Embodiment
Figure 1 shows that a kind of transient response of the present invention circuit diagram of DC-DC converter 100 fast.Usually, DC-DC converter 100 makes output voltage V out112 stable according to the reference signal of the input of comparator.In the transient response, the process that switches to another dc state from a dc state, need output loading.DC-DC converter 100 has reduced the recovery time of transient response effectively by the adjustment duty ratio, thereby controls Vout112 to desirable stable state.
DC-DC converter 100 comprises: one with reference to direct voltage source Vref114, reference signal generator 116, comparator 118, a driver 120 and a pair of switches 122.Signal generator 116 produces a reference signal 126, this signal is preferably the sawtooth signal of 300 KHz, the perhaps cyclical signal of any waveform (for example triangular signal or sine wave signal), and have a direct current biasing that direct voltage determined that produces by Vref114.Comparator 118 receives reference signal 126 as its first input.Output voltage V out112 feeds back to comparator 118 by feedback loop 124, and second input of device 118 as a comparison.Comparator 118 compares Vout112 and reference signal 126, and produces a pulse-width signal 128, and its duty ratio decision increases Vout112 and still reduces Vout112.In more detail, if Vout112 less than or greater than signal 126,118 of comparators force Vout112 tracking reference signal 126 by the pulsewidth that increases or reduce its output pulse width modulation signal 128.Specifically, driver 120 receives the input of pulse-width signal 128 as it, and driving switch 122.This switch preferably realized by mos field effect transistor (MOSFETs), and high-end MOSFET and low side MOSFET alternate conduction are controlled Vout112.Preferably Vout112 is near Vref, and remains in the scope of reference signal 126.For example, reference signal generator 116 produces a sawtooth waveforms reference signal 126 at a specific direct current Vref voltage place, and the peak-peak sawtooth waveforms fluctuation of this signal is 100 millivolts, i.e. Vref-50 millivolt<Vout<Vref+50 millivolt.In addition, 112 and inductance capacitances of output loading (Vout) (LC) low pass filter polyphone.The electric induction of the inductance 130 of low pass filter is as much as possible little, thereby reduces the recovery time to load transient response.
Figure 2 shows that the example use circuit 200 of a DC-DC converter circuit 100 in the application drawing 1.Circuit 200 (for example adopts an integrated reference voltage generator, D1 (TL431) 202) variation to input voltage 114 compensates, thereby the pulse-width signal 128 of guaranteeing comparator 118 generations is adjusted output voltage V out according to aforesaid reference voltage.Ramp generator 116 is made of parts U3 (LM311) 204, and produces the triangular signal 126 that a peak-to-peak amplitude is about 100 millivolts.Aforesaid comparator 118 is made of U2 (LM311) 206, receives output voltage V out112 and triangular signal 126 as input, and produces a pulse-width signal 128.Driver 120 in this example use is made of U1 (TPS2830) 208.At last, power module 210 control output voltage Vout, this power module comprises: MOSFETs Q1 and Q2,122; Inductance L 1,130; Resistance R 10; With capacitor C 4.This DC-DC converter circuit is used for improving the recovery time to load transient response.It should be noted that this invention comprises the element and the circuit of the application schematic diagram among Fig. 2, but be not subject to these elements and circuit.
An alternative embodiment of the invention be for comprising two or more converter circuits 100 in heterogeneous structure, wherein the angle of phase displacement between two circuit is according to the number of phases that is adopted and difference.For example, in one four phase structure, angle of phase displacement is 90 degree.The problem of heterogeneous structure is that the electric current of not expecting is arranged between two phases.For example, when a load puts on output, if one transfers to the electric current of load and is far longer than the electric current that another exports load mutually to, conversion efficiency will be had a strong impact on.This question marks are similar to two voltage source parallel connections.If the voltage difference of two voltage sources will have electric current to flow through between them.In order to solve this problem of multi-phase dc/dc transducer, then need a current balance type structure.For example, in a two-phase DC-DC converter, adopt a current balance module to adjust the output voltage of this second phase, make it equal with this first mutually output voltage.By adopting current sense resistor, this current balance module obtains this current information, and produces the output voltage that a bias voltage is adjusted this second phase.Realize that this current balance type structure has two kinds of systems of selection: (1) is by revising the reference voltage of this second phase; Or (2) are by revising the feedback voltage of this second phase.
Figure 3 shows that an embodiment with two-phase DC-DC converter 300 of a current balance module, this current balance module acts on the reference signal of this second phase.The first phase 100a produces output voltage 112 according to the reference signal 126a of the input of comparator 118.Send the second phase 100b to after the direct current component adjustment of current balance module 301 with reference signal 116, thereby make the current amplitude that equates that whenever transfers.Suppose to flow through the electric current of the first phase 100a greater than the electric current of the second phase 100b that flows through, then the voltage of the in-phase input end of error amplifier 302 will be greater than the voltage of its inverting input.The effect of error amplifier 302 is the values that reduce bias voltage 303, and like this, the direct current component of the reference voltage of the second phase 100b will increase.Therefore, the duty ratio of the second phase 100b will increase.So, the current value of second phase 100b transmission is greater than former current value.When the electric current that whenever transfers all equates, bias voltage 303 will keep this value, thereby reach the current balance type of each phase.
Figure 4 shows that another has the embodiment of the two-phase DC-DC converter 400 of a current balance module, this current balance module acts on the feedback fraction of the second phase 100b.The first phase 100a produces output voltage V out112 according to the reference signal 126a of comparator 128 inputs.Current balance module 401 is given the second phase 100b with the direct current component translation of feedback voltage, thereby makes and whenever transfer equal current amplitude.Suppose to flow through the electric current of the first phase 100a greater than the electric current of the second phase 100b that flows through, then the voltage of the inverting input of error amplifier 402 is greater than the voltage of its in-phase input end.The effect of error amplifier 402 is the values that increase bias voltage 403, and like this, the feedback voltage of the second phase 100b will reduce.Therefore, the duty ratio of the second phase 100b will increase.So, the current value of second phase 100b generation is greater than former current value.When every electric current that produces mutually all equates, bias voltage 403 will keep this value constant, thereby reach the current balance type of each phase.It should be noted that because the current balance module among Fig. 4 acts on feedback voltage, so the anti-phase and in-phase input end of the current balance module among the anti-phase and in-phase input end of the current balance module among Fig. 4 and Fig. 3 is opposite.
The major advantage of Fig. 3 and the current balance type structure that transducer adopted shown in Figure 4 is that two-phase is all moved, and makes output voltage return to stable state when the variation of load produces transient response.Because the work of the every phase in the transient response basic identical (only having little difference) owing to the difference of the component values that is adopted, current balance circuit only need be by trickle correction, promptly finely tune the reference section among Fig. 3 or the bias voltage of the feedback fraction among Fig. 4, and the current balance type that makes two-phase is to new stable state.
Current balance method that it should be noted that two types can be used in the heterogeneous structure, wherein current balance module will be from the current information of every N phase and output voltage as input, and provide bias voltage to the 2nd to the N phase, thereby balance each other with first mutually the electric current.
Fig. 5 A is depicted as the schematic diagram that output voltage changes along with input voltage.For a specific input voltage vin, because reference signal is a constant, so duty ratio D1=Vout1/Vin.To be duty ratio by voltage Vout1 and reference signal intersect obtains.For example, if input voltage is decreased to k*Vin (wherein k<1), this stylish duty ratio is D2=Vout2/k*Vin, so output voltage will reduce to increase duty ratio.Therefore, output voltage reduces along with the value of (D2-D1) * (amplitude of sawtooth waveforms reference signal).Even for the very low reference signal of amplitude, owing to input voltage can change in the larger context, so output voltage still changes along with input voltage.
Fig. 5 B is depicted as a kind of method that compensates output voltage under the situation that input voltage changes.A kind ofly prevent that method that output voltage changes along with input voltage is for producing an amplitude and input voltage is proportional, peak value remains on a fixing DC voltage level Vref sawtooth signal.This means the input voltage that equates for Vin, output voltage V out 1 is corresponding with duty ratio, and wherein duty ratio is intersected by output voltage and reference signal and obtains, and is D1=Vout1/Vin.Therefore, if the amplitude of sawtooth signal is that Asawtooth, peak value are Vref, Vout1=Vref-D1*Asawtooth so, i.e. Vout1=Vref-Vout1*Asawtooth/Vin, or Vout1=Vref/ (1+Asawtooth/Vin).
When input voltage reduced along with coefficient k<1, the amplitude of sawtooth waveforms was along with same coefficient k reduces, and the peak value of sawtooth signal remains on Vref simultaneously.According to new input voltage value, duty ratio is D2=Vout2/ (k*Vin).Yet since Vout2=Vref-D2* (k*Asawtooth)=Vref-Vout2*k*Asawtooth/ (k*Vin), Vout2=Vref/ (1+Asawtooth/Vin).Be Vout1=Vout2.Therefore, output voltage is along with input voltage changes.
The major advantage of aforesaid method is: (1) output voltage does not rely on input voltage; (2) gain in loop does not rely on input voltage, and so, for various input voltages, it is identical that the performance of DC-DC converter still keeps.The gain in loop is actually Vin/Asawtooth.Because Asawtooth and Vin are proportional, so gain is constant; (3) at higher input voltage place, owing to the switching of switch causes output that higher noise is arranged.When the sawtooth signal amplitude increases, pulse-width modulation comparator operate as normal, and can not produce spurious pulse owing to the noise of output voltage.
Figure 6 shows that the circuit diagram of the method for compensation output voltage under a kind of situation of the variation at input voltage.Clock pulse 601 is with the 602 closed a bit of times of switch, and this time enough charges to the Vref value with electric capacity 603.Like this, the peak value of sawtooth signal just in time is Vref.Switch 602 disconnects, and electric capacity 603 discharges with the proportional constant current of input voltage with one.The element of this circuit will be adjusted to the sawtooth waveforms amplitude that reaches desired.This circuit can compensate output voltage under the input voltage situation of change.A kind of application of this circuit is in notebook computer, and wherein input voltage can be cell voltage or adaptor voltages.Adaptor voltages is generally 20V, and wherein discharge battery voltage can be low to moderate 8V or littler.This system need work in gamut.
Figure 7 shows that the oscillogram that puts on a two-phase DC-DC converter or the transient response when this transducer is removed when a load.The amplitude of variation of load current is 20 amperes.CH1 is the waveform of output voltage (Vout).CH2 is the waveform of the pulse-width signal of first phase (PWM1).CH3 is the waveform of the pulse-width signal of second phase (PWM2).CH4 is the waveform of 1/2 load current.When adding this load (being that electric current is increased to 20 amperes from 0 ampere), Vout descends.Because the duty ratio of this transducer increases, a bit of time (transient response of this transducer was about for 100 nanoseconds, and this makes that recovery time is less than 10 microseconds) afterwards output voltage get back to its stable state.When this load was removed, this transducer reduced duty and recently recovers Vout.As shown in Figure 7, every phase pulse-width signal of all adjusting oneself to recover Vout from transient behaviour.Therefore, when adopting a heterogeneous structure, the number of phase is depended in the recovery of the transient response of Vout.
Figure 8 shows that another embodiment of a DC-DC converter 800 of the present invention, wherein can adopt a kind of method to revise the DC voltage level of signal 126, thereby improve the accuracy of the output voltage of DC-DC converter 800.Usually, DC loop that comprises an accuracy circuit 802 can be adjusted the voltage level of the reference signal 126 that is produced by reference direct voltage source 114.Difference between the voltage level that bias voltage source 806 also can produce according to the output-voltage levels Vout of 112 ends with reference to direct voltage source 114 is adjusted the voltage level of reference signal 126.Except bias voltage source 806, accuracy circuit 802 also can comprise an error amplifier 804.
The signal of the output-voltage levels of an expression DC-DC converter 800 can feed back to an input (for example inverting input) of error amplifier 804 via path 810.Another expression can offer another input (for example in-phase input end) of error amplifier 804 via path 812 with reference to the signal of direct voltage source 114.Error amplifier 804 compares these two signals, and controls signal to bias voltage source 806 according to their one of difference output.
If the voltage level that the converter output voltage level of 112 ends produces less than reference direct voltage source 114, error amplifier 804 will be exported a control signal so, this control signal order bias voltage generator 806 produces a positive bias voltage level, the voltage level addition that this positive bias voltage level will produce with reference direct voltage source 114.Therefore, the DC level of oblique wave reference signal 126 will correspondingly increase.Because the D. C. value of oblique wave reference signal 126 is higher, so comparator 118 will increase the duty ratio of its output pulse width modulation signal 128.So, the converter output voltage of 112 ends will increase, up to reaching the reference dc voltage value that produces with reference to direct voltage source 114.
If the voltage level that the converter output voltage level of 112 ends produces greater than reference direct voltage source 114, error amplifier 804 will be exported a control signal so, this control signal order bias voltage generator 806 produces a negative bias voltage level, the voltage level addition that this negative bias voltage level will produce with reference direct voltage source 114.Therefore, the DC level of oblique wave reference signal 126 will correspondingly reduce.Because the D. C. value of oblique wave reference signal 126 is lower, so comparator 128 will reduce the duty ratio of its output pulse width modulation signal 128.So, the output voltage of transducer 112 ends will reduce, up to reaching the reference dc voltage value that produces with reference to direct voltage source 114.The reference signal DC level that direct voltage source 114 produces is adjusted in this direct current accuracy loop 812, adjust this reference signal DC level as bias voltage source 806, this direct current accuracy loop is a loop at a slow speed, like this, the voltage of bias voltage source 806 can change lentamente, and for example, the compensation in this loop is adopted in the following method and finished, promptly under the dual limit of inductance capacitance (LC), just has gain in the time of at least one ten times less than a unit.
Figure 9 shows that another embodiment of a DC-DC converter 900 of the present invention, wherein can adopt the value of feedback of a kind of method adjustment, thereby improve the accuracy of transducer 900 from 112 end Vout to comparator 118.Usually, a DC loop that comprises an accuracy circuit 902 can be adjusted a feedback signal according to converter output voltage level Vout with reference to the difference between the voltage level of direct voltage source 114 generations, and this feedback signal is represented the output voltage of transducer 900.Accuracy circuit 902 can comprise an error amplifier 904 and a bias voltage source 906.
The signal of the output-voltage levels of an expression DC-DC converter 900 can feed back to an input (for example in-phase input end) of error amplifier 904 via path 910.Another expression can offer another input (for example inverting input) of error amplifier 904 via path 912 with reference to the signal of the VD level of direct voltage source 114.Error amplifier 904 compares these two signals, and provides one to control signal to bias voltage source 906 according to the difference of these two signals.It should be noted that because the accuracy circuit 902 among Fig. 9 acts on feedback voltage, so the anti-phase and in-phase input end of the error amplifier 804 among the anti-phase and in-phase input end of the error amplifier 904 among Fig. 9 and Fig. 8 is opposite.
If the voltage level that the converter output voltage level of 112 ends produces less than reference direct voltage source 114, error amplifier 904 will be exported a control signal so, this control signal order bias voltage generator 906 produces a negative bias voltage level, this negative bias voltage level will with this feedback signal addition, this feedback signal is correspondingly reduced.Since via path 914 to the signal of comparator 118 less than this feedback signal (otherwise need not negative bias in this case), so the duty ratio of the pulse-width signal 128 of comparator 118 will increase.Then, the duty ratio of increase increases the output voltage at output 112 places of transducer 900, up to reaching the reference value that produces with reference to direct voltage source 114.
On the contrary, if the voltage level that the output-voltage levels of transducer 112 ends produces greater than reference direct voltage source 114, error amplifier 904 will be exported a control signal so, this control signal order bias voltage generator 906 produces a positive bias voltage level, this positive bias voltage level will with the feedback signal addition, this feedback signal is correspondingly increased.Since via path 914 to the signal of comparator 118 greater than this feedback signal (otherwise need not positive bias in this case), so the duty ratio of the pulse-width signal 128 of comparator 118 outputs will reduce.Then, the duty ratio that reduces reduces the output voltage at output 112 places of transducer 900, up to reaching the reference value that produces with reference to direct voltage source 114.The direct current accuracy loop 912 of adjusting the feedback voltage level of comparator 118 is a loop at a slow speed, thereby the voltage of bias voltage source 906 can change lentamente.
The stability of DC-DC converter of the present invention can be improved by adopting inductive current information (Figure 10 to Figure 11) or alternating current information (Figure 12 to Figure 13).Figure 10 shows that another embodiment of DC-DC converter 1000 of the present invention, this embodiment adopts inductive current information to improve stability.Usually, to comparator 118, this feedback voltage can improve by a stability circuit 1022 the feedback voltage value of Vout112 end via a feedback path, thereby strengthens the stability of DC-DC converter 1000.
Stability circuit 1022 can comprise an operational amplifier 1026, and resistance R 1 and R2.Detecting resistance 1030 also can connect with inductance L 1.The voltage that detects resistance 1030 two ends represent the to flow through electric current of inductance L 1.The electric current of the inductance L of flowing through 1 is amplified by the coefficient that resistance R 1 and resistance R 2 are provided with, and equals Acurrent=1+R2/R1.So, in the embodiment of Figure 10, the feedback voltage value that feeds back to the inverting input of comparator 118 is provided by equation (1).
(1)VPWM?comparator=Vout+(1+R2/R1)*Iinductor*RCS;
In equation (1), Vout is the output voltage of DC-DC converter 1000, and R1 and R2 are respectively the resistance value of resistance R 1 and R2, and Iinductor flows through the inductive current of inductance L 1 and RCS for detecting the resistance value of resistance 1030.So, stability is owing to an inductive current translation 90 degree are improved.In addition, output voltage V out increases along with inductive current and reduces, thereby has reduced the scope of output voltage during transient response.
Stability circuit 1103 shown in Figure 11 also can comprise resistance capacitance (RC) circuit 1102 of being made up of resistance 1140 and electric capacity 1142.So, stability also can be improved by increasing in the frequency range of the dual limit of being made up of inductance L 1 and capacitor C 1 zero point.
Stability also can be improved by utilizing alternating current information.For example, stability circuit 1203 shown in Figure 12 can comprise an inductance capacitance (RC) circuit 1226, and this LC circuit 1226 adds a zero point in the frequency range of the dual limit of being made up of inductance L 1 and capacitor C 1.LC circuit 1226 can comprise parallel resistor R1 and R2 and capacitor C comp.The voltage divider of being made up of resistance R 1 and R2 is decreased to a desired value in proportion with output voltage.Should select the value of capacitor C comp, make LC circuit 1226 in the frequency range of the dual limit of inductance L 1 and capacitor C 1 composition, can add a zero point.Relation between dual pole location of the inductance capacitance of LC circuit 1226 and the inductance capacitance time constant is drawn by experiment, and obtains simulating, verifying, and is provided by equation (2).
The amplifier 1324 that to Figure 13 shows that an amplification coefficient be N adds stability circuit 1342.The input of amplifier 1324 can link to each other with node 1346, and the output of amplifier 1324 can link to each other with capacitor C comp.So, the output of amplifier 1324 links to each other with the feedback loop divider that R2 composes in parallel with resistance R 1 by capacitor C comp.LC circuit 1326 comprises capacitor C comp and parallel resistor R1 and R2.So, the stability of DC-DC converter 1300 also can be improved by amplifying alternating current information.Yet, producing clear, stable width-modulation pulse in order to keep comparator 118, the size of amplification coefficient N has a specific scope.For example, feedback signal interchange peak-peak amplitude should be less than the amplitude of oblique wave reference signal 126.So, will meet this requirement by restriction amplification coefficient N.For example, be 100 millivolts if the peak-to-peak value of the voltage ripple at node 1346 places is the amplitude of 10 millivolts and oblique wave reference signal 126, the amplification coefficient of amplifier 1324 should be less than 10 so.The ripple that amplifier 1324 the amplifies capacitor C comp that flows through, and at the ripple frequency place, this ripple voltage will with the amplitude at the common node place of resistance R 1 and R2 and Ccomp much at one.In one embodiment, amplification coefficient N be about 5 or 6 comparatively suitable.
Be applied to a single-phase DC/direct current transducer though those skilled in the art understands Fig. 9 to the improvement to accuracy and stability shown in Figure 13, these improve and equally also are applicable to the multi-phase dc/dc transducer.
Embodiment described herein just adopts of the present invention wherein several, but is not limited to the present invention.Obviously, the embodiment that does not break away from the defined the spirit and scope of the present invention of accessory claim that also exists other those skilled in the art to understand.