CN104242623A - Quick start method and quick start control circuit of switching power supply - Google Patents

Quick start method and quick start control circuit of switching power supply Download PDF

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Publication number
CN104242623A
CN104242623A CN201410451636.8A CN201410451636A CN104242623A CN 104242623 A CN104242623 A CN 104242623A CN 201410451636 A CN201410451636 A CN 201410451636A CN 104242623 A CN104242623 A CN 104242623A
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voltage
power supply
current
switching power
output
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CN201410451636.8A
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CN104242623B (en
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危立辉
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中南民族大学
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Abstract

The invention discloses a quick start method and quick start control circuit of a switching power supply. Through the arrangement of conversion voltage, when output voltage of the switching power supply is lower than the conversion voltage, inductive current is controlled to be set as inductive current; when the output voltage of the switching power supply is higher than the conversion voltage, the output voltage of the switching power supply is controlled to work in a voltage stabilization mode. According to one scheme, an artificial circuit mode is adopted in a starting stage to control the inductive current to be the given inductive current, and the output voltage is controlled to be stable when the output voltage reaches the conversion voltage. According to the other scheme, a MCU control circuit is adopted to replace the artificial circuit to complete the same control process. According to the quick start method and quick start control circuit of the switching power supply, a digit circuit load can reset and work reliably in the process of electrification and voltage drop, functional load devices like a laser power supply and a high-power DC servo motor of the switching power supply are started quickly, and influences of voltage drop on the load of the switching power supply can be reduced when network voltage drops.

Description

A kind of quick start method of Switching Power Supply and start control circuit fast
Technical field
The invention belongs to field of switch power, more specifically, relate to a kind of Switching Power Supply quick start method and start control circuit fast.
Background technology
Because switched power output exists very large electric capacity, start-up course comprises the process of output capacitance charging, and voltage rise causes charging current larger sooner.For preventing excessive charging current, the conventional Starting mode of Switching Power Supply adopts soft starting mode.Namely, when power initiation, duty ratio slowly increases until switch power source output voltage reaches rated voltage by zero.Switching device when soft Starting Technology can prevent from starting in Switching Power Supply damages because of overcurrent, but soft start also cause simultaneously startup stage Switching Power Supply output voltage rise slowly.The soft start of usual Switching Power Supply cause the output voltage of Switching Power Supply from zero to settling time of rated voltage be a few tens of milliseconds to hundreds of millisecond not etc.
Traditional Switching Power Supply generally adopts voltage mode (or claiming voltage-type) pulse-width modulation (PWM) technology, and current-mode (or claiming current mode) PWM technology obtains develop rapidly in recent years, comparison with voltage pattern PWM, current mode PWM has better voltage regulation and load regulation, and the stability of system and dynamic characteristic are also able to obvious improvement.
Voltage type PWM controls and current type PWM control all belongs to analogue enlargement, digital controlly at present just progressively replaces analogue enlargement in some aspects with its many advantage.Digital PWM controller obtains and more designs freedom, easily can realize the digital algorithm of various complexity, intelligence.
Application scenario below, the quick startup of Switching Power Supply has specific advantage:
(1) electrification reset of digital circuit and supply power voltage fall after process
When the load circuit of Switching Power Supply is digital circuit (comprising microprocessor and peripheral circuit thereof), obtain the logic state that stable Dingan County of determining is complete for making digital circuit after the power-up, it usually produces reset signal by supply power voltage rising edge.If supply power voltage rises too slow, the state of circuit after electrification reset can be made uncertain.The existing method addressed this problem at present adopts special reset circuit, and arrange comparison threshold value to supply power voltage, when supply power voltage exceeds threshold value, reset circuit just produces rising edge precipitous duration sufficiently long reset signal.In actual use, even if adopt this kind of reset circuit, also can there is electrification reset and make a mistake.
Another kind of situation is, when its supply power voltage of the digital circuit of normal work falls suddenly, at this moment the electric capacity being connected to both ends of power in digital circuit can maintain a period of time and power, if supply power voltage drop-out time exceeds this sustain time, digital circuit will be in unstable logic state.The existing method addressed this problem adopts special power supply monitoring circuit.The function of this circuit is when Voltage Drop, produces rising edge precipitous duration sufficiently long reset signal, makes digital circuit reset to obtain the operating state determined safely.Even if adopt special power supply monitoring circuit, still there is supply power voltage in actual applications and fall, the situation of digital circuit state confusion.
(2) when the load of Switching Power Supply is high-power function device, as high power DC electric machine or high power laser power supply etc., Switching Power Supply adopts soft starting mode, and these function devices just need could start for a long time.In case of emergency, these equipment are sometimes needed to devote oneself to work fast.
(3) can cause Voltage Drop when other powerful device starts on electrical network, such as high power DC electric machine starts the Voltage Drop caused, and thisly falls the Switching Power Supply that can affect in same supply line.After input voltage falls, in order to reduce the impact on on-line apparatus as far as possible, need Switching Power Supply to start fast, make direct voltage go back up to normal value fast.
Summary of the invention
For the defect of prior art, the object of the present invention is to provide one to start fast, switching device can be allowed again not produce the Switching Power Supply quick start method of overcurrent and start control circuit fast.
The invention provides a kind of Switching Power Supply quick start method, comprise the steps:
(1) at electric current ascent stage, inductive current is promoted, until inductive current reaches setting inductive current with maximum permission duty ratio;
(2) in the constant current operation stage, control inductive current by the duty ratio of control switch device and make described inductive current maintain described setting inductive current, until the output voltage of Switching Power Supply is changing voltage;
(3) at voltage stabilizing working stage, make the output voltage of described Switching Power Supply maintain rated voltage thus realize Switching Power Supply to start fast by the duty ratio of control switch device.
Wherein, in step (1), described maximum permission duty ratio is the maximum duty cycle that Switching Power Supply main circuit can allow; When the converter in described Switching Power Supply main circuit is step-down DC/DC converter, described maximum permission duty ratio is 1; When the converter in described Switching Power Supply main circuit is bridge-type non-isolated converter, half-bridge or full-bridge isolated converter, described maximum permission duty ratio is 0.5 deduct Dead Time part; When the converter in described Switching Power Supply main circuit be single end flyback converter or single-ended forward converter time, described maximum permission duty ratio is 0.5.
Wherein, described setting inductive current equals maximum trouble free service electric current I st(0.5-0.9) doubly.
Wherein, described changing voltage is (0.85-1) times of rated voltage.
Present invention also offers a kind of Switching Power Supply and start control circuit fast, comprise comparator U1, voltage comparator U2, analog switch U3, current regulator U6, rest-set flip-flop U7, PWM output module U8, oscillator U9, resistance R f, resistance R jwith electric capacity C f; The first input end of described comparator U1 connects changing voltage V t, second input of described comparator U1 connects output voltage V 0; Described resistance R jone end for receiving output voltage V 0, described resistance R jthe other end be connected to the first input end of described voltage comparator U2, second input of described voltage comparator U2 is for connecting reference voltage V f, described resistance R fwith described electric capacity C fbe sequentially connected in series between the first input end and the output of described voltage comparator U2 of described voltage comparator U2; The first input end of described analog switch U3 is connected to the output of described voltage comparator U2, and second input of described analog switch U3 is for connecting setting inductive current I s; The control end of described analog switch U3 is connected to the output of comparator U1; The first input end of described current regulator U6 is connected to the output of analog switch U3, and second input of described current regulator U6 connects inductive current I l; The R end of described rest-set flip-flop U7 is connected to the output of described current regulator U6, and the S end of described rest-set flip-flop U7 connects described oscillator U9; The input of described PWM output module U8 is connected to the Q end of described rest-set flip-flop U7, and the output of described PWM output module U8 is for exporting pwm control signal and control switch device break-make.
Wherein, described setting inductive current I sequal maximum trouble free service electric current I st(0.5-0.9) doubly.
Wherein, described changing voltage V tfor (0.85-1) times of rated voltage.
Wherein, described reference voltage V fset-point needed for switch power source output voltage.
Present invention also offers a kind of Switching Power Supply and start control circuit fast, comprise MCU control module, be connected to voltage sample module and the current sample module of the input of described MCU control module, and be connected to the PWM generator of output of described MCU control module; Described MCU control module comprises subtracter, voltage regulator, voltage comparator, switch, subtracter and current regulator; The first input end of described subtracter connects reference voltage V f, the second input is for receiving output voltage V 0, the output of described subtracter connects voltage regulator, the first input end of the output connecting valve of voltage regulator, and the second input of switch is for connecting setting inductive current I s, the output of switch connects the first input end of subtracter, and the second input of subtracter is for connecting inductive current I l, the output of subtracter connects the input of current regulator, and the output of current regulator is used for output duty cycle control switch device.
Wherein, described setting inductive current I sequal maximum trouble free service electric current I st(0.5-0.9) doubly.
In the present invention, startup stage first make switching device electric current reach maximum trouble free service electric current fast, then this electric current is maintained, the energy absorbed from input in guarantor unit's time and maximum to exporting the energy provided, until output voltage is close to rated output voltage value; Switching device trouble free service not Quick energizing quantity while overcurrent can be made like this.
Accompanying drawing explanation
Fig. 1 is the simplified structure schematic diagram of Switching Power Supply centered by inductance;
Fig. 2 is that Switching Power Supply performance during rapid starting period analyzes schematic diagram; The startup stage that wherein (a) being, inductance peak current changes schematic diagram in time, and the startup stage that (b) being, output voltage changes schematic diagram in time, and the startup stage that (c) being, duty ratio changes schematic diagram in time;
Fig. 3 is the theory structure block diagram that the Switching Power Supply adopting electric current PWM to control starts control circuit fast;
Fig. 4 is the theory structure block diagram adopting the Switching Power Supply of digital PWM control to start control circuit fast;
Fig. 5 is the internal structure schematic diagram adopting the Switching Power Supply of digital PWM control to start MCU control module in control circuit fast;
Fig. 6 is the Switching Power Supply fast starting sequence schematic flow sheet adopting digital PWM control.
Embodiment
In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.
Switching Power Supply in the present invention is its input is direct current or interchange, and output is direct current; Its input and output can pass through transformer isolation, also can not isolate.Switching device in the present invention refers to the switch triode in Switching Power Supply, and typical in Power bipolar transistor, MOS, IGBT etc., its turn-on and turn-off are controlled.
The present invention relates to the knowledge altogether of Switching Power Supply inductance energy storage exoergic: the switching device in Switching Power Supply works on off state, when switch device conductive, inductive energy storage, by input power stored energy in inductance; When switching device turns off, inductance exoergic.For single-ended reverse exciting circuit, inductance is usually said transformer, and in other converter, inductance is exactly output inductor.
Several inductive currents related in the present invention, have done as given a definition.Inductance ratings electric current: refer to that Switching Power Supply is operated in rated power, namely exports rated current under rated voltage, now the peak value of electric current in inductance.Maximum trouble free service electric current I st: when the switching device operating current in Switching Power Supply exceedes the maximum permission operating current of device, switching device may damage, the switching device that engineering designs maximum permission operating current is known, now by experiment or the current peak calculating corresponding inductance, the maximum trouble free service electric current I namely herein defined st.I mbe the limiting value of inductive current, if inductive current exceeds this value, Switching Power Supply may be damaged.
Soft start can make switching device not overcurrent when starting, and according to conventional quick start method, switching device just has overcurrent danger.Therefore the technical problem to be solved in the present invention is: should start fast, namely reduces switch power source output voltage from the time being raised to normal value above freezing, but otherwise allow switching device not produce overcurrent danger, namely switching device works under maximum safe current.
Must absorb energy from input fast and provide energy to output startup stage of namely, these energy set up output voltage on the one hand output capacitance quick charge fast, provide energy on the other hand to load; To notice that the precondition of Quick energizing quantity is that switching device wants trouble free service can not overcurrent simultaneously.For reaching this target, give a setting inductive current in the present invention, this setting inductor current value is between inductance ratings electric current and maximum trouble free service electric current.Startup stage first make switching device electric current reach setting inductive current fast, then maintain this electric current, the energy absorbed from input in guarantor unit's time and maximum to exporting the energy provided, until output voltage is close to rated output voltage value.
As Fig. 1, Switching Power Supply can be reduced to converter, inductance L, output capacitance C, load R.During converter breaker in middle break-over of device, inductive current increases, inductive energy storage; When converter breaker in middle device turns off, inductive current reduces, and inductance is to output capacitance and load exoergic.There is corresponding relation in inductive current size and switching device size of current.The maximum operating currenbt of switching device is corresponding, and inductive current is maximum trouble free service electric current I st.The present invention makes full use of inductive energy storage exergonic process in Switching Power Supply, solves the problems of the technologies described above.Its course of work is divided into three phases.
(1) electric current ascent stage, promotes inductive current, until inductive current reaches setting inductive current with maximum permission duty ratio.Here maximum permission duty ratio is the maximum duty cycle that Switching Power Supply main circuit can allow, 1 for step-down DC/DC converter, for boosting DC/DC converter 1, being 0.5 deduct Dead Time part for bridge-type non-isolated converter, half-bridge or full-bridge isolated converter, is 0.5 for single end flyback converter, single-ended forward converter.Setting inductive current is less than the maximum trouble free service electric current I of inductance st, preferred proportion coefficient is 0.5-0.9.This coefficient is too little can increase Switching Power Supply start-up time, and too conference increases the danger that switching device damages.This stage switch electric power output voltage is lower.
(2) the constant current operation stage, terminate rear inductive current on last stage and reach setting inductive current, by the make-and-break time of control switch device, normally duty ratio, control inductive current, maintain inductive current for setting inductive current, until the output voltage of Switching Power Supply is close to rated output voltage, this voltage is called changing voltage.Changing voltage is less than rated output voltage, and the preferred proportion of changing voltage and rated output voltage is 0.85-1.The too little meeting of this ratio makes power source integral start-up time extend, and may cause output voltage overshoot too greatly.Arrange inductor current value in first stage larger, the time that in second stage, output voltage rises is shorter.
(3) voltage stabilizing working stage, at the end of constant-current phase, the output voltage of Switching Power Supply is changing voltage, Switching Power Supply enters the voltage stabilizing stage subsequently, be stabilized in rated voltage as control objectives using switch power source output voltage, make Switching Power Supply voltage stabilizing work by controlling duty ratio, this one-phase inductive current can decline, when accessing nominal load, last inductive current works in inductance ratings electric current.
One of realizing circuit of Switching Power Supply quick start method of the present invention adopts current type PWM to control.Current type PWM controls to comprise the voltage control loop as outer shroud and the current regulator as inner ring.Current regulator is used for controlling the size of inductive current, when output voltage is lower than changing voltage, voltage error amplifier quits work, given electric current and inductive current are as two input signals of current regulator, current regulator exports and produces pwm signal pulse, controls inductive current for setting inductor current value; When output voltage reaches changing voltage, voltage error amplifier is devoted oneself to work, exported by voltage error amplifier and two input signals of inductive current as current regulator, current regulator exports and produces pwm signal pulse, and controlling output voltage is rated output voltage value.
Another implementation of Switching Power Supply quick start method of the present invention uses digital PWM controller.Digital PWM controller comprises the voltage control loop as outer shroud and the electric current loop as inner ring.When output voltage is less than changing voltage, running current control ring, operation result controls the pulse conducting width of pwm signal, controls inductive current peak for setting inductor current value; When output voltage equals to be greater than changing voltage, working voltage control ring and current regulator carry out double-loop control, and operation result controls the pulse conducting width of pwm signal, and controlling output voltage is rated output voltage value.
Method and circuits of the present invention can make Switching Power Supply start fast, makes Switching Power Supply have following advantage:
(1) when digital circuit powers on, or when supplying digital circuits voltage falls suddenly, make supply power voltage be raised to normal value from above freezing fast, the possibility that nondeterministic statement appears in digital circuit can be reduced.
(2) when the load of Switching Power Supply is high-power function device, the quick startup of Switching Power Supply, the loading functional equipment that Switching Power Supply can be made to power is devoted oneself to work fast, and such as high-voltage laser power supply starts fast can make laser equipment devote oneself to work fast; The quick startup of the power supply driving power of high power DC servomotor can make servo system put into operation fast.
(3) can cause Voltage Drop when other powerful device starts on electrical network, such as high power DC electric machine starts the Voltage Drop caused, and thisly falls the Switching Power Supply that can affect in same supply line.After input voltage falls, the Switching Power Supply of resuming work fast can reduce this impact falling load on Switching Power Supply.
As shown in Figure 2, the startup stage that (a) being, inductive current iL changes schematic diagram in time, and the startup stage that (b) being, duty ratio ɑ changes schematic diagram in time, and the startup stage that (c) being, output voltage uo changes schematic diagram in time.The startup completing Switching Power Supply of the present invention is divided into three phases, and its time is respectively T1, T2, T3.
Electric current ascent stage, as the T1 stage in figure, this one-phase promotes inductive current, until current peak reaches setting inductive current with maximum permission duty ratio.Inductance is less, and during switch device conductive, inductive current rises faster.Switching device blocking interval, output voltage is lower, and inductive current declines fewer, and now output voltage is almost nil, and switching device blocking interval inductive current declines hardly.This one-phase, by big space rate, can make inductive current rise very soon.Inductive current rises must a limit value, and inductive current is when this value, and Switching Power Supply energy trouble free service, sets inductor current value in the present invention that Here it is.When inductive current is for setting inductor current value or when setting below inductor current value, now corresponding switching device trouble free service.
Under normal loading conditions there is the specified device operation current value of in switching device, also there is an inductance ratings electric current under corresponding normal loading conditions.In addition, the working current value that one maximum is had in the absolute rating of switching device, switching device operating current exceeds this value just may be damaged, so during selected switching device, maximum operating currenbt limiting value will leave enough surpluses, chooses 2.5 to 3.5 times that the maximum working current value of switching device is specified working current value in engineer applied.For inductance, namely maximum trouble free service electric current is 2.5 to 3.5 times of inductance ratings electric current.
The inductance peak current value that the maximum operating current of switching device is corresponding is called maximum trouble free service current value, setting inductive current I svalue should be less than maximum trouble free service current value, preferably sets inductive current I svalue and maximum trouble free service electric current I stthe proportionality coefficient of value is 0.5-0.9.This coefficient is too little can increase Switching Power Supply start-up time, and too conference increases the danger that switching device damages.
The constant current operation stage, as the T2 stage in Fig. 2.This stage, normally duty ratio, controlled inductive current by the make-and-break time of control switch device, maintained inductive current peak for setting inductor current value.Constant current operation stage inductive current maintains setting inductor current value, is the technique guarantee that Switching Power Supply starts fast.Setting inductor current value is larger, and institute's time spent that constant current operation stage switch electric power output voltage rises is shorter.
When output voltage is close to rated output voltage, second stage terminates; Output voltage is now called changing voltage.Changing voltage should be less than rated output voltage, and the preferred proportion of changing voltage and rated output voltage is 0.85-1.The too little meeting of this ratio makes power source integral extend start-up time, and output voltage may be caused to exceed rated output voltage to during voltage stabilizing working stage in constant current operation step transition too greatly, this is unallowed in engineer applied in a lot of Switching Power Supply.
Voltage stabilizing working stage, as the T3 stage in Fig. 2, at the end of the constant current operation stage, output voltage equals changing voltage, voltage stabilizing working stage with output voltage stabilization at rated operational voltage for control objectives.After entering voltage stabilizing working stage, inductive current can decline, until Switching Power Supply steady operation.So far, Switching Power Supply start-up course terminates.
One of realizing circuit of Switching Power Supply quick start method of the present invention adopts current type PWM control circuit.As shown in Figure 3, the quick startup control circuit of Switching Power Supply comprises: comparator U1, voltage comparator U2, analog switch U3, current regulator U6, rest-set flip-flop U7, PWM output module U8, oscillator U9, resistance R f, resistance R jwith electric capacity C f; Wherein the first input end of comparator U1 connects changing voltage V t, second input of comparator U1 connects output voltage V 0; Resistance R jone end for receiving output voltage V 0, resistance R jthe other end be connected to the first input end of voltage comparator U2, second input of voltage comparator U2 is for connecting reference voltage V f, resistance R fwith electric capacity C fbe sequentially connected in series between the first input end and the output of voltage comparator U2 of voltage comparator U2; The first input end of analog switch U3 is connected to the output of voltage comparator U2, and second input of analog switch U3 is for connecting setting inductive current I s; The control end of analog switch U3 is connected to the output of comparator U1; The first input end of current regulator U6 is connected to the output of analog switch U3, and second input of current regulator U6 connects inductive current I l; The R end of rest-set flip-flop U7 is connected to the output of current regulator U6, and the S of rest-set flip-flop U7 holds connection oscillator U9; The input of PWM output module U8 is connected to the Q end of rest-set flip-flop U7, and the output of PWM output module U8 is for exporting pwm control signal control switch device break-make.
Wherein, U2 can be voltage error amplifier, and form voltage regulator, two input signal is switch power source output voltage V respectively 0with reference voltage V f.The control objectives of existing Switching Power Supply is all by output voltage stabilization in reference voltage, and when reference voltage changes, by controlling duty ratio size, switch power source output voltage also changes.General Switching Power Supply reference voltage has the change of about 10%, and special key power supply such as experiment Switching Power Supply reference voltage changes from zero to rated value.Adopt Switching Power Supply of the present invention can to all functions examining voltage required for existing Switching Power Supply ginseng.U6 is current regulator, and an one input signal is from analog switch U3, and another input is from inductor current signal I l.U3 is an analog switch, and two input signal one is the output of voltage regulator, and another comes from setting inductive current I s; Analog switch U3 selects one to export as it in two input signals.U1 is a comparator, by output voltage V 0with changing voltage V tcompare, the output control simulation switch U3 of comparator.U9 is oscillator, and U7 is rest-set flip-flop, for generation of pwm signal.Oscillator U9 exports the S end connecting rest-set flip-flop U7, and the output of current regulator U6 connects the R end of rest-set flip-flop U7.The width of PWM changes with the change of current regulator U6 output voltage.U8 is PWM output module, and its output can be a road PWM, also can be that the PWM of two-way complementation exports.
As a whole, current type PWM controls to comprise the voltage control loop as outer shroud and the current regulator as inner ring.Current regulator is used for controlling the size of inductive current, when output voltage is lower than changing voltage V ttime, signal switching is become setting inductive current I by comparing control simulation switch U3 by comparator U1 s, now voltage regulator is on output duty cycle without impact, and current regulator will regulate duty ratio.If inductive current I lbe less than set point inductive current I s, duty ratio is then maximum duty cycle, Here it is electric current ascent stage; As inductive current I lreach setting inductive current I stime, current regulator makes inductive current I lconstant in setting inductive current I s.Now voltage error amplifier quits work.
When output voltage reaches changing voltage V ttime, signal switching becomes voltage regulator to export by comparing control simulation switch U3 by comparator U1, now voltage error amplifier U2 devotes oneself to work, voltage error amplifier is exported and two input signals of inductive current as current regulator U6, produced the pulse conducting width of pwm signal by the output control trigger of current comparator, control duty ratio and make output voltage be rated output voltage value.
Another implementation of Switching Power Supply quick start method of the present invention uses digital PWM controller, and the signal of its principle as shown in Figure 4.Adopt this scheme, the quick startup control circuit of Switching Power Supply comprises: voltage sample module 3, current sample module 4, MCU control module 5 and PWM generator 6; MCU control module 5 is sampled to the output voltage of Switching Power Supply, inductive current respectively, by computing output pwm signal, and control switch device break-make.The sample rate of described voltage sample module 3 and current sample module 4 is higher than PWM control frequency more than four times, and to ensure that both can obtain some row instantaneous values at sampling, MCU control module can obtain peak value or mean value from these instantaneous values.
As shown in Figure 5, MCU control module 5 comprises: subtracter 50, voltage regulator 51, voltage comparator 52, switch 53, subtracter 55 and current regulator 54, and the first input end of subtracter 50 connects reference voltage V f, the second input is for receiving output voltage V 0, the output of subtracter 50 connects voltage regulator 51, the first input end of the output connecting valve 53 of voltage regulator 51, and the second input of switch 53 is setting inductive current I s, the output of switch 53 connects the first input end of subtracter 55, and the second input of subtracter 55 is inductive current I l, the output of subtracter 55 is current regulators 54, current regulator 54 output duty cycle control switch device.Output voltage V 0connect the first input end of comparator 52, changing voltage V tconnect the second input of comparator, the control end of the output connecting valve 53 of comparator, the output of this control section energy control switch 53 is communicated with first input end or the second input.
Voltage regulator 51 is with reference to voltage V fwith output voltage V 0difference carry out computing, operation result delivers to software switch 53, and another input of software switch 53 is setting inductive current I s; Voltage comparator 52 is by output voltage V 0with changing voltage V tcompare, its output control switch 53.Switch 53 can be the software switch of alternative, as output voltage V 0lower than changing voltage V ttime the startup stage that namely Switching Power Supply being in, switch 53 gating I s, when output voltage is higher than V stat the end of namely Switching Power Supply starts, software switch selects the output of voltage regulator.By the output of switch 53 and inductive current I ldifference carry out computing, its export control PWM generator, the pwm signal that output duty cycle is controlled.PWM generator, its output can be a road PWM, also can be that the PWM of two-way complementation exports.
Digital PWM controller program package is containing voltage regulator, current regulator.Program circuit schematic diagram as shown in Figure 6.When output voltage is less than changing voltage, set-point is setting inductive current I s, then carry out Current adjustment computing, running current control ring, operation result controls the pulse conducting width of pwm signal, controls inductive current peak for setting current value; When output voltage equals to be greater than changing voltage, output voltage is carried out voltage-regulation computing, working voltage control ring and current regulator carry out double-loop control, and operation result controls the pulse conducting width of pwm signal, and controlling output voltage is rated output voltage value.
In embodiment above in the present invention, the sampled point of electric current is using inductive current as embodiment, other sampled point can also be had in practical application, current sample is carried out to other sampled points and electric current employing is carried out to inductance, change on its current value obtained is only proportional, starting implementation fast to the quick Starting mode of the Switching Power Supply in the present invention and two kinds of Switching Power Supplies does not have other to affect.For concrete switching power converters, its current sample point is described below:
For step-down DC/DC converter, its current sample point can be switching device electric current or inductive current or their combination;
For boosting DC/DC converter, its current sample point can be switching device electric current or inductive current or their combination;
For bridge-type non-isolated converter, its current sample point can be inductive current;
For single end flyback converter, its current sample point can be switching device electric current or primary side current of transformer or their combination;
For single-ended forward converter, its current sample point can be switching device electric current or primary side current of transformer or transformer time limit or inductive current or their combination;
For half-bridge or full-bridge isolated converter, its current sample point can be primary side current of transformer or transformer time limit electric current or inductive current or their combination.
Those skilled in the art will readily understand; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (9)

1. a Switching Power Supply quick start method, is characterized in that, comprises the steps:
(1) at electric current ascent stage, inductive current is promoted, until inductive current reaches setting inductive current with maximum permission duty ratio;
(2) in the constant current operation stage, control inductive current by the duty ratio of control switch device and make described inductive current maintain described setting inductive current, until the output voltage of Switching Power Supply is changing voltage;
(3) at voltage stabilizing working stage, make the output voltage of described Switching Power Supply maintain rated voltage thus realize Switching Power Supply to start fast by the duty ratio of control switch device.
2. Switching Power Supply quick start method as claimed in claim 1, it is characterized in that, in step (1), described maximum permission duty ratio is the maximum duty cycle that Switching Power Supply main circuit can allow; When the converter in described Switching Power Supply main circuit is step-down DC/DC converter, described maximum permission duty ratio is 1; When the converter in described Switching Power Supply main circuit is bridge-type non-isolated converter, half-bridge or full-bridge isolated converter, described maximum permission duty ratio is 0.5 deduct Dead Time part; When the converter in described Switching Power Supply main circuit be single end flyback converter or single-ended forward converter time, described maximum permission duty ratio is 0.5.
3. Switching Power Supply quick start method as claimed in claim 1, it is characterized in that, described setting inductive current equals maximum trouble free service electric current I st(0.5-0.9) doubly.
4. Switching Power Supply quick start method as claimed in claim 1, is characterized in that, described changing voltage is (0.85-1) times of rated voltage.
5. Switching Power Supply starts a control circuit fast, it is characterized in that, comprises comparator U1, voltage comparator U2, analog switch U3, current regulator U6, rest-set flip-flop U7, PWM output module U8, oscillator U9, resistance R f, resistance R jwith electric capacity C f;
The first input end of described comparator U1 connects changing voltage V t, second input of described comparator U1 connects output voltage V 0; Described resistance R jone end for receiving output voltage V 0, described resistance R jthe other end be connected to the first input end of described voltage comparator U2, second input of described voltage comparator U2 is for connecting reference voltage V f, described resistance R fwith described electric capacity C fbe sequentially connected in series between the first input end and the output of described voltage comparator U2 of described voltage comparator U2; The first input end of described analog switch U3 is connected to the output of described voltage comparator U2, and second input of described analog switch U3 is for connecting setting inductive current I s; The control end of described analog switch U3 is connected to the output of comparator U1; The first input end of described current regulator U6 is connected to the output of analog switch U3, and second input of described current regulator U6 connects inductive current I l; The R end of described rest-set flip-flop U7 is connected to the output of described current regulator U6, and the S end of described rest-set flip-flop U7 connects described oscillator U9; The input of described PWM output module U8 is connected to the Q end of described rest-set flip-flop U7, and the output of described PWM output module U8 is for exporting pwm control signal and control switch device break-make.
6. Switching Power Supply as claimed in claim 5 starts control circuit fast, it is characterized in that, described setting inductive current I sequal maximum trouble free service electric current I st(0.5-0.9) doubly.
7. the Switching Power Supply as described in claim 5 or 6 starts control circuit fast, it is characterized in that, described changing voltage V tfor (0.85-1) times of rated voltage.
8. a Switching Power Supply starts control circuit fast, it is characterized in that, comprise MCU control module (5), be connected to voltage sample module (3) and the current sample module (4) of the input of described MCU control module (5), and be connected to the PWM generator (6) of output of described MCU control module (5);
Described MCU control module (5) comprises subtracter (50), voltage regulator (51), voltage comparator (52), switch (53), subtracter (55) and current regulator (54);
The first input end of described subtracter (50) connects reference voltage V f, the second input is for receiving output voltage V 0the output of described subtracter (50) connects voltage regulator (51), the first input end of the output connecting valve (53) of voltage regulator (51), the second input of switch (53) is for connecting setting inductive current I s, the output of switch (53) connects the first input end of subtracter (55), and the second input of subtracter (55) is for connecting inductive current I l, the output of subtracter (55) connects the input of current regulator (54), and the output of current regulator (54) is used for output duty cycle control switch device.
9. Switching Power Supply as claimed in claim 8 starts control circuit fast, it is characterized in that, described setting inductive current I sequal maximum trouble free service electric current I st(0.5-0.9) doubly.
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