}1}*V_{\mathrm{GS}}*V_{\mathrm{IN}}*F_{\mathrm{SW}}}{R_{Q1}*D}}$

From above formula, for different conditions of work, select corresponding k value, the corresponding I of above formula can be made _oUTefficiency during following load is improved, loss with load variations visual picture as shown in Figure 5.Namely, when underloading, by turning off the partially conductive raceway groove of main switch Q1, the object improving DC-DC converter light-load efficiency can be reached.

Because whole DC-DC converter comprises main switch Q1 and synchro switch pipe Q2, conduction loss, the driving loss of DC-DC converter are produced jointly by main switch Q1, synchro switch pipe Q2, therefore the above-mentioned analysis conclusion for main switch and main switch Q1 is equally applicable to synchro switch pipe Q2, and is applicable to different working modes.Namely in above-mentioned DC-DC converter, by the breadth length ratio of adjustment main switch Q1 conducting channel and the breadth length ratio of adjustment synchro switch pipe Q2 conducting channel, or regulate the breadth length ratio of main switch Q1, synchro switch pipe Q2 conducting channel simultaneously, being less than main switch Q1 to make the loss recruitment of main switch Q1 conducting resistance drives the reduction of loss and/or the loss recruitment of synchro switch pipe Q2 conducting resistance to be less than the reduction of synchro switch pipe Q2 driving loss, improves the delivery efficiency to load resistance R.

Further, as shown in Figure 3: after above-mentioned equivalence, the output of the first controller is connected with the gate terminal of switching tube QH2, the output of second controller is connected with the gate terminal of switching tube QL2, meanwhile, the gate terminal of switching tube QH1 is connected with signal HDRV1, and the gate terminal of switching tube QL1 is connected with signal LDRV1, signal HDRV1 inputs in the first controller, and signal LDRV1 inputs in second controller.Current threshold setting module receives the voltage V of input voltage source VIN _iN, the voltage Vout of load resistance in DC-DC converter, current threshold setting module is according to voltage V _iN, voltage Vout, duty ratio D and operating frequency F _sWcomputing obtains pre-set current value IDC, and described pre-set current value IDC can carry out computing according to above-mentioned formula (10) and obtain, and during according to different loads, can obtain different pre-set current value IDC.The end of oppisite phase of described pre-set current value IDC input comparator, the in-phase end of comparator is load current Iout, when load current Iout is lower than pre-set current value IDC, comparator output low level signal, and EN_LOAD is low level signal.Low level signal EN_LOAD, with door U2 logic control in the first controller, HDRV2 signal is just low, on-off switching tube QH2, reaches the object regulating main switch Q1 conducting channel breadth length ratio.The adjustment state of synchro switch pipe Q2 is identical with the process of main switch Q1, no longer describes in detail herein.

As shown in Figure 4: described first controller comprises height and turns low level shift unit, with door U2 and lowly turn high level shift unit; Described height turns low level shift unit and is connected with an input of door U2, the output of comparator is connected with another input of door U2, be connected with the low high level shift unit that turns with the output of door U2, the described low output turning high level shift unit is connected with the gate terminal of main switch Q1.Second controller is identical with the structure of the first controller, repeats no more herein.

Inside side circuit, the general low-voltage device of control circuit is generally the current potential of 5V relative to ground, due to drain electrode end and the voltage V of switching tube QH1, switching tube QH2 _iNbe connected, pipe in driving, then need the current potential using relative SW, have employed height and turn low level shift unit and lowly turn high level shift unit in described first controller.

Signal HDRV1, signal LDRV1 are controlled to produce by whole system, by feedback voltage through inner PWM comparator, produce a pulse width signal, and obtain through level shift conversion and driving stage circuit, the signal production process of signal HDRV1, signal LDRV1, known by the art, repeats no more herein.When the bearing power of DC-DC converter is higher than set point, namely when pre-set current value IDC is greater than load current Iout, it is 1 that the EN_LOAD signal that comparator exports exports, now signal HDRV2, signal LDRV2 signal are identical with HDRV1, LDRV2, namely switching tube QH2, the switching tube QL2 of equivalence also participate in work, i.e. the conducting channel all-pass conducting of main switch Q1 and synchro switch pipe Q2.When load is lower than set point, the EN_LOAD signal that comparator exports is 0, now signal HDRV2, signal LDRV2 are always logic low, switching tube QH2, the switching tube QL2 of equivalence are in off state all the time, namely under light condition, the partially conductive raceway groove turning off main switch Q1 and/or synchro switch pipe Q2 is passed through, to improve the delivery efficiency of whole DC-DC converter.

As shown in Figure 5, P _{cOND_Q1}conduction loss during conducting whole in switching tube, P _sWITCHswitching loss during conducting whole in switching tube, P _tOTALtotal loss during conducting whole in switching tube.And P ' _{cOND_Q1}, P ' _sWITCH, P ' _tOTALbe respectively every loss during partial switch conducting.Relatively P _tOTALwith P ' _tOTAL, both point of intersection illustrates that total losses are consistent, and lower than the load below intersection point, and the total loss of cutoff switch is lower.Higher than load more than intersection point, the total loss of whole conducting is lower.

Drive circuit of the present invention is connected with the gate terminal of main switch Q1 and the gate terminal of synchro switch pipe Q2, described drive circuit is according to the breadth length ratio of the corresponding conducting channel of the voltage-regulation main switch Q1 of load current Iout, input voltage source VIN and/or synchro switch pipe Q2, being less than main switch Q1 to make the loss recruitment of main switch Q1 conducting resistance drives the reduction of loss and/or the loss recruitment of synchro switch pipe Q2 conducting resistance to be less than the reduction of synchro switch pipe Q2 driving loss, improves the delivery efficiency to load resistance R.

Claims (2)

1. one kind is improved the method for DC-DC converter light-load efficiency, comprise synchro switch pipe (Q2) and for connecting load resistance (R) and input voltage source (VIN) and the main switch (Q1) of regulating load resistance (R) and input voltage source (VIN) connection status, the gate terminal of described main switch (Q1) and the gate terminal of synchro switch pipe (Q2) are all connected with drive circuit; It is characterized in that: the voltage-regulation main switch (Q1) of described drive circuit according to load current Iout, input voltage source (VIN) and/or the breadth length ratio of synchro switch pipe (Q2) corresponding conducting channel, to make the loss recruitment of main switch (Q1) conducting resistance be less than main switch (Q1) drive the loss recruitment of the reduction of loss and/or synchro switch pipe (Q2) conducting resistance to be less than reduction that synchro switch pipe (Q2) drives loss, improve the delivery efficiency to load resistance (R);

Described drive circuit comprises current threshold setting module, the described output of current threshold setting module is connected with the end of oppisite phase of comparator, the in-phase end input load electric current I out of comparator, the output of comparator is connected with the first controller and second controller, the output of described first controller is connected with the gate terminal of main switch (Q1), and the output of described second controller is connected with the gate terminal of synchro switch pipe (Q2);

Described drive circuit regulates the breadth length ratio of the conducting channel of main switch (Q1), makes the loss recruitment of main switch (Q1) conducting resistance be less than main switch (Q1) when driving the decrease of loss, obtains

$I_{\mathrm{OUT}}<\sqrt{k*\frac{C_{\mathrm{GS}1}*V_{\mathrm{GS}}*V_{\mathrm{IN}}*F_{\mathrm{SW}}}{R_{Q1}*D}}$

Wherein, k represents proportionality coefficient, 0<k≤1, C _gS1represent the parasitic grid source electric capacity in main switch (Q1), V _gSrepresent gate source voltage, F _sWrepresent operating frequency, R _q1for the conducting resistance of main switch (Q1), D are duty ratio, V _iNrepresent the magnitude of voltage of input voltage source;

Described first controller comprises height and turns low level shift unit, with door (U2) and lowly turn high level shift unit; Described height turns low level shift unit and is connected with an input of door (U2), the output of comparator is connected with another input of door (U2), be connected with the low high level shift unit that turns with the output of door (U2), the described low output turning high level shift unit is connected with the gate terminal of main switch (Q1).

2. one kind is improved the circuit of DC-DC converter light-load efficiency, it is characterized in that: comprise synchro switch pipe (Q2) and for connecting load resistance (R) and input voltage source (VIN) and the main switch (Q1) of regulating load resistance (R) and input voltage source (VIN) connection status, the gate terminal of described main switch (Q1) and the gate terminal of synchro switch pipe (Q2) are all connected with drive circuit; The drain electrode end of synchro switch pipe (Q2) is connected with the source terminal of main switch (Q1), the drain electrode end of main switch (Q1) is connected with one end of input voltage source (VIN), and the other end of input voltage source (VIN) is connected with the source terminal of synchro switch pipe (Q2); The drain electrode end of synchro switch pipe (Q2) is connected with load resistance (R) by energy storage inductor (L); The voltage-regulation main switch (Q1) of described drive circuit according to load current Iout, input voltage source (VIN) and/or the breadth length ratio of synchro switch pipe (Q2) corresponding conducting channel, to make the loss recruitment of main switch (Q1) conducting resistance be less than main switch (Q1) drive the loss recruitment of the reduction of loss and/or synchro switch pipe (Q2) conducting resistance to be less than reduction that synchro switch pipe (Q2) drives loss, improve the delivery efficiency to load resistance (R);

Described drive circuit comprises current threshold setting module, the described output of current threshold setting module is connected with the end of oppisite phase of comparator, the in-phase end input load electric current I out of comparator, the output of comparator is connected with the first controller and second controller, the output of described first controller is connected with the gate terminal of main switch (Q1), and the output of described second controller is connected with the gate terminal of synchro switch pipe (Q2);

Described first controller comprises height and turns low level shift unit, with door (U2) and lowly turn high level shift unit; Described height turns low level shift unit and is connected with an input of door (U2), the output of comparator is connected with another input of door (U2), be connected with the low high level shift unit that turns with the output of door (U2), the described low output turning high level shift unit is connected with the gate terminal of main switch (Q1);

The two ends of described load resistance (R) are parallel with filter branch, the capacitor equivalent series resistance (Rc) that described filter branch comprises filter capacitor (C) and connects with described filter capacitor (C).