A kind of buck-boost converter for defibrillation pace-making power supply
Technical field
The present invention relates to the power supply buck-boost converter, relate in particular to a kind of buck-boost converter for defibrillation pace-making power supply.
Background technology
Defibrillation monitor has the noinvasive pacing function, can apply electricity irritation by the electrode on patient's chest surface, and the bradycardia after defibrillation is carried out emergency treatment.For the defibrillation pace-making, need to be applied to the voltage controlled (being controlled Control of Voltage) on electrode, and one adjustable continuously in a big way, namely in its range of accommodation, output voltage may be higher or lower than input voltage.Because electrode directly acts on human body, the output voltage that is applied on electrode needs and the input voltage isolation, guarantees to use safety.
At present, the implementation of wide output voltage mainly adopts the BUCK-BOOST changer, and this changer both can be realized boost function, can realize buck functionality again.Fig. 1 is a kind of BUCK-BOOST circuit, and in this changer, Q1, Q2 open simultaneously or turn-off simultaneously.During higher than output voltage, the effect of Q1 is the same with the BUCK switch when input voltage, and D1 makes fly-wheel diode.When Q1, Q2 opened simultaneously, input voltage was added to inductance two ends, and inductive current rises; When Q1, Q2 turn-offed simultaneously, inductive current was changed on D1, and the automatic forward conduction of D2 is identical with BUCK changer mode of operation.During lower than output voltage, the effect of Q2 is similar to flyback switching when input voltage, and same Q1, Q2 be turn-on and turn-off simultaneously, and during shutoff, inductive current is changed on D2, the automatic conducting of D1.Thereby can realize boost function.Identical main circuit without working mode change, not only can be realized boost function but also can realize buck functionality, controls voltage by adjustment, completes the output of wide-range voltage.
But adopt the BUCK-BOOST changer of existing technology in defibrillation pace-making applied environment, have following shortcoming:
1) main circuit can not be realized the isolation of input and output, and the input and output of BUCK-BOOST circuit can not be satisfied the requirement that the input and output of pace-making power supply must be isolated altogether.
2) although BUCK-BOOST can realize larger output voltage range, but when the output voltage excursion is large, such as when output changes from 10V to 150V, circuit can be changed between discontinuous current pattern, electric current critical conduction mode and continuous current mode, therefore, changer loop stability Design becomes very difficult, can not guarantee that under three kinds of mode of operations, circuit is all stable.
3) drive circuit is complicated.Need to have 2 switching tube Q1, Q2 in circuit, Q1 need to adopt flash to drive, Q2 adopts low limit to drive, usually adopt the gate-drive transformator to realize, increased step, cost and the complexity of drive circuit, the more important thing is, because driving transformer need to have resetting time, make the maximum duty cycle of circuit be restricted, output voltage is restricted simultaneously.
Therefore, because there is defects in prior art, need to provide a kind of buck-boost converter that is applicable in defibrillation pace-making power supply.
Summary of the invention
Technical problem to be solved by this invention is: a kind of buck-boost converter that is applicable in defibrillation pace-making power supply is provided.This buck-boost converter can be depressed at certain input dc power, by controlling voltage, realize the continuous wave output voltage below or above the wide variation of input voltage, and input and output is isolated mutually.
The present invention solves the problems of the technologies described above the technical scheme that adopts to be:
A kind of buck-boost converter for defibrillation pace-making power supply comprises an anti exciting converter, a PWM controller, and isolation feedback circuit;
In described anti exciting converter after the former limit winding of transformator serial connection switching tube as the input of this anti exciting converter, after its secondary winding serial connection commutation diode as the outfan of this anti exciting converter;
One input of described isolation feedback circuit connects described anti exciting converter outfan, its another input termination one control signal, described isolation feedback circuit is used for sampled signal and the described control signal of anti exciting converter output voltage are superposeed, and exports one and adjust the feedback voltage end that voltage acts on described PWM controller; Described PWM controller changes the anti exciting converter output voltage according to this ON time of adjusting the described switching tube of Control of Voltage.
Described buck-boost converter, wherein: described control signal is current controling signal, and described buck-boost converter also comprises an adjustable constant-flow source, described adjustable constant-flow source is used for controlling voltage transitions with one and becomes proportional described current controling signal with it, makes anti exciting converter output voltage and described control voltage linear.
Described buck-boost converter, wherein: described PWM controller is the PWM controller that is operated in the critical current pattern, include the zero current detection end, its gate signal outfan connects the control end of described switching tube, and its feedback voltage end connects described isolation feedback circuit outfan; Described buck-boost converter also comprises a zero current detecting circuit, electric current for detection of the described commutation diode of flowing through, and when the electric current of the described commutation diode of flowing through is zero, provide zero-signal and act on described zero current detection end, be used for the output that set again is operated in the PWM controller of critical current pattern, make described switching tube begin the conducting in a new cycle.
Described buck-boost converter, wherein: described zero current detecting circuit comprises an auxiliary winding and detects resistance, one end of described auxiliary winding connects described zero current detection end through described detection resistance, its other end ground connection, described auxiliary winding by with the coupling of described secondary winding, obtain and the proportional boost voltage of described output voltage, when the electric current of the described commutation diode of flowing through is zero, described boost voltage drops to zero, and acting on the zero current detection end by described detection resistance is zero-signal.
Described buck-boost converter, wherein: described isolation feedback circuit comprises a photo-coupler, three-terminal voltage regulator, and sample circuit; Described sample circuit comprises the 4th and the 3rd resistance, both is serially connected between anti exciting converter output voltage terminal and ground, and the 3rd resistance is sample resistance; Described three-terminal voltage regulator is serially connected between the light-emitting diodes tube cathode and ground of photo-coupler, and it adjusts the node of end connection the described the 4th and the 3rd resistance, the described adjustment voltage of photocell output of described photo-coupler.
Described buck-boost converter, wherein: described adjustable constant-flow source comprises an error amplifier, and electric current adjustment pipe, the positive input terminal of described error amplifier applies described control voltage, its negative input end is connected by the second resistance eutral grounding with the emitter-base bandgap grading that described electric current is adjusted pipe, its outfan connects through the 5th resistance the control end that described electric current is adjusted pipe, and described electric current is adjusted the colelctor electrode described isolation feedback circuit the 4th of connection of pipe and the node of the 3rd resistance.
Beneficial effect of the present invention is: buck-boost converter of the present invention is because main circuit is anti exciting converter (FLYBACK changer), realized the isolation between input and output, guaranteed security of system, and because the FLYBACK changer only needs a switching tube, can adopt low limit to drive, the PWM controller does not need the outer circuit of plus, can directly drive, circuit is simple and reliable, and output voltage can be changing below or above input voltage on a large scale continuously.
Work in the critical current mode of operation because of FLYBACK changer of the present invention again, compare with the fixed switching frequency mode of operation, under identical power conditions, because the critical current mode of operation does not have Dead Time, its peak point current is lower, and the power consumption of circuit is lower, and in the situation that the output voltage excursion is larger, owing to only there being a kind of critical current mode of operation, the stability of changer loop is more directly simple, is convenient to the circuit stability design.
Simultaneously the present invention realizes controlling voltage the linear scale of output voltage is controlled relation owing to adopting the adjustable constant-flow source to adjust output voltage, can improve the adjustment precision of output voltage.
Description of drawings
Fig. 1 is the BUCK-BOOST circuit theory diagrams of prior art;
Fig. 2 is buck-boost converter theory diagram of the present invention;
Fig. 3 is the schematic diagram of buck-boost converter specific implementation of the present invention;
Fig. 4 is isolation feedback circuit of the present invention and adjustable current source schematic diagram.
The specific embodiment
The below is described in further detail the present invention according to drawings and embodiments:
As shown in Fig. 2,3, buck-boost converter of the present invention comprises 4 partial circuits, is respectively anti exciting converter (FLYBACK changer), PDM keyer (PWM controller), isolation feedback circuit (Isolated Feedback) and adjustable current source.
The FLYBACK changer comprises transformator T1, switching tube Q2, commutation diode D1 and capacitor C 1, after transformer primary side winding N1 serial connection switching tube Q2 as the input of FLYBACK changer, after its secondary winding of transformator N2 serial connection commutation diode D1, as the outfan of this FLYBACK changer, capacitor C 1 is connected in parallel on the FLYBACK converter output terminal.The FLYBACK changer is as the main circuit of lifting changer of the present invention, in order to realize the electrical isolation between voltage transformation and input and output.
The closed loop control of isolation feedback circuit in order to realize exporting and inputting, and reach the purpose of isolation safely.Isolation feedback circuit has two inputs and an outfan, and wherein an input connects the output voltage VO UT end of FLYBACK changer, another input termination one control signal, and this control signal can be voltage control signal, can be also current controling signal.The operation principle of isolation feedback circuit is that after FLYBACK changer output voltage sampled signal and control signal are carried out overlap-add procedure, the feedback voltage end (FB end) that voltage acts on the PWM controller is adjusted in output one, the FB terminal voltage of adjustment PWM controller.And the FB terminal voltage of PWM controller has directly determined the ON time ton of switching tube Q2, the transformator T1 storage power of FLYBACK changer during the Q2 conducting, when Q2 ends, the energy that transformator T1 stores is sent to capacitor C 1 and load through D1, and the upper voltage of winding N2 this moment is approximately equal to output voltage VO UT.The adjustment voltage that the PWM controller is exported according to isolation feedback circuit, the ON time of gauge tap pipe Q2, thus control FLYBACK changer dutycycle, realize FLYBACK changer output voltage VO UT is adjusted on a large scale.
In order to improve the adjustment precision of output voltage, the present invention has adopted adjustable current source, is used for controlling voltage V with one
CConvert proportional current controling signal with it to, and make current controling signal act on the input of isolation feedback circuit, realize controlling voltage V
CLinear scale to output voltage VO UT is controlled relation.In order to realize that the FLYBACK changer works in the critical current mode of operation, the driving of FLYBACK changer is realized by the PWM controller U4 that works in the critical current pattern simultaneously.the PWM controller that is operated in the critical current pattern has zero current detection end (ZCD end-zero current detection), and need to increase a zero current detecting circuit, this zero current detecting circuit is for detection of the electric current of the FLYBACK changer commutation diode D1 that flows through, when transformator T1 energy transmits complete fully, when the electric current of commutation diode D1 of flowing through is zero, zero current detecting circuit provides zero-signal and acts on the ZCD end, be used for the output that set again is operated in the PWM controller U4 of critical current pattern, make switching tube Q2 begin the conducting of new one-period, thereby realize the control of FLYBACK changer critical current pattern.
zero current detecting circuit can adopt multiple circuit to realize, preferred version of the present invention comprises an auxiliary winding N3 and detects resistance R 1, auxiliary winding N3 is as a winding on the former limit of FLYBACK changer, one end resistance R 1 after testing connects the ZCD end of the PWM controller U4 that is operated in the critical current pattern, other end ground connection, auxiliary winding N3 by with the coupling of secondary winding N2, make the N3 Same Name of Ends also produce proportional boost voltage to output voltage VO UT, when transformator T1 energy transmit fully complete after, N3 Same Name of Ends voltage reduces to zero, be equivalent to by resistance R 1 to ZCD end one zero-signal, the ZCD end that is operated in the PWM controller U4 of critical current pattern detects this voltage reduce to zero after the output of set U4 again, by its gate signal outfan (GATE end) driving switch pipe Q2, make Q2 begin the conducting of new one-period, thereby realize the control of FLYBACK changer critical current pattern.Under this mode of operation, flyback converter does not almost have Dead Time, so its peak point current is lower, and the power consumption of circuit is lower.
Isolation feedback circuit and adjustable constant-flow source can adopt multiple circuit-mode to realize, the preferred implementing circuit that the present invention adopts is as shown in Fig. 3,4.Isolation feedback circuit adopts the optocoupler feedback to realize, the optocoupler feedback is a kind of scheme of the common reliable and economic the most that adopts of Switching Power Supply, and has the function of safety isolation.U3 is photo-coupler, and U2 is three-terminal voltage regulator ZR431, and the 4th resistance R 4 and the 3rd resistance R 3 are composed in series sample circuit, another termination FLYBACK changer output voltage VO UT end of R4, R3 other end ground connection.Three-terminal voltage regulator U2 is serially connected between the light-emitting diodes tube cathode and ground of photo-coupler U3, the adjustment terminating resistor R4 of U2 and the node of R3, because output voltage can reach 150V, surpass three-terminal voltage regulator ZR431 and can accept voltage range, therefore needed independently+5V reference voltage to provide bias current by resistance R 6 for U2.The photocell of photo-coupler U3 is as the outfan of isolation feedback circuit, and output is adjusted voltage to the FB end of critical current pattern PWM controller U4.Constant-current source is by error amplifier U1, electric current adjustment pipe Q1, and the second resistance R 2, the 5th resistance R 5 consist of.Control voltage V
CAct on the positive input terminal of error amplifier U1, the negative input end of U1 is connected with the emitter stage of electric current adjustment pipe Q1, and through resistance R 2 ground connection, the outfan of U1 connects the control end of Q1 through resistance R 5, and the colelctor electrode of electric current adjustment pipe Q1 connects the node of isolation feedback circuit resistance R 4 and R3.The resistance R 4 of isolation feedback circuit, R3 and the adjustable current source that is made of U1, Q1, R2, R5 provide adjustable VD to control, and control voltage V
CVariation can cause the reference voltage V of three-terminal voltage regulator U2
431refMinor variations occurs, and cause that the FB terminal voltage changes, thereby change the dutycycle of FLYBACK changer, and then realize regulation output voltage V
OUT
Below to do further quantitative analysis explanation for buck-boost converter circuit of the present invention shown in Figure 3:
1, FLYBACK changer due to the existence of isolating transformer, can be realized the isolation of input and output.The FLYBACK changer works in critical conduction mode, according to the weber equilibrium principle, can draw following equation:
VIN×D×N=V
OUT×(1-D)
Therefore,
Wherein: N is the turn ratio, N=N2: N1, D are FLYBACK changer work dutycycle, V
INBe FLYBACK changer input voltage, V
OUTBe FLYBACK changer output voltage.
As can be seen from the above equation, under the condition of stationary transformer turn ratio N, adjust FLYBACK changer work dutycycle D, its output voltage V
OUTBoth can be greater than input voltage V
IN, also can be less than input voltage V
IN
2, as shown in Figure 3 adjustable constant-flow source circuit, the major function of realization are controlling a voltage V
CBe converted to constant current Ir, to control output voltage.According to Fig. 3 circuit, can controlled voltage V
CWith output voltage V
OUTBetween relation:
-----------------formula 1
----------------formula 2
Formula 2 substitution formula 1, can get:
----------------formula 3
Wherein: V
431refBe the reference voltage of three-terminal voltage regulator U2, V
CFor controlling voltage;
Can be found out by formula 3, by selecting suitable resistance value and reference voltage V
431ref, just can realize controlling voltage V
CWith output voltage V
OUT(10V-150V output) is linear.
By above-mentioned quantitative analysis explanation, further prove buck-boost converter of the present invention by working in the FLYBACK circuit of critical current pattern, realized the function of isolation BUCK-BOOST circuit, realized control voltage V by the adjustable constant-flow source circuit
CTo output voltage V
OUTLinear scale control relation, be highly suitable for the applied environment of defibrillation pace-making power supply.
Be understandable that, for those of ordinary skills, can be equal to replacement or change according to technical scheme of the present invention and inventive concept thereof, and all these changes or replacement all should belong to the protection domain of the appended claim of the present invention.